JP7132796B2 - Cherenkov detector, Cherenkov detector setting method and PET device - Google Patents

Description

The present invention relates to a Cherenkov detector, a Cerenkov detector setting method, and a PET apparatus.

As detectors for detecting incident particles such as photons, those described in Non-Patent Documents 1 and 2 are known. These detectors can, for example, detect the time of arrival of a gamma ray photon.

The detector described in Non-Patent Document 1 includes a scintillator and SiPM (Silicon Photomultiplier). In this detector, for example, when gamma-ray photons are incident on a scintillator, the scintillator generates scintillation light in response to the incidence of the photons, the scintillation light is detected by the SiPM, and the SiPM outputs an electric pulse signal.

The detector described in Non-Patent Document 2 comprises a Cerenkov radiator and a SiPM. For example, when a gamma ray photon is incident on a Cherenkov radiator, the detector generates Cherenkov light in the Cherenkov radiator in response to the incidence of the photon. Output.

If the moving speed of charged particles (for example, electrons, muons) in the radiator is higher than the speed of light in the radiator, the interaction between the charged particles and the radiator causes light to be emitted. In addition, uncharged particles (e.g., gamma rays, neutrinos) may generate charged particles such as electrons due to the photoelectric effect in the radiator, and the moving speed of the charged particles is faster than the speed of light in the radiator. Light is emitted at high speed. Such a phenomenon is called the Cherenkov effect or Cherenkov radiation, and the emitted light is called Cherenkov radiation or Cherenkov light.

A detector that detects γ-rays is used, for example, in a tomographic image acquisition device. A PET (Positron Emission Tomography) device, which is a type of tomographic image acquisition device, places an object into which a RI (Radio Isotope) ray source is injected into a measurement space, and the pair annihilation of electrons and positrons in the object generates The photon pairs of the gamma rays are detected by the coincidence counting method to collect coincidence counting information, and a tomographic image of the subject is acquired based on the collected coincidence counting information. A typical PET apparatus reconstructs a tomographic image of the subject by performing iterative calculation according to a predetermined algorithm based on the collected coincidence count information.

On the other hand, the TOF (Time of Flight)-PET system, which is expected to be a next-generation PET system, uses two detectors to detect photon pairs for each electron-positron pair annihilation event in the specimen. Based on the difference in photon detection time between the two detectors, the pair annihilation position on the coincidence line connecting these two detectors is determined. A TOF-PET apparatus acquires a tomographic image of a subject from the annihilation position obtained for each annihilation event of electrons and positrons in the subject.

If the TOF-PET apparatus obtains the annihilation position with the same degree of accuracy as the pixel pitch of the tomographic image, iterative calculations for image reconstruction required by the ordinary PET apparatus are unnecessary. Further, tomographic images obtained by image reconstruction in a normal PET apparatus contain artifacts, which are statistical noises, whereas tomographic images obtained by a TOF-PET apparatus do not contain artifacts. The pixel pitch of the tomographic image is, for example, 5 mm.

S. Seifert, et al., IEEE Trans. Nucl. Sci. 59 2012. R. Dolenec, et al., 4th Conference on PET/MR and SPECT/MR (PSMR) 2015.

Conventional detectors, including those described in Non-Patent Documents 1 and 2, have poor temporal resolution. Therefore, iterative calculations for image reconstruction are required. Also, the tomographic image contains artifacts.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a Cherenkov detector capable of having excellent time resolution.

The Cherenkov detector according to the first aspect of the present invention comprises: (1) a radiator that generates Cherenkov light by interacting with incident particles, and a photoelectric converter that emits electrons in response to the incidence of the Cherenkov light generated by the radiator. an electron multiplying unit having one or more microchannel plates for multiplying and outputting electrons emitted from the photoelectric conversion unit; and collecting the electrons output by the electron multiplying unit and generating electricity (2) a storage unit for storing the waveform of the electrical pulse signal output from the anode for each interaction event in the radiator; and (3) stored by the storage unit. Using the waveforms of a plurality of electrical pulse signals, an analysis unit that obtains a specific range of the pulse magnitude and threshold of the electrical pulse signal in which the magnitude of the variation in the time at which the value of the electrical pulse signal reaches the threshold is equal to or less than the allowable value. and (4) the value of an electrical pulse signal having a pulse magnitude within a specific range among the plurality of electrical pulse signals stored by the storage unit reaches a threshold value corresponding to the pulse magnitude within the specific range. a time detection unit that detects time as an interaction time in the radiator.

