U.S. patent application number 11/516729 was filed with the patent office on 2007-03-15 for radiological imaging apparatus.
Invention is credited to Kensuke Amemiya, Hiroshi Kitaguchi, Shinichi Kojima, Yuuichirou Ueno, Kikuo Umegaki, Norihito Yanagita, Kazuma Yokoi.
Application Number | 20070058773 11/516729 |
Document ID | / |
Family ID | 32064327 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070058773 |
Kind Code |
A1 |
Ueno; Yuuichirou ; et
al. |
March 15, 2007 |
Radiological imaging apparatus
Abstract
The image pickup apparatus of the radiological imaging apparatus
of the present invention includes many detector units, a
ring-shaped detector support member and an X-ray source
circumferential transport apparatus. Each of the detector units is
attached to the detector support section in a detachable manner. A
plurality of radiation detectors provided for the detector units
are arranged in three layers in the radius direction of the
detector support member and in three columns in the axial direction
of the detector support member. Since the radiation detectors are
arranged in three layers in the radius direction, it is possible to
recognize the detection position of radiation in the radius
direction in detail. Furthermore, since the detector units are
attached in a detachable manner, it is easy to replace damaged
radiation detectors.
Inventors: |
Ueno; Yuuichirou; (Hitachi,
JP) ; Kitaguchi; Hiroshi; (Naka, JP) ;
Amemiya; Kensuke; (Hitachinaka, JP) ; Umegaki;
Kikuo; (Hitachinaka, JP) ; Yanagita; Norihito;
(Hitachi, JP) ; Kojima; Shinichi; (Hitachi,
JP) ; Yokoi; Kazuma; (Higashikanesawa, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
32064327 |
Appl. No.: |
11/516729 |
Filed: |
September 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10688977 |
Oct 21, 2003 |
7154989 |
|
|
11516729 |
Sep 7, 2006 |
|
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Current U.S.
Class: |
378/19 |
Current CPC
Class: |
A61B 6/5235 20130101;
A61B 6/037 20130101; G01T 1/2985 20130101; A61B 6/032 20130101;
G01T 1/1644 20130101; G01T 1/1615 20130101 |
Class at
Publication: |
378/019 |
International
Class: |
H05G 1/60 20060101
H05G001/60; A61B 6/00 20060101 A61B006/00; G01N 23/00 20060101
G01N023/00; G21K 1/12 20060101 G21K001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2002 |
JP |
2002-307785 |
Claims
1. A radiological imaging apparatus comprising: a detector support
member which extends in the longitudinal direction of a bed for
supporting an examinee and is arranged around said bed; and a
radiation detection apparatus including a plurality of radiation
detector units arranged in the longitudinal direction of said bed
and around said bed, said plurality of detector units being
attached to said detector support member in a detachable manner,
wherein said detector unit comprises a plurality of radiation
detectors for detecting radiation and is provided with some of said
radiation detectors for detecting said radiation that has passed
through other said radiation detectors.
2-25. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a radiological imaging
apparatus, and more particularly, to a radiological imaging
apparatus ideally applicable to radiological two-dimensional image
pickup apparatus, X-ray computed tomography (hereinafter referred
to as "X-ray CT"), positron emission computed tomography
(hereinafter referred to as "PET") and single photon emission
computed tomography (hereinafter referred to as "SPECT").
[0002] Among typical radiological imaging apparatuses, which is a
non-invasive imaging technology for examining functions and
conformation of the body of a medical examinee, are radiological
two-dimensional image pickup apparatus, X-ray CT, PET and SPECT,
etc.
[0003] PET inspection is an inspection consisting of administering
radiopharmaceutical (hereinafter referred to as "PET
radiopharmaceutical") including positron emitters (.sup.15O,
.sup.13N, .sup.1C, .sup.18F, etc.) to the examinee and examining
locations in the body where more PET radiopharmaceutical is
consumed. The PET inspection is an action of detecting .gamma.-rays
emitted from the body of the examinee caused by PET
radiopharmaceutical using a radiation detector. More specifically,
one positron emitted from a positron emitter in the PET
radiopharmaceutical couples with an electron of a neighboring cell
(cancerous cell), disappears and at the same time irradiates a pair
of .gamma.-rays (called ".gamma.-ray pair") having energy of 511
keV. These .gamma.-rays are emitted in directions opposite to each
other (180.degree..+-.0.6.degree.). Detecting this pair of
.gamma.-rays using a radiation detector makes it possible to know
between which pair of radiation detectors the positron is emitted.
Detecting those many .gamma.-ray pairs makes it possible to
identify locations where more PET radiopharmaceutical is consumed.
For example, when PET radiopharmaceutical created by coupling
positron emitters and carbohydrate is used, it is possible to
discover cancer focuses having hyperactive carbohydrate metabolism.
One example of the radiological imaging apparatus used for PET is
described in JP-A-7-20245. The data obtained is converted to data
of each voxel using the Filtered Back Projection method described
in non-patent document 1 (IEEE Transaction on Nuclear Science, Vol.
NS-21, pp. 228-229). Positron emitters (.sup.15O, .sup.13N,
.sup.11C and .sup.18F, etc.) used for the PET inspection have a
half life of 2 to 110 minutes.
[0004] The SPECT administers radiopharmaceutical (hereinafter
referred to as "SPECT radiopharmaceutical") including single photon
emitters (.sup.99Tc, .sup.67Ga, .sup.201Tl, etc.) and matters
(e.g., carbohydrate) having a property of concentrating on a
specific tumor or specific molecule to an examinee and detects
.gamma.-rays emitted from the emitters using a radiation detector.
The energy of .gamma.-rays emitted from the single photon emitters
often used for inspection using the SPECT is around several 100
keV. In the case of the SPECT, single .gamma.-rays are emitted, and
therefore it is not possible to obtain their angle of incidence
upon the radiation detector. Thus, angle information is obtained by
detecting only .gamma.-rays incident from a specific angle through
a collimator using the radiation detector. The SPECT is an
inspection method of identifying locations where more SPECT
radiopharmaceutical is consumed by detecting .gamma.-rays generated
in the body caused by the SPECT radiopharmaceutical. One example of
the radiological imaging apparatus used for the SPECT is described
in JP-A-9-5441. The SPECT also converts data obtained to data of
each voxel using a method such as Filtered Back Projection. The
SPECT may also take transmission images. .sup.99Tc, .sup.67Ga and
.sup.201Tl used for the SPECT have a half life longer than that of
radionuclide used for the PET, for example, 6 hours to 3 days.
SUMMARY OF THE INVENTION
[0005] There is a demand for further improvement of diagnostic
accuracy in the position and size, etc., of an affected area such
as malignant tumor and there is also a demand for improvement of
accuracy of images including the affected area created by a
radiological imaging apparatus. It is also an important challenge
to allow a damaged radiation detector to be replaced in a short
time.
[0006] It is an object of the present invention to provide a
radiological imaging apparatus capable of improving the accuracy of
an image created and easily replacing a damaged radiation
detector.
[0007] A feature of the present invention to attain the
above-described object is that a detection unit is attached to a
detector support member in a detachable manner and the detection
unit is provided with a plurality of radiation detectors that
detect radiation and other radiation detectors that detect
radiation which has passed through some of the above described
radiation detectors.
[0008] Since the other radiation detectors for detecting radiation
that has passed through some radiation detectors are provided, it
is possible to detect radiation emitted from the examinee by the
some radiation detectors or the other radiation detectors and
accurately confirm the position the radiation has reached from the
some radiation detectors facing the examinee in the depth direction
(position at which the radiation has been detected). Thus, it is
possible to obtain an accurate image illustrating the condition of
the body of the examinee. Furthermore, since the detector unit is
attached to the detector support member in a detachable manner, a
damaged radiation detector can be replaced easily.
[0009] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a longitudinal sectional view of a radiological
imaging apparatus of Embodiment 1 which is a preferred embodiment
of the present invention;
[0011] FIG. 2 is a sectional view along a line II--II of FIG.
1;
[0012] FIG. 3 is an enlarged view of the section III of FIG. 1;
[0013] FIG. 4 is a sectional view along a line IV--IV of FIG.
3;
[0014] FIG. 5 is a perspective view of the detector unit in FIG.
1;
[0015] FIG. 6 is a sectional view of the detector support member in
the radius direction of the detector unit in FIG. 5;
[0016] FIG. 7 shows a detailed structure of the signal
discriminator in FIG. 1;
[0017] FIG. 8 illustrates a procedure for creating a tomographic
image executed by the computer in FIG. 1;
[0018] FIGS. 9A and 9B illustrate a state of .gamma.-ray detection
in the embodiment shown in FIG. 1;
[0019] FIG. 10 is a perspective view of a detector unit applied to
a radiological imaging apparatus according to Embodiment 2 which is
another embodiment of the present invention;
[0020] FIG. 11 is a sectional view of the detector support member
in the radius direction of the detector unit in FIG. 10;
[0021] FIG. 12 is a perspective view of a detector unit applied to
a radiological imaging apparatus according to Embodiment 3 which is
a further embodiment of the present invention; and
[0022] FIG. 13 is a sectional view of the detector support member
in the radius direction of the detector unit in FIG. 11.
