U.S. patent application number 14/229128 was filed with the patent office on 2014-10-02 for radiation image detecting device and operating method thereof, and radiation imaging system.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Kentaro NOMA, Yasufumi ODA, Keita WATANABE.
Application Number | 20140291541 14/229128 |
Document ID | / |
Family ID | 51590780 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140291541 |
Kind Code |
A1 |
WATANABE; Keita ; et
al. |
October 2, 2014 |
RADIATION IMAGE DETECTING DEVICE AND OPERATING METHOD THEREOF, AND
RADIATION IMAGING SYSTEM
Abstract
Binning readout reads out electric charge accumulated in pixels
to signal lines in blocks of a plurality of adjoining pixel-rows. A
correction image generator of a line defect corrector scales up an
image size of a reference frame image RP outputted by the binning
readout and corrects pixel values of the reference frame image RP,
to produce a correction image RPC to be used for correction of a
line defect occurring in an X-ray image XP. The scale-up is
performed by applying row interpolation processing to the reference
frame image RP. The correction of the pixel values is performed by
multiplying the reference frame image RP after being subjected to
the row interpolation processing by a correction coefficient. An
adder adds the correction image RPC to the X-ray image XP, and
produces an X-ray image XPC in which the line defect is
corrected.
Inventors: |
WATANABE; Keita;
(Ashigarakami-gun, JP) ; NOMA; Kentaro;
(Ashigarakami-gun, JP) ; ODA; Yasufumi;
(Ashigarakami-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
51590780 |
Appl. No.: |
14/229128 |
Filed: |
March 28, 2014 |
Current U.S.
Class: |
250/394 |
Current CPC
Class: |
H04N 5/32 20130101; G01T
1/16 20130101; G01N 2223/505 20130101; H04N 5/367 20130101; H04N
5/3658 20130101; H04N 5/347 20130101; G01N 23/04 20130101; H04N
5/3655 20130101 |
Class at
Publication: |
250/394 |
International
Class: |
G01T 1/16 20060101
G01T001/16; G01N 23/04 20060101 G01N023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2013 |
JP |
2013-073591 |
Mar 19, 2014 |
JP |
2014-057061 |
Claims
1. A radiation image detecting device comprising: a panel unit
having an image capturing field for imaging a radiographic image of
an object by receiving radiation emitted from a radiation source; a
plurality of pixels arranged in said panel unit in a
two-dimensional array having a plurality of pixel-rows and a
pixel-column, each of said pixels producing and accumulating
electric charge; a plurality of scan lines provided in said panel
unit on a pixel-row basis, for making said pixel-row having said
pixels from which said electric charge is to be read out in an ON
state; a signal line provided in said panel unit on a pixel-column
basis, for reading out said electric charge from said pixels on a
pixel-column basis; a controller for controlling said panel unit to
perform three types of operations of a pre-emission readout
operation, an accumulation operation, and an image readout
operation, wherein in said pre-emission readout operation, a
plurality of adjoining said pixel-rows are set as a binning
pixel-row, and binning readout of said electric charge is performed
on a binning pixel-row basis sequentially from a first binning
pixel-row to a last binning pixel-row and repeated from said first
binning pixel-row upon reaching said last binning pixel-row, in
order to obtain reference line images each having a pixel value
being a sum of said electric charge of a plurality of said pixels
in a same pixel-column, said accumulation operation is performed
instead of said pre-emission readout operation, in a case where
said radiation source starts emitting said radiation while said
binning readout of said electric charge is repeated on a binning
pixel-row basis, for accumulating said electric charge in said
pixels in accordance with said radiation, and said image readout
operation is started after completion of emission of said radiation
from said radiation source, for reading out said electric charge
from said pixels on a pixel-row basis and converting said electric
charge to pixel values for forming said radiographic image; a
reference line image record controller for obtaining said reference
line images of a plurality of said binning pixel-rows by
sequentially recording said reference line images to a memory
whenever performing said binning readout; an emission start judging
unit for judging start of emission of said radiation from said
radiation source; a correction image generator for producing a
correction image used for correcting a strip-shape line defect
occurring in a pixel-row direction of said radiographic image due
to a time delay between start of emission of said radiation and a
judgment of the start of emission, by scaling up an image size of
said reference line images of said plurality of binning pixel-rows
in a pixel-column direction and correcting said pixel values; and a
line defect corrector for correcting said line defect by adding
said correction image to said radiographic image.
2. The radiation image detecting device according to claim 1,
wherein said correction image generator corrects said pixel value
of said reference line image based on an immediately-preceding
reference line image obtained immediately before stopping said
pre-emission readout operation, out of said reference line images
of said plurality of binning pixel-rows.
3. The radiation image detecting device according to claim 2,
wherein said correction image generator includes: a correction
coefficient calculator for calculating a correction coefficient
used for converting said pixel value of said reference line image
to a value corresponding to a pixel value of said radiographic
image; and a pixel value corrector for multiplying said pixel value
of said reference line image by said correction coefficient
calculated by said correction coefficient calculator.
4. The radiation image detecting device according to claim 3,
wherein said correction coefficient calculator calculates a ratio
.DELTA.D/SQ as said correction coefficient, wherein SQ represents a
pixel value of said immediately-preceding reference line image; and
.DELTA.D represents a difference amount being a maximum value of
difference in a pixel value D of said radiographic image between
adjoining two of said pixel-rows caused by said line defect.
5. The radiation image detecting device according to claim 3,
wherein said correction coefficient calculator calculates a ratio
.DELTA.DR/SQR as said correction coefficient, wherein SQR
represents a typical value of a pixel value SQ of said
immediately-preceding reference line image; and .DELTA.DR
represents a typical value of a difference amount .DELTA.D being a
maximum value of difference in a pixel value D of said radiographic
image between adjoining two of said pixel-rows caused by said line
defect.
6. The radiation image detecting device according to claim 5,
wherein said typical value SQR is an average SQave of said pixel
values SQ; and said typical value .DELTA.DR is an average
.DELTA.Dave of said difference amounts .DELTA.D.
7. The radiation image detecting device according to claim 6,
wherein said correction coefficient calculator calculates said
average SQave and said average .DELTA.Dave with excluding a pixel
value of a defect pixel from said pixel values SQ and said pixel
values D that are used for calculation of said average SQave and
said average .DELTA.Dave.
8. The radiation image detecting device according to claim 5,
wherein said typical value SQR is a median value SQC of said pixel
values SQ; and said typical value .DELTA.DR is a median value
.DELTA.DC of said difference amounts .DELTA.D.
9. The radiation image detecting device according to claim 3,
wherein said correction coefficient calculator calculates a
reciprocal of a number of said pixel-rows composing said binning
pixel-row, as said correction coefficient.
10. The radiation image detecting device according to claim 2,
wherein said correction image generator extracts said
immediately-preceding reference line image and a plurality of said
reference line images next to said immediately-preceding reference
line image as line-defect-corresponding reference line images, out
of said reference line images of said plurality of binning
pixel-rows, and produces said correction image based on said
line-defect-corresponding reference line images alone.
11. The radiation image detecting device according to claim 10,
wherein said pixel value corrector uniformly multiplies said pixel
values of said line-defect-corresponding reference line images by
said correction coefficient calculated by said correction
coefficient calculator.
12. The radiation image detecting device according to claim 10,
further comprising: a correction coefficient modifier for modifying
said correction coefficient calculated by said correction
coefficient calculator to a correction coefficient specific to said
line-defect-corresponding reference line image other than said
immediately-preceding reference line image, wherein said pixel
value corrector multiplies a pixel value of said
immediately-preceding reference line image by said correction
coefficient calculated by said correction coefficient calculator,
and multiplies a pixel value of said line-defect-corresponding
reference line image other than said immediately-preceding
reference line image by said correction coefficient modified by
said correction coefficient modifier.
13. The radiation image detecting device according to claim 1,
wherein said correction image generator scales up an image size of
said reference line images of said plurality of binning pixel-rows
in said pixel-column direction by row interpolation processing.
14. The radiation image detecting device according to claim 13,
wherein said row interpolation processing applies linear
interpolation or spline interpolation between said reference line
images next to each other.
15. The radiation image detecting device according to claim 1,
wherein said reference line images of said plurality of binning
pixel-rows coincide with said reference line images of one frame
extending from said first binning pixel-row to said last binning
pixel-row.
16. The radiation image detecting device according to claim 15,
wherein in a case where said pre-emission readout operation of one
frame extending from said first binning pixel-row to said last
binning pixel-row is set as one cycle, said reference line image
record controller sequentially updates said reference line images
of one frame obtained in said pre-emission readout operation of an
Sk-th cycle with said reference line images obtained in said
pre-emission readout operation of an (Sk+1)-th cycle on a binning
pixel-row basis.
17. The radiation image detecting device according to claim 1,
wherein said emission start judging unit judges the start of
emission of said radiation based on said reference line images.
18. The radiation image detecting device according to claim 1,
further comprising: a leak corrector for subtracting a pixel value
based on leak current leaking from said pixel according to
application of said radiation from a pixel value of said reference
line image, before said correction image generator generates said
correction image.
19. The radiation image detecting device according to claim 1,
wherein said controller also functions as said reference line image
record controller.
20. The radiation image detecting device according to claim 1,
wherein said controller also functions as said line defect
corrector.
21. The radiation image detecting device according to claim 1,
wherein said line defect corrector also functions as said
correction image generator.
22. An operating method of a radiation image detecting device
including a panel unit having an image capturing field for imaging
a radiographic image of an object by receiving radiation emitted
from a radiation source; a plurality of pixels arranged in said
panel unit in a two-dimensional array having a plurality of
pixel-rows and a pixel-column, each of said pixels producing and
accumulating electric charge; a plurality of scan lines provided in
said panel unit on a pixel-row basis, for making said pixel-row
having said pixels from which said electric charge is to be read
out in an ON state; a signal line provided in said panel unit on a
pixel-column basis, for reading out said electric charge from said
pixels on a pixel-column basis; a controller for controlling said
panel unit to perform three types of operations of a pre-emission
readout operation, an accumulation operation for accumulating said
electric charge in said pixels in accordance with said radiation,
and an image readout operation for reading out said electric charge
from said pixels on a pixel-row basis and converting said electric
charge into pixel values for forming said radiographic image; and
an emission start judging unit for judging start of emission of
said radiation from said radiation source; said operating method
comprising the steps of: A. performing said pre-emission readout
operation, until said emission start judging unit judges the start
of emission; B. in said pre-emission readout operation, setting a
plurality of adjoining said pixel-rows as a binning pixel-row, and
performing binning readout of said electric charge on a binning
pixel-row basis sequentially from a first binning pixel-row to a
last binning pixel-row and repeating said binning readout from said
first binning pixel-row upon reaching said last binning pixel-row,
in order to obtain reference line images each having a pixel value
being a sum of said electric charge of a plurality of said pixels
in a same pixel-column; C. judging the start of emission by said
emission start judging unit, while said binning readout of said
electric charge is repeated on a binning pixel-row basis; D.
performing said accumulation operation instead of said pre-emission
readout operation, when said emission start judgment unit judges
the start of emission; E. performing said image readout operation
after completion of emission of said radiation from said radiation
source; F. producing by a correction image generator a correction
image used for correcting a strip-shape line defect occurring in a
pixel-row direction of said radiographic image due to a time delay
between the start of emission of said radiation and the judgment of
the start of emission, by scaling up an image size of said
reference line images of a plurality of said binning pixel-rows in
a pixel-column direction and correcting said pixel values; and G.
correcting said line defect by a line defect corrector by adding
said correction image to said radiographic image.
