WO2011145139A1 - ポジトロンct装置およびタイミング補正方法 - Google Patents
ポジトロンct装置およびタイミング補正方法 Download PDFInfo
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- A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
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- A61B6/03—Computed tomography [CT]
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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- A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
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Definitions
- the present invention relates to a positron CT apparatus and timing correction method for detecting radiation emitted from a positron radiopharmaceutical administered into a subject.
- a positron CT device ie, a PET (Positron EmissionographyTomography) device, detects positrons (Positron), that is, a plurality of ⁇ -rays generated by annihilation of positrons, and a plurality of detectors simultaneously detect ⁇ -rays ( In other words, only when simultaneous counting is performed, the image of the subject is reconstructed.
- positron positron
- TOF Time Of Flight
- TOF uses the fact that the annihilation radiation is at the speed of light, and converts the time difference from the annihilation occurrence point to the detector into the distance difference from the annihilation occurrence point to the light source generation position by the scintillator element of the detector. This is a technology for finding the point of occurrence of annihilation.
- the detector detects the radiation emitted from the radiation source, and inputs a timing signal indicating the radiation incident timing at which the radiation is incident on the detector to the coincidence counting circuit via the delay adjustment circuit.
- the output of the coincidence counting circuit is measured, and the sensitivity (ie, counting) of radiation is measured for each signal channel. Thereafter, the sensitivity is measured while changing the delay amount adjusted by the delay adjustment circuit, and a sensitivity distribution with respect to the delay amount change is obtained. By using the delay amount with the highest measured sensitivity in the delay adjustment circuit, the time delay of the signal is corrected.
- a calibration radiation source (external radiation source) is installed in the field of view (FOV) of the PET device.
- a plurality of detectors are arranged in a ring (annular).
- the timing values of a plurality of detectors having a common field of view with the reference detector are averaged, and the averaged timing value is obtained as a time delay value for the reference detector.
- a time delay value is similarly obtained using a detector adjacent to the reference detector as a reference, and a difference between the time delay value obtained first and the time delay value obtained next is obtained as a reference correction value.
- Timing correction is performed by aligning the time using the reference correction value. Thereafter, the same calculation is performed on the adjacent detectors in order, so that timing correction for all detectors is performed when the detector makes one turn on the ring.
- the simulation signal output from the simulation signal generator is input to each of a plurality of signal processors (signal processing units), and calibration data is generated based on the output of each signal processor to correct timing.
- a DOI detector capable of discriminating a depth-of-interaction light source position (DOI: Depth of Interaction) is incorporated into a TOF type PET apparatus.
- the DOI detector is constructed by laminating each scintillator element in the depth direction of radiation (here, ⁇ -rays), and the depth direction and the lateral direction (direction parallel to the incident surface) that caused the interaction. ) And the coordinate information with the center of gravity.
- the detection time correction information corresponding to the coordinate information is written and stored in the table, and the detection time correction information is referred to thereby improving the information accuracy of the flight time difference.
- Japanese Patent Publication No. 6-19436 Japanese Patent No. 3343122 JP 2006-90827 A JP 2008-51701 A
- the present invention has been made in view of such circumstances, and it is an object of the present invention to provide a positron CT apparatus and a timing correction method capable of accurately simultaneously counting without repeating many measurements and calculations. To do.
- the present invention has the following configuration. That is, the positron CT apparatus of the present invention is a positron CT apparatus having a plurality of detectors for detecting radiation emitted from a positron radiopharmaceutical administered into a subject, and each detector for simultaneously counting radiation. With respect to a time difference histogram representing a count value distribution for each pair of time difference changes, two detectors to be simultaneously counted are selected, and one of the two selected detectors is selected, and When a detector different from the other detector is selected and the selection is repeated, the time difference histogram relating to the two detectors selected in the past is used as a reference, and the detector selected this time is selected.
- the calculation means performs the following calculation on the time difference histogram representing the count value distribution with respect to the time difference change of each pair of detectors that simultaneously count radiation. That is, two detectors to be simultaneously counted are selected, one of the two selected detectors is selected, and another detector is selected from the other detector, When the selection is repeated, the time difference histograms related to the two detectors selected this time are corrected based on the time difference histograms related to the two detectors selected in the past. Then, the operation based on the time difference histogram relating to the two corrected detectors is newly performed.
- the time difference histograms related to the two detectors selected this time are corrected based on the reference, and the two corrected detectors are corrected.
- the time difference histogram as a reference for example, as in Patent Document 2 described above, convergence can be obtained when obtaining an optimum time difference histogram, compared to the case where the timing values of a plurality of detectors are averaged. Good. Therefore, an optimal time difference histogram can be obtained without repeating many measurements and calculations.
- the coincidence counting circuit simultaneously counts the radiation based on the time difference histogram of each pair of the detectors corrected repeatedly as described above, the coincidence can be accurately performed. As a result, simultaneous counting can be performed accurately without repeating many measurements and calculations.
- the timing correction method of the present invention is a timing correction method used for simultaneously counting radiation emitted from a positron radiopharmaceutical administered into a subject, and is a pair of detectors that simultaneously count radiation.
- a time difference histogram representing a count value distribution for each time difference change
- two detectors to be simultaneously counted are selected, one of the two selected detectors is selected, and the other detector is selected.
- the time difference histograms related to the two detectors selected in the past are used as a reference, and the two selected this time based on the reference. Correct the time difference histogram related to the detector, and repeat the work using the corrected time difference histogram related to the two detectors as a new reference. It is characterized in further comprising a cormorants histogram correction process.
- the timing correction method of the present invention the following correction is performed in the histogram correction step with respect to the time difference histogram for each detector pair. That is, two detectors to be simultaneously counted are selected, one of the two selected detectors is selected, and another detector is selected from the other detector, When the selection is repeated, the time difference histograms related to the two detectors selected this time are corrected based on the time difference histograms related to the two detectors selected in the past. Then, the operation based on the time difference histogram relating to the two corrected detectors is newly performed. As a result, timing correction can be performed accurately without repeating many measurements and calculations.
- One example of these positron CT devices and timing correction methods described above uses the time difference at which the total count value in the time difference histogram based on the above reference is the maximum as a reference value, and corrects the time difference of the time difference histogram based on the above reference value. It is.
- the time point at which the total count value in the time difference histogram is maximum is the timing at which coincidence counting is most likely to occur. Therefore, by correcting the time difference of the time difference histogram based on the reference value that is the timing, it is possible to align at that timing.
- Another example of the above-described positron CT apparatus and timing correction method is to calculate a time difference that is an intermediate value between the time difference at which the total count value is maximum and the time difference at which the total count value is the second largest in the reference time difference histogram.
- the reference value is used to correct the time difference of the time difference histogram based on the above-described reference value.
- the timing at which the scintillator element of the other detector detects the most radiation from the self-radiation of the scintillator element of one detector is the time point where the total count value is maximum, or the total count value is the second largest It is a time point. Therefore, the intermediate value between the two time differences, which are these timings, is the timing at which coincidence counting is most likely to occur. Therefore, by correcting the time difference of the time difference histogram based on the reference value of the intermediate value that is the timing, it is possible to align at that timing.
- the above-described detector has a structure including a plurality of scintillator elements in addition to a structure including a single scintillator element.
