JPH09152484A - Single photon ect apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the exposure amount of a body to be inspected to radiation, reduce costs, facilitate handling and maintenance of an apparatus and restrict an artifact, by correcting projection data with a preliminarily stored correction coefficient for correcting the absorption caused by a top plate. SOLUTION: A correction coefficient is preliminarily stored in a correction coefficient-storing part 14 so as to correct influences of the absorption of gamma rays emitted from a body M to be inspected and absorbed when the rays pass through a top plate 5b. A projection data-correcting part 15 corrects projection data (influenced by the absorption by the top plate 5b) stored in a projection data-storing part 13 with the correction coefficient in the storing part 14. Then, an image re-constituting part 16 re-constitutes an RI distribution image based on the corrected projection data of the correcting part 15, and displays the image at a monitor 17. Accordingly, a constitution for obtaining the correction coefficient is eliminated, thereby simplifying the apparatus in constitution. The exposure amount of the body to be inspected to radiation is decreased, and the apparatus costs less. At the same time, since a radiation source is not provided, the apparatus can be handled and maintained with ease.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a gamma ray emitted from a subject administered with a radioisotope RI (radioisotope) to obtain an RI distribution image in a tomographic plane.
ion CT) device, and more particularly to a technique for correcting absorption of gamma rays by a top plate.

[0002]

2. Description of the Related Art Conventional devices of this type include, for example,
There are two devices as shown below. First, as the "first device", for example, a top plate on which a subject to which the radioisotope RI has been administered is placed, and while rotating around the top plate, is emitted from a region of interest of the subject. A detection unit that detects gamma rays, a collection unit that collects projection data of a region of interest of a subject through the detection unit, a projection data storage unit that stores the collected projection data, and a projection data storage unit that stores the projection data. An image reconstruction unit that reconstructs an RI distribution image on the tomographic plane of the region of interest of the subject based on the projected projection data, and the RI reconstructed by this image reconstruction unit.
There is a single photon ECT device that includes a display unit that displays a distribution image.

In the apparatus constructed as described above, the gamma ray emitted to the periphery of the subject placed on the top plate is detected while rotating the detection portion, and based on only the projection data thereof. The RI distribution image in the region of interest is reconstructed and displayed on the display unit.

The "second device" includes, in addition to the components provided in the first device, an external gamma ray source for irradiating a gamma ray which can be discriminated from a gamma ray emitted from a subject, and an external gamma ray source. An absorption measuring section composed of an external gamma ray detecting section arranged opposite to each other, and the absorption measuring section is rotated around the top plate together with the above-mentioned detecting section and is emitted from a region of interest of the subject. There is a device that detects gamma rays and measures the degree of absorption of an external gamma ray source by the subject and the top plate.

In the apparatus thus constructed, the gamma rays emitted from the subject are detected, the projection data thereof is corrected based on the degree of absorption measured by the absorption measuring section, and the RI distribution at the region of interest is detected. The image is reconstructed and displayed on the display unit.

[0006]

By the way, in the apparatus for reconstructing a tomographic image of only the head of the subject, the head holding portion of the top plate can be made of carbon fiber which absorbs less gamma rays. Even if the influence of absorption is neglected, even if the tomographic image is reconstructed based on only the projection data as in the first apparatus, an RI distribution image with almost no artifacts can be obtained. However, even if a carbon fiber with low absorption is adopted, the influence of absorption cannot be ignored depending on its thickness, and an artifact is generated in the reconstructed RI distribution image. Further, the entire top plate is made of carbon fiber, which has not been performed mainly from the viewpoint of cost, and when there is a region of interest in the body trunk of the subject, absorption in this top plate part is about Since it reaches as high as 20%, gamma rays detected when the detector is located below the table or diagonally below the table are greatly affected by absorption, and the reconstructed RI distribution is affected by this effect. There is a problem that artifacts occur in the image. Therefore, the diagnosis made by observing this RI distribution image is adversely affected.

