U.S. patent application number 10/139677 was filed with the patent office on 2002-12-12 for image sensing apparatus and image sensing method, x-ray photographing system and its control method.
Invention is credited to Tamura, Toshikazu, Tsuchiya, Keiji.
Application Number | 20020186813 10/139677 |
Document ID | / |
Family ID | 26614756 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020186813 |
Kind Code |
A1 |
Tamura, Toshikazu ; et
al. |
December 12, 2002 |
Image sensing apparatus and image sensing method, X-ray
photographing system and its control method
Abstract
Since the duration of an idling drive period is not defined (not
specified) in practical use, T1 is set to be longer than that in a
normal photographing operation to make idling-dedicated idle read
frames Fi in which the ON time of a TFT (82) is shorter than the
normal read drive frame, so as to minimize read operations that
impose a heavy load on a photodetector array (58) (especially, the
TFT (82)).
Inventors: |
Tamura, Toshikazu; (Tochigi,
JP) ; Tsuchiya, Keiji; (Tochigi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 PARK AVENUE
NEW YORK
NY
10154
US
|
Family ID: |
26614756 |
Appl. No.: |
10/139677 |
Filed: |
May 2, 2002 |
Current U.S.
Class: |
378/98.8 ;
348/E5.081; 348/E5.087 |
Current CPC
Class: |
H04N 5/3597 20130101;
H04N 5/321 20130101; H04N 5/367 20130101; H04N 5/361 20130101; H04N
5/3651 20130101 |
Class at
Publication: |
378/98.8 |
International
Class: |
H05G 001/64 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2001 |
JP |
2001-137718 |
Jul 19, 2001 |
JP |
2001-220144 |
Claims
What is claimed is:
1. An image sensing apparatus comprising: an image sensing region
for sensing an object image; and a drive circuit for resetting said
image sensing region at a first time interval during a first period
before an image sensing operation, and for resetting said image
sensing region at a second time interval during a second period
prior to the first period, wherein the first time interval is
different from the second time interval.
2. The apparatus according to claim 1, wherein the second time
interval is longer than the first time interval.
3. An image sensing apparatus comprising: an image sensing region
for sensing an object image; and a drive circuit for resetting said
image sensing region at a predetermined interval during a first
time period before an image sensing operation, and for resetting
said image sensing region at a predetermined interval during a
second time period prior to the first time period, wherein the
first time period is different from the second time period.
4. The apparatus according to claim 3, wherein the second time
period is shorter than the first time period.
5. The apparatus according to claim 1, wherein said image sensing
apparatus senses the object image by radiation exposure, and the
first period is generated in response to a radiation exposure
request before the radiation exposure.
6. The apparatus according to claim 3, wherein said image sensing
apparatus senses the object image by radiation exposure, and the
first time period starts in response to a radiation exposure
request before the radiation exposure.
7. The apparatus according to claim 1, wherein said image sensing
apparatus senses the object image by radiation exposure, and
further comprises a control circuit which controls to start
radiation exposure upon completion of the reset operation when a
radiation exposure request before the radiation exposure is
received during the reset operation.
8. The apparatus according to claim 3, wherein said image sensing
apparatus senses the object image by radiation exposure, and
further comprises a control circuit which controls to start
radiation exposure upon completion of the reset operation when a
radiation exposure request before the radiation exposure is
received during the reset operation.
9. The apparatus according to claim 1, wherein said drive means
reads an image charge signal in a predetermined column direction,
and drives for each predetermined row at a predetermined
period.
10. An image sensing method comprising the step of: resetting an
image sensing region used to sense an object image at a first time
interval during a first period before an image sensing operation,
and resetting the image sensing region at a second time interval
during a second period prior to the first period, wherein the first
time interval is different from the second time interval.
11. An image sensing method comprising the step of: resetting an
image sensing region used to sense an object image at a
predetermined interval during a first time period before an image
sensing operation, and resetting the image sensing region at a
predetermined interval during a second time period prior to the
first time period, wherein the first time period is different from
the second time period.
12. A computer-readable storage medium that stores a program for
making a computer function as means which form an image sensing
apparatus cited in claim 1.
13. A computer-readable storage medium that stores a program for
making a computer execute the processing step of an image sensing
method cited in claim 10.
14. A program for making a computer function as means which form an
image sensing apparatus cited in claim 1.
15. A program for making a computer execute the processing step of
an image sensing method cited in claim 10.
16. A radiography system which comprises a detector for detecting
radiation generated by a radiation generation device, and a
detector controller for initializing said detector at a
predetermined timing, and controlling said detector, and takes a
radiation image on the basis of the radiation detected by said
detector, wherein said detector controller comprises: storage means
for acquiring and storing a time period from when initialization of
said detector starts until a radiation irradiation request signal
is received; and instruction means for, when the radiation
irradiation request signal is received during an initialization
process of said detector, instructing to execute a wait process for
the stored time period after the initialization process, and upon
completion of the wait process by said instruction means, a
radiography permission signal is sent to said radiation generation
device.
17. A radiography system which comprises a detector for detecting
radiation generated by a radiation generation device, and a
detector controller for initializing said detector at a
predetermined timing, and controlling said detector, and takes a
radiation image on the basis of the radiation detected by said
detector, wherein when a radiation irradiation request signal is
received during an initialization process of said detector, said
detector controller sends a radiography permission signal to said
radiation generation device after completion of the initialization
process.
18. A method of controlling a radiography system which comprises a
detector for detecting radiation generated by a radiation
generation device, and a detector controller for initializing said
detector at a predetermined timing, and controlling said detector,
and takes a radiation image on the basis of the radiation detected
by said detector, wherein said detector controller acquires and
stores a time period from when initialization of said detector
starts until a radiation irradiation request signal is received,
when said detector controller receives the radiation irradiation
request signal during an initialization process of said detector,
said detector controller instructs to execute a wait process for
the stored time period after the initialization process, and said
detector controller sends a radiography permission signal to said
radiation generation device upon completion of the wait process
based on the instruction.
19. A method of controlling a radiography system which comprises a
detector for detecting radiation generated by a radiation
generation device, and a detector controller for initializing said
detector at a predetermined timing, and controlling said detector,
and takes a radiation image on the basis of the radiation detected
by said detector, wherein when a radiation irradiation request
signal is received during an initialization process of said
detector, said detector controller sends a radiography permission
signal to said radiation generation device after completion of the
initialization process.
20. A program code for making an information processing apparatus
execute a method of controlling a radiography system cited in claim
18 when said program code is loaded by said information processing
apparatus.
21. A computer-readable storage medium which stores a program code
cited in claim 20.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an image sensing apparatus
and image sensing method for sensing an object image and, more
particularly, to an X-ray image sensing apparatus for sensing an
object image by irradiating an object with X-rays.
BACKGROUND OF THE INVENTION
[0002] In a conventional X-ray image sensing apparatus, an X-ray
beam is projected from an X-ray source via an object to be analyzed
such as a patient under medical treatment. Normally, after the beam
is transmitted through the object to be analyzed, an image
intensifier converts X-ray radiation into a visible image, and a
video camera generates an analog video signal from the visible
image and displays it on a monitor. Since the analog video signal
is generated, an image process for automatic luminance adjustment
and image emphasis is done in the analog domain.
[0003] A high-resolution solid-state X-ray detector has already
been proposed, and comprises a two-dimensional array using 3000 to
4000 detection elements represented by photodiodes or the like.
Each element generates an electrical signal corresponding to the
pixel luminance of an X-ray image projected onto the detector.
Signals from the respective detection elements are individually
read and converted into digital signals, which then undergo an
image process, storage, and display.
[0004] Upon obtaining a medical X-ray image using a large-screen
X-ray detector, the X-ray detector requires a certain time until
actual X-ray exposure, and is driven in a preparation state to
shorten that time.
[0005] In the preparation state of the detector, in order to avoid
the elements in the detector from being held in a saturation state
due to gradually accumulated dark currents, a dedicated read drive
process is repeated at given intervals. This repetitive drive
process will be referred to as "idling drive" hereinafter. Since
the duration of this idling drive period is not defined in
practical use, if the idling drive period is long, it shortens the
service life of the apparatus, and promotes aging of various
characteristics associated with detection.
[0006] The present invention has been made in consideration of the
above problems, and has as its object to provide an image sensing
apparatus and image sensing method, which can implement highly
reliable image sensing by suppressing shortening of the service
life of the apparatus and aging of various characteristics
associated with detection even when the idling drive period, which
is difficult to be defined in practical use, is long.
[0007] In medical radiography as that for the purpose of medical
diagnosis, (spot) photographing uses X-ray photography as a
combination of an intensifying screen and X-ray photo film.
[0008] When radiation such as X-rays or the like that have been
transmitted through an object to be examined become incident on the
intensifying screen, a phosphor contained in the intensifying
screen absorbs this X-ray energy and emits fluorescence. This
fluorescence exposes the X-ray photo film to form a radiation image
on it. By developing and fixing the film, an X-ray image can be
visualized.
[0009] Recently, various schemes for digitally capturing a
radiation image have been developed. In one scheme, using an X-ray
image detector which comprises a photoelectric conversion element
which has sensitivity to X-rays, converts detected X-rays into
electrical signals corresponding to their intensity levels, and
outputs the electrical signals, or a combination of a phosphor
which absorbs X-ray energy and emits fluorescence with intensity
corresponding to the absorbed energy, and a photoelectric
conversion element which has sensitivity to visible light and
outputs an electrical signal corresponding to its intensity, an
X-ray image is converted into an electrical signal, and the
electrical signal is A/D-converted to capture a digital image.
[0010] FIG. 21 is a schematic block diagram showing an example of
an X-ray photographing system.
[0011] Referring to FIG. 21, reference numeral 5001 denotes an
X-ray generation device; 5002, a host computer; 5003, a phosphor;
5004, a flat-panel detector as a two-dimensional array of a large
number of photoelectric conversion elements each of which comprises
a photodetector and switching element; 5005, a flat-panel detector
controller for controlling the flat-panel detector 5004; and 5006,
an object. The X-ray photographing apparatus comprises the phosphor
5003, flat-panel detector 5004, and flat-panel detector controller
5005.
[0012] The X-ray generation device 5001 has an X-ray radiation
switch (not shown). When the X-ray radiation switch is pressed, a
signal indicating that an X-ray generation request is generated is
sent to the host computer 5002. The host computer 5002 informs the
flat-panel detector controller 5005 of generation of the X-ray
radiation request. Upon receiving the X-ray radiation request, the
flat-panel detector controller 5005 initializes the flat-panel
detector 5004. Upon completion of initialization of the flat-panel
detector 5004, the flat-panel detector controller 5005 sends an
X-ray radiation permission signal to the host computer 5002. Upon
receiving the X-ray radiation permission signal, the host computer
5002 sends a signal indicating that X-ray radiation is permitted to
the X-ray generation device 5001. Then, the X-ray generation device
5001 radiates X-rays. The radiated X-rays are transmitted through
the object 5006 and are converted by the phosphor 5003 into light
proportional to the incoming X-ray dose. This light is converted
into an electrical signal by the flat-panel detector 5004. The
flat-panel detector controller 5005 reads this electrical signal,
and transfers an X-ray digital image to the host computer 5002 at
the same time. The transferred X-ray digital image undergoes an
image process by the host computer 5002, and the taken X-ray
digital image is displayed on a display device (not shown).
[0013] FIG. 22 shows an equivalent circuit of one photoelectric
conversion element. In the following description, an amorphous
silicon sensor will be exemplified as the photoelectric conversion
element. However, the photoelectric conversion element need not be
particularly limited and, for example, elements such as other
solid-state image sensing elements (charge-coupled element and the
like), a photomultiplier, or the like may be used.
[0014] Referring to FIG. 22, one photoelectric conversion element
5020 comprises a photodetector 5021 and a switching element 5022
for controlling charge accumulation and read. In general, the
element 20 is formed on a glass substrate using amorphous silicon
(.alpha.-Si).
[0015] A capacitor 5021C in the photodiode 5021C can simply be a
photodiode having a parasitic capacitance, or be a photodetector
which includes a parallel circuit of a photodiode 5021D and
additional capacitor 5021C to improve the dynamic range of the
photodiode 5021D and detector. When X-rays hit the photodetector
5021, the photodiode 5021D generates a charge corresponding to the
X-ray dose, and the generated charge is accumulated on the
capacitor 5021C.
[0016] An anode A of the diode 5021D is connected to a refresh
control circuit 5023. The refresh control circuit 5023 normally
outputs a bias voltage Vs, but can temporarily output a refresh
voltage Vr to initialize the capacitor 5021C.
[0017] A cathode K of the diode 5021D is connected to the
controllable switching element 5022 used to read the charge
accumulated on the capacitor 5021C. In this example, the switching
element 5022 is a thin-film transistor connected between the
cathode K of the diode 5021D and a charge read amplifier 5025.
[0018] A gate G of the switching element 5022 is connected to a
gate control circuit 5024, which outputs a gate signal Vg to read
the charge accumulated on the capacitor 5021C. The read charge is
amplified by the amplifier 5025, and is A/D-converted by an A/D
converter 5027 via a sample/hold circuit 5026, thereby converting
the charge accumulated on the capacitor 5021C into digital
data.
[0019] An initialization process of one photoelectric conversion
element 5020 will be described below using FIG. 23.
[0020] Referring to FIG. 23, a refresh signal indicates the output
signal from the refresh control circuit 5023, a gate signal
indicates the output signal from the gate control circuit 5024, and
a dark current indicates a current that flows the capacitor 5021C.
Normally, the voltage of the refresh signal is equal to the bias
voltage Vs, that of the gate signal is 0 V, and nearly no dark
current flows.
