JP2014197015A - RADIOACTIVITY ABSOLUTE MEASURING METHOD OF POSITIVE ELECTRON DECAY NUCLIDE RELEASING γ RAY, DETECTION EFFICIENCY DETERMINATION METHOD OF RADIATION DETECTOR AGGREGATE, AND CALIBRATION METHOD OF RADIATION MEASURING APPARATUS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the uncertainty in the radioactivity absolute value by achieving radioactivity measurement considering the influence of multiple scattering and pileup of radiation.SOLUTION: When pileup is detected through a pileup event energy window of an electron-positive-electron-pair annihilation photon and another photon, the number of detected photons on an energy window of an electron-positive-electron-pair annihilation photon is added and corrected, and it is considered that a photon detection event on an another-photon energy window and a simultaneous detection event of an electron-positive-electron-pair annihilation photon and another photon occur.

Description

  The present invention relates to an absolute radioactivity measurement method, a detection efficiency determination method for a radiation detector assembly, and a calibration method for a radiation (radioactivity) measurement device (collectively referred to as a radiation measurement device), and in particular, positron emission tomography. (Positron Emission Tomography: PET) Absolute radioactivity measurement method for absolute measurement of radioactivity of nuclides emitting a plurality of photons of different positron and energy, suitable for use in calibration of an apparatus The present invention also relates to a method for determining the detection efficiency of a radiation detector assembly using the absolute radioactivity measurement method, and a calibration method for a radiation measurement device used in medical diagnostic equipment, non-destructive inspection devices, and the like.

  The PET apparatus is a nuclear medicine imaging apparatus using a positron emitting nuclide and is widely applied to cancer diagnosis and molecular imaging. In addition, the open PET device used in combination with the radiotherapy device will visualize the radiation dose distribution in the affected area, or the microdosing test will progress with a PET device that can estimate the efficacy before full-scale administration. The spread is expected.

Positron emitting nuclides are unstable isotopes due to the excessive number of protons in the nucleus compared to the number of neutrons, such as ¹⁸ F, and have the property of emitting positrons and neutrinos with β ⁺ decay. . Since the emitted positron is an antimatter of electrons, when it meets an electron, it annihilates and all the masses of both are converted into energy. This energy is emitted in the form of high energy electromagnetic waves called annihilation radiation. Since the momentum conservation law is maintained before and after the pair annihilation, two annihilation radiations are mainly emitted in almost opposite directions at the same time. Strictly speaking, there are cases in which only one emission or three or more emission occurs, but since the ratio is less than 1% of the total, it can be ignored in imaging. When emitting two, each energy corresponds to the mass of one (positive) electron, and is about 511 keV.

  The principle of imaging is as follows. When simultaneous counting of annihilation radiation occurs, that is, when 511 keV radiation is measured at approximately the same time by two opposing radiation detectors, the positrons may have disappeared on a straight line connecting the two radiation detectors. Most likely. As shown in FIG. 1, this information is collected using a number of radiation detectors 16 arranged around the subject 10 in a ring shape, and is reconstructed by a mathematical method similar to that for X-ray CT. A tomographic image that approximates the distribution of the positron emitting nuclide 12 in the specimen 10 is obtained. In the figure, 14 is annihilation radiation, and 18 is a bed.

Therefore, the performance required for the radiation detector 16 is that the incident position, energy, and incident time of the annihilation radiation 14 can be measured as accurately as possible. Here, the almost same time is a time within about 15 nanoseconds (nano is 10 ⁻⁹ ), and when the time determination accuracy of the radiation detector is high, it is set to 10 nanoseconds or less, or 5 nanoseconds or less. be able to.

  As a detector for this PET apparatus, a set of radiation detectors capable of obtaining depth direction interaction position (DOI) information composed of a number of radiation detector elements as shown in FIG. A body (also referred to as a DOI detector) 20 has been proposed. In the figure, 21-24 are scintillator arrays of each layer, and 26 is a light receiving element.

  A radiation detector assembly loaded inside a PET device or the like is a device that relatively measures the radioactivity of an object to be measured, and its detection efficiency (sensitivity) is a standard radiation source that has been given a radioactivity value in advance. A change over time in the relative detection efficiency (sensitivity) of the radiation detector assembly has been required depending on the radiation source to which the radiation detector is assigned or an approximate radioactivity value. Radiation sources have a half-life and must be replaced regularly. However, if the radiation source is replaced, the accuracy of the radiation value of the radiation source will be poor, so the radiation detection loaded inside the PET device etc. The measured value of the detection efficiency (sensitivity) of the vessel assembly has also changed as illustrated in FIG. Therefore, it has been required to improve the accuracy of the detection efficiency (sensitivity) of the radiation detector assembly loaded inside the PET apparatus or the like.

On the other hand, the radioactivity of radiation sources that emit β-rays, X-rays, Auger electrons and γ-rays, such as ⁵⁷ Co, ⁵⁴ Mn, and ¹³⁴ Cs, has been measured by a radiation detector such as a 4πβ-γ simultaneous measurement device. . If a certain energy radiation (Radiation 1) and a certain energy radiation (Radiation 2) are emitted from the source continuously in a single decay with a certain probability, the counting rate for detecting radiation 1, radiation 2 It is generally known that the radioactivity of a radiation source can be absolutely measured by using the count rate for detecting the radiation and the count rate for simultaneously detecting the radiation 1 and the radiation 2 (referred to as a coincidence method) (Non-Patent Document) 1).

  Therefore, when measuring the radioactivity absolutely, as illustrated in FIG. 4, a radiation detector (detector 1) for detecting radiation 1 and a radiation detector (detector 2) for detecting radiation 2 have been used. . Here, 100 is a radiation source, 110 is a beta ray or X-ray as radiation 1, Auger electrons, 112 is a gamma ray as radiation 2, 120 is a proportional counter as detector 1, for example, 130 and 132 are detectors For example, NaI (T1) scintillator as 2, 140 is a coincidence counting circuit.

  In this method, the β-ray 110 is counted by the proportional counter 120, the γ-ray 112 is counted by the scintillators 130 and 132, and the events in which the β-ray and the γ-ray are simultaneously detected by the coincidence counting circuit 140 are also counted. The detector 1 may detect the radiation 2 and the like, and an extrapolation method is used to correct them (see Non-Patent Document 1).

  This method is based on a count rate for detecting radiation 1, a count rate for detecting radiation 2 and a count rate for detecting radiation 1 and radiation 2 at the same time. Detection efficiency) and apparent radioactivity value are used, and as shown in FIG. 5, a relational expression between the detection inefficiency value and the apparent radioactivity value is obtained. When the detection inefficiency value is 0, that is, when the detection efficiency is 100%, Radioactivity is an absolute value.

