KR101175697B1 - Method of improving LCE and linearity of relationship between gamma-ray's energy and the number of photons impinged on photosensor array in PET module - Google Patents

Abstract

The present invention relates to a method for improving linearity between photon collection efficiency (LCE) in a PET module and the number of incident gamma-ray energy versus the number of electrons output from the photovoltaic array. A PET module comprising a light guide for spreading a light into an optoelectronic device array, and an optoelectronic device array for converting the light passing through the light guide into an electrical signal, wherein the light is located between the scintillation crystal and the optoelectronic device array. The thickness of the guide is increased, and the size of the microcells constituting the photovoltaic device array is increased, and the thickness of the light guide despite the phenomenon that the nonlinearity increases with the GAPD having the large area microcells. Photons are incident on a large number of GAPDs, resulting in high energy and high It may provide haeneung information at the same time, improve the non-linearity.

Description

Method of improving LCE and linearity of relationship between gamma-ray's energy and the number of photons impinged on photosensor array in PET module}

The present invention relates to a PET detector module, and more particularly, to a method of improving linearity between photon collection efficiency in a PET module and incident gamma ray energy versus the number of electrons output from an optoelectronic array.

Positron emission tomography (PET), one of the nuclear medical imaging devices, is a representative imaging technology in the field of nuclear medicine that can image biochemical changes in the human body.

Among the methods of constructing the PET module, the 1: 1 scintillation crystal-photo sensor coupling method can maintain the light loss to a minimum, but there is a difficulty in constructing a PET detector that provides high resolution information.

Among the methods of constituting the PET detector module, the method using light sharing is the most easily used to construct a PET detector that provides high resolution information, but energy information is lost due to the light loss generated in the light distribution process. Have a downside

Until now, PET module that can provide high resolution and high energy information at the same time has not been developed.We try to reduce energy information loss as much as possible while obtaining high resolution information using thinner quartz. I'm doing it.

On the other hand, GAPD (Geiger-mode avalanche photodiode) used in PET detector module is generally two-dimensional array of hundreds or thousands of microcells in 1 mm ² ~ 9 mm ² cross-sectional area, each microcell operates in Geiger mode It consists of an avalanche photodiode, a suppression resistor, and a bias voltage input part. Each microcell acts as an on-off switch for incident photons, and the total number of microcells that are ON reflects the number of photons absorbed and the incident gamma ray energy. However, since the number of micro cells is finite, the linearity has a considerable deviation when the number of photons converted from gamma rays to visible light is relatively larger than the number of micro cells.

A widely used method for solving such a nonlinearity is to construct a PET detector module using GAPD having a large number of microcells, that is, a small area of microcells. However, GAPD having a small area of microcells has a disadvantage in that the effective sensor area is inevitably reduced due to the physical structure, thereby reducing the light detection efficiency and gain.

Therefore, there is a need for a PET detector module that can provide high energy and high resolution information and improve nonlinearity by using GAPD having a large area of microcells.

Accordingly, an object of the present invention is to provide a method of improving linearity between photon collection efficiency and incident gamma ray energy in the PET detector module versus the number of electrons output from the photoelectric device array.

In order to achieve the above object, the present invention provides a flash crystal for generating a flash from gamma rays, a light guide for spreading the flash from the flash crystal to the photoelectric element array, and converting the flash light passing through the light guide into an electrical signal. A PET module comprising an optoelectronic array, comprising: increasing the thickness of a light guide located between the scintillation crystal and the optoelectronic array, thereby increasing the photo collection efficiency (LCE) and incident gamma ray energy to the optoelectronic array. It provides a method to improve the linearity between the number of electrons output from.

According to an embodiment of the present invention, by increasing the size of the microcells constituting the optoelectronic device array, the linearity between photon collection efficiency (LCE) and incident gamma ray energy versus the number of electrons output from the optoelectronic device array may be improved. have.

