JP2013007585A - Positron emission computer tomographic imaging apparatus and x-ray ct (computed tomography) device - Google Patents

Abstract

To provide a positron emission computed tomography apparatus and an X-ray CT apparatus capable of appropriately adjusting a data amount at a high count rate.
A positron emission computed tomography apparatus according to an embodiment includes a detector, a count rate measurement unit, a generation unit, and a control unit. The detector detects annihilation radiation. The count rate measuring unit measures the count rate of events for detecting annihilation radiation by the detector. The generating unit generates annihilation radiation data detected by the detector for each event. When the count rate exceeds a threshold, the control unit controls the data transfer according to the energy value of the annihilation radiation.
[Selection] Figure 6

Description

  Embodiments described herein relate generally to a positron emission computed tomography apparatus and an X-ray CT apparatus.

  Conventionally, a positron emission computed tomography (PET) apparatus is known as a nuclear medicine imaging apparatus. In imaging by a PET apparatus, a compound labeled with a positron emitting nuclide or a radiopharmaceutical is administered to a subject. The administered compound or radiopharmaceutical moves in the subject, and the positron emitting nuclide is taken into the living tissue in the subject. This positron emitting nuclide emits positrons, and the emitted positrons combine with electrons and disappear. At this time, the positron emits a pair of annihilation radiations (also referred to as gamma rays and annihilation gamma rays) in almost opposite directions. On the other hand, the PET apparatus detects annihilation radiation using a detector arranged in a ring shape around the subject, and generates coincidence count information (Coincidence List) from the detection result. Then, the PET apparatus performs reconstruction by back projection processing using the generated coincidence information, and generates a PET image.

  Incidentally, in the process of generating coincidence counting information from the detection result, the PET apparatus generates data based on the output signal of the detector and transfers the generated data for subsequent processing. Since this transfer and subsequent processing are limited by hardware, the PET apparatus normally adjusts the amount of data to be transferred by providing a buffer for storing data. However, when the count rate of events for detecting annihilation radiation (the number of events occurring per unit time) is high (hereinafter, when the count rate is high), appropriate adjustment may not be performed. The same situation can occur in an X-ray CT apparatus provided with a photon counting type detector.

Edited by the Japan Society for Imaging and Medical Systems “Medical Image / Radiology Equipment Handbook” Nagoya Art Printing Co., Ltd. 2001, P.190-191

  The problem to be solved by the present invention is to provide a positron emission computed tomography apparatus and an X-ray CT apparatus capable of appropriately adjusting the amount of data at a high count rate.

  The positron emission computed tomography apparatus according to the embodiment includes a detector, a count rate measurement unit, a generation unit, and a control unit. The detector detects annihilation radiation. The count rate measuring unit measures the count rate of events for detecting annihilation radiation by the detector. The generating unit generates annihilation radiation data detected by the detector for each event. When the count rate exceeds a threshold, the control unit controls the data transfer according to the energy value of the annihilation radiation.

  The X-ray CT apparatus of the embodiment includes a photon counting type detector, a count rate measurement unit, a generation unit, and a control unit. The detector detects X-rays. The count rate measuring unit measures the count rate of an event for detecting X-rays by the detector. The generation unit generates X-ray data detected by the detector for each event. When the count rate exceeds a threshold, the control unit controls the data transfer according to the energy value of the X-ray.

FIG. 1 is a block diagram showing the configuration of the PET apparatus according to the first embodiment. FIG. 2 is a diagram for explaining the detector module according to the first embodiment. FIG. 3 is a block diagram illustrating a configuration of the event data collection unit according to the first embodiment. FIG. 4 is an example of event data according to the first embodiment. FIG. 5 is a diagram for explaining an energy window according to the first embodiment. FIG. 6 is a diagram for explaining an energy window according to the first embodiment. FIG. 7 is a diagram for explaining an energy window according to the first embodiment. FIG. 8 is a flowchart illustrating a processing procedure performed by the event data amount adjustment unit according to the first embodiment. FIG. 9 is a block diagram showing a configuration of an X-ray CT apparatus according to the second embodiment. FIG. 10 is a block diagram illustrating a configuration of an event data collection unit according to the second embodiment. FIG. 11 is a diagram for explaining the relationship between the detector and the X-ray according to the second embodiment. FIG. 12 is a diagram for explaining an energy window according to the second embodiment. FIG. 13 is a diagram for explaining an energy window according to the second embodiment.