23. A radiation imaging system comprising a radiation image
detecting device for detecting a radiographic image of an object by
receiving radiation emitted from a radiation source, and a line
defect correction device for correcting a strip-shape line defect
occurring in said radiographic image, A. said radiation image
detecting device including: a panel unit having an image capturing
field for imaging said radiographic image; a plurality of pixels
arranged in said panel unit in a two-dimensional array having a
plurality of pixel-rows and a pixel-column, each of said pixels
producing and accumulating electric charge; a plurality of scan
lines provided in said panel unit on a pixel-row basis, for making
said pixel-row having said pixels from which said electric charge
is to be read out in an ON state; a signal line provided in said
panel unit on a pixel-column basis, for reading out said electric
charge from said pixels on a pixel-column basis; a controller for
controlling said panel unit to perform three types of operations of
a pre-emission readout operation, an accumulation operation, and an
image readout operation, wherein in said pre-emission readout
operation, a plurality of adjoining said pixel-rows are set as a
binning pixel-row, and binning readout of said electric charge is
performed on a binning pixel-row basis sequentially from a first
binning pixel-row to a last binning pixel-row and repeated from
said first binning pixel-row upon reaching said last binning
pixel-row, in order to obtain reference line images each having a
pixel value being a sum of said electric charge of a plurality of
said pixels in a same pixel-column, said accumulation operation is
performed instead of said pre-emission readout operation, in a case
where said radiation source starts emitting said radiation while
said binning readout of said electric charge is repeated on a
binning pixel-row basis, for accumulating said electric charge in
said pixels in accordance with said radiation, and said image
readout operation is started after completion of emission of said
radiation from said radiation source, for reading out said electric
charge from said pixels on a pixel-row basis and converting said
electric charge to pixel values for forming said radiographic
image; a reference line image record controller for obtaining said
reference line images of a plurality of said binning pixel-rows by
sequentially recording said reference line images to a memory
whenever performing said binning readout; and an emission start
judging unit for judging start of emission of said radiation from
said radiation source; B. a line defect correction device
including: a correction image generator for producing a correction
image used for correcting said line defect occurring in a pixel-row
direction due to a time delay between the start of emission of said
radiation and a judgment of the start of emission, by scaling up an
image size of said reference line images of said plurality of
binning pixel-rows in a pixel-column direction and correcting said
pixel values; and a line defect corrector for correcting said line
defect by adding said correction image to said radiographic image.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a radiation image detecting
device having a line defect correction function for correcting a
strip-shaped line defect occurring in a radiographic image, an
operating method of the radiation image detecting device, and a
radiation imaging system.
[0003] 2. Description Related to the Prior Art
[0004] In a medical field, an X-ray imaging system using X-rays, as
a kind of radiation, is known. The X-ray imaging system is
constituted of an X-ray generating apparatus for generating the
X-rays, and an X-ray imaging apparatus for taking an X-ray image of
an object (a patient) by receiving the X-rays passed through the
object. The X-ray generating apparatus includes an X-ray source for
emitting the X-rays to the object, a source control unit for
controlling the operation of the X-ray source, and an emission
switch for inputting a command to actuate the X-ray source to the
source control unit. The X-ray imaging apparatus includes an X-ray
image detecting device for detecting the X-ray image that is
produced from the X-rays passed through the object, and a console
for controlling the operation of the X-ray image detecting device
and storing and displaying the X-ray image.
[0005] A kind of the X-ray image detecting device using an image
detector (a flat panel detector, FPD) that detects the X-ray image
as an electric signal has become widespread. The image detector is
constituted of a panel unit and a circuit unit. The panel unit has
an image capturing field for capturing a radiographic image of the
object. The panel unit has a plurality of pixels arranged in two
dimensions and signal lines. The pixels each for accumulating
electric charge produced in accordance with an X-ray amount
incident thereon are arranged in a plurality of pixel-rows and
pixel-columns. The electric charge is read out from the pixels
through the signal lines on a pixel-row basis. Each pixel is
provided with a photoelectric conversion element for producing and
accumulating the electric charge, and a switching element such as a
TFT (thin film transistor). The circuit unit includes a gate
driver, a signal processing circuit, and a controller for
controlling the operation of the panel unit through the gate driver
and the signal processing circuit.
[0006] The gate driver issues gate pulses to drive the switching
elements through scan lines provided on a pixel-row basis. The
signal processing circuit outputs voltage in accordance with the
electric charge read out through the signal lines provided on a
pixel-column basis. The controller makes the panel unit perform
three operations, that is, a pixel reset operation for discharging
the electric charge accumulated in the pixels, an accumulation
operation for accumulating the electric charge in the pixels by
turning off the switching element of every pixel, and an image
readout operation for reading out the electric charge from the
first pixel-row to the last pixel-row on a pixel-row basis after
the completion of the accumulation operation to capture an X-ray
image of one frame (one screen) to a frame memory.
[0007] The pixel reset operation is an operation for removing dark
charge accumulated in the pixels. The dark charge, which is based
on dark current, becomes a noise component of the X-ray image, and
hence the pixel reset operation is carried out. In the pixel reset
operation, pixels are sequentially reset from the first pixel-row
to the last pixel-row on a pixel-row basis, and after completing
the reset of the last pixel-row, the reset is repeated again from
the first pixel-row.
[0008] In order to appropriately take the X-ray image, the X-ray
imaging apparatus requires information on the start of X-ray
emission from the X-ray source. Japanese Patent Laid-Open
Publication No. 2011-254971 discloses a communication method in
which a signal related to the X-ray emission is communicated
between the X-ray generating apparatus and the X-ray imaging
apparatus, and a self-judgment method in which the X-ray image
detecting device judges the start of the X-ray emission.
[0009] In the communication method, the X-ray image detecting
device performs the pixel reset operation before the start of the
X-ray emission. In the pixel reset operation, the electric charge
accumulated in the pixels is read out and discharged on a pixel-row
basis. If an emission start request is sent from the X-ray
generating apparatus to the X-ray image detecting device during the
pixel reset operation, the X-ray image detecting device permits the
X-ray generating apparatus to start the X-ray emission at the time
of completing the reset of the pixels of the last row. After the
permission of the start of the X-ray emission, the X-ray image
detecting device is shifted from the pixel reset operation to the
accumulation operation.
[0010] In the self-judgment method, on the other hand, the start of
the X-ray emission is judged by detecting variation of the signal
due to the X-rays during the operation of the X-ray image detecting
device. The X-ray image detecting device performs the accumulation
operation between two types of readout operations, that is, a
pre-emission readout operation for reading out the electric charge
in predetermined cycles on a pixel-row basis and the image readout
operation. If the X-ray emission is started during the pre-emission
readout operation, the electric charge of each pixel rapidly
increases and the signal varies largely, and thereby the start of
the X-ray emission is detected. Upon detecting the start of the
X-ray emission, the pre-emission readout operation is stopped and
shifted to the accumulation operation. After a lapse of
predetermined emission time, the image readout operation is carried
out to sequentially read out the electric charge of the pixels from
the first row on a pixel-row basis and produce the X-ray image
based on the X-ray emission.
[0011] In the communication method, the accumulation operation is
carried out and no electric charge is read out during the X-ray
emission. According to the self-judgment method, on the other hand,
in the duration between the start of the X-ray emission and the
judgment of the emission start, the electric charge of a plurality
of pixel-rows is read out by the pre-emission readout operation.
Thus, not only the dark charge but also the electric charge
produced by the X-ray emission is read out from the plurality of
pixel-rows. This electric charge that is readout in advance is
turned to be a deficit, and therefore a line of low density i.e. a
line defect appears in the X-ray image.
[0012] According to the X-ray image detecting device described in
the Japanese Patent Laid-Open Publication No. 2011-254971, the line
defect is corrected based on a reference line image in which output
of the electric charge read out sequentially in the pre-emission
readout operation is recorded on a pixel-row basis. This X-ray
image detecting device uses the reference line image for the
judgment of the emission start too.
[0013] To be more specific, as shown in FIG. 18, in a standby state
before the X-ray emission, the pre-emission readout operation is
performed in which the gate driver sequentially issues gate pulses
G(1) to G(N) (N is the number of the pixel-rows) at predetermined
intervals H to read out the electric charge from the pixels of the
first pixel-row to the last pixel-row on a pixel-row basis. Upon
completing the reset of the last pixel-row, the readout is repeated
from the first pixel-row. The output of the electric charge that is
read out of the one pixel-row is recorded to the frame memory, as
the reference line image.
[0014] By completing the readout of one frame, a reference frame
image RP, which is composed of the reference line images of one
frame, is recorded. A readout period of one frame is defined as one
cycle. Upon completing the one cycle, the next cycle is started and
the readout is repeated from the first pixel-row. Concurrently, the
reference frame image RP is updated on a pixel-row basis using the
reference line images of the next cycle.
[0015] In the judgment of the emission start, as shown in FIG. 19,
a typical value of pixel values S of the reference line image
sequentially outputted at the intervals H is compared with a
predetermined judgment threshold value Th. As the typical value of
the pixel values S of the reference line image to be compared with
the judgment threshold value Th, a maximum value of the pixel
values S of one pixel-row, or an average value or a sum value of
the pixel values S of one pixel-row is used. As shown in an X-ray
emission profile, which represents time-variation in an X-ray dose
applied from the X-ray source per unit of time, the X-ray dose
applied per unit of time is low immediately after the start of the
X-ray emission, and is gradually increased to a set dose value
determined in accordance with tube current. Round marks indicated
with "E" represent the output timing of the reference line images.
Letters "C", "C-1", and the like represent the pixel-rows from
which the reference line images are outputted.
[0016] Before the start of the X-ray emission from the X-ray
source, the pixel values S of the reference line image correspond
to output according to the dark charge, and are much smaller than
output according to the X-ray dose. Thus, the pixel value S
according to the dark charge is regarded as a level of
approximately zero in FIG. 19. After the start of the X-ray
emission, the pixel values S of the reference line image are
increased in accordance with the X-ray emission profile. After
that, the typical value of the pixel values S exceeds the judgment
threshold value Th. At the instant when the typical value of the
pixel values S of the reference line image exceeds the judgment
threshold value Th, the X-ray emission from the X-ray source is
judged to be started.
[0017] As shown in FIG. 18, as soon as the X-ray emission is judged
to be started, the controller immediately stops issuing the gate
pulses and shifts the panel unit from the pre-emission readout
operation to the accumulation operation. After a lapse of time
determined in an imaging condition, the X-ray emission is expected
to be completed, and the panel unit shifts to the image readout
operation. The electric charge is read out on a pixel-row basis and
an X-ray image XP is outputted. After the image readout operation,
the panel unit shifts to the pre-emission readout operation again
in a case where a reservation for the next imaging is made. The
panel unit completes its operation in the case of no reservation
for the next imaging.
[0018] FIGS. 18 and 19 show a state in which the typical value of
the pixel values S of the reference line image of the Cth pixel-row
exceeds the judgment threshold value Th, and hence the judgment of
the emission start is made at the Cth pixel-row. However, the X-ray
emission is actually started just moments before reading out the
reference line image of the (C-2)th pixel-row, which is two
pixel-rows previous to the Cth pixel-row (just moments before
inputting the gate pulse (C-2) to the pixels of the (C-2)th
pixel-row). Such a time delay between the start of the X-ray
emission and the judgment of the emission start causes the readout
of three pixel-rows, including the Cth pixel-row immediately before
the stop of the pre-emission readout operation and the (C-1)th and
(C-2)th pixel-rows being next previous to the Cth pixel-row, during
the X-ray emission. This brings about the deficit in the electric
charge.
[0019] Such a deficit in the electric charge manifests itself as a
strip-shaped line defect extending in a pixel-row direction (X
direction) in the X-ray image XP, as shown in FIG. 20. In the
drawing, a right graph shows a plot of pixel values D of an
arbitrary column X (X=1 to M, M is the number of the pixel-columns)
in the X-ray image XP along a pixel-column direction (Y direction).
The pixel value D begins decreasing from the (C-2)th pixel-row at
which the pre-emission readout operation is performed just moments
after the start of the X-ray emission, and comes to the lowest at
the Cth pixel-row at which the judgment of the emission start is
made and just moments before stopping the pre-emission readout
operation. Accordingly, the line defect becomes severer in a
stepwise manner from the (C-2)th pixel-row to the Cth pixel-row,
and the severest at the Cth pixel-row. A difference in density is
conspicuous between the Cth pixel-row and the next (C+1)th
pixel-row, due to a difference in the pixel values D. Note that,
the plot does not show an effect of attenuation of the X-rays by
the object and an offset of the dark charge (the same goes for FIG.
21).
[0020] As shown in FIG. 21, the reference frame image RP represents
the offset caused by the dark charge of the pixels before the X-ray
emission. However, the reference line images of the three
pixel-rows, i.e. from the (C-2)th pixel-row at which the
pre-emission readout operation is firstly performed after the start
of the X-ray emission to the Cth pixel-row at which the judgment of
the emission start is made and just moments before the stop of the
pre-emission readout operation, represent output according to the
X-ray dose and correspond to the line defect in the X-ray image
XP.
[0021] The pixel values S of the reference line images of the three
pixel-rows corresponding to the line defect are increased in a
stepwise manner from the (C-2)th pixel-row to the Cth pixel-row,
oppositely to the line defect in the X-ray image XP. In FIG. 21, a
right graph shows a plot of pixel values S of the arbitrary
pixel-column X in the reference frame image RP along the Y
direction, just as with the plot of FIG. 20. The pixel values S of
the reference frame image RP are approximately zero from the first
pixel-row to the (C-3)th pixel-row before the start of the X-ray
emission. The pixel value S begins increasing from the (C-2)th
pixel-row, and comes to the highest at the Cth pixel-row. The
typical value of the pixel values S exceeds the judgment threshold
value Th at the Cth pixel-row. The pixel values S of the (C+1)th
pixel-row to the Nth pixel-row are obtained in the pre-emission
readout operation of the previous cycle, and are approximately zero
just as with the pixel values S of the first to (C-3)th
pixel-rows.