In the above-mentioned second apparatus, the degree of absorption by the subject and the top plate is measured, and the projection data is corrected by the degree of absorption, so that the reconstructed RI distribution image does not have an artifact, but However, since it is necessary to provide an absorption measuring unit, there is a problem that the cost of the device becomes very high. Further, since the gamma ray emitted from the subject is detected and the subject is irradiated with the external gamma ray, there is a problem that the amount of exposure of the subject increases. Further, since the external gamma ray source emits radiation, it is necessary to pay close attention to its handling and management.

The present invention has been made in view of such circumstances, and the projection data is corrected by a correction coefficient for correcting absorption caused by the top plate stored in advance, so that The amount of exposure can be reduced, the cost is low, the device is easy to handle and manage,
Moreover, it aims at providing the single photon ECT apparatus which can suppress an artifact.

[0009]

The present invention has the following configuration to achieve the above object. That is, the single-photon ECT device according to the present invention is emitted from a region of interest of the subject while rotating the top plate on which the subject to which the radioisotope RI has been administered is placed and the periphery of the top plate. Detecting means for detecting gamma rays, collecting means for collecting projection data of a region of interest of the subject via the detecting means, projection data storing means for storing the collected projection data, and the projection data storing means. Image reconstruction means for reconstructing the RI distribution image on the tomographic plane of the region of interest based on the projection data stored in, and display means for displaying the reconstructed RI distribution image. In a single-photon ECT device, an absorption coefficient measured over the entire circumference of a specific portion of the top plate that corresponds to just below the region of interest,
Between a correction coefficient storage unit that stores in advance a correction coefficient that is calculated based on the cross-sectional shape of the specific region and that corrects the projection data of the region of interest; and between the projection data storage unit and the image reconstruction unit. And a projection data correction unit that intervenes to correct the projection data by reading the correction coefficient from the correction coefficient storage unit and output the corrected projection data to the image reconstructing unit. Is.

[0010]

The operation of the present invention is as follows. First, the absorption coefficient is obtained in advance by measuring projection data, for example, by an external gamma ray source and an external gamma ray detection unit over the entire circumference of a specific portion of the top plate that is substantially directly below the region of interest of the subject. Then, based on the cross-sectional shape of the top plate and the obtained absorption coefficient, a correction coefficient for correcting the influence of absorption on the gamma rays emitted from the region of interest is calculated in advance and stored in the correction coefficient storage means. . Therefore, when obtaining the absorption coefficient, the subject is not irradiated with external gamma rays, so that it is possible to reduce the gamma ray irradiation amount to the subject, and it is necessary to equip the apparatus with each configuration for obtaining the correction coefficient. Therefore, the number of components of the device can be reduced.

When detecting gamma rays from the subject, the subject administered with the radioisotope RI is placed on the table, and the detecting means is rotated around the table, and the interest of the object is detected. Detect gamma rays emitted from the site. At this time, the gamma rays detected when the detection means is located below or obliquely below the top plate are absorbed and attenuated when passing through the top plate. The gamma rays detected by the detection means are collected as projection data by the collection means and stored in the projection data storage means. In other words, since the projection data stored in the projection data storage means is affected by absorption, if the RI distribution image is reconstructed by the image reconstruction means based only on this projection data, the reconstructed image will have artifacts. Will occur. Therefore, the projection data correction means, which is interposed between the projection data storage means and the image reconstruction means, reads the correction coefficient from the correction coefficient storage means and corrects the projection data, that is, a specific portion of the tabletop. By correcting the absorption due to and outputting the corrected projection data to the image reconstructing means,
The influence of absorption on the reconstructed RI distribution image can be suppressed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. A single photon ECT apparatus according to an embodiment will be described with reference to FIGS. 1 and 2. 1 is a block diagram showing a schematic configuration of the device, and FIG. 2 is a front view showing a gantry of this device.