In the Cerenkov detector according to the first aspect of the present invention, the time detection unit detects that the value of the electrical pulse signal having a pulse magnitude within a specific range among the electrical pulse signals output from the anode is equal to the value of the pulse within the specific range. Preferably, the time when a threshold value corresponding to the magnitude of is reached is detected as the interaction time in the radiator.

The Cherenkov detector according to the second aspect of the present invention comprises: (1) a radiator that generates Cherenkov light by interacting with incident particles, and a photoelectric converter that emits electrons in response to the incidence of the Cherenkov light generated by the radiator. an electron multiplying unit having one or more microchannel plates for multiplying and outputting electrons emitted from the photoelectric conversion unit; and collecting the electrons output by the electron multiplying unit and generating electricity (2) an electrical pulse signal output from the anode whose pulse magnitude is within a specific range; and a time detection unit that detects the time at which a threshold value corresponding to the magnitude of is reached as the interaction time in the radiator.

The Cherenkov detector according to the second aspect of the present invention comprises: (3) a storage unit that stores the waveform of the electrical pulse signal output from the anode for each interaction event in the radiator; an analysis unit that uses the waveform of the electric pulse signal to determine a specific range of the magnitude of the electric pulse signal and the threshold value that makes the magnitude of the variation in the time when the value of the electric pulse signal reaches the threshold value equal to or less than the allowable value; is preferably further provided.

A Cherenkov detector setting method of the present invention is a method of setting a specific range in the Cherenkov detector of the second aspect of the present invention, comprising: (1) electricity output from the anode for each interaction event in the radiator; (2) using the waveforms of the plurality of electrical pulse signals stored in the storage step, the magnitude of variation in the time when the value of the electrical pulse signal reaches the threshold value is equal to or less than an allowable value; and an analysis step of determining a specific range of the pulse magnitude and the threshold value of the electrical pulse signal.

The PET apparatus of the present invention uses a coincidence counting method to detect photon pairs of gamma rays generated by pair annihilation of electrons and positrons in a subject placed in a measurement space with an RI radiation source, and obtains coincidence counting information. and obtains a tomographic image of a subject based on the collected coincidence information, wherein the Cherenkov A detector is provided.

The Cerenkov detector of the present invention can have excellent temporal resolution. When the Cerenkov detector of the present invention is used in a TOF-PET apparatus, a tomographic image with good spatial resolution can be acquired.

FIG. 1 is a diagram showing the configuration of a Cerenkov detector 1A according to the first embodiment. FIG. 2 is a diagram showing the configuration of a system used when storing waveforms of electrical pulse signals in the storage unit 21 of the signal processing unit 20A. FIG. 3 is a diagram showing a histogram of pulse magnitudes of a plurality of electrical pulse signals stored in the storage section 21 of the signal processing section 20A. FIG. 4 is a diagram showing the relationship between the waveform of a certain electrical pulse signal and the threshold value stored in the storage section 21 of the signal processing section 20A. FIG. 5 is a flowchart illustrating an example of processing by the analysis unit 22 of the signal processing unit 20A. FIG. 6 is a flowchart illustrating another example of processing by the analysis unit 22 of the signal processing unit 20A. FIG. 7 is a diagram showing the relationship between the pulse area and threshold value of the electrical pulse signal output from the detection unit and the time resolution. FIG. 7(a) is a diagram showing the distribution of time resolution. FIG. 7B is a graph showing variations in γ detection time. FIG. 8 is a diagram showing the configuration of the Cerenkov detector 1B of the second embodiment. FIG. 9 is a diagram showing the configuration of a Cerenkov detector 1C according to the third embodiment. FIG. 10 is a diagram showing the configuration of the Cerenkov detector 1D of the fourth embodiment. FIG. 11 is a diagram showing the configuration of the PET device 2. As shown in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope of equivalents of the scope of the claims.

FIG. 1 is a diagram showing the configuration of a Cerenkov detector 1A according to the first embodiment. The Cerenkov detector 1A includes a detection section 10 and a signal processing section 20A.