  In order to perform absolute measurement with the former 4πβ-γ simultaneous measurement apparatus, two types of detectors were required. In addition, when the count rate is high, a plurality of radiations are incident on the detector at the same time and are detected as if they were one other radiation (pile-up) as shown in FIG. There is. For this reason, in the conventional method, a radiation source having a radioactivity value of about several kBq is measured, and it is difficult to absolutely measure high intensity radioactivity used in a PET apparatus. In order to solve this, there has been proposed a method of absolute measurement of the radioactivity of a high-intensity radiation source with one type of detector using a radiation detector assembly (Patent Document 2).

Japanese Patent Laying-Open No. 2004-279057 (FIG. 1) JP 2008-249337 A

ICRU report 52, Particle counting in radioactivity measurements, International Commission on radiation units and measurements, vol.1, 1994

  However, since the method requires extrapolation, a large number of measurement points are necessary. Therefore, in order to obtain radioactivity, a large number of the same calculation circuits are required, a large number of parts are required, repeated calculation is required many times, and calculation time is required. In addition, the uncertainty of radioactivity due to extrapolation accounted for most of the overall uncertainty.

  The present invention has been made to solve the above-mentioned conventional problems, and reduces the uncertainty of the radioactivity absolute value by realizing radioactivity measurement in consideration of the effects of multiple scattering and pileup of radiation. Is the first problem.

  Another object of the present invention is to make it possible to determine the detection efficiency of the radiation detector assembly.

  It is a third object of the present invention to make it possible to calibrate a radiation measuring apparatus using a radiation detector assembly.

  The present invention is a radioactivity absolute measurement method based on the premise that it is difficult to completely discriminate between electron positron pair annihilation photons and other photons, and other photons are counted as electron positron pair annihilation photons.

  That is, the present invention adds and corrects the number of photon detections in the electron positron pair annihilation photon energy window when pileup is detected in the pileup event energy window of electron positron pair annihilation photon and other photon. The first problem is solved by assuming that there is a photon detection event in a window and a simultaneous detection event of an electron positron annihilation photon and another photon.

  The present invention also provides an electron positron pair annihilation photon energy window, an other photon energy window, an electron positron pair annihilation photon and another photon pileup event energy window with respect to the radiation spectrum. The effect of low energy scattered radiation is reduced over the part.

  In the present invention, the detection efficiency of the radiation detector assembly is obtained from the photon count rate of the radiation detector assembly using the radioactivity absolute value determined by the above method. This is a solution to this problem.

  Further, the third problem is solved by calibrating the radiation measuring apparatus provided with the radiation detector assembly using the radioactivity absolute value determined by the above method.

  Here, the radiation measurement apparatus may be a PET apparatus.

  The radiation detector assembly is carried into a work site as an intermediary standard for calibration, a radioactivity absolute value is given to a radiation source at the work site, and this radiation source is used at the work site. And the output of the radiation measuring apparatus can be related to the absolute value of radioactivity.

  Also, the radiation source is dispensed and divided into a radiation source for the radiation detector assembly and a radiation source for the radiation measuring apparatus, the weight of each radiation source is measured, and the radiation source for the radiation detector assembly is measured by the radiation detector. Measure with the aggregate and give the radioactivity absolute value. From the radioactivity absolute value and the weight of the radiation source, give the radioactivity absolute value to the radiation source for the radiation measurement device. The source can be measured with a radiation measurement device at the work site, and the output value of the radiation measurement device and the radioactivity absolute value of the radiation source for the radiation measurement device can be related.

  According to the present invention, the effect of pileup can be reduced with a PET apparatus equipped with a radiation detector assembly and the radioactivity absolute measurement can be performed with high accuracy. Therefore, the PET apparatus or the like using a radiation source to which no radioactivity value is given. Detection efficiency (sensitivity) can be determined. At this time, since the detection efficiency (sensitivity) can be obtained directly from the absolute value of radioactivity, the detection efficiency (sensitivity) can be determined stably and accurately.

  In addition, when a radiation detector is calibrated using the radiation detector assembly as an intermediary standard device, the absolute value of radioactivity is accurately given to radiation sources that were difficult to transport or measure because of their short lifetime. The radiation detector can be calibrated with high accuracy using the radiation source to which the absolute value of radioactivity is given. Moreover, even if the radiation source can be transported, there is a risk of loss or theft during transportation. However, according to the present invention, it is not necessary to transport the radiation source, and the calibration can be performed safely.

  These effects can be realized at a lower cost than an apparatus that measures the absolute radiation value using extrapolation, and the calculation speed for obtaining the absolute radioactivity value can be improved. Furthermore, the uncertainty of the radioactivity absolute value can be reduced.

  In addition, these effects can be realized with less radio uncertainty compared to the conventional method particularly for a radioactivity measurement apparatus including a PET apparatus having a large number of radiation detection elements.

Sectional drawing which shows schematic structure of the conventional PET apparatus. The perspective view which shows the structural example of the conventional DOI detector. The figure which shows the problem in the calibration of the conventional PET apparatus Block diagram showing the configuration of an example of a conventional 4πβ-γ simultaneous measurement apparatus Diagram showing an example of absolute value measurement by efficiency extrapolation Diagram showing an example of spectrum pileup Diagram showing reference form The block diagram which shows the example of the radioactivity absolute value calculation circuit incorporated in the counting device of a reference form Similarly, a block diagram showing another example of a radioactivity absolute value calculation circuit A flowchart showing the first half of an example of an algorithm that is also implemented in a computer Flow chart showing the second half A flow chart showing another example of an algorithm that is also implemented in the computer The figure which shows the multiple scattering which is a subject of 1st Embodiment of this invention The block diagram which shows the example of the radioactive absolute value calculation circuit incorporated in the counting device of 1st Embodiment of this invention Diagram showing an example of the photoelectric absorption energy range The flowchart which shows the first half of the example of the algorithm mounted in the computer by 1st Embodiment Flow chart showing the second half The figure which shows 2nd Embodiment of this invention. The figure which similarly shows 3rd Embodiment The figure which similarly shows 4th Embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 7 is a reference form showing an absolute radioactivity measurement method using a radiation detector assembly without extrapolation and a detection efficiency (sensitivity) measurement method of the radiation detector assembly. In the figure, 200 is a radiation source, 210 and 212 are radiation detector assemblies, for example, DOI detectors, 220 is a counting device, 240 is a calculator, 250 is an input device, and 260 is a display device.

  A plurality of photons are emitted from the radiation source 200. Photons are incident on the radiation detector assemblies 210 and 212, and the counting device 220 counts the incident time of the photons, the energy of the photons, and the identification number of the detection element that detected the photons as a set. Stored in a storage device. Further, when the radioactivity value is calculated by the counting device 220, the radioactivity value is output to the calculator 240. The calculator 240 is operated by the input device 250 and the input content and result are displayed by the display device 260.

  In the case of a system capable of calculating a radioactivity value while counting photons, a circuit having an algorithm as shown in FIG. 8 or FIG. The case of FIG. 8 is as follows. A set of photon incident time, photon energy, and identification number of the detection element that has detected the photon is sent to energy filters 221 and 222 that pass only the set including the energy of interest. Here, 221 passes the one having the photoelectric absorption energy range (energy window A) of electron-positron pair annihilation photons, and 222 passes the one having the photoelectric absorption energy range (energy window G) of other photons.

