WO2016162962A1

WO2016162962A1 - Radiation imaging device

Info

Publication number: WO2016162962A1
Application number: PCT/JP2015/060905
Authority: WO
Inventors: 敦郎鈴木; 崇章石津; 渉竹内; 上野　雄一郎
Original assignee: 株式会社日立製作所
Priority date: 2015-04-08
Filing date: 2015-04-08
Publication date: 2016-10-13

Abstract

Provided is a high-resolution radiation imaging device using a pixel-type detector. The present invention is a radiation imaging device having a collimator for limiting incident radiation, a detector panel provided with a plurality of detection elements for detecting the radiation having passed through the collimator, and a gantry for supporting the detector panel, wherein the collimator has a plurality of through holes delimited by septa, the detector panel is such that a plurality of modules are aligned that are each provided with a plurality of detection elements, and the thickness T2 of the septa positioned between the plurality of modules is thicker than the thickness T1 of the septa within the modules.

Description

Radiation imaging device

The present invention relates to a radiation imaging apparatus for imaging an incident radiation distribution and a nuclear medicine diagnosis apparatus using the radiation imaging apparatus.

There is a single photon emission computed tomography (SPECT) using a gamma camera as an application of radiation measurement equipment in the field of nuclear medicine. SPECT measures the distribution of compounds containing radioisotopes and provides an image of the tomographic plane. In the conventional SPECT apparatus, a combination of a scintillator made of a single crystal and a plurality of photomultiplier tubes is the mainstream. These SPECT devices obtain the position of radiation by the center of gravity calculation. However, this method has a limit of about 10 mm resolution and is insufficient for use in clinical settings. Therefore, a SPECT apparatus with higher resolution is being sought.

In recent years, pixel-type detectors have been developed as having higher resolution. Pixel type detectors include those composed of scintillators and those composed of semiconductors. In either case, the position signal is acquired in units of small detection elements, that is, in units of pixels. Therefore, the intrinsic resolution of the detector is determined by the pixel size and performs spatially discrete measurements. Pixels with a pixel size of 1 or 2 mm have also been developed, achieving a resolution of 10 mm or less, which has been greatly improved.

Also, the reconstruction method of the fault plane has been developed and improved, greatly contributing to the improvement of resolution. Until now, the filter-corrected back projection method (filtered back-projection method: FBP method) and the successive approximation method without resolution correction (Maximum-likelihood-expectation-maximization: MLEM, -Ordered-subset-expectation-maximization: OSEM etc.) have been used. In recent years, successive approximation methods with resolution correction have been developed. This method can be reconfigured taking into account physical factors such as the geometry of the collimator and detector, the attenuation of gamma rays by the subject, and scattered radiation. Therefore, a more accurate image can be provided.

Special table 2008-506945

As an example of providing a high-resolution image by taking advantage of the high intrinsic spatial resolution of the pixel-type semiconductor detector, Patent Document 1 discloses that the length of the detection element at the end of the module is shortened by reducing the lateral length of the detection element. A method for keeping the pitch the same is disclosed. However, it is necessary to make the detection element small, and the sensitivity is lowered at the end of the module.

An object of the present invention is to provide a high-resolution radiation imaging apparatus using a pixel type detector.

In order to solve the above problems, a radiation imaging apparatus of the present invention includes a collimator that limits incident radiation, a detector panel that includes a plurality of detection elements that detect radiation that has passed through the collimator, and the detector panel. A gantry to support the collimator, the collimator having a plurality of through-holes separated by a septa, and the detector panel having a plurality of modules each having a plurality of detection elements, The thickness T2 of the septa located between the modules is thicker than the thickness T1 of the septa located in the module.

According to the present invention, it is possible to provide a high-resolution radiation imaging apparatus using a pixel type detector.