  Hereinafter, a positron emission computed tomography apparatus and an X-ray CT apparatus according to embodiments will be described with reference to the drawings.

(First embodiment)
A first embodiment will be described. The PET apparatus 100 according to the first embodiment controls the transfer of event data according to the energy value of annihilation radiation at the time of a high count rate. That is, when the number of events that occur per unit time is large, the amount of event data generated for each event is also large. For this reason, if event data is transferred without considering the high count rate, for example, overflow may occur at any stage in the subsequent processing, and event data may be randomly lost.

  In this regard, since the PET apparatus 100 according to the first embodiment controls the transfer of event data according to the energy value of the annihilation radiation at the time of a high count rate, event data is not randomly lost. In addition, since the selection is based on the energy value, there is little risk of losing useful event data. The PET apparatus 100 according to the first embodiment realizes such control by a DAS (Data Acquisition System) (corresponding to the event data collection unit 15) included in the detector module 14 described later. Hereinafter, after describing the overall configuration, the configuration of the event data collection unit 15 will be described.

  FIG. 1 is a block diagram showing a configuration of a PET apparatus 100 according to the first embodiment. As shown in FIG. 1, the PET device 100 according to the first embodiment includes a gantry device 10 and a console device 16.

  As shown in FIG. 1, the gantry device 10 includes a top board 11, a bed 12, a bed driving unit 13, and a plurality of detector modules 14. In addition, the gantry device 10 has a cavity serving as a photographing port. The top plate 11 is a bed on which the subject P lies, and is placed on the bed 12. The couch driving unit 13 moves the couchtop 11 under the control of a couch control unit 23 described later. For example, the bed driving unit 13 moves the subject P into the imaging port of the gantry device 10 by moving the top plate 11.

  The detector module 14 detects annihilation radiation emitted from the subject P. As shown in FIG. 1, a plurality of detector modules 14 are arranged in the gantry device 10 so as to surround the subject P in a ring shape.

  FIG. 2 is a diagram for explaining the detector module 14 according to the first embodiment. The detector module 14 is a photon counting type and anger type detector, and includes a scintillator 141, a photomultiplier tube (PMT (Photomultiplier Tube)) 142, and a light guide 143 as shown in FIG. 2. The detector module 14 according to the first embodiment is merely an example, and may have a semiconductor instead of a photomultiplier tube, for example.

  The scintillator 141 converts annihilation radiation emitted from the subject P and incident into visible light (hereinafter referred to as scintillation light), and outputs the converted scintillation light. The scintillator 141 is formed of a scintillator crystal such as NaI (Sodium Iodide), BGO (Bismuth Germanate), LYSO (Lutetium Yttrium Oxyorthosilicate), LSO (Lutetium Oxyorthosilicate), LGSO (Lutetium Gadolinium Oxyorthosilicate), and the like, as shown in FIG. Arranged in two dimensions. The photomultiplier tube 142 multiplies the scintillation light output from the scintillator 141 and converts it into an electrical signal. As shown in FIG. 2, a plurality of photomultiplier tubes 142 are arranged. The light guide 143 transmits the scintillation light output from the scintillator 141 to the photomultiplier tube 142. The light guide 143 is formed of, for example, a plastic material having excellent light transmittance.

  The photomultiplier tube 142 includes a photocathode that receives scintillation light and generates photoelectrons, a multistage dynode that provides an electric field that accelerates the generated photoelectrons, and an anode that is an outlet for electrons. Electrons emitted from the photocathode due to the photoelectric effect are accelerated toward the dynode, collide with the surface of the dynode, and knock out a plurality of electrons. By repeating this phenomenon over multiple dynodes, the number of electrons is avalancheally increased, and the number of electrons at the anode reaches about 1 million. In such an example, the gain factor of the photomultiplier tube 142 is 1 million times. In addition, a voltage of 1000 volts or more is usually applied between the dynode and the anode for amplification using the avalanche phenomenon.

  Thus, the detector module 14 converts the annihilation radiation emitted from the subject P into scintillation light by the scintillator 141, and converts the converted scintillation light into an electrical signal (hereinafter referred to as detector signal) by the photomultiplier tube 142. By converting, annihilation radiation emitted from the subject P is detected.

  By the way, in 1st Embodiment, the some detector module 14 is divided into several blocks, and has the event data collection part 15 for every block. For example, in the first embodiment, one detector module 14 is one block. For this reason, each detector module 14 has an event data collection unit 15. The correspondence relationship between the number of one block and the detector module 14 is arbitrary. The event data collection unit 15 will be described in detail later.