In the figure, reference numeral 1 is a single photon ECT.
Device. This apparatus 1 includes a gantry 2 for detecting gamma rays emitted from a subject M administered with a radioisotope RI, and a bed 5 for placing the subject M thereon.
And a control device 10 for controlling them.

The gantry 2 has an opening 2a substantially in the center of its front surface, and a detector 2b for detecting gamma rays is built in the opening 2a. The detector 2b is driven to rotate around the rotation center P ₁ by the control device 10 described later. In the detector 2b, the range in the longitudinal direction of the subject M capable of detecting gamma rays is set as the imaging visual field d.

A bed 5 is arranged at a position separated from the front of the gantry 2 by a predetermined distance. The bed 5 is a base 5a fixed to the floor and configured to be vertically movable.
And a top plate 5b disposed above the top plate 5b, and an advance / retreat drive unit 5c for driving the top plate 5b in the horizontal direction from the base 5a to the gantry 2. Forward / backward drive unit 5
c has a position detector (not shown) (for example, an encoder), and when the controller 10 is driven back and forth, the feed amount is accurately output to the controller 10. The top plate 5b is formed with a shallow recess near the center in plan view so that the subject M can be mounted stably, and the cross-sectional shape is different at each position along the longitudinal direction. Also, this top plate 5
b includes various mechanisms (not shown) when being driven by the advancing / retreating drive unit 5c, and gamma rays emitted downward from the subject M are absorbed by these. In the following description, the direction away from the gantry 2 along the longitudinal direction is defined as the z-axis, with the end of the top plate 5b on the gantry 2 side as a reference. Therefore, the cross-sectional shape is
Different at each position on the z-axis.

The control device 10 has a console 11 for the photographer to give various instructions, a control unit 12 for controlling each component, and a projection for storing data on the detected gamma rays as projection data. A correction coefficient (described later) for correcting the influence of absorption by the data storage unit 13 and the top plate 5b.
And a projection data correction unit 15 that performs a process of correcting projection data with a correction coefficient,
The image reconstructing unit 16 reconstructs the RI distribution image based on the corrected projection data, and the monitor 17 for displaying the reconstructed RI distribution image.

The control unit 12 controls the forward / backward drive of the top plate 5b via the forward / backward drive unit 5c based on an instruction from the console 11, or drives the detector 2b to rotate about the rotation center P ₁ . Z based on the feed amount output from the advancing / retreating drive unit 5c
It has a function of associating the axial position information with the projection data output from the detector 2b and storing them in the projection data storage unit 13 and instructing the correction process by the projection data correction unit 15. The control unit 12 corresponds to the collecting means in this invention.

The projection data storage unit 13 is composed of a hard disk device or the like, and the control unit 12
Thus, the top plate 5b is advanced into the opening 2a, and at that time, the projection data collected while rotating the detector 2b around the subject M is stored in a manner described later. Also, the projection data instructed by the control unit 12 is output to the projection data correction unit 15. The projection data storage unit 13
Corresponds to the projection data storage means in the present invention.

The correction coefficient storage unit 14 will be described in detail later, but the gamma rays emitted from the subject M are subject to the top plate 5b.
Since the light is absorbed when passing through, the correction coefficient for correcting the influence of this absorption is stored in advance. The correction coefficient storage unit 14 corresponds to the correction coefficient storage means in the present invention.

The projection data correction unit 15 uses the correction coefficient stored in the correction coefficient storage unit 14 for the projection data stored in the projection data storage unit 13 [affected by absorption by the top plate 5b]. The correction process is performed. The projection data correction unit 15 corresponds to the projection data correction means in this invention.

The image reconstructing section 16 includes a projection data correcting section 1
It has a function of reconstructing the RI distribution image based on the projection data in which the influence of absorption is corrected by 5. The reconstructed RI distribution image is displayed on the monitor 17. In addition,
The image reconstructing section 16 and the monitor 17 correspond to the image reconstructing means and the display means in the present invention, respectively.