  A circuit 223 discriminates the number of detected photons in the energy window A.

  224 and 225 are circuits for discriminating the simultaneous detection of photons within a certain time width in the energy window A and the energy window G, and 224 is used when one or more photons are detected in the energy window A. 225 is used when a single photon is detected in the energy window A.

  226, 227, 228, 229, 230 are counters, and during the measurement time, 226 is a count of single or multiple photon detection events in energy window A, and 227 is a single photon detection event in energy window A. Count 228 is a coincidence of a photon detection event in energy window A and a photon detection event in energy window G over a period of time, and 229 is a photon detection event in energy window A. A coincidence of photon detection events in energy window G over a period of time, 230 is a count of photon detection events in energy window G.

Reference numeral 231 denotes a radioactivity absolute value calculation circuit, which is based on the counter value from 226 to 230 and the measurement time, and the counting rate ρ _a of single or plural detection events of photons in the energy window A, in the energy window A Photon single detection event count rate ρ _as , photon detection event count rate ρ _γ in energy window G, photon single or multiple photon detection event in energy window A and photon detection event in energy window G coincidence ratio [rho _c of, the coincidence rate [rho _cs of at photon detection events singular detection events and energy window G of in photon energy window a is determined, from these radioactive absolute value a is calculated.

The formula for calculating the radioactivity absolute value A is, for example, as follows in the case of ²² Na.

Here, alpha _beta, alpha _ec is the branching ratio that disintegrate the energy level by a branch ratio and EC ^{collapse 22} Na collapses the energy level of 1245keV of ²² Ne by beta ⁺ decay. Similarly, radioactivity is obtained by formulating a calculation formula according to the nuclear decay mode for each nuclide.

  The obtained radioactivity absolute value is sent to the computer 240 shown in FIG.

  The case of FIG. 9 is as follows. A set of photon incidence time, photon energy, and identification number of the detection element that has detected the photon is sent to energy filters 271 and 272 that pass only the set including the energy of interest, and further sent to the spectrum analyzer 273. Here, the energy filter 271 passes the one having the photoelectric absorption energy range (energy window A) of electron-positron pair annihilation photons, and the energy filter 272 passes the one having the photoelectric absorption energy range (energy window G) of other photons. The spectrum analyzer 273 also receives all data sets and creates a photon spectrum.

  The simultaneous event detection circuit 274 detects simultaneous detection of a photon in the energy window A and a photon in the energy window G in a certain time width.

  Counters 275, 276, and 277 respectively count photon detection events in energy window A, and coincidence of photon detection events in energy window A and photon detection events in energy window G over a period of time. The photon detection event is counted in the energy window G.

The count rate ratio calculation circuit 278 separates the peak portion and the continuous portion for the energy window A from the photon spectrum obtained by the spectrum analyzer 273, obtains the count of the peak portion and the count of the continuous portion, and determines the electron based on this and the measurement time. The ratio of the count rate due to non-photo absorption of other photons to the count rate due to photoelectric absorption of positron pair annihilation photons is obtained. For the separation of the peak portion count and the continuous portion count, the method described in the Ministry of Education, Culture, Sports, Science and Technology's Radioactivity Measurement Series 7, gamma-ray spectrometry using a germanium semiconductor detector can be used. From the count rate ρ _{peak of the peak} portion and the count rate ρ _{cont of the} continuous portion, the count rate ratio is obtained as ρ _cont / ρ _peak .

In the radioactivity absolute value calculation circuit 279, the counting rate ρ _a of photon detection events in the energy window A from the measurement time and the counts obtained from the counters 275, 276, 277, and the photon detection events in the energy window G are calculated. The count rate ρ _γ , the coincidence count rate ρ _c of the photon detection event in the energy window A and the photon detection event in the energy window G is obtained, and the count rate ratio ρ _cont / ρ is obtained from the count rate ratio calculation circuit 278. Obtain the _peak and calculate the radioactivity absolute value A.

The calculation method of the radioactivity absolute value A is, for example, in the case of ²² Na as follows:

Here, α _β and α _ec are the branch ratio at which ²² Na decays to the energy level of 12N keV of ²² Ne due to β ⁺ decay and the branch ratio at which the decay to the same energy level due to EC decay. Similarly, radioactivity is obtained by formulating a calculation formula according to the nuclear decay mode for each nuclide.

  The computer 240 shown in FIG. 7 may be omitted, and the input device 250 and the display device 260 may be directly connected to the counting device 220.

  On the other hand, when the radioactivity calculation is performed by the computer 240 instead of the counting device 220, the counting device 220 outputs a set of data of the incident time of the photon, the energy of the photon, and the number of the detection element that has detected the photon. 8 or 9 is implemented in the computer 240, or the photon incident time, the photon energy, and the data of the detection element number that detected the photon are output as a set from the counting device 220. The radioactivity can be calculated by an algorithm as shown in FIGS. 10 to 11 and 12 installed in the computer 240 after being temporarily stored in a storage device in the computer 240.

  Specifically, first, in step 301 of FIG. 10, the photoelectric absorption energy range (energy window A) of electron-positron pair annihilation photons and the photoelectric absorption energy range (energy window G) of other photons are determined.

  Next, in step 302, the data string 1 in the energy window A, arranged in the order of the photon incidence time of only the photon incidence time, the photon energy, and the number of the detection element number detecting the photon, and the energy window A data string 2 is formed in G, which is arranged in the order of the photon incidence times of only the photon incidence time, the energy of the photon, and the data number of the detection element that detected the photon.

  Next, in step 303, the data set having the oldest incident time among the data sets not yet read is read from the data string 1 or the data string 2.

  Next, in step 304, it is determined whether or not the data string 1 has been read. If the determination result in step 304 is “Yes”, the process proceeds to step 305.

  In step 305, it is determined whether there is a data set having the same time incidence in the time width in the data string 1. If the determination result in step 305 is “Yes”, the process proceeds to step 306. In step 306, the data set at the same time incidence is read from the data string 1, and the count value of the photon single or plural detection events in the energy window A is incremented by one. Note that even if there are two or more sets of data incident at the same time, the count value is increased by one.

  Next, in step 307, it is determined whether there is a set of incidents at the same time with a time width in the data string 2. If the determination result in step 307 is “Yes”, the process proceeds to step 308.

  In step 308, data is read from the data string 2, and the count value of the photon detection event in the energy window G is incremented by one. Furthermore, the count value of the simultaneous event of the photon detection event in the energy window A and the photon detection event in the energy window G is increased by one.

  On the other hand, if the determination result in step 305 is “No”, the process proceeds to step 309.

  In step 309, the count value of the single photon detection event in the energy window A is incremented by 1, and further, the count value of the single photon detection event or multiple detection events in the energy window A is incremented by one.