[0022] The difference in the pixel value D of the X-ray image XP
between the Cth pixel-row just moments before stopping the
pre-emission readout operation and the next (C+1)th pixel-row
becomes maximum, as for the difference in the pixel value D between
adjoining two pixel-rows of the pixel-rows corresponding to the
line defect of the X-ray image XP. This difference is called a
difference amount. Representing an absolute value of the difference
amount as .DELTA.D (see FIG. 20), the difference amount .DELTA.D is
equal to a pixel value SQ (see FIG. 21) of the Cth pixel-row in the
reference frame image RP. Furthermore, a falling gradient of the
pixel value D from the (C-2)th pixel-row to the Cth pixel-row in
the X-ray image XP coincides with a rising gradient of the pixel
value S from the (C-2)th pixel-row to the Cth pixel-row in the
reference frame image RP. In other words, the complementary
relation holds between the pixel values D of the pixel-rows having
the line defect in the X-ray image XP and the pixel values S of the
pixel-rows corresponding to the line defect in the reference frame
image RP. Therefore, in the Japanese Patent Laid-Open Publication
No. 2011-254971, the reference frame image RP is used as a
correction image for correcting the line defect. The line defect of
the X-ray image XP is corrected by adding the pixel values S of the
pixel-rows corresponding to the line defect in the reference frame
image RP to the pixel values D of the pixel-rows having the line
defect in the X-ray image XP.
[0023] By the way, according to another method of the readout
operation, gate pulses are concurrently inputted to a plurality of
adjoining pixel-rows and the electric charge accumulated in the
pixels is discharged from the plurality of pixel-rows at a time to
the signal lines, in order to shorten time required for the one
cycle. In reading out the electric charge from the plurality of
adjoining pixel-rows at a time, the electric charge of the pixels
of the plural pixel-rows is added in each signal line on a
pixel-column basis. Such a readout operation by which the electric
charge is readout from the plurality of pixel-rows in a state of
addition is called binning readout. Also, the plurality of
adjoining pixel-rows from which the electric charge is read out at
a time is called a binning pixel-row. The binning readout can
shorten time required for the one cycle of the readout from the
first row to the last row, as compared with the case of the readout
on a pixel-row basis, and hence facilitates reducing the dark
charge accumulated in the pixels.
[0024] However, in the case of performing the binning readout as
the pre-emission readout operation, there is a problem that the
line defect of the X-ray image XP cannot be corrected in the method
described above, that is, by simply adding the pixel values S of
the reference frame image RP to the pixel values D of the X-ray
image XP.
[0025] This is because in the binning readout, the electric charge
is discharged at a time from the pixels of the plurality of
pixel-rows composing one binning pixel-row. Thus, the reference
line image is composed of values each of which corresponds to the
electric charge of the plurality of pixels, for example, four
pixels, outputted in a state of being added on a column-by-column
basis. Sequentially recording the reference line images on a
binning pixel-row basis allows obtainment of the reference frame
image RP. On the other hand, the X-ray image XP is read out on a
pixel-row basis. Thus, the pixel value SQ of the reference frame
image RP recorded by the binning readout at a part corresponding to
the line defect is larger than the difference amount .DELTA.D in
the X-ray image XP at a part of the line defect, and the values do
not coincide each other. In the reference frame image RP recorded
by the binning readout, since the one binning pixel-row is composed
of the plurality of pixel-rows, the number of the binning
pixel-rows of the reference frame image RP is less than the number
of the pixel-rows of the X-ray image XP. Setting the four
pixel-rows as the one binning pixel-row, for example, the number of
the binning pixel-rows of the reference frame image RP is a quarter
of the number of the pixel-rows of the X-ray image XP. Thus, the
reference frame image RP recorded in the binning readout is of the
same image size as the X-ray image XP in the pixel-row direction,
and of smaller image size in the pixel-column direction. Therefore,
the complementary relation between the pixel values D of the
pixel-rows having the line defect in the X-ray image XP and the
pixel values S of the pixel-rows corresponding to the line defect
of the reference frame image RP does not hold true. Therefore, the
line defect of the X-ray image XP cannot be corrected by simply
adding the reference frame image RP to the X-ray image XP, as
described in the Japanese Patent Laid-Open Publication No.
2011-254971.
SUMMARY OF THE INVENTION
[0026] An object of the present invention is to provide a radiation
image detecting device, an operating method thereof, and a
radiation imaging system that can correct a line defect of a
radiographic image with the use of reference line images recorded
by binning readout.
[0027] To achieve the above and other objects, a radiation image
detecting device according to the present invention includes a
panel unit, a plurality of pixels, a plurality of scan lines, a
signal line, a controller, a reference line image record
controller, an emission start judging unit, a correction image
generator, and a line defect corrector. The panel unit has an image
capturing field for imaging a radiographic image of an object by
receiving radiation emitted from a radiation source. The plurality
of pixels are arranged in the panel unit in a two-dimensional array
having a plurality of pixel-rows and a pixel-column. Each of the
pixels produces and accumulates electric charge. The plurality of
scan lines are provided in the panel unit on a pixel-row basis, and
makes the pixel-row having the pixels from which the electric
charge is to be read out in an ON state. The signal line is
provided in the panel unit on a pixel-column basis, for reading out
the electric charge from the pixels on a pixel-column basis. The
controller controls the panel unit to perform three types of
operations of a pre-emission readout operation, an accumulation
operation, and an image readout operation. In the pre-emission
readout operation, a plurality of adjoining pixel-rows are set as a
binning pixel-row. Binning readout of the electric charge is
performed on a binning pixel-row basis sequentially from a first
binning pixel-row to a last binning pixel-row and repeated from the
first binning pixel-row upon reaching the last binning pixel-row,
in order to obtain reference line images each having a pixel value
being a sum of the electric charge of a plurality of pixels in a
same pixel-column. The accumulation operation is performed instead
of the pre-emission readout operation, in a case where the
radiation source starts emitting the radiation while the binning
readout of the electric charge is repeated on a binning pixel-row
basis, for accumulating the electric charge in the pixels in
accordance with the radiation. The image readout operation is
started after completion of emission of the radiation from the
radiation source, for reading out the electric charge from the
pixels on a pixel-row basis and converting the electric charge to
pixel values for forming the radiographic image. The reference line
image record controller obtains the reference line images of a
plurality of binning pixel-rows by sequentially recording the
reference line images to a memory whenever performing the binning
readout. The emission start judging unit judges the start of
emission of the radiation from the radiation source. The correction
image generator produces a correction image used for correcting a
strip-shape line defect occurring in a pixel-row direction of the
radiographic image due to a time delay between the start of
emission of the radiation and a judgment of the start of emission,
by scaling up an image size of the reference line images of the
plurality of binning pixel-rows in a pixel-column direction and
correcting the pixel values. The line defect corrector corrects the
line defect by adding the correction image to the radiographic
image.
[0028] The correction image generator preferably corrects the pixel
value of the reference line image based on an immediately-preceding
reference line image that is obtained immediately before stopping
the pre-emission readout operation, out of the reference line
images of the plurality of binning pixel-rows.
[0029] The correction image generator preferably includes a
correction coefficient calculator for calculating a correction
coefficient used for converting the pixel value of the reference
line image to a value corresponding to a pixel value of the
radiographic image; and a pixel value corrector for multiplying the
pixel value of the reference line image by the correction
coefficient calculated by the correction coefficient
calculator.
[0030] The correction coefficient calculator may calculate a ratio
.DELTA.D/SQ as the correction coefficient. SQ represents a pixel
value of the immediately-preceding reference line image. .DELTA.D
represents a difference amount being a maximum value of difference
in a pixel value D of the radiographic image between adjoining two
of the pixel-rows caused by the line defect.
[0031] The correction coefficient calculator may calculate a ratio
.DELTA.DR/SQR as the correction coefficient. SQR represents a
typical value of a pixel value SQ of the immediately-preceding
reference line image. .DELTA.DR represents a typical value of a
difference amount .DELTA.D being a maximum value of difference in a
pixel value D of the radiographic image between adjoining two of
the pixel-rows caused by the line defect.
[0032] The typical value SQR may be an average SQave of the pixel
values SQ, and the typical value .DELTA.DR may be an average
.DELTA.Dave of the difference amounts .DELTA.D.
[0033] The correction coefficient calculator preferably calculates
the average SQave and the average .DELTA.Dave with excluding a
pixel value of a defect pixel from the pixel values SQ and the
pixel values D that are used for calculation of the average SQave
and the average .DELTA.Dave.
[0034] The typical value SQR may be a median value SQC of the pixel
values SQ, and the typical value .DELTA.DR may be a median value
.DELTA.DC of the difference amounts .DELTA.D.
[0035] The correction coefficient calculator may calculate a
reciprocal of a number of the pixel-rows composing the binning
pixel-row, as the correction coefficient.
[0036] The correction image generator preferably extracts the
immediately-preceding reference line image and a plurality of the
reference line images next to the immediately-preceding reference
line image as line-defect-corresponding reference line images, out
of the reference line images of the plurality of binning
pixel-rows, and produces the correction image based on the
line-defect-corresponding reference line images alone.
[0037] The pixel value corrector may uniformly multiply the pixel
values of the line-defect-corresponding reference line images by
the correction coefficient calculated by the correction coefficient
calculator.
[0038] It is preferable that the radiation image detecting device
further includes a correction coefficient modifier for modifying
the correction coefficient calculated by the correction coefficient
calculator to a correction coefficient specific to the
line-defect-corresponding reference line image other than the
immediately-preceding reference line image. The pixel value
corrector multiplies a pixel value of the immediately-preceding
reference line image by the correction coefficient calculated by
the correction coefficient calculator, and multiplies a pixel value
of the line-defect-corresponding reference line image other than
the immediately-preceding reference line image by the correction
coefficient modified by the correction coefficient modifier.
[0039] The correction image generator preferably scales up an image
size of the reference line images of the plurality of binning
pixel-rows in the pixel-column direction by row interpolation
processing.
[0040] The row interpolation processing may apply linear
interpolation or spline interpolation between the reference line
images next to each other.
[0041] The reference line images of the plurality of binning
pixel-rows may coincide with the reference line images of one frame
extending from the first binning pixel-row to the last binning
pixel-row.
[0042] In a case where the pre-emission readout operation of one
frame extending from the first binning pixel-row to the last
binning pixel-row is set as one cycle, the reference line image
record controller preferably sequentially updates the reference
line images of one frame obtained in the pre-emission readout
operation of an Sk-th cycle with the reference line images obtained
in the pre-emission readout operation of an (Sk+1)-th cycle on a
binning pixel-row basis.
[0043] The emission start judging unit preferably judges the start
of emission of the radiation based on the reference line
images.
[0044] The radiation image detecting device may further include a
leak corrector for subtracting a pixel value based on leak current
leaking from the pixel according to application of the radiation
from a pixel value of the reference line image, before the
correction image generator generates the correction image.
[0045] The controller may also function as the reference line image
record controller. The controller may also function as the line
defect corrector. The line defect corrector may also function as
the correction image generator.
[0046] An operating method of a radiation image detecting device
includes the steps of performing the pre-emission readout
operation, until the emission start judging unit judges the start
of emission; in the pre-emission readout operation, setting a
plurality of adjoining pixel-rows as a binning pixel-row, and
performing binning readout of the electric charge on a binning
pixel-row basis sequentially from a first binning pixel-row to a
last binning pixel-row and repeating the binning readout from the
first binning pixel-row upon reaching the last binning pixel-row,
in order to obtain reference line images each having a pixel value
being a sum of the electric charge of a plurality of pixels in a
same pixel-column; judging the start of emission by the emission
start judging unit, while the binning readout of the electric
charge is repeated on a binning pixel-row basis; performing the
accumulation operation instead of the pre-emission readout
operation, when the emission start judgment unit judges the start
of emission; performing the image readout operation after
completion of emission of the radiation from the radiation source;
producing by a correction image generator a correction image used
for correcting a strip-shape line defect occurring in a pixel-row
direction of the radiographic image due to a time delay between the
start of emission of the radiation and the judgment of the start of
emission, by scaling up an image size of the reference line images
of a plurality of binning pixel-rows in a pixel-column direction
and correcting the pixel values; and correcting the line defect by
a line defect corrector by adding the correction image to the
radiographic image.
[0047] A radiation imaging system according to the present
invention includes a radiation image detecting device for detecting
a radiographic image of an object by receiving radiation emitted
from a radiation source, and a line defect correction device for
correcting a strip-shape line defect occurring in the radiographic
image.
[0048] According to the present invention, the correction image,
which is to be used for correcting the line defect occurring in the
radiographic image, is produced by applying the scale-up of the
image size and the correction of the pixel values to the reference
line images recorded by the binning readout. Thus, it is possible
to provide the radiation image detecting device that can correct
the line defect in the radiographic image by using the reference
line images recorded by the binning readout.
BRIEF DESCRIPTION OF DRAWINGS
[0049] For more complete understanding of the present invention,
and the advantage thereof, reference is now made to the subsequent
descriptions taken in conjunction with the accompanying drawings,
in which:
[0050] FIG. 1 is a schematic view of an X-ray imaging system;
[0051] FIG. 2 is a drawing of an imaging condition table;
[0052] FIG. 3 is a block diagram of a source control unit;
[0053] FIG. 4 is a perspective view of an electronic cassette;
[0054] FIG. 5 is a block diagram of an image detector;
[0055] FIG. 6 is a timing chart of the operation of a panel
unit;
[0056] FIG. 7 is a drawing showing a second storage area of a frame
memory for recording a reference frame image;
[0057] FIG. 8 is an explanatory view showing the relation among an
X-ray emission profile, a pixel value S, and a judgment of an
emission start;
[0058] FIG. 9 is an explanatory view of a line defect occurring in
an X-ray image XP and variation in a pixel value D in a Y
direction;
[0059] FIG. 10 is an explanatory view of a line defect occurring in
a reference frame image RP and variation in a pixel value S in the
Y direction;
[0060] FIG. 11 is a block diagram showing various types of
correctors provided in a controller;
[0061] FIG. 12 is a schematic explanatory view of linear
interpolation;
[0062] FIG. 13 is a drawing showing a state of outputting a
corrected X-ray image XPC in which the linear defect is corrected
by adding a correction image RPC to the X-ray image XP;
[0063] FIG. 14 is a flowchart showing the operation of the image
detector;
[0064] FIG. 15 is an explanatory view of the extraction of
reference line images corresponding to the line defect;
[0065] FIG. 16 is a drawing of a third embodiment having a
correction coefficient proofreader;
[0066] FIG. 17 is a drawing of a fourth embodiment having a leak
corrector;
[0067] FIG. 18 is a timing chart of the operation of a conventional
panel unit;
[0068] FIG. 19 is an explanatory view of the conventional relation
among an X-ray emission profile, a pixel value S, and a judgment of
an emission start;
[0069] FIG. 20 is an explanatory view showing a line defect
occurring in a conventional X-ray image XP and variation in a pixel
value D in the Y direction; and
[0070] FIG. 21 is an explanatory view showing a line defect
occurring in a conventional reference frame image RP and variation
in a pixel value S in the Y direction.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0071] In FIG. 1, an X-ray imaging system 2 is constituted of an
X-ray generating apparatus 2a and an X-ray imaging apparatus 2b.
The X-ray generating apparatus 2a includes an X-ray source 10, a
source control unit 11 for controlling the operation of the X-ray
source 10, and an emission switch 12 for commanding the X-ray
source 10 to start a warm-up and an X-ray emission. The X-ray
imaging apparatus 2b, being a portable X-ray image detecting
device, includes an electronic cassette 13 and a console 14 that is
in charge of operation control of the electronic cassette 13 and
display processing of an X-ray image. In addition, the X-ray
imaging system 2 is provided with an imaging stand 15 for imaging
an object in a standing position, an imaging table 16 for imaging
the object in a lying position, and a source shift device (not
shown) for setting the X-ray source 10 in a desired orientation and
position. The source shift device shifts the X-ray source 10 so as
to be opposed to the imaging stand 15 or the imaging table 16.
[0072] No electric connection is established between the X-ray
generating apparatus 2a and the X-ray imaging apparatus 2b, and
therefore no synchronization signal for synchronizing the X-ray
generating apparatus 2a and the X-ray imaging apparatus 2b is
communicated therebetween. However, the electronic cassette 13 has
the function of making a judgment of a emission start i.e. judging
whether or not the X-ray emission has been started. Thereby, it is
possible to synchronize the operation of the electronic cassette 13
to the start of the X-ray emission by the X-ray generating
apparatus 2a.
[0073] As is widely known, the X-ray source 10 has an X-ray tube
and an irradiation field limiter (collimator) for limiting an
irradiation field of the X-rays radiating from the X-ray tube. The
X-ray tube has a cathode being a filament for emitting
thermoelectrons, and an anode (target) that radiates the X-rays by
collision of the thermoelectrons emitted from the cathode. In
response to a warm-up start command, the filament is preheated and
the anode starts rotating. The warm-up is completed when the
preheat of the filament is completed and the RPM of the anode
reaches a predetermined value. The irradiation field limiter is
composed of, for example, four lead plates for blocking the X-rays.
The four lead plates are disposed in each side of a rectangle so as
to form a rectangular irradiation opening in a middle to pass the
X-rays therethrough. Shifting the position of the lead plates
varies the size of the irradiation opening to limit the irradiation
field.
[0074] The console 14 is coomunicatably connected to the electronic
cassette 13 by a wired or wireless method. The console 14 controls
the operation of the electronic cassette 13 in response to input by
an operator such as a radiological technician from an input device
14a such as a keyboard. An X-ray image from the electronic cassette
13 is displayed on a display 14b of the console 14. Data of the
X-ray image is stored to a storage device 14c including a hard disk
and a memory of the console 14, an image storage server connected
to the console 14 through a network, or the like.
[0075] The console 14 receives input of an examination order
including information about sex and age of an object, a body part
to be imaged, an examination purpose, and the like and displays the
examination order on the display 14b. The examination order is
inputted from an external system e.g. a HIS (hospital information
system) or a RIS (radiography information system) that manages
object data and examination data related to radiography, or
inputted manually by the operator. The examination order includes
an item of the body part to be imaged e.g. a head, a chest, an
abdomen, a hand, fingers, and the like. The operator confirms the
contents of the examination order on the display 14b, and inputs an
imaging condition corresponding to the contents through an
operation screen on the display 14b.
[0076] In FIG. 2, the storage device 14c stores an imaging
condition table 20. The imaging condition includes information
about the object such as the body part to be imaged, the sex of the
object, the age of the object, and a body thickness of the object,
and an emission condition of the X-rays from the X-ray source 10.
The emission condition is determined in consideration of the
information about the body part and the object. The emission
condition includes tube voltage (in units of kV) for determining an
energy spectrum of the X-rays emitted from the X-ray source 10,
tube current (in units of mA) for determining an emission dose per
unit of time, and emission time (in units of s) of the X-rays. The
imaging condition table 20 stores the correlation between the body
part to be imaged including the chest, the abdomen, and the like
and the emission condition corresponding to the body part. By
choosing the body part, the emission condition corresponding to the
body part is read out. Each value of the emission condition (the
tube voltage, the tube current, and the emission time) read out of
the imaging condition table 20 can be finely adjusted in accordance
with the sex, the age, and the body thickness of the object. The
tube current and the emission time are recorded independently in
the imaging condition table 20 of this embodiment. However, since a
total emission dose depends on the product of the tube current and
the emission time, a value of a tube current-time product (mAs
value), being the product of the tube current and the emission
time, may be recorded instead.
[0077] In FIG. 3, the source control unit 11 is provided with a
high voltage generator 21 that generates the high tube voltage by
multiplying input voltage using a transformer and supplies the high
tube voltage to the X-ray source 10 through a high voltage cable, a
source controller 22 that controls the tube voltage and the tube
current to be applied to the X-ray source 10 and the emission time
of the X-rays, a memory 23, and a touch panel 24.
[0078] To the source controller 22, the emission switch 12, the
high voltage generator 21, the memory 23, and the touch panel 24
are connected. The emission switch 12 is a two-step press switch
for inputting commands to the source controller 22. Upon a
first-step press (half push) of the emission switch 12, the source
controller 22 issues a warm-up command signal to the high voltage
generator 21 to start warming up the X-ray source 10. Upon a
second-step press (full push) of the emission switch 12, the source
controller 22 issues an emission command signal to the high voltage
generator 21 to start an X-ray emission from the X-ray source
10.
[0079] The memory 23 stores in advance a plurality of types of
imaging conditions including the emission conditions such as the
tube voltage, the tube current, and the emission time, as with the
storage device 14c of the console 14. The imaging condition is set
manually by the operator through the touch panel 24. The plurality
of types of imaging conditions are readout of the memory 23 and
displayed on the touch panel 24. The operator chooses the same
imaging condition as that inputted to the console 14 out of the
imaging conditions read out of the memory 24, and thereby the
imaging condition is set in the source control unit 11. As in the
case of the console 14, each value of the imaging condition is
finely adjustable. The source controller 22 contains a timer 25 in
order to stop the X-ray emission when the set emission time has
elapsed.
[0080] In FIG. 4, the electronic cassette 13, which detects the
X-rays passed through the object and outputs the X-ray image, is
composed of an image detector 30 and a flat box-shaped portable
housing 31 containing the image detector 30. The housing 31 is made
of a conductive resin, for example. The housing 31 has a
rectangular opening at its front surface 31a on which the X-rays
are incident. A X-ray transparent plate 32 being a top plate is
fitted into the opening. The X-ray transparent plate 32 is made of
a carbon material possessing light weight, high stiffness, and high
X-ray transmittance. The housing 31 also functions as an
electromagnetic shield, which prevents entry of electromagnetic
noise to the electronic cassette 13 and radiation of
electromagnetic noise from the electronic cassette 13 to the
outside. In addition to the image detector 30, the housing 31
contains a battery (secondary battery) for supplying electric power
to drive the electronic cassette 13 and an antenna for establishing
wireless communication of data such as the X-ray image with the
console 14.
[0081] The housing 31 is of a size compatible with the
International Standard ISO4090:2001, as with the film cassette and
the IP cassette. The electronic cassette 13 is detachably loaded in
a holder 15a, 16a (see FIG. 1) of the imaging stand 15 or the
imaging table 16 in such a position that the front surface 31a of
the housing 31 is opposed to the X-ray source 10. The source shift
device shifts the X-ray source 10 depending on which one of the
imaging stand 15 and the imaging table 16 to use.
[0082] The electronic cassette 13 can be used by itself, instead of
being loaded in the imaging stand 15 or the imaging table 16, in a
state of being put on a bed under the object lying or held by the
object himself/herself. Furthermore, the electronic cassette 13 is
approximately of the same size as the film cassette and the IP
cassette, and is loadable in an existing imaging stand or table
designed for the film cassette and the IP cassette. Note that, the
housing 31 may not be of the size compatible with the International
Standard ISO4090:2001.
[0083] In FIG. 5, the image detector 30 is constituted of a panel
unit 35 and a circuit unit for controlling the operation of the
panel unit 35. The panel unit 35 has a TFT active matrix substrate
and an image capturing field 40 formed in the substrate. In the
image capturing field 40, a plurality of pixels 41 each for
accumulating electric charge in accordance with an X-ray dose
incident thereon are arranged into a matrix of N pixel-rows (Y
direction) by M pixel-columns (X direction) at a predetermined
pitch. N and M are integers of 2 or more, and N, M.apprxeq.2000,
for example. Note that, the pixels 41 may not be in a rectangular
matrix array, but in a honeycomb array.
[0084] The panel unit 35 is of an indirect conversion type, having
a scintillator (phosphor, not shown) for converting the X-rays into
visible light. The pixels 41 perform photoelectric conversion of
the visible light converted by the scintillator. The scintillator
is made of CsI:Tl (thallium activated cesium iodide), GOS
(Gd2O2S:Tb, terbium activated gadolinium oxysulfide), or the like,
and is opposed to the entire image capturing field 40 having the
matrix of pixels 41. Note that, the scintillator and the active
matrix substrate may be disposed in either a PSS (penetration side
sampling) method in which the scintillator and the substrate are
disposed in this order from an X-ray incident side, or an ISS
(irradiation side sampling) method in which the substrate and the
scintillator are disposed in this order, oppositely to the PSS
method. Also, a panel unit of a direct conversion type, which has a
conversion layer (amorphous selenium or the like) for directly
converting the X-rays into the electric charge without using the
scintillator, may be used instead.
[0085] As is widely known, the pixel 41 is composed of a
photoelectric conversion element 42 that produces the electric
charge (electron and hole pairs) upon incidence of the visible
light and accumulates the electric charge, and a TFT 43 being a
switching element.
[0086] The photoelectric conversion element 42 has a semiconducting
layer (of PIN (p-intrinsic-n) type, for example) for producing the
electric charge, and an upper electrode and a lower electrode
disposed on the top and bottom of the semiconducting layer. The
lower electrode of the photoelectric conversion element 42 is
connected to the TFT 43, and the upper electrode of the
photoelectric conversion element 42 is connected to a bias line.
There are a same number of bias lines provided as the number (N
pixel-rows) of the pixel-rows of the pixels 41. All the bias lines
are coupled to a bus. The bus is connected to a bias power supply.
A bias voltage is applied from the bias power supply to the upper
electrodes of the photoelectric conversion elements 42 through the
bus and the bias lines. Since the application of the bias voltage
produces an electric field in the semiconducting layer, the
electric charge (electron and hole pairs) produced in the
semiconducting layer by the photoelectric conversion is attracted
to the upper and lower electrodes, one of which has a positive
polarity and the other of which has a negative polarity. Thereby,
the electric charge is accumulated in the photoelectric conversion
element 42.
[0087] A gate electrode of the TFT 43 is connected to a scan line
44, a source electrode thereof is connected to s signal line 45,
and a drain electrode thereof is connected to the photoelectric
conversion element 42. The scan lines 44 and the signal lines 45
are routed into a lattice in the image capturing field 40. The
number of the scan lines 44 coincides with the number (N
pixel-rows) of the pixel-rows of the pixels 41, and the pixels 41
of one pixel-row are connected to the common scan line 44. The
number of the signal lines 45 coincides with the number (M
pixel-columns) of the columns of the pixels 41, and the pixels 41
of one pixel-column are connected to the common signal line 45. All
the scan lines 44 are connected to the gate driver 46. All the
signal lines 45 are connected to a signal processing circuit
47.
[0088] The circuit unit for controlling the operation of the panel
unit 35 includes the gate driver 46, the signal processing circuit
47, a controller 48, and the like. The gate driver 46 outputs a
gate pulse G to the gate electrodes of the TFTs 43 of the same
pixel-row through the scan line 44, to switch the TFTs 43 between
an ON state and an OFF state. A duration of the ON state of the TFT
43 is defined by a pulse width of the gate pulse G. After a lapse
of time defined by the pulse width, the TFT 43 returns to the OFF
state. In the ON state of the TFT 43, the electric charge
accumulated in the photoelectric conversion element 42 of the pixel
41 is inputted to the signal processing circuit 47 through the
signal line 45. The controller 48 makes the panel unit 35 perform a
pre-emission readout operation, an accumulation operation, and an
image readout operation. In the pre-emission readout operation, the
electric charge accumulated in the pixels 41 before the X-ray
emission is read out and recorded to a frame memory 54 through the
signal processing circuit 47. In the accumulation operation, the
electric charge is accumulated in accordance with the X-ray dose
incident thereon. In the image readout operation, the electric
charge accumulated in the pixels 41 are read out after the
completion of the X-ray emission, and recorded to the frame memory
54 through the signal processing circuit 47.
[0089] The signal processing circuit 47 includes integrators 49,
correlated double sampling circuits (CDSs) 50, a multiplexer (MUX)
51, an analog-to-digital converter (A/D) 52, and the like. The
integrator 49 is connected to each signal line 45 on a one-by-one
basis. The integrator 49 is composed of an operational amplifier
49a and a capacitor 49b connected between input and output
terminals of the operational amplifier 49a. The signal line 45 is
connected to one of the input terminals of the operational
amplifier 49a. The other input terminal of the operational
amplifier 49a is connected to a ground (GND). A reset switch 49c is
connected in parallel to the capacitor 49b. The integrator 49
integrates the electric charge inputted from the signal line 45.
Then, the integrators 49 convert the integrated electric charge
into analog voltage signals V(1) to V(M), and output the voltage
signals V(1) to V(M).
[0090] The output terminal of the operational amplifier 49a of each
pixel-column is connected to the MUX 51 through an amplifier 53 and
the CDS 50. Output of the MUX 51 is connected to the A/D 52. The
CDS 50 has sample holder circuits. The CDS 50 applies correlation
double sampling to an output voltage signal of the integrator 49 to
remove a reset noise component of the integrator 49, and holds
(sample holds) the voltage signal outputted from the integrator 49
for a predetermined time period in its sample hold circuit. The MUX
51 sequentially selects one of the CDSs 50 connected in parallel by
an electronic switch based on an operation control signal from a
shift resistor (not shown), and inputs the voltage signals V(1) to
V(M) outputted from the selected CDSs 50 in series to the A/D 52.
Note that, another amplifier may be connected between the MUX 51
and the A/D 52.
[0091] The A/D 52 converts the inputted analog voltage signals V(1)
to V(M) of one pixel-row into digital values (pixel values), and
outputs the pixel values to the frame memory 54 contained in the
electronic cassette 13. The frame memory 54 stores the pixel values
of the one pixel-row that are read out at a time with being
associated with coordinates of individual pixels 41.
[0092] As soon as the MUX 51 reads out the voltage signals V(1) to
V(M) of one pixel-row from the integrators 49, the controller 48
outputs an amplifier reset pulse RST to the integrators 49 to turn
on the reset switches 49c. Thereby, the electric charge of the one
pixel-row accumulated in the capacitors 49b is discharged and the
integrators 49 are reset. After the reset of the integrators 49,
the reset switches 49c are turned off again as a preparation to
readout of the next pixel-row.
[0093] The frame memory 54 has a first storage area 54a for
recording an X-ray image XP (see FIGS. 6 and 9) obtained in the
image readout operation, and a second storage area 54b for
recording a reference frame image RP (see FIGS. 6 and 10) obtained
in the pre-emission readout operation.
[0094] The communication I/F 55 is wiredly or wirelessly connected
to the console 14 to mediate transmission and reception of
information to and from the console 14. The communication I/F 55
receives information on the imaging condition from the console 14,
and outputs the information to the controller 48. The communication
I/F 55 also receives the X-ray image after being subjected to the
various types of processing from the frame memory 54 via the
controller 48, and transmits the X-ray image to the console 14.
[0095] The controller 48 contains a timer 56. Out of the imaging
condition set in the console 14, the emission time is set in the
timer 56. The timer 56 starts measuring time at the instant when an
emission start judging unit 57 judges that the X-ray emission has
been started. The controller 48 judges that the X-ray emission is
stopped when the emission time, which is determined depending on
the body part to be imaged and the like, has elapsed in a time
measured by the timer 56.
[0096] The controller 48 controls the operation of the emission
start judging unit 57. To detect the start of the X-ray emission,
the emission start judging unit 57 performs an emission start
judgment, which judges whether or not the X-ray emission has been
started based on a reference line image RL (see FIG. 7 and the
like) outputted in the pre-emission readout operation.
[0097] Referring to FIG. 6, the controller 48 makes the panel unit
35 start the pre-emission readout operation, when the controller 48
receives the information on the imaging condition from the console
14 through the communication I/F 55 in a standby state before the
X-ray emission. In the pre-emission readout operation, binning
readout is carried out in which adjoining four pixel-rows are set
as one binning pixel-row, and the gate pulse G is issued to the
adjoining four pixel-rows at a time. By repeating the issue of the
gate pulse G, the scan lines 44 are sequentially activated on a
four-pixel-row basis and the TFTs 43 are turned on in
four-pixel-row blocks, for the purpose of save time for the readout
from the first pixel-row (the 1st pixel-row) to the last pixel-row
(the Nth pixel-row). The electric charge is accumulated in each
pixel 41 in a period of time between the binning readout of a
preceding cycle of the pre-emission readout operation of one frame
and the binning readout of the following cycle.
[0098] By performing the binning readout in the four-pixel-row
blocks, the electric charge of the four pixels 41 adjoining in the
Y direction are added in each signal line 45 and flows into the
integrator 49. The controller 48 sequentially selects one of the
integrators 49 using the MUX 51 and reads out output (voltage) of
each integrator 49. The controller 48 converts the output of
integrators 49 into digital values (pixel values S) by the A/D 52,
and outputs the pixel values S to the frame memory 54 as the
reference line image RL. Each pixel value S of the reference line
image RL represents the sum of the pixel values of the four pixels
41 of each pixel-column.
[0099] Note that, in this specification, "RP" represents the
reference line images of one frame, that is, a reference frame
image. "RL" represents the reference line image of each binning
pixel-row included in the reference frame image RP. "XP" represents
the X-ray image of one frame. "XL" represents the X-ray image of
each pixel-row included in the X-ray image XP. As shown on a left
side of FIG. 6, the binning readout of the 1st binning pixel-row,
including the 1st pixel-row to the 4th pixel-row, allows obtainment
of the reference line image RL(1) of one binning-row. The binning
readout of the 2nd binning pixel-row, including the 5th pixel-row
to the 8th pixel-row, allows obtainment of the reference line image
RL(2). Likewise, the binning readout of the (C-3)th pixel-row to
the Cth pixel-row allows obtainment of the reference line image
RL(c). Whenever the binning readout is performed, the controller 48
inputs the amplifier reset pulse PST to the integrators 49 to reset
the integrators 49.
[0100] "RL(c)" represents the reference line image of the (C-3)th
pixel-row to the Cth pixel-row. "RL(c-1)" represents the reference
line image of the next preceding four pixel-rows (the (C-7)th
pixel-row to the (C-4)th pixel-row). "RL (c-2)" represents the
reference line image of the further next preceding four pixel-rows
(the (C-11)th pixel-row to the (C-8)th pixel-row). As described
above, a lower-case letter "c" is used for representing the binning
pixel-row of the reference line image RL. This is because the
binning readout causes a mismatch between the pixel-row and the
binning pixel-row of the reference line image RL. The Cth pixel-row
is the pixel-row having a line defect in the X-ray image XP, while
the cth binning pixel-row is the binning pixel-row corresponding to
the line defect. To distinguish between the pixel-row and the
binning pixel-row, the upper-case letter "C" is used for
representing the pixel-row, while the lower-case letter "c" is used
for representing the binning pixel-row of the reference line image
RL.
[0101] The controller 48 makes the panel unit 35 perform the
binning readout from the first binning pixel-row (the 1st binning
pixel-row) to the last binning pixel-row (the N/4th binning
pixel-row). In the pre-emission readout operation, since the
one-time binning readout corresponds to the readout of the four
pixel-rows, the readout of every pixel-row (the N pixel-rows) of
the image capturing field 40 is repeated in a cycle of the N/4-time
binning readout. In the binning readout of one cycle, the reference
line images RL of the N/4 binning pixel-rows are sequentially read
out at time intervals of H and recorded to the frame memory 54, and
therefore, the reference frame image RP being the reference line
images RL of one frame is obtained.
[0102] In FIG. 5, the controller 48 has a reference line image
record controller (hereinafter called a RL image record controller)
48a. As shown in FIG. 7, the RL image record controller 48a
controls the operation of the A/D 52 so as to record the reference
frame image RP to the second storage area 54b of the frame memory
54. Whenever performing the one-time binning readout, the reference
line image RL is recorded to the second storage area 54b. When the
reference line image RL is obtained at a certain cycle Sk of the
binning readout, the reference line image RL of the same binning
pixel-row obtained in the immediately preceding cycle (Sk-1) is
updated with the reference line image RL obtained in this cycle Sk.
For example, when the reference line image RL(1) of the 1st binning
pixel-row is obtained in the cycle Sk, the reference line image
RL(1) obtained in the preceding cycle (Sk-1) is updated with the
reference line image RL(1) of this cycle Sk. Thus, at that point in
time when the reference line image RL(1) of the 1st binning
pixel-row to the reference line image RL(n) of the nth binning
pixel-row obtained in this cycle Sk have been updated, for example,
the reference line images RL(1) to RL(n) of the 1st to nth binning
pixel-rows are ones obtained in this cycle Sk, while the reference
line images RL(n+1) to RL(N/4) of the (n+1)th to N/4th binning
pixel-rows are ones obtained in the preceding cycle (Sk-1).
[0103] In FIG. 8, the emission start judging unit 57 compares a
typical value of the pixel values S of the reference line image RL,
which is sequentially outputted at the intervals H, with a
predetermined judgment threshold value Th. For the quick judgment
of the emission start, a large value that has little effect of
attenuation by the object is preferably used as the typical value.
Thus, as the typical value to be compared with the judgment
threshold value Th, a maximum value of the pixel values S of the
reference line image RL is preferably used. Note that, an average
or sum of the pixel values S may be used instead as the typical
value. As described with referring to FIG. 19, the pixel values S
of each reference line image RL outputted at each timing E are at a
level of approximately zero before the start of the X-ray emission,
and increased in accordance with the X-ray emission profile after
the start of the X-ray emission. Then, the typical value of the
pixel values S reaches a level exceeding the judgment threshold
value Th. As soon as the typical value of the pixel values S
exceeds the judgment threshold value Th, the emission start judging
unit 57 judges that the X-ray emission has been started.