[0021] In this state, the refresh voltage Vr is output at time T1
to initialize the capacitor 5021C. When the refresh signal has
reached the refresh voltage Vr, a minus dark current flows, and the
charge accumulated on the capacitor 5021C is swept out. A time
period (a time period from time T1 to time T2) in which the refresh
signal is equal to the refresh voltage Vr is determined in advance
so as to sufficiently reduce the charge accumulated on the
capacitor 5021C.
[0022] At time T2, the voltage of the refresh signal is changed to
the bias voltage Vs. An operation in which the refresh control
circuit 5023 temporarily outputs the refresh signal (=voltage Vr)
to initialize the capacitor 5021C will be referred to as "refresh"
hereinafter. Immediately after the bias voltage Vs is switched, a
large plus dark current is generated, and is accumulated as a
charge on the capacitor 5021C. As is known, noise to be superposed
on a taken X-ray image is proportional to the square root of the
charge accumulated due to the dark current.
[0023] After the refresh process, the gate control circuit 5024
temporarily outputs the gate signal Vg at time T3. As a result, the
charge accumulated on the capacitor 5021C is swept out.
[0024] Time T3 is determined in advance to sufficiently reduce the
dark current. In the following description, an operation in which
the gate control circuit 5024 temporarily outputs the gate signal
Vg to sweep out the charge accumulated on the capacitor 5021C due
to the dark current will be referred to as "idle read". When the
charge accumulated on the capacitor 5021C is sufficiently swept
out, the gate signal is set at 0 V at time T5. A time period (a
time period from time T3 to time T5) in which the gate signal is
equal to the gate voltage Vg is determined in advance so as to
sufficiently reduce the charge accumulated on the capacitor
5021C.
[0025] However, even after idle read, since a slight dark current
is still flowing, the capacitor 5021C gradually accumulates a
charge. For this reason, the initialization process of the
photoelectric conversion element 5020, which includes the refresh
process and idle read process, is repeated periodically. Also, for
the same reason as above, the initialization process of the
photoelectric conversion element 5020 is done immediately before
X-ray photographing.
[0026] FIG. 24 is a block diagram showing an example of the
flat-panel detector 5004 and flat-panel detector controller
5005.
[0027] Referring to FIG. 24, reference numeral 5007 denotes a CPU
for reading an X-ray digital image from a flat-panel detector 5004,
and a refresh control circuit 5008, row address select circuit
5009, and column address select circuit 5010 are connected to the
CPU 5007. The CPU 5007 can control these circuits. The CPU 5007 is
connected to the host computer 5002 (not shown in FIG. 24), and can
transfer an X-ray digital image read from the flat-panel detector
5004 to the host computer 5002.
[0028] The flat-panel detector 5004 comprises a two-dimensional
array of a large number of photoelectric conversion elements 5020
shown in FIG. 22. However, in FIG. 24, photoelectric conversion
elements 5020 are two-dimensionally arranged in a 2.times.2
(row.times.column) matrix for the sake of simplicity.
[0029] As described above, the photoelectric conversion element
5020 for one pixel comprises the photodiode 5021 and switching TFT
5022. Photodetectors 5021(1,1) to 5021(2,2) correspond to the
aforementioned photodetector 5021, and K and A respectively
represent the cathode and anode sides of the photodetector 5021.
The TFTs 5022(1,1) to 5022(2,2) correspond to the switching TFT
5022, and S, G, and D respectively represent the source, gate, and
drain electrodes of the TFT.
[0030] The gate electrodes G of the TFTs 5022 of each row are
connected to the row address select circuit 5009, which comprises
the aforementioned gate control circuit 5024 and switches SWr1 and
SWr2.
[0031] The drain electrodes D of the TFTs 5022 of each column are
connected to the column address select circuit 5010, which
comprises the amplifier 5025, sample/hold circuit 5026, and
switches SWc1 and SWc2.
[0032] The anode sides of all the photodetectors 5021 are connected
to the refresh control circuit 5008, which normally outputs a bias
voltage Vs, and also outputs a refresh voltage Vr as a refresh
signal. The refresh control circuit 5008 is the same as the refresh
control circuit 5023 shown in FIG. 22.
[0033] The initialization process of the plurality of photoelectric
conversion elements 5020 shown in FIG. 25 in the arrangement shown
in FIG. 24 will be explained below.
[0034] Referring to FIG. 25, a refresh signal indicates the output
signal from the refresh control circuit 5008, a gate signal
indicates the output signal from the gate control circuit 5024, and
SWr1 and SWr2 indicate the switches SWr1 and SWr2 in the row
address select circuit 5009. Normally, the voltage of the refresh
signal is equal to the bias voltage Vs, that of the gate signal is
0 V, and the switches SWr1 and SWr2 are OFF. Therefore, the anode
sides A of all the photodetectors 5021(1,1) to 5021(2,2) are set at
the bias voltage Vs, and the gate electrodes G of all the TFTs
5022(1,1) to 5022(2,2) are set at 0 V.
[0035] In this state, the refresh voltage Vr is output at time T1
to initialize all the photodetectors 5021. When the refresh signal
has reached the refresh voltage Vr, a minus dark current flows, and
the charge accumulated on the capacitor 5021C of each photodetector
5021 is swept out. At time T2, the voltage of the refresh signal is
set at the bias voltage Vs. Immediately after refresh signal is
switched to the bias voltage Vs, a large plus dark current is
generated, and is accumulated on the capacitor 5021C of each
photodetector 5021 as a charge. Hence, after the refresh process,
the gate control circuit 5024 temporarily outputs a gate signal Vg
at time T3 to turn on the switch SWr1. As a result, the voltages at
the gate electrodes G of the TFTs 5022(1,1) and 5022(1,2) of the
first row change to Vg, and the charges accumulated on the
capacitors 5021C in the photodetectors 5021 of the first row are
swept out. At time T4, the switch SWr1 is turned off, and the
switch SWr2 is turned on. The voltages at the gate electrodes G of
the TFTs 5022(1,1) and 5022(1,2) of the first row change to 0 V,
and those at the gate electrodes G of the TFTs 5022(2,1) and
5022(2,2) of the second row change to Vg. Hence, the charges
accumulated on the capacitors 5021C in the photodetectors 5021 of
the second row are swept out.
[0036] When the gate signal is set at 0 V and the switch SWr2 is
turned off at time T5, the gate electrodes G of all the TFTs
5022(1,1) to 5022(2,2) change to 0 V, thus ending the
initialization process. The initialization process is executed
during the period from time T1 to time T5.
[0037] FIG. 26 shows the relationship between the initialization
process of the photoelectric conversion elements 5020 and X-ray
photographing. As shown in FIG. 26, when no X-ray photographing is
made, the refresh and idle read processes (initialization process)
are periodically repeated at intervals TI. FIG. 26 shows a case
wherein the X-ray radiation switch of the X-ray generation device
5001 is pressed at time T1 (a timing other than those of the
refresh and idle read processes), and the X-ray radiation request
reaches the flat-panel detector controller 5005 via the host
computer 5002. Upon generation of the X-ray radiation request, the
host computer 5002 that has received this request changes an X-ray
radiation request signal to Low.
[0038] When the X-ray radiation request signal has changed to Low,
the refresh and idle read processes are executed again. Upon
completion of these processes, the flat-panel detector controller
5005 outputs an X-ray radiation permission signal at time T5. That
is, the controller 5005 changes the X-ray radiation permission
signal to Low. When the X-ray radiation permission signal has
changed to Low, X-ray radiation is permitted. Note that the time
period from when the X-ray radiation request signal has changed to
Low until the X-ray radiation permission signal changes to Low is
called an exposure delay time period, and is indicated by TD1 in
FIG. 26.
[0039] When the X-ray radiation permission signal has reached the
X-ray generation device 5001 via the host computer 5002, the X-ray
generation device 5001 radiates X-rays, as shown in FIG. 26. When
the X-ray generation device 5001 radiates X-rays, the radiated
X-rays are transmitted through the object 5006, and are converted
into light proportional to the incoming X-ray dose by the phosphor
5003, and charges corresponding to the light are accumulated on the
capacitors 5021C.
[0040] Upon completion of X-ray radiation, the host computer 5002
changes the X-ray radiation permission signal to High at time T6,
and outputs it to the X-ray generation device 5001. When the X-ray
radiation permission signal has changed to High, the X-ray
radiation request signal goes High.
[0041] Also, upon completion of X-ray radiation, the gate signal is
set at Vg and the switch SWr1 is turned on at time T6. As a result,
the voltages at the gate electrodes G of the TFTs 5022(1,1) and
5022(1,2) of the first row shown in FIG. 24 change to Vg, the
charges accumulated on the capacitors 5021C in the photodetectors
5021 of the first row are read, and the read signals are held via
the amplifier 5025 and sample/hold circuit 5026. When the switch
SWc1 is turned on at time T6, the held signal of the photodetector
5021(1,1) is converted into a digital value by the A/D converter
5027, and that value is transferred to the host computer 5002.
Also, when the switch SWc1 is turned off and the switch SWc2 is
turned on at time T7, the held signal of the photodetector
5021(1,2) is converted into a digital value by the A/D converter
5027, and that value is transferred to the host computer 5002.
[0042] When the switch SWr1 is turned off and the switch SWr2 is
turned on at time T8, the voltages at the gate electrodes G of the
TFTs 5022(2,1) and 5022(2,2) of the second row shown in FIG. 24
change to Vg, the charges accumulated on the capacitors 5021C in
the photodetectors 5021 of the second row are read, and the read
signals are held via the amplifier 5025 and sample/hold circuit
5026. When the switch SWc1 is turned on at time T8, the held signal
of the photodetector 5021(2,1) is converted into a digital value by
the A/D converter 5027, and that value is transferred to the host
computer 5002. Also, when the switch SWc1 is turned off and the
switch SWc2 is turned on at time T9, the held signal of the
photodetector 5021(2,2) is converted into a digital value by the
A/D converter 5027, and that value is transferred to the host
computer 5002.
[0043] After all the charges accumulated on the flat-panel detector
5004 are transferred to the host computer 5002, the gate signal is
set at 0 V, and the switches SWr1, SWr2, SWc1, and SWc2 are turned
off at time T10. In the following description, an operation in
which all charges accumulated on the flat-panel detector 5004 are
read by setting the gate signal at Vg, and temporarily turning on
the switches SWr1, SWr2, SWc1, and SWc2 will be referred to as
"main read".
[0044] In the aforementioned prior art, as shown in FIG. 26, when
the X-ray radiation switch is pressed at a timing other than the
initialization process, and the X-ray radiation request signal goes
Low, the refresh and idle read processes are immediately
executed.
[0045] However, when the X-ray radiation switch is pressed during
the initialization process, and the X-ray radiation request signal
goes Low, the current initialization process is interrupted, and is
redone from the beginning. Upon generation of an X-ray radiation
request, if the initialization process is interrupted and the
refresh process is executed immediately, a dark current flows. As a
result, many charges are accumulated on the capacitors 5021C, and
some charges remain even after the idle read process. Since it is
known that noise to be superposed on a taken X-ray image is
proportional to the square root of the charge accumulated due to
the dark current, if X-rays are radiated in this state, noise on
the taken X-ray image is emphasized.
[0046] The present invention has been made in consideration of the
aforementioned problems, and has as its object to prevent noise in
an taken X-ray image from increasing even when an X-ray radiation
request is received during initialization of a detector.
[0047] It is preferable to shorten the time period from when the
X-ray radiation request is received until X-ray photographing is
permitted. Therefore, it is another object of the present invention
to shorten the exposure delay time period upon receiving an X-ray
radiation request during initialization of the detector.
SUMMARY OF THE INVENTION
[0048] In order to achieve the object of the present invention, an
image sensing apparatus of the present invention comprising: an
image sensing region for sensing an object image; and
[0049] a drive circuit for resetting the image sensing region at a
first time interval during a first period before an image sensing
operation, and for resetting the image sensing region at a second
time interval during a second period prior to the first period,
[0050] wherein the first time interval is different from the second
time interval.
[0051] In order to achieve the object of the present invention, an
sensing apparatus of the present invention comprising: an image
sensing region for sensing an object image; and
[0052] a drive circuit for resetting the image sensing region at a
predetermined interval during a first time period before an image
sensing operation, and for resetting the image sensing region at a
predetermined interval during a second time period prior to the
first time period,
[0053] wherein the first time period is different from the second
time period.
[0054] In order to achieve the object of the present invention, an
image sensing method of the present invention comprising: resetting
an image sensing region used to sense an object image at a first
time interval during a first period before an image sensing
operation, and resetting the image sensing region at a second time
interval during a second period prior to the first period,
[0055] wherein the first time interval is different from the second
time interval.
[0056] In order to achieve the object of the present invention, an
image sensing method of the present invention comprising: resetting
an image sensing region used to sense an object image at a
predetermined interval during a first time period before an image
sensing operation, and resetting the image sensing region at a
predetermined interval during a second time period prior to the
first time period,
[0057] wherein the first time period is different from the second
time period.
[0058] In order to achieve the object of the present invention, a
radiography system of the present invention comprising: a
radiography system which comprises a detector for detecting
radiation generated by a radiation generation device, and a
detector controller for initializing the detector at a
predetermined timing, and controlling the detector, and takes a
radiation image on the basis of the radiation detected by the
detector,
[0059] wherein the detector controller comprises:
[0060] storage means for acquiring and storing a time period from
when initialization of the detector starts until a radiation
irradiation request signal is received; and
[0061] instruction means for, when the radiation irradiation
request signal is received during an initialization process of the
detector, instructing to execute a wait process for the stored time
period after the initialization process, and
[0062] upon completion of the wait process by the instruction
means, a radiography permission signal is sent to the radiation
generation device.