  Returning to FIG. 1, the console device 16 includes an input unit 17, a display unit 18, a system control unit 19, a data storage unit 20, a coincidence information generation unit 21, an image reconstruction unit 22, and a bed control unit. 23. Each part of the console device 16 is connected via an internal bus.

  The input unit 17 is a mouse or a keyboard used for inputting various instructions and various settings by an operator of the PET apparatus 100, and transfers the various instructions and various settings that are input to the system control unit 19. The display unit 18 is a monitor or the like that is referred to by an operator, and displays a PET image and receives a GUI (Graphical User Interface) for receiving various instructions and settings from the operator under the control of the system control unit 19. Is displayed.

  The system control unit 19 performs overall control of the PET apparatus 100 by controlling the gantry device 10 and the console device 16. For example, the system control unit 19 controls imaging in the PET apparatus 100.

  The data storage unit 20 stores various data used in the PET apparatus 100. For example, the data storage unit 20 stores the event data transferred from the gantry device 10, the coincidence counting information generated by the coincidence counting information generation unit 21, the PET image reconstructed by the image reconstruction unit 22, and the like. The data storage unit 20 is realized by, for example, a semiconductor memory element such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like.

  The coincidence counting information generating unit 21 generates coincidence counting information using the event data collected by the event data collecting unit 15. Specifically, the coincidence information generation unit 21 reads the event data stored in the data storage unit 20 and searches for a pair of event data in which a pair of annihilation radiations emitted from the positrons are simultaneously counted. The coincidence count information generation unit 21 generates the searched event data pair as coincidence count information, and stores the generated coincidence count information in the data storage unit 20.

  The image reconstruction unit 22 reconstructs a PET image. Specifically, the image reconstruction unit 22 reads the coincidence counting information stored in the data storage unit 20 as projection data, and performs a back projection process on the read projection data to reconstruct a PET image. The image reconstruction unit 22 stores the reconstructed PET image in the data storage unit 20. The couch control unit 23 controls the couch driving unit 13.

  Each of the above-described coincidence information generation unit 21, image reconstruction unit 22, and system control unit 19 includes an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), a central processing unit (CPU). Units) and MPUs (Micro Processing Units) and other electronic circuits.

  Next, the event data collection unit 15 according to the first embodiment will be described in detail. FIG. 3 is a block diagram illustrating a configuration of the event data collection unit 15 according to the first embodiment. As shown in FIG. 3, the event data collection unit 15 includes an A / D (Analog / Digital) converter 15a, a buffer 15b, a count rate measurement unit 15c, and an event data amount adjustment unit 15d. Hereinafter, the operation of each unit will be described.

  The A / D converter 15a generates event data 15f for each event. Specifically, when receiving the input of the detector signal 15e that is analog data, the A / D converter 15a converts it into digital data to generate event data 15f, and outputs the generated event data 15f to the buffer 15b. To do. The event data 15f includes an annihilation radiation detection position (for example, identification information of the detector module 14 and identification information of the scintillator 141), an energy value (for example, the intensity of the detector signal 15e), and a detection time (for example, an absolute time). , Elapsed time from the start of shooting, etc.).

FIG. 4 is an example of the event data 15f according to the first embodiment. As shown in FIG. 4, the event data 15f includes, for example, “D ₁ ”, “P” which are values of “module ID” and “scintillator ID” (detection position), “energy value”, and “detection time”. ₁ ”,“ E ₁ ”, and“ T ₁ ”.

  Further, when receiving the input of the detector signal 15e, the A / D converter 15a generates one pulse signal 15g and outputs the generated pulse signal 15g to the count rate measuring unit 15c. The A / D converter 15a accepts input of a plurality of detector signals 15e as time elapses, but generates one pulse signal 15g each time the input is accepted.

  The buffer 15b temporarily stores event data 15f. Specifically, when receiving the input of the event data 15f, the buffer 15b stores it according to a write signal (not shown). The buffer 15b outputs the stored event data 15f in accordance with a read signal (not shown).