[0104] In a case where it is judged that the X-ray emission from
the X-ray source 10 has been started, the emission start judging
unit 57 outputs an emission start judgment signal to the controller
48. Upon receiving the emission start judgment signal from the
emission start judging unit 57, the controller 48 makes the panel
unit 35 stop the pre-emission readout operation and immediately
shift to the accumulation operation.
[0105] In FIG. 6, the gate driver 46 is stopped in the accumulation
operation. Since the TFT 43 of every pixel 41 is turned off, the
pixel 41 accumulates the electric charge in accordance with the
X-ray amount incident thereon. When the measured time of the timer
56 reaches the emission time set in the imaging condition, the
controller 48 makes the panel unit 35 complete the accumulation
operation and start the image readout operation. In the image
readout operation, the gate driver 46 sequentially issues the gate
pulses G to each pixel-row at the predetermined intervals H, so as
to sequentially activate the scan lines on a pixel-row basis and
turn on the TFTs 43 in one-pixel-row blocks. Thus, the X-ray image
XP is recorded to the first storage area 54a of the frame memory
54. As described above, how to issue the gate pulses G is different
between in the pre-emission readout operation and in the image
readout operation. After the completion of the image readout
operation, controller 48 gets the panel unit 35 back to the
pre-emission readout operation in the case of continuously
performing the next imaging, while stops the operation in the case
of not performing the next imaging. Note that, in this embodiment,
the issuing intervals H of the gate pulses G are the same between
the pre-emission readout operation and the image readout
operation.
[0106] FIGS. 6 to 8 show a state in which the X-ray emission is
started moments before inputting the gate pulse G to the TFTs 43 of
the pixels 41 of the (c-2)th binning pixel-row (the (C-11)th
pixel-row to the (C-8)th pixel-row). Then, when the typical value
of the pixel values S of the reference line image RL(c) obtained by
the input of the gate pulse G to the TFTs 43 of the pixels 41 of
the cth binning pixel-row (the (C-3)th pixel-row to the C-th
pixel-row) exceeds the judgment threshold value Th, the emission
start judging unit 57 judges that the X-ray emission has been
started. The start of the X-ray emission is judged from the
reference line image RL(c), and the pre-emission readout operation
is stopped immediately after outputting the reference line image
RL(c). For this reason, the reference line image RL(c) is called an
immediately-preceding reference line image RL(c), as distinguished
from the reference line images of the other binning pixel-rows.
Upon judging the start of the X-ray emission, the controller 48
determines the coordinates of the binning pixel-row of the
immediately-preceding reference line image RL(c) in the reference
frame image RP, and the coordinates of the pixel-rows (the (C-3)th
pixel-row to the Cth pixel-row) corresponding to the binning
pixel-row of the immediately-preceding reference line image RL(c).
Row coordinate information in which the coordinates of the binning
pixel-row and the coordinates of the pixel-rows are related to each
other is recorded to an internal memory 69 (see FIG. 11).
[0107] Ina case where the judgment of the emission start is delayed
from the start of the X-ray emission in the pre-emission readout
operation, a strip-shaped line defect occurs in the X-ray image XP,
as shown in FIG. 9. In this case, the line defect occurs in twelve
pixel-rows in total, including the X-ray images XL(C-11) to XL(C-8)
of the four pixel-rows from the (C-11)th pixel-row to the (C-8)th
pixel-row corresponding to the reference line image RL(c-2)
recorded in the binning readout immediately after the start of the
X-ray emission, the X-ray images XL(C-3) to XL(C) of the four
pixel-rows from the (C-3)th pixel-row to the Cth pixel-row
corresponding to the immediately-preceding reference line image
RL(c) on which the judgment of the emission start is made, and
X-ray images XL(C-7) to XL(C-4) of the four pixel-rows
therebetween. According to a plot of the pixel values D of an
arbitrary pixel-column X of the X-ray image XP along the Y
direction, the pixel value D starts falling from around the
(C-11)th pixel-row, and is the lowest at the Cth pixel-row.
[0108] With respect to the X-ray image XP shown in FIG. 9, in the
reference frame images RP, as shown in FIG. 10, the pixel values S
are increased by the electric charge in a portion corresponding to
the line defect of the X-ray image XP. This increase portion of the
pixel values S extends from the (c-2)th binning pixel-row at which
the X-ray emission is started to the cth binning pixel-row at which
the start of the X-ray emission is judged. A plot of the pixel
values S of the arbitrary pixel-column X of the reference frame
image RP along the Y direction is approximately zero from the 1st
binning pixel-row to the (c-3)th binning pixel-row immediately
before the start of the X-ray emission. The pixel values S start
rising from the (c-2)th binning pixel-row, and is the highest at
the cth binning pixel-row. The pixel values S of the (c+1)th
binning pixel-row to the N/4th binning pixel-row are obtained from
the pre-emission readout operation of the next preceding cycle
before the judgment the emission start, and are approximately zero,
just as with the pixel values S of the 1st binning pixel-row to the
(c-3)th binning pixel-row.
[0109] Although shape is similar between a line defect portion of
the X-ray image XP and the increase portion of the reference frame
image RP corresponding to the line defect, the pixel values D of
the X-ray image XP at the pixel-rows having the line defect are
different from the pixel values S of the increase portion of the
reference frame image RP corresponding to the line defect, because
of performing the binning readout in the pre-emission readout
operation. Also, since the number of the binning pixel-rows of the
reference frame image RP is N/4, the reference frame image RP is
different in image size in the pixel-column direction (Y direction)
from the X-ray image XP having the N pixel-rows.
[0110] Accordingly, simply adding the reference frame image RP to
the X-ray image XP, as described in the Japanese Patent Laid-Open
Publication No. 2011-254971, cannot correct the line defect of the
X-ray image XP.
[0111] As shown in FIG. 11, the controller 48 has a line defect
corrector 70 for the X-ray image XP. The line defect corrector 70
is provided with a correction image generator 71 for producing a
correction image, which is used for correcting the line defect of
the X-ray image, based on the reference frame image RP.
[0112] After the completion of the image readout operation, the
line defect corrector 70 reads out the X-ray image XP from the
first storage area 54a and the reference frame image RP from the
second storage area 54b, to perform various types of processing
described later on. The line defect corrector 70 also reads out the
row coordinate information, which is recorded upon the judgment of
the emission start, from the internal memory 69 of the controller
48 to determine the position of the line defect.
[0113] The line defect corrector 70 is provided with an
interpolator 75, a correction coefficient calculator 76, a pixel
value corrector 77, and an adder 78. The interpolator 75, the
correction coefficient calculator 76, and the pixel value corrector
77 compose the correction image generator 71. Since the size of the
reference frame image RP in the pixel-column direction is a quarter
of the image size of the X-ray image XP, the interpolator 75
applies row interpolation processing to the reference frame image
RP, in order to scale up the image size in the pixel-column
direction to the same image size as the X-ray image XP.
[0114] In the row interpolation processing, as schematically shown
in FIG. 12, for example, linear interpolation is performed based on
the signal values S of the reference line images RL of the
adjoining two binning-rows. For example, the pixel value S of the
reference line image RL(1) of the 1st binning pixel-row and the
pixel value S of the reset image RL(2) of the 2nd binning pixel-row
are added and divided by two, in order to obtain an interpolated
reference line image RL. The correspondence of the binning
pixel-rows between before and after the interpolation is shown
using arrows. The reference line image RL(1) of the 1st binning
pixel-row and the reference line image RL(2) of the 2nd binning
pixel-row before the interpolation become the reference line image
RL(1) of the 1st interpolated binning pixel-row and the reference
line image RL(3) of the 3rd interpolated binning pixel-row after
the interpolation, respectively. The reference line image RL
obtained by the linear interpolation is inserted as the reference
line image RL(2) of the 2nd interpolated binning pixel-row. Then,
the linear interpolation is performed using the reference line
image RL(2) of the 2nd binning pixel-row and the reference line
image RL(3) of the 3rd binning pixel-row, and obtains the reference
line image RL to be interpolated. The reference line image RL(3) of
the 3rd binning pixel-row before the interpolation becomes the
reference line image RL(5) of the 5th interpolated binning
pixel-row, and the newly obtained reset image RL is interpolated as
the reference line image RL(4) of the 4th interpolated binning
pixel-row. By applying such row interpolation processing to every
pixel-row, a reference frame image RP of twice size in the
pixel-column direction can be obtained. Furthermore, applying the
same row interpolation processing to the twice-sized reference
frame image RP allows obtainment of a reference frame image RP that
is scaled up by four times in the pixel-column direction. Note
that, FIG. 12 schematically shows a part of the row interpolation
processing, and the image size of the reference frame image RP in
the pixel-column direction is not necessarily scaled up by twice
and four times of that before the interpolation. However, the image
size of the entire reference frame image RP in the pixel-column
direction is scaled up by twice and four times, in actual fact.
Note that, instead of the linear interpolation, spline
interpolation may be used.
[0115] Since the row coordinate of the reference line image RL of
each binning pixel-row is changed between before and after the
interpolation, the controller 48 corrects the row coordinate
information of the immediately-preceding reference line image RL(c)
recorded to the internal memory 69 in accordance with the
coordinates after the interpolation.
[0116] Since the reference line image RL is obtained by the binning
readout of the four pixel-rows, the pixel values S of the reference
line image RL is larger than the pixel values D of the X-ray image
XL, which is read out on a pixel-row basis. The correction
coefficient calculator 76 calculates a correction coefficient to be
used for correcting the reference frame image RP, so as to convert
the pixel values S of the reference line image RL into values
corresponding to the pixel values D of the X-ray image XL.
[0117] The correction coefficient calculator 76 extracts the pixel
values SQ of the immediately-preceding reference line image RL(c)
based on the row coordinate information. Then, the correction
coefficient calculator 76 calculates an average SQave=ES/M, which
is obtained by integrating the pixel values SQ of the binning
pixel-row of the immediately-preceding reference line image RL(c)
and dividing the integrated value by the number M of the
pixel-columns, as a typical value SQR of the pixel values SQ used
in calculating the correction coefficient. The correction
coefficient calculator 76 calculates a difference amount .DELTA.D
(see FIG. 9), which represents a maximum value in difference in the
pixel value D between the adjoining pixel-rows, occurring in the
X-ray image XP due to the line defect, based on the row coordinate
information. The difference in the pixel value D is maximized at
between the Cth pixel-row having the lowest pixel value D and the
next (C+1)th pixel-row. More specifically, the line defect
corrector 70 calculates an absolute value of the difference between
the pixel value D of the X-ray image XL(C) of the Cth pixel-row and
the pixel value D of the X-ray image XL(C+1) of the (C+1)th
pixel-row on a column-by-column basis. Then, the line defect
corrector 70 calculates an average .DELTA.Dave=.SIGMA..DELTA.D/M by
integrating the absolute values and dividing the integrated value
by the number M of the pixel-columns, as a typical value .DELTA.DR
of the difference amount .DELTA.D used in calculating the
correction coefficient. The correction coefficient calculator 76
calculates .DELTA.Dave/SQave, being the ratio between SQave and
.DELTA.Dave, as the correction coefficient. The correction
coefficient calculator 76 outputs the obtained correction
coefficient to the internal memory 69.
[0118] The pixel value corrector 77 reads out the reference frame
image RP after being subjected to the row interpolation process
from the second storage area 54b. The pixel value corrector 77
multiplies the pixel values S of the reference frame image RP by
the correction coefficient .DELTA.Dave/SQave calculated by the
correction coefficient calculator 76, to produce a correction image
RPC (see FIG. 13). The correction image RPC is recorded to the
second storage area 54b.
[0119] The adder 78 reads out the X-ray image XP from the first
storage area 54a, and reads out the correction image RPC from the
second storage area 54b. As shown in FIG. 13, the adder 78 adds the
pixel value D and the pixel value S on a pixel-by-pixel basis, and
produces a corrected X-ray image XPC. The adder 78 records the
corrected X-ray image XPC to the first storage area 54a, instead of
the X-ray image XP.
[0120] By multiplying the reference frame image RP by the
correction coefficient .DELTA.Dave/SQave, the pixel value SQ of the
immediately-preceding reference line image RL(c) of the corrected
image RPC is equal to the difference amount .DELTA.D in the X-ray
image XP. Accordingly, the difference amount .DELTA.D of the Cth
pixel-row, which causes the line defect, disappears in the
corrected X-ray image XPC, by addition of the pixel values of the
correction image RPC. As for the (C-11)th pixel-row to the (C-1)th
pixel-row corresponding to the line defect other than the C-th
pixel-row, the addition of the pixel values of the correction image
RPC makes the line defect inconspicuous in the corrected X-ray
image XPC. The correction image RPC is produced based on the
reference frame image RP having the rising gradient in which the
falling gradient owing to the line defect is reflected, so that it
is possible to make an appropriate correction to the X-ray image XP
in accordance with the falling gradient due to the line defect.