[0063] In order to achieve the object of the present invention, a
radiography system of the present invention comprising: a
radiography system which comprises a detector for detecting
radiation generated by a radiation generation device, and a
detector controller for initializing the detector at a
predetermined timing, and controlling the detector, and takes a
radiation image on the basis of the radiation detected by the
detector,
[0064] wherein when a radiation irradiation request signal is
received during an initialization process of the detector, the
detector controller sends a radiography permission signal to the
radiation generation device after completion of the initialization
process.
[0065] In order to achieve the object of the present invention, a
method of controlling a radiography system of the present invention
comprising: a method of controlling a radiography system which
comprises a detector for detecting radiation generated by a
radiation generation device, and a detector controller for
initializing the detector at a predetermined timing, and
controlling the detector, and takes a radiation image on the basis
of the radiation detected by the detector,
[0066] wherein the detector controller acquires and stores a time
period from when initialization of the detector starts until a
radiation irradiation request signal is received,
[0067] when the detector controller receives the radiation
irradiation request signal during an initialization process of the
detector, the detector controller instructs to execute a wait
process for the stored time period after the initialization
process, and
[0068] the detector controller sends a radiography permission
signal to the radiation generation device upon completion of the
wait process based on the instruction.
[0069] In order to achieve the object of the present invention, a
method of controlling a radiography system of the present invention
comprising: a method of controlling a radiography system which
comprises a detector for detecting radiation generated by a
radiation generation device, and a detector controller for
initializing the detector at a predetermined timing, and
controlling the detector, and takes a radiation image on the basis
of the radiation detected by the detector,
[0070] wherein when a radiation irradiation request signal is
received during an initialization process of the detector, the
detector controller sends a radiography permission signal to the
radiation generation device after completion of the initialization
process.
[0071] Other features and advantages of the present invention will
be apparent from the following descriptions taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the descriptions, serve to explain
the principle of the invention.
[0073] FIG. 1 is a block diagram showing the arrangement of an
X-ray image sensing system according to an embodiment of the
present invention;
[0074] FIG. 2 is an equivalent circuit diagram of a building unit
of a photodetector array;
[0075] FIG. 3A is a diagram for explaining the device operation of
the photodetector;
[0076] FIG. 3B is a diagram for explaining the device operation of
the photodetector;
[0077] FIG. 3C is a diagram for explaining the device operation of
the photodetector;
[0078] FIG. 4 is an equivalent circuit diagram of a building unit
of a photodetector array;
[0079] FIG. 5 is an equivalent circuit diagram of a photodetector
array which comprises a two-dimensional matrix of photoelectric
conversion elements;
[0080] FIG. 6 is a timing chart showing an outline of a sensor read
process;
[0081] FIG. 7 is a timing chart including an image sensing
operation of an X-ray detector;
[0082] FIG. 8 is a schematic block diagram showing the arrangement
of an image processor;
[0083] FIG. 9 is a timing chart for explaining a drive process of a
dedicated frame;
[0084] FIG. 10 is a timing chart showing a charge accumulation
start-dedicated idle read frame Fpf, X-ray image capture frame
Frxo, and correction image capture frame Frno;
[0085] FIG. 11 is a timing chart showing an idling-dedicated idle
read frame Fi;
[0086] FIG. 12 is a timing chart showing the operation of a TFT 82
of a charge sweep-out idle read frame Fp for an image sensing
sequence;
[0087] FIG. 13 is a timing chart showing an example of a drive
process in which a time period per line is equal to a normal image
capture frame, and only the ON time period of a TFT is
shortened;
[0088] FIG. 14 is a block diagram showing the internal arrangement
of a general personal user terminal;
[0089] FIG. 15 is a timing chart showing the relationship between
the initialization process and X-ray photographing when an X-ray
radiation request is generated during the initialization process of
photoelectric conversion elements 5020 in the second embodiment of
the present invention;
[0090] FIG. 16 is a flow chart showing the main routine of an X-ray
photographing method in the second embodiment of the present
invention;
[0091] FIG. 17 is a flow chart showing the subroutine of an
initialization process in an X-ray photographing method in the
third embodiment of the present invention;
[0092] FIG. 18 is a timing chart showing the relationship between
the initialization process and X-ray photographing when an X-ray
radiation request is generated during the initialization process of
photoelectric conversion elements 5020 in the third embodiment of
the present invention;
[0093] FIG. 19 is a flow chart showing the main routine of an X-ray
photographing method in the third embodiment of the present
invention;
[0094] FIG. 20 is a flow chart showing the subroutine of an
initialization process in the X-ray photographing method in the
third embodiment of the present invention;
[0095] FIG. 21 is a schematic block diagram showing an example of a
conventional X-ray photographing system;
[0096] FIG. 22 is an equivalent circuit diagram of one
photoelectric conversion element;
[0097] FIG. 23 is a timing chart for explaining the initialization
process of one photoelectric conversion element 5020;
[0098] FIG. 24 is a block diagram showing an example of a
flat-panel detector 5004 and flat-panel detector controller
5005;
[0099] FIG. 25 is a timing chart for explaining the initialization
process of a plurality of photoelectric conversion elements
5020;
[0100] FIG. 26 is a timing chart showing the relationship between
the initialization process of photoelectric conversion elements
5020 and X-ray photographing;
[0101] FIG. 27 is a block diagram showing the basic arrangement of
a host computer 5002; and
[0102] FIG. 28 is a view for explaining a memory included in a CPU
5007.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0103] Preferred embodiments of the present invention will now be
described in detail in accordance with the accompanying
drawings.
[0104] [First Embodiment]
[0105] FIG. 1 is a block diagram showing the arrangement of an
X-ray image sensing system according to an embodiment of the
present invention. Referring to FIG. 1, reference numeral 10
denotes an X-ray room; 12, an X-ray control room; and 14, a
diagnosis room. In the X-ray control room 12, a system controller
20 that controls the overall operations of the X-ray image sensing
system of this embodiment is arranged. An operator interface 22,
which includes an X-ray exposure request switch (SW), touch panel,
mouse, keyboard, joystick, foot switch, and the like, is operated
by an operator 21 to input various commands to the system
controller 20. The instruction contents of the operator 21 include,
for example, photographing conditions (still image/moving image,
X-ray tube voltage, tube current, X-ray irradiation time, and the
like), a photographing timing, image processing conditions, a
patient ID, a processing method of a captured image, and the like.
An image sensing controller 24 controls an X-ray image sensing
system set in the X-ray room 10, and an image processor 26 executes
image processes of an image sensed by the X-ray sensing system in
the X-ray room 10. The image processes by the image processor 26
include, for example, correction, spatial filtering, a recursive
process, tone process, a scattered ray correction & dynamic
range (DR) compression process, and the like of image data.
[0106] Reference numeral 28 denotes a large-size, high-speed
storage device for storing basic image data processed by the image
processor 26. The storage device 28 comprises, for example, a RAID
hard disk array. Reference numeral 30 denotes a monitor display (to
be simply referred to as a monitor hereinafter) for displaying a
video; 32, a display controller for controlling the monitor 30 to
display various characters and images; 34, a large-size external
storage device (e.g., a magnetooptical disk); and 36, a LAN board
which connects devices in the X-ray control room 12 and those in
the diagnosis room 14 to transfer, e.g., an image taken in the
X-ray room 10 to the devices in the diagnosis room 14.
[0107] In the X-ray room 10, an X-ray generator 40 for generating
X-rays is set. The X-ray generator 40 comprises an X-ray tube 42
for generating X-rays, a high-voltage generation source 44 for
driving the X-ray tube 42 under the control of the image sensing
controller 24, and an X-ray stop 46 for stopping down an X-ray beam
generated by the X-ray tube 42 to a desired image sensing region,
and a patient 50 as an object to be examined lies on a
photographing bed 48. The photographing bed 48 is driven in
accordance with a control signal from the image sensing controller
24, and can change the direction of the patient with respect to the
X-ray beam coming from the X-ray generator 40. Under the
photographing bed 48, an X-ray detector 52 for detecting the X-ray
beam that has been transmitted through the patient 50 and
photographing bed 48 is arranged.
[0108] The X-ray detector 52 comprises a multilayered structure of
a grid 54, scintillator 56, photodetector array 58, and X-ray
exposure amount monitor 60, and a driver 62 for driving the
photodetector array 58. The grid 54 is used to reduce the influence
of scattered X-rays generated when X-rays are transmitted through
the patient 50. The grid 54 is made up of X-ray low- and
high-absorption members, and comprises a stripe structure of Al and
Pb. The X-ray detector 52 drives the grid 54 in accordance with a
control signal from the driver 62 upon X-ray radiation, so as to
prevent moir from being generated by the grating ratio between the
photodetector array 58 and grid 54.
[0109] In the scintillator 56, the matrix material of a phosphor is
excited (to absorb X-rays) by X-rays with high energy, and
fluorescence in the visible range is generated by recombination
energy generated at that time. That is, the scintillator 56
converts X-rays into visible light. The fluorescence may be
generated by the matrix substance itself such as CaWo.sub.4,
CdWo.sub.4, or the like, or a luminescence center material such as
CsI:Ti, ZnS:Ag, or the like added in the matrix substance. The
photodetector array 58 converts visible light generated by the
scintillator 56 into an electrical signal.
[0110] In this embodiment, the scintillator 56 and photodetector
array 58 are independently arranged. Of course, the present
invention can be applied to a detector that directly converts
X-rays into electrons. For example, a radiation (X-ray) detector,
which comprises a light-receiving unit of amorphous Se, PbI.sub.2,
or the like, an amorphous silicon TFT, and the like, may be
used.
[0111] The X-ray exposure amount monitor 60 is arranged for the
purpose of monitoring the X-ray transmission amount. As the X-ray
exposure amount monitor 60, X-rays may be directly detected using a
light-receiving element of crystalline silicon or the like, or
fluorescence generated by the scintillator 56 may be detected. In
this embodiment, the X-ray exposure amount monitor 60 comprises an
amorphous silicon receiving element formed on the rear surface of a
substrate of the photodetector array 58. The X-ray exposure amount
monitor 60 detects light (proportional to the X-ray dose)
transmitted through the photodetector array 58, and sends that
light amount information to the image sensing controller 24. The
image sensing controller 24 controls the high-voltage generation
source 40 on the basis of the information received from the X-ray
exposure amount monitor 60, thereby controlling the X-ray dose.
[0112] The driver 62 drives the photodetector array 58 under the
control of the image sensing controller 24, and reads signals from
respective pixels. The operations of the photodetector array 58 and
driver 62 will be described in detail later.
[0113] In the diagnosis room 14, an image processing terminal 70
which is used to execute image processes of an image transferred
via the LAN board 36 and to help diagnosis, a video display monitor
72 and image printer 74 for outputting an image (moving image/still
image) transferred via the LAN board 36, and a file server 76 for
storing image data are equipped.
[0114] Note that control signals from the system controller 20 to
respective devices can be generated in response to instructions
from the operator interface 22 in the X-ray control room 12 or from
the image processing terminal 70 in the diagnosis room 14.
[0115] The basic operation of the system controller 20 will be
described below.
[0116] The system controller 20 sends a photographing condition
command to the image sensing controller 24 that controls the
sequence of the X-ray image sensing system on the basis of an
instruction from the operator 21, and the image sensing controller
24 drives the X-ray generator 40, photographing bed 48, and X-ray
detector 52 on the basis of the command, thus taking an X-ray
image. An X-ray image signal output from the X-ray detector 52 is
supplied to the image processor 26, and undergoes image processes
designated by the operator 21. The processed image is displayed on
the monitor 30, and is simultaneously stored in the storage device
28 as basic image data. Furthermore, the system controller 20
executes re-image processes and displays an image as a result of
the processes, and transfers image data to a device on the network
to save, display, and execute a film print process of the image
data, on the basis of an instruction from the operator 21.
[0117] The basic operation of the system shown in FIG. 1 will be
described below along the flow of signals.
[0118] The high-voltage generation source 44 of the X-ray generator
40 applies a high voltage for X-ray generation to the X-ray tube
42. In response to this voltage, the X-ray tube 42 generates an
X-ray beam. The patient 50 as an object to be examined is
irradiated with the generated X-ray beam via the X-ray stop 46. The
X-ray stop 46 is controlled by the image sensing controller 24 in
correspondence with the position to be irradiated with the X-ray
beams. That is, the X-ray stop 46 shapes the X-ray beam to avoid
unnecessary X-ray radiation in correspondence with a change in
image sensing region.
[0119] The X-ray beam output from the X-ray generator 40 is
transmitted through the patient 50 who lies on the X-ray
transmission photographing bed 48, and the photographing bed 48,
and enters the X-ray detector 52. Note that the photographing bed
48 is controlled by the image sensing controller 24 so that an
X-ray beam is transmitted through different portions of the object
to be examined or through the object in different directions.
[0120] The grid 54 of the X-ray detector 52 reduces the influence
of scattered X-rays generated when the X-ray beam is transmitted
through the patient 50. The image sensing controller 24 vibrates
the grid 54 upon X-ray radiation so as not to generate moir due to
the grating ratio between the photodetector array 58 and grid 54.
In the scintillator 56, the matrix material of the phosphor is
excited (to absorb X-rays) by X-rays with high energy, and
fluorescence in the visible range is generated by recombination
energy generated at that time. The photodetector array 58 arranged
in the neighborhood of the scintillator 58 converts the
fluorescence generated by the scintillator 56 into an electrical
signal.