DESCRIPTION OF THE INVENTION
(Embodiment 1)
[0023] With reference now to FIG. 1 and FIG. 2, a radiological
imaging apparatus which is a preferred embodiment of the present
invention will be explained below. A radiological imaging apparatus
1 of this embodiment is used for a PET inspection. The radiological
imaging apparatus 1 is provided with an image pickup apparatus 2, a
signal processing apparatus 40, a tomographic image creation
apparatus 35, an examinee holding apparatus 18, a drive apparatus
control apparatus 21 and an X-ray source control apparatus 22. The
examinee holding apparatus 18 includes a bed 20 on top of a bed
support section 19 in such a way that the bed 20 is movable in the
longitudinal direction.
[0024] The image pickup apparatus 2 includes a casing 3, many
detector units 4, a ring-shaped detector support member 8 and an
X-ray source circumferential transport apparatus 13. As shown in
FIG. 3 and FIG. 4, the detector support member 8 includes a
ring-shaped detector support section 23 attached to a support
member 39 and a cover member 24. The cover member 24 is attached to
the detector support section 23, covering a signal discrimination
unit housing space 44 formed in the detector support section
23.
[0025] The X-ray source circumferential transport apparatus 13 is
provided with a guide rail 12 and an X-ray source apparatus 14. The
ring-shaped guide rail 12 is attached to the examinee holding
apparatus 18 on the side of the detector support member 8, more
specifically, on the side of the detector support section 23 so as
to surround a through hole section 41 into which the bed 20 is
inserted. The X-ray source apparatus 14 includes an X-ray source
drive apparatus 15, a telescopic arm 16 and an X-ray source 17. The
X-ray source drive apparatus 15 is attached to the guide rail 12 in
a movable manner. The X-ray source drive apparatus 15 includes a
pinion (not shown) which engages with the rack of the guide rail 12
and a motor which rotates this pinion through a deceleration
mechanism. The telescopic arm 16 is attached to a casing (not
shown) of the X-ray source drive apparatus 15 and can zoom in and
out in the horizontal direction. The X-ray source 17 is attached to
the end of the telescopic arm 16.
[0026] Though not shown, the X-ray source 17 includes a publicly
known X-ray tube. This X-ray tube is provided with an anode, a
cathode, a current source for the cathode and a voltage source for
applying a voltage to between the anode and cathode inside the
external cylinder. The cathode is a tungsten filament. When a
current flows from the current source to the cathode, electrons are
emitted from the filament. These electrons are accelerated by a
voltage (several hundred kV) applied from the voltage source to
between the cathode and anode and collide with the anode (W, Mo,
etc.), the target. Collision of electrons with the anode produces
X-rays of 80 keV. These X-rays are radiated from the X-ray source
17.
[0027] The tomographic image creation apparatus 35 is provided with
a computer 36 and a storage apparatus 37. The computer 36 is
connected to a coincidence counter 34 and the storage apparatus 37
is connected to the computer 36. The computer 36 is a tomographic
image creation section. A display device 38 is connected to the
computer 36.
[0028] As shown in FIG. 5 and FIG. 6, the detector unit 4 has a
structure in which a plurality (e.g., 9) of radiation detectors 5
are arranged on one side of the support substrate 6 and a connector
section 7 is attached to the support substrate 6. Nine radiation
detectors 5 are arranged in 3 rows and 3 columns on the support
substrate 6. The "circumferential direction" shown in FIG. 4 refers
to the circumferential direction of the detector support member 8,
the "axial direction" refers to the axial direction of the detector
support member 8 and the "radius direction" refers to the "radius
direction of the detector support member 8 (the same applies to
FIG. 10 and FIG. 12). Cathode electrodes K1, K2 and K3 of one
column of the three radiation detectors 5 arranged in the radius
direction of the detector support member 8, that is, radiation
detectors 5A, 5B and 5C are connected to a grounding wire 45. The
grounding wire 45 is connected to a connector terminal 7D of the
connector section 7. A wire 46 connected to an anode electrode A1
of the radiation detector 5A is connected to a connector terminal
7A. A wire 47 connected to an anode electrode A2 of the radiation
detector 5B is connected to a connector terminal 7B of the
connector section 7. Furthermore, a wire 48 connected to an anode
electrode A3 of the radiation detector 5C is connected to a
connector terminal 7C of the connector section 7. The radiation
detectors 5 included in other two columns are likewise connected to
the other connector terminals provided for the connector section 7.
The grounding wire 45 and wires 46, 47 and 48 are all set in the
support substrate 6. The many detector units 4 are set and held in
the detector support section 23 by engaging their respective
connector terminals such as the connector terminal 7A with the
connector section 11 provided in the detector support section 23.
The detector units 4 surround the through hole section 41 and many
of them are arranged in the circumferential direction and axial
direction of the through hole section 41. These detector units 4
are attached to the detector support section 23 in a detachable
manner.
[0029] The casing 3 is attached to the detector support section 23
so as to cover the detector units 4 (FIG. 4). Furthermore, the
casing 3 extends in the horizontal direction and forms the hole
section (through hole section) 41 into which the bed 20 is inserted
during an inspection (FIG. 1).
[0030] With the arrangement of these detector units 4, many
radiation detectors (e.g., 10,000 in total) 5 are arranged in the
casing 3 on the inner side of the ring-shaped detector support
member 8. These radiation detectors 5 are arranged in the radius
direction of the detector support member 8 in multilayers (e.g.,
three layers) and also arranged in the axial direction of the
detector support member 8 over a plurality of columns. The three
radiation detectors 5 (radiation detectors 5A) located farthest
from the connector section 7 of the radiation detectors 5 arranged
in the respective detector units 4 are located closest to the
central axis of the through hole section 41 and are called "first
layer radiation detectors." The three radiation detectors 5
(radiation detectors 5C) located closest to the connector section 7
are located farthest from the central axis of the through hole
section 41 and are called "third layer radiation detectors." The
three radiation detectors 5 (radiation detectors 5B) located
between the first layer and third layer in the detector unit 4 are
called "second layer radiation detectors."
[0031] The radiation detection apparatus 43 includes the
aforementioned many radiation detection units 4. The radiation
detection apparatus 43 includes many radiation detectors 5 arranged
in the radius direction of the detector support member 8 from the
first layer to the third layer and arranged in the axial direction
of the detector support member 8.
[0032] Examples of typical radiation detectors include a
semiconductor radiation detector and scintillator. For the
scintillator, a photoelectron multiplier, etc., needs to be
arranged behind a crystal (BGO, NaI, etc.) which is a radiation
detection section, and therefore it is unsuitable for a multilayer
arrangement (e.g., three layers as described above). Since the
semiconductor radiation detector requires no photoelectron
multiplier, etc., it is suitable for a multilayer arrangement. In
this embodiment, semiconductor radiation detectors are used for the
radiation detectors 5 and a 5 mm cube which is a detection section
is made of cadmium telluride (CdTe). The detection section may also
be made of gallium arsenide (GaAs) or cadmium zinc telluride
(CZT).
[0033] The signal processing apparatus 40 includes a signal
discriminator 27, .gamma.-ray discriminator 32 and the coincidence
counter 34. One signal discriminator 27 is provided for each
radiation detector 5 on the first layer. Furthermore, one
.gamma.-ray discriminator 32 is provided for each radiation
detector 5 on the second layer and the third layer respectively.
These three signal discriminators 27 and six .gamma.-ray
discriminators 32 are set on one substrate 26. A signal
discrimination unit 25 is made up of the three signal
discriminators 27 and six .gamma.-ray discriminators 32 set on one
substrate 26. The substrate 26 is attached to a unit support member
66. Each signal discrimination unit 25 provided for every detector
unit 4 is attached to the unit support member 66 arranged in a
signal discrimination unit housing space 44 as shown in FIG. 4. The
unit support member 66 is attached to the detector support member
23. The signal discrimination unit 25 is set in the unit support
member 66 and is thereby supported to the detector support member
8. It is also possible to attach the substrate 26 directly to the
detector support member 23 as the support substrate without using
the unit support member 66.
[0034] As shown in FIG. 7, the signal discriminator 27 includes a
changeover switch 28, a .gamma.-ray discriminator 32 and an X-ray
signal processing apparatus 33. The changeover switch 28 includes a
movable terminal 29 and fixed terminals 30 and 31. The .gamma.-ray
discriminator 32 is connected to the fixed terminal 30 and the
X-ray signal processing apparatus 33 is connected to the fixed
terminal 31. The connector terminal 7A connected to the first layer
radiation detector 5A has contact with a connector terminal 11A
provided for the connector section 11 through the engagement of the
connector section 7 with the connector section 11. The movable
terminal 29 is connected to the connector terminal 11A through a
wire 49. The wire 49 is set in the unit support member 66. The
minus terminal of a power supply 50 is connected to the wire 46 and
the plus terminal of the power supply 50 is connected to the
radiation detector 5A. The .gamma.-ray discriminators 32 in all the
signal discriminators 27 are connected to the coincidence counter
34 through a wire 52. On the other hand, the X-ray signal
processing apparatuses 33 in all the signal discriminators 27 are
connected to the computer 36 through a wire 53.