FIG. 2 is a diagram showing a module 210 and a collimator 206 of a detection element 201. FIG. 5 is a diagram showing a state in which a positional deviation has occurred between a detection element 201 and a collimator 206. 1 is a diagram showing a SPECT device 1 (gamma camera). FIG. By setting a gap 211 between the modules 210 and setting the pitch of the through-holes 207 of the collimator 206 across the gap 211 to a length corresponding to the gap 211, the positional deviation between the detection element 201 and the through-holes 207 of the collimator 206 is reduced. It is the figure which showed a mode that there is no. FIG. 5 is a diagram showing a state where gamma rays 202 pass through a scepter 208 that straddles a gap 211 between modules 210. FIG. 6 is a diagram showing a state in which gamma rays 202 are generated from a point source 212 and a point response function. FIG. 5 is a diagram showing a case where a gap 211 between modules 210 is set in the x direction and the y direction. FIG. 6 is a diagram showing a case where a gap 211 between modules 210 is set in the y direction. FIG. 5 is a diagram showing a case where four detection elements 201 are included in one through hole 207 of the collimator 206. FIG. 3 is a diagram showing a detector panel 11 configured by arranging a plurality of collimator / detector modules 213.

In the SPECT apparatus, a collimator is mounted in front of the detector in order to limit the incident direction of gamma rays. In the example of the detector shown in FIG. 1, the collimator 206 includes a septa 208 and a through hole 207. In the SPECT apparatus using a pixel type detector, the positions of the through hole 207 and the detection element 201 of the collimator 206 are a pair. It corresponds to one. In order to provide a high-resolution image by taking advantage of the high intrinsic spatial resolution of the pixel type semiconductor detector, high accuracy is required for alignment of the through-hole 207 of the collimator 206 and the detection element 201.
There are two types of SPECT devices: a whole-body machine with a wide field of view capable of whole-body imaging, a heart / head combined machine for the heart and head, and a dedicated heart machine for only the heart. At present, as a commercial SPECT apparatus using a pixel type semiconductor detector, there is only a cardiac dedicated machine with a small imaging field of view, and there is no whole-body machine with a large field of view. The reason is that it is difficult to create a large-area panel in which the detection elements are mounted at an equal pitch. This is because a panel using a semiconductor detector is generally mounted in units of modules in which a plurality of detection elements are arranged, and there is no need to eliminate gaps between modules, that is, gaps between detection elements at the end of the module. This is because it is difficult. Therefore, as the number of modules to be mounted increases as in the whole body machine, the position shift between the detection element and the through hole of the collimator due to the gap between the modules becomes more significant, resulting in a decrease in sensitivity and artifacts. FIG. 2 is an arrangement relation diagram of the collimator 206, the through hole 207, the septa 208, the detection element 201, the module 210, and the gap 211, showing the state of this positional deviation.

As a prior art in which the pitch of the through holes 207 of the collimator 206 and the pitch of the detection element 201 are the same, Patent Document 1 discloses that the detection element 201 is shortened in the lateral direction at the end of the module 210 by detecting A method of keeping the pitch of 201 the same is disclosed. However, a reduction in sensitivity at the end of the module 210 occurs by making the detection element 201 small.

The radiation imaging apparatus of the embodiment described below has a module 210 composed of a plurality of detection elements 201 as means for solving the above-mentioned problems, and one or a plurality of modules composed of a plurality of the modules 210 It has a detector panel 11, between the module 210 has a value G of the gap 211 between the module 210, the detecting element 201 are arranged at a pitch D ₁ in said module 210, the gaps between the modules 210 the detecting element 201 across the 211 are arranged at a pitch D _2, the pitch D ₂ is larger than the pitch D _1, has a collimator 206 having a plurality of through-holes 207 and septum 208, the collimator 206 radiation It is disposed on the front surface that is the direction of incidence on the detector panel 11, and one through hole 207 includes N detection elements 201 in a one-dimensional direction, and the through hole 207 is formed in the module 210. Are arranged at a pitch H ₁ in the region corresponding to the detecting element 201, the pitch of the through hole 207 across the gap 211 between the modules 210 are arranged in H _2, the pitch H ₁ relationship N × D ₁ It met, wherein the septum 208a in a region corresponding to the detecting element 201 in the module 210 are arranged at a pitch S _1, septa 208a of the septum 208b and its neighboring across the gap 211 between the module 210 pitch S ₂ The pitch S ₂ is longer than the pitch S ₁ , and the thickness of the septa 208a in the region corresponding to the detection element 201 in the module 210 is a thickness T ₁ , the thickness of the septum 208b across the gap 211 between the thickness T _2, the detector panel 11 detects the radiation while rotating around the subject, the as geometry of the sensing element 201 and the collimator 206 Mogi The value G of the gap 211 between Lumpur 210, pitch D _1, D ₂ of the detecting element 201, the pitch H _1, H ₂ of the through hole 207, the pitch S _1, S ₂ of the septa 208, the septum 208 The radiation imaging apparatus has means for imaging the radiation generation position and density by an image reconstruction method incorporating a point response function in consideration of the thicknesses T ₁ and T ₂ .