[0121] In other words, the scintillator 56 converts an X-ray image
into a visible light image, and the photodetector array 58 converts
the visible light image into an electrical signal. The X-ray
exposure amount monitor 60 detects visible light (proportional to
the X-ray dose) transmitted through the photodetector array 58, and
supplies the detected amount information to the image sensing
controller 24. The image sensing controller 24 controls the
high-voltage generation source 44 based on the X-ray exposure
amount information to intercept or adjust X-rays. The driver 62
drives the photodetector array 58 under the control of the image
sensing controller 24 to read pixel signals from respective
photodetectors. Details of the photodetector array 58 and driver 62
will be described later.
[0122] Pixel signals output from the X-ray detector 52 are supplied
to the image processor 26 in the X-ray control room 12. Since large
noise is generated inside the X-ray room upon generation of X-rays,
a signal transmission path from the X-ray detector 52 to the image
processor 26 must have high noise resistance. More specifically, a
digital transmission system having an advanced error correction
function, or a twisted pair cable or optical fiber with a shield by
means of a differential driver is preferably used.
[0123] As will be described in detail later, the image processor 26
switches the display format of an image signal on the basis of a
command from the system controller 20. In addition, the image
processor 26 makes correction, spatial filtering, recursive
process, and the like of an image signal in real time, and can
execute a tone process, scattered ray correction & DR
compression process, and the like. The image processed by the image
processor 26 is displayed on the screen of the monitor 30.
[0124] Simultaneously with the real-time image processes, image
information (basic image) that has undergone only image correction
is saved in the storage device 28. Also, based on an instruction
from the operator 21, the image information stored in the storage
device 28 is reconstructed to satisfy a predetermined format (e.g.,
Image Save & Carry (IS&C)), and is then stored in the
external storage device 34 and a hard disk or the like in the file
server 76.
[0125] The devices in the X-ray control room 12 are connected to a
LAN (or WAN) via the LAN board 36.
[0126] A plurality of X-ray image sensing systems can be connected
to the LAN. The LAN board 36 outputs image data in accordance with
a predetermined protocol (for example, Digital Imaging and
Communications in Medicine (DICOM)). When an X-ray image is
displayed on the screen of the monitor 72 connected to the LAN (or
WAN) as a high-resolution still image/moving image, a doctor can
make remote diagnosis in real time at substantially the same timing
as X-ray photographing.
[0127] FIG. 2 is an equivalent circuit diagram of a building unit
of the photodetector array 58.
[0128] One element comprises a photodetector 80 and a switching
thin-film transistor (TFT) 82 that controls charge accumulation and
read. In general, the element formed on a glass substrate using
amorphous silicon (.alpha.-Si). The photodetector 80 comprises a
parallel circuit of a photodiode 80a and capacitor 80b, and a
capacitor 80c connected in series with the capacitor 80b. Also, the
charge obtained as a result of a photoelectric effect is expressed
as a constant current source 81. The capacitor 80b can be the
parasitic capacitance of the photodiode 80a or an additional
capacitor used to improve the dynamic range of the photodiode 80a.
A common bias electrode (to be referred to as a D electrode
hereinafter) of the photodetector 80 is connected to a bias power
supply 84 via a bias line Lb. An electrode on the switching TFT 82
side (to be referred to as a G electrode hereinafter) of the
photodetector 80 is connected to a capacitor 86 and charge read
pre-amplifier 88 via a switching TFT 82. The input of the
pre-amplifier 88 is connected to the ground via a reset switch 90
and signal line bias power supply 91.
[0129] The device operation of the photodetector 80 will be
explained below using FIG. 3.
[0130] FIGS. 3A and 3B are energy band diagrams respectively
showing the refresh and photoelectric conversion mode operations of
a photoelectric conversion element of this embodiment, and
illustrate the states in the direction of thickness of respective
layers.
[0131] Reference numeral 301 denotes a lower electrode (G
electrode) formed of Cr. Reference numeral 302 denotes an SiN
insulating layer that blocks passage of both electrons and holes.
The thickness of the insulating layer 302 is set to be 50 nm or
more, which does not allow electron/hole movement by a tunnel
effect. Reference numeral 303 denotes a photoelectric conversion
semiconductor layer formed of an intrinsic semiconductor i-layer of
amorphous silicon (a-Si) hydride; 304, an injection blocking layer
of an a-Si n-layer, which blocks injection of holes into the
photoelectric conversion semiconductor layer 303; and 305, an upper
electrode (D electrode) made up of Al. In this embodiment, although
the D electrode does not completely cover the n-layer, since
electrons can move freely between the D electrode and n-layer, the
D electrode and n-layer always have equal potentials, and the
following explanation will be given under the condition of that
fact. The photoelectric conversion element has two different
operations, i.e., a refresh mode and photoelectric conversion mode,
depending on the way a voltage is applied to the G electrode.
[0132] In FIG. 3A, a negative potential with respect to the G
electrode is applied to the D electrode, and holes indicated by
full circles in the i-layer 303 are guided to the D electrode by
the electric field. At the same time, electrons indicates by open
circles are injected into the i-layer 303. At the same time, some
holes and electrons recombine and disappear in the n-layer 304 and
i-layer 303. If this state continues for a sufficiently long period
of time, holes in the i-layer 303 are swept out from the i-layer
303.
[0133] In order to set the photoelectric conversion mode (FIG. 3B)
from the aforementioned state, a positive potential with respect to
the G electrode is applied to the D electrode. Then, electrons in
the i-layer 303 are instantaneously guided to the D electrode.
However, since the n-layer serves as an injection blocking layer,
holes are never guided to the i-layer 303. When light becomes
incident on the i-layer 303 in this state, the light is absorbed to
generate an electron-hole pair. This electron is guided to the D
electrode by the electric field, and the hole moves in the i-layer
303 and reaches the interface between the i-layer 303 and
insulating layer 302. However, since the hole cannot move into the
insulating layer 302, it moves to the interface with the insulating
layer 302 in the i-layer 303, and a current for maintaining
electroneutrality in the element flows from the G electrode. Since
this current corresponds to the electron.cndot.hole pair generated
by the light, it is proportional to the incoming light.
[0134] After the state of the photoelectric conversion mode shown
(FIG. 3B) is maintained for a given period of time, if the state of
the refresh mode (FIG. 3A) is set, holes which stay in the i-layer
303 are guided to the D electrode, as described above, and a
current corresponding to these holes flows at the same time. The
quantity of holes corresponds to the total amount of incoming light
during the photoelectric conversion mode period. At this time, a
current corresponding to the quantity of electrons injected into
the i-layer 303 also flows. However, since this quantity is nearly
constant, it can be subtracted upon detection. That is, the
photoelectric conversion element in this embodiment can output the
amount of incoming light in real time, and can also output the
total amount of incoming light during a given period.
[0135] However, when the photoelectric conversion mode period is
prolonged for some reason, or when incoming light has high
illuminance, a current does not often flow although light enters.
Such phenomenon occurs since a large number of holes stay in the
i-layer 303 and a newly generated electron is recombined with a
hole in the i-layer 303 due to the presence of those holes. If the
incoming light state changes in this state, a current often flows
unstably. However, if the refresh mode is set again, holes in the
i-layer 303 are swept out, and a current proportional to light
flows again in the next photoelectric conversion mode.
[0136] In the above description, when holes in the i-layer 303 are
swept out in the refresh mode, it is ideal to sweep out all holes,
but it is still effective to sweep out only some holes. In this
case, a current equal to that described above can be obtained, and
no problem is posed. That is, it is required to only prevent the
state shown in FIG. 3C at the detection opportunity of the next
photoelectric conversion mode, and the potential of the D electrode
with respect to the G electrode in the refresh mode, the period of
the refresh mode, and the characteristics of the injection blocking
layer of the n-layer 304 need only be determined to meet such
requirement.
[0137] Furthermore, injection of electrons into the i-layer 303 in
the refresh mode is not a necessary condition, and the potential of
the D electrode with respect to the G electrode is not limited to
negative. When a large number of holes stay in the i-layer 303,
even when the potential of the D electrode with respect to the G
electrode is positive, the electric field in the i-layer 303 acts
in a direction to guide the holes toward the D electrode. Likewise,
in the characteristics of the injection blocking layer of the
n-layer 304, whether or not electrons can be injected into the
i-layer 303 is not a necessary condition.
[0138] Referring back to FIG. 2, read of a signal from one pixel
will be explained.
[0139] The switching TFT 82 and reset switch 90 are temporarily
turned on to set the bias power supply 84 at a potential in the
refresh mode. After the capacitors 80b and 80c are reset, the bias
power supply 84 is set at a potential in the photoelectric
conversion mode, and the switching TFT 82 and reset switch 90 are
sequentially turned off. After that, X-rays are generated to
irradiate the patient 50 with them. The scintillator 54 converts an
X-ray image that has been transmitted through the patient 50 into a
visible light image, and the photodiode 80a is enabled by that
visible light image to discharge the charge on the capacitor 80b.
The switching TFT 82 is turned on to connect the capacitors 80b and
86. In this manner, the information in the capacitor 80c is also
supplied to the capacitor 86. A voltage corresponding to the charge
accumulated on the capacitor 86 is amplified by the pre-amplifier
88, or that charge is charge-voltage converted by a capacitor 89
indicated by the dotted line, and the voltage is externally
output.
[0140] FIG. 4 is an equivalent circuit diagram of a building unit
of the photodetector array 58.
[0141] One element comprises a photodetector 80 and a switching
thin-film transistor (TFT) 82 that controls charge accumulation and
read. In general, the element is formed on a glass substrate using
amorphous silicon (.alpha.-Si). The photodetector 80 comprises a
parallel circuit of a photodiode 80a and capacitor 80b, and a
charge obtained as a result of a photoelectric effect is expressed
as a constant current source 81. The capacitor 80b can be a
parasitic capacitance of the photodiode 80a or an additional
capacitor used to improve the dynamic range of the photodiode 80a.
The cathode of the photodetector 80 (photodiode 80a) is connected
to a bias power supply 85 via a bias line Lb which serves as a
common electrode (D electrode). The anode of the photodetector 80
(photodiode 80a) is connected from the gate electrode (G electrode)
to a capacitor 86 and charge read preamplifier 88 via the switching
TFT 82. The input of the pre-amplifier 88 is connected to the
ground via a reset switch 90 and signal line bias power supply
91.
[0142] The switching TFT 82 and reset switch 90 are temporarily
turned on to reset the capacitor 80b, and are then turned off.
After that, X-rays are generated to irradiate the patient 50 with
them. The scintillator 54 converts an X-ray image that has been
transmitted through the patient 50 into a visible light image, and
the photodiode 80a is enabled by that visible light image to
discharge the charge on the capacitor 80b. The switching TFT 82 is
turned on to connect the capacitors 80b and 86. In this manner,
information in the capacitor 80c is also supplied to the capacitor
86. A voltage corresponding to the charge accumulated on the
capacitor 86 is amplified by the pre-amplifier 88, or the charge is
charge-voltage converted by a capacitor 89 indicated by the dotted
line, and the voltage is externally output.
[0143] The photoelectric conversion operation using a
two-dimensional matrix of the photoelectric conversion elements
shown in FIG. 2 or 4 will be explained below.
[0144] FIG. 5 is an equivalent circuit diagram of the photodetector
array 58 which comprises a two-dimensional matrix of photoelectric
conversion elements.
[0145] Since the aforementioned two different equivalent circuits
undergo the same two-dimensional read operation, FIG. 5 is
expressed using the equivalent circuit shown in FIG. 4.
[0146] The photodetector array 58 comprises about 2000.times.2000
to 4000.times.4000 pixels, and has an array area of about 200
mm.times.200 mm to 500 mm.times.500 mm. In FIG. 5, the
photodetector array 58 comprises 4096.times.4096 pixels, and has an
array area of 430 mm.times.430 mm. Therefore, one pixel size is
about 105 .mu.m.times.105 .mu.m. 4096 pixels arranged in the
horizontal direction to form one block, and 4096 blocks are
arranged in the vertical direction to form a two-dimensional
matrix.
[0147] In FIG. 5, the photodetector array consisting of
4096.times.4096 pixels is formed on a single substrate, but four
photodetector arrays each having 2048.times.2048 pixels may be
combined. In this case, although labor for assembling the four
photodetector arrays is required, since the yield of each
photodetector array can be improved, the total yield can also be
improved.
[0148] As has been explained using FIGS. 2 and 4, one pixel
comprises one photodetector 80 and switching TFT 82. Photoelectric
conversion elements PD(1,1) to PD(4096, 4096) correspond to the
photodetector 80, and transfer switches SW(1,1) to SW(4096, 4096)
correspond to the switching TFT 82. The gate electrode of a
photoelectric conversion element PD(m, n) is connected to a column
signal line Lcm common to that column via a corresponding switch
SW(m, n). For example, photoelectric conversion elements PD(1, 1)
to PD(4096, 1) of the first column are connected to a first column
signal line Lc1. The common electrode (D electrode) of each
photoelectric conversion element PD(m, n) is connected to a bias
power supply 85 via a bias line Lb.
[0149] The control terminal of a switch SW(m, n) of a given row is
connected to a common row select line Lrn. For example, the
switches SW(1, 1) to SW(1, 4096) of the first row are connected to
a row select line Lr1. Row select lines Lr1 to Lr4096 are connected
to the image sensing controller 24 via a line selector 92.
[0150] The line selector 92 comprises an address decoder 94 which
decodes a control signal from the image sensing controller 24 and
determines a line from which signal charges of photoelectric
conversion elements are to be read, and 4096 switches 96 which are
turned on/off in accordance with the output from the address
decoder 94. With this arrangement, signal charges of photoelectric
conversion elements PD(m, n) connected to switches SW(m, n), which
are connected to an arbitrary line Lrn, can be read. In the
simplest arrangement, the line selector 92 may comprise a shift
register used in a liquid crystal display or the like.