The detector 10 includes a radiator 11 , an intermediate layer 12 , a photoelectric converter 13 , an electron multiplier 14 , an anode 15 and a housing 16 . The detector 10 outputs an electric pulse signal from the anode 15 for each event of interaction with an incident particle (eg, γ-ray) in the radiator 11 .

The radiator 11 generates Cerenkov light through interaction with incident particles. The radiator 11 is made of a material with a known refractive index and with which the Cerenkov effect can occur. The radiator 11 is preferably made of a material that hardly generates scintillation light. The material of the radiator 11 is, for example, lead glass (SiO ₂ +PbO), lead fluoride (PbF ₂ ), PWO (PbWO ₄ ), bismuth fluoride (BiF ₃ ), or the like. The radiator 11 preferably has a flat plate shape with a uniform thickness.

Lead glass is amorphous glass containing several percent or more of lead. Lead glass is a material with good workability and can be easily processed into various shapes and thicknesses. Lead glass is characterized in that the higher the lead content, the higher the efficiency of converting γ-rays into Cerenkov light, and the higher the transmittance and refractive index of light with a wavelength of 400 nm or less.

The intermediate layer 12 is provided between the radiator 11 and the photoelectric conversion section 13 . The intermediate layer 12 is a barrier layer that blocks reaction between the lead contained in the radiator 11 and the photoelectric conversion section 13 . Note that the intermediate layer 12 is unnecessary if the reaction between the radiator 11 and the photoelectric conversion section 13 does not matter.

Materials of the intermediate layer 12 are, for example, aluminum oxide (Al ₂ O ₃ ), zinc oxide (ZnO), hafnium oxide (HfO ₂ ), titanium oxide (TiO ₂ ), and the like. The intermediate layer 12 is preferably a dense layer with a uniform thickness. The thickness of the intermediate layer 12 is preferably equal to or less than the wavelength of Cerenkov light emitted by interaction of γ-rays with the radiator 11 . The thickness of the intermediate layer 12 is preferably sufficiently smaller than the wavelength of the Cerenkov light, and is preferably about 10 nm, for example. The intermediate layer 12 is formed on the radiator 11 by, for example, atomic layer deposition (ALD).

The photoelectric conversion section 13 is provided with the intermediate layer 12 sandwiched between it and the radiator 11 . The photoelectric conversion unit 13 emits electrons in response to incidence of Cerenkov light generated by the radiator 11 . The material of the photoelectric conversion section 13 contains an alkali metal element, such as alkali-antimony. The photoelectric conversion unit 13 has a uniform thickness. The radiator 11, the intermediate layer 12 and the photoelectric conversion section 13 may be laminated in this order and integrated.

An electric field is formed between the photoelectric conversion portion 13 and the electron multiplier portion 14 so that the electrons emitted from the photoelectric conversion portion 13 are directed toward the electron multiplier portion 14 . The electron multiplier 14 receives electrons emitted from the photoelectric conversion unit 13, multiplies the electrons, and outputs the electrons. The electron multiplier section 14 has one or more micro channel plates (MCP: Micro Channel Plate). A high voltage for multiplying electrons is applied between both surfaces of the MCP (the surface on the photoelectric conversion part 13 side and the surface on the anode 15 side). If the electron multiplication factor of one MCP is not sufficient, it is preferable to stack two or more MCPs. By stacking two MCPs, an electron multiplication factor of about 10 ⁶ can be obtained.

If the base material of the MCP contains lead, the interaction of gamma rays with the MCP can become noise. Therefore, the MCP is preferably formed from a lead-free (or very low lead content) matrix.

An electric field is formed between the electron multiplier 14 and the anode 15 so that the electrons multiplied by the electron multiplier 14 and output are directed toward the anode 15 . The anode 15 collects the electrons multiplied and output by the electron multiplier 14 and outputs an electrical pulse signal S to the outside. Since the electric pulse signal S is a negative pulse, it is displayed as a downward pulse in this figure.

At least the electron multiplier 14 and the anode 15 are arranged inside the housing 16 . The housing 16 is airtight, and the interior of the housing 16 is maintained in a vacuum (or a very low atmospheric pressure). The photoelectric conversion unit 13 may be a window of the housing 16. In this case, the housing 16 and the photoelectric conversion unit 13 form an airtight closed space. Moreover, the radiator 11 may be a window of the housing 16. In this case, the housing 16 and the radiator 11 form an airtight closed space.