  Next, at step 310, it is determined whether or not there is a set having the same time incidence in the time width in the data string 2. If the determination result in step 310 is “Yes”, the process proceeds to step 311.

  In step 311, the data is read from the data string 2, the count value of the photon detection event in the energy window G is incremented by 1, and further, the single photon detection in the energy window A and the photon detection in the energy window G are detected. , And the photon detection event in energy window A and the photon detection event in energy window G are incremented by one.

  On the other hand, if the determination result in step 304 is “NO”, the process proceeds to step 312 in FIG. 11 to increment the photon detection event count value in the energy window G by one.

  Next, in step 313, it is determined whether or not a data set having the same time incidence with a certain time width exists in the data string 1. If the determination result in step 313 is “Yes”, the process proceeds to step 314.

  In step 314, a data set at the same time is read from the data string 1.

  Next, in step 315, it is determined whether there is a set of incidents at the same time with a time width in the data string 1. If the determination result in step 315 is “Yes”, the process proceeds to step 316.

  In step 316, data is read from data string 1. Increase the count of photon singularity / plurality detection events in energy window A by one, and increment the count of simultaneous photon detection / single event detections in energy window A and photon detection in energy window G by one. increase.

  On the other hand, if the determination result in step 315 is “No”, the process proceeds to step 317 where the count value of the photon singularity detection event in the energy window A is incremented by 1, and the photon singularity detection in the energy window A and the energy are detected. Increment the photon detection count in window G by one. Further, the count value of the photon detection event in the energy window A is incremented by 1, and the count value of the simultaneous photon detection event in the energy window A and the photon detection in the energy window G is increased. Increase by one.

  After Steps 308 and 311 in FIG. 10, 316 and 317 in FIG. 11, or when the determination result in Steps 307 and 310 in FIG. 10 and 313 in FIG. 11 is “No”, the process proceeds to Step 318 in FIG. Determine whether all data sets have been read. If the determination result in step 318 is “Yes”, the process proceeds to step 319, where the counting rate of the single photon detection event count in the energy window A, which is obtained from the measurement time and each count value, in the energy window A Photon single or multiple detection events count rate, photon single detection event in energy window A and photon detection event coincidence in energy window G, photon single and multiple detection events in energy window A and energy window The absolute value of radioactivity is calculated using the coincidence rate of photon detection events in G, the count rate of photon detection events in energy window G, and equations (1) to (2), for example. On the other hand, if the determination result in step 318 is “No”, the process proceeds to step 303 in FIG.

  In FIG. 12, in step 331, a photon energy spectrum is created using all data.

Next, in step 332, the peak portion and the continuous portion are separated from the obtained photon energy spectrum in the energy window A, and the count of the peak portion and the count of the continuous portion are obtained. A count rate ratio ρ _cont / ρ _peak is obtained by dividing the count rate ρ _cont in the electron positron pair annihilation photon energy window due to the non-photo absorption of other photons by the count rate ρ _peak due to the photoelectric absorption. For the separation of the peak portion count and the continuous portion count, the method described in the Ministry of Education, Culture, Sports, Science and Technology's Radioactivity Measurement Series 7, gamma-ray spectrometry using a germanium semiconductor detector can be used.

  Next, in step 333, the photoelectric absorption energy range (energy window A) of the electron-positron pair annihilation photon and the photoelectric absorption energy range (energy window G) of other photons are determined.

  Next, in step 334, the data sequence 1 arranged in the order of the photon incidence time of only the photon incidence time in the energy window A, the photon energy, and the detection element number data set that detected the photon, and the energy window G The data string 2 is formed in the order of the photon incident time of only the data set of the photon incident time, the energy of the photon, and the number of the detection element that has detected the photon.

  Next, in step 335, the data set having the oldest incident time among the data sets not yet read is read from the data string 1 or the data string 2.

  Next, in step 336, it is determined whether data is read from the data string 1. If the determination result in step 336 is “Yes”, the process proceeds to step 337.

  In step 337, the photon detection event count in energy window A is incremented by one.

  Next, in step 338, it is determined whether or not the data string 2 has a set of incidents at the same time with a certain time width. If the determination result in step 338 is “Yes”, the process proceeds to step 339.

  In step 339, the data is read from the data string 2, the count value of the photon detection event in the energy window G is incremented by 1, and the simultaneous detection event of the photon in the energy window A and the photon in the energy window G is performed. Is incremented by one.

  On the other hand, if the determination result of step 336 is “No”, the process proceeds to step 340.

  In step 340, the photon detection event count in the energy window G is incremented by one.

  Next, in step 341, it is determined whether there is a set having the same time incidence with a time width in the data string 1. If the determination result in step 341 is “Yes”, the process proceeds to step 342.

  In step 342, the data is read from the data string 1, the count value of the photon detection event in the energy window A is incremented by 1, and the simultaneous detection event of the photon in the energy window A and the photon in the energy window G is performed. Is incremented by one.

  After Steps 339 and 342 are completed, or when the determination result of Steps 338 and 341 is “No”, the process proceeds to Step 343.

  In step 343, it is determined whether all data sets have been read. If the determination result in step 343 is “Yes”, the process proceeds to step 344.

In step 344, the photon detection event count rate ρ _{a in} the energy window A, the photon detection event count rate ρ _γ in the energy window G, the photon detection event in the energy window A and the energy window A The coincidence rate ρ _c of the photon detection event, the count rate ρ _peak of the peak portion due to the photoelectric absorption of the electron-positron pair annihilation photon in the energy window A, and the count rate ratio ρ divided by the count rate ρ _cont of the continuous portion due to other photons _{Using cont} / ρ _peak , for example, the radioactivity absolute value A is calculated by the above equation (3).

  On the other hand, if the determination result in step 343 is “No”, the process returns to step 335.

As described above, since the radioactivity absolute value of the radiation source can be calculated by the radiation detector assembly, the number of photons incident on the radiation detector assembly per unit time can be calculated based on this value. The emission rate of the radiation emitted from the radiation source per nuclear decay is Table of Isotopes, eight edition, volume I, II, R.I. B. Firestone and V. S. Can be referenced from nuclear data such as Shirley, Wiley Interscience, Table of radionuclides, Volume 1, 2, 3, Monoguraphie BIPM-5, Bureau International Des Poids et Mesures, Recommended data, the Laboratoire National Henri Becquerel, and the location of the source The number of radiation per unit time incident on the radiation detector assembly can be calculated from the coefficients according to the geometric relationship between the radiation detector assembly and the numerical values obtained from these values and the radiation activity of the source. it can. The detection efficiency (sensitivity) of the radiation detector assembly is obtained by dividing the photon counting rate of the radiation detector assembly by the photons incident on the radiation detector assembly per unit time. Also, the detection efficiency (sensitivity) may be calculated by dividing the photon counting rate of the radiation detector assembly by the number of photons generated from the source per unit time or the radiation of the source. It is.