In addition, the scintillation crystal may be configured with an N × M matrix size (N and M are arbitrary natural numbers).

In addition, the matrix size of the optoelectronic device array may be configured to be smaller than the matrix size of the scintillation crystal.

In addition, the microcells constituting the photoelectric device array may have a size between 10 × 10 μm ² and 200 × 200 μm ² , and the thickness of the light guide may be 0.1 mm to 10 mm.

According to another embodiment of the present invention, the photoelectric device array may be a GAPD array composed of micro cells, and the flash may be visible light.

According to another embodiment of the present invention, the PET module may further include a position detection unit for detecting the position of the scintillation crystal generated the glare from the gamma rays.

According to the present invention, despite the phenomenon in which nonlinearity increases with GAPD having large area microcells, photons are incident on a large number of GAPDs by increasing the thickness of the light guide, thereby simultaneously providing high energy and high resolution information. And improve nonlinearity. In addition, according to the present invention, it is possible to configure a detector module having a PDE (photo detection efficiency) of 50%.

1 is a perspective view showing a PET module using an optoelectronic device according to an embodiment of the present invention.
Figure 2 shows a PET module using a photoelectric device when there is no light guide.
3 shows a PET module using an optoelectronic device when the light guide thickness is small.
Figure 4 shows a PET module using a photoelectric device when the light guide thickness is large.
5 shows the relationship between the light guide thickness and the number of photons incident on the photoelectric device and the relationship between the light guide thickness and the LCE.
FIG. 6 illustrates the relationship between the incident gamma ray energy and the number of electrons output from the photovoltaic device array by the light guide thickness in the PET module using the photoelectric device.

Prior to the description of the specific contents of the present invention, for the convenience of understanding, the outline of the solution of the problem to be solved by the present invention or the core of the technical idea will be presented first.

According to an embodiment of the present invention, a method of improving linearity between photon collection efficiency (LCE) and incident gamma ray energy versus the number of electrons output from the photovoltaic array includes a flash crystal that generates flash from gamma rays, and a flash from the scintillation crystal. A PET module comprising a light guide to spread to an optoelectronic device array, and an optoelectronic device array for converting the light passing through the light guide into an electrical signal, the light guide positioned between the scintillation crystal and the optoelectronic device array. It is achieved by increasing the thickness of and increasing the size of the micro cells constituting the optoelectronic device array.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby. The configuration of the invention for clarifying the solution to the problem to be solved by the present invention will be described in detail with reference to the accompanying drawings based on the preferred embodiment of the present invention, the same in the reference numerals to the components of the drawings The same reference numerals are given to the components even though they are on different drawings, and it is to be noted that in the description of the drawings, components of other drawings may be cited if necessary. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

1 is a perspective view showing a PET module using an optoelectronic device according to an embodiment of the present invention.

Referring to FIG. 1, the PET module using the photoelectric device according to the present exemplary embodiment includes a scintillation crystal part 100, a light guide 110, and a photoelectric device 120.

The scintillation crystal part 100 includes a scintillation crystal 111 that receives gamma rays, and generates visible light therefrom, and a reflector 112 for preventing flash from spreading from one scintillation crystal to another scintillation crystal.

The scintillation crystal part 100 forms an array of at least one scintillation crystal 111, and each scintillation crystal 111 is enclosed by the reflector 112.

The scintillation crystal part 100 may arrange the scintillation crystal 111 surrounded by the reflector 112 in a matrix form, that is, N × M where N and M are natural numbers.

As the scintillation crystal 111, LSO, BGO, LYSO, LaBr ₃ , NaI, LGSO, or the like may be used, and these may be configured in a single layer or a multilayer form.

The light guide 110 is to spread the visible light generated by the scintillation crystal part 100 to the photoelectric device 120 disposed below the light guide 110.

The light guide 110 may use quartz or flexiglass.