Moreover, it is preferable that a shielding film that absorbs Cerenkov light is provided on the outer surface of the radiator 11 (the surface opposite to the photoelectric conversion section 13). By providing such a shielding film, it is possible to prevent Cherenkov light generated by the radiator 11 from entering the photoelectric conversion section 13 after being reflected by the outer surface of the radiator 11 .

The signal processing unit 20A receives the electric pulse signal output from the anode 15 for each interaction event in the radiator 11 of the detection unit 10, and performs required processing on the electric pulse signal. Signal processing unit 20A includes storage unit 21 , analysis unit 22 and time detection unit 23 .

The storage unit 21 stores the waveform of the electrical pulse signal output from the anode 15 for each interaction event in the radiator 11 of the detection unit 10 as a digital signal waveform.

The analysis unit 22 uses the waveforms of the plurality of electric pulse signals stored in the storage unit 21 to analyze the pulses of the electric pulse signal whose magnitude of variation in the time when the value of the electric pulse signal reaches the threshold value is equal to or less than the allowable value. Find a specific range of magnitudes and thresholds. This specific range is a range defined by two variables, ie, the pulse magnitude of the electrical pulse signal and the threshold value. The specified range may be the range of a single compartment or the range of multiple compartments. The pulse magnitude of the electric pulse signal corresponds to the energy of the electric pulse signal, and may be the pulse peak value or the pulse area.

The time detection unit 23 determines that the value of the electric pulse signal whose pulse magnitude is within the specific range among the plurality of electric pulse signals stored by the storage unit 21 corresponds to the pulse magnitude within the specific range. The time at which the threshold value is reached is detected as the interaction time in the radiator 11 .

Next, the processing of the signal processing section 20A (especially the setting of the specific range in the analysis section 22) will be described with reference to FIGS. 2 to 7. FIG.

FIG. 2 is a diagram showing the configuration of a system used when storing waveforms of electrical pulse signals in the storage unit 21 of the signal processing unit 20A. Two detection units 10 are arranged facing each other. An RI source 31 is placed at the center of a line segment connecting the two detectors 10 . A collimator 32 is arranged between one detector 10 and the RI radiation source 31 . The two detectors 10 detect photon pairs flying on a coincidence line passing through the collimator 32 among photon pairs of gamma rays generated by pair annihilation of electrons and positrons at the position where the RI radiation source 31 is arranged. can be counted simultaneously. The digital oscilloscope 33 receives electrical pulse signals output from the two detection units 10 and stores waveforms of the electrical pulse signals as digital signal waveforms.

The data presented in the following description were collected and analyzed under the following conditions. The two detection units 10 shown in FIG. 2 are hereinafter referred to as a detection unit A and a detection unit B. As shown in FIG. As the radiator 11 of the detectors A and B, one made of lead glass with a diameter of 11 mm and a thickness of 3.2 mm was used. As the electron multipliers 14 of the detectors A and B, two MCPs stacked were used. The interval between the detection portion A and the detection portion B was set to 120 mm. ²² Na was used as the RI source 31 . As the collimator 32, a lead material with a thickness of 50 mm and a through hole with a diameter of 1.0 mm was used. As the digital oscilloscope 33, Keysight's DSO-404A was used. This digital oscilloscope has a bandwidth of 4.2 GHz and a maximum sampling rate of 20 GS/s.

FIG. 3 is a diagram showing a histogram of pulse magnitudes of a plurality of electrical pulse signals stored in the storage section 21 of the signal processing section 20A. The total number of electrical pulse signals stored is 20,000. The horizontal axis is the pulse area of the electrical pulse signal. The vertical axis is the number of electrical pulse signals. Even if the energy of γ-rays generated by pair annihilation of electrons and positrons is constant at 511 keV, the energy of the electric pulse signal output from the detector has a certain distribution as shown in this figure. This is because the number of photons generated in each event of interaction with gamma rays in the radiator 11 has a certain distribution, the number of electrons emitted in the photoelectric conversion section 13 also has a certain distribution, and , the electron multiplication factor in the electron multiplier 14 also has a certain distribution.