[0035] Three of the six .gamma.-ray discriminators 32 other than
the signal discriminator 27 provided in the signal discrimination
unit 25 are connected to a connector terminal 11B of the connector
section 11 (not shown) through a wire 54. The connector terminal
11B contacts the connector terminal 7B to which the second layer
radiation detectors 5B are connected. The remaining three
.gamma.-ray discriminators 32 are connected to a connector terminal
11C (not shown) of the connector section 11 through another wire
54. The connector terminal 11B contacts the connector terminal 7C
to which the third layer radiation detectors 5C are connected. The
six .gamma.-ray discriminators 32 other than the signal
discriminator 27 are each connected to the coincidence counter 34
through a wire 55. FIG. 1 shows the signal discrimination unit 25
and wires 54 and 56 outside the detector support member 8 and this
is intended to make the wiring connection states of the signal
discriminator 27 and .gamma.-ray discriminators 32 provided for the
signal discrimination unit 25 easy to understand. The signal
discrimination unit 25 is actually set in the detector support
member 8 as shown in FIG. 3 and FIG. 4 and the wires 52, 53 and 55
are drawn out of the detector support member 8.
[0036] Before specifically explaining the radiological inspection
in this embodiment, the principle of radiation detection of this
embodiment will be explained. Data of an X-ray CT image
(tomographic image including an image of internal organs and bones
of an examinee obtained through X-ray CT) is created by irradiating
X-rays radiated from the X-ray source onto an examinee in a
specific direction for a predetermined time and repeating an
operation of detecting (scanning) X-rays that have passed through
the body using radiation detectors and based on the intensity of
X-rays detected by a plurality of radiation detectors. In order to
obtain accurate X-ray CT image data, it is preferable not to allow
.gamma.-rays emitted from the inside of the examinee caused by PET
radiopharmaceutical to enter the radiation detectors which are
detecting X-rays during an X-ray CT inspection. With regard to one
radiation detector, if the time of X-ray irradiation onto the
examinee is shortened in accordance with a rate of incidence of
.gamma.-rays, influences of .gamma.-rays can be ignored, and
therefore this system is designed to shorten the time of X-ray
irradiation onto the examinee. To calculate the X-ray irradiation
time T, a rate of incidence of .gamma.-rays on one radiation
detector is considered first. Suppose radioactivity in the body
based on PET radiopharmaceutical administered to the examinee in a
PET inspection is N (Bq), rate of generated .gamma.-rays passing
through the body is A, the rate of incidence calculated from the
solid angle of one radiation detector is B and sensitivity of the
detection element is C. Then, rate a (counts/sec) of .gamma.-rays
detected by one radiation detector is given by Expression (1).
.alpha.=2NABC (1) In Expression (1), coefficient "2" means that a
pair (two) of .gamma.-rays are emitted for annihilation of one
positron. The probability W that .gamma.-rays are detected by one
detection element within the irradiation time T is given by
Expression (2). W=1-exp (-T.alpha.) (2) By determining the
irradiation time T so that the value of W in Expression (2) is
reduced, the influence of .gamma.-rays incident on one radiation
detector is reduced to a level as small as negligible during an
X-ray CT inspection.
[0037] An example of the X-ray irradiation time T will be explained
below. A specific X-ray irradiation time T was calculated based on
Expressions (1) and (2). The intensity of radiation in the body
caused by PET radiopharmaceutical administered to the examinee in a
PET inspection is a maximum of approximately 370 MBq (N=370 MBq)
and the rate of passage A of .gamma.-rays through the body is on
the order of 0.6 (A=0.6) when the body of the examinee is assumed
to be water having a radius of 15 cm. For example, assuming a case
where a radiation detector having a size of 5 mm per side is
arranged in the shape of a ring having a radius of 50 cm, the rate
of incidence B calculated from the solid angle of one radiation
detector is 8.times.10.sup.-8 (B=8.times.10.sup.-8). Furthermore,
detection sensitivity C of the radiation detector is a maximum of
approximately 0.6 (C=0.6) when a semiconductor radiation detector
is used. From these values, the .gamma.-ray detection rate a of one
radiation detector is on the order of 2000 (counts/sec). Suppose
the X-ray irradiation time T is 1.5 .mu.sec, for example. Then, the
probability W that one radiation detector will detect .gamma.-rays
during X-ray detection is 0.003 and most of these .gamma.-rays can
be ignored. When radioactivity in the body is 370 MBq or less, if
the X-ray irradiation time is 1.5 .mu.sec or less, W<0.003, that
is, the probability W of .gamma.-ray detection is 0.3% or less,
which is negligible.
[0038] An X-ray CT inspection and a PET inspection in this
embodiment where the above described principle is applied and the
image pickup apparatus 2B is used will be explained more
specifically.
[0039] An X-ray CT inspection and a PET inspection in this
embodiment will be explained. PET radiopharmaceutical is
administered to the examinee 42 using a method like injection in
such a way that radioactivity in the body becomes 370 MBq. Then,
the examinee 42 waits for a predetermined time until the PET
radiopharmaceutical is spread in the body of the examinee 42,
concentrated on an affected area (e.g., affected area of cancer)
and image pickup is possible. PET radiopharmaceutical is selected
according to the affected area to be inspected. After the lapse of
the predetermined time, the bed 20 on which the examinee 42 lies is
inserted into the through hole section 41 of the image pickup
apparatus 2 together with the examinee 42. An X-ray CT inspection
and a PET inspection are carried out using the image pickup
apparatus 2. The examinee 42 with the PET radiopharmaceutical
administered is inserted into the through hole section 41, a
voltage is applied from the power supply 50 to the respective
radiation detectors 5 and then the radiation detectors 5 detect
.gamma.-rays emitted from the examinee 42. That is, a PET
inspection is started. After the PET inspection is started, an
X-ray CT inspection is started.
[0040] The X-ray CT inspection will be explained. When the X-ray CT
inspection is started, the drive apparatus control apparatus 21
outputs a drive start signal and closes the breaker (hereinafter
referred to as "motor breaker") connected to the motor of the X-ray
source drive apparatus 15 and connected to the power supply. The
torque of the motor is transmitted to the pinion through the
deceleration mechanism and the X-ray source apparatus 14, that is,
the X-ray source 17 moves along the guide rail 12 in the
circumferential direction. The X-ray source 17 moves around the
examinee 42 at a set speed while being inserted in the through hole
section 41. When the X-ray CT inspection is completed, the drive
apparatus control apparatus 21 outputs a drive stop signal and
opens the motor breaker. This stops the movement of the X-ray
source 17 in the circumferential direction. In this embodiment, all
the radiation detectors 5 move neither in the circumferential
direction nor in the axial direction of the through hole section
41. The drive apparatus control apparatus 21 and X-ray source
control apparatus 22 are set in the detector support member 8. A
publicly known technology is applied to transmission of a control
signal from the drive apparatus control apparatus 21 and X-ray
source control apparatus 22 to the moving X-ray source apparatus 14
without interfering with the movement of the X-ray source apparatus
14.
[0041] The X-ray source control apparatus 22 controls the time of
radiation of X-rays from the X-ray source 17. That is, the X-ray
source control apparatus 22 outputs X-ray generation signals and
X-ray stop signals repeatedly. The first X-ray generation signal is
outputted based on the input of the above drive start signal to the
X-ray source control apparatus 22. In response to the output of an
X-ray generation signal, the breaker provided between the anode (or
cathode) of the X-ray tube of the X-ray source 17 and the power
supply (hereinafter referred to as "X-ray source breaker", not
shown) is closed, an X-ray stop signal is outputted after a lapse
of a first set time, the X-ray source breaker is opened and the
X-ray source breaker is closed after a lapse of a second set time,
and this control is repeated. Between the anode and cathode, a
voltage is applied during the first set time, but no voltage is
applied during the second set time. With such control by the X-ray
source control apparatus 22, pulse-shaped 80 keV X-rays are
radiated from the X-ray tube. An irradiation time T which is the
first set time is set, for example, to 1 .mu.sec so that the
probability of detection of .gamma.-rays at the radiation detector
5 can be ignored. The second set time is a time T0 during which the
X-ray source 17 moves between one radiation detector 5 and another
radiation detector 5 which is adjacent thereto in the
circumferential direction and is determined by the moving speed of
the X-ray source 17 in the circumferential direction of the guide
rail 12. The first and second set times are stored in the X-ray
source control apparatus 22.
[0042] In response to repeated outputs of X-ray stop signals and
X-ray generation signals, the X-ray source 17 radiates X-rays
during the first set time, that is, for 1 .mu.sec and stops
radiation of X-rays during the second set time. This radiation and
stop of X-rays are repeated during a period during which the X-ray
source 17 is moving in the circumferential direction.
[0043] The X-rays 57 radiated from the X-ray source 17 are
irradiated onto the examinee 42 in a fan-beam shape. The examinee
42 receives irradiation of X-rays 57 as the X-ray source 17 moves
in the circumferential direction. The X-rays 57 which have passed
through the examinee 42 (e.g., X-rays that have passed through the
affected area 56) are detected by a plurality of radiation
detectors 5 located in the circumferential direction centered on
the radiation detector 5 located at the position 180.degree. from
the X-ray source 17 relative to the central axis of the through
hole section 41. These radiation detectors 5 output the detection
signals of the X-rays 57. These X-ray detection signals are
inputted to their respective signal S discriminators 27 through the
corresponding wires 49. The radiation detectors 5 that detect the
above described X-rays are referred to as first radiation detectors
5 for the purpose of convenience.