  The count rate measuring unit 15c measures the count rate of events. Specifically, the count rate measuring unit 15c counts the number of pulse signals 15g input per unit time using a clock signal (not shown), and indicates a count rate indicating the number of events that occurred during the unit time. Information 15h is generated. In addition, the count rate measuring unit 15c outputs the generated count rate information 15h to the event data amount adjusting unit 15d. Note that the count rate measurement unit 15c according to the first embodiment is described as periodically generating and outputting the count rate information 15h, but is not limited thereto. For example, the count rate measuring unit 15c may output the count rate information 15h only at a high count rate (for example, only when a first threshold described later is exceeded).

  The event data amount adjusting unit 15d controls the transfer of event data according to the energy value of annihilation radiation. Specifically, the event data amount adjustment unit 15d according to the first embodiment sets the count rate threshold and the energy window in a stepwise manner. Then, when receiving the input of the count rate information 15h, the event data amount adjusting unit 15d determines whether or not the count rate exceeds a threshold value, and if it is determined that the count rate exceeds, transfers the event data 15f for subsequent processing. Is controlled according to the energy value of each event data 15f. As a result, the amount of event data 15f transferred for subsequent processing is flexibly adjusted.

  FIGS. 5-7 is a figure for demonstrating the energy window which concerns on 1st Embodiment. The horizontal axis indicates the energy value of each event data 15f. The vertical axis represents the number of event data 15f classified for each energy value (corresponding to the number of events). Normally, as shown in FIG. 5, event data 15f having various energy values is sequentially stored in the buffer 15b.

  The event data amount adjustment unit 15d according to the first embodiment provides a first threshold value and a second threshold value for the count rate. The second threshold is a higher count rate than the first threshold. Then, the event data amount adjustment unit 15d opens the entire energy window and stores it in the buffer 15b as shown in FIG. 5 in the “step below the first threshold”, that is, the step where the count rate is relatively low. All of the event data 15f that has been sent is transferred for subsequent processing without sorting.

  In addition, the event data amount adjustment unit 15d determines that, for example, at the stage where the count rate is higher than the first threshold and lower than the second threshold, that is, the count rate is relatively high, as shown in FIG. By changing the value and the upper limit value, the opening width of the energy window is narrowed to ½. Then, the event data amount adjusting unit 15d transfers only the event data 15f having the energy value within the first energy window with the opening width narrowed toward the subsequent processing. On the other hand, the event data amount adjusting unit 15d discards the event data 15f (shaded portion in FIG. 6) having an energy value outside the first energy window without transferring it.

  In addition, the event data amount adjustment unit 15d further sets the lower limit value and the upper limit value of the energy window, for example, as shown in FIG. 7 in the “stage exceeding the second threshold”, that is, the stage where the count rate is considerably high. By changing, the opening width of the energy window is reduced to ¼. Then, the event data amount adjustment unit 15d transfers only the event data 15f having the energy value within the second energy window with the opening width narrowed toward the subsequent processing. On the other hand, the event data amount adjusting unit 15d discards the event data 15f (shaded portion in FIG. 7) having an energy value outside the second energy window without transferring it.

  FIG. 8 is a flowchart showing a processing procedure by the event data amount adjusting unit 15d according to the first embodiment. As illustrated in FIG. 8, when the event data amount adjustment unit 15d receives the input of the count rate information 15h (Yes in step S101), whether or not the count rate indicated by the count rate information 15h exceeds the first threshold value. Is determined (step S102).

  When the value is below the first threshold (No at Step S102), the event data amount adjusting unit 15d opens and transfers all energy windows (Step S103). In other words, the event data amount adjustment unit 15d reads the event data 15f stored in the buffer 15b in accordance with a read signal (not shown) and transfers it for subsequent processing, but all the event data 15f stored in the buffer 15b. Transfer without sorting.

  When exceeding the first threshold value in step S102 (step S102, Yes), the event data amount adjustment unit 15d determines whether or not the count rate indicated by the count rate information 15h exceeds the second threshold value (step S104). ).

  If the value is below the second threshold (No at Step S104), the event data amount adjustment unit 15d adjusts the data amount by the first energy window (see FIG. 6) and transfers the data (Step S105). That is, the event data amount adjusting unit 15d refers to the energy value of each event data 15f stored in the buffer 15b, and determines whether or not it is within the first energy window. The event data amount adjustment unit 15d transfers the event data 15f if it is within the first energy window, and does not transfer it if it is outside the first energy window.