FIG. 4 is a diagram showing the relationship between the waveform of a certain electrical pulse signal and the threshold value stored in the storage section 21 of the signal processing section 20A. The horizontal axis is time, and the vertical axis is the value (voltage value) of the electric pulse signal. The time on the horizontal axis indicates that the value of the electric pulse signal output from the detector that detected the photon later among the two detectors A and B that coincidentally counted the photon pairs of the γ-ray reached the set threshold value of the digital oscilloscope 33. The time is used as the reference time. This figure shows the waveform of the electrical pulse signal output from the detector that previously detected the photon.

As shown in this figure, the time of γ-ray detection by the detection unit obtained from the waveform of the electric pulse signal differs depending on the setting of the threshold. Further, the time of γ-ray detection by the detection unit obtained from the waveform of the electric pulse signal has variations depending on the pulse magnitude (pulse area or pulse peak value) of the electric pulse signal and the threshold value. Therefore, the analysis unit 22 uses the waveforms of a plurality of electric pulse signals stored in the storage unit 21 to determine the magnitude of variation in the time when the value of the electric pulse signal reaches the threshold value is equal to or less than the allowable value. A specific range of pulse magnitudes and thresholds is determined.

FIG. 5 is a flowchart illustrating an example of processing by the analysis unit 22 of the signal processing unit 20A.

In step S11, the range of the pulse area (pulse area window) of the electric pulse signal output from the detection unit _A is set to _{pa to p a +} δa. After step S11, the process proceeds to step S12.

In step S12, the threshold value of the electrical pulse signal output from the detector _A is set to va. After step S12, the process proceeds to step S13.

In step S13, the pulse area range (pulse area window) of the electrical pulse signal output from the detection unit B is set to p _b to p _b +δ _b . After step S13, the process proceeds to step S14.

In step S14, the threshold value of the electrical pulse signal output from the detector _B is set to vb. After step S14, the process proceeds to step S15.

For example, p _a and p _b set in steps S11 to S14 are 0.01, δ _a and δ _b are 0.01, and v _a and v _b are 2 mV.

In step S15, a histogram of γ-ray detection time differences between the detectors A and B is generated to evaluate the magnitude of variation in γ-ray detection times, that is, temporal resolution. After step S15, the process proceeds to step S16.

In step S16, it is determined whether or not _vb exceeds the upper limit value V. If _vb exceeds the upper limit V, the process proceeds to step S17. If _vb does not exceed the upper limit V, the process proceeds to step S24. In step S24, the value obtained by adding _Δvb to _vb is set as new _vb , and the process proceeds to step S15.

In step S17, it is determined whether or not _pb has exceeded the upper limit value P. If _pb exceeds the upper limit P, the process proceeds to step S18. If _pb does not exceed the upper limit P, the process proceeds to step S23. In step S23, the value obtained by adding _Δpb to _pb is set as new _pb , and the process proceeds to step S14.

In step S18, it is determined whether or not _va exceeds the upper limit value V. If v _a exceeds the upper limit value V, the process proceeds to step S19. If v _a does not exceed the upper limit V, the process proceeds to step S22. In step S22, the value obtained by adding Δv _a to v _a is set as new v _a , and the process proceeds to step S13.

In step S19, it is determined whether _pa exceeds the upper limit value P or not. _If pa exceeds the upper limit P, the process proceeds to step S31. _If pa does not exceed the upper limit P, the process proceeds to step S21. In step S21, the value obtained by adding Δp _a to _pa is set as new _pa , and the process proceeds to step S12.

At steps S16 and S18, the upper limit value V is, for example, 10 mV. At steps S17 and S19, the upper limit value P is, for example, 0.1. In steps S21 and S23, the added values Δp _a and Δp _b are, for example, 0.001. In steps S22 and S24, the added values Δv _a and Δv _b are 1 mV, for example.

At the time when the process proceeds to step S31, the pulse area range (pulse area window) and the threshold for the electrical pulse signals output from the detection units A and B are set to the lower limit values (p _a , p _b , v _a , v _b ) to the upper limit (P, V) are scanned with predetermined shift amounts (Δp _a , Δp _b , Δv _a , Δv _b ).

Then, in step S31, a specific range of the pulse area of the electrical pulse signal and the threshold is determined such that the magnitude of variation in the time at which the value of the electrical pulse signal reaches the threshold is equal to or less than the allowable value (that is, the time resolution is within the allowable range). Ask.

FIG. 6 is a flowchart illustrating another example of processing by the analysis unit 22 of the signal processing unit 20A. If the detectors A and B have the same configuration and are expected to have the same characteristics, the following processing is possible.