- correction may be performed for each scintillator element group (that is, detector unit) composed of a plurality of scintillator elements, but correction is performed for each scintillator element unit composed of one scintillator element as described below. To improve accuracy.
- the following calculation / correction is performed on the time difference histogram for each pair of scintillator elements composed of one scintillator element of each detector that simultaneously counts radiation. That is, two scintillator element units of a detector to be simultaneously counted are selected, and one scintillator element unit of one detector is selected from the two selected scintillator element units.
- the time difference histogram for the scintillator element units of the two detectors selected in the past is used as a reference, and this time, The time difference histogram relating to the scintillator element unit of the two detectors selected in (1) is corrected.
- a time difference histogram for each pair of a scintillator element group composed of a plurality of scintillator elements of one detector and a scintillator element unit composed of one scintillator element of the other detector is performed.
- the scintillator element group of one detector and the scintillator element unit of the other detector selects the scintillator element group of one detector and the scintillator element unit of the other detector, and out of the selected scintillator element group and the scintillator element unit,
- the scintillator element group and the scintillator element unit selected in the past The time difference histogram relating to the scintillator element group selected this time and the scintillator element unit is corrected based on the reference.
- the operation based on the time difference histogram relating to the corrected scintillator element group and scintillator element unit is newly performed. Since correction is performed for each scintillator element group and each scintillator element in this way, the accuracy can be further improved compared to when correction is performed for each detector unit. In addition, the calculation time and burden can be reduced compared to when correction is performed for each scintillator element unit.
- the above-described detector may be a DOI detector configured by laminating each scintillator element in the depth direction of the radiation.
- positron CT apparatuses and timing correction methods described above include an external radiation source that irradiates the same type of radiation as that of the above-described radiopharmaceutical or a phantom that irradiates the same type of radiation as that of the radiopharmaceutical from the inside.
- the detector may be acquired based on radiation from a radiation source or a phantom, or the detector may include a scintillator element having self-radiation, and the above-described time difference histogram may be acquired based on radiation from the self-radioactivity. .
- the positron CT apparatus and the timing correction method according to the present invention, two detectors to be simultaneously counted are selected, one of the two selected detectors is selected, and the other is selected.
- the time difference histograms related to the two detectors selected in the past are used as a reference, and the 2 selected this time is selected based on the reference. Correct the time difference histogram for two detectors. Then, the operation based on the time difference histogram relating to the two corrected detectors is newly performed. As a result, timing correction can be performed accurately without repeating many measurements and calculations.
- PET Positron
- A is a schematic perspective view of a gamma ray detector. It is the front view of the gamma ray detector arranged in the shape of a ring in a PET device, and a block diagram about it. It is a flowchart which shows the flow of a series of timing correction methods.
- A is a front view of a ⁇ -ray detector when an external radiation source is installed
- (b) is a front view of the ⁇ -ray detector when a phantom is installed.
- A), (b) is explanatory drawing of a time difference histogram.
- FIGS. 8A to 8C are front views showing an embodiment of switching between a reference detector and a correction target detector in another embodiment different from FIG. (A) to (c) are front views showing an embodiment of switching between a reference scintillator element unit and a correction target scintillator element unit.
- (A) to (c) are front views showing an embodiment of switching between a reference scintillator element group and a correction target scintillator element unit.
- (A), (b) is explanatory drawing of the time difference histogram at the time of the scintillator element with a self-radioactivity.
- FIG. 1 is a side view and block diagram of a PET (Positron Emission Tomography) apparatus according to a first embodiment
- FIG. 2 is a schematic perspective view of a ⁇ -ray detector
- FIG. 3 is a ring shape of the PET apparatus. It is the front view of the arrange
- the PET apparatus includes a top plate 1 on which the subject M is placed as shown in FIG.
- the top plate 1 is configured to move up and down and translate along the body axis Z of the subject M.
- the subject M placed on the top 1 is scanned from the head to the abdomen and foot sequentially through the opening 2a of the gantry 2, which will be described later. Get the image. Note that there is no particular limitation on the scanned part and the scanning order of each part.
- the PET apparatus includes a gantry 2 having an opening 2a and a ⁇ -ray detector 3.
- the ⁇ -ray detector 3 is arranged in a ring shape so as to surround the body axis Z of the subject M, and is embedded in the gantry 2.
- the ⁇ -ray detector 3 corresponds to the detector in the present invention.
- the PET apparatus includes a top board driving unit 4, a controller 5, an input unit 6, an output unit 7, a memory unit 8, a detector signal processing unit 9, a coincidence counting circuit 10, a data collecting / A control unit 11 and a reconstruction processing unit 12 are provided.
- the top plate driving unit 6 is a mechanism for driving the top plate 1 so as to perform the above-described movement, and is configured by a motor or the like not shown.
- the coincidence circuit 10 corresponds to the coincidence circuit in the present invention
- the data collection / control unit 11 corresponds to the computing means in the present invention.
- the controller 5 comprehensively controls each part constituting the PET apparatus according to the first embodiment.
- the controller 5 and the data collection / control unit 11 include a central processing unit (CPU).
- the input unit 6 sends data and commands input by the operator to the controller 5.
- the input unit 6 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like.
- the output unit 7 includes a display unit represented by a monitor, a printer, and the like.
- the memory unit 8 includes a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like.
- the count value (count) simultaneously counted by the coincidence circuit 10 data relating to coincidence counting such as a detector pair including two ⁇ -ray detectors 3 and LOR that have been simultaneously counted, and the reconstruction processing unit 12.
- the image processed in step 1 is written and stored in the RAM, and is read from the RAM as necessary.
- the ROM stores in advance a program for performing imaging including various types of nuclear medicine diagnosis, and the controller 5 and the data collection / control unit 11 execute the program so that the nuclear medicine corresponding to the program is stored. Make each diagnosis.
- LOR Line Of Response
- LOR Line Of Response
- the reconfiguration processing unit 12 causes the controller 5 to execute, for example, a program stored in a ROM of a storage medium represented by the memory unit 8 or the like described above, or a command input by a pointing device represented by the input unit 6 or the like. It is realized with.
- the ⁇ -rays generated from the subject M to which the radiopharmaceutical is administered are converted into light by the scintillator block 31 (see FIG. 2) of the ⁇ -ray detector 3, and the converted light is photoelectron of the ⁇ -ray detector 3.
- a multiplier tube (PMT: Photo Multiplier Tube) 33 (see FIG. 2) multiplies and converts it into an electrical signal. The electric signal is sent to the coincidence counting circuit 10 through the detector signal processing unit 9.
- the coincidence circuit 10 checks the position of the scintillator block 31 (see FIG. 2) and the incident timing of ⁇ rays, and only when ⁇ rays are simultaneously incident on the two scintillator blocks 31 on both sides of the subject M. The sent event is determined to be appropriate data.
- the coincidence counting circuit 10 rejects. That is, the coincidence counting circuit 10 detects that ⁇ rays are simultaneously observed in the two ⁇ ray detectors 3 based on the above-described electrical signal.
- an electrical signal that has been simultaneously observed is determined as image information, and the image information is sent to the reconstruction processing unit 12 via the data collection / control unit 11.
- the reconstruction processing unit 12 obtains an image of the subject M by performing image reconstruction by forward projection processing or back projection processing.