The light guide 110 may have a thickness of 0.1 mm to 10 mm, and the width of the light guide corresponding to each of the scintillation crystals 111 may be the same as that of the scintillation crystal 111.

1 to 4 show an example in which the optoelectronic devices are arranged in a 4 × 4 square matrix.

The photoelectric element 120 is a device for converting an optical signal passing through the light guide 110 into an electrical signal. According to an embodiment of the present invention, the optical signal may be visible light converted from gamma rays.

In addition, the optoelectronic device 120 may be a Geger-mode avalanche photodiode (GAPD) in the form of a matrix.

The photovoltaic device 120 is also known as a solid state photomultiplier (SSPM), silicon photomultiplier (SiPM), multi pixel photon counters (MPPC), micro-pixel avalanche photodiode (MAPD), and avalanche photodiode operating in Geiger mode. Can be.

The optoelectronic device 120 is composed of a plurality of micro cells, and the plurality of micro cells substantially detect an optical signal. According to an embodiment of the present invention relates to a PET module using GAPD composed of a plurality of micro cells.

The optoelectronic devices 120 may be arranged to correspond to each of the scintillation crystals 111 one by one, or a plurality of scintillation crystals 111 may be arranged in a matrix form with respect to one optoelectronic device 120.

According to another embodiment of the present invention, a flash position determiner (not shown) for determining the scintillation crystal 111 that caused the gamma ray reaction from each electrical signal of the photoelectric device 120 may be further provided.

When the optoelectronic device 120 is a 4 × 4 array type GAPD, the number of channels is reduced from 16 to 4 through the Anger circuit, and the flash position can be determined by a unique Anger equation.

Figure 2 shows a PET module using a photoelectric device when there is no light guide.

Photoelectric element 210 in which the scintillation crystal 111 is arranged in the form of a 4 × 4 square matrix, Photoelectric element 120 in the form of 4 × 4 square matrix, and the optoelectronic device under the scintillation crystal 111 State 230 is shown where 120 is located.

Referring to the side cross-sectional view 240 of the PET module using the optoelectronic device shown in Figure 2, when the flash is generated in the flash crystal 111, most of the optical signal is incident to the photoelectric device directly below the flash crystal in which the flash occurs It can be seen that. This is because the optical signal does not spread because there is no light guide between the scintillation crystal and the optoelectronic device.

3 shows a PET module using an optoelectronic device when the light guide thickness is small.

The photoelectric device is arranged in the form of 4 × 4 square matrix 310, the flash crystal is arranged in the form of 8 × 8 square matrix 320, and the light guide is positioned under the scintillation crystal, and the photoelectric device is located under the light guide. State 330 is shown.

Referring to the side cross-sectional view 340 of the PET module using the optoelectronic device shown in Figure 3, when the flash is generated in the scintillation crystal 111, it is passed through the light guide 110, a part of the optical signal is incident to the adjacent optoelectronic device Able to know.

Figure 4 shows a PET module using a photoelectric device when the light guide thickness is large.

The photoelectric element is arranged in the form of a 4 × 4 square matrix (410), the scintillation crystal is arranged in the form of an 8 × 8 square matrix (420), and the light guide is located under the scintillation crystal, and the photoelectric element is located under the light guide. State 430 is shown.

Referring to the side cross-sectional view 440 of the PET module using the optoelectronic device shown in Figure 4, when the flash is generated in the scintillation crystal 111, while the optical signal passes through the thick light guide 110, the optical signal in FIG. It can be seen that the optical signal is distributed and incident on more adjacent optoelectronic devices than incident photoelectric devices.

Referring to FIG. 2, when the scintillation crystal and the photoelectric device are combined 1: 1, only one photoelectric device receives an optical signal. Since optoelectronic devices generally have an on-off switch function, the result of turning on an optical signal no matter how many optical signals are received when a predetermined level or more of optical signals is received is the same.