In the reference mode, for example, when the nuclide is ²² Na, it is assumed that other photons enter the energy window of 511 keV only once as illustrated in FIG. 13A. However, when the number of detection elements increases. As illustrated in FIG. 13B, it is inevitable that other photons are affected by multiple scattering of radiation in which two photons are counted simultaneously in an energy window of 511 keV. Furthermore, although it has been difficult for pile-up to occur by using a large number of detection elements, no case has been dealt with when pile-up occurs. Hereinafter, a first embodiment of the present invention that solves such a problem will be described.

  The overall configuration of this embodiment is the same as that of the reference embodiment shown in FIG.

  In contrast to FIG. 8 of the reference form, in this embodiment, a circuit having an algorithm as shown in FIG. A set of photon incident time, photon energy, and identification number of the detection element that has detected the photon is sent to energy filters 281, 282, and 283 that pass only the set including the energy of interest. Here, 281 passes the one having the photoelectric absorption energy range (energy window A) of the electron positron pair annihilation photon, 282 passes the one having the photoelectric absorption energy range (energy window G) of other photons, and 283 denotes the electron positron. A pair having an energy range (energy window P) of pile-up due to photoelectric absorption of pair annihilation photons and photoelectric absorption of other photons is passed.

  Here, the photoelectric absorption energy range is not necessarily the entire photoelectric absorption energy peak range. For example, as shown in FIG. 15, by reducing the influence of low energy scattered photons due to the Compton effect by using the high energy side half of the photoelectric absorption energy peak as the photoelectric absorption energy range, by using only the portion due to the photoelectric effect. It is also possible to suppress radioactivity measurement uncertainty. The photoelectric absorption energy range is not limited to the high energy side half, and may be cut on the low energy side. If the photoelectric absorption energy range is set narrow, it is possible to further reduce the influence of low energy scattered photons, but it is necessary to lengthen the measurement time in order to reduce the counting rate and reduce the radioactivity measurement uncertainty. Therefore, the photoelectric absorption energy range is set in consideration of the measurement time. The portion of the energy window P in FIG. 15 is the pile-up portion that was ignored in the reference embodiment.

  The data passing through the energy filter 283 is handled in the subsequent circuits so that the data passes through the energy filter 281 (that is, energy window A) and the energy filter 282 (that is, energy window G) one by one at the same time. That is, it is assumed that one photon is detected in the energy window A and one photon is detected in the energy window G. Further, this does not prevent other data from passing through the energy windows A and G at the same time. When other data passes through the energy windows A and G at the same time, the number of simultaneously detected photons is added.

  A circuit 284 discriminates the number of photons detected in the energy window A.

  Reference numerals 285, 290, and 294 denote circuits for discriminating simultaneous detection of photons in the energy window A and photons in the energy window G in a certain time width. Reference numeral 285 denotes detection of one or more photons in the energy window A. 290 is used when a single photon is detected in the energy window A, and 294 is used when two photons are detected in the energy window A.

  286, 287, 288, 291, 292, 295, 296 are counters, and during the measurement time, 286 is a count of single or multiple photon detection events in energy window A, and 287 is a photon count in energy window G. Counting detection events 288 is a coincidence of photon detection events in energy window A and photon detection events in energy window G over a period of time, and 291 is the number of photons in energy window A. A single detection event count, 292 is a coincidence count of a single photon detection event in energy window A and a photon detection event in energy window G over a period of time, 295 is a two-photon detection in energy window A Event count, 296 is the two-photon detection event in energy window A and energy window G Kicking performing coincidence at a certain time width of detection events of a photon.

  Reference numerals 293 and 297 denote circuit units that perform photon detection in the energy window A and simultaneous photon detection in the energy window A and energy window G. If necessary, three-photon detection in the energy window A, energy The number of circuit units can be increased, such as four-photon detection in window A.

Reference numeral 289 denotes a radioactivity absolute value calculation circuit, which is based on the counter value of 296, 297, etc., and the measurement time, the count rate ρ _a of the photon single or plural detection events in the energy window A, and the photon in the energy window G Detecting event count rate ρ _g , photon single or multiple detection events in energy window A and photon detection event coincidence rate in energy window G ρ _ag , photon single detection event count rate in energy window A ρ _as , a coincidence rate ρ _{asg of} a single photon detection event in the energy window A and a photon detection event in the energy window G ρ _asg , a count rate ρ _ad of the two photon detection event in the energy window A, and an energy window A coincidence ratio [rho _adg etc. in two-photon detection event and in photon detection events to the energy window G are obtained, from these Ino absolute value A is calculated.

The calculation formula of the radioactivity absolute value A is as follows, for example, when the nuclide is ²² Na and the number of photons detected in the energy window A is single or plural, single photon, two photons.

Here, alpha _beta, alpha _ec is the branching ratio that disintegrate the energy level by a branch ratio and EC ^{collapse 22} Na collapses the energy level of 1245keV of ²² Ne by beta ⁺ decay. Similarly, the radioactivity is obtained by formulating a calculation formula corresponding to the nuclear decay mode for each nuclide and using the data of the number of counting rates as required.

  The obtained radioactivity absolute value is sent to the computer 240 shown in FIG.

  On the other hand, when the radioactivity calculation is performed by the computer 240 instead of the counting device 220, the counting device 220 outputs a set of data of the incident time of the photon, the energy of the photon, and the number of the detection element that has detected the photon. 14 is implemented in the computer 240, or the counting device 220 outputs the photon incident time, the energy of the photon, and the data of the number of the detection element that detected the photon as a set, and the computer 240 Once stored in the storage device, the radioactivity can be calculated by an algorithm as shown in FIGS.

  Specifically, first, in Step 351 of FIG. 16, the photoelectric absorption energy range (energy window A) of the electron positron pair annihilation photon, the photoelectric absorption energy range of other photons (energy window G), and the photoelectric of the electron positron pair annihilation photon. The energy range (energy window P) of the pileup of absorption and photoelectric absorption of other photons is determined. Here, the photoelectric absorption energy range is not necessarily the entire photoelectric absorption energy peak range. For example, as shown in FIG. 15, it is also possible to reduce the influence of low energy scattered photons and suppress the radioactivity measurement uncertainty by setting the photoelectric absorption energy range to the high energy side half of the photoelectric absorption energy peak. It is. If the photoelectric absorption energy range is set narrow, the influence of low energy scattered photons can be further reduced, but the counting rate is lowered and it is necessary to lengthen the measurement time in order to reduce the radioactivity measurement uncertainty. Therefore, the photoelectric absorption energy range is set in consideration of the measurement time.