- the image is sent to the output unit 7 via the controller 5.
- nuclear medicine diagnosis is performed based on the image obtained by the reconstruction processing unit 12.
- a known successive approximation algorithm such as DRAMA method (Dynamic Row-Action Maximum Likelihood Algorithm) is applied. Specific functions of the detector signal processing unit 9 and the data collection / control unit 11 will be described later.
- the ⁇ -ray detector 3 includes a scintillator block 31, a light guide 32 optically coupled to the scintillator block 31, and photoelectrons optically coupled to the light guide 32.
- a multiplier (hereinafter simply abbreviated as “PMT”) 33 is provided.
- Each scintillator element constituting the scintillator block 31 converts ⁇ rays into light by emitting light with the incidence of ⁇ rays. By this conversion, the scintillator element detects ⁇ rays. Light emitted from the scintillator element is sufficiently diffused by the scintillator block 31 and input to the PMT 33 via the light guide 32.
- the PMT 33 multiplies the light converted by the scintillator block 31 and converts it into an electric signal.
- the electric signal is sent to the coincidence counting circuit 10 through the detector signal processing unit 9 as described above.
- the scintillator block 31 corresponds to the scintillator element in the present invention
- the PMT 33 corresponds to the photoelectric conversion means in the present invention.
- the ⁇ -ray detector 3 shown in FIG. 2 includes a plurality of scintillator blocks 31 that fluoresce when ⁇ -rays are incident, and a PMT 33 that detects ⁇ -rays by photoelectrically converting light from each scintillator block 31. It has.
- the ⁇ -ray detector 3 shown in FIG. 2 is a DOI detector configured by laminating the respective scintillator blocks 31 in the ⁇ -ray depth direction (stacked in four layers in FIG. 2).
- the ⁇ -ray detector 3 In imaging in a nuclear medicine diagnosis using a normal subject M, the ⁇ -ray detector 3 detects ⁇ -rays generated from the subject M to which a radiopharmaceutical has been administered, and the detector signal processing unit 9 performs simultaneous counting. The data is sent to the reconstruction processing unit 12 via the circuit 10 via the data collection / control unit 11 without timing correction. On the other hand, in data collection using an external source or phantom, the ⁇ -ray detector 3 detects ⁇ -rays from the external source or phantom, and the data is collected through the detector signal processing unit 9 and the coincidence counting circuit 10. Data is sent to the control unit 11, and the data collection / control unit 11 performs feedback correction to the timing correction table 9 b of the detector signal processing unit 9 to perform timing correction, thereby adjusting the delay amount in each coincidence circuit 10. .
- the detector signal processing unit 9 generates a signal (hereinafter also referred to as “time stamp”) representing the ⁇ -ray incident timing based on the electrical signal output from the PMT 33 of the ⁇ -ray detector 3. And the above-described timing correction table 9b.
- time stamp a signal representing the ⁇ -ray incident timing based on the electrical signal output from the PMT 33 of the ⁇ -ray detector 3.
- the above-described timing correction table 9b As described above, each ⁇ -ray detector 3 is arranged in a ring shape, and each ⁇ -ray detector 3 is connected to the timing signal generation circuit 9a of the detector signal processing unit 9 (in FIG. 3, Only two timing signal generation circuits 9a are shown).
- the timing signal generation circuit 9 a is connected to the timing correction table 9 b, and the timing correction table 9 b is connected to the coincidence counting circuit 10.
- FIG. 4 is a flowchart showing a flow of a series of timing correction methods
- FIG. 5 is a front view of a ⁇ -ray detector when an external radiation source or a phantom is installed
- FIG. 6 is an explanatory diagram of a time difference histogram.
- FIG. 7 is a front view showing an embodiment of switching between the reference detector and the correction target detector
- FIG. 8 is an embodiment different from FIG. 7 in the reference detector and the correction target detection. It is a front view which shows one embodiment of switching with a vessel.
- Step S1 Measurement of Correction Data
- an external radiation source RI for irradiating a radioactive medicine that is, a radiation of the same kind as a radioisotope (RI) (gamma rays in the first embodiment) is used.
- the two ⁇ -ray detectors 3 facing each other by about 180 ° can detect the radiation from the external radiation source RI almost simultaneously. Only the time delay of the signal in the signal channel from the line detector 3 to the coincidence circuit 10 is subject to timing correction.
- a phantom Ph that irradiates the same type of radiation as the radioactive drug from the inside may be installed in the visual field of the PET apparatus. Even when the phantom Ph is installed, it is preferably installed in the central region within the field of view.
- the external radiation source RI corresponds to the external radiation source in the present invention
- the phantom Ph corresponds to the phantom in the present invention.
- the radiation from the external radiation source RI or phantom Ph is detected by the ⁇ -ray detector 3 and acquired as correction data, and sent to the coincidence circuit 10 via the detector signal processing unit 9. As shown in FIG. 5, correction data is measured and acquired by all the ⁇ -ray detectors 3.
- Step S2 Creation of Time Difference Histogram
- a time difference histogram is created for each pair of ⁇ -ray detectors 3 that simultaneously count radiation based on the correction data measured in step S1.
- the time difference histogram is obtained by taking a time stamp difference (that is, time difference) (indicated as “Difference Time” in FIG. 6) for each pair of ⁇ -ray detectors 3 on the horizontal axis, and counting values (FIG. 6).
- time difference Time that is, time difference
- FIG. 6 it is a count value distribution with respect to the time difference change when the vertical axis is “Event Counts”.
- the time difference histogram is obtained as a frequency distribution centered on “0” as shown in FIG.
- the time difference histogram shifts to the left and right as shown by the solid line in FIG. Therefore, a shift amount that returns the time difference histogram to a frequency distribution centered on “0” shown by the dotted line from the solid line in FIG. 6B is considered as the correction amount.
- Step S3 Setting of Reference Detector and Correction Target Detector
- a reference detector and a correction target detector are set.
- one ⁇ -ray detector 3 is set as a reference
- the ⁇ -ray detector 3 set as the reference is a reference detector.
- Each pair of ⁇ -ray detectors 3 in the field of view of the PET apparatus viewed from the reference detector S is set as a correction target
- the ⁇ -ray detector 3 set as the correction target is set as a correction target detector C. .
- the ⁇ -ray detector 3 facing the reference detector S by about 180 ° is selected. Assuming that the reference detector S is the “1” -th ⁇ -ray detector 3 and serial numbers are assigned in the clockwise direction, as shown in FIG. This ⁇ -ray detector 3 becomes the ⁇ -ray detector 3 facing the reference detector S by 180 °. In the case of a total of an odd number of ⁇ -ray detectors, the ⁇ -ray detectors 3 facing each other by 180 ° cannot be selected. Therefore, the ⁇ -ray detectors 3 facing each other by about 180 ° may be selected.
- the ⁇ -ray detector 3 (refer to the gray color in FIG. 7A) facing the reference detector S by about 180 ° is set as the counter detector O.
- the reference detector S that is the “1” -th ⁇ -ray detector 3 and 180 ° to it.
- the opposite “61” -th ⁇ -ray detector 3 is selected.
- the time difference histogram relating to the selected reference detector S, which is the “1” -th ⁇ -ray detector 3, and the “61” -th ⁇ -ray detector 3 (opposite detector O) opposed to the reference detector S by 180 ° is used as a reference.