However, referring to FIG. 4, by placing a thick light guide between the scintillation crystal and the optoelectronic device, an optical signal is incident on more photoelectric devices than in FIG. 2 or 3.

In more detail, the optoelectronic device 120 is composed of a plurality of micro cells, the size of each micro cell is in the range of 10 μm x 10 μm to 200 μm x 200 μm. The light guide 110 may have a thickness of about 0.1 mm to about 10 mm.

Thousands of incident photons generated in the scintillation crystal 111 are spread through the light guide 110 between adjacent optoelectronic devices 120, for example, GAPD pixels.

Thereafter, only a few hundred photons enter each GAPD, and although the GAPD operates non-linearly for thousands of photons, it operates linearly for hundreds of photons. Therefore, when hundreds of photons are incident to GAPD, the GAPD can be operated without saturation, and the total incident gamma ray energy can be expressed as the sum of the gamma ray energy incident to the GAPDs.

This method is advantageous for increasing the number of micro cells that detect photons through a light sharing environment without modifying the size of the micro cells. As a result, it is possible to improve linearity and light collection efficiency (LCE) without changing the PDE (photo detection efficiency) and GAPD gain.

LCE means photon collection efficiency, which means the number of photons colliding with the photoelectric device divided by the number of photons incident to the photoelectric device.

5 shows the relationship between the light guide thickness and the number of photons incident on the photoelectric device and the relationship between the light guide thickness and the LCE.

Three types of 4x4 optoelectronics: PSPMT with 25% QE, most commonly used for PET detectors, GAPD1 with 30% PDE and large area microcells. Configured to count incident photons using GAPD2 with 45% PDE. Each optoelectronic pixel has an active area of 3 x 3 mm ² . PSPMT compares with the performance of the other two types of GAPD, which consist of 50 × 50 μm ² and 100 × 100 μm ² microcells.

FIG. 5A illustrates the relationship between the thickness of the light guide and the number of photons incident on the photoelectric device for each type of photoelectric device (PSPMT, GAPD) in the PET module using the photoelectric device. In particular, when the photoelectric device is GAPD, the size of the microcell is 50 μm x 50 μm compared with the case of 100 μm x 100 μm.

The number of photons counted for 511 keV gamma rays increases as the thickness of the light guide increases for GAPD. In particular, when the size of the microcell is 100 μm × 100 μm, and the thickness of the light guide is 2 mm or more, the number of incident photons is significantly greater than that of other optoelectronic devices. On the other hand, PSPMT decreases slightly.

FIG. 5B illustrates a relationship between a light guide thickness and a light collection efficiency (LCE) for each type of photoelectric device (PSPMT and GAPD) in a PET module using an optoelectronic device.

As in FIG. 5A, when the photoelectric device is GAPD, the case where the size of the microcell is 50 μm × 50 μm and 100 μm × 100 μm was compared.

The LCE of GAPD1 (50 × 50 μm ² microcells) improved from 24% to 30%, and the LCE of GAPD2 (100 × 100 μm ² microcells) increased from 14% to 41% It can be seen that the LCE is improved as is increased.

5A and 5B, it can be seen that the thicker the light guide, the better the number of photons incident on the photoelectric device and the LCE. In addition, it can be seen that the larger the size of the microcell constituting the GAPD, the number of photons incident on the photoelectric device and the LCE are improved.

FIG. 6 illustrates the relationship between the incident gamma ray energy and the number of electrons output from the photovoltaic device array by the light guide thickness in the PET module using the photoelectric device.

FIG. 6A illustrates the relationship between the incident gamma ray energy and the number of electrons output from the photoelectric device array according to the light guide thickness when the microcell size is 50 μm × 50 μm in the PET module using the photoelectric device.

FIG. 6B illustrates the relationship between the incident gamma ray energy and the number of electrons output from the photoelectric device array for each light guide thickness when the microcell is 100 μm × 100 μm in the PET module using the photoelectric device.