[0121] In FIG. 11, the controller 48 is provided with correctors
80, 81, and 82 that apply various types of image processing
including offset correct, sensitivity correction, and defect pixel
correction, to the corrected X-ray image XPC. Each of the
correctors 80 to 82 gets access to the first storage area 54a of
the frame memory 54 and reads out the corrected X-ray image XPC.
After the various types of image processing are applied to the
corrected X-ray image XPC, the processed data is write back to the
first storage area 54a.
[0122] The offset corrector 80 subtracts an offset correction
image, which is obtained without applying the X-rays, from the
corrected X-ray image XPC on a pixel-by-pixel basis, to remove a
noise component caused by the dark charge contained in the electric
charge. Although the dark charge is cancelled from the pixels 41 by
the pre-emission readout operation, cancelling the entire dark
charge of the pixels 41 requires time of one cycle, so the amount
of the remaining dark charge is different from one binning
pixel-row to another. The offset correction removes the remaining
dark charge.
[0123] The sensitivity corrector 81, which is also called gain
corrector, corrects fixed pattern noise caused by variations in the
sensitivity of the photoelectric conversion element 42 among the
pixels 41, variations in the output properties of the signal
processing circuit 47, and the like. The defect pixel corrector 82
corrects a pixel value of a defect pixel with a pixel value of a
normal pixel nearby by linear interpolation based on defect pixel
information produced before shipping or in a routine checkup. The
corrected X-ray image XPC after being subjected to the above image
processing is transmitted to the console 14 through the
communication I/F 55.
[0124] Next, a procedure of the X-ray imaging using the X-ray
imaging system 2 will be described with referring to a flowchart of
FIG. 14. Firstly, the object is set in an imaging position in the
imaging stand 15 or the imaging table 16. The height and horizontal
position of the electronic cassette 13 are adjusted in accordance
with the body part to be imaged and the position of the object. The
height and horizontal position of the X-ray source 10 and the size
of the irradiation field are adjusted in accordance with the
position of the electronic cassette 13 and the size of the body
part to be imaged. Then, the imaging condition is set in the source
control unit 11 and the console 14. The imaging condition set in
the console 14 is transmitted to the electronic cassette 13.
[0125] After making preparation for imaging, the operator half
presses the emission switch 12. Upon the half press of the emission
switch 12, the warm-up command signal is issued to start warming up
the X-ray source 10.
[0126] As shown in S10 of FIG. 14, in response to receiving the
imaging condition from the console 14 through the communication I/F
55 (YES in S10), the controller 48 makes the panel unit 35 start
the pre-emission readout operation (S11). In the pre-emission
readout operation, the binning readout is performed in
four-pixel-row blocks. Thus, the electric charge accumulated in the
four pixels 41 are added and discharged to the signal line 45 of
each pixel-column. Whenever performing the binning readout, the RL
image record controller 48a records the reference line image RL to
the second storage area 54b (S12). By the binning readout of the
1st binning pixel-row to the N/4th binning pixel row, the reference
frame image RP is recorded to the second storage area 54b.
[0127] Whenever the reference line image RL is recorded to the
second storage area 54b, the emission start judging unit 57 reads
out the reference line image RL and compares the typical value of
the pixel values S of the reference line image RL with the judgment
threshold value Th (S13). Before the start of the X-ray emission,
the typical value of the pixel values S does not exceed the
judgment threshold value Th, because the pixel values S include
only output of the dark charge.
[0128] Upon the full press of the emission switch 12 by the
operator, the X-ray source 10 starts emitting the X-rays. The X-ray
dose per unit of time is low immediately after the start of the
X-ray emission, and increased gradually. Thus, the pixel values S
are low immediately after the start of the X-ray emission from the
X-ray source 10. With increase in the X-ray dose, the amount of the
electric charge produced in each pixel 41 is increased. Therefore,
the pixel values S of the reference line image RL obtained in the
binning readout are increased. After that, the typical value of the
pixel values S exceeds the judgment threshold value Th. The
emission start judging unit 57 judges that the X-ray emission has
been started at this point in time (YES in S13).
[0129] The binning readout is performed in the pre-emission readout
operation, so time required for reading out the one reference frame
image RP is short. This allows reduction of the amount of the dark
charge accumulated in each pixel. Also, in the case of judging the
start of the X-ray emission based on the pixel values S of the
reference line image RL obtained in the pre-emission readout
operation, as described in the above embodiment, the pixel values S
of the reference line image RL obtained by the binning readout are
larger than those of a reference line image obtained by the readout
in one-pixel-row blocks. Thus, the S/N ratio of the pixel value S
is increased, and this facilitates making a quick and correct
judgment of the emission start.
[0130] In a case where the emission start judging unit 57 judges
that the X-ray emission has been started, the controller 48 turns
off all the TFTs 43 and stops the pre-emission readout operation.
The controller 48 makes the panel unit 35 start the accumulation
operation (S14). Therefore, the timing of starting the X-ray
emission and the timing of starting the accumulation operation are
synchronized with each other. At the same time, the timer 56 of the
controller 48 starts measuring time.
[0131] The controller 48 records to the internal memory 69 the row
coordinate information, which represents the correlation between
the binning pixel-row coordinates of the immediately-preceding
reference line image RL(c) obtained in the binning readout
immediately before stopping the pre-emission readout operation in
the reference frame image RP and the pixel-row coordinates (the
(C-3)th pixel-row to the Cth pixel-row) corresponding to the
reference line image RL(c) in the image capturing field 40.
[0132] When the measured time of the timer 25 has reached the set
emission time, the source control unit 11 stops the X-ray emission
from the X-ray source 10. When the measured time of the time 56 has
reached the emission time set in the imaging condition (YES in
S15), the controller 48 shifts the panel unit 35 from the
accumulation operation to the image readout operation (S16). In the
image readout operation, the electric charge is read out on a
pixel-row basis, and converted into the pixel values D by the
signal processing circuit 47. The pixel values D are recorded to
the first storage area 54a as the X-ray image XP.
[0133] After the image readout operation, the interpolator 75 of
the correction image generator 71 applies the row interpolation
processing to the reference frame image RP to scale up the image
size in the pixel-column direction. Thus, the image size of the
reference frame image RP becomes equal to that of the X-ray image
XP (S17). The correction coefficient calculator 76 calculates the
difference amount .DELTA.D, being the absolute value of the
difference between the pixel value D of the X-ray image XL(C) at
which the pixel value D becomes the lowest in the line defect
portion in the X-ray image XP and the pixel value D of the
adjoining X-ray image XL(C+1). Then, the correction coefficient
.DELTA.Dave/SQave is calculated, which is the ratio between the
average .DELTA.Dave of the difference amounts .DELTA.D and the
average SQave of the pixel values SQ of the immediately-preceding
reference line image RL(c) (S18). The pixel value corrector 77
multiplies each pixel value S of the reference frame image RP after
being subjected to the row interpolation processing by the
correction coefficient .DELTA.Dave/SQave, to produce the corrected
image RPC (S19).
[0134] The adder 78 adds the correction image RPC to the X-ray
image XP and produces the corrected X-ray image XPC in which the
line defect is corrected (S20). Since the correction image RPC is
produced based on the reference frame image RP having the increase
portion in which the falling gradient corresponding to the line
defect is reflected, the X-ray image XP is corrected appropriately
in accordance with the falling gradient of the line defect, and
thereby the corrected X-ray image XPC is produced.
[0135] Each of the correctors 80 to 82 applies the image processing
including the offset correction, the sensitivity correction, and
the defect correction to the corrected X-ray image XPC. The
corrected X-ray image XPC after being subjected to the image
processing is transmitted to the console 14 through the
communication I/F 55. The corrected and processed X-ray image XPC
is displayed on the display 14b and used in a diagnosis.
[0136] In the above first embodiment, the controller 48 has the RL
image record controller 48a, and the controller 48 also functions
as the RL image record controller 48a. However, the controller 48
and the RL image record controller 48a may be independent of each
other. Likewise, the controller 48 having the line defect corrector
70 also functions as the line defect corrector 70, but the
controller 48 and the line defect corrector 70 may be independent
of each other. Furthermore, the line defect corrector 70 having the
correction image generator 71 also functions as the correction
image generator 71, but the line defect corrector 70 and the
correction image generator 71 may be independent of each other.
[0137] In the above first embodiment, the one frame memory 54 is
provided with the first storage area 54a for recording the X-ray
image XP and the second storage area 54b for recording the
reference frame image RP, but two frame memories one of which
records the X-ray image XP and the other records the reference
frame image RP may be provided independently. Instead of the frame
memory, a line memory for recording the reference line image RL of
a plurality of binning pixel-rows may be provided.
[0138] In the above first embodiment, as the typical value
.DELTA.DR of the difference amounts .DELTA.D, the average
.DELTA.Dave of the absolute values .DELTA.D of the difference
between the pixel value D of the X-ray image XL(C) corresponding to
the line defect and the pixel value D of the X-ray image XL(C+1) is
used. As the typical value SQR of the pixel values SQ, the average
SQave of the pixel values SQ of the immediately-preceding reference
line image RL(c) is used. Then, the reference frame image RP is
uniformly multiplied by the correction coefficient
.DELTA.Dave/SQave, being the ratio between .DELTA.Dave and SQave.
Therefore it is possible to accelerate processing speed, as
compared with the case of calculating the correction coefficient
.DELTA.D/SQ on a pixel-column basis using the pixel value D of each
pixel-column and the pixel value SQ of each pixel-column and
performing the multiplication on a pixel-column basis. As a matter
of course, in the case of giving a higher priority to accuracy, the
multiplication may be performed on a pixel-column basis with the
use of the correction coefficient .DELTA.D/SQ that is calculated on
a pixel-column basis using the pixel value D of each pixel-column
and the pixel value SQ of each pixel-column. Note that, a pixel
value of a defect pixel is much higher than that of a normal pixel,
so calculating the average SQave and the average .DELTA.Dave from
the pixel values of the pixels including the defect pixel causes
deterioration in the accuracy of the correction coefficient
.DELTA.Dave/SQave. Thus, it is preferable that the correction
coefficient calculator 76 excludes the pixel value of the defect
pixel from the pixel values SQ of the immediately-preceding
reference line image RL(c) and the pixel values D of the X-ray
image XL(C) of the Cth pixel-row and the X-ray image XL(C+1) of the
(C+1)th pixel-row used for calculating the difference amount
.DELTA.D, and then the average SQave and the average .DELTA.Dave
are obtained. As a method for excluding the pixel value of the
defect pixel, there are a method of using the defect pixel
information produced in shipping or routine checkup, and a method
of detecting and removing a pixel value of an expected defect pixel
by using a low-pass filter from the pixel values SQ of the
immediately-preceding reference line image RL(c) and the pixel
values D of the X-ray image XL(C) of the Cth pixel-row and the
X-ray image XL(C+1) of the (C+1)th pixel-row used for calculating
the difference amount .DELTA.D.
[0139] The typical value SQR of the pixel values SQ and the typical
value .DELTA.DR of the difference amounts .DELTA.D are not limited
to the averages SQave and .DELTA.Dave, as described in the above
first embodiment. For example, the typical value SQR may be a
median value SQC of the pixel values SQ of the
immediately-preceding reference line image RL(c) (a value
positioned at the center in increasing order of the pixel values SQ
of the immediately-preceding reference line image RL(c)). The
typical value .DELTA.DR may be a median value .DELTA.DC of the
difference amounts .DELTA.D. Using the median values is preferable,
considering the fact that the pixel value of the defect pixel,
which is much higher than the pixel value of the normal pixel, is
excluded by itself.
Second Embodiment
[0140] In the above first embodiment, the correction image RPC is
produced based on the reference frame image RP. However, the pixel
values S of the reference frame image RP are approximately zero in
the binning pixel-rows except for the increase portion
corresponding to the line defect, and have little effect on the
correction of the line defect. Thus, as shown in FIG. 15, the
correction image generator 71 may extract the immediately-preceding
reference line images RL(c) and the reference line images RL(c-1)
and RL(c-2) of a plurality of binning pixel-rows next to the
immediately-preceding reference line image RL(c), as
line-defect-corresponding reference line images RLp. The correction
image RPC may be produced based on the line-defect-corresponding
reference line images RLp alone. This eliminates the need for
multiplying the pixel values S of an approximately zero level by
the correction coefficient and adding the pixel values S of the
approximately zero level to the pixel values D, and hence
facilitates speedup of the processing.