In the following description, the fixed coordinate system and the rotating coordinate system in the single photon ECT device 1 are defined as shown in FIG. That is, the vertical direction including the imaging center is the y axis, the horizontal direction orthogonal to the y axis and including the imaging center is the x axis, and the coordinates rotate with the rotation angle θ of the detector 2b. The axis corresponding to the y-axis is the t-axis, and the axis corresponding to the x-axis in the fixed coordinate system is the s-axis.

Next, with reference to FIGS. 3 and 4, a correction coefficient calculation device 50 for calculating the correction coefficient of the top plate 5b of the single photon ECT device 1 will be described. 3 is a block diagram showing a schematic configuration of the device, and FIG. 4 is a front view showing a gantry of this device.

The bed 5 is composed of the single photon E described above.
The CT device 1 is made of the same material and has the same geometrical dimensions, and defines the z-axis as described above. A gantry 55 for measuring an absorption coefficient is provided at a position separated from the bed 5 by a predetermined distance. The gantry 55 is provided with an external gamma ray source 55a at its upper part and a gamma camera 55b at its opposite position, and an absorption measuring section 55c constituted by these is rotationally driven around a rotation center P ₂ . The range in which gamma rays of the gamma camera 55b can be detected is set to the field of view d like the single-photon ECT device 1 described above, but if the absorption coefficient along the z-axis, which will be described later, can be measured, the field of view in both devices is particularly high. It does not have to match.

To calculate the correction coefficient, first, the measurement control unit 61 controls the advancing / retreating drive unit 5c and the gantry 55 on the basis of an instruction from the operator console 60, and [the subject M is not placed] in the sky. This is performed by storing the projection data in the projection data storage unit 62 while rotating the absorption measuring unit 55c while the plate 5b is fed to the gantry 55 side by a predetermined amount. In addition,
At this time, the z-axis position information calculated based on the feed amount output from the advancing / retreating drive unit 5c and the relative positional relationship between the gantry 55 and the bed 5 is stored in association with the projection data. The correction coefficient calculation unit 63 calculates the cross-sectional shape and the absorption coefficient of the top plate 5b along the z-axis by the method described later using the stored projection data, and based on these, calculates the correction coefficient along the z-axis. Have. The calculated correction coefficient along the z-axis is transferred to the correction coefficient storage unit 14 of the single photon ECT device 1. Alternatively, instead of transferring, for example, the correction coefficient may be written in a storage medium such as a magneto-optical disk having a large storage capacity, and the correction coefficient may be read by the single photon ECT device 1 side. Further, as the absorption measurement unit 55c of the correction coefficient calculation device 50,
An X-ray CT apparatus that can determine the degree of absorption of radiation may be used instead. The above-described calculation of the correction coefficient may be performed, for example, only by the manufacturer of the single photon ECT device 1, and need not be performed by the user of the device 1.

Incidentally, each coordinate system of the correction coefficient calculation device 50 has the same coordinate system as that of the above-described single photon ECT device 1.
Each of the fixed coordinate system and the rotating coordinate system is defined as shown in FIG. That is, it is a coordinate that rotates in accordance with the rotation angle θ of the gamma camera 55b, where the vertical direction including the photographing center is the y-axis, and the horizontal direction including the photographing center is the x-axis.
The axis corresponding to the y axis in the fixed coordinate system is the t axis, and the axis corresponding to the x axis in the fixed coordinate system is the s axis.