  Next, in step 352, the data string 1 arranged in the order of the photon incidence time of only the photon incidence time, the photon energy, and the number of the detection element number detecting the photon, which is the energy in the energy window A, A data string 2 is created, which is arranged in the order of the photon incidence time of only the photon incidence time, the energy of the photon, and the data number of the detection element that detected the photon, which is the energy in the energy window G. At this time, for the data set of the photon incident time, the photon energy, and the detection element number that detected the photon, which is the energy in the energy window P, the photon incident time, which is the energy in the energy window A, A set of data of photon energy and the number of the detection element that detected the photon, and a set of data of the photon incident time, photon energy, and the number of the detection element that detected the photon, which are the energy within the energy window G, respectively. Treat as one by one.

  Next, in step 353, the data set having the oldest incident time among the data sets not yet read is read from the data string 1 or the data string 2.

  Next, in step 354, it is determined whether or not the data string 1 has been read. If the determination result in step 354 is “Yes”, the process proceeds to step 355.

  In step 355, it is determined how many data sets have the same time incidence in the time width in the data string 1. If the determination result in step 355 is “not applicable to other branch”, the process proceeds to step 356.

  In step 356, a set of data incident at the same time with a certain time width is read from the data string 1, and the count value of the photon singular or plural detection events in the energy window A is incremented by one. Note that even if there are two or more (multiple) sets of data incident at the same time, only one count value is increased.

  Next, in step 357, it is determined whether or not there is a set of incidents at the same time with a time width in the data string 2. If the determination result in step 357 is “Yes”, the process proceeds to step 358.

  In step 358, data is read from the data string 2, and the count value of the photon detection event in the energy window G is incremented by one. Furthermore, the count value of the simultaneous event of the photon detection event in the energy window A and the photon detection event in the energy window G is increased by one.

  On the other hand, when the determination result in step 355 is “1”, the process proceeds to step 359 of the component 362.

  In step 359, the count value of the single photon detection event in the energy window A is incremented by 1, and further, the count value of the single photon detection event or multiple detection events in the energy window A is incremented by one.

  Next, in step 360, it is determined whether or not there is a set having the same time incidence in the time width in the data string 2. If the determination result in step 360 is “Yes”, the process proceeds to step 361.

  In step 361, the data is read from the data string 2, the count value of the photon detection event in the energy window G is incremented by 1, and the photon singularity detection in the energy window A and the photon detection in the energy window G are detected. , And the photon detection event in energy window A and the photon detection event in energy window G are incremented by one.

  On the other hand, if the determination result in step 355 is “2”, the process proceeds to step 363 in the component 366 where a set of simultaneously incident data with a certain time width is read from the data string 1 and the two-photon detection event in the energy window A And the count of photon single or multiple detection events in energy window A is incremented by one.

  Next, in step 364, it is determined whether or not there is a set having the same time incidence in the time width in the data string 2. If the determination result in step 364 is “Yes”, the process proceeds to step 365.

  In step 365, data is read from the data string 2, the count value of the photon detection event in the energy window G is incremented by 1, and further, the two-photon detection in the energy window A and the photon detection in the energy window G are detected. , And the photon detection event in energy window A and the photon detection event in energy window G are incremented by one.

  The component 362 and the component 366 are parts that perform counting based on the number of detected photons in the energy window A. The component 362 is when the number of photons is 1, and the component 366 is when the number of photons is 2. If necessary, the same algorithm can be increased when the number of photons is 3 and when the number of photons is 4.

  On the other hand, if the decision result in the step 354 is “No”, the process advances to a step 367 in FIG. 17 to increment the photon detection event count value in the energy window G by one.

  Next, in step 368, it is determined whether or not a data set having the same time incidence with a certain time width exists in the data string 1. If the determination result in step 368 is “Yes”, the process proceeds to step 369.

  In step 369, a data set of the same time incident with a certain time width is read from the data string 1.

  Next, in step 370, it is determined how many pairs of the same time incidence exist in the time width in the data string 1. If the determination result in step 370 is “not applicable to other branch”, the process proceeds to step 371.

  In step 371, data is read from data string 1. Increase the count of photon singularity / plurality detection events in energy window A by one, and increment the count of simultaneous photon detection / single event detections in energy window A and photon detection in energy window G by one. increase.

  On the other hand, when the determination result in step 370 is “1”, the process proceeds to step 372, where the count value of the photon singularity detection event in the energy window A is incremented by 1, and the photon singularity detection in the energy window A and the energy are detected. Increment the photon detection count in window G by one. Further, the count value of the photon detection event in the energy window A is incremented by 1, and the count value of the simultaneous photon detection event in the energy window A and the photon detection in the energy window G is increased. Increase by one.

  If the determination result in step 370 is “2”, the process proceeds to step 373, where a set of simultaneously incident data in a certain time width is read from the data string 1, and the count value of the two-photon detection event in the energy window A is set to 1. And the count of simultaneous events of two-photon detection in energy window A and photon detection in energy window G is increased by one. Further, the count value of the photon detection event in the energy window A is incremented by 1, and the count value of the simultaneous photon detection event in the energy window A and the photon detection in the energy window G is increased. Increase by one.

  Steps 372 and 373 represent processing when the number of detected photons in the energy window A is 1 and 2, and the number of detected photons in the energy window A is 3 if necessary. In the case of 4, the number of steps can be increased.

  When Steps 358, 361, 365 of FIG. 16 and Steps 371, 372, 373 of FIG. 17 are completed, or when the determination results of Steps 357, 360, 364 of FIG. 16 and Step 368 of FIG. Proceeding to step 374 in FIG. 17, it is determined whether all data sets have been read.

If the determination result in step 374 is “Yes”, the process proceeds to step 375, where the count rate ρ _a of the photon single or plural detection events in the energy window A and the energy window G obtained from the measurement time and each count value are obtained. The photon detection event count rate ρ _{g in} the energy window A, the coincidence count rate ρ _ag of the photon detection event in the energy window A and the energy window G, and the photon detection event rate in the energy window A Count rate ρ _as , coincidence rate ρ _asg of single detection event in energy window A and photon detection event in energy window G, count rate ρ _ad of two photon detection event in energy window A, energy window A using coincidence ratio [rho _adg etc. in photon detection events in a two-photon detection event and the energy window G that put in, for example, ²² N For, for example using Equation (4) to calculate the radioactivity absolute value.

  On the other hand, if the decision result in the step 374 is “No”, the process returns to the step 353 in FIG.

  As described above, since the radioactivity absolute value of the radiation source can be calculated by the radiation detector assembly, the number of photons incident on the radiation detector assembly per unit time can be calculated based on this value. The emission rate of the radiation emitted from the radiation source per nuclear decay is Table of Isotopes, eight edition, volume I, II, R.I. B. Firestone and V. S. Can be referenced from nuclear data such as Shirley, Wiley Interscience, Table of radionuclides, Volume 1, 2, 3, Monoguraphie BIPM-5, Bureau International Des Poids et Mesures, Recommended data, the Laboratoire National Henri Becquerel, and the location of the source The number of radiation per unit time incident on the radiation detector assembly can be calculated from the coefficients according to the geometric relationship between the radiation detector assembly and the numerical values obtained from these values and the radiation activity of the source. it can. The detection efficiency (sensitivity) of the radiation detector assembly is obtained by dividing the photon counting rate of the radiation detector assembly by the photons incident on the radiation detector assembly per unit time. Also, the detection efficiency (sensitivity) may be calculated by dividing the photon counting rate of the radiation detector assembly by the number of photons generated from the source per unit time or the radiation of the source. It is.