[0044] From the affected area (affected area of cancer) of the
examinee 42 on the bed 16, .gamma.-rays 58 of 511 keV caused by PET
radiopharmaceutical are emitted. The radiation detectors 5 other
than the first radiation detectors 5 detect the .gamma.-rays 58 and
output .gamma.-ray detection signals. The radiation detectors 5
detecting .gamma.-rays are called "second radiation detectors 5"
for the purpose of convenience. The .gamma.-ray detection signals
outputted from the second radiation detectors 5 located on the
first layer out of the second radiation detectors are inputted to
their respective signal discriminators 27 through the corresponding
wires 49 and the .gamma.-ray detection signals outputted from the
second radiation detectors 5 located on the second layer and third
layer are inputted to their respective .gamma.-ray discriminators
32 through the corresponding wires 54. Only the radiation detectors
5 located on the first layer are connected to the signal
discriminator 61 having the X-ray signal processing apparatus 33.
This is because energy of the X-rays is 80 keV and most (90% or
more) of the X-rays that have passed through the examinee 42 are
detected by the first layer radiation detectors 5.
[0045] In the signal discriminators 27, the .gamma.-ray detection
signals outputted from the first layer second radiation detectors 5
are transmitted to the .gamma.-ray discriminators 32 and the X-ray
detection signals outputted from the first radiation detectors 5
are transmitted to the X-ray signal processing apparatus 33. Such
transmission of each detection signal is performed according to the
changeover operation of the changeover switch 28 of the signal
discriminator 27. The changeover operation for connecting the
movable terminal 29 of the changeover switch 28 to the fixed
terminal 30 or fixed terminal 31 is performed based on the
changeover control signal which is the output of the drive
apparatus control apparatus 21. During an X-ray ray CT inspection,
the drive apparatus control apparatus 22 selects the first
radiation detectors 5 of the first layer radiation detectors 5 and
connects the movable terminal 29 of the signal discriminators 27
connected to these first radiation detector 5 to the fixed terminal
31.
[0046] The selection of the first radiation detectors 5 will be
explained. The motor in the X-ray source drive apparatus 15 is
connected with an encoder (not shown). The drive apparatus control
apparatus 22 receives a detection signal of the encoder and
calculates the position of the X-ray source drive apparatus 15 in
the circumferential direction of the detector support member 8
(through hole section 41), that is, the position of the X-ray
source 17 and selects the radiation detector 5 located 180.degree.
opposite to the position of the X-ray source 17 using the stored
data of the position of each radiation detector 5. The X-rays 57
radiated from the X-ray source 17 has a certain width in the
circumferential direction of the guide rail 12, and therefore there
are a plurality of radiation detectors 5 in the circumferential
direction other than the selected radiation detectors 5 which
detect the X-rays 57 that have passed through the examinee 42. The
drive apparatus control apparatus 22 selects those plurality of
radiation detectors 5, too. These radiation detectors 5 are the
first radiation detectors 5. The first radiation detectors 5 also
change depending on the movement of the X-ray source 17 in the
circumferential direction. As the X-ray source 17 moves in the
circumferential direction, the first radiation detectors 5 also
seem to move in the circumferential direction. When the drive
apparatus control apparatus 22 selects other radiation detectors 5
as the X-ray source 17 moves in the circumferential direction, the
movable terminal 29 connected to the radiation detectors 5 which
become the new first radiation detectors 5 is connected to the
fixed terminal 31. The movable terminal 29 connected to the
radiation detectors 5 which are no longer the first radiation
detectors 5 as the X-ray source 17 moves in the circumferential
direction is connected to the fixed terminal 30 by the drive
apparatus control apparatus 22. According to the positional
relationship with the X-ray source 17, the first layer radiation
detectors 5 sometimes become the first radiation detectors 5 and
sometimes become the second radiation detectors 5. For this reason,
one radiation detector 5 on the first layer outputs both an X-ray
detection signal and .gamma.-ray detection signal with a time shift
in between.
[0047] The first radiation detectors 5 receive irradiation from the
X-ray source 17 for 1 .mu.sec which is the first set time and
detect X-rays which have passed through the examinee 42. The
probability that the first radiation detectors 5 detect
.gamma.-rays emitted from the examinee 42 for 1 .mu.sec is as small
as negligible as described above. Many .gamma.-rays 58 generated at
the affected area 56 of the examinee 42 caused by PET
radiopharmaceutical are not emitted in a specific direction but
emitted in all directions. These .gamma.-rays 58 form pairs and are
emitted in directions opposite to each other
(180.degree..+-.0.6.degree.) as described above and detected by
either one of the second radiation detectors 5.
[0048] The signal processing of the signal discriminators 27 when
the X-ray detection signals and .gamma.-ray detection signals
outputted from the first layer radiation detectors 5 are inputted
will be explained. As described above, the X-ray detection signals
outputted from the first layer radiation detectors 5 are inputted
to the X-ray signal processing apparatus 33. The X-ray signal
processing apparatus 33 integrates the input X-ray detection
signals using an integration apparatus and outputs the X-ray
detection signal integrated value, that is, information on the
intensity of the measured X-rays. The intensity information of the
X-ray detection signals is transmitted to the computer 26 through
the wire 53 and stored in the storage apparatus 37.
[0049] The .gamma.-ray detection signals outputted from the first
layer second radiation detectors 5 are inputted to the .gamma.-ray
discriminators 32 by an action of the changeover switch 28. By
annihilation of positrons emitted from PET radiopharmaceutical,
energy of .gamma.-rays emitted from the affected area 56 is 511
keV. However, when .gamma.-rays are scattered in the body of the
examinee 42, the energy falls below 511 keV. To remove scattered
.gamma.-rays, the .gamma.-ray discriminators 32 is provided with a
filter (not shown) which allows .gamma.-ray detection signals
having energy equal to or greater than an energy set value of 400
keV which is lower than 511 keV to pass. This filter receives the
.gamma.-ray detection signals outputted from the fixed terminal 30.
Here, 400 keV was used as the energy set value because variations
of the .gamma.-ray detection signals produces when .gamma.-rays of
511 keV enter the radiation detectors 5 are taken into
consideration. The .gamma.-ray discriminators 32 generate a pulse
signal having predetermined energy when .gamma.-ray detection
signals having energy equal to or greater than the energy set value
(400 keV) are inputted. The .gamma.-ray discriminator 32 is a
.gamma.-ray detection signal processing apparatus and gives the
pulse signal to be output time information and position information
indicating the position of the radiation detector 5 connected to
the .gamma.-ray discriminator 32. The time information is either
the information when .gamma.-ray detection signals are inputted to
the .gamma.-ray discriminator 32 or information when a pulse signal
is outputted from the .gamma.-ray discriminator 32.
[0050] All the second layer and third layer radiation detectors 5
are the second radiation detectors. The .gamma.-ray discriminators
32 connected to these second layer and third layer radiation
detectors 5 through the wire 54 also exhibits the same functions as
those of the .gamma.-ray discriminators 32 in the above described
signal discriminators 27.
[0051] The coincidence counter 34 receives pulse signals outputted
from all the .gamma.-ray discriminators 32. The coincidence counter
34 performs simultaneous counting using pulse signals for
respective .gamma.-ray detection signals outputted from the two
second radiation detectors 5 which have detected each .gamma.-ray
58 of the .gamma.-ray pair (a pair of the second radiation
detectors which exist at substantially 180.degree. (more precisely
180.degree..+-.0.60.degree.) different positions centered on the
central axis of the through hole section 41) and calculates the
count rate (.gamma.-ray count information) corresponding to their
respective .gamma.-ray detection signals. The coincidence counter
34 decides whether each pulse signal corresponds to the respective
.gamma.-ray detection signals of the .gamma.-ray pair or not based
on the time information given to each pulse signal. That is, if the
difference between two time information pieces is within a set time
(e.g., 10 nsec), the coincidence counter 34 decides that the pulse
signal corresponds to a pair of .gamma.-rays 58 generated by
annihilation of one positron. Furthermore, the coincidence counter
34 creates data from the position information given to those pulse
signals as the position of the corresponding pair of second
radiation detectors 5, that is, the position information of each
.gamma.-ray detection point. The coincidence counter 34 outputs the
count rate information corresponding to each .gamma.-ray detection
signal and the position information of the two detection points at
which the .gamma.-ray pair is detected. The count rate and position
information are transmitted to the computer 36 and stored in the
storage apparatus 37.
[0052] The computer 36 carries out processing based on the
processing procedure in steps 60 to 65 shown in FIG. 8. The
computer 36 that carries out such processing is a tomography
creation section that creates first tomographic image information
using first information (more specifically, .gamma.-ray count
information and position information of the .gamma.-ray detection
point), creates second tomographic image information (more
specifically, X-ray CT image data) using second information (more
specifically, X-ray intensity information and X-ray detection
position information) and third tomographic image information (more
specifically, combined tomography data) including the first
tomographic image information and second tomographic image
information using those tomographic image information pieces. The
count rate information of the .gamma.-ray detection signal counted
by the coincidence counter 34, position information of the
.gamma.-ray detection signal outputted from the coincidence counter
34, X-ray intensity information outputted from the X-ray signal
processing apparatus 33 and X-ray detection position information
given to the X-ray intensity are inputted (step 60). The inputted
count rate information of the .gamma.-ray detection signal,
position information of the .gamma.-ray detection point, X-ray
intensity information and X-ray detection position information are
stored in the storage apparatus 37 (step 61).