[0151] Column signal lines Lc1 to Cl4096 are connected to a signal
read circuit 100, which is controlled by the image sensing
controller 24. In the signal read circuit 100, reference numerals
102-1 to 102-4096 denote reset switches for respectively resetting
the column signal lines Lc1 to Lc4096 to a reset reference
potential 101. Reference numerals 106-1 to 106-4096 denote
pre-amplifiers for amplifying signal potentials from the column
signal lines Lc1 to Lc4096, respectively; 108-1 to 108-4096,
sample/hold (S/H) circuits for sampling and holding the outputs
from the pre-amplifiers 106-1 to 106-4096; 110, an analog
multiplexer for multiplexing the outputs from the S/H circuits
108-1 to 108-4096 on the time axis; and 112, an A/D converter for
converting an analog output from the multiplexer 110 into a digital
signal. The output from the A/D converter 112 is supplied to the
image processor 26.
[0152] In the photodetector array shown in FIG. 5, 4096.times.4096
pixels are divided into 4096 columns by the column signal lines Lc1
to Lc4096, signal charges from 4096 pixels per row are
simultaneously read, the read charges are transferred to the analog
multiplexer 110 via the column signal lines Lc1 to Lc4096,
pre-amplifiers 106-1 to 106-4096, and S/H circuits 108-1 to
108-4096, the transferred charges are multiplexed by the analog
multiplexer 110 on the time axis, and the multiplexed signal is
converted into a digital signal by the A/D converter 112.
[0153] In FIG. 5, the signal read circuit 100 is illustrated to
have only one A/D converter 112. However, in practice, four to 32
A/D converters simultaneously execute A/D conversion. This is
because it is required to shorten the image signal read time
without needlessly increasing the analog signal band and A/D
conversion rate. The signal charge accumulation time and A/D
conversion time are closely related. If A/D conversion is done at
high speed, the bandwidth of an analog circuit broadens, and it
becomes difficult to attain a desired S/N ratio. For this reason,
it is normally required to shorten the image signal read time
without needlessly increasing the A/D conversion rate. In this
case, the output from the multiplexer 110 can be A/D-converted
using many A/D converters. However, if a large number of A/D
converters are used, the cost increases accordingly. Therefore, in
consideration of the above situations, an appropriate number of A/D
converters are used.
[0154] Since the X-ray irradiation time is approximately 10 to 500
msec, it is appropriate to set the capture time or charge
accumulation time of the entire frame on the order of 100 msec or
shorter.
[0155] For example, in order to drive all pixels in turn and to
capture an image in 100 msec, if the analog signal frequency band
is set to be about 50 MHz and A/D conversion is done at a sampling
rate of 10 MHz, at least four A/D converters are required. In this
embodiment, 16 A/D converters simultaneously execute A/D
conversion. The outputs from the 16 A/D converters are input to 16
memories (FIFOs or the like; not shown). By selectively switching
these memories, image data corresponding to one, continuous scan
line is transferred to the image processor 26.
[0156] FIG. 6 is a timing chart showing an outline of a sensor read
process, and the two-dimensional drive process upon sensing a still
image by one-shot X-ray irradiation will be explained below using
both FIGS. 5 and 6.
[0157] Reference numeral 601 denotes an exposure request control
signal to the X-ray source; 602, an X-ray exposure state; 603, a
current of the constant current source 81 in the sensor; 604, a
control state of the row select line Lrn; and 605, an analog input
to the A/D converter 112.
[0158] In the equivalent circuit sensor shown in FIG. 2, the driver
62 sets the bias line to be a bias value Vr in the refresh mode,
connects all the column signal lines Lc1 to Lc4096 to the reset
reference potential 101 to reset them to an initial bias value of
the column signal lines Lc, and applies a positive voltage Vgh to
all the row select lines Lr1 to Lr4096. As a result, the switches
SW(1, 1) to SW(4096, 4096) are turned on, and the G and D
electrodes of all the photoelectric conversion elements are
respectively refreshed to Vbt and Vr.
[0159] After that, the driver 62 sets the bias line Lb to be a bias
value Vs in the photoelectric conversion mode, disconnects all the
column signal lines Lc1 to Lc4096 from the reset reference
potential 101, and applies a voltage Vg1 to all the row select
lines Lr1 to Lr4096 to turn off the switches SW(1, 1) to SW(4096,
4096). In this manner, the control enters the photoelectric
conversion mode.
[0160] Since the following operations are common to the equivalent
circuit sensors shown in FIGS. 2 and 4, they will be explained
simultaneously.
[0161] All the column signal lines Lc are connected to the reset
reference potential 101 while the bias line maintains the bias
value Vs in the photoelectric conversion mode, thereby resetting
the column signal lines. After that, a positive voltage Vgh is
applied to the row select line Lr1 to turn on the switches SW(1, 1)
to SW(1, 4096), thus resetting the G electrodes of the
photoelectric conversion elements of the first column to Vbt. A
positive voltage Vg1 is then applied to the row select line Lr1 to
turn off the switches SW(1, 1) to SW(1, 4096). Row selection is
repeated in turn to reset all the pixels, thus completing
photographing preparation. The aforementioned operation is
substantially the same as the signal charge read operation, except
for whether or not signal charges are captured. Hence, this reset
operation will be referred to as an "idle read" operation
hereinafter. During this idle read operation, it is possible to
simultaneously set all the row select lines Lr at Vgh. However, in
this case, the signal line potential largely deviates from the
reset voltage Vbt at the time of completion of read preparation,
and it becomes difficult to obtain a high S/N signal. In the above
example, the row select lines are reset in turn from 1 to 4096, but
they can be reset in an arbitrary order under the control of the
driver 62 on the basis of the setup of the image sensing controller
24.
[0162] The idle read operation is repeated, and the control waits
for an X-ray exposure request.
[0163] Upon generation of the exposure request, the idle read
operation is redone to prepare for image capture, i.e., X-ray
exposure. Upon completion of image capture preparation, X-ray
exposure starts in accordance with an instruction from the image
sensing controller 24.
[0164] After X-ray exposure, signal charges on the photoelectric
conversion elements 80 are read. A voltage Vgh is applied to a row
select line Lr corresponding to an arbitrary row (e.g., Lr1) of the
photoelectric conversion element array to output accumulated charge
signals onto the signal lines Lc1 to Lc4096. From the column signal
lines Lc1 to Lc4096, signals for 4096 pixels are simultaneously
read column by column.
[0165] A voltage Vgh is applied to another row select line Lr
(e.g., Lr2) to output accumulated charge signals onto the signal
lines Lc1 to Lc4096. From the column signal lines Lc1 to Lc4096,
signals for 4096 pixels are simultaneously read column by column.
By repeating this operation in turn for 4096 signal lines, all the
pieces of image information are read.
[0166] During the above operations, the charge accumulation time of
each sensor is defined by the time period from when the reset
operation is completed, i.e., the TFT 82 is turned off in the idle
read operation, until that TFT 82 is turned on to read a charge.
Therefore, the respective row select lines have different
accumulation time periods and timings.
[0167] After an X-ray image is read, a correction image is
captured. This correction image is correction data which is used to
correct the X-ray image, and is required to capture a high-quality
image. The basic image capture method is substantially the same as
the X-ray image capture method, except that no X-ray exposure is
made. The charge accumulation time upon reading an X-ray image is
the same as that upon reading the correction image.
[0168] When high-resolution image information is not required or
when image data is captured at high speed, all pieces of image
information need not always be captured, and the image sensing
controller 24 sets decimation, pixel average, and region extraction
drive instructions in the driver 62 in accordance with the
photographing method selected by the operator 21.
[0169] Decimation is attained as follows. That is, when the row
select line Lr1 is selected, and signals are output from the column
signal lines Lc, a read operation for each column is made by, e.g.,
incrementing n (n: natural number) of Lc2n-1 by one from zero.
After that, upon selecting a row, m (m: natural number) of a row
select line Lr2m-1 is incremented by one from 1 to read signals for
one row. In this example, the number of pixels is decimated to 1/4.
Also, the driver 62 decimates the number of pixels to {fraction
(1/9)}, {fraction (1/16)}, and the like in accordance with the
setup instruction of the image sensing controller 24.
[0170] As for the pixel average, during the aforementioned
operations, a voltage Vgh is simultaneously applied to row select
lines Lr2m and Lr2m+1 to simultaneously turn on TFTs (2m, 2n) and
(2 m+1, 2n), thus allowing analog addition of two pixels in the
column direction. In this process, the number of pixels to be added
is not limited to two, but a plurality of pixels in the column
signal line direction can easily undergo analog addition.
Furthermore, as for addition in the row direction, when neighboring
pixels (Lc2n and Lc2n+1) undergo digital addition after A/D
conversion, the sum of a 2.times.2 pixel matrix can be obtained in
combination with the above analog addition. In this manner, data
can be read at high speed without wasting irradiated X-rays. As
another method of achieving a high-speed process by reducing the
total number of pixels, a method of limiting the image capture
region is available.
[0171] In this method, the operator 21 inputs a required region
from the operator interface 22, the image sensing controller 24
issues an instruction to the driver 62 on the basis of the input
region, and the driver 62 changes the data capture range to drive
the two-dimensional photodetector array.
[0172] In this embodiment, in a high-speed capture mode,
1024.times.1024 pixels are captured at 30 F/S. That is, the
addition process of 4.times.4 pixels is executed for the entire
region of the two-dimensional photodetector array to decimate
pixels to {fraction (1/16)}. In the smallest range, an image of a
1024.times.1024 region is sensed without decimation. With this
image sensing, a digital zoom image is obtained.
[0173] FIG. 7 is a timing chart including the image sensing
operation of the X-ray detector 52. The operation of the X-ray
detector 52 will be explained below mainly using FIG. 7. Reference
numeral 701 denotes an image sensing request signal to the operator
interface 22; 702, an actual X-ray exposure state; 703, an image
sensing request signal from the image sensing controller 24 to the
driver 62 on the basis of an instruction of the operator 21; 704, a
photographing ready signal of the X-ray detector 52; 705, a drive
signal of the grid 54; 706, a power control signal in the X-ray
detector 52; and 707, a drive state of the X-ray detector
(especially, a charge read operation from the photodetector array
58). Reference numeral 708 generally denotes a transfer state,
image process, and display state of image data.
[0174] The driver 62 stands by while setting the power control OFF,
as indicated by 706, until it receives a detector preparation
request or photographing request from the operator 21. More
specifically, in FIG. 5, the driver 62 maintains the potentials of
the row select lines Lr, column signal lines Lc, and bias line Lb
to be the same potential (especially, signal GND level) using
switches (not shown), and does not apply any bias to the
photodetector array 58. Furthermore, the driver 62 may maintain the
potentials of the row select lines Lr, column signal lines Lc, and
bias line Lb to be the GND potential by shutting off the signal
read circuit 100, line selector 92, and power supplies including
the bias power supply 84 or 85.
[0175] When the operator 21 inputs a photographing preparation
request instruction (701: 1st SW) at the operator interface 22, the
image sensing controller 24 shifts the X-ray generator 40 to a
photographing ready state, and issues an instruction for shifting
the X-ray detector 52 to a photographing preparation state to the
X-ray detector 52. Upon receiving the instruction, the driver 62
applies a bias to the photodetector array 58 and repeats (refresh
and) idle read frames Fi. The request instruction is issued to
start preparation for the X-ray detector 52 when the 1st switch
(normally, rotor up of the tube or the like starts) of an exposure
request SW to the X-ray generation device or the X-ray detector 52
requires a predetermined period of time (several sec or more) for
photographing preparation. In this case, the operator 21 need not
intentionally issue the photographing preparation request
instruction. That is, when the operator inputs patient information,
photographing information, or the like at the operator interface
22, the image sensing controller 24 may interpret that information
as a detector preparation request instruction, and may shift the
X-ray detector 52 to a detector preparation state.
[0176] In the detector preparation state, in order to prevent the
capacitors 80b (80c) from being held in a saturation state due to
dark currents gradually accumulated in the photodetectors 80 in the
photoelectric conversion mode after idle read, (refresh R and) idle
read frames Fi are repeated at predetermined intervals. This drive
process to be done during a period in which no actual X-ray
exposure request is generated after generation of the photographing
preparation request from the operator 21, i.e., the drive process
that repeats idle read frames Fi to be done in the detector
preparation state at predetermined time intervals T1, will be
referred to as "idling drive" hereinafter, and the period of the
detector preparation state in which the idling drive is done will
be referred to as an "idling drive period" hereinafter. Since the
duration of the idling drive period is not defined (not specified)
in practical use, idling-dedicated idle read frames Fi in which T1
is set to be longer than a normal photographing operation and the
ON time period of the TFTs 82 is shorter than a normal read drive
frame Fr are made so as to minimize read operations that impose
heavy loads on the photodetector array 58 (especially, TFTs 82). In
case of a sensor that requires a refresh R operation, the refresh R
operation is made once per several idle read frames Fi.
[0177] The X-ray image capture process around the X-ray detector 52
will be explained below.
[0178] The drive process of the X-ray detector 52 upon capturing an
X-ray image roughly includes two image capture processes. As
indicated by 707, one process is an X-ray image capture drive
process, and the other process is a correction dark image capture
drive process. These drive processes are substantially the same,
except for whether or not X-ray exposure is made. Furthermore, each
drive process includes three parts, i.e., an image sensing
preparation sequence, charge accumulation (exposure window), and
image read.