In step S41, the pulse area range (pulse area window) of the electrical pulse signals output from the detection units A and B is set to p to p+δ. For example, p set here is 0.01 and δ is 0.01. After step S41, the process proceeds to step S42.

In step S42, the threshold v is set for the electrical pulse signals output from the detection units A and B. FIG. For example, v set here is 2 mV. After step S42, the process proceeds to step S43.

In step S43, a histogram of the γ-ray detection time difference between the detectors A and B is generated to evaluate the magnitude of variation in γ-ray detection time, that is, the temporal resolution. After step S43, the process proceeds to step S44.

In step S44, it is determined whether or not v exceeds the upper limit value V. The upper limit value V is, for example, 10 mV. If v exceeds the upper limit value V, the process proceeds to step S45. If v does not exceed the upper limit value V, the process proceeds to step S47. In step S47, the value obtained by adding Δv to v is set as new v, and the process proceeds to step S43.

In step S45, it is determined whether or not p exceeds the upper limit P. The upper limit value P is 10, for example. If p exceeds the upper limit P, the process proceeds to step S48. If p does not exceed the upper limit P, the process proceeds to step S46. In step S46, the value obtained by adding Δp to p is set as new p, and the process proceeds to step S42.

Then, in step S48, a specific range of the pulse area and the threshold value of the electric pulse signal is determined such that the variation in the time when the value of the electric pulse signal reaches the threshold value is equal to or less than the allowable value (that is, the time resolution is within the allowable range). Ask.

FIG. 7 is a diagram showing the relationship between the pulse area and threshold value of the electrical pulse signal output from the detection unit and the time resolution. In FIG. 7A, the horizontal axis is the threshold and the vertical axis is the pulse area. In FIG. 7(a), the temporal resolution obtained by the processing of FIG. 6 is indicated by shading. The time resolution shown here is the Coincidence Time Resolution (CTR) expressed in Full Width at Half Maximum (FWHM). Hereinafter, CTR represented by FWHM is simply called CTR. FIG. 7(b) is a graph showing variations in γ detection time when a certain range of pulse areas and threshold values in FIG. 7(a) is selected. In this example, the CTR is 28.0ps.

By the way, the spatial resolution of a tomographic image acquired by a normal PET device is about 5 mm. In order to make the spatial resolution of the tomographic image acquired by the TOF-PET apparatus about 5 mm or less, the CTR of the detector must be about 35 ps or less. The Cerenkov detector 1A of this embodiment can have a CTR of 35 ps or less, and can also have a CTR of 30 ps or less. The analysis unit 22 determines the specific range of the pulse magnitude of the electrical pulse signal and the threshold value according to the required CTR, that is, according to the allowable value for the magnitude of variation in the time when the value of the electrical pulse signal reaches the threshold value. You can ask for A TOF-PET apparatus using the Cerenkov detector 1A of the present embodiment acquires a tomographic image that does not contain artifacts without performing image reconstruction processing, compared to conventional PET apparatuses and TOF-PET apparatuses. be able to.

The Cerenkov detector of the present invention may have the configurations of the embodiments shown in FIGS. 8-10. The detection unit 10 shown in each of FIGS. 8 to 10 has the same configuration as that described using FIG.

FIG. 8 is a diagram showing the configuration of the Cerenkov detector 1B of the second embodiment. Compared with the configuration of the Cherenkov detector 1A of the first embodiment shown in FIG. 1, the Cherenkov detector 1B of the second embodiment shown in FIG. 8 includes a signal processing unit 20B instead of the signal processing unit 20A. They are different in that respect.

The time detection unit 23 of the signal processing unit 20A in the first embodiment determines whether or not the pulse magnitude of each of the waveforms of the plurality of electrical pulse signals stored by the storage unit 21 is within a specific range.

On the other hand, the time detection unit 23 of the signal processing unit 20B in the second embodiment determines whether or not the pulse magnitudes of the waveforms of the plurality of electrical pulse signals stored in the storage unit 21 are within a specific range. In addition, it is also determined whether or not the pulse magnitude of the electrical pulse signal output from the anode 15 is within a specific range.

Then, the time detection unit 23 determines that the electric pulse signal output from the anode 15 also has a value of the electric pulse signal whose pulse magnitude is determined to be within the specific range. The time when the threshold value corresponding to the distance is reached is detected as the interaction time in the radiator 11 .