[0053] The tomographic image of the cross section (hereinafter the
"cross section" will refer to the cross section when the examinee
is in standing posture) of the examinee 42 is reconstructed using
the X-ray intensity information and X-ray detection position
information (step 62). The reconstructed tomographic image is
called an "X-ray CT image." Specific processing of reconstruction
of this tomographic image will be explained. First, the attenuation
rate of X-rays in each voxel in the body of the examinee 42 is
calculated using the X-ray intensity information. This attenuation
rate is stored in the storage apparatus 37. To reconstruct the
X-ray CT image, the linear attenuation coefficient in the body of
the examinee 42 between the position of the X-ray source 17 and the
position of the radiation detector 5 which has detected the X-rays
(obtained from the X-ray detection position information) is
calculated using the attenuation rate of the X-ray detection signal
read from the storage apparatus 37. The position of the X-ray
source 17 during movement detected by the encoder is given to the
X-ray intensity information by each X-ray signal processing
apparatus 33 and transmitted to the computer 36. The CT value of
each voxel is calculated based on the value of the linear
attenuation coefficient obtained by the filtered back projection
method using the linear attenuation coefficient. The data of the
X-ray CT image is obtained using those CT values and stored in the
storage apparatus 37. In step 62, the X-ray CT image on the cross
section that passes through the affected area where PET
radiopharmaceutical is concentrated is also reconstructed.
[0054] The tomographic image of the cross section of the examinee
42 including the affected area (e.g., the affected area of cancer)
is reconstructed using the count rate of the .gamma.-ray detection
signal at the corresponding position (step 63). The tomographic
image reconstructed using the count rate of the .gamma.-ray
detection signal is called a "PET image". This processing will be
explained in detail. Using the count rate of the .gamma.-ray
detection signal read from the storage device 37, the number of
.gamma.-ray pairs generated (the number of .gamma.-ray pairs
generated according to annihilation of a plurality of positrons) in
the body between the semiconductor devices of a pair of the second
radiation detectors 5 (specified by position information of the
.gamma.-ray detection point) is calculated. Using this number of
.gamma.-ray pairs generated, a .gamma.-ray pair generation density
of each voxel is calculated according to the filtered back
projection method. PET image data can be obtained based on this
.gamma.-ray pair generation density. This PET image data is stored
in the storage device 37.
[0055] The PET image data is combined with the X-ray CT image data
to obtain combined tomographic data including both data pieces and
stored in the storage device 37 (step 64). The PET image data at
the position of the affected area and X-ray CT image data at the
position are combined to obtain combined tomographic image data on
the cross section of the examinee 42 at the position of the
affected area. The combination of the PET image data and X-ray CT
image data can be performed easily and accurately by aligning the
central axis of the through hole section 41 in both image data
pieces. That is, the PET image data and X-ray CT image data are
created based on the detection signals outputted from the shared
radiation detector 5, and therefore alignment can be performed
accurately as described above. The combined tomographic data is
called from the storage device 37 and output to the display device
38 (step 65) and displayed on the display device 38. The combined
tomographic image displayed on the display device 38 includes an
X-ray CT image, and therefore it is possible to easily check the
position in the body of the examinee 42 of the affected area in the
PET image. That is, since the X-ray CT image includes images of
internal organs and bones, doctors can identify the position of the
affected area (e.g., the affected area of cancer) from the
relationship with the internal organs or bones.
[0056] The radiological imaging apparatus 1 comprises a plurality
of radiation detectors 5 multilayered in the radius direction of
the through hole section 41 (FIG. 1 to FIG. 4) and this multilayer
arrangement can bring out the following new function. For example,
suppose a case where two .gamma.-rays 58a and 58b emitted from a
point of .gamma.-ray pair generation 70 (in the affected area 56)
in the body of the examinee 42 as shown in FIG. 9A enter radiation
detectors 5f and 5g. It is unknown at which position in the
radiation detector the .gamma.-rays have attenuated, and therefore
the conventional method considers a line connecting the end
positions of the pair of the radiation detectors 5f and 5h, that
is, a line 71 shown in FIG. 9B as a detection line. However, since
the radiological imaging apparatus 1 adopts the multilayer
arrangement of the radiation detectors 5 in the radius direction of
the through hole section 41, it is possible to obtain a .gamma.-ray
detection signal of the radiation detector 5g located outside in
the radius direction and consider a line 72 connecting the
radiation detector 5f and radiation detector 5g as a detection
line. That is, it is possible to grasp the attenuation position in
the depth direction of the radiation detectors 5 which have been
unknown in the conventional example. As a result, the detection
line 72 precisely passes through the position at which a pair of
.gamma.-rays are generated and therefore the accuracy of the image
improves. As a result, the detection line is brought closer to the
actual point of generation of the pair of .gamma.-rays and accuracy
of measured data improves.
[0057] In this embodiment, the radiation detection apparatus 43
comprises a plurality of radiation detectors 5 which output both
X-ray detection signals and .gamma.-ray detection signals, and
therefore the radiation detection apparatus 43 functions as a
.gamma.-ray detection section as well as an X-ray detection
section. That is, the radiation detection apparatus 43 has both
functions of the .gamma.-ray detection section and X-ray detection
section. In this embodiment, the X-ray detection section is
positioned in an area formed between one end of the .gamma.-ray
detection section and the other end of the .gamma.-ray detection
section in the longitudinal direction of the bed 20. Furthermore,
the radiation detection apparatus 43 is an X-ray detection section
that detects X-ray 57 which is irradiated from the X-ray source 17
and passes through the examinee 42 and outputs a detection signal
of this X-ray 57 and at the same time is a .gamma.-ray detection
section that detects a .gamma.-ray 58 emitted caused by PET
radiopharmaceutical from the area (affected area 56) through which
the X-ray 57 in the examinee 42 passes at the position of the
examinee 42 irradiated with the X-ray 57 and outputs a detection
signal of this .gamma.-ray 58.
[0058] This embodiment can attain the effects described below.
[0059] (1) In this embodiment, a plurality of detection units 4 are
attached to the detector support member 8 through the connector,
section, and therefore these detection units 4, or more
specifically, many radiation detectors 5 can be attached in a short
time. This makes it possible to shorten the time for manufacturing
the image pickup apparatus 2, that is, the radiological imaging
apparatus 1. [0060] (2) Since the detection units 4 are attached to
the detector support member 8 through the connector section in a
detachable manner, when a radiation detector 5 has trouble, the
detection unit 4 including the radiation detector 5 in trouble can
be easily removed from the detector support member 8. Furthermore,
a new detection unit 4 can be easily attached to the detector
support member 8 at the position of the removed detector unit.
Thus, this embodiment allows a damaged radiation detector 5 to be
replaced easily. [0061] (3) This embodiment arranges the plurality
of radiation detectors 5 not only in the axial direction and
circumferential direction of the through hole section 41 (detector
support member 8) but also in the radius direction, and can thereby
obtain .gamma.-ray detection signals at the positions subdivided in
the radius direction of the through hole section 41 without
reducing signal transmission substances as in the case of
conventional radiation detectors used for a PET inspection. Thus,
this embodiment can obtain precise information on the position that
.gamma.-rays reach in the radius direction of the through hole
section 41 (position information of the radiation detectors 5 which
have output .gamma.-ray detection signals). In a conventional PET
inspection, one radiation detector is placed in the radius
direction of the through hole section 41, a reflector is placed
inside this radiation detector and the information on the position
that .gamma.-rays have reached in the radius direction of the
through hole section 41 is obtained according to a pattern with
which the signal transmission substance reaches the photoelectron
multiplier. At this moment, part of the signal transmission
substance attenuates in the radiation detector because of the
reflector and is reflected to the outside of the radiation
detector, which reduces the signal transmission substance and
reduces energy resolution. [0062] (4) This embodiment arranges a
plurality of independent radiation detectors 5 in the radius
direction of the through hole section 41, and can thereby use all
the signal transmission substance of the radiation detectors 5 for
detection of .gamma.-rays and improve energy resolution of the
radiation detectors 5. Use of the radiation detectors 5 with high
energy resolution for a PET inspection makes it possible to
distinguish .gamma.-rays whose energy has attenuated due to
scattering from un-scattered .gamma.-rays having energy of 511 keV.
As a result, it is possible to remove more scattered radiation
through a filter of the .gamma.-ray discriminator 32. [0063] (5)
This embodiment can acquire precise information on the position
that .gamma.-rays reach in the radius direction of the through hole
section 41 without reducing the number of signal transmission
substances in the radiation detectors, and therefore using the
precise information on the position that .gamma.-rays reach
improves the accuracy of tomography, eliminates the need for the
reflector for the radiation detectors and can thereby prevent the
reduction of the signal transmission substances, improve the energy
resolution and suppress influences of scattered rays on the
reconstruction of the tomography. As a result, this embodiment can
improve the accuracy of tomography, that is, diagnostic accuracy of
a PET inspection. [0064] (6) This embodiment uses semiconductor
radiation detectors as the radiation detectors 5, and can thereby
arrange a plurality of radiation detectors 5 in the radius
direction of the through hole section 41 and such an arrangement of
the plurality of radiation detectors 5 does not increase the size
of the image pickup apparatus 2. [0065] (7) Using semiconductor
radiation detectors for the radiation detectors 5, this embodiment
eliminates the need for any photoelectron multiplier which is
required for radiation detectors using a scintillator and can
thereby reduce the size of the image pickup apparatus 2. [0066] (8)
Arranging the radiation detectors 5 which are semiconductor
radiation detectors on the support substrate, this embodiment
allows the radiation detectors 5 to be arranged densely. Allowing
especially radiation detectors 5 with small detector widths to be
arranged densely in the circumferential direction of the through
hole section 41, this embodiment can realize high resolution (small
image voxel size) of the tomographic image. [0067] (9) Adopting the
configuration of arranging the radiation detectors 5 on the support
substrate 6, this embodiment allows the radiation detectors 5 to be
arranged densely. This allows an arrangement of a plurality of
radiation detectors 5 in the radius direction of the through hole
section 41 in particular and realizes high detection efficiency.