Referring to FIG. 6, it can be seen that the relationship between the incident gamma ray energy and the number of electrons output from the photoelectric device array is improved as the thickness of the light guide is thicker and the size of the microcell is larger.

Referring to FIGS. 5 and 6, in the PET module using the photoelectric device, the linearity between the GaPD having wider microcells and the thicker light guide, the incident gamma ray energy versus the number of electrons output from the photoelectric device array, It can be seen that energy and spatial resolution information can be improved simultaneously. That is, as the degree of light spread through the light guide after the gamma ray reaction in the scintillation crystal is larger and the microcell area is larger, higher energy information can be obtained.

In the present invention as described above has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from these descriptions.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

The present invention can be utilized in PET detectors requiring high resolution. In particular, it is a technology that can be used not only small animal PET, but also whole body PET.

100: flash crystal part 110: light guide
120: photoelectric element 111: flash crystal
112: reflector
210: the state in which the flash crystal 111 is arranged in the form of a 4 × 4 square matrix
220: Photoelectric element 120 is arranged in the form of 4 × 4 square matrix
230: Photoelectric device 120 is positioned below the flash crystal 111
240: side sectional view of a PET module using a photoelectric device
310: the scintillation crystal 111 is arranged 4 × 4 in the form of a square matrix
320: Photoelectric device 120 is arranged in the form of an 8 × 8 square matrix
330: Light guide 110 is positioned below the scintillation crystal 111, the photoelectric device 120 is positioned below the light guide 110
340: side cross-sectional view of a PET module using a photoelectric device
410: The state in which the flash crystal 111 is arranged in the form of a square matrix 4 × 4
420: Photoelectric element 120 is arranged in the form of an 8 × 8 square matrix
430: The light guide 110 is positioned below the scintillation crystal 111, the photoelectric device 120 is positioned below the light guide 110
440: side cross-sectional view of a PET module using a photoelectric device

Claims (9)

PET detector module comprising a flash crystal for generating flash from gamma rays, a light guide for spreading the flash from the flash crystal to the photoelectric element array, and an photoelectric element array for converting the flash light passing through the light guide into an electrical signal. A method of improving linearity between the photon collection efficiency (LCE) and the incident gamma ray energy versus the number of electrons output from the optoelectronic array,
The light guide has a thickness of 2 mm or more and 10 mm or less,
When the size of the microcells constituting the optoelectronic device array is 50 × 50 μm ² or more and 200 × 200 μm ² or less, the number of electrons and the photon collection efficiency (LCE) output from the optoelectronic device array are maximized.
A linearity improvement method between photon collection efficiency (LCE) and incident gamma-ray energy versus the number of electrons output from the photonic device array, characterized in that the linearity between the incident gamma ray energy and the number of electrons output from the optoelectronic device array is maximized. . delete The method of claim 1,
And said scintillation crystal is an N × M matrix size (where N and M are any natural numbers) and linearity between photon collection efficiency (LCE) and incident gamma ray energy versus the number of electrons output from the optoelectronic array. The method of claim 1,
Wherein the matrix size of the optoelectronic device array is smaller than the matrix size of the scintillation crystal; photon collection efficiency (LCE) and the incident gamma ray energy versus the number of electrons output from the optoelectronic device array. delete delete The method of claim 1,
And said photoelectron array is a GAPD array of microcells. The method of improving linearity between photon collection efficiency (LCE) and incident gamma ray energy versus the number of electrons output from the photoelectric array. The method of claim 1,
The PET module further includes a position detector for detecting a position of a scintillation crystal that generated scintillation from the gamma rays, between the photon collection efficiency (LCE) and the number of incident gamma ray energy versus the number of electrons output from the photoelectric element array. How to improve linearity. The method of claim 1,
And said strobe light is visible light. The method of improving linearity between photon collection efficiency (LCE) and incident gamma ray energy versus the number of electrons output from an optoelectronic array.

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