- the time difference histogram based on this reference is a frequency distribution centered on “0” as shown in FIG. Accordingly, the time difference at which the total count value in the reference time difference histogram is maximum is set to “0”, and this time difference “0” is set as the reference value.
- Step S4 Extraction of Time Difference Histogram to be Corrected Among the two ⁇ -ray detectors 3 composed of the reference detector S and the counter detector O selected in step S3, the reference detector is one ⁇ -ray detector 3. While selecting S, a correction target detector C different from the counter detector O which is the other ⁇ -ray detector 3 is selected. That is, the correction target detector C and the reference detector S other than the counter detector O are selected, and the time difference histogram to be corrected is extracted. In the case shown in FIG. 7A, the correction target detector C including the “61” -th ⁇ -ray detector 3 (opposite detector O) in the step S3 has the “49” -th to “73” -th total.
- time difference histograms relating to the “th” to “60” th and “62” to “73” th correction target detectors C are extracted as the time difference histograms relating to the two ⁇ -ray detectors 3 selected this time.
- Step S5 Calculation of Correction Amount
- the time difference histogram relating to the correction target detector C other than the counter detector O and the reference detector S is deviated from the reference time difference histogram.
- FIG. Shift to the left and right as shown by the solid line. Therefore, the shift amount is corrected so that the time difference histogram relating to the two ⁇ -ray detectors 3 selected at this time in step S4 is returned to the frequency distribution centered on “0” shown by the dotted line from the solid line in FIG.
- the data collection / control unit 11 obtains the quantity.
- Step S6 Completion of calculation of correction amounts for all detectors? It is determined whether or not the calculation of the correction amount of all the ⁇ -ray detectors 3 has been completed. If not completed, the process proceeds to step S7. If completed, the process proceeds to step S8.
- Step S7 Application of correction amount Applying the correction amount obtained in step S5, the time difference histogram relating to the two ⁇ -ray detectors 3 selected this time is a frequency centered on “0” by the correction amount.
- the time difference histogram is corrected by shifting to return to the distribution. That is, the time difference histogram is corrected based on the time difference “0” that is the reference value.
- the reference detector S which is the “1” -th ⁇ -ray detector 3, and the “49” th to “60” th and “62” th to “73” th respectively.
- step S7 If the correction amount is applied and corrected in step S7, the process returns to step S3, and the work based on the two ⁇ -ray detectors 3 corrected in step S7 is newly performed.
- the correction target detector among the corrected “49” th to “60” th and “62” th to “73” th correction target detectors C.
- the “49” -th and “73” -th ⁇ -ray detectors 3 at both ends of C are newly used as a reference.
- step S 3 as shown in FIG. 7B, the “49” -th ⁇ -ray detector 3 and the “73” -th ⁇ -ray detector 3 (see the black painting in FIG. 7B).
- the reference detector S is assumed.
- each pair of ⁇ -ray detectors in the field of view of the PET apparatus viewed from each reference detector S is set as a correction target, and the ⁇ -ray detection set as the correction target is set.
- the device 3 is a correction target detector C.
- the correction target detector C is a total of 24 ⁇ -ray detectors 3 from the “97” th to “120” th with respect to the reference detector S which is the “49th” ⁇ -ray detector 3.
- the reference detector S which is the “73” th ⁇ -ray detector 3 there are a total of 24 ⁇ -ray detectors 3 from the “2” th to “25” th.
- the reference detector S which is the “49” -th ⁇ -ray detector 3, and the “109” -th ⁇ -ray detector 3 (opposite detector O) opposed to the reference detector S by 180 ° (see the gray color in FIG. 7B)
- the reference detector S which is the “73” th ⁇ -ray detector 3 and the “13th” ⁇ -ray detector 3 (opposite detector O) which is 180 ° opposite to the reference detector S (FIG. 7B ) (See gray).
- step S4 the reference detector S that is the “49” -th ⁇ -ray detector 3 and “97” other than the “109” -th ⁇ -ray detector 3 (opposite detector O).
- the time difference histograms related to the “C” to “108” and “110” to “120” correction target detectors C are extracted as the time difference histograms related to the two ⁇ -ray detectors 3 selected this time.
- the time difference histograms related to the “14” th to “25” th correction target detectors C are extracted as the time difference histograms related to the two ⁇ -ray detectors 3 selected this time.
- step S5 the correction amount is obtained in step S5
- step S6 the correction amount calculation completion is determined in step S6, and if not completed, the process proceeds to step S7.
- step S7 the correction amount is applied to perform correction, and the process returns to step S3, and the work based on the two ⁇ -ray detectors 3 corrected in step S7 is newly performed.
- a total of four ends of the correction target detector C see the hatched lines in FIG. 7B.
- the “25” -th and “97” -th ⁇ -ray detectors 3 on the lower side are newly set as a reference.
- step S3 the “25” -th ⁇ -ray detector 3 and the “97” -th ⁇ -ray detector 3 (see black in FIG. 7C).
- the reference detector S is assumed.
- Each ⁇ -ray detector 3 pair within the field of view of the PET apparatus viewed from each reference detector S is set as a correction target, and the ⁇ -ray detector 3 set as the correction target is set as a correction target detector C.
- the correction target detector C is a total of 23 ⁇ -ray detectors 3 from “74” to “96” with respect to the reference detector S which is the “25” -th ⁇ -ray detector 3.
- the reference detector S which is the “97” -th ⁇ -ray detector 3 there are a total of 23 ⁇ -ray detectors 3 from the “26” th to “48” th.
- the reference detector S which is the “25” -th ⁇ -ray detector 3, and the “85” -th ⁇ -ray detector 3 (opposite detector O) opposed to the reference detector S by 180 ° (see the gray color in FIG. 7C)
- the reference detector S which is the “97” -th ⁇ -ray detector 3, and the “37” -th ⁇ -ray detector 3 (opposite detector O) opposite to the reference detector S by 180 ° (FIG. 7C ) (See gray).
- step S4 the reference detector S which is the “25” -th ⁇ -ray detector 3 and the “74” -th to “84” -th and “-” other than the “85” -th ⁇ -ray detector 3 (opposite detector O).
- the time difference histogram relating to each of the 86th to 96th correction target detectors C is extracted as the time difference histogram relating to the two ⁇ -ray detectors 3 selected this time.
- step S4 the reference detector S which is the “97” -th ⁇ -ray detector 3 and the “26” -th to “36” -th other than the “37” -th ⁇ -ray detector 3 (opposite detector O).
- the time difference histograms relating to each of the “38” th to “48” th correction target detectors C are extracted as time difference histograms relating to the two ⁇ -ray detectors 3 selected this time.
- step S5 the correction amount is obtained.
- step S6 it is determined whether the correction amount has been calculated. If not, the process proceeds to step S7.
- step S7 the correction amount is applied to perform correction, and the process returns to step S3.
- the third iteration of steps S6, S7, and S3 to S5 completes the calculation of the correction amounts of all the ⁇ -ray detectors 3 from the “1” to the “120”, and is completed in step S6. to decide. Then, the process proceeds to step S8.
- Step S8 Setting of Timing Correction Table
- the correction amount obtained in these steps S3 to S6 (three iteration loops in the case of the embodiment of FIG. 7) is detected from the data collection / control unit 11 by detector signal processing.