[0141] With respect to the immediately-preceding reference line
image RL(c), for example, a predetermined number of reference line
images RL next previous to the immediately-preceding reference line
image RL(c) are determined as the line-defect-corresponding
reference line images RLp. Since the controller 48 recognizes the
time of the judgment of the emission start, the correction image
generator 71 can determine the immediately-preceding reference line
image RL(c) and the coordinates of the binning pixel-row of the
immediately-preceding reference line image RL(c). However, the
controller 48 cannot precisely recognize that at which binning
pixel-row the X-ray emission is started. For this reason, the
immediately-preceding reference line image RL(c) and the next
previous reference line images RL of a predetermined number of
binning pixel-rows are determined as the line-defect-corresponding
reference line images RLp.
[0142] The correction image generator 71 applies the row
interpolation processing and the calculation processing of the
correction coefficient .DELTA.D/SQ to the line-defect-corresponding
reference line images RLp, to produce the correction image RPC
corresponding to the line-defect-corresponding reference line
images RLp. The adder 78 adds the correction image RPC to the line
defect portion of the X-ray image XP.
[0143] Note that, instead of using the predetermined number of
binning pixel-rows for determining the line-defect-corresponding
reference line images RLp, the line-defect-corresponding reference
line images RLp may be determined based on the pixel values S, for
the purpose of improving accuracy. To be more specific, the pixel
values S of the reference frame image RP in an arbitrary
pixel-column X are scanned in the Y direction and plotted, just as
with a graph on a right side of FIG. 10 or 15. According to the
plot, a binning pixel-row having a pixel value S other than zero is
retrieved. At this time, the binning pixel-row having the increase
portion corresponding to the line defect is already known by the
row coordinate information, so the pixel values S of the binning
pixel-rows next previous thereto are checked. The reference line
images RL of the retrieved binning pixel-rows are determined as the
line-defect-corresponding reference line images RLp. Note that, one
or a plurality of columns of the reference frame images RP are used
for analyzing variation in the pixel value S in the Y direction.
The variation in the pixel value S may be analyzed with respect to
every column, and the binning pixel-rows corresponding to the line
defect may be determined in each column. The
line-defect-corresponding reference line images RLp may be
determined in accordance with the number of times each binning
pixel-row is determined to correspond to the line defect. Depending
on the timing of the judgment of the emission start, the increase
portion of the reference frame image RP, corresponding to the line
defect of the X-ray image XP, may extend from the N/4th binning
pixel-row to the 1st binning pixel-row. Thus, in retrieving the
binning pixel-row having a pixel value other than zero, the N/4th
binning pixel-row of the cycle (Sk-1) is preferably checked.
Third Embodiment
[0144] In the above second embodiment, the pixel value corrector 77
uniformly multiplies the line-defect-corresponding reference line
images RLp by the correction coefficient calculated by the
correction coefficient calculator 76. However, the correction
coefficient calculated by the correction coefficient calculator 76
is a value specific to the correction of the pixel value SQ of the
immediately-preceding reference line image RL(c). Accordingly, in
the case of multiplying the line-defect-corresponding reference
line images RLp, which include the reference line images RL other
than the immediately-preceding reference line image RL(c), by the
correction coefficient calculated by the correction coefficient
calculator 76, as described in the second embodiment, the line
defect becomes inconspicuous but is preferably corrected more
precisely.
[0145] According to this embodiment, as shown in FIG. 16, a
correction coefficient modifier 90 is provided, which modifies the
correction coefficient calculated by the correction coefficient
calculator 76 to values (hereinafter called modified correction
coefficients) for use in the line-defect-corresponding reference
line images RLp.
[0146] As shown in FIG. 8, the pixel values S of the
line-defect-corresponding reference line images RLp gradually
increase to the pixel value SQ of the immediately-preceding
reference line image RL(c) in accordance with the X-ray emission
profile. The pixel values D of the X-ray image XP corresponding to
the line-defect-corresponding reference line images RLp gradually
decrease in accordance with the X-ray emission profile. To
calculated the modified correction coefficient, the correction
coefficient modifier 90 multiplies the correction coefficient
calculated by the correction coefficient calculator 76 by a
modification value, in which an increase rate of the pixel values S
of the line-defect-corresponding reference line images RLp and a
decrease rate of the pixel values D of the X-ray image XP are
reflected.
[0147] More specifically, a rising gradient of the X-ray dose
immediately after the start of the X-ray emission mainly depends on
the tube voltage in the X-ray emission profile, so a modification
value table 91, which represents the relation between the tube
voltage and the modification value, is stored in advance. In the
modification value table 91, the modification values corresponding
to line-defect-corresponding the reference line images RLp are
recorded on a tube voltage basis. For example, "modification value
1" corresponds to the reference line image RL(c-1), and
"modification value 2" corresponds to the reference line image
RL(c-2). The modification value is a numerical value of 0 or more
and less than 1, such that the "modification value 1" is 0.9 and
the "modification value 2" is 0.8. The correction coefficient
modifier 90 reads out the modification values corresponding to the
tube voltage, and multiplies the correction coefficient calculated
by the correction coefficient calculator 76 by each of the read
modification values to obtain the modified correction
coefficients.
[0148] The pixel value corrector 77 multiplies the pixel value SQ
of the immediately-preceding reference line image RL(c) by the
correction coefficient calculated by the correction coefficient
calculator 76. The pixel value corrector 77 multiplies the pixel
value S of the line-defect-corresponding reference line image RLp
other than the immediately-preceding reference line image RL(c) by
the modified correction coefficient. Thus, the line defect
correction is performed more precisely, as compared with the
instance of uniformly multiplying the line-defect-corresponding
reference line images RLp by the correction coefficient calculated
by the correction coefficient calculator 76. Note that, as the
modification value, a plurality of types of values may be prepared
on a tube voltage basis, as described above, or one type of value
may be used irrespective of the tube voltage.
[0149] As the correction coefficient calculated by the correction
coefficient calculator 76, the reciprocal of the number of the
pixel-rows composing one binning pixel-row may be used, instead of
the ratio between the difference amount .DELTA.Dave and the pixel
value SQave or the like, as described in the first embodiment.
Taking the above first embodiment as an example, since the binning
readout is carried out in four-pixel-row blocks, the correction
coefficient is set at 1/4. The pixel value corrector 77 multiplies
the pixel value S of the reference frame image RP by the reciprocal
of the number of the pixel-rows composing the binning pixel-row.
However, it is preferable to use .DELTA.D/SQ in which the actual
pixel values D and S are reflected, for the sake of accuracy.
[0150] Instead of performing the row interpolation processing using
the linear interpolation described in the above first embodiment,
the pixel value S of each reference line image RL may be simply
copied to scale up the image size of the reference frame image RP
in the pixel-column direction.
[0151] In the above first embodiment, the reference frame image RP
obtained in the pre-emission readout operation of a cycle of Sk is
sequentially updated with the reference line images RL obtained in
the pre-emission readout operation of a cycle of (Sk+1) on a
binning pixel-row basis. Instead, two frame memories may be
provided to record the reference frame images RP of two cycles.
When a reference frame image RP is recorded to one of the frame
memories, the reference frame image RP transferred to the other
frame memory to empty the one frame memory. Then, the reference
frame image RP of the next cycle is recorded to the empty frame
memory.
[0152] According to this structure, the two reference frame images
RP obtained in the cycles (Sk-1) and Sk are recorded. To determine
the line-defect-corresponding reference line images RLp, it is
preferable to retrieve the binning pixel-row having the pixel value
S other than zero in the two reference frame images RP, in
consideration of a case where the increase portion corresponding to
the line defect extends to the two reference frame images RP,
depending on the timing of the judgment of the emission start.
[0153] In the above first embodiment, the judgment of the emission
start is performed based on the pixel values S of the reference
line images RL, and thus the pixel 41 functions as an X-ray
detector. Instead of this, another X-ray detector other than the
pixel 41 may be provided, and the judgment of the emission start
may be performed based on output of this X-ray detector. However,
using the pixel as the X-ray detector, as described in the first
embodiment, has a cost advantage over providing another X-ray
detector.
[0154] With taking advantage of the fact that electric current
flowing through the bias line, which applies the bias voltage to
each pixel, is in proportional to the electric charge produced in
the pixel, the X-ray dose may be detected based on the electric
current flowing through the bias line connected to a specific
pixel. In this case, an electric current detector for detecting the
electric current of the bias line functions as the X-ray
detector.
[0155] An X-ray detector other than the pixel may be provided
around the image capturing field. Otherwise, an X-ray detector that
is completely independent of the panel unit may be provided in the
housing of the electronic cassette, or attached to the periphery of
the housing.
[0156] In the above first embodiment, the offset correction is
applied to the corrected X-ray image XPC. The offset correction may
be applied before the line defect correction to the reference frame
image RP and the X-ray image XP. Note that, a frame memory for
recording a plurality of reference frame images RP is prepared, and
an average of pixel values of the plurality of reference frame
images RP obtained before application of the X-rays may be used as
the offset correction image. The gate pulses G are issued at the
same intervals H between the pre-emission readout operation and the
image readout operation. However, for the purpose of enhancing
responsivity in the judgment of the emission start based on the
pixel values of the reference line images, the gate pulses G may be
issued at shorter intervals in the pre-emission readout operation
than in the image readout operation so as to shorten output
intervals of the reference line images.
Fourth Embodiment
[0157] Note that, before the X-ray emission, the reference line
image RL has a pixel value based on an offset of the dark charge of
the pixel 41. After the X-ray emission, the reference line image RL
has a pixel value based on leak current, which leaks from the
pixels in the pixel-rows other than the pixel-row to be read out in
the binning readout, in addition to the pixel value based on the
offset and a pixel value based on the electric charge produced by
the incidence of the X-rays. The pixel value based on the leak
current, together with the pixel value based on the offset, becomes
noise of the pixel value S, and deteriorates the accuracy of the
line defect correction.
[0158] Accordingly, in this embodiment, as shown in FIG. 17, the
controller 48 is provided with a leak corrector 100. Before the
correction image generator 71 produces the correction image RPC,
the leak corrector 100 reads out the reference frame image RP from
the second storage area 54b, and performs leak correction to remove
the pixel value based on the leak current from the reference frame
image RP.
[0159] The level of the pixel value based on the leak current
depends on the width of the irradiation field in the Y direction.
Specifically speaking, the pixel value based on the leak current is
relatively small, if the width of the irradiation field in the Y
direction is narrow. The pixel value based on the leak current is
increased with increase in the width of the irradiation field in
the Y direction. In a case where the width of the irradiation field
in the Y direction is equal to the width of the image capturing
field 40, the pixel value based on the leak current is maximized.
There is the correlation between the level of the pixel value based
on the leak current and the width of the irradiation field in the Y
direction. Thus, leak correction information, e.g. a data table or
the like is prepared in advance that represents the correlation
between the width of the irradiation field in the Y direction and
the level of the pixel value based on the leak current. The leak
corrector 100 reads out from the leak correction information the
pixel value based on the leak current in accordance with the width
of the irradiation field in the Y direction, and subtracts the read
pixel value from the pixel value S of the reference frame image RP.
This reduces an adverse effect of the pixel value based on the leak
current on the accuracy of the line defect correction.
[0160] As a method of obtaining information on the width of the
irradiation field in the Y direction, there are a method of
determining the irradiation field by an image analysis of the X-ray
image XP, a method of inputting irradiation field setting
information of the irradiation field limiter to the console 14 and
transferring the information to the electronic cassette 13, and the
like. The leak corrector 100 may be provided independently of the
controller 48.
[0161] The line defect corrector is provided in the controller of
the electronic cassette in the above first embodiment, but may be
provided in the console 14. In this case, after the completion of
the image readout operation, the X-ray image XP is read out of the
first storage area 54a, and the reference frame image RP is read
out of the second storage area 54b. The X-ray image XP and the
reference frame image RP are transmitted to the console 14 through
the communication I/F 55, with being associated with the row
coordinate information. Note that, in a like manner, the other
correctors 80 to 82 and 100 may be provided in the console 14 so
that the console 14 performs the various types of image
processing.
[0162] In addition to the electronic cassette and the console, an
imaging control device that performs a part of an electronic
cassette control function of the console may be connected between
the electronic cassette and the console. The line defect corrector
described in the above embodiments may be provided in this imaging
control device, or in a device other than the console 14 or the
imaging control device.
[0163] The present invention may be applied to an X-ray image
detecting device loaded in the imaging stand or table, instead of
or in addition to the electronic cassette being the portable X-ray
image detecting device. Furthermore, the present invention is
applicable to a device using another type of radiation such as
.gamma.-rays, instead of the X-rays.
[0164] Although the present invention has been fully described by
the way of the preferred embodiment thereof with reference to the
accompanying drawings, various changes and modifications will be
apparent to those having skill in this field. Therefore, unless
otherwise these changes and modifications depart from the scope of
the present invention, they should be construed as included
therein.
* * * * *