[0179] The X-ray image capture process will be explained in turn
below.
[0180] When the operator 21 inputs a photographing request
instruction (701: 2nd SW) at the operator interface 22, the image
sensing controller 24 controls the photographing operation while
synchronizing the X-ray generator 40 and X-ray detector 52. That
is, the controller 24 asserts an image sensing request signal to
the X-ray detector at a timing indicated by the X-ray exposure
request signal 703 in accordance with the photographing request
instruction (701: 2nd SW). The driver makes predetermined image
sensing preparation sequence drive, as indicated by the image
sensing drive state 707, in response to the image sensing request
signal.
[0181] More specifically, the refresh operation is done if it is
required, a predetermined number of times of charge sweep-out idle
read frames FP for the image sensing sequence and a charge
accumulation start-dedicated idle read frame Fpf are executed, and
the control shifts to the charge accumulation state (image sensing
window: T4). In this case, the number of times and time intervals
T2 of the charge sweep-out idle read frames Fp are determined based
on values set by the image sensing controller 24 prior to the image
sensing request. An optimal drive process is automatically selected
depending on whether importance is attached to operability or image
quality, or an image sensing portion in accordance with the request
from the operator 21.
[0182] Normally, a drive process is made in a short period of time
(about 1 ms) to improve response to the exposure request. Since a
period (T3) from the exposure request until completion of
photographing preparation is required to be short in practical use,
the image sensing preparation sequence charge sweep-out idle read
frame Fp is executed for this purpose. Upon generation of the
exposure request, since the image sensing preparation sequence
drive immediately starts independently of the idling drive state,
the period (T3) from the exposure request until completion of
photographing preparation can be shortened, thereby improving
operability.
[0183] The driver 62 begins to move the grid 54 in synchronism with
image sensing preparation of the photodetector array 58. This is to
sense an image in an optimal moving state of the grid in
synchronism with actual X-ray exposure 702. In this case, as well,
the grid begins to move at an optimal grid movement start timing
and optimal grid moving speed, which are set by the image sensing
controller.
[0184] Since this embodiment recognizes vibrations generated upon
operation of the grid 54 as a problem, the start of the grid 54 is
controlled to minimize a change in acceleration, and the grid 54 is
preferably controlled to move at a constant speed upon executing
the charge accumulation start-dedicated idle read frame Fpf which
is readily influenced by vibrations.
[0185] When the X-ray detector 52 is ready to sense an image, the
driver 62 returns an X-ray detector ready signal 704 to the image
sensing controller 24, which asserts an X-ray generation request
signal 702 to the X-ray generator 40 on the basis of the change in
signal 704. The X-ray generator 40 generates X-rays while it
receives the X-ray generation request signal 702. After a
predetermined X-ray dose is generated, the image sensing controller
24 negates the X-ray generation request signal 702, and also
negates the X-ray image sensing request signal 703 to inform the
X-ray detector 52 of an image capture timing. Based on this timing,
the driver 62 immediately stops the grid 54, and starts the
operation of the signal read circuit 100, which is in the standby
state. After an elapse of the stop time of the grid 54 and a
predetermined wait time required until the signal read circuit 100
becomes stable, image data is read out from the X-ray photodetector
array 58 based on the driver 62, thus capturing a raw image in the
image processor 26. Upon completion of transfer, the driver 62 sets
the read circuit 100 in the standby state again.
[0186] Since this embodiment recognizes vibrations generated upon
operation of the grid 54 as a problem, it is desirable that the
grid 54 reaches constant-speed motion (including a still state)
before driving of an X-ray image capture frame Frxo, which is most
readily influenced by vibration noise. Furthermore, a vibration
sensor may be attached inside the X-ray detector 52 to measure
vibrations, and after it is confirmed vibrations caused by the grid
or other factors have subsided to a predetermined value or less,
the driving of the X-ray image capture frame Frxo may be
started.
[0187] Subsequently, the X-ray detector 52 captures a correction
image. That is, the previous image sensing sequence for image
sensing is repeated to capture a dark image without X-ray
irradiation, and the correction dark image is transferred to the
image processor 26.
[0188] At this time, the image sensing sequence may have a slightly
different X-ray exposure time or the like for each photographing.
An image with higher quality can be obtained by reproducing the
same photographing sequence as well as such different X-ray
exposure time upon capturing a dark image. However, the grid 54
stands still upon capturing a dark image so as to suppress the
influence of vibrations. After the dark image is captured, the grid
54 is initialized at a predetermined timing that does not influence
image quality.
[0189] FIG. 8 shows the image processor 26, and also the flow of
image data. Reference numeral 801 denotes a multiplexer for
selecting a data path; 802 and 803, frame memories for an X-ray
image and dark image, respectively; 804, an offset correction
circuit; 805, a gain correction data frame memory; 806, a gain
correction circuit; 807, a defect correction circuit; and 808,
another image processing circuit.
[0190] An X-ray image captured by the X-ray image capture frame
Frxo in FIG. 7 is stored in the X-ray image frame memory 802 via
the multiplexer 801, and a correction image captured by the
correction image capture frame Frno is similarly stored in the dark
image frame memory 803 via the multiplexer 801. After the dark
image is stored, the offset correction circuit 804 makes offset
correction (e.g., Frxo-Frno), and the gain correction circuit 806
then makes gain correction (e.g., Frxo-Frno)/Fg) using gain
correction data Fg, which is captured in advance and is stored in
the gain correction frame memory.
[0191] Subsequently, image data transferred to the defect
correction circuit 807 is continuously corrected to prevent
unnaturalness at defective pixels, joint portions of the X-ray
detector 52, which is formed by a plurality of panels, and the
like, thus completing a sensor-dependent correction process
resulting from the X-ray detector 52. Furthermore, the image data
undergoes other general image processes such as a tone process,
frequency process, emphasis process, and the like by the image
processing circuit 808, and the processed data is transferred to
the display controller 32 to display a taken image on the monitor
30.
[0192] Prior to the description of the drive process of the
dedicated frames in FIG. 7 in this embodiment, the image capture
process will be explained again using FIG. 9. Reference numerals
901-1, 902-2, 901-3, . . . denote the outputs from the TFT switch
elements 96-1, 96-2, 96-3, . . . ; 902, an analog output from the
pre-amplifier 106-n; 903, a control signal of the S/H circuit
108-n; and 904, a control signal of the reset switch 102-n of the
column signal line Lc.
[0193] The column signal line Lc-n is reset, so that a signal
charge can be output onto the column signal line Lc-n. The switch
element 901-1 is then turned on to select the row select line Lr-1.
A charge signal is output onto the column signal line Lc-n, and the
pre-amplifier 902 generates an output corresponding to the received
X-ray dose. A time period until this signal output becomes stable
is determined by the charge transfer performance (ON resistance:
about several M.OMEGA.) of the TFT 82, the signal line capacitance
(capacitor 86: several pF to several ten pF), and the like. In this
embodiment, several ten .mu.s to several hundred .mu.s are
required, and the TFT is normally enabled during this period. After
the charge transfer becomes stable, the S/H circuit 108-n is
controlled (903) to receive the dose signal. A description of the
capture system after the S/H circuits will be omitted here.
[0194] In order to read a charge on the row select line Lr-2, the
column signal lines Lc are reset (904). At the reset completion
timing, the row select line Lr-2 is selected (901-2). Likewise, a
charge signal corresponding to the X-ray dose is output onto the
column signal line Lc-n. After that, dose data are similarly read
up to the line Lr-4096. In the idle read operation, charges on the
photodetectors 80 are reset by executing the aforementioned
operations without capturing any image.
[0195] FIG. 10 shows the operations of the charge accumulation
start-dedicated idle read frame Fpf, X-ray image capture frame
Frxo, and correction image capture frame Frno, FIG. 11 shows the
operation of the idling-dedicated idle read frame Fi, and FIG. 12
shows the operation of the charge sweep-out idle read frame Fp for
the image sensing sequence.
[0196] As is known, the drive process of the X-ray image capture
frame Frxo is the same as that of the correction image capture
frame Frno. In the charge accumulation start-dedicated idle read
frame Fpf, after TFT of each row select line is turned off,
accumulation of the photodetector 80 connected to that row select
line Lr starts. For this reason, in order to adjust the
accumulation times of the respective rows, the image capture frame
and charge accumulation start frame must inevitably have the same
drive process.
[0197] In the idling-dedicated idle read frame Fi, the drive
process is done to shorten the ON time of each TFT. In FIG. 11, the
read time per line is also halved. In this embodiment, the ON
voltage of the TFT is 12 to 20 V, while its OFF voltage is -5 V to
GND level. Therefore, as the ON time of the TFT is longer, the
threshold voltage of the TFT shifts, resulting in performance
deterioration of the TFT transfer performance.
[0198] Since the duration of the idling drive period is unknown in
practical use, the ON time of the TFT is preferably as short as
possible. As described above using FIG. 7, a long interval T1 is
assured (>1 sec) between neighboring idling-dedicated idle read
frames Fi, and the drive time is halved in the idling-dedicated
idle read frame Fi compared to a normal photographing drive time to
shorten the ON time of the TFT. Although the ON time of the TFT is
halved, since a charge to be transferred is based on only a dark
current, no problem is posed in terms of characteristics even by
the aforementioned drive process. Just for reference, as shown in
FIG. 13, the drive process may be made, so that the time per line
remains the same as the normal image capture frame, and only the ON
time of the TFT is shortened. In case of a sensor that requires the
refresh R operation, since several minutes to several ten minutes
are required until a sensor saturation state is reached due to the
accumulated dark currents, the refresh R operation can be made once
per several idling-dedicated idle read frames Fi.
[0199] Since the charge sweep-out idle read frame FP for the image
sensing sequence is made for the purposes of sweeping out charges
in the photodetectors 80, and of reducing the time period before
X-ray exposure, the time required to drive one line is set to be
short (1/2 that of the normal image capture frame in FIG. 12), and
the ON time of each TFT is set to be equal to a 1-line drive time
to sweep out a charge.
[0200] As described above, according to this embodiment, even when
the idling drive period which is hard to specify in practical use
continues long, highly reliable image sensing can be realized while
suppressing a decrease in service life and aging of various
characteristics that pertain to detection of the X-ray image
sensing apparatus (system).
[0201] FIG. 14 is a block diagram showing the internal arrangement
of a general personal user terminal. Referring to FIG. 14,
reference numeral 1200 denotes a computer PC. The PC 1200 comprises
a CPU 1201, and executes device control software stored in a ROM
1202 or hard disk (HD) 1211 or supplied from a flexible disk drive
(FD) 1212 to systematically control respective devices connected
via a system bus 1204.
[0202] The CPU 1201 of the PC 1200 and the program stored in the
ROM 1202 or hard disk (HD) 1211 implement the functions of
respective building components of the X-ray image sensing apparatus
(system) of this embodiment.
[0203] Reference numeral 1203 denotes a RAM, which serves as a main
memory, work area, and the like of the CPU 1201. Reference numeral
1205 denotes a keyboard controller (KBC), which controls
instruction inputs from a keyboard (KB) 1209, a device (not shown),
and the like.
[0204] Reference numeral 1206 denotes a CRT controller (CRTC) which
controls display of a CRT display (CRT) 1210. Reference numeral
1207 denotes a disk controller (DKC), which controls accesses to
the hard disk (HD) 1211 and flexible disk (FD) 1212, which store a
boot program (startup program: a program for starting execution
(operation) of hardware and software of a personal computer), a
plurality of application programs, edit files, user files, network
management program, and the like.
[0205] Reference numeral 1208 denotes a network interface card
(NIC) which exchanges data in two ways with a network printer,
other network devices, or other PCs via a LAN 1220.
[0206] The sequence of the X-ray image sensing method explained in
this embodiment can be implemented when the program stored in the
RAM, ROM, or the like of the computer runs. This program and a
computer-readable storage medium that records the program are
included in an embodiment of the present invention.
[0207] More specifically, the program is supplied to the computer
via a recording medium such as a CD-ROM or the like that records
the program or various transmission media. As the recording medium
which records the program, a flexible disk, hard disk, magnetic
tape, magnetooptical disk, nonvolatile memory card, and the like
can be used in addition to the CD-ROM. On the other hand, as the
program transmission medium, communication media (wired channels
such as optical fibers, wireless channels, and the like) in
computer network (LAN, WAN such as the Internet or the like,
wireless communication network, and the like) system for supplying
program information by transmitting it as a carrier can be
used.
[0208] Such program is also included in an embodiment of the
present invention when the functions of the above embodiment are
implemented not only by executing the supplied program by the
computer but also by collaboration of the computer, and an OS
(operating system) running on the computer, another application
software, or the like, and by executing some or all processes of
the supplied program by a function extension board or unit of the
computer.
[0209] According to the image sensing apparatus and image sensing
method of the present invention, even when the idling drive period
which is hard to specify in practical use continues long, highly
reliable image sensing can be realized while suppressing a decrease
in service life and aging of various characteristics that pertain
to detection of the apparatus.
[0210] [Second Embodiment]
[0211] In this embodiment, an X-ray photographing system which
includes an X-ray photographing apparatus as a combination of a
phosphor and photoelectric conversion element and its process will
be explained below. The arrangement of the X-ray photographing
system of this embodiment is the same as that shown in FIG. 21.
Also, since a flat-panel detector 5004 and flat-panel detector
controller 5005 of this embodiment are the same as those shown in
FIG. 10, a description thereof will be omitted.
[0212] FIG. 27 shows the basic arrangement of a host computer 5002
used in this embodiment.
[0213] Reference numeral 51301 denotes a CPU which controls the
overall host computer 5002 using programs and data stored in a RAM
51302 and ROM 51303, and also controls exchange of signals with an
X-ray photographing apparatus 5001 and the flat-panel detector
controller 5005.