- the timing correction table is set by writing in the timing correction table 9b of the unit 9.
- the total number of ⁇ -ray detectors 120 is 120, but the number of ⁇ -ray detectors is not particularly limited.
- the correction target detector C is “1” th.
- the “36” th and “54th” ⁇ -ray detectors 3 at both ends of the correction target detector C are newly used as a reference.
- the correction target detector C is “71” to “88” with respect to the reference detector S which is the “36” -th ⁇ -ray detector 3 (the counter detector O is “80”). ”) And a total of 18 ⁇ -ray detectors 3 with respect to the reference detector S that is the“ 54 ”-th ⁇ -ray detector 3, the“ 2 ”-th to“ 19 ”-th (opposite detector) O is the “10th”).
- the “19” th and “71” th ⁇ -ray detectors 3 on the lower side of the total four ends of the correction target detector C are newly set as a reference.
- the correction target detector C is “55” th to “70” -th with respect to the reference detector S which is the “19” -th ⁇ -ray detector 3 (the counter detector O is “63”). ”Th) 16 ⁇ -ray detectors 3 in total, and“ 20 ”th to“ 35 ”th (opposite detector) with respect to the reference detector S which is the“ 71 ”th ⁇ -ray detector 3 O is the “27th”).
- the number of loops in steps S6, S7, and S3 to S5 is three, but the number of loops is not particularly limited.
- the outline of the setting of the reference detector S and the correction target detector O in the embodiment of FIG. 8 will be described.
- the first loop as shown in FIG. 3 and the “61” -th ⁇ -ray detector 3 (opposite detector O) facing each other by 180 ° are selected, and the “60” -th and “62” on both sides adjacent to the counter-detector O are selected.
- the ⁇ -ray detector 3 is referred to as a correction target detector C.
- a time difference histogram relating to the selected reference detector S which is the “1” -th ⁇ -ray detector 3 and the “61” -th ⁇ -ray detector 3 (opposite detector O) opposed to the reference detector S by 180 ° is obtained.
- the standard One of the two ⁇ -ray detectors 3 including the reference detector S which is the selected “1” -th ⁇ -ray detector 3 and the “61” -th ⁇ -ray detector 3 (opposite detector O).
- the reference detector S is selected as the ⁇ -ray detector 3, and the above-mentioned “60” -th and “62” -th correction target detectors C different from the opposing detector O which is the other ⁇ -ray detector 3. Select.
- the correction target detector C detects the “120” th counter detection with respect to the reference detector S which is the “60th” ⁇ -ray detector 3.
- the “119” -th ⁇ -ray detector 3 adjacent to the detector O and adjacent to the “2” -th counter detector O with respect to the reference detector S which is the “62” -th ⁇ -ray detector 3 This is the “3” th ⁇ -ray detector 3.
- the “1” -th ⁇ -ray detector 3 adjacent to the “120” -th counter detector O and adjacent to the “2” -th counter detector O is already selected and thus excluded.
- the “3” -th and “119” -th ⁇ -ray detectors 3 of the correction target detector C are newly set as a reference.
- the correction target detector C detects the “63” th counter detection with respect to the reference detector S which is the “3” th ⁇ -ray detector 3.
- the “64” -th ⁇ -ray detector 3 adjacent to the detector O and adjacent to the “59” -th counter detector O with respect to the reference detector S which is the “119” -th ⁇ -ray detector 3 This is the “58” -th ⁇ -ray detector 3.
- the “60” -th ⁇ -ray detector 3 adjacent to the “59” -th counter detector O and the “62” -th ⁇ -ray detector 3 adjacent to the “63” -th counter detector O are as follows. Exclude it because it is already selected. After the correction, the “58” th and “64th” ⁇ -ray detectors 3 of the correction target detector C are newly set as a reference.
- the series of timing corrections shown in FIG. 4 is preferably performed periodically according to the secular change of the time delay of each channel. Further, the correction table is filed and written and stored in the storage medium of the data collection / control unit 11 or the memory unit 8 described above. When the PET apparatus is turned off and turned on again, the storage medium or It is preferable to read from the memory unit 8 and rewrite it in the timing correction table 9b.
- the data collection / control unit 11 performs the following correction calculation in steps S3 to S6. That is, two ⁇ -ray detectors 3 to be simultaneously counted are selected (in the case of FIG. 7A, the “61” th reference detector S and the “61” th reference detector 180 ° opposite thereto.
- the counter detector O selects the reference detector S which is one of the two selected ⁇ -ray detectors 3 and a ⁇ -ray detector 3 different from the other counter-detector O.
- the time difference histograms related to the two ⁇ -ray detectors 3 selected this time are corrected based on the reference.
- the coincidence circuit 10 simultaneously counts radiation (gamma rays in the first embodiment) based on the time difference histogram for each pair of each ⁇ -ray detector 3 that has been repeatedly corrected as described above. be able to. As a result, it is possible to accurately perform coincidence counting and timing correction without repeating many measurements and calculations.
- the time difference at which the total count value in the time difference histogram based on the reference is the maximum is used as the reference value, and the time difference in the time difference histogram is corrected based on the reference value.
- the time point at which the total count value in the time difference histogram is maximum is the timing at which coincidence counting is most likely to occur. Therefore, by correcting the time difference of the time difference histogram based on the reference value that is the timing, it is possible to align at that timing.
- the ⁇ -ray detector 3 is a DOI detector configured by laminating the scintillator blocks 31 in the ⁇ -ray depth direction.
- detection time correction information corresponding to coordinate information such as the depth direction in which the interaction occurs as in Patent Document 4 described above is required.
- the detection time correction information can be obtained. That is, after performing a series of timing corrections shown in FIG. 4, the light source position in the depth direction is specified by the center of gravity calculation, and the detection time correction information corresponding to the coordinate information such as the depth direction is obtained.
- an external radiation source RI that irradiates the same kind of radiation as the radiopharmaceutical or a phantom Ph that radiates the same kind of radiation as the radiopharmaceutical from the inside is provided, and the above time difference histogram is obtained from the external radiation source RI or phantom Ph. Obtained based on radiation.
- FIG. 9 is a front view showing one embodiment of switching between the reference scintillator element unit and the correction target scintillator element unit.
- the PET apparatus according to the second embodiment including the third and fourth embodiments described later is the block diagram shown in FIG. Moreover, the same code
- one scintillator block 31 of a certain ⁇ -ray detector is set as a reference, and one scintillator block 31 set as the reference is set as a reference scintillator element unit S.
- One scintillator block 31 of a ⁇ -ray detector different from the reference scintillator element unit S is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C.
- the specific timing correction is the same method except that it is changed from the detector unit of the first embodiment to the scintillator element unit of the second embodiment, and thus the description thereof is omitted.
- the corrected scintillator element unit C after correction is a new reference
- the reference scintillator element unit S is shown in FIG. 9B.
- One scintillator block 31 of a ⁇ -ray detector different from the reference scintillator element unit S is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C.
- the corrected scintillator element unit C after correction is set as a reference scintillator element unit S as shown in FIG.
- One scintillator block 31 of a ⁇ -ray detector different from the reference scintillator element unit S is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C. In this manner, timing correction is performed in the same manner in the scintillator element units of other detectors.
- two scintillator element units of the ⁇ -ray detector to be simultaneously counted are selected, and the two selected scintillator elements Among the units, a scintillator element unit of one ⁇ -ray detector (reference scintillator element unit S in the case of FIG. 9) is selected, and a scintillator element unit different from the scintillator element unit of the other ⁇ -ray detector ( In the case of FIG.
- FIG. 10 is a front view showing one embodiment of switching between the reference scintillator element group and the correction target scintillator element unit.
- the PET apparatus according to the third embodiment including the fourth embodiment which will be described later is the block diagram shown in FIG.
- the same reference numerals are given to portions common to the above-described first and second embodiments, and the description thereof is omitted.
- correction is performed for each scintillator element group (that is, in units of detectors) composed of a plurality of scintillator elements (scintillator blocks 31), but in the third embodiment, as in the second embodiment described above.
- the accuracy is further improved by performing correction for each scintillator element unit composed of one scintillator element as described below.
- FIG. 9 of the second embodiment only the scintillator block 31 is shown in FIG. 10, and the other structures (light guide 32 and PMT 33) are not shown.
- a plurality of scintillator blocks 31 of a certain ⁇ -ray detector are set as a reference, and the plurality of scintillator blocks 31 set as the reference are set as a reference scintillator element group S.
- One scintillator block 31 of a ⁇ -ray detector different from the reference scintillator element group S is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C.
- the specific timing correction is the same method except that it is changed from the detector unit of the first embodiment to the scintillator element unit of the third embodiment, and thus the description thereof is omitted.
- the previously selected reference scintillator element group S Based on A scintillator block 31 different from the correction target scintillator element unit C shown in FIG. 10A is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C.
- the total number of corrected correction target scintillator element units C is integrated into a new standard.
- a reference scintillator element group S is assumed.
- a ⁇ -ray detector different from the reference scintillator element unit S (in FIG. 9, a ⁇ -ray detector adjacent to the ⁇ -ray detector of the reference scintillator element group S in FIGS. 9A and 9B).
- One scintillator block 31 is set as a correction target, and one scintillator block 31 set as the correction target is set as a correction target scintillator element unit C. In this manner, timing correction is performed in the same manner in the scintillator element units of other detectors.
- the scintillator element group of one ⁇ -ray detector (in the case of FIG. 10).
- the scintillator element group and the scintillator element group selected this time based on the time difference histogram.
- the operation based on the time difference histogram relating to the corrected scintillator element group and scintillator element unit is newly performed. Since the correction is performed for each scintillator element group and each scintillator element in this way, the accuracy can be further improved as compared with the case where the correction is performed for each detector as in the first embodiment. In addition, the calculation time and burden can be reduced as compared with the case where correction is performed for each scintillator element as in the second embodiment.
- FIG. 11 is an explanatory diagram of a time difference histogram for a scintillator element having self-radiation.
- the PET apparatus according to the fourth embodiment is a block diagram shown in FIG.
- the same reference numerals are given to portions common to the above-described first to third embodiments, and description thereof is omitted.
- the scintillator block is a substance to which self-radiation (an element that simultaneously emits a plurality of radiations) represented by Lu-176 or the like is added.
- the scintillator block is a scintillator element having self-radiation
- the detector includes a scintillator element having self-radiation.
- a scintillator block may be configured by attaching a thin film tape made of a substance to which self-radiation is added to a crystal element having no self-radiation (for example, GSO).
- a scintillator block may be configured by applying a coating agent made of the above substance to a crystal element having no self-radiation.
- the scintillator element with self-radiation includes nuclides that cause ⁇ or ⁇ -decay and emit ⁇ rays accompanying the ⁇ or ⁇ -decay.
- the time difference histogram is acquired based on the radiation from the self-radioactivity (here, ⁇ rays).
- the time difference histogram is a time stamp difference (ie, time difference) for each pair of detectors 3 (indicated as “Difference Time” in FIG. 11). Is a distribution of count values with respect to a change in time difference when a count value (indicated as “Event Counts” in FIG. 11) is plotted on the vertical axis.
- the time difference histogram shows a time point where the total count value is maximum and a time point where the total count value is the second largest. Therefore, in the fourth embodiment, a time difference that is an intermediate value between the time difference at which the total count value is maximum in the reference time difference histogram and the time difference at which the total count value is the second largest is used as the reference value. This reference value is set to “0”.
- the time difference histogram to be corrected is shifted from the reference time difference histogram and is shifted left and right as shown by the solid line in FIG. Therefore, a shift amount for returning “0” shown by the dotted line from the solid line in FIG. 11B to the reference value is obtained as a correction amount for the time difference histogram to be corrected. Then, the time difference histogram is corrected by applying this correction amount.
- an intermediate value between the time difference at which the total count value is maximum in the reference time difference histogram and the time difference at which the total count value is the second largest is obtained.
- a certain time difference is used as a reference value, and the time difference in the time difference histogram is corrected based on the above-described reference value.
- the scintillator element of the other detector detects the most radiation from the self-radiation of the scintillator element of one detector.
- the timing at which the scintillator element of one detector detects the most radiation from the self-radioactivity of the scintillator element of the other detector is the time point where the total count value is maximum, or the total count value is This is the second largest time point. Therefore, the intermediate value between the two time differences, which are these timings, is the timing at which coincidence counting is most likely to occur. Therefore, by correcting the time difference of the time difference histogram based on the reference value of the intermediate value that is the timing, it is possible to align at that timing.
- the present invention is not limited to the above embodiment, and can be modified as follows.
- the positron CT apparatus PET apparatus
- PET apparatus positron CT apparatus
- ⁇ rays are taken as an example of radiation, but ⁇ rays, ⁇ rays, or the like may be used.
- the detector is provided with a scintillator element having self-radiation as in the fourth embodiment, in the case where the detector of the scintillator element in which ⁇ or ⁇ -decay has occurred detects ⁇ rays or ⁇ rays.
- a time difference histogram may be used.
- the DOI detector is used.
- the present invention can also be applied to a detector that does not distinguish the depth direction.
- the present invention can also be applied to a detector having a structure including a single scintillator element.
- the present invention is applied to detectors arranged in a ring shape, but the present invention can be applied even when a plurality of detectors are provided without being installed in a ring shape. .