  When exceeding a 2nd threshold value in step S104 (step S104, Yes), the event data amount adjustment part 15d adjusts a data amount with a 2nd energy window (refer FIG. 7), and transfers (step S106). That is, the event data amount adjusting unit 15d refers to the energy value of each event data 15f stored in the buffer 15b, and determines whether or not it is within the second energy window. Then, the event data amount adjustment unit 15d transfers the event data 15f if it is within the second energy window, and does not transfer it if it is outside the second energy window.

  Further, the event data amount adjustment unit 15d according to the first embodiment periodically receives input of the count rate information 15h. For this reason, the event data amount adjustment unit 15d determines that the count rate information 15h received after narrowing the opening width of the energy window once indicates that the count rate is at a relatively low stage, for example, the total energy again. Open the window. In the case of a method of accepting the input of the count rate information 15h only at a high count rate, for example, the event data amount adjusting unit 15d may open the entire energy window again after a predetermined time has elapsed. Alternatively, the event data amount adjustment unit 15d may sequentially open the energy windows, such as the second energy window, the first energy window, and the total energy window, as time elapses.

  Further, the energy window shown in the first embodiment is merely an example. For example, a single threshold value may be used without providing a plurality of threshold values. Further, for example, more threshold values such as a third threshold value and a fourth threshold value may be set, and the opening width of the energy window at each stage may be set more finely.

  For this reason, according to the first embodiment, the data amount can be appropriately adjusted at the time of a high count rate. As a result, sufficient image quality can be ensured even at high count rates. Further, according to the first embodiment, the data amount can be adjusted effectively and efficiently so that both of the paired event data are transferred.

  This point will be described. If event data is randomly lost, if n event data is lost, 2n pairs of event data are lost. For this reason, the event data cannot be sufficiently effectively used from the viewpoint of image quality, and there is a possibility that an image with artifacts may be output.

  Here, the paired event data has a property of having an equivalent energy value. For example, when there is event data having an energy value of about “511 keV” and event data having an energy value of about “200 keV”, for example, the latter is event data detected by scattering, for example. it is conceivable that. That is, event data that is valid as paired event data is event data having an energy value of about “511 keV”, and event data having an energy value of about “200 keV” is not valid event data in the first place. . If so, according to the first embodiment in which event data is selected according to the energy value and transferred to subsequent processing, both event data of a pair having an effective energy value are transferred. Thus, the data amount can be adjusted effectively and efficiently.

(Second Embodiment)
A second embodiment will be described. The X-ray CT apparatus 200 according to the second embodiment includes a photon counting type detector, and controls the transfer of event data according to the energy value of the X-ray at a high count rate. That is, when the number of events that occur per unit time is large, the amount of event data generated for each event is also large. For this reason, if event data is transferred without considering the high count rate, for example, overflow may occur at any stage in the subsequent processing, and event data may be randomly lost.

  In this regard, the X-ray CT apparatus 200 according to the second embodiment controls the transfer of event data according to the X-ray energy value at a high count rate, so that event data is not randomly lost. . In addition, since the selection is based on the energy value, there is little risk of losing useful event data. The X-ray CT apparatus 200 according to the second embodiment realizes such control by a DAS (corresponding to the event data collection unit 215) provided in the detector 214b described later.

  FIG. 9 is a block diagram showing a configuration of an X-ray CT apparatus 200 according to the second embodiment. As shown in FIG. 9, the X-ray CT apparatus 200 according to the second embodiment includes a gantry device 210 and a console device 216.

  As shown in FIG. 9, the gantry device 210 includes a top plate 211, a bed 212, a bed driving unit 213, an X-ray tube 214a, and a detector 214b. Further, the gantry device 210 has a cavity serving as a photographing port. The top plate 211 is a bed on which the subject P lies, and is disposed on the bed 212. The bed driving unit 213 moves the top plate 211 under the control of a bed control unit 223 described later. For example, the bed driving unit 213 moves the subject P into the imaging port of the gantry device 210 by moving the top plate 211.

  The X-ray tube 214a and the detector 214b are supported by an annular rotating frame so as to face each other with the subject P interposed therebetween, and continuously rotate on a circular orbit centering on the subject P. The X-ray tube 214a generates X-rays and irradiates the subject P with the generated X-rays. The detector 214b detects X-rays that have passed through the subject P and X-rays that have directly entered without passing through the subject P.

  Here, the detector 214b according to the second embodiment is a photon counting type detector 214b. For example, the detector 214b has a plurality of detector modules similar to the detector module 14 described in the first embodiment. In the second embodiment, the detector 214b is divided into a plurality of blocks, and has an event data collection unit 215 for each block. For example, in the second embodiment, one detector module is one block. For this reason, each detector module has an event data collection unit 215. The correspondence relationship between the number of one block and the detector module is arbitrary.

  Returning to FIG. 9, the console device 216 includes an input unit 217, a display unit 218, a system control unit 219, a data storage unit 220, an energy separation unit 221, an image reconstruction unit 222, and a bed control unit 223. Have Each unit included in the console device 216 is connected via an internal bus.

  The input unit 217 is a mouse or a keyboard used for inputting various instructions and various settings by the operator of the X-ray CT apparatus 200, and transfers the various instructions and various settings that are input to the system control unit 219. The display unit 218 is a monitor or the like referred to by the operator, and displays an X-ray image under the control of the system control unit 219 or displays a GUI for receiving various instructions and various settings from the operator. To do.

  The system control unit 219 controls the X-ray CT apparatus 200 as a whole by controlling the gantry apparatus 210 and the console apparatus 216. For example, the system control unit 219 controls imaging in the X-ray CT apparatus 200.

  The data storage unit 220 stores various data used in the X-ray CT apparatus 200. For example, the data storage unit 220 stores event data transferred from the gantry device 210, an X-ray image reconstructed by the image reconstruction unit 222, and the like. Note that the data storage unit 220 is realized by, for example, a semiconductor memory element such as a RAM or a flash memory, a hard disk, an optical disk, or the like.

  The energy separation unit 221 separates the event data collected by the event data collection unit 215 according to the energy value. Specifically, the energy sorting unit 221 reads event data stored in the data storage unit 220, refers to the energy value of each event data, and sorts each event data according to the energy value. The energy sorting unit 221 stores the event data sorted according to the energy value in the data storage unit 220.

  The image reconstruction unit 222 reconstructs an X-ray image. Specifically, the image reconstruction unit 222 reads the event data stored in the data storage unit 20 (event data sorted according to the energy value) as projection data, and performs a back projection process on the read projection data. Thus, the X-ray image is reconstructed. Further, the image reconstruction unit 222 stores the reconstructed X-ray image in the data storage unit 220. The bed control unit 223 controls the bed driving unit 213.

  Note that each of the energy sorting unit 221, the image reconstruction unit 222, and the system control unit 219 described above is realized by an integrated circuit such as an ASIC or FPGA, or an electronic circuit such as a CPU or MPU.

  Next, the event data collection unit 215 according to the second embodiment will be described. FIG. 10 is a block diagram illustrating a configuration of the event data collection unit 215 according to the second embodiment. As shown in FIG. 10, the event data collection unit 215 includes an A / D converter 215a, a buffer 215b, a count rate measurement unit 215c, and an event data amount adjustment unit 215d. Each of these units corresponds to the A / D converter 15a, the buffer 15b, the count rate measuring unit 15c, and the event data amount adjusting unit 15d described with reference to FIG. 3, and has the same function.

  In other words, the event data amount adjustment unit 215d according to the second embodiment controls the transfer of event data according to the energy value of the X-rays, similarly to the event data amount adjustment unit 15d according to the first embodiment. Specifically, the event data amount adjustment unit 215d according to the second embodiment sets the threshold value of the count rate and the energy window in stages. When the event data amount adjustment unit 215d receives the input of the count rate information 215h, the event data amount adjustment unit 215d determines whether or not the count rate exceeds the threshold value. Is controlled according to the energy value of each event data 215f. As a result, the amount of event data 215f transferred for subsequent processing is flexibly adjusted. The energy window is the same as that described with reference to FIGS. 5 to 7, and the processing procedure by the event data amount adjusting unit 215d is the processing procedure by the event data amount adjusting unit 15d described with reference to FIG. It is the same.

  For this reason, according to the second embodiment, the data amount can be appropriately adjusted at the time of a high count rate. As a result, sufficient image quality can be ensured even at high count rates. For example, streak artifacts can be reduced.

  Here, the meaning at the time of the high count rate in the second embodiment will be examined. FIG. 11 is a diagram for explaining the relationship between the detector and the X-ray according to the second embodiment. As shown in FIG. 11, the X-ray tube 214 a emits X-rays toward the subject P. The X-ray m irradiated by the X-ray tube 214a is directly incident on the detector 214b without passing through the subject P. On the other hand, the X-ray n irradiated by the X-ray tube 214a passes through the subject P and then enters the detector 214b.