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In the following examples, an example of a SPECT apparatus is used as a radiation imaging apparatus. First, the configuration and image reconstruction of the SPECT apparatus 1 of the present embodiment will be described. Next, a method that enables high-resolution whole-body SPECT imaging using a pixel-type semiconductor detector by performing alignment of the through-hole 207 of the collimator 206 と and the detection element 201 with high accuracy will be described.

First, the configuration of the SPECT apparatus 1 will be briefly described. As shown in FIG. 3, the SPECT apparatus 1 includes a gantry 10, detector panels 11a and 11b, a data processing device 12, a display device 13, and the like. Subject 15 is administered a radioactive drug, for example, a drug containing ^99m Tc with a half-life of 6 hours. A gamma ray 202 emitted from ^99m Tc in the body of the subject 15 placed on the bed 14 is detected by the detector panel 11 supported by the gantry 10 to capture a tomographic image.

The detector panel 11 includes a collimator 206 and a detection element 201. The collimator 206 has a function of selecting gamma rays 202 emitted from the body of the subject 15 and allowing only gamma rays 202 in a certain direction to pass therethrough. The gamma ray 202 that has passed through the collimator 206 is detected by the detection element 201. The detector panel 11 includes an application specific integrated circuit (Application ASIC) 205 for measuring a detection signal of the gamma ray 202. As the detection signal of the gamma ray 202, the ID of the detection element 201 that detected the gamma ray 202, the peak value of the detected gamma ray 202, and the detection time are input to the ASIC 205 via the detector substrate 203 and the ASIC substrate 204. A light shielding / gamma ray / electromagnetic shield 209 made of iron, lead or the like surrounds the detection element 201, the detector substrate 203, the ASIC substrate 204, the ASIC 205, and the collimator 206, and blocks light, gamma ray 202, and electromagnetic waves. The data processing device 12 includes a storage device and a tomogram information creation device (not shown). The data processing device 12 captures packet data including the measured peak value of the gamma ray 202, detection time data, and detector (channel) ID, and generates a planar image or converts it into sinogram data to generate tomographic image information. Is displayed on the display device 13.

The detector panel 11 is movable in the radial direction, rotational direction, and tangential direction of the gantry 10. At the time of tomographic imaging, the detector panel 11 rotates around the gantry mounting portion and detects the gamma rays 202 generated from the radiopharmaceutical accumulated in the tumor in the body of the subject 15 to identify the position of the tumor.

Next, image reconstruction executed by the data processing apparatus will be described. When the detector panel 11 is at an angle with respect to the measurement object, the count number y _i of the detection element i is λ _j as the count number of the reconstructed pixel j.

It becomes. Here, C _ij represents the probability of being detected by the detection element i. From the above equation, images are reconstructed using successive approximation reconstruction methods (MLEM, OSEM, etc.). It is possible to correct the spatial resolution by incorporating the point response function of the detection element 201 into the successive approximation image reconstruction. The point response function is a probability that the detection element 201 detects the radiation generated from the point source 212, and is equal to the detection probability C _ij in the equation (1). By using this point response function, a more accurate image can be reconstructed from a successive approximation reconstruction method such as MLEM or OSEM.

Next, in the SPECT device 1 using the detector panel 11 in which pixel type semiconductor detectors are mounted in units of modules 210, the through hole 207 of the collimator 206 and the detection element 201 can be aligned with high accuracy, and the sensitivity decreases. A method for suppressing artifacts and providing a high-resolution image will be described. In general, when the detector panel 11 is configured by mounting the module 210 unit, it is difficult to eliminate the gap 211 between the modules 210. Therefore, the position of the through hole 207 of the collimator 206 and the position of the detection element 201 as shown in FIG. Deviation occurs. Therefore, in this embodiment, as shown in FIG. 4, a distance G is set as a gap 211 between the detection elements 201 at the ends of the module 210 in the x direction. The pitch of the detection elements 201 in the module 210 is set to D ₁ , and the pitch between the detection elements 201 at the ends of the module 210 is set to D ₂ . Here, the pitch D ₂ by the gap 211 between the module 210 is longer than the pitch _{_{_{D 1, D 2 = D 1}}} + relationship G is established.

Pitch septum 208a of module 210 is a S _1, the pitch of the septum 208b and septa 208a of the adjacent across the gap 211 between the module 210 and S _2. Here, a pitch S ₂ by the gap 211 between the module 210 is longer than the pitch _{_{_{S 1, S 2 = S 1}}} + G / 2 relationship is established. Thus, by considering the gap 211 between the module 210 to the pitch S _2, it is possible to align the through hole 207 of the collimator 206 detector elements 201 with high accuracy. The thickness of the septum 208a of module 210 is set to T _1, the thickness of the septum 208b across the gap 211 between the module 210 and T _2. In this case, the pitch S ₂ is longer than the pitch S _1, by setting the thickness of the septum 208b for the same as T _1, penetration of the gamma ray 202 is increased, which may affect the image quality. Therefore, it is desirable to set the thickness of the septa 208b so that the penetration of the gamma ray 202 does not affect the image. For example, as shown in FIG. 5, the hole length of the collimator 206 is L, the length of the gamma ray 202 passing through the apexes P ₁ and P ₂ of the septa 208a crossing the septa 208b is A, and the attenuation coefficient of the gamma ray 202 with respect to the collimator is Assuming that μ, the thickness T ₂ of the septa 208b that satisfies the expressions (2) and (3) for which the penetration probability B is 5% or less is used.

The pitch of the through holes 207 in the area corresponding to the detection element 201 in the module 210 is H _1, and the pitch of the through holes 207 across the gap 211 between the modules 210 is H ₂ . In this embodiment, in order to align the through hole 207 of the detecting element 201 and the collimator 206, the pitch D ₁ and the pitch H ₁ is equal. The pitch H ₂ is expressed by H ₂ = S ₁ + G / 2 + T ₂ / 2-T _1/2 .

In this embodiment, the pitch of the detection elements 201 in the modules 210 and the pitch of the through holes 207 of the collimator 206 are made equal. On the other hand, the gap 211 is set between the modules 210, so The pitch of the detection elements 201 is different from the pitch of the detection elements 201 in the module 210. Therefore, if normal image reconstruction is executed, artifacts will occur in the image. Therefore, as shown in FIG. 6, the detection probability when the point source 212 is measured in the arrangement of the collimator 206 and the detection element 201 of the present embodiment, that is, the point response function is obtained in the entire region, and the successive approximation image reconstruction method By using the point response function obtained for the detection probability at, the value G of the gap 211 between the modules 210, the pitches D ₁ and D _{2 of} the detection element 201, the pitches H ₁ and H ₂ of the through holes 207 of the collimator 206, and the septa The thicknesses T ₁ and T _{2 of} 208 and the hole length L of the collimator 206 can be modeled, and no artifact is generated in the acquired image. Note that the image reconstruction method can be applied to both SPECT imaging and planar imaging.

Alternatively, since the projected image of the gamma ray 202 acquired in the present embodiment is expressed with a nonuniform pitch, the projected image is assigned to a coordinate system with a uniform pitch of the detected position using interpolation processing. Thus, it is also possible to create a projection image when the detection elements 201 are arranged at a uniform pitch.

Up to this point, the arrangement of the detection element 201 in the x direction and the through hole 207 of the collimator 206 has been described. However, as shown in FIG. 7, the detector panel in which the gap 211 between the modules 210 exists in both the x direction and the y direction. The concept of the present embodiment may be applied to 11, or may be applied to the detector panel 11 in which the gap 211 between the modules 210 exists only in one direction as shown in FIG.

In this embodiment, one detection element 201 corresponds to one through hole 207 of the collimator 206. However, as shown in FIG. 9, N _x pieces in the x direction and N in the y direction correspond to one through hole 207. _y detection elements 201 may be included. Here, FIG. 9 shows a case where N _x = N _y = 2. At this time, a relationship of H ₁ = D ₁ × N _x = D ₁ × N _y is established between the pitch D ₁ of the detection elements 201 and the pitch H ₁ of the through holes 207 in the module 210. Furthermore, the number of N _x and N _y need not be the same, and may be different.

The collimator 206 of the present embodiment is an integral collimator 206, and the collimator 206 can be easily separated from the detector panel 11. Further, since the through holes 207 are arranged in consideration of the gap 211 between the modules 210, the collimator 206 and the detection element 201 can be easily aligned. Therefore, it is possible to provide an image with high diagnostic accuracy by replacing the collimator 206 with the optimum performance according to the imaging purpose.

As a modification, as shown in FIG. 10, the system of the present invention is used by using a detector panel 11 configured by arranging a plurality of collimator / detector modules 213 each having a collimator 206 mounted on a module 210 basis. May be configured. At this time, the thickness of the septa 208b across the gap 211 between the collimator / detector module 213 is set so that the influence of penetration can be reduced as described above.

The radiation imaging apparatus according to each embodiment described above includes a collimator 206 that limits incident radiation, a detector panel 11 that includes a plurality of detection elements 201 that detect radiation that has passed through the collimator 206, and a detector panel 11. The collimator 206 has a plurality of through-holes 207 separated by a septa 208, and the detector panel 11 includes a plurality of modules 210 each having a plurality of detection elements 201. is there.

Since the thickness T _{2 of the} septa 208 located between the modules 210 is thicker than the thickness T _{1 of} the septa located in the module 210, high-accuracy imaging can be performed while suppressing the influence of the gap between the modules 210. It is. Further, as in each embodiment, the pitch S ₂ between the septa 208 corresponding to the end of the module 210 and the other septa 208 and the pitch S ₁ between the septa 208 not corresponding to the end of the module 210 are more equal. preferable.

With such a configuration, high-resolution whole-body SPECT imaging using a pixel type semiconductor detector can be performed by positioning the through hole 207 of the collimator 206 and the detection element 201 with high accuracy.

1 SPECT device (gamma camera)
10 Gantry
11a, 11b detector panel
12 Data processing equipment
13 Image display device
14 beds
15 Subject
16 axis of rotation
17 Protective material
201 sensing element
202 Gamma rays
203 Detector board
204 ASIC board
205 Integrated Circuit (ASIC)
206 Collimator
207 Through hole
208 Septa
208a Septa (area in the module)
208b Septa (module end)
209 Shading, gamma rays, electromagnetic shielding
210 modules
211 gap
212 Point source
213 Collimator / detector module

Claims

A collimator to limit the incident radiation;
A detector panel comprising a plurality of detection elements for detecting radiation that has passed through the collimator;
A gantry that supports the detector panel;
The collimator has a plurality of through holes separated by a septa;
The detector panel is a plurality of modules each having a plurality of detection elements,
A radiation imaging apparatus in which a thickness T 2 of a septum located between the plurality of modules is thicker than a thickness T 1 of a septa located in the module.
The radiation imaging apparatus according to claim 1,
The pitch S2 of between the septum and the other of said septa corresponding to the end of the module, the pitch S 1 is equal to a radiation imaging apparatus between septa each other do not correspond to the end of the module.
The radiation imaging apparatus according to claim 1,
When the gap between the modules is G, the pitch of the septa is S 1 , the hole length of the collimator is L, and the attenuation coefficient of radiation with respect to the collimator is μ

The radiation imaging device characterized by satisfying the relationship:
The radiation imaging apparatus according to claim 1,
Radiation by an image reconstruction method incorporating a point response function that takes into account all the gaps between the modules, the pitch of the septa, the pitch of the through holes, the thickness of the septa, the hole length of the collimator as geometric parameters. A radiation imaging apparatus having means for imaging the generation position and density of the.
The radiation imaging apparatus according to claim 1,
A radiation imaging apparatus having means for imaging a radiation generation position and density using a projection image having a uniform detection element pitch created by assigning to a coordinate system having a uniform detection element pitch by interpolation processing.
The radiation imaging apparatus according to claim 1,
The detector panel is a radiation imaging apparatus in which a plurality of the modules are two-dimensionally arranged in the x direction and the y direction.
The radiation imaging apparatus according to claim 1,
The detector panel is a radiation imaging apparatus in which a plurality of modules are arranged in the x direction and a single two-dimensionally arranged in the y direction.
The radiation imaging apparatus according to claim 1,
The number of the collimators is the same as that of the modules.
The radiation imaging apparatus according to claim 1,
A radiation imaging apparatus in which a plurality of the detection elements are positioned for each of the through holes.