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Abstract
Description
すなわち、この発明のポジトロンCT装置は、被検体内に投与されたポジトロン放射性薬剤から放出される放射線を検出する複数の検出器を備えたポジトロンCT装置であって、放射線を同時計数する各検出器の対ごとの時間差変化に対する計数値分布を表す時間差ヒストグラムに関して、同時計数する対象の検出器を2つ選択して、当該選択された2つの検出器のうち、一方の検出器を選択するとともに、他方の検出器とは別の検出器を選択し、その選択を繰り返し行った際に、過去に選択された2つの検出器に関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択された2つの検出器に関する時間差ヒストグラムを補正し、当該補正された2つの検出器に関する時間差ヒストグラムを新たに基準とする作業を繰り返し行う演算手段と、前記演算手段で繰り返し補正された各検出器の対ごとの前記時間差ヒストグラムに基づいて、放射線を同時計数する同時計数回路とを備えることを特徴とするものである。
11 … データ収集・制御部
3 … γ線検出器
31 … シンチレータブロック
33 … 光電子増倍管(PMT)
RI … 外部線源
Ph … ファントム
S … 基準検出器、基準シンチレータ素子単位、基準シンチレータ素子群
C … 補正対象検出器、補正対象シンチレータ素子単位
O … 対向検出器
M … 被検体
図5(a)に示すように、放射性薬剤、すなわち放射性同位元素(RI)と同種の放射線(本実施例1ではγ線)を照射する外部線源RIをPET装置の視野内に設置する。好ましくは、外部線源RIを視野内の中央領域に設置することで、約180°対向した2つのγ線検出器3が外部線源RIからの放射線をほぼ同時に検出することができ、各γ線検出器3から同時計数回路10までの信号チャンネルでの信号の時間遅れのみがタイミング補正の対象となる。したがって、タイミング補正を行うのみでγ線が同時計数回路10に到達するタイミングを一致させることができる。なお、外部線源RI以外にも、図5(b)に示すように、放射性薬剤と同種の放射線を内部から照射するファントムPhをPET装置の視野内に設置してもよい。ファントムPhを設置する場合においても、好ましくは視野内の中央領域に設置する。外部線源RIは、この発明における外部線源に相当し、ファントムPhは、この発明におけるファントムに相当する。
ステップS1で測定された補正用データに基づいて、放射線を同時計数する各γ線検出器3の対ごとに時間差ヒストグラムを作成する。図6に示すように、時間差ヒストグラムは、各γ線検出器3の対ごとにタイムスタンプの差分(すなわち時間差)(図6では「Difference Time」で表記)を横軸にとり、計数値(図6では「Event Counts」で表記)を縦軸にとったときの時間差変化に対する計数値分布である。
次に、基準検出器と補正対象検出器とをそれぞれ設定する。図7(a)に示すように、1つのγ線検出器3を基準として設定し、その基準として設定されたγ線検出器3(図7(a)の黒塗りを参照)を基準検出器Sとする。この基準検出器Sから見たPET装置の視野内になるそれぞれのγ線検出器3対を補正対象として設定し、その補正対象として設定されたγ線検出器3を補正対象検出器Cとする。
ステップS3で選択された基準検出器Sおよび対向検出器Oからなる2つのγ線検出器3のうち、一方のγ線検出器3として基準検出器Sを選択するとともに、他方のγ線検出器3である対向検出器Oとは別の補正対象検出器Cを選択する。つまり、対向検出器O以外の補正対象検出器Cと基準検出器Sとをそれぞれ選択して、補正対象となる時間差ヒストグラムを抽出する。図7(a)に示す場合には、ステップS3において「61」番目のγ線検出器3(対向検出器O)も含めて補正対象検出器Cは「49」番目~「73」番目の合計25個のγ線検出器3であって、「1」番目のγ線検出器3である基準検出器Sと、「61」番目のγ線検出器3(対向検出器O)以外の「49」番目~「60」番目および「62」番目~「73」番目の各々の補正対象検出器Cとに関する時間差ヒストグラムを、今回で選択された2つのγ線検出器3に関する時間差ヒストグラムとして抽出する。
対向検出器O以外の補正対象検出器Cと基準検出器Sとに関する時間差ヒストグラムは、基準とした時間差ヒストグラムに対してズレが生じ、上述したように図6(b)の実線に示すように左右にシフトする。そこで、ステップS4において今回で選択された2つのγ線検出器3に関する時間差ヒストグラムを、図6(b)の実線から点線に示す“0”を中心とした度数分布に戻すようなシフト量を補正量としてデータ収集・制御部11は求める。
全てのγ線検出器3の補正量の算出が完了したか否かを判定する。完了していない場合には、ステップS7に進み、完了した場合には、ステップS8に進む。
ステップS5で求められた補正量を適用して、今回で選択された2つのγ線検出器3に関する時間差ヒストグラムを補正量の分だけ“0”を中心とした度数分布に戻すようにシフトさせて、当該時間差ヒストグラムをそれぞれ補正する。つまり、基準値である時間差“0”に基づいて当該時間差ヒストグラムをそれぞれ補正する。図7(a)に示す場合には、「1」番目のγ線検出器3である基準検出器Sと、「49」番目~「60」番目および「62」番目~「73」番目の各々の補正対象検出器Cとに関する時間差ヒストグラムを、過去に選択された「1」番目のγ線検出器3である基準検出器Sと、それに180°対向した「61」番目のγ線検出器3(対向検出器O)とに関する時間差ヒストグラムに基づいて補正する。
これらのステップS3~S6(図7の実施形態の場合には3回の繰り返しループ)で求められた補正量を、データ収集・制御部11から検出器信号処理部9のタイミング補正テーブル9bに書き込むことで、タイミング補正テーブルを設定する。この設定された補正量を、通常の被検体Mを用いた核医学診断での撮像に適用することで、タイミング調整を高精度に行うことが可能となり、上述の撮像を行うときに画質の優れた画像を取得することができる。
Claims (15)
- 被検体内に投与されたポジトロン放射性薬剤から放出される放射線を検出する複数の検出器を備えたポジトロンCT装置であって、
放射線を同時計数する各検出器の対ごとの時間差変化に対する計数値分布を表す時間差ヒストグラムに関して、同時計数する対象の検出器を2つ選択して、当該選択された2つの検出器のうち、一方の検出器を選択するとともに、他方の検出器とは別の検出器を選択し、その選択を繰り返し行った際に、過去に選択された2つの検出器に関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択された2つの検出器に関する時間差ヒストグラムを補正し、当該補正された2つの検出器に関する時間差ヒストグラムを新たに基準とする作業を繰り返し行う演算手段と、
前記演算手段で繰り返し補正された各検出器の対ごとの前記時間差ヒストグラムに基づいて、放射線を同時計数する同時計数回路と
を備えることを特徴とするポジトロンCT装置。 - 請求項1に記載のポジトロンCT装置において、
前記基準とした前記時間差ヒストグラムにおける総計数値が最大となる時間差を基準値とし、
前記演算手段は、前記基準値に基づいて時間差ヒストグラムの時間差を補正することを特徴とするポジトロンCT装置。 - 請求項1に記載のポジトロンCT装置において、
前記基準とした前記時間差ヒストグラムにおける総計数値が最大となる時間差と、総計数値が二番目に大きい時間差との中間値にある時間差を基準値とし、
前記演算手段は、前記基準値に基づいて時間差ヒストグラムの時間差を補正することを特徴とするポジトロンCT装置。 - 請求項1から請求項3のいずれかに記載のポジトロンCT装置において、
前記検出器は、
放射線の入射により蛍光する複数のシンチレータ素子と、
各シンチレータ素子からの光を光電変換することで放射線を検出する光電変換手段と
を備え、
放射線を同時計数する各検出器の1つのシンチレータ素子からなるシンチレータ素子単位の対ごとの前記時間差ヒストグラムに関して、同時計数する対象の検出器のシンチレータ素子単位を2つ選択して、当該選択された2つのシンチレータ素子単位のうち、一方の検出器のシンチレータ素子単位を選択するとともに、他方の検出器のシンチレータ素子単位とは別のシンチレータ素子単位を選択し、その選択を繰り返し行った際に、過去に選択された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを補正し、当該補正された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを新たに基準とする作業を前記演算手段は繰り返し行い、