[0214] Reference numeral 51302 denotes a RAM which has an area for
temporarily storing programs and data loaded from an external
storage device 51304 and storage medium drive 51309, and also a
work area temporarily used by the CPU 51301 upon executing
respective processes.
[0215] Reference numeral 51303 denotes a ROM which stores a boot
program, setup data, overall control program, data, and the like of
the host computer 5002.
[0216] Reference numeral 51304 denotes an external storage device
such as a hard disk or the like, which saves programs, data, and
the like installed from the storage medium driver 51309. When the
work area size has exceeded the size of the RAM 51302, the external
storage device 51304 can provide a corresponding area as a
file.
[0217] Reference numerals 51305 and 51306 denote a keyboard and
mouse, respectively, which serve as pointing devices and can input
various instructions to the host computer 5002.
[0218] Reference numeral 51307 denotes a display device, which
comprises a CRT, liquid crystal display, or the like and can
display system messages and the like as text information and image
information.
[0219] Reference numeral 51308 denotes an interface (I/F), which
can be connected to networks such as the Internet, LAN, and the
like, and external apparatuses. Note that the number of I/Fs is one
in FIG. 27. However, the present invention is not limited to this,
and a plurality of I/Fs may be provided. In this embodiment, the
X-ray photographing apparatus and flat-panel detector controller
5005 can be connected using respective I/Fs and signals can be
exchanged with these apparatuses.
[0220] Reference numeral 51309 denotes a storage medium drive,
which comprises a CD-ROM drive, DVD drive, floppy disk drive, or
the like, and can load programs and data from a storage medium such
as a CD-ROM, DVD-ROM, or the like.
[0221] Reference numeral 51310 denotes a bus for connecting the
aforementioned units.
[0222] FIG. 15 shows the relationship between the initialization
process and X-ray photographing when an X-ray radiation request is
generated during the initialization process of photoelectric
conversion elements 5020. As shown in FIG. 15, refresh and idle
read (initialization) processes are periodically repeated at
intervals TI when no X-ray photographing is done.
[0223] FIG. 15 shows a case wherein an X-ray radiation switch of an
X-ray generation device 5001 has been pressed at time TX during the
idle read process, and an X-ray radiation request reaches the
flat-panel detector controller 5005 via the host computer 5002.
Upon generation of the X-ray radiation request, the host computer
5002 that received this request changes an X-ray radiation request
signal to Low. When the X-ray radiation request signal goes Low,
the flat-panel detector controller 5005 that received the X-ray
radiation request signal stores a time period TW from refresh
process start time T1 to the time at which the X-ray radiation
request signal goes Low in a memory (see FIG. 28) included in a CPU
5007 (CPU 51301). Note that this memory need not be included in the
CPU 5007, but may be arranged outside the CPU 5007.
[0224] When the idle read process is completed by setting a gate
signal at 0 V at time T5, the control waits for an elapse of the
stored time period TW. After the elapse of the time period TW, the
flat-panel detector controller 5005 changes an X-ray radiation
permission signal to Low at time T11.
[0225] After the initialization process, the CPU 5007 of the
flat-panel detector controller 5005 reads out TW stored in the
aforementioned memory, and waits for an elapse of the time TW (wait
process). As a result, a time period TD1 required for the
initialization process becomes equal to a time period TD1 from when
the X-ray radiation request signal goes Low until the X-ray
radiation permission signal changes to Low. Hence, the exposure
delay time always becomes a constant time period TD1.
[0226] When the X-ray radiation permission signal goes Low, this
signal reaches the X-ray generation device 5001 via the host
computer 5002, and the X-ray generation device 5001 radiates
X-rays, as shown in FIG. 15. The radiated X-rays are transmitted
through an object 5006 and are converted by a phosphor 5003 into
light proportional to the incoming X-ray dose, and charges
corresponding to that light are accumulated on capacitors
5021C.
[0227] Upon completion of X-ray radiation, the flat-panel detector
controller 5005 changes the X-ray radiation permission signal to
High at time T6. When X-ray radiation permission signal goes High,
this signal reaches the X-ray generation device 5001 via the host
computer 5002, and the X-ray generation device 5001 changes the
X-ray radiation request signal to High.
[0228] Also, upon completion of X-ray radiation, a gate signal is
set to be Vg and a switch SWr1 is turned on at time T6. Then, the
voltages at the gate electrodes G of the TFTs 5022(1,1) and
5022(1,2) of the first row shown in FIG. 24 change to Vg, and the
charges accumulated on the capacitors 5021C in photodetectors 5021
of the first row are read. The read charges are held by a
sample/hold (S/H) circuit 5026 via an amplifier 5025. When the
switch SWc1 is turned on at time T6, the held signal of the
photodetector 5021(1,1) is converted into a digital value by an A/D
converter 5027, and that value is transferred to the host computer.
Also, when the switch SWc1 is turned off and the switch SWc2 is
turned on at time T7, the held signal of the photodetector
5021(1,2) is converted into a digital value by the A/D converter
5027, and that value is transferred to the host computer 5002.
[0229] When the switch SWr1 is turned off and the switch SWr2 is
turned on at time T8, the voltages at the gate electrodes G of the
TFTs 5022(2,1) and 5022(2,2) of the second row shown in FIG. 24
change to Vg, and the charges accumulated on the capacitors 5021C
in the photodetectors 5021 of the second row are read. The read
signals are held via the amplifier 5025 and S/H circuit 5026. When
the switch SWc1 is turned on at time T8, the held signal of the
photodetector 5021(2,1) is converted into a digital value by the
A/D converter 5027, and that value is transferred to the host
computer 5002. Also, when the switch SWc1 is turned off and the
switch SWc2 is turned on at time T9, the held signal of the
photodetector 5021(2,2) is converted into a digital value by the
A/D converter 5027, and that value is transferred to the host
computer 5002.
[0230] After all the charges accumulated on the flat-panel detector
5004 are transferred to the host computer 5002, the gate signal is
set at 0 V, and the switches SWr1, SWr2, SWc1, and SWc2 are turned
off at time T10.
[0231] When an X-ray radiation request is generated at a timing
other than that during the initialization process of the
photoelectric conversion elements 5020, the same process as that
shown in FIG. 26 which has already been explained earlier is
executed. For this reason, a description of the process executed
when the X-ray radiation request is generated at a timing other
than that during the initialization process of the photoelectric
conversion elements 5020 will be omitted.
[0232] FIGS. 16 and 17 are flow charts of the X-ray photographing
method of this embodiment. FIG. 16 shows the main routine of the
X-ray photographing method, and FIG. 17 shows the subroutine of the
initialization process.
[0233] Referring to FIG. 16, the value of a timer (TM) is reset to
zero (step S5201). This timer is a hardware timer, which may be
incorporated in the CPU 5007 or may be arranged outside the CPU.
This timer automatically counts up at given time intervals (e.g.,
1-ms intervals).
[0234] The initialization process of the photoelectric conversion
elements 5020 is executed (step S5202). The initialization process
is executed as a subroutine. The subroutine of the initialization
process will be described in detail later.
[0235] It is then checked if XFLG is 1 (step S5203). XFLG is set to
be 1 when the X-ray radiation request signal goes Low during the
initialization process in step S5202, or remains zero when the
X-ray radiation request signal does not go Low during the
initialization process in step S5202. If it is determined in step
S5203 that XFLG.noteq.1, the flow advances to step S5204 to check
if the trailing edge of the X-ray radiation request signal is
detected (step S5204). If it is determined in step S5204 that the
trailing edge of the X-ray radiation request signal is detected
(the X-ray radiation signal goes Low), the flow jumps to step
S5206; otherwise, the value of the timer (TM) is compared with an
initialization process interval TI (step S5205). As a result of the
comparison process, if TM is smaller than the initialization
process interval TI, steps S5204 and S5205 are repeated. Note that
TI indicates the initialization process interval shown in FIG. 15.
If it is determined in step S5205 that TM>TI, the flow returns
to step S5201 to repeat the processes from steps S5201 to
S5205.
[0236] If it is determined in step S5203 that XFLG=1, the value of
a timer (TT) is reset to zero (step S5211). This timer is a
hardware timer, which may be incorporated in the CPU 5007 or may be
arranged outside the CPU. This timer automatically counts up at
given time intervals (e.g., 1-ms intervals). The value of the timer
(TT) is compared with that of TW (step S5212). If TT<TW, the
process in step S5212 is repeated. If it is determined in step
S5212 that TT.gtoreq.TW, the flow advances to step S5207. Note that
TW is a time period which is set in the subroutine of the
initialization process in step S5202, and is required from the
beginning of the initialization process until the X-ray radiation
request signal goes Low.
[0237] If it is determined in step S5204 that the X-ray radiation
request signal goes Low, the initialization process of the
photoelectric conversion elements 5020 is immediately executed
(step S5206). Upon completion of the initialization process, the
X-ray radiation permission signal is changed to Low (step S5207).
The X-ray generation device then radiates X-rays, and an X-ray
image is taken (step S5208). After that, the X-ray radiation
permission signal is changed to High (step S5209), and a main read
process for reading the taken X-ray image is done (step S5210).
Upon completion of the main read process, the flow returns to step
S5201 to repeat the aforementioned processes. After the main read
process, the taken X-ray digital image is transferred to the host
computer, and is displayed on the display device after image
processes and the like.
[0238] The subroutine of the initialization process in step S5202
will be described below using FIG. 17.
[0239] Initially, the values of a timer (TS) and XFLG are reset to
zero (step S5301). This timer is a hardware timer, which may be
incorporated in the CPU 5007 or may be arranged outside the CPU.
This timer automatically counts up at given time intervals (e.g.,
1-ms intervals). Also, XFLG is a flag indicating whether or not the
tailing edge of the X-ray radiation request signal is detected (the
X-ray radiation signal goes Low) during the initialization
process.
[0240] After that, a refresh signal is set at Vr (step S5302), and
it is checked if the trailing edge of the X-ray radiation request
signal is detected (step S5303). If the trailing edge of the X-ray
radiation request signal is not detected, the value of the timer
(TS) is compared to a refresh time period T2 (step S5304). If
TS<T2, steps S5303 and S5304 are repeated. In FIG. 15, assuming
that time T1 is zero, T2 is a time period in which the refresh
signal is set at Vr. If it is determined in step S5303 that the
trailing edge of the X-ray radiation request signal is detected,
the flow advances to step S5317 to save the value of the timer (TS)
in a variable TW and to set XFLG to be 1. Therefore, TW indicates a
time period from the beginning of the initialization process until
the trailing edge of the X-ray radiation request signal is
detected.
[0241] If it is determined in step S5304 that TS.gtoreq.T2, the
flow advances to step S5305 to set the refresh signal at Vs (step
S5305).
[0242] It is then checked if the trailing edge of the X-ray
radiation signal is detected (step S5306). If the trailing edge of
the X-ray radiation signal is detected, the flow advances to step
S5318. On the other hand, if the trailing edge of the X-ray
radiation signal is not detected, the value of the timer (TS) is
compared with idle read start time T3 (step S5307). If TS<T3,
steps S5306 and S5307 are repeated. Note that T3 is the time at
which the idle read process starts, as shown in FIG. 15. If it is
determined in step S5306 that the trailing edge of the X-ray
radiation signal is detected, the flow advances to step S5318 to
save the value of the timer (TS) in the variable TW and to set XFLG
to be 1.
[0243] If it is determined in step S5307 that TS.gtoreq.T3, the
gate signal is set at Vg (step S5308), and the value of a variable
n is set to be 1 (step S5309). Since n=1, the switch SWr1 is turned
on (step S5310), and it is detected if the trailing edge of the
X-ray radiation request signal is detected (step S5311). If the
trailing edge of the X-ray radiation request signal is detected,
the flow advances to step S5319. On the other hand, if the trailing
edge of the X-ray radiation request signal is not detected, the
value of the timer (TS) is compared with time T4 since n=1 (step
S5312). If TS<T4, steps S5311 and S5312 are repeated. Note that
T4 is time at which SWr1 which is ON is to be turned off, as shown
in FIG. 15. If it is determined in step S5311 that the trailing
edge of the X-ray radiation request signal is detected, the flow
advances to step S5319 to save the value of the timer (TS) in the
variable TW and to set XFLG to be 1.
[0244] If it is determined in step S5312 that TS.gtoreq.T4, the
flow advances to step S5313 to turn off the switch SWr1 (step
S5313). After that, the value of the variable n is incremented by 1
(step S5314), and it is checked if the variable n.ltoreq.2 (step
S5315). In this embodiment, since the photoelectric conversion
elements are arranged in a 2.times.2 (row x column) matrix, as
shown in FIG. 24, it is checked in step S5315 if the variable
n.ltoreq.2. However, if the elements are arranged in a 3.times.3
(row x column) matrix, it is checked in step S5315 if the variable
n.ltoreq.3.
[0245] If n.ltoreq.2, the flow returns to step S5310. In this case,
since n=2, the switch SWr2 is turned on, and the processes in steps
S5310 to S5315 are repeated. If it is determined in step S5315 that
n>2, the gate signal is set at 0 V in step S5316, thus ending
this subroutine.
[0246] In this way, in the subroutine of the initialization
process, if the trailing edge of the X-ray radiation request signal
is detected, the value of the timer (TS) is saved in TW, and XFLG
is set to be 1.
[0247] [Third Embodiment]
[0248] In this embodiment, an X-ray photographing system which can
shorten the exposure delay time further and its process will be
explained below. FIG. 18 shows the relationship between the
initialization process and X-ray photographing when an X-ray
radiation request is generated during the initialization process of
the photoelectric conversion elements 5020.