Next, the calculation of the correction coefficient by the device 50 will be described with reference to FIGS. The absorption coefficient is μ (cm ⁻¹ ) and the thickness of the absorber, that is, the top plate 5b is L (cm) (see FIG. 5), and the external gamma ray source 55a
If the count value of the gamma rays and I _O, the count value after receiving absorbed by the top plate 5b was I, the count value after the absorption is expressed by the following equation (1). I = I _O exp (−μL) ………… (1)

Therefore, the count value before being absorbed is expressed by the following equation (2). I _O = I exp (μL) ………… (2)

By the way, the top plate 5b that absorbs gamma rays is
Since the shapes and materials are different in the three directions of the x, y, and z axes, the absorption coefficient μ is also different in the three directions. Therefore, the absorption coefficient μ must be replaced by the absorption coefficient μ (x, y, z). Therefore, the correction coefficient is expressed by a function of the horizontal axis coordinate s and the rotation angle θ in the rotation coordinate system, and the top plate 5b is a minute area (pixel) corresponding to the resolution of the gamma camera 55b.
The number of pixels through which gamma rays penetrate when divided into n is n, and the distance when gamma rays penetrate each pixel is ΔL.
(Cm), the correction coefficient is obtained by calculating the sum of each pixel,

[0030]

(Equation 1)

## EQU1 ##

The correction coefficient calculation unit 63 calculates the absorption coefficient μ (x, y, z) from the above formula based on the projection data stored in the projection data storage unit 62, and also the cross section of the top plate 5b. Calculate the shape. Calculation of this cross-sectional shape is
It can be calculated by extracting the contour of the reconstructed image based on the projection data, but it may be calculated based on the geometrical dimension in design. Then, for each of the s-axis and the rotation angle θ of the rotating coordinate system, the path through which the gamma ray passes through the top plate 5b is calculated, the transmission path ΔL included in each pixel is calculated, and finally the absorption coefficient μ (x, y ，
The correction coefficient f (s, θ) can be calculated using z).

Next, a specific example will be described with reference to FIG. In addition, in this figure, for convenience of explanation, the top plate 5b is a
The pixel is divided into × 3 pixels PX1 to PX9, and the gamma rays (dotted lines in the figure) represent pixels PX3, PX2, PX5, and PX7.
Shall be transmitted. In this case, the correction coefficient f (s,
θ) is expressed by the following expression (4) from the above expression (3). f (s, θ) = exp (μ3 ΔL3) ・ exp (μ2 ΔL2) ・ exp (μ5 ΔL5) ・ exp (μ7 ΔL7) ……… (4)

## EQU1 ## Then, the correction coefficient is calculated for all s and θ, and further calculated for each position on the z axis. These calculated correction coefficients are stored in the correction coefficient storage unit 14.

It should be noted that when collecting the projection data, FIG.
As shown in, the top plate 5b is first fed into the visual field width d, and then is controlled to be fed by the visual field width d. Therefore, in the z-axis direction of the top plate 5b, Z
₁ , Z ₂ , ..., The correction coefficients calculated as described above are stored in the correction coefficient storage unit 1 for each rotation angle θ.
Stored in 4. FIG. 8 schematically shows this storage mode. In this figure, the correction coefficient f (s, θ) for each rotation angle θ is shown in the front direction from the paper surface. Note that, as is apparent from FIG. 5, gamma rays do not pass through the top plate 5b depending on the rotation angle θ, and in such a case, the correction coefficient f (s, θ) = 1.

In this way, since the correction coefficient is calculated in advance and stored in the correction coefficient storage unit 14, the single photon E
The CT device 1 does not need to include the absorption measurement unit 55c.
Therefore, the number of components of the device can be reduced, and the device cost can be reduced accordingly. Also,
Since the external gamma ray source 55a, which is a radiation source, is not provided, the handling and management of the device becomes easier as compared with the case where it is provided. Furthermore, the external gamma ray source 5 is applied to the subject.
Since the gamma ray from 5a is not irradiated, it is possible to reduce the exposure dose of the subject.

Next, referring to the flowchart of FIG.
Imaging of the RI distribution image by the above-described single photon ECT device 1 will be described. The region of interest of the subject M will be represented by a region R as shown in FIG.

First, in step S1, the region of interest is sent into the field of view for imaging. Specifically, the top plate 5b is fed into the opening 2a of the gantry 2 via the advancing / retreating drive mechanism 5c so that the region of interest R of the subject M is located within the imaging visual field d (see FIG. 10). In this case, since the length of the region of interest R in the body axis direction is longer than the imaging field of view d, the imaging is performed in two steps as described below. At this time, within the field of view d, from the position Z _a to the position Z on the top plate 5b.
_{Let b} be located.

In step S2, the projection data is detected by the detector 2
It is collected via b and is stored in the projection data storage unit 13 in association with the z-axis position information. A schematic view of the projection data stored at this time is shown in FIG. That is, projection data D ₁ based on gamma rays emitted from the site of interest R in the position Z _a of the top plate 5b in the range of Z _b (z-axis position information) is stored for each rotation angle theta. The projection data D ₁ is affected by absorption by the top plate 5b.

In step S3, the process branches depending on whether or not the data collection of the region of interest is completed. here,
Since the region of interest R is not within the imaging field of view d, the process returns to step S1 and the next region of interest R is sent into the imaging field of view d. At this time, the top plate 5b may be fed so that the photographed regions of interest overlap. Then, shooting is performed as described above. As a result, a schematic diagram of the projection data D ₂ stored in the projection data storage unit 13 is shown in FIG.
1 (b). Like the projection data D _1, this is also influenced by the absorption of the top plate 5b.

The acquisition of the projection data D ₁ and D ₂ based on the gamma rays emitted from the region of interest R is completed by these _two imagings, and the process proceeds to step S4. In step S4, the projection data correction unit 15 reads out the correction coefficient corresponding to each projection data D ₁ and D ₂ from the correction coefficient storage unit 14. Since the processing performed on each projection data D ₁ and D ₂ is the same, only the projection data D ₁ will be described below.

As shown in FIG. 12, the correction coefficient storage unit 14
The correction coefficient corresponding to the projection data D ₁ is read out from the correction coefficients stored in the table 1. However, the correction coefficient storage unit 14 stores all the correction coefficients on the z-axis of the top plate 5b (in the gantry 2). Of the projection data D ₁ is stored because the correction coefficient of the portion (which is sent into the imaging field of view d) is stored.
Only the portion corresponding to the position on the axis (specific portion) needs to be read. That is, the projection data D ₁ is Z on the z-axis.
Since it is the data of the specific part from _a to Z _b , only that part of the correction coefficient is read. Then, each of the projection data D ₁ for each rotation angle θ is multiplied by the correction coefficient for each rotation angle θ to perform the correction calculation process (step S5).
This makes it possible to correct the influence of absorption by the top plate 5b (positions Z _a to Z _b ) received by the projection data D ₁ obtained from the region of interest R for each rotation angle θ (this correction was performed). The projection data D ₁ will be referred to as projection data D ₁ ′). This makes it possible to regard the projection data collected via the top plate 5b as the projection data collected in the ideal state, which was collected without the top plate 5b. In this way, the projection data D ₂ is similarly corrected by multiplying it by the corresponding correction coefficient, and thus the influence of absorption by the top plate 5b (positions Z _b to Z _c ) can be similarly corrected. .

The corrected projection data D ₁ and D ₂ are output to the image reconstructing section 16 in step S6. The image reconstructing unit 16 reconstructs an RI distribution image of a desired tomographic plane based on a photographer's instruction from the console 11 based on the corrected projection data D ₁ and D ₂ . The reconstructed RI distribution image is output to the monitor 17 and displayed. The RI distribution image on the desired tomographic plane displayed on the monitor 17 is an image in which artifacts are suppressed because the influence of absorption by the top plate 5b is corrected. In addition, in the image reconstruction unit 16, the subject M
The RI distribution image may be reconstructed after processing is performed so as to correct the effect of gamma ray absorption by the region of interest R.

In order to ensure that the region of interest R of the subject M is located at a specific region of the top plate 5b, for example, the region of interest must be located within the positions Z _a to Z _c on the z axis of the top plate 5b in FIG. When the subject M is placed so that R is located,
It is not necessary to store the correction coefficients for all positions on the top plate 5b on the z-axis in the correction coefficient storage unit 14, and only the correction coefficients within the range need be stored. The storage capacity can be reduced.