前記演算手段で繰り返し補正された各検出器のシンチレータ素子単位の対ごとの前記時間差ヒストグラムに基づいて、前記同時計数回路は放射線を同時計数することを特徴とするポジトロンCT装置。 - 請求項1から請求項3のいずれかに記載のポジトロンCT装置において、
前記検出器は、
放射線の入射により蛍光する複数のシンチレータ素子と、
各シンチレータ素子からの光を光電変換することで放射線を検出する光電変換手段と
を備え、
放射線を同時計数する各検出器のうち、一方の検出器の複数のシンチレータ素子からなるシンチレータ素子群と他方の検出器の1つのシンチレータ素子からなるシンチレータ素子単位との対ごとの前記時間差ヒストグラムに関して、同時計数する対象の検出器のうち、一方の検出器のシンチレータ素子群と他方の検出器のシンチレータ素子単位とを選択して、当該選択されたシンチレータ素子群とシンチレータ素子単位とのうち、当該シンチレータ素子群を選択するとともに、前記他方の検出器のシンチレータ素子単位とは別のシンチレータ素子単位を選択し、その選択を繰り返し行った際に、過去に選択されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを補正し、当該補正されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを新たに基準とする作業を前記演算手段は繰り返し行い、
前記演算手段で繰り返し補正されたシンチレータ素子群とシンチレータ素子単位との対ごとの前記時間差ヒストグラムに基づいて、前記同時計数回路は放射線を同時計数することを特徴とするポジトロンCT装置。 - 請求項1から請求項5のいずれかに記載のポジトロンCT装置において、
前記検出器は、
放射線の入射により蛍光する複数のシンチレータ素子と、
各シンチレータ素子からの光を光電変換することで放射線を検出する光電変換手段と
を備え、
前記検出器は、各々の前記シンチレータ素子を放射線の深さ方向に積層して構成されたDOI検出器であることを特徴とするポジトロンCT装置。 - 請求項1から請求項6のいずれかに記載のポジトロンCT装置において、
前記放射性薬剤と同種の放射線を照射する外部線源、または前記放射性薬剤と同種の放射線を内部から照射するファントムを備え、
前記時間差ヒストグラムを前記外部線源または前記ファントムからの放射線に基づいて取得することを特徴とするポジトロンCT装置。 - 請求項1から請求項6のいずれかに記載のポジトロンCT装置において、
前記検出器は、自己放射能を持つシンチレータ素子を備え、
前記時間差ヒストグラムを前記自己放射能からの放射線に基づいて取得することを特徴とするポジトロンCT装置。 - 被検体内に投与されたポジトロン放射性薬剤から放出される放射線を同時計数するために用いられるタイミング補正方法であって、
放射線を同時計数する各検出器の対ごとの時間差変化に対する計数値分布を表す時間差ヒストグラムに関して、同時計数する対象の検出器を2つ選択して、当該選択された2つの検出器のうち、一方の検出器を選択するとともに、他方の検出器とは別の検出器を選択し、その選択を繰り返し行った際に、過去に選択された2つの検出器に関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択された2つの検出器に関する時間差ヒストグラムを補正し、当該補正された2つの検出器に関する時間差ヒストグラムを新たに基準とする作業を繰り返し行うヒストグラム補正工程
を備えることを特徴とするタイミング補正方法。 - 請求項9に記載のタイミング補正方法において、
前記基準とした前記時間差ヒストグラムにおける総計数値が最大となる時間差を基準値とし、
前記ヒストグラム補正工程では、前記基準値に基づいて時間差ヒストグラムの時間差を補正することを特徴とするタイミング補正方法。 - 請求項9に記載のタイミング補正方法において、
前記基準とした前記時間差ヒストグラムにおける総計数値が最大となる時間差と、総計数値が二番目に大きい時間差との中間値にある時間差を基準値とし、
前記ヒストグラム補正工程では、前記基準値に基づいて時間差ヒストグラムの時間差を補正することを特徴とするタイミング補正方法。 - 請求項9から請求項11のいずれかに記載のタイミング補正方法において、
放射線を同時計数する各検出器の1つのシンチレータ素子からなるシンチレータ素子単位の対ごとの前記時間差ヒストグラムに関して、同時計数する対象の検出器のシンチレータ素子単位を2つ選択して、当該選択された2つのシンチレータ素子単位のうち、一方の検出器のシンチレータ素子単位を選択するとともに、他方の検出器のシンチレータ素子単位とは別のシンチレータ素子単位を選択し、その選択を繰り返し行った際に、前記ヒストグラム補正工程では、過去に選択された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを補正し、当該補正された2つの検出器のシンチレータ素子単位に関する時間差ヒストグラムを新たに基準とする作業を繰り返し行うことで、タイミング補正を行うことを特徴とするタイミング補正方法。 - 請求項9から請求項11のいずれかに記載のタイミング補正方法において、
放射線を同時計数する各検出器のうち、一方の検出器の複数のシンチレータ素子からなるシンチレータ素子群と他方の検出器の1つのシンチレータ素子からなるシンチレータ素子単位との対ごとの前記時間差ヒストグラムに関して、同時計数する対象の検出器のうち、一方の検出器のシンチレータ素子群と他方の検出器のシンチレータ素子単位とを選択して、当該選択されたシンチレータ素子群とシンチレータ素子単位とのうち、当該シンチレータ素子群を選択するとともに、前記他方の検出器のシンチレータ素子単位とは別のシンチレータ素子単位を選択し、その選択を繰り返し行った際に、前記ヒストグラム補正工程では、過去に選択されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを基準として、当該基準に基づいて、今回で選択されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを補正し、当該補正されたシンチレータ素子群とシンチレータ素子単位とに関する時間差ヒストグラムを新たに基準とする作業を繰り返し行うことで、タイミング補正を行うことを特徴とするタイミング補正方法。 - 請求項9から請求項13のいずれかに記載のタイミング補正方法において、
前記時間差ヒストグラムは、前記放射性薬剤と同種の放射線を照射する外部線源、または前記放射性薬剤と同種の放射線を内部から照射するファントムからの放射線に基づいて取得されたデータであることを特徴とするタイミング補正方法。 - 請求項9から請求項13のいずれかに記載のタイミング補正方法において、
前記時間差ヒストグラムは、自己放射能からの放射線に基づいて取得されたデータであることを特徴とするタイミング補正方法。
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JP7247745B2 (ja) | 2019-05-21 | 2023-03-29 | 株式会社島津製作所 | 放射線検出装置の2次元位置マップの校正方法および放射線検出装置 |
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EP2573588B1 (en) | 2017-09-27 |
CN102906595A (zh) | 2013-01-30 |
EP2573588A4 (en) | 2015-10-14 |
TW201200894A (en) | 2012-01-01 |
CN102906595B (zh) | 2014-12-31 |
EP2573588A1 (en) | 2013-03-27 |
US20130062526A1 (en) | 2013-03-14 |
US9360569B2 (en) | 2016-06-07 |
US9844351B2 (en) | 2017-12-19 |
US20160242706A1 (en) | 2016-08-25 |
TWI444646B (zh) | 2014-07-11 |
JP5459397B2 (ja) | 2014-04-02 |
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