  Next, FIG. 18 shows a second embodiment showing a calibration method of the radiation measuring apparatus by the radiation detector assembly according to the present invention. In the figure, 400 is a radiation source, 410 is, for example, a PET apparatus including a radiation detector assembly 412 composed of a number of DOI detectors, 220 is a counting device similar to the reference embodiment, 240 is a computer, 250 Is an input device, and 260 is a display device.

  In this embodiment, after measuring the radioactivity absolute value of the radiation source 400 by the same method as in the first embodiment, the detection efficiency (sensitivity) of the PET apparatus 410 is determined using the radioactivity absolute value, Calibrate.

  Specifically, for example, using the algorithm of FIG. 8 or FIG. 9, the counting device 220 and the computer 240 count the number of photons or detection events in the energy window A, and the number of photons in the energy window A. Count rate of detection events, count rate of photon detection events in energy window G, single or multiple photon detection events in energy window A and coincidence rate of photon detection events in energy window G, energy window From the coincidence rate of the single photon detection event in A and the photon detection event in the energy window G, the absolute activity value is determined.

  Or, for example, using the algorithm of FIG. 14, the counting device 220 and the calculator 240 consider the energy window P and also count the number of photon singularity and multiple detection events in the energy window A, in the energy window G. Photon detection event count rate, photon single and multiple detection events in energy window A and photon detection event coincidence rate in energy window G, photon single detection event count rate in energy window A, energy window Photon single detection event count rate in A and photon detection event coincidence rate in energy window G, two photon detection event count rate in energy window A, two photon detection event in energy window A And the coincidence rate of photon detection events in the energy window G, Ino to determine the absolute values.

  Then, the number of radiation incident on the PET apparatus 410 per unit time from the radioactivity is calculated from the geometric conditions and, for example, the release rate of the radiation by the nuclear data Recommended data, the Laboratoire National Henri Becquerel.

  Then, the detection efficiency (sensitivity) is determined by dividing the counting rate of the PET apparatus 410 by the number of radiation incident on the PET apparatus 410 per unit time. Also, detection efficiency (sensitivity) can be obtained by dividing the count rate of the PET apparatus 410 by the number of photons emitted from the radiation source 400 per unit time.

  According to the present embodiment, the radiation source 400 can be calibrated using the radiation detector assembly 412 originally provided in the PET apparatus 410.

  Next, FIG. 19 shows a third embodiment illustrating a calibration method for a radiation measuring apparatus using a radiation detector assembly according to the present invention. In the figure, 500 is a radiation source at the work site, 510 is a radiation detector assembly which is a DOI detector, for example, and 520 is a radiation measurement apparatus used at the work site.

  The radiation source 500 manufactured or used at the work site is measured by the radiation detector assembly 510, and an absolute value of radioactivity is given to the radiation source 500. The radiation source 500 to which the radioactivity absolute value is given is measured by the radiation measurement apparatus 520 at the work site, and the output value of the radiation measurement apparatus 520 and the radioactivity absolute value of the radiation source 500 are related to each other. Thereby, the radiation measuring apparatus 520 can be calibrated.

  Next, FIG. 20 shows a fourth embodiment showing a calibration method of the radiation measuring apparatus by the radiation detector assembly according to the present invention. In the figure, 600 is a liquid radiation source, 602 and 604 are dispensed radiation sources, 610 is a radiation detector assembly including, for example, a DOI detector, and 620 is a radiation measurement apparatus used at a work site. .

  A liquid radiation source 600 manufactured or used at the work site is dispensed into a radiation source 602 for the radiation detector assembly 610 and a radiation source 604 for the radiation measuring device 620. . The weight of each radiation source 602, 604 is measured.

  The radiation source 602 is measured by the radiation detector assembly 610, and an absolute radioactivity value is given to the radiation source 602. The radiation activity absolute value is given to the radiation source 604 from the radiation activity absolute value and the weight of the radiation source. The radiation source 604 is measured by the radiation measuring device 620 at the work site, and the output value and radiation of the radiation measuring device 620 are measured. The radioactivity absolute value of the source 604 is related and the radiation measurement device 620 is calibrated.

[Reference Example 1]
In the configuration of FIG. 7, a ²² Na ray source is used as the radiation source 200, and a DOI detector is used as the radiation detector assemblies 210 and 212. The radiation source 200 was installed at a predetermined position with respect to the DOI detector (210, 212). Of the spectrum output from the DOI detector (210, 212), the energy window A applied to a part of the photoelectric absorption peak of the 511 keV electron-positron pair annihilation photon, and the photoelectric absorption peak of 1275 keV gamma ray (other photons). Energy window G applied to a portion of the photon, the counting rate of single or multiple photon detection events in energy window A, the counting rate of single photon detection events in energy window A, and the photons in energy window G Detecting event count rate, photon single or multiple photon detection events in energy window A and photon detection event coincidence rate in energy window G, photon single detection event in energy window A and energy window G 8 and 9, the coincidence rate of photon detection events was measured. The counting method, it was possible to determine the radioactivity absolute value of ²² Na-ray source (200).

[Reference Example 2]
As a reference example of the calibration method of the detection efficiency (sensitivity) of the radiation detector assembly, photons emitted from the ²² Na radiation source (400) were detected by the PET apparatus 410 in the configuration of FIG. The energy window A applied to a part of the photoelectric absorption peak of the 511 keV electron-positron pair annihilation photon and the energy window G applied to a part of the photoelectric absorption peak of 1275 keV γ-ray (other photon), as shown in FIG. In the energy window A, the counting device 220 and the computer 240 count the number of photon detection events in the energy window A, the number of photon detection events in the energy window A, and the energy window G. Photon detection event count rate in the energy window A, single or multiple photon detection event in the energy window A and photon detection event coincidence rate in the energy window G, single photon detection event and energy in the energy window A Measuring the coincidence rate of photon detection events in window G We were determined. The number of electron-positron annihilation photons emitted from the radiation source was calculated from the radiation emission rate by the radioactivity and nuclear data Recommended data, the Laboratoire National Henri Becquerel. The detection efficiency (sensitivity) could be determined by dividing the counting rate of the PET apparatus 410 by the number of electron-positron pair annihilation photons emitted per unit time.