That is, the Cherenkov detector 1B of the second embodiment detects the interaction time in the radiator 11 not only for the electrical pulse signals stored in the storage unit 21 but also for the electrical pulse signals not stored in the storage unit 21. can be output.

FIG. 9 is a diagram showing the configuration of a Cerenkov detector 1C according to the third embodiment. Compared with the configuration of the Cherenkov detector 1B of the second embodiment shown in FIG. 8, the Cherenkov detector 1C of the third embodiment shown in FIG. 9 includes a signal processing unit 20C instead of the signal processing unit 20B. They are different in that respect.

The signal processing unit 20C in the third embodiment is composed of the time detection unit 23. FIG. The signal processing unit 20C stores a specific range of the magnitude of the pulse of the electric pulse signal and the threshold at which the degree of variation in the time when the value of the electric pulse signal reaches the threshold is equal to or less than the allowable value. Based on the stored specific range, the time detection unit 23 determines that the value of the electrical pulse signal having the pulse magnitude within the specific range among the electrical pulse signals output from the anode 15 is within the specific range. The time when the threshold value corresponding to the magnitude of the pulse is reached is detected as the interaction time in the radiator 11 .

The specific range stored by the signal processing unit 20C can be set by the method described with reference to FIGS. 2 to 7. FIG. That is, in this Cerenkov detector setting method, the waveform of the electrical pulse signal output from the anode 15 for each interaction event in the radiator 11 is stored in the storage unit (storage step), and the stored plurality of electrical pulse signals Using the waveform of , a specific range of the magnitude of the electric pulse signal and the threshold value is obtained in which the magnitude of variation in the time at which the value of the electric pulse signal reaches the threshold value is equal to or less than the allowable value (analysis step).

FIG. 10 is a diagram showing the configuration of the Cerenkov detector 1D of the fourth embodiment. Compared with the configuration of the Cherenkov detector 1C of the third embodiment shown in FIG. 9, the Cherenkov detector 1D of the fourth embodiment shown in FIG. 10 includes a signal processing unit 20D instead of the signal processing unit 20C. They are different in that respect.

While the signal processing unit 20C in the third embodiment includes the time detection unit 23, the signal processing unit 20D in the fourth embodiment includes the time detection unit 23 and the same memory as in the first embodiment. It also includes a section 21 and an analysis section 22 . In the fourth embodiment, the waveforms of the plurality of electrical pulse signals stored in the storage section 21 are used for processing by the analysis section 22 but are not used for processing by the time detection section 23 .

Based on the specific range obtained by the processing in the analysis unit 22, the time detection unit 23 detects the value of the electric pulse signal having a pulse magnitude within the specific range among the electric pulse signals output from the anode 15. The time at which the threshold value corresponding to the magnitude of the pulse within a specific range is reached is detected as the interaction time at the radiator 11 .

In any of the above-described embodiments, the time detection unit 23 includes an ADC (Analog-to-Digital Converter) that converts an input electrical pulse signal into a digital signal and a logic circuit that performs logical operations based on this digital signal. The included arrangement allows the pulse magnitude of the electrical pulse signal to be determined. In addition, a configuration including a comparator that compares the value of the input electric pulse signal with a threshold value and a TDC (Time-to-Digital Converter) circuit that obtains the time when the output value from this comparator is logically inverted, It is possible to obtain the time when the value of the electric pulse signal reaches a predetermined threshold.

FIG. 11 is a diagram showing the configuration of the PET device 2. As shown in FIG. The PET apparatus 2 detects photon pairs of gamma rays generated by pair annihilation of electrons and positrons in a subject 3 placed in a measurement space with an RI ray source applied, using a coincidence counting method, and obtains coincidence counting information. This device acquires a tomographic image of the subject 3 based on the collected coincidence count information. The PET device 2 may be a normal PET device, but is preferably a TOF-PET device.

The PET device 2 includes a plurality of detectors 10 , signal processors 20 and tomographic image generators 40 . Each detection unit 10 has a configuration similar to that described with reference to FIG. A plurality of detection units 10 are provided around the measurement space, and can detect γ-rays coming from the subject 3 .