[0249] As shown in FIG. 18, refresh and idle read (initialization)
processes are periodically repeated at intervals TI when no X-ray
photographing is done.
[0250] FIG. 18 shows a case wherein the X-ray radiation switch of
the X-ray generation device 5001 has been pressed at time TX during
the idle read process, and an X-ray radiation request reaches the
flat-panel detector controller 5005 via the host computer 5002, as
in FIG. 15. Upon generation of the X-ray radiation request, the
host computer 5002 that received this X-ray radiation request
changes an X-ray radiation request signal to Low.
[0251] When the idle read process is completed by setting a gate
signal at 0 V at time T5, the flat-panel detector controller 5005
immediately changes an X-ray radiation permission signal to
Low.
[0252] As a result, since the flat-panel detector controller 5005
changes the X-ray radiation permission signal to Low immediately
after the initialization process, a time period (exposure delay
time) TD2 from when the X-ray radiation request signal goes Low
until the X-ray radiation permission signal changes to Low can be
shorter than that in, e.g., the method described in the second
embodiment.
[0253] When the X-ray radiation permission signal goes Low, this
signal reaches the X-ray generation device 5001 via the host
computer 5002, and the X-ray generation device 5001 radiates
X-rays, as shown in FIG. 18. The radiated X-rays are transmitted
through the object 5006 and are converted by the phosphor 5003 F
into light proportional to the incoming X-ray dose, and charges
corresponding to that light are accumulated on the capacitors
5021C.
[0254] Upon completion of X-ray radiation, the flat-panel detector
controller 5005 changes the X-ray radiation permission signal to
High at time T6. When X-ray radiation permission signal goes High,
this signal reaches the X-ray generation device 5001 via the host
computer 5002. The X-ray generation device 5001 changes the X-ray
radiation request signal to High.
[0255] Also, upon completion of X-ray radiation, a gate signal is
set to be Vg and the switch SWr1 is turned on at time T6. Then, the
voltages at the gate electrodes G of the TFTs 5022(1,1) and
5022(1,2) of the first row shown in FIG. 24 change to Vg, and the
charges accumulated on the capacitors 5021C in the photodetectors
5021 of the first row are read. The read charges are held by the
S/H circuit 5026 via the amplifier 5025. When the switch SWc1 is
turned on at time T6, the held signal of the photodetector
5021(1,1) is converted into a digital value by the A/D converter
5027, and that value is transferred to the host computer. Also,
when the switch SWc1 is turned off and the switch SWc2 is turned on
at time T7, the held signal of the photodetector 5021(1,2) is
converted into a digital value by the A/D converter 5027, and that
value is transferred to the host computer 5002.
[0256] When the switch SWr1 is turned off and the switch SWr2 is
turned on at time T8, the voltages at the gate electrodes G of the
TFTs 5022(2,1) and 5022(2,2) of the second row shown in FIG. 24
change to Vg, and the charges accumulated on the capacitors 5021C
in the photodetectors 5021 of the second row are read. The read
signals are held via the amplifier 5025 and S/H circuit 5026. When
the switch SWc1 is turned on at time T8, the held signal of the
photodetector 5021(2,1) is converted into a digital value by the
A/D converter 5027, and that value is transferred to the host
computer 5002. Also, when the switch SWc1 is turned off and the
switch SWc2 is turned on at time T9, the held signal of the
photodetector 5021(2,2) is converted into a digital value by the
A/D converter 5027, and that value is transferred to the host
computer 5002.
[0257] After all the charges accumulated on the flat-panel detector
5004 are transferred to the host computer 5002, the gate signal is
set at 0 V, and the switches SWr1, SWr2, SWc1, and SWc2 are turned
off at time T10.
[0258] When an X-ray radiation request is generated at a timing
other than that during the initialization process of the
photoelectric conversion elements 5020, the same process as that
shown in FIG. 26 which has already been explained earlier is
executed. For this reason, a description of the process executed
when the X-ray radiation request is generated at a timing other
than that during the initialization process of the photoelectric
conversion elements 5020 will be omitted.
[0259] Therefore, according to this embodiment, the exposure delay
time when the X-ray radiation request is generated at a timing
other than that in the initialization process is TD1 and that when
the X-ray radiation request is generated during the initialization
process is TD2. Since TD2.ltoreq.TD1, the exposure delay time is
TD1 at a maximum. As a result, when the X-ray radiation request is
generated during the initialization process, the exposure delay
time can be shorter than that in the second embodiment.
[0260] FIGS. 19 and 20 are flow charts of the X-ray photographing
method of this embodiment. FIG. 19 shows the main routine of the
X-ray photographing method, and FIG. 20 shows the subroutine of the
initialization process.
[0261] Referring to FIG. 19, the value of a timer (TM) is reset to
zero (step S5501). This timer is a hardware timer, which may be
incorporated in the CPU 5007 or may be arranged outside the CPU.
This timer automatically counts up at given time intervals (e.g.,
1-ms intervals).
[0262] The initialization process of the photoelectric conversion
elements 5020 is executed (step S5502). The initialization process
is executed as a subroutine. The subroutine of the initialization
process will be described in detail later.
[0263] It is then checked if XFLG is 1 (step S5503). XFLG is set to
be 1 when the X-ray radiation request signal goes Low during the
initialization process in step S5502, or remains zero when the
X-ray radiation request signal does not go Low during the
initialization process in step S5502. If it is determined in step
S5503 that XFLG.noteq.1, the flow advances to step S5504 to check
if the trailing edge of the X-ray radiation request signal is
detected (step S5504). If it is determined in step S5504 that the
trailing edge of the X-ray radiation request signal is detected,
the flow jumps to step S5506. On the other hand, if the trailing
edge of the X-ray radiation request signal is not detected, the
value of the timer (TM) is compared with an initialization process
interval TI (step S5505). If TM is smaller than the initialization
process interval TI, steps S5504 and S5505 are repeated. Note that
TI indicates the initialization process interval shown in FIG. 18.
If it is determined in step S5505 that TM.gtoreq.TI, the flow
returns to step S5501 to repeat the processes from steps S5501 to
S5505.
[0264] If it is determined in step S5503 that XFLG=1, the flow
jumps to step S5507 to change an X-ray radiation permission signal
to Low (step S5507). Therefore, if the X-ray radiation request
signal goes Low during the initialization process in step S5502,
the initialization process in step S5506 is skipped.
[0265] If it is determined in step S5504 that the X-ray radiation
request signal goes Low, the flow jumps to step S5506 to
immediately execute the initialization process of the photoelectric
conversion elements 5020 (step S5506). Upon completion of the
initialization process, the X-ray radiation permission signal is
changed to Low (step S5507). The X-ray generation device then
radiates X-rays, and an X-ray image is taken (step S5508). After
that, the X-ray radiation permission signal is changed to High
(step S5509), and a main read process for reading the taken X-ray
image is done (step S5510). Upon completion of the main read
process, the flow returns to step S5501 to repeat the
aforementioned processes. After the main read process, the taken
X-ray digital image is transferred to the host computer 5002, and
is displayed on the display device after image processes and the
like.
[0266] The initialization routine in step S5502 will be described
with reference to FIG. 20.
[0267] Initially, the values of a timer (TS) and XFLG are reset to
zero (step S5601). This timer is a hardware timer, which may be
incorporated in the CPU 5007 or may be arranged outside the CPU.
This timer automatically counts up at given time intervals (e.g.,
1-ms intervals). Also, XFLG is a flag indicating whether or not the
tailing edge of the X-ray radiation request signal is detected (the
X-ray radiation signal goes Low) during the initialization
process.
[0268] After that, a refresh signal is set at Vr (step S5602), and
it is checked if the trailing edge of the X-ray radiation request
signal is detected (step S5603). If the trailing edge of the X-ray
radiation request signal is not detected, the value of the timer
(TS) is compared to a refresh time period T2 (step S5604). If
TS<T2, steps S5603 and S5604 are repeated. In FIG. 15, assuming
that time T1 is zero, T2 is a time period in which the refresh
signal is set at Vr. If it is determined in step S5603 that the
trailing edge of the X-ray radiation request signal is detected,
the flow advances to step S5617 to set XFLG to be 1. If it is
determined in step S5604 that TS.gtoreq.T2, the flow advances to
step S5605 to set the refresh signal at Vs (step S5605).
[0269] It is then checked if the trailing edge of the X-ray
radiation signal is detected (step S5606). If the trailing edge of
the X-ray radiation signal is detected, the flow advances to step
S5618. On the other hand, if the trailing edge of the X-ray
radiation signal is not detected, the value of the timer (TS) is
compared with idle read start time T3 (step S5607). If TS<T3,
steps S5606 and S5607 are repeated. Note that T3 is the time at
which the idle read process starts, as shown in FIG. 18. If it is
determined in step S5606 that the trailing edge of the X-ray
radiation signal is detected, the flow advances to step S5618 to
set XFLG to be 1.
[0270] If it is determined in step S5607 that TS.gtoreq.T3, the
gate signal is set at Vg (step S5608), and the value of a variable
n is set to be 1 (step S5609). Since n=1, the switch SWr1 is turned
on (step S5610), and it is detected if the trailing edge of the
X-ray radiation request signal is detected (step S5611). If the
trailing edge of the X-ray radiation request signal is detected,
the flow advances to step S5619. On the other hand, if the trailing
edge of the X-ray radiation request signal is not detected, the
value of the timer (TS) is compared with time T4 since n=1 (step
S5612). If TS<T4, steps S5611 and S5612 are repeated. Note that
T4 is the time at which SWr1 which is ON is to be turned off, as
shown in FIG. 18. If it is determined in step S5611 that the
trailing edge of the X-ray radiation request signal is detected,
the flow advances to step S5619 to set XFLG to be 1.
[0271] If it is determined in step S5612 that TS.gtoreq.T4, the
flow advances to step S5613 to turn off the switch SWr1 (step
S5613). After that, the value of the variable n is incremented by 1
(step S5614), and it is checked if the variable n.ltoreq.2 (step
S5615). In this embodiment, since the photoelectric conversion
elements are arranged in a 2.times.2 (row x column) matrix, as
shown in FIG. 24, it is checked in step S5615 if the variable
n.ltoreq.2. However, if the elements are arranged in a 3.times.3
(row x column) matrix, it is checked in step S5615 if the variable
n.ltoreq.3.
[0272] If n.ltoreq.2, the flow returns to step S5610. In this case,
since n=2, the switch SWr2 is turned on, and the processes in steps
S5610 to S5615 are repeated. If it is determined in step S5615 that
n>2, the gate signal is set at 0 V in step S5616, thus ending
this subroutine.
[0273] In this manner, in the subroutine of the initialization
process, XFLG is set to be 1 when the trailing edge of the X-ray
radiation request signal is detected.
[0274] In this embodiment, the initialization process includes one
refresh process and one idle read process. However, the present
invention is not limited to such specific process, and the
initialization process may include one refresh process and a
plurality of idle read processes.
[0275] In the flat-panel detector 5004, the photoelectric
conversion elements are two-dimensionally arranged in a 2.times.2
(row x column) matrix. However, the present invention is not
limited to such specific arrangement. In practice, photoelectric
conversion elements are normally arranged in a 1000 to
4000.times.1000 to 4000 (row x column) matrix. The present
invention is not limited to this, either, and the number of
photoelectric conversion elements in one direction can be smaller
or larger than the above value.
[0276] In this embodiment, the row address select circuit 5009
comprises the gate control circuit 5024 and switches SWr1 and SWr2.
However, the present invention is not limited to such specific
arrangement, and any other arrangements may be used as long as the
photoelectric conversion elements 5020 in the row direction can be
selected.
[0277] In this embodiment, the column address select circuit 5010
comprises the amplifiers 5025, S/H circuits 5026, and switches SWc1
and SWc2. However, the present invention is not limited to such
specific arrangement, and any other arrangements may be used as
long as the photoelectric conversion elements 5020 in the column
direction can be selected.
[0278] [Another Embodiment]
[0279] The present invention is not limited to the apparatus and
method alone for implementing the aforementioned embodiments, but
the scope of the present invention includes a case wherein the
above embodiments are achieved by supplying a program code of
software that can implement the functions of the above-mentioned
embodiments to a computer (or a CPU or MPU) in a system or
apparatus, and making the computer control various devices in the
system or apparatus.
[0280] In this case, the program code itself read out from the
storage medium implements the functions of the above-mentioned
embodiments, and the program code itself, and means for supplying
the program code to the computer (i.e., a storage medium which
stores the program code) are included in the scope of the present
invention.
[0281] As the storage medium for storing such program code, for
example, a floppy disk, hard disk, optical disk, magnetooptical
disk, CD-ROM, magnetic tape, nonvolatile memory card, ROM, and the
like may be used.
[0282] The program code is included in the scope of the embodiments
not only when the functions of the above embodiments are
implemented by controlling various devices according to the
supplied program code alone but also when the functions of the
embodiments are implemented by collaboration of the program code
and an OS (operating system) or another application software
running on the computer.
[0283] Furthermore, the scope of the present invention includes a
case wherein the functions of the above-mentioned embodiments are
implemented by some or all of actual processing operations executed
by a CPU or the like arranged in a function extension board or a
function extension unit, which is inserted in or connected to the
computer, after the supplied program code is written in a memory of
the extension board or unit.
[0284] As described above, according to the present invention, even
when an X-ray radiation request is received during initialization
of the detector, noise in a taken X-ray image can be suppressed.
Also, when the X-ray radiation request is received during
initialization of the detector, the exposure delay time can be
shortened.
[0285] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the appended claims.
* * * * *