In the configuration of FIG. 7, a ²² Na ray source is used as the radiation source 200, and a DOI detector is used as the radiation detector assemblies 210 and 212. The radiation source 200 was installed at a predetermined position with respect to the DOI detector (210, 212). Of the spectrum output from the DOI detector (210, 212), the energy window A applied to a part of the photoelectric absorption peak of the 511 keV electron-positron pair annihilation photon, and the photoelectric absorption peak of 1275 keV gamma ray (other photons). Energy window G applied to a part of the energy window A, the energy window P applied to a part of the pileup peak of the photoelectric absorption of the 511 keV electron-positron pair annihilation photon and the photoelectric absorption of 1275 keV gamma rays (other photons). Photon single and multiple detection events in energy window G, photon detection event count rate in energy window G, photon single and multiple detection events in energy window A and photon detection event in energy window G simultaneously Count rate, count rate of single photon detection event in energy window A, Count rate of single photon detection event in energy window A and coincidence rate of photon detection event in energy window G, count rate of two photon detection event in energy window A, two photon in energy window A Measure the count rate of detection events and the coincidence rate of photon detection events in the energy window G, and determine the absolute value of the radioactivity of the ²² Na source (200) by the coincidence method shown in FIG. I was able to.

As an example of the calibration method of the detection efficiency (sensitivity) of the radiation detector assembly, photons emitted from the ²² Na radiation source (400) were detected by the PET apparatus 410 in the configuration of FIG. Using the algorithm of FIG. 14, the counting device 220 and the computer 240 apply a part of the photoelectric absorption peak of the 511 keV electron positron pair annihilation photon with the 511 keV electron positron pair annihilation photon and the 1275 keV gamma ray (other photons). Energy window A, energy window G applied to a part of the photoelectric absorption peak of γ-rays (other photons) of 1275 keV, 511 keV electron-positron annihilation photon, and pile of photoelectric absorptions of γ-rays (other photons) of 1275 keV By setting an energy window P applied to a part of the up-peak, the counting rate of single and multiple photon detection events in the energy window A, the counting rate of photon detection events in the energy window G, and the energy window A Photon single and multiple detection events and photon detection in the energy window G Coincidence rate of events, count rate of single photon detection events in energy window A, count rate of single photon detection events in energy window A and coincidence rate of photon detection events in energy window G, energy window Determine the absolute value of the radioactivity by measuring the count rate of the two-photon detection event in A, the count rate of the two-photon detection event in the energy window A, and the coincidence count of the photon detection event in the energy window G did. The number of electron-positron annihilation photons emitted from the radiation source was calculated from the radiation emission rate by the radioactivity and nuclear data Recommended data, the Laboratoire National Henri Becquerel. The detection efficiency (sensitivity) could be determined by dividing the counting rate of the PET apparatus 410 by the number of electron-positron pair annihilation photons emitted per unit time.

In the configuration of FIG. 19, a ⁶⁸ Ge— ⁶⁸ Ga ray source is used as the radiation source 500, a DOI detector is used as the radiation detector assembly 510, and an RI calibrator is used as the radiation measurement apparatus 520. ^{A 68} Ge- ⁶⁸ Ga radiation source (500) was measured by a DOI detector (510) to give an absolute value of radioactivity. Also in the RI calibrator (520), the ⁶⁸ Ge- ⁶⁸ Ga radiation source (500) was measured, and the relationship between the output value of the RI calibrator (520) and the radioactivity value of the ⁶⁸ Ge- ⁶⁸ Ga radiation source (500) was determined. Thereby, the RI calibrator (520) could be calibrated.

In the configuration of FIG. 20, a ²² Na ray source is used as the radiation source 600, a DOI detector is used as the radiation detector assembly 610, and an RI calibrator is used as the radiation measurement device 620. ²² Dispensing the Na-ray source (600), manufacturing the DOI detector radiation source (602) and the RI calibrator radiation source (604), measuring the weight of each radiation source, then measuring each I did it.

The absolute value of the radioactivity of the radiation source (602) was determined by the DOI detector (610), and the radioactivity concentration of the ²² Na radiation source (600) was determined from the weight at the time of dispensing. The radioactivity value of the RI calibrator radiation source (604) is obtained from this radioactivity concentration, and the relationship between the output value of the RI calibrator (620) and the radioactivity value of the RI calibrator radiation source (604) is obtained. The RI calibrator (620) could be calibrated.

  In the above embodiment, two or many radiation detector assemblies are used, but the number of radiation detector assemblies may be one. Further, the radiation detector assembly is not limited to the DOI detector, and the number of elements is not limited. The type of radiation source and radiation are not limited to the above embodiment.

  The present invention is used for absolute radioactivity measurement. Moreover, it is used for the measurement efficiency (sensitivity) measurement of radiation detectors, such as a radiological medical device and a nondestructive inspection device. Furthermore, it can be used for calibration of radiation measuring devices such as medical radioactivity measuring devices.

100, 200, 400, 500, 600, 602, 604 ... Radiation source 210, 212, 412, 510, 610 ... Radiation detector aggregate 220 ... Counting device 240 ... Calculator 250 ... Input device 260 ... Display device 410 ... PET device 520, 620 ... Radiation measurement device

Claims (7)

  When pileup is detected in the energy window of the electron positron pair annihilation photon and other photons, the number of photons detected in the electron positron pair annihilation photon energy window is added and corrected to detect the photons in the other photon energy window. An absolute radioactivity measurement method characterized in that an event and an electron-positron pair annihilation photon and other photon are detected simultaneously.   Low energy scattering of the electron spectrum, the electron positron annihilation photon energy window, the other photon energy window, the electron positron pair annihilation photon and other photon pile-up event energy windows over the high energy side of the photon peak An absolute radioactivity measurement method characterized by reducing the influence of radiation.   Radiation detection, wherein the radiation detector aggregate detection efficiency is obtained from the photon count rate of the radiation detector aggregate using the radioactivity absolute value determined by the method according to claim 1 or 2. For determining the detection efficiency of a vessel assembly.   A radiation measuring apparatus calibration method comprising calibrating a radiation measuring apparatus including a radiation detector assembly using the radioactivity absolute value determined by the method according to claim 1.   The radiation measurement apparatus calibration method according to claim 4, wherein the radiation measurement apparatus is a PET apparatus.   The radiation detector assembly is brought into the work site as an intermediary standard for calibration, an absolute radioactivity value is given to the radiation source at the work site, and this radiation source is measured by a radiation measuring device used at the work site. The radiation measurement apparatus calibration method according to claim 4, wherein an output of the radiation measurement apparatus is associated with an absolute value of radioactivity.   Distributing the radiation source, dividing it into a radiation source for the radiation detector assembly and a radiation source for the radiation measuring device, measuring the weight of each radiation source, and then radiating the radiation source for the radiation detector assembly to the radiation detector assembly The radioactivity absolute value is given, and the radioactivity absolute value is given to the radiation source for the radiation measurement device from the radioactivity absolute value and the weight of the radiation source. 5. The calibration of the radiation measuring apparatus according to claim 4, wherein the radiation measuring apparatus is measured with a radiation measuring apparatus at a work site, and an output value of the radiation measuring apparatus is correlated with an absolute value of the radioactivity of the radiation source for the radiation measuring apparatus. Method.

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