Moreover, since the radiation detectors 5 in the radius direction
can detect .gamma.-rays independently, the resolution in the radius
direction improves. In a 3D (three-dimensional) PET inspection in
particular, there may be a case where .gamma.-rays enter the
radiation detectors 5 diagonally, but with an improvement of the
resolution in the radius direction, it is possible to grasp the
direction of incidence of .gamma.-rays accurately. This can improve
the quality of PET images obtained. [0068] (10) According to this
embodiment, wires connected to the radiation detectors 5 are
arranged in the support substrate 6, and therefore it is possible
to shorten the distance between the radiation detectors 5 in the
circumferential direction and axial direction of the through hole
section 41. The shortening of the distance between the radiation
detectors 5 reduces omissions in .gamma.-ray detection and
substantially increases the .gamma.-ray detection efficiency. The
substantial increase of .gamma.-ray detection efficiency can
shorten a PET inspection time. [0069] (11) Using the radiation
detectors 5 which have detected .gamma.-rays as the radiation
detectors 5 to detect X-rays, the radiological imaging apparatus 1
need not provide the radiation detectors 5 to detect X-rays and the
radiation detectors 5 to detect .gamma.-rays separately, and can
thereby simplify the configuration and reduce the size of the
apparatus. The radiation detectors 5 output both X-ray detection
signals and .gamma.-ray detection signals. [0070] (12) In this
embodiment, the X-ray detection section is positioned in an area
formed between one end of the .gamma.-ray detection section and the
other end of the .gamma.-ray detection section in the longitudinal
direction of the bed 20, and therefore even when the examinee 42
moves during an inspection independently of the movement of the bed
20, it is possible to combine the information of the first
tomographic image (PET image) created based on the first
information obtained from a .gamma.-ray detection signal outputted
from the .gamma.-ray detection section and the information of the
second tomographic image (X-ray computer tomographic image)
obtained from the X-ray detection signal outputted from the X-ray
detection section and improve the accuracy of the created
tomographic image of the examinee 42. Using the tomographic image
can improve the accuracy of diagnosis of the examinee. More
specifically, the position and size of the affected area of cancer
can be recognized accurately. It is especially possible to diagnose
cancer of lymph gland which is a small organ. [0071] (13) As
described above, according to this embodiment, the radiation
detection apparatus 43 consists of a plurality of radiation
detectors 5 which output both X-ray detection signals and
.gamma.-ray detection signals (detection of X-rays to obtain X-ray
detection signals is performed using the radiation detectors 5 to
detect .gamma.-rays to obtain .gamma.-ray detection signals) and
therefore the radiation detection apparatus 43 is provided with
both functions of the .gamma.-ray detection section and X-ray
detection section. The radiation detection apparatus 43 can be said
to arrange the .gamma.-ray detection section and X-ray detection
section coaxially. For this reason, this embodiment can reconstruct
the first tomographic image at the position of an affected area
(where PET radiopharmaceutical is concentrated) including internal
organs and bones of the examinee 42 and reconstruct the second
tomographic image including the image of the affected area of the
examinee 42 using the .gamma.-ray detection signals which are other
output signals of the radiation detectors 5. The data of the first
tomographic image and data of the second tomographic image are
reconstructed based on the output signals of the radiation
detectors 5 which detect both transmitted X-rays and .gamma.-rays,
and therefore it is possible to combine the data of the first
tomographic image and the data of the second tomographic image
aligned with each other with high accuracy. In this way, it is
possible to easily obtain an accurate tomographic image (combined
tomographic image) including images of the affected area, internal
organs and bones, etc. According to this combined tomographic
image, it is possible to accurately identify the position of the
affected area from the relationship with the internal organs or
bones. For example, by aligning the data of the first tomographic
image and the second tomographic image based on the central axis of
the detector support member 8 (or through hole section 41) of the
image pickup apparatus 2, it is possible to easily obtain image
data combining both tomographic images. [0072] (14) In this
embodiment, the X-ray detection section detects X-rays 57 which
have been radiated from the X-ray source 17 and pass through the
affected area 56 of the examinee 42 and the .gamma.-ray detection
section detects .gamma.-rays emitted caused by radiopharmaceutical
from the area (affected area) in the body of the examinee 42
through which X-rays pass at the position of the examinee
irradiated with the X-rays, and therefore it is possible to carry
out an X-ray CT inspection and PET inspection at the same position
without moving the examinee 42 with the bed 20. During both
inspections, the X-ray detection section outputs a detection signal
of X-rays that have passed through the affected area 56 of the
examinee 42 and the .gamma.-ray detection section outputs a
detection signal of .gamma.-rays emitted from the affected area 56.
The first tomographic image data at the position of the affected
area 56 obtained based on the X-ray detection signal is combined
with the second tomographic image data at the position of the
affected area obtained based on the .gamma.-ray detection signal,
and therefore even if the examinee 42 can no longer keep the same
posture moves on the bed 20 during an inspection, it is possible to
combine those tomographic image data pieces accurately. That is,
this embodiment can obtain combined tomographic image data with a
high degree of accuracy. Thus, using the combined tomographic image
data (combined tomographic image) at the position of the affected
area 56 displayed on the display device 38 can improve the accuracy
of diagnosis of the affected area 56. Even when the affected area
is located especially in a place where organs intercross, the
combined tomographic image data obtained in this embodiment makes
it possible to keep track of the position of the affected area
appropriately and improve the accuracy of diagnosis of the affected
area. [0073] (15) According to this embodiment, using the X-ray
source axial transport apparatus (e.g., axial transport arm 16),
the X-ray source 17 can be transported in the axial direction of
the radiation detector 5 during radiological inspection, and
therefore an X-ray CT inspection can be carried out on the range of
the inspection target while carrying out a PET inspection on the
range of the inspection target without transporting the examinee 42
in the axial direction of the radiation detection apparatus 43.
When an X-ray CT inspection is carried out on the range of the
inspection target while moving the examinee 42 by transporting the
bed 20 without moving the X-ray source 17 in the axial direction,
the position of the area where PET radiopharmaceutical is
concentrated also moves in the axial direction. This means that the
position at which a .gamma.-ray pair is generated is moved in the
axial direction, resulting in increased noise when PET image data
is created, failing to obtain accurate PET image data. In this
embodiment, the position at which a .gamma.-ray pair is generated
is not moved in the axial direction, resulting in accurate PET
image data and improved accuracy of combined tomographic image
data. [0074] (16) According to this embodiment, it is possible to
detect a plurality of .gamma.-ray pairs emitted from the examinee
42 using the radiation detectors 5 included in the radiation
detection apparatus 43 and also detect X-rays which have been
radiated from the X-ray source 17 moving in the circumferential
direction and passed through the examinee 42. In this way, while
the conventional art requires an image pickup apparatus for
detecting X-rays and another image pickup apparatus for detecting
.gamma.-rays, this embodiment only requires a single image pickup
apparatus to detect X-rays and .gamma.-rays and simplifies the
configuration of the radiological imaging apparatus capable of
executing both X-ray CT inspection and PET inspection. [0075] (17)
This embodiment allows the common radiation detectors 5 to obtain
X-ray detection signals necessary for creating a first tomographic
image and .gamma.-ray detection signals necessary for creating a
second tomographic image, making it possible to drastically shorten
the time required to inspect the examinee 42 (inspection time). In
other words, it is possible to obtain X-ray detection signals
necessary for creating a first tomographic image and .gamma.-ray
detection signals necessary for creating a second tomographic image
in a short inspection time. This embodiment eliminates the need in
the prior art for transporting the examinee 42 from one image
pickup apparatus for detecting transmitting X-rays to another image
pickup apparatus for detecting .gamma.-rays, and therefore further
contributes to a reduction of the inspection time of the examinee
42. [0076] (18) This embodiment rotates the X-ray source 17 and
moves the radiation detection apparatus 43 in neither the
circumferential direction nor axial direction of the through hole
section 41, can thereby reduce the capacity of the motor for
rotating the X-ray source
17 compared to the motor necessary to move the radiation detection
apparatus 43. Power consumption necessary for driving the motor of
the latter can also be reduced compared to power consumption of the
motor of the former. [0077] (19) Since .gamma.-ray detection
signals are inputted to the X-ray signal processing apparatus 33,
that is, the first signal processing apparatus is reduced
drastically, it is possible to obtain an accurate first tomographic
image data. Thus, using image data obtained by combining the first
tomographic image data and second tomographic image data allows the
position of the affected area to be known precisely. [0078] (20) In
this embodiment, the X-ray source 17 rotates inside the radiation
detection apparatus 43, and therefore the inner diameter of the
detector support member 8 increases and the number of radiation
detectors 5 that can be provided in the circumferential direction
inside the detector support member 8 can be increased. An increase
in the number of radiation detectors 5 in the circumferential
direction results in an improvement in sensitivity and resolution
and improves the resolution of the tomographic image on the cross
section of the examinee 42. [0079] (21) Since the axial transport
arm 16 and X-ray source 17 are located inside the radiation
detection apparatus 43, they intercept .gamma.-rays emitted from
the examinee 42 during an X-ray CT inspection and the radiation
detectors 5 located right behind them cannot detect the
.gamma.-rays, which may cause detection data necessary for creation
of a PET image to be lost. However, since the X-ray source drive
apparatus 15 rotates the X-ray source 17 and the axial transport
arm 16 in the circumferential direction as described above, the
loss of data substantially causes no problem. Especially, the
rotational speed of the X-ray source 17 and the axial transport arm
16 is approximately 1 sec/1 slice, which is short enough when
compared to a time required for a PET inspection which takes
approximately a few minutes at the shortest. The loss of the data
is therefore substantially no problem. Furthermore, when a PET
inspection is carried out without any X-ray CT inspection, the
X-ray source 17 is housed in the X-ray source drive apparatus 15
and therefore the X-ray source 17 and the axial transport arm 16 do
not constitute obstacles to detection of .gamma.-rays.