The signal processing section 20 has the same configuration as any one of the signal processing sections 20A to 20D described with reference to FIGS. The signal processing units 20 may be provided on a one-to-one basis with respect to the detection units 10 , or one signal processing unit 20 may be provided in common for a plurality of detection units 10 . The detection unit 10 and the signal processing unit 20 have the same configuration as any of the Cerenkov detectors 1A to 1D described above.

The tomographic image creating unit 40 creates a tomographic image of the subject 3 based on the time information of γ-ray detection by each detecting unit 10 output from the signal processing unit 20 . Since this PET apparatus 2 detects γ-rays using the Cerenkov detector of this embodiment, it is possible to obtain a tomographic image with excellent spatial resolution.

1A to 1D... Cerenkov detector, 2... PET device, 10... detector, 11... radiator, 12... intermediate layer, 13... photoelectric converter, 14... electron multiplier, 15... anode, 16... housing, Reference numerals 20A to 20D, 20: signal processing unit, 21: storage unit, 22: analysis unit, 23: time detection unit, 31: RI radiation source, 32: collimator, 33: digital oscilloscope, 40: tomographic image creation unit.

Claims (6)

A radiator that generates Cherenkov light by interaction with incident particles, a photoelectric conversion unit that emits electrons in response to the incidence of the Cherenkov light generated by the radiator, and an increase in the electrons emitted from the photoelectric conversion unit. A detector comprising: an electron multiplier having one or more microchannel plates that multiply and output; and an anode that collects the electrons multiplied and output by the electron multiplier and outputs an electric pulse signal. When,
a storage unit that stores waveforms of electrical pulse signals output from the anode for each interaction event in the radiator;
Using the waveforms of a plurality of electric pulse signals stored in the storage unit, the magnitude of the pulse of the electric pulse signal and the threshold value are such that the magnitude of variation in the time at which the value of the electric pulse signal reaches the threshold is equal to or less than an allowable value. an analysis unit for obtaining a specific range;
The time at which the value of the electrical pulse signal whose pulse magnitude is within the specific range among the plurality of electrical pulse signals stored by the storage unit reaches a threshold value corresponding to the pulse magnitude within the specific range. , a time detection unit that detects as an interaction time in the radiator;
A Cerenkov detector with The time detection unit is configured such that a value of an electrical pulse signal having a pulse magnitude within the specific range among the electrical pulse signals output from the anode reaches a threshold value corresponding to the pulse magnitude within the specific range. Detecting the reaching time as the interaction time in the radiator,
Cerenkov detector according to claim 1. A radiator that generates Cherenkov light by interaction with incident particles, a photoelectric conversion unit that emits electrons in response to the incidence of the Cherenkov light generated by the radiator, and an increase in the electrons emitted from the photoelectric conversion unit. A detector comprising: an electron multiplier having one or more microchannel plates that multiply and output; and an anode that collects the electrons multiplied and output by the electron multiplier and outputs an electric pulse signal. When,
A pulse of the electrical pulse signal output from the anode based on a specific range of the pulse magnitude and the threshold value of the electrical pulse signal at which the magnitude of the variation in the time when the value of the electrical pulse signal reaches the threshold value is equal to or less than the allowable value. a time detection unit that detects, as an interaction time in the radiator, the time at which the value of the electrical pulse signal whose magnitude is within the specific range reaches a threshold value corresponding to the magnitude of the pulse within the specific range; ,
A Cerenkov detector with a storage unit that stores waveforms of electrical pulse signals output from the anode for each interaction event in the radiator;
an analysis unit that obtains the specific range using waveforms of a plurality of electrical pulse signals stored in the storage unit;
4. The Cerenkov detector of claim 3, further comprising: A method for setting the specific range in the Cerenkov detector according to claim 3, comprising:
a storage step of storing waveforms of electrical pulse signals output from the anode for each interaction event in the radiator;
an analysis step of obtaining the specific range using the waveforms of the plurality of electrical pulse signals stored in the storage step;
A Cerenkov detector setup method comprising: The photon pairs of gamma rays generated by pair annihilation of electrons and positrons are detected by the coincidence counting method in the subject placed in the measurement space after the RI radiation source is turned on, and the coincidence counting information is collected. A device for acquiring a tomographic image of the subject based on coincidence information,
The Cherenkov detector according to any one of claims 1 to 4 is provided as each of a plurality of detectors that are provided around the measurement space and detect gamma rays,
PET device.

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