In the above description, the top plate 5b is used.
The correction coefficient at each position was calculated along the longitudinal direction (z axis) and stored in the correction coefficient storage unit 14.
For example, when the top plate 5b has a uniform cross-sectional shape and the material thereof along the longitudinal direction, the absorption coefficient is the same at any position on the z-axis, so that the correction coefficient only for a specific part of the top plate 5b. It is only necessary to calculate As a result, the storage capacity of the correction coefficient storage unit 14 can be further reduced. Further, by doing so, the number of times the projection data correction unit 15 accesses the correction coefficient storage unit 14 can be reduced, so that the time required for the correction calculation processing of the projection data can be shortened. Of course, in the case of such a top plate, the specific portion may be any position on the top plate 5b.

[0046]

As is apparent from the above description, according to the present invention, the correction coefficient for correcting the projection data is stored in advance in the correction coefficient storage means to obtain the correction coefficient. It is possible to reduce the amount of exposure of the subject and the cost of the device because the device configuration can be simplified by that much, and since there is no radiation source, handling and management of the device is possible. Can be facilitated.

Further, since the influence of absorption caused by a specific portion of the top plate can be corrected by the correction coefficient, it is possible to suppress the occurrence of artifacts in the RI distribution image reconstructed based on the corrected projection data. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a single photon ECT apparatus according to an embodiment.

FIG. 2 is a front view of a gantry of a single photon ECT device.

FIG. 3 is a block diagram showing a schematic configuration of a correction coefficient calculation device.

FIG. 4 is a front view of a gantry of the correction coefficient calculation device.

FIG. 5 is a diagram for explaining a method of calculating a correction coefficient.

FIG. 6 is a diagram for explaining a method of calculating a correction coefficient.

FIG. 7 is a diagram for explaining a method of calculating a correction coefficient.

FIG. 8 is a schematic diagram showing calculated correction coefficients.

FIG. 9 is a flowchart showing capturing of an RI distribution image.

FIG. 10 is a diagram for explaining the capturing of an RI distribution image.

FIG. 11 is a schematic diagram showing collected projection data.

FIG. 12 is a schematic diagram showing a process of correcting projection data.

[Explanation of symbols]

 1 ... Single photon ECT device 2 ... Gantry 2b ... Detector 5 ... Bed 5b ... Top plate 13 ... Projection data storage unit 14 ... Correction coefficient storage unit 15 ... Projection data correction unit 16 ... Image reconstruction unit 17 ... Monitor 50 ... Correction Coefficient calculation device 55 ... Absorption coefficient measurement gantry 55a ... External gamma ray source 55b ... Gamma camera 55c ... Absorption measurement unit M ... Subject R ... Region of interest

Claims (1)

[Claims] 1. A top plate on which a subject to which the radioisotope RI has been administered is placed, and detection means for detecting gamma rays emitted from a region of interest of the subject while rotating around the top plate. Collecting means for collecting projection data of the region of interest of the subject through the detecting means, projection data storing means for storing the collected projection data, and projection data stored in the projection data storing means On the basis of,
A single photon ECT comprising: an image reconstruction unit that reconstructs an RI distribution image on the tomographic plane of the region of interest; and a display unit that displays the reconstructed RI distribution image.
In the device, with respect to a specific portion of the top plate that is substantially directly below the region of interest, the projection data of the region of interest calculated based on the absorption coefficient obtained over the entire circumference and the cross-sectional shape of the specific region. Is interposed between the correction coefficient storage means for storing in advance a correction coefficient for correcting the projection data, the projection data storage means and the image reconstruction means, and reads the correction coefficient from the correction coefficient storage means to correct the projection data. And a projection data correction means for outputting the corrected projection data to the image reconstructing means, the single photon ECT apparatus.