[0080] Moreover, the inspection time necessary to obtain an X-ray
detection signal necessary to create an X-ray CT image is shorter
than the inspection time necessary to obtain a .gamma.-ray image
pickup signal necessary to create a PET image. Thus, during an
inspection time to obtain a .gamma.-ray detection signal, X-rays
are always irradiated from the X-ray source 17 onto the examinee 42
to obtain an X-ray detection signal and in this way even when the
examinee 42 moves during an inspection, it is also possible to
correct a data shift of the PET image caused by the movement of the
examinee 42 from successive X-ray CT images obtained based on the
X-ray detection signal.
[0081] The wires connected to the radiation detectors 5 are
arranged inside the support substrate 6, but it is also possible to
form a through hole in the support substrate 6, pass the wires from
the side of the support substrate 6 on which the radiation
detectors 5 are arranged through the through hole, pull the wires
out of the opposite side and arrange the wires on the surface of
the support substrate 6 on the side on which no radiation detectors
5 are arranged. In that case, it is also possible to form grooves
on the surface of the side of the support substrate 6 on which no
radiation detectors 5 are arranged and set the wires in the
grooves. Furthermore, it is also possible to use a multilayer wire
board as the support substrate and set wires inside the multilayer
wiring board. Furthermore, use of the multilayer wiring board
allows the radiation detectors 5 to be arranged on both sides of
the multilayer wiring board.
(Embodiment 2)
[0082] A radiological imaging apparatus according to Embodiment 2
which is another preferred embodiment of the present invention will
be explained below. The radiological imaging apparatus in this
embodiment only differs from the configuration of the radiological
imaging apparatus 1 of Embodiment 1 in the configuration of the
detector unit 4. A detector unit 4A used in this embodiment having
a configuration different from that of the detector unit 4 used in
Embodiment 1 will be explained with reference to FIG. 10 and FIG.
11.
[0083] The detector unit 4A consists of a plurality (e.g., 9) of
radiation detectors 5D arranged in 3 rows and 3 columns on one side
of a support substrate 6. Each radiation detector 5D is the same
semiconductor radiation detector as the radiation detector 5 and
three layers of the radiation detectors 5D are arranged in the
radius direction of a detector support member 8. Of one column in
the radius direction of the detector support member 8, a radiation
detector 5A.sub.1, radiation detector 5B.sub.1 and radiation
detector 5C.sub.1 are arranged on the first layer, second layer and
third layer respectively.
[0084] The radiation detector 5A.sub.1 consists of five detection
elements, that is, detection elements 74A, 74B, 74C, 74D and 74E.
The detection elements 74A, 74B, 74C, 74D and 74E are arranged in
that order from the inner side in the radius direction of the
detector support member 8. The detection element 74A is arranged on
the innermost side, while the detection element 74E is arranged on
the outermost side. A cathode electrode 77A is provided on the
inner side of the detection element 74A. The detection element 74A
and detection element 74B are adjacent to each other with an anode
electrode 78A sandwiched between the outer surface of the detection
element 74A and the inner surface of the detection element 74B. The
detection element 74B and detection element 74C are adjacent to
each other with a cathode electrode 77B sandwiched between the
outer surface of the detection element 74B and the inner surface of
the detection element 74C. The detection element 74C and detection
element 74D are adjacent to each other with an anode electrode 78B
sandwiched between the outer surface of the detection element 74C
and the inner surface of the detection element 74D. The detection
element 74D and detection element 74E are adjacent to each other
with a cathode electrode 77C sandwiched between the outer surface
of the detection element 74D and the inner surface of the detection
element 74E. An anode electrode 78C is provided on the outer
surface of the detection element 74E.
[0085] The radiation detector 5B.sub.1 consists of five detection
elements, that is, detection elements 75A, 75B, 75C, 75D and 75E.
The detection elements 75A, 75B, 75C, 75D and 75E are arranged in
that order from the inner side in the radius direction of the
detector support member 8. The detection element 75A is arranged on
the innermost side, while the detection element 75E is arranged on
the outermost side. A cathode electrode 79A is provided on the
inner side of the detection element 75A. The detection element 75A
and detection element 75B are adjacent to each other with an anode
electrode 80A sandwiched between the outer surface of the detection
element 75A and the inner surface of the detection element 75B. The
detection element 75B and detection element 75C are adjacent to
each other with a cathode electrode 79B sandwiched between the
outer surface of the detection element 75B and the inner surface of
the detection element 75C. The detection element 75C and detection
element 75D are adjacent to each other with an anode electrode 80B
sandwiched between the outer surface of the detection element 75C
and the inner surface of the detection element 75D. The detection
element 75D and detection element 75E are adjacent to each other
with a cathode electrode 79C sandwiched between the outer surface
of the detection element 75D and the inner surface of the detection
element 75E. An anode electrode 80C is provided on the outer
surface of the detection element 75E.
[0086] The radiation detector 5C.sub.1, consists of five detection
elements, that is, detection elements 76A, 76B, 76C, 76D and 76E.
The detection elements 76A, 76B, 76C, 76D and 76E are arranged in
that order from the inner side in the radius direction of the
detector support member 8. The detection element 76A is arranged on
the innermost side, while the detection element 76E is arranged on
the outermost side. A cathode electrode 81A is provided on the
inner side of the detection element 76A. The detection element 76A
and detection element 76B are adjacent to each other with an anode
electrode 82A sandwiched between the outer surface of the detection
element 76A and the inner surface of the detection element 76B. The
detection element 76B and detection element 76C are adjacent to
each other with a cathode electrode 81B sandwiched between the
outer surface of the detection element 76B and the inner surface of
the detection element 76C. The detection element 76C and detection
element 76D are adjacent to each other with an anode electrode 82B
sandwiched between the outer surface of the detection element 76C
and the inner surface of the detection element 76D. The detection
element 76D and detection element 76E are adjacent to each other
with a cathode electrode 81C sandwiched between the outer surface
of the detection element 76D and the inner surface of the detection
element 76E. An anode electrode 82C is provided on the outer
surface of the detection element 76E.
[0087] A grounding wire 45 is connected to the cathode electrodes
77A, 77B, 77C, 79A, 79B, 79C, 81A, 81B and 81C. A wire 74 is
connected to the anode electrodes 78A, 78B and 78C. A wire 75 is
connected to the anode electrodes 80A, 80B and 80C. A wire 76 is
connected to the anode electrodes 82A, 82B and 82C. The grounding
wire 45 is connected to a connector terminal 7D of the connector
section 7. The wire 74 is connected to a connector terminal 7A of
the connector section 7. The wire 75 is connected to a connector
terminal 7B of the connector section 7. The wire 76 is connected to
a connector terminal 7C of the connector section 7. The radiation
detectors 5D included in other two columns are likewise connected
to other connector terminals provided for the connector section 7.
All of the grounding wires 45, 74, 75 and 76 are set in the support
substrate 6. Many detector units 4A are attached to a detector
support section 23 and held by fitting connector terminals such as
the connector terminal 7A provided respectively into the connector
section 11 provided for the detector support section 23. As in the
case of the detector units 4, many detector units 4A are arranged
surrounding the through hole section 41 in the circumferential
direction and axial direction of the through hole section 41.
[0088] The radiation detectors 5A.sub.1, 5B.sub.1, and 5C.sub.1
comprise three or more detection elements having at least two
surfaces, that is, semiconductor elements and arrange anode
electrodes and cathode electrodes alternately between different
semiconductor elements. More specific explains will be given using
the radiation detectors 5A.sub.1. The radiation detector 5A.sub.1
comprises anode electrodes and cathode electrodes alternately
between different detection elements, that is, between the
detection element 74A and detection element 74B, between the
detection element 74B and detection element 74C, between the
detection element 74C and detection element 74D and between the
detection element 74D and detection element 74E, for example, the
anode electrode 78A between the detection element 74A and detection
element 74B, or the cathode electrode 77B between the detection
element 74B and detection element 74C.