  The number of X-ray photons decreases as it passes through the subject P. For this reason, the number of photons in the case where X-rays directly enter the detector 214b without passing through the subject P is larger than that in the case where the X-rays enter the detector 214b after passing through the subject P. That is, in the former case, more events occur per unit time and the count rate is higher. In addition, it can be said that the event data of X-rays that are directly incident on the detector 214b without passing through the subject P are event data having low usefulness.

  If this is the case, when a high count rate is reached in a certain block among a plurality of blocks included in the detector 214b, the detector module of this block detects X-rays that do not pass through the subject P. There is a high possibility that the event data collection unit 215 of this block is collecting event data with low usefulness. Therefore, in the second embodiment, the event data collection unit 215 of the block that has reached the high count rate controls the data transfer according to the energy value, and the event data collection unit 215 of the other blocks Such control is not performed.

  That is, controlling the data transfer according to the energy value itself is intended to select highly useful event data, but in the second embodiment, it is a block at the high count rate in the first place. It can be said that the selection is also performed in terms of whether or not. As described above, since the X-ray tube 214a and the detector 214b continuously rotate on a circular orbit centered on the subject P, the relationship of which block has a high count rate is considered to vary. It is done.

  The energy window shown in the second embodiment is merely an example. For example, a single threshold value may be used without providing a plurality of threshold values. Further, for example, more threshold values such as a third threshold value and a fourth threshold value may be set, and the opening width of the energy window at each stage may be set more finely.

  Furthermore, an energy window as shown in FIGS. 12 and 13 may be set. 12 and 13 are views for explaining an energy window according to the second embodiment. For example, imaging by the X-ray CT apparatus 200 may be performed by paying attention to a specific energy value. In such a case, for example, when the counting rate is relatively high, the energy windows x and y are opened as shown in FIG. 12, and when the counting rate is considerably high, as shown in FIG. Settings such as opening only y may be made. In this case as well, the operation may be performed with one threshold without providing a plurality of thresholds. Alternatively, an operation in which a plurality of energy windows are set and the opening width of each energy window is gradually narrowed according to the count rate stage may be used.

  The embodiment is not limited to the first and second embodiments described above. For example, in the first and second embodiments, the data transfer control has been described as processing executed in the event data collection unit included in the detector module. However, the present invention is not limited to this. For example, the problem of data transfer can also occur on the console device 16 side shown in FIG. 1 and the console device 216 side shown in FIG. In this case, for example, the control described in the first embodiment and the control described in the second embodiment can be similarly applied to the console device 16 and the console device 216. Moreover, the measurement of the count rate is not limited to the method shown in the first and second embodiments. For example, a buffer in which event data is stored may be monitored, and the count rate may be measured by the number of event data written per unit time.

  According to the PET apparatus of at least one embodiment described above, the data amount can be appropriately adjusted at a high count rate. As a result, sufficient image quality can be ensured even at high count rates.

  In addition, according to the X-ray CT apparatus of at least one embodiment described above, the data amount can be adjusted appropriately at a high count rate. As a result, sufficient image quality can be ensured even at high count rates.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

15 Event data collection unit 15a A / D converter 15b Buffer 15c Count rate measurement unit 15d Event data amount adjustment unit

Claims (4)

A detector for detecting annihilation radiation;
A count rate measuring unit for measuring a count rate of an event for detecting annihilation radiation by the detector;
A generator for generating data of annihilation radiation detected by the detector for each event;
A positron emission computed tomography apparatus comprising: a control unit that controls transfer of the data according to an energy value of the annihilation radiation when the count rate exceeds a threshold value.   2. The positron emission computer according to claim 1, wherein the control unit sets a plurality of threshold values in a stepwise manner, and performs control so that a range of energy values that allow the data transfer is narrowed in a stepwise manner. Tomography equipment. A photon counting detector that detects X-rays;
A count rate measuring unit for measuring a count rate of events for detecting X-rays by the detector;
A generating unit that generates X-ray data detected by the detector for each event;
An X-ray CT (Computed Tomography) apparatus, comprising: a control unit that controls transfer of the data according to an energy value of the X-ray when the count rate exceeds a threshold value.   The X-ray CT according to claim 3, wherein the control unit sets a plurality of threshold values in a stepwise manner, and performs control so that a range of energy values that allow the data transfer is narrowed in a stepwise manner. apparatus.

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