[0089] When the connector section 7 is engaged with the connector
section 11, the three radiation detectors 5A.sub.1 on the first
layer are connected to three signal discriminators 27 in a signal
discrimination unit 25 separately. Furthermore, the three radiation
detectors 5B.sub.1 on the second layer and the three radiation
detectors 5C.sub.1 on the third layer are connected to six
.gamma.-ray discriminators 32 other than the signal discriminators
27 provided in the signal discrimination unit 25 separately.
[0090] The radiological imaging apparatus of this embodiment
incorporating the radiation detector units 4A can achieve the
effects (1) to (21) produced by the radiological imaging apparatus
1 of Embodiment 1. Furthermore, this embodiment can achieve effects
(22) and (23) shown below. [0091] (22) According to this
embodiment, the radiation detector 5D has a multilayered structure
of a plurality of detection elements, which reduces the thickness
of the respective detection elements between the anode electrode
and cathode electrode and suppresses reductions of detection
signals due to re-coupling between electrons and holes. This
improves energy resolution. Furthermore, the time until a detection
signal is outputted is shortened and so the time resolution also
improves. With the improved energy resolution, it is possible to
set a high energy threshold and thereby remove more .gamma.-rays
whose energy has decreased due to scattering. Moreover, with the
improved time resolution, it is possible to reduce the time window
and thereby reduce .gamma.-rays which are detected accidentally
within the time window. That is, it is possible to suppress
scattering phenomena and accidental phenomena which constitute
noise components to a low level and thereby improve the image
quality of a PET image. [0092] (23) According to this embodiment,
the radiation detector 5D has a multilayered structure of a
plurality of detection elements, and therefore the thickness of
detection elements between the anode electrode and cathode
electrode is reduced and a bias voltage to be applied can be
reduced. With a reduced bias voltage, it is possible to reduce a
withstand voltage of parts around various wires. Furthermore, the
size of the power supply itself can be reduced. (Embodiment 3)
[0093] A radiological imaging apparatus according to Embodiment 3
which is another preferred embodiment of the present invention will
be explained below. The radiological imaging apparatus in this
embodiment only differs from the configuration of the radiological
imaging apparatus 1 of Embodiment 1 in the configuration of the
detector unit. A detector unit 4B used in this embodiment having a
configuration different from that of the detector unit 4 used in
Embodiment 1 will be explained with reference to FIG. 12 and FIG.
13.
[0094] The detector unit 4B consists of a plurality (e.g., 9) of
radiation detectors 5E arranged in 3 rows and 3 columns on one side
of a support substrate 6. Each radiation detector 5E is the same
semiconductor radiation detector as the radiation detector 5 and
three layers of the radiation detectors 5E are arranged in the
radius direction of a detector support member 8. In the radius
direction of the detector support member 8, radiation detectors
5Aa, 5Ab and 5Ac, radiation detectors 5Ba, 5Bb and 5Bc, and
radiation detectors 5Ca, 5Cb and 5Cc are arranged on the first
layer, second layer and third layer respectively. The radiation
detectors 5Aa, 5Ab and 5Ac arranged in the circumferential
direction of the detector support member 8 are multilayered in the
circumferential direction thereof. The radiation detectors 5Ba, 5Bb
and 5Bc on the second layer and radiation detectors 5Ca, 5Cb and
5Cc on the third layer are likewise multilayered in the
circumferential direction of the detector support member 8. This
multilayered structure will be explained by taking the radiation
detectors 5Aa, 5Ab and 5Ac as an example.
[0095] The radiation detector 5Aa comprises four detection
elements, that is, detection elements 83A, 83B, 83C and 83D. The
detection elements 83A, 83B, 83C and 83D are arranged in that order
in the circumferential direction of the detector support member 8.
The radiation detector 5Ab comprises detection elements 84A, 84B,
84C and 84D. The detection elements 84A, 84B, 84C and 84D are
arranged in that order in the circumferential direction of the
detector support member 8. The radiation detector 5Ac comprises
detection elements 85A, 85B, 85C and 85D. The detection elements
85A, 85B, 85C and 85D are arranged in that order in the
circumferential direction of the detector support member 8.
[0096] A cathode electrode 86A is provided on one side of the
detection element 83A. The detection element 83A and detection
element 83B are adjacent to each other with an anode electrode 87A
sandwiched between the other side of the detection element 83A and
one side of the detection element 83B. Here, one side refers to one
side of the detection element in the circumferential direction of
the detector support member 8 and the other side refers to the
remaining side of the detection element in the circumferential
direction of the detector support member 8. The detection element
83B and detection element 83C are adjacent to each other with a
cathode 86B provided between the other side of the detection
element 83B and one side of the detection element 83C. The
detection element 83C and detection element 83D are adjacent to
each other with an anode 87B provided between the other side of the
detection element 83C and one side of the detection element
83D.
[0097] The detection element 83D and detection element 84A are
adjacent to each other with a cathode electrode 88A provided
between the other side of the detection element 83D and one side of
the detection element 84A. The detection element 84A and detection
element 84B are adjacent to each other with an anode electrode 89A
provided between the other side of the detection element 84A and
one side of the detection element 84B. The detection element 84B
and detection element 84C are adjacent to each other with a cathode
electrode 88B provided between the other side of the detection
element 84B and one side of the detection element 84C. The
detection element 84C and detection element 84D are adjacent to
each other with an anode electrode 89B provided between the other
side of the detection element 84C and one side of the detection
element 84D.
[0098] The detection element 84D and detection element 85A are
adjacent to each other with a cathode electrode 90A provided
between the other side of the detection element 84D and one side of
the detection element 85A. The detection element 85A and detection
element 85B are adjacent to each other with an anode electrode 91A
provided between the other side of the detection element 85A and
one side of the detection element 85B. The detection element 85B
and detection element 85C are adjacent to each other with a cathode
electrode 90B provided between the other side of the detection
element 85B and one side of the detection element 85C. The
detection element 85C and detection element 85D are adjacent to
each other with an anode electrode 91B provided between the other
side of the detection element 85C and one side of the detection
element 85D. A cathode electrode 90C is provided on the other side
of the detection element 85D.
[0099] A grounding wire 92 is connected to the cathode electrodes
86A, 86B, 88A, 88B, 90A, 90B and 90C. A wire 93 is connected to the
anode electrodes 87A and 87B. A wire 94 is connected to the anode
electrodes 89A and 89B. A wire 95 is connected to the anode
electrodes 91A and 91B. The grounding wire 92 is connected to a
connector terminal 7D of a connector section 7. The wire 93 is
connected to a connector terminal 7A of the connector section 7.
The wire 94 is connected to a connector terminal 7B of the
connector section 7. The wire 95 is connected to a connector
terminal 7C of the connector section 7. The radiation detectors 5E
on the second layer and third layer are likewise connected to other
connector terminals provided on the connector section 7. All of the
grounding wire 92 and wires 93, 94 and 95 are set inside the
support substrate 6. Many detector units 4B are attached to the
detector support section 23 and held by fitting connector terminals
such as the connector terminal 7A provided respectively into the
connector section 11 provided for the detector support section 23.
As in the case of the detector units 4, the detector units 4B are
arranged surrounding the through hole section 41 in the
circumferential direction and axial direction of the through hole
section 41.
[0100] When the connector section 7 is engaged with the connector
section 11, the radiation detectors 5Aa, 5Ab and 5Ac on the first
layer are connected to three signal discriminators 27 in the signal
discrimination unit 25 separately. The radiation detectors 5Ba, 5Bb
and 5Bc on the second layer and the radiation detectors 5Ca, 5Cb
and 5Cc on the third layer are connected to six .gamma.-ray
discriminators 32 other than the signal discriminator 27 provided
in the signal discrimination unit 25 separately.
[0101] The radiological imaging apparatus incorporating the
detector units 4B of this embodiment can achieve the effects (1) to
(21) produced by the radiological imaging apparatus 1 of Embodiment
1 and the effects (22) and (23) produced by the radiological
imaging apparatus of Embodiment 2. Furthermore, this embodiment can
achieve the following effect (24). [0102] (24) According to this
embodiment, each radiation detector 5E has a multilayered structure
of a plurality of detection elements, and therefore it is possible
to use both sides of the adjacent radiation detectors 5E as cathode
electrodes and allow those radiation detectors 5E to share the
cathode electrodes. This allows the three radiation detectors 5E
arranged in the circumferential direction of the detector support
member 8 to be arranged close to one another. That is, it is
possible to completely eliminate spaces between the radiation
detectors 5E in the circumferential direction and considerably
reduce omissions in .gamma.-ray detection between the radiation
detectors 5E in the circumferential direction. This leads to a
substantial increase in .gamma.-ray detection efficiency and
shortening of an inspection time as well.
[0103] Embodiments 1 to 3 have a configuration in which detector
units comprising radiation detectors arranged in multilayers in the
radius direction of the detector support member 8 (through hole
section 41 into which the bed 20 is inserted) are applied to a
radiological imaging apparatus which can irradiate X-rays from the
X-ray source 17 onto an examinee and. detect .gamma.-rays and
X-rays. However, the detector units can also be applied to a PET
radiological imaging apparatus which does not irradiate X-rays but
only detects .gamma.-rays emitted from an examinee caused by
radiopharmaceutical which has passed through the examinee.
Furthermore, the detector units can also be applied to a SPECT
radiological imaging apparatus.
[0104] The present invention can improve the accuracy of images
created and facilitate replacement of damaged radiation
detectors.
[0105] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *