JP6645846B2 - Photon counting type X-ray CT system - Google Patents

Description

  Embodiments of the present invention relate to a photon counting X-ray CT apparatus.

  Since the DAS (Data Acquisition System) of the X-ray CT apparatus is fixed to a rotating frame that holds the X-ray tube and the detector, it rotates with the X-ray tube and the detector. The DAS of the integrating X-ray CT apparatus calculates the effective energy of X-rays and generates projection data. The DAS of the photon counting X-ray CT apparatus generates count data in which the number of X-ray photons is counted for each energy band set on the X-ray energy distribution. Since the count data is generated for each energy band set on the X-ray energy distribution, the data amount is larger than the projection data generated by the integral X-ray CT apparatus.

  Therefore, the conventional photon counting X-ray CT apparatus suppresses an increase in the capacity of the communication path between the DAS, which is a bottleneck when transmitting the count data to the console, and the fixed portion of the gantry, as follows. According to the method, the count data is transmitted to the console.

  For example, a DAS of a conventional photon counting X-ray CT apparatus compresses the count data and transmits the compressed data to a console. Alternatively, the DAS of the conventional photon counting type X-ray CT apparatus temporarily stores the count data in a memory provided in the DAS, so that the communication path capacity between the DAS and the fixed part of the gantry has a margin. Send count data to the console at some point.

  However, since the conventional photon counting X-ray CT apparatus transmits the count data to the console by the above-described method, it is sometimes difficult to display CT image data immediately after imaging. Further, if the communication channel capacity is increased to display CT image data immediately after imaging, the manufacturing cost of the photon counting type X-ray CT apparatus increases.

U.S. Pat. No. 8,406,537

  An object of the present invention is to provide a photon counting X-ray CT apparatus capable of realizing display of CT image data immediately after imaging without increasing the communication channel capacity.

The photon counting X-ray CT apparatus according to the embodiment includes a rotating frame, a photon counting unit, a generation unit, a setting unit, and a transmission unit. The rotating frame holds an X-ray tube for irradiating the subject with X-rays and a detector having a plurality of detection elements for detecting incident photons of the X-rays. The photon counting unit is fixed to the rotating frame, and counts the number of photons of the X-rays for each energy band set on the energy distribution of the X-rays, the position of the X-ray tube, and the detection element. Collect data. The generation unit is configured to generate a plurality of approximate count data having a smaller data amount than the count data, based on the count data, fixed to the rotation frame. The setting unit sets a priority order in the order of smaller data amount in the plurality of rough count data. The transmission unit is fixed to the rotation frame and transmits the plurality of rough count data before the count data. The transmitting unit transmits the plurality of rough count data according to the priority.

FIG. 1 is a diagram illustrating a configuration example of a photon counting X-ray CT apparatus according to an embodiment. FIG. 2 is a flowchart illustrating an example of a process performed by the photon counting X-ray CT apparatus according to the embodiment. FIG. 3 is a diagram illustrating an example of an energy band set on the energy distribution of X-rays. FIG. 4 is a diagram illustrating an example of the number of photons for each energy band in a certain view of a count data and a certain channel. FIG. 5 is a diagram illustrating an example of the number of photons for each energy band in a certain view of a rough count data and a certain channel. FIG. 6 is a diagram showing an example of the number of photons for each energy band in a certain view of a rough count data and a certain channel. FIG. 7 is a diagram illustrating an example of the number of photons for each energy band in a certain view of a rough count data and a certain channel. FIG. 8 is a diagram illustrating an example of CT image data generated by reconstructing the rough count data. FIG. 9 is a diagram showing projection information derived from the CT image data shown in FIG. FIG. 10 is a diagram illustrating an example of the energy dependence of the X-ray line attenuation coefficient near the K absorption edge of the target substance.

  Hereinafter, a photon counting X-ray CT apparatus according to an embodiment will be described with reference to the drawings. In the following embodiments, overlapping descriptions will be omitted as appropriate.

(Embodiment)
The configuration of the photon counting X-ray CT apparatus 1 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration example of a photon counting X-ray CT apparatus according to an embodiment. As shown in FIG. 1, the photon counting X-ray CT apparatus 1 includes a gantry 10, a bed 20, and a console 30. Note that the configuration of the photon counting X-ray CT apparatus 1 is not limited to the following configuration.

  The gantry 10 includes a high voltage generation circuit 101, a collimator adjustment circuit 102, a gantry drive circuit 103, an X-ray irradiation device 104, a detector 105, a rotating frame 106, a data collection circuit 107, a transmission circuit 108, , A buffer circuit 109, and a receiving circuit 110.

  The high voltage generation circuit 101 supplies a tube voltage to an X-ray tube 1041 described below. The high-voltage generation circuit 101 realizes its function by reading and executing a program stored in a storage circuit 35 described later.

  The collimator adjustment circuit 102 adjusts an opening degree and a position of a collimator 1043 described later. Thereby, the collimator adjustment circuit 102 adjusts the irradiation range of the X-rays that the X-ray tube 1041 irradiates the subject P. The collimator adjustment circuit 102 realizes its function by reading and executing a program stored in a storage circuit 35 described later.

  The gantry drive circuit 103 rotates the rotating frame 106. Accordingly, the gantry drive circuit 103 rotates the X-ray irradiator 104 and the detector 105 on a circular orbit around the subject P. The gantry drive circuit 103 realizes its function by reading and executing a program stored in a storage circuit 35 described later.

  The X-ray irradiation device 104 includes an X-ray tube 1041, a wedge 1042, and a collimator 1043. The X-ray tube 1041 irradiates the subject P with X-rays. The X-ray tube 1041 generates beam-shaped X-rays by using a tube voltage supplied by the high voltage generation circuit 101. This beam-shaped X-ray is also called a cone beam. The wedge 1042 is an X-ray filter for adjusting the dose of X-rays emitted from the X-ray tube 1041. The collimator 1043 is a slit for adjusting the X-ray irradiation range. The aperture and the position of the collimator 1043 are adjusted by the collimator adjustment circuit 102. By adjusting the aperture of the collimator 1043, for example, the fan angle and cone angle of the cone beam are adjusted.

  The detector 105 has a plurality of detection elements for detecting incident X-ray photons. The plurality of detection elements are regularly arranged in a first direction and a second direction intersecting the first direction. For example, the first direction is a circumferential direction of the rotating frame 106, and the second direction is a slice direction. Here, the slice direction is the body axis direction. Note that such a detector is called a multi-row detector.

  The detection element has a scintillator, a photodiode, and a photon counting type detection circuit. A detector in which the detection element has a scintillator and a photodiode is called a solid state detector. The input terminal of the photon counting type detection circuit is connected to the output terminal of the photodiode. The output terminal of the photon counting type detection circuit is connected to the input terminal of the data collection circuit 107.

  The detection element converts the incident X-ray photon into a response waveform by the following method. The detection element converts the incident X-ray photons into light using a scintillator. The detection element converts this light into electric charge by the photodiode. This charge is output to the photon counting type detection circuit. The photon counting type detection circuit outputs a response waveform to the data collection circuit 107 based on this charge. The response waveform is data in which pulses generated by individual photons incident on each detection element at each position of the X-ray tube 1041 are arranged in time series.

  Note that the detector 105 may be a direct conversion type detector. The direct conversion type detector is a detector that directly converts X-ray photons incident on the detection element into electric charges. This electric charge is that electrons generated by the incidence of X-ray photons move toward the positive potential collector electrode, and holes generated by the X-ray incidence move toward the negative potential collector electrode. Is output by at least one of

  The rotating frame 106 is an annular frame that holds the X-ray irradiator 104 and the detector 105 so as to face each other across the subject P. That is, the rotating frame 106 holds the X-ray tube 1041 for irradiating X-rays and the detector 105 having a plurality of detection elements for detecting incident X-ray photons. The rotating frame 106 is driven by the gantry driving circuit 103 and rotates at high speed on a circular orbit around the subject P.

  The data collection circuit 107 has a photon counting function 1071, a generation function 1072, and a setting function 1073. Details of these functions will be described later. The data collection circuit 107 is fixed to the rotating frame 106. Therefore, when the photon counting X-ray CT apparatus 1 scans the subject P, the data collection circuit 107 rotates together with the rotating frame 106. The data collection circuit 107 is realized by, for example, a processor. Note that the data collection circuit 107 is also called a DAS.

  The transmission circuit 108 transmits the rough count data before the count data. Further, the transmission circuit 108 transmits the approximate count data to the reception circuit 110 according to the priority. Further, the transmission circuit 108 transmits the count data to the reception circuit 110. The transmission circuit 108 transmits the approximate count data and the count data to the reception circuit 110 by using, for example, a radio or a slip ring. Therefore, a bottleneck in a communication path from the transmission circuit 108 to the data storage circuit 33 described later is a communication path between the transmission circuit 108 and the reception circuit 110. The transmission circuit 108 transmits the count data and the approximate count data to the buffer circuit 109 when there is not enough free space in the communication path capacity from the transmission circuit 108 to the data storage circuit 33 described later.

  The transmission circuit 108 is fixed to the rotating frame 106. For this reason, the transmission circuit 108 rotates together with the rotating frame 106 when the photon counting X-ray CT apparatus 1 scans the subject P. Note that the transmission circuit 108 is realized by, for example, a processor.

  When there is not enough space in the communication path capacity from the transmission circuit 108 to the data storage circuit 33 described later, the buffer circuit 109 receives the count data and the approximate count data from the transmission circuit 108 and temporarily stores them. The buffer circuit 109 transmits the stored count data and the approximate count data to the transmission circuit 108 when there is sufficient space in the communication path capacity from the transmission circuit 108 to the data storage circuit 33 described later. Further, the buffer circuit 109 is fixed to the rotating frame 106. Therefore, the buffer circuit 109 rotates together with the rotating frame 106 when the photon counting X-ray CT apparatus 1 scans the subject P. Note that the buffer circuit 109 is realized by, for example, a processor. Further, the buffer circuit 109 includes a nonvolatile memory or a volatile memory.

  The receiving circuit 110 receives the count data and the approximate count data from the transmission circuit 108 and transmits them to the data storage circuit 33 described later. The receiving circuit 110 is not fixed to the rotating frame 106. Therefore, the receiving circuit 110 does not rotate with the rotating frame 106 when the photon counting X-ray CT apparatus 1 scans the subject P. The receiving circuit 110 is realized by, for example, a processor.

  The couch 20 includes a couchtop 21 and a couch drive circuit 22. The top 21 is a plate-shaped member on which the subject P is placed. The couch driving circuit 22 moves the subject P within the imaging opening of the gantry 10 by moving the table 21 on which the subject P is placed in the body axis direction. The couch drive circuit 22 realizes its function by reading and executing a program stored in a storage circuit 35 described later. The couch driving circuit 22 is realized by, for example, a processor.

  The console 30 includes an input circuit 31, a display 32, a data storage circuit 33, an image storage circuit 34, a storage circuit 35, and a processing circuit 36.

  The input circuit 31 is used by a user who inputs instructions and settings. The input circuit 31 is included in, for example, a mouse and a keyboard. The input circuit 31 transfers the instructions and settings input by the user to the processing circuit 36. The input circuit 31 is realized by, for example, a processor.

  The display 32 is a monitor to which the user refers. The display 32 is, for example, a liquid crystal display or an organic EL (Electroluminescence) display. The display 32 receives from the processing circuit 36, for example, CT image data, a GUI (Graphical User Interface) used when the user inputs instructions and settings, and an instruction to display an index to be referred to during diagnosis. The display 32 displays, for example, CT image data, a GUI, and an index to be referred at the time of diagnosis based on the instruction. The CT image data means the CT image itself or data on which the CT image is displayed.

  The data storage circuit 33 receives the count data and the approximate count data from the reception circuit 110 and stores them. Further, the data storage circuit 33 receives the count data and the approximate count data subjected to the pre-processing by the pre-processing function 362 described later, and stores them. Note that the count data and the approximate count data on which the preprocessing function 362 has performed the preprocessing are also referred to as raw data (Raw Data). The image storage circuit 34 stores CT image data generated by an image generation function 363 described later.

  The storage circuit 35 stores a program for the high voltage generation circuit 101, the collimator adjustment circuit 102, the gantry drive circuit 103, the data collection circuit 107, the transmission circuit 108, the buffer circuit 109, and the reception circuit 110 to realize the above-described functions. . The storage circuit 35 stores a program for the bed driving circuit 22 to realize the above-described functions. The storage circuit 35 stores a program for the processing circuit 36 to realize each function described later.

  The processing circuit 36 has a scan control function 361, a pre-processing function 362, an image generation function 363, and a control function 364. Details of these functions will be described later. The control function 364 includes a function of operating each component of the gantry 10, the bed 20, and the console 30 at an appropriate timing according to the purpose, and other functions. The processing circuit 36 is realized by, for example, a processor.

  The data storage circuit 33, the image storage circuit 34, and the storage circuit 35 each include a storage medium from which stored information can be read by a computer. The storage medium is, for example, a hard disk.

  An example of the process of the photon counting X-ray CT apparatus 1 according to the embodiment will be described with reference to FIGS. FIG. 2 is a flowchart illustrating an example of a process performed by the photon counting X-ray CT apparatus according to the embodiment. FIG. 3 is a diagram illustrating an example of an energy band set on the energy distribution of X-rays. FIG. 4 is a diagram illustrating an example of the number of photons for each energy band in a certain view of a count data and a certain channel. 5 to 7 are diagrams illustrating an example of the number of photons for each energy band in a certain view of the rough count data and a certain channel. In the following description, as shown in FIG. 3, a case where energy bands B1, B2,..., B16 are set on the energy distribution of X-rays will be described as an example.

  The processing circuit 36 collects the count data as shown in FIG. 2 (Step S1). The process in step S1 is, for example, as follows.

  The processing circuit 36 reads a program corresponding to the scan control function 361 from the storage circuit 35 and executes the program. The scan control function 361 is a function for controlling the photon counting X-ray CT apparatus 1 to execute a scan. The processing circuit 36 controls the photon counting X-ray CT apparatus 1 as follows, for example, by executing the scan control function 361.

  The processing circuit 36 moves the subject P into the imaging opening of the gantry 10 by controlling the bed driving circuit 22. The processing circuit 36 controls the gantry drive circuit 103 to execute scanning of the subject P. Specifically, the processing circuit 36 controls the high voltage generation circuit 101 to supply a tube voltage to the X-ray tube 1041. The processing circuit 36 controls the collimator adjustment circuit 102 to adjust the aperture and the position of the collimator 1043. Further, the processing circuit 36 controls the gantry driving circuit 103 to rotate the rotating frame 106.

  The scans executed by the photon counting X-ray CT apparatus 1 are, for example, a conventional scan, a helical scan, and a step and shoot. In the conventional scan, the subject P is scanned while the position of the subject P placed on the table 21 is fixed. The helical scan is a method of scanning the subject P while moving the subject P placed on the top 21 in the body axis direction. The step-and-shoot method is a method in which the position of the subject P placed on the table 21 is moved at regular intervals, and a conventional scan is performed in a plurality of scan areas.

  The processing circuit 36 controls the data collection circuit 107 to collect count data. The data collection circuit 107 performs, for example, the following processing.

  The data collection circuit 107 reads out a program corresponding to the photon counting function 1071 from the storage circuit 35 and executes it. The photon counting function 1071 collects count data obtained by counting the number of X-ray photons for each energy band set on the X-ray energy distribution, the position of the X-ray tube 1041, and each detection element.

  Specifically, the photon counting function 1071 counts the number of events in which the state where the response waveform output from the photon counting type detection circuit exceeds a predetermined threshold continues. As a result, the photon counting function 1071 counts the number of X-ray photons incident on the detection element. Further, the photon counting function 1071 calculates the wave height and the waveform area of the response waveform output from the detection element. Thus, the photon counting function 1071 calculates the energy of the X-ray photons incident on the detection element. Therefore, the photon counting function 1071 can count the number of X-ray photons for each energy band set on the X-ray energy distribution, the position of the X-ray tube 1041, and the detection element.

  The count data is data in which the number of X-ray photons incident on each detection element at each position, each detection element, and each energy band of the X-ray tube 1041 is arranged. Here, the position of the X-ray tube 1041 is called a view. The circumferential array of rotating frames 106 of the sensing elements in a view is called a channel. That is, the count data is data in which the number of X-ray photons is assigned to a three-dimensional orthogonal coordinate system having the view direction, the channel direction, and the energy direction as axes. Therefore, the number of photons for each energy band in a certain view and a certain channel of the count data is, for example, a histogram C16 shown in FIG. The histogram C16 is obtained by counting the number of X-ray photons for each energy band B1, B2,..., B16 shown in FIGS. 3 and 4 in a certain view and a certain channel. Note that the count data is a type of energy band view data.

  The data collection circuit 107 generates rough count data as shown in FIG. 2 (Step S2). The process in step S2 is, for example, as follows.

  The data collection circuit 107 reads a program corresponding to the generation function 1072 from the storage circuit 35 and executes the program. The generation function 1072 generates approximate count data having a smaller data amount than the count data based on the count data.

  The generation function 1072 generates first addition count data, for example, as follows. The generation function 1072 generates, as approximate count data, addition count data in which the position of the X-ray tube 1041 and the number of photons of the same count data by the detection element are added over all energy bands. Specifically, the generating function 1072 determines the position of the X-ray tube 1041 and the number of photons of the count data having the same detection element over the energy bands B1, B2,..., B16 shown in FIGS. The added count data is generated. Such added count data is also called total count view data.

  The generation function 1072 generates the second addition count data, the third addition count data, and the fourth addition count data, for example, as follows. The generation function 1072 generates, as the approximate count data, a plurality of pieces of additional count data in which the position of the X-ray tube 1041 and the number of photons of the same count data by the detection element are added over a plurality of energy bands.

  The generation function 1072 generates the second addition count data, for example, as follows. The generation function 1072 adds the number of photons of the count data at each position and each detection element of the X-ray tube 1041 over the energy bands B1, B2,..., B8 shown in FIGS. The generation function 1072 adds the number of photons of the count data at each position and each detection element of the X-ray tube 1041 over the energy bands B9, B10, ..., B16.

  The number of photons for each energy band in a certain view and a certain channel of the rough count data is represented by, for example, a histogram A2 shown in FIG. The histogram A2 is obtained by counting the number of X-ray photons for each energy band B21 and energy band B22 shown in FIG. 5 in a certain view and a certain channel. The energy band B21 is a combination of the energy bands B1, B2,..., B8 shown in FIGS. The energy band B22 is a combination of the energy bands B9, B10,..., B16 shown in FIGS.

  The generation function 1072 generates the third addition count data as follows. The generation function 1072 adds the number of photons of the count data at each position and each detection element of the X-ray tube 1041 over the energy bands B1, B2,..., B4 shown in FIGS. The generation function 1072 adds the number of photons of the count data at each position and each detection element of the X-ray tube 1041 over the energy bands B5, B6, ..., B8. The generation function 1072 adds the number of photons of the count data at each position and each detection element of the X-ray tube 1041 over the energy bands B9, B10, ..., B12. The generation function 1072 adds the number of photons of the count data over the energy bands B13, B14,..., B16 at each position and each detection element of the X-ray tube 1041.

  The number of photons for each energy band in a certain view and a certain channel of the rough count data is represented, for example, by a histogram A4 shown in FIG. The histogram A4 is obtained by counting the number of X-ray photons for each energy band B41, energy band B42, energy band B43, and energy band B44 shown in FIG. 6 in a certain view and a certain channel. The energy band B41 is a combination of the energy bands B1, B2,..., B4 shown in FIGS. Energy band B42 is a combination of energy bands B5, B6,..., B8. Energy band B43 is a combination of energy bands B9, B10,..., B12. Energy band B44 is a combination of energy bands B13, B14,..., B16.

  The generation function 1072 generates the fourth addition count data as follows. The generation function 1072 adds the number of photons in the energy bands B1 and B2 of the count data shown in FIGS. 3 and 4 at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B3 and B4 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B5 and B6 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B7 and B8 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy band B9 and the energy band B10 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B11 and B12 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B13 and B14 of the count data at each position and each detection element of the X-ray tube 1041. The generation function 1072 adds the number of photons in the energy bands B15 and B16 of the count data at each position and each detection element of the X-ray tube 1041.

  The number of photons for each energy band in a certain view and a certain channel of the rough count data is represented by, for example, a histogram A8 shown in FIG. The histogram A8 is obtained by counting the number of X-ray photons for each energy band B81, B82,..., B88 shown in FIG. 7 in a certain view and a certain channel. The energy band B81 is a combination of the energy band B1 and the energy band B2 shown in FIGS. Energy band B82 is a combination of energy band B3 and energy band B4. Energy band B83 is a combination of energy band B5 and energy band B6. Energy band B84 is a combination of energy band B7 and energy band B8. Energy band B85 is a combination of energy band B9 and energy band B10. Energy band B86 is a combination of energy band B11 and energy band B12. Energy band B87 is a combination of energy band B13 and energy band B14. Energy band B88 is a combination of energy band B15 and energy band B16.

  The rough count data generated in step S2 is a kind of energy band view data.

  As shown in FIG. 2, the data collection circuit 107 sets priorities in order of the data amount in the count data and the approximate count data in ascending order, and transmits the priorities to the transmission circuit 108 (step S3). The process in step S3 is, for example, as follows.

  The data collection circuit 107 reads a program corresponding to the setting function 1073 from the storage circuit 35 and executes the program. The setting function 1073 sets priorities in the order of the data amount in the approximate count data in ascending order.

  The photon counting function 1071 has collected the count data in step S1. The generation function 1072 has generated the first addition count data, the second addition count data, the third addition count data, and the fourth addition count data in step S2. The data amount of these data decreases in the order of the count data, the fourth count data, the third count data, the second count data, and the first count data. Therefore, the setting function 1073 sets the following priorities for these data. The setting function 1073 sets the priority “1” to the first addition count data. The setting function 1073 sets the priority “2” to the second addition count data. The setting function 1073 sets the priority “3” to the third addition count data. The setting function 1073 sets the priority “4” to the fourth addition count data. The setting function 1073 sets a priority “5” to the count data.

  As shown in FIG. 2, the transmission circuit 108 transmits the count data and the approximate count data according to the priority (Step S4). The process in step S4 is, for example, as follows.

  First, the transmission circuit 108 transmits, to the reception circuit 110, the first addition count data in which the priority order “1” is set. Next, the transmission circuit 108 transmits the second addition count data to which the priority order “2” has been set to the reception circuit 110. Next, the transmission circuit 108 transmits, to the reception circuit 110, the third addition count data in which the priority order “3” is set. Next, the transmission circuit 108 transmits the fourth addition count data to which the priority order “4” has been set, to the reception circuit 110. Finally, the transmission circuit 108 transmits the count data to which the priority “5” has been set to the reception circuit 110.

  The processing circuit 36 performs preprocessing on the count data and the approximate count data as shown in FIG. 2 (step S5). The processing circuit 36 reads a program corresponding to the preprocessing function 362 from the storage circuit 35 and executes the program. The preprocessing function 362 is a function for correcting the count data and the approximate count data. This correction is, for example, logarithmic conversion, offset correction, sensitivity correction, beam hardening correction, and scattered radiation correction. The count data and the approximate count data pre-processed by the pre-processing function 362 are stored in the data storage circuit 33.

  As shown in FIG. 2, the processing circuit 36 reconstructs the count data and the rough count data according to the priority order, and generates CT image data (step S6).

  The processing circuit 36 reads a program corresponding to the image generation function 363 from the storage circuit 35 and executes the program. The image generation function 363 is a function of reconstructing the count data and the approximate count data stored in the data storage circuit 33 to generate CT image data. The reconstruction method is, for example, a back projection method or a successive approximation method. The back projection method is, for example, an FBP (Filtered Back Projection) method.

  First, the image generation function 363 reconstructs the first addition count data to which the priority “1” is set, and generates CT image data. Next, the image generation function 363 reconstructs the second addition count data to which the priority order “2” is set, and generates CT image data. Next, the image generation function 363 reconstructs the third addition count data to which the priority order “3” is set, and generates CT image data. Next, the image generation function 363 reconstructs the fourth addition count data to which the priority order “4” is set, and generates CT image data. Finally, the image generation function 363 reconstructs the count data to which the priority “5” is set, and generates CT image data. These CT image data are stored in the image storage circuit 34.

  The display 32 displays the CT image data according to the priority order as shown in FIG. 2 (Step S7). The process of step S7 is, for example, as follows.

  The processing circuit 36 reads a program corresponding to the control function 364 from the storage circuit 35 and executes it. First, the control function 364 displays the CT image data generated from the first addition count data to which the priority “1” is set. Next, the control function 364 displays the CT image data generated from the second addition count data to which the priority order “2” is set. Next, the control function 364 displays the CT image data generated from the third addition count data to which the priority order “3” is set. Next, the control function 364 displays the CT image data generated from the fourth addition count data to which the priority order “4” is set. Finally, the control function 364 displays the CT image data generated from the count data set with the priority “5”.

  The photon counting X-ray CT apparatus 1 according to the embodiment has been described above. As described above, the data collection circuit 107 generates rough count data having a smaller data amount than the count data based on the count data, and transmits the rough count data before the count data. For this reason, the photon counting X-ray CT apparatus 1 can display CT image data immediately after imaging without increasing the communication channel capacity of the count data and the approximate count data. Further, the photon counting type X-ray CT apparatus 1 does not need to increase the communication channel capacity of the count data and the rough count data. Therefore, the photon counting X-ray CT apparatus 1 can increase the width of the layout in the gantry 10. Further, the manufacturing cost of the photon counting X-ray CT apparatus 1 is suppressed.

  Further, the data collection circuit 107 first transmits the total count view data. Since the total count view data has a small data amount, it is quickly transmitted from the transmission circuit 108 to the data storage circuit 33. Further, the total count view data is suitable for quickly generating, for example, CT image data that clearly shows the structure of the imaging region, the state of puncture, and the state of injection of the contrast agent. For this reason, the photon counting X-ray CT apparatus 1 can quickly generate and display such CT image data.

  Further, the data collection circuit 107 sets priorities in the order of the data amount of the rough count data in ascending order, and transmits the rough count data in accordance with the priority. Specifically, the data collection circuit 107 transmits the first addition count data, the second addition count data, the third addition count data, the fourth addition count data, and the count data to the reception circuit 110 according to the priority. I do. For this reason, the photon counting X-ray CT apparatus 1 can display CT image data necessary for diagnosis one by one without increasing the communication channel capacity of the count data and the approximate count data. Further, the photon counting X-ray CT apparatus 1 can gradually increase the types of substances that can be subjected to substance discrimination, and can improve the accuracy of substance discrimination. Thus, the photon counting X-ray CT apparatus 1 can generate and display CT image data more suitable for diagnosis one by one.

  The rough count data is not limited to the above. For example, even if the data collection circuit 107 generates rough count data described below, the above-described effects can be obtained.

  The generation function 1072 may generate, as the approximate count data, one piece of count data obtained by adding the number of photons of the same count data to the position of the X-ray tube 1041 and the detection element over a plurality of energy bands. . Such addition count data is also a kind of energy band view data. The generation function 1072 is, for example, as the approximate count data, the addition count data obtained by adding the number of photons of the count data having the same position and the same detection element to the X-ray tube 1041 over the energy bands other than the energy band having the minimum energy. May be generated. The generation function 1072, for example, converts the position of the X-ray tube 1041 and the number of photons of the same count data into the energy bands B3, B4,..., B16 shown in FIGS. It is also possible to generate addition count data that is added over the entire range. The number of X-ray photons counted in the lowest energy band may include the effects of noise generated by the photon counting detector circuit. Therefore, the added count data does not include the influence of noise generated in the photon counting type detection circuit.

  Further, the generation function 1072 provides, as the approximate count data, all the products of the product of the number of photons of the count data and the energy of the energy band in which the number of the photons is counted, where the position of the X-ray tube 1041 and the detection element are the same. The sum over the energy band may be calculated. This is also called energy integration view data. The energy integration view data has the same effect as the total count view data.

  Alternatively, the generation function 1072 may use a part of the count data as the approximate count data. The generation function 1072 converts a part of the count data into approximate count data, for example, as follows.

  FIG. 8 is a diagram illustrating an example of CT image data generated by reconstructing the rough count data. FIG. 9 is a diagram showing projection information derived from the CT image data shown in FIG.

  The CT image data Im shown in FIG. 8 is a tomographic image parallel to a plane orthogonal to the body axis direction of the subject P. The CT image data Im is generated, for example, by reconstructing the total count view data and the energy integration view data. Therefore, the CT image data Im accurately represents the structure of the subject P. The CT image data Im includes a region B, a region S, a dotted line R, and a region M. The region B is a region corresponding to a certain organ in the subject P. The region S is a region corresponding to an organ other than a certain organ in the subject P. A dotted line R indicates a region of interest. The region M is a region corresponding to air existing outside the subject P.

  The projection information PJ shown in FIG. 9 is derived from the CT image data Im by a projection process based on the geometric arrangement of the X-ray tube 1041 and the detector 105 and the direction in which the projection is performed. The projection information PJ includes a region BP, a region SP, a dotted line RP, and a region MP. The area BP corresponds to the area B of the CT image data Im. The area SP corresponds to the area S of the CT image data Im. The area surrounded by the dotted line RP corresponds to the area surrounded by the dotted line R in the CT image data Im. The area MP corresponds to the area M of the CT image data Im.

  The generation function 1072 sets data corresponding to the region of interest in the count data as approximate count data. For example, the generation function 1072 sets the area surrounded by the dotted line RP of the projection information PJ in the count data as the approximate count data. The image generation function 363 can generate CT image data of the region of interest of the subject P by reconstructing the rough count data. Note that the generation function 1072 may specify a part of the count data to be the approximate count data based on the count data instead of the projection information PJ.

  Alternatively, the generation function 1072 may use a portion corresponding to the slice direction including the region of interest in the count data as the approximate count data.

  Alternatively, the generation function 1072 may use, as the approximate count data, data in which at least one of the position of the X-ray tube 1041 and the detection element is at a predetermined position among the count data. For example, the generation function 1072 selects a view at predetermined intervals from the count data, and sets the selected view as the approximate count data. Further, for example, the generation function 1072 selects a channel from the count data at a predetermined interval, and sets the selected one as the approximate count data.

  Alternatively, the generation function 1072 may use the data of the energy band lower and higher than the K absorption edge of the target substance in the count data as the approximate count data.

  FIG. 10 is a diagram illustrating an example of the energy dependence of the X-ray line attenuation coefficient near the K absorption edge of the target substance. The line L shown in FIG. 10 represents the energy dependence of the X-ray line attenuation coefficient near the K absorption edge of the substance of interest. Further, as shown in FIG. 10, an energy band B101, an energy band B102, an energy band B103, and an energy band B104 are set. As shown in FIG. 10, in the energy bands B101 and B102, the linear attenuation coefficient of the substance of interest monotonously decreases as the energy of the X-ray photons increases. Similarly, in energy bands B103 and B104, the linear attenuation coefficient of the substance of interest monotonically decreases as the energy of the X-ray photons increases. Further, as shown in FIG. 10, a K absorption edge BK exists at the boundary between the energy bands B102 and B103. At the K absorption edge BK, the linear attenuation coefficient of the substance of interest increases significantly.

  Specifically, the generation function 1072 sets, for example, data of the energy band B102 and the energy band B103 higher than the K absorption edge BK of the target substance in the count data as the approximate count data. Alternatively, the generation function 1072 sets the data of the energy band B101 and the energy band B104 higher than the K absorption edge BK of the target substance in the count data as the approximate count data. Alternatively, the generation function 1072 sets the data of the energy band B102 and the energy band B104 higher than the K absorption edge BK of the target substance in the count data as the approximate count data. Further, the generation function 1072 may generate, for example, these approximate count data instead of the second addition count data generated in step S2 described above.

  The image generation function 363 reconstructs data in the energy band lower and higher than the K absorption edge of the substance of interest, and generates two CT image data. Then, the image generation function 363 calculates the difference between these two pieces of CT image data, and generates CT image data that clearly shows the contrast agent. Further, the image generation function 363 subtracts the CT image data from the CT image data obtained by reconstructing the total count view data and the energy integration view data, so that the contrast agent is obtained from the CT image data including the contrast agent. Can generate CT image data in which is not shown. Such a CT image is called a VNC (virtual non-contrast) image.

  The photon counting X-ray CT apparatus 1 can generate CT image data in which a contrast agent is captured and CT image data in which a contrast agent is not captured in one scan by the above-described method. That is, the photon counting X-ray CT apparatus 1 can generate CT image data showing the contrast agent and CT image data not showing the contrast agent while suppressing the exposure dose and the examination time of the subject P. . Note that an X-ray CT apparatus capable of dual energy CT imaging can also generate CT image data in which a contrast agent is captured and CT image data in which a contrast agent is not captured in a single scan by the above-described method.

  Alternatively, the generation function 1072 may generate the approximate count data using data compression. Here, the data compression is lossless compression or lossy compression. For example, the count data is data obtained by subtracting half of the fourth count data from the original count data for each energy band (difference between the histogram C16 and the histogram A8), and the fourth count data is the original count data. The data (the difference between the histogram A8 and the histogram A4) obtained by subtracting half of the third added count data from the fourth added count data for each energy band, and the third added count data is the original third added count data. Data obtained by subtracting half of the second added count data from the added count data for each energy band (difference between the histogram A4 and the histogram A2), and the second added count data is obtained from the original second added count data. If transmitted as data (difference between histogram A4 and histogram A2) obtained by subtracting half of the first addition count data for each energy band, the information amount will be duplicated. Rukoto free transmission and reception is possible. As a similar data operation method (also referred to as an encoding method), a multi-resolution analysis such as a wavelet transform or a Fourier transform can be used. If all necessary addition count data or base coefficients are transmitted, lossless compression is performed. Lossless compression can be achieved by not transmitting the lower-order bits of the addition count data (the fourth and third addition count data, etc.) or the higher-dimensional basis coefficient having the larger data amount. Even if the generation function 1072 uses lossy compression, if the data necessary for diagnosis can be reproduced, the photon counting type X-ray CT apparatus 1 can increase the communication channel capacity of the count data and the approximate count data. No, CT image data can be displayed immediately after imaging.

  Note that the above-described count data and approximate count data may be affected by pulse pile-up. Here, the pulse pile-up is a phenomenon in which when many photons enter the detection element at once, the pulses generated by the individual photons overlap, and a plurality of photons are counted as one photon. In this case, the generation function 1072 multiplies the counted number of X-ray photons by a coefficient that corrects for the effect of pulse pile-up.

  The above-described processor is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (Programmable Logic Device: PLD), a field programmable gate array. (Field Programmable Gate Array: FPGA). Further, the programmable logic device (PLD) is, for example, a simple programmable logic device (SPLD) or a complex programmable logic device (CPLD).

  In the above-described embodiment, the high voltage generation circuit 101, the collimator adjustment circuit 102, the gantry drive circuit 103, the data collection circuit 107, the transmission circuit 108, the buffer circuit 109, the reception circuit 110, the bed drive circuit 22, and the processing circuit 36 The function is realized by reading and executing the program stored in the circuit 35, but the present invention is not limited to this. Instead of storing the program in the storage circuit 35, the program may be directly incorporated in each of these circuits. In this case, these circuits realize their functions by reading and executing a directly incorporated program.

  Each circuit shown in FIG. 1 may be appropriately dispersed or integrated. For example, the data collection circuit 107 may be distributed to a photon counting circuit, a generation circuit, and a setting circuit that perform the respective functions of the photon counting function 1071, the generation function 1072, and the setting function 1073. Further, for example, the processing circuit 36 is distributed to a scan control circuit, a preprocessing circuit, an image generation circuit, and a control circuit that execute the respective functions of the scan control function 361, the preprocessing function 362, the image generation function 363, and the control function 364. You may.

  The high-voltage generation circuit 101, the collimator adjustment circuit 102, the gantry drive circuit 103, the data collection circuit 107, the transmission circuit 108, the buffer circuit 109, the reception circuit 110, the bed drive circuit 22, and the processing circuit 36 are arbitrarily integrated. Is also good. However, the data collection circuit 107 and the transmission circuit 108 are fixed to the rotating frame 106. The receiving circuit 110 is not fixed to the rotating frame 106.

  According to at least one embodiment described above, diagnosis using a reconstructed image can be appropriately performed.

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

106 rotating frame 1071 photon counting function 1072 generation function 108 transmission circuit

Claims (11)

An X-ray tube that irradiates the subject with X-rays, and a rotating frame that holds a detector having a plurality of detection elements that detect incident photons of the X-rays;
Photons that are fixed to the rotating frame and collect count data obtained by counting the number of photons of the X-rays for each energy band set on the energy distribution of the X-rays, the position of the X-ray tube, and the detection element. A counting unit;
A generator fixed to the rotating frame, based on the count data, generating a plurality of approximate count data having a smaller data amount than the count data,
A setting unit that sets a priority order in a smaller data amount to the plurality of rough count data;
A transmission unit that is fixed to the rotation frame and transmits a plurality of the rough count data before the count data,
Equipped with a,
The said transmission part is a photon-counting X-ray CT apparatus which transmits several said rough count data according to the said priority . The photon counting X-ray CT apparatus according to claim 1 , wherein the generation unit sets a part of the count data as the approximate count data. The photon counting X-ray according to claim 2 , wherein the generation unit sets, as the approximate count data, data in which at least one of the position of the X-ray tube and the detection element is at a predetermined position in the count data. CT device. The photon counting X-ray CT apparatus according to claim 2 , wherein the generation unit sets data corresponding to a region of interest in the count data as the approximate count data. The photon counting X-ray CT apparatus according to claim 2 , wherein the generation unit sets a portion corresponding to a slice direction including a region of interest in the count data as the approximate count data. The photon according to any one of claims 1 to 5 , wherein the generation unit uses data of an energy band lower and higher than the K absorption edge of the target substance in the count data as the approximate count data. Counting X-ray CT system. The generator uses the data compression to generate the summary count data, photon counting X-ray CT apparatus according to any one of claims 1 to 5. The generating unit generates, as the approximate count data, addition count data obtained by adding the number of photons of the same count data as the position of the X-ray tube and the detection element over a plurality of energy bands, The photon counting X-ray CT apparatus according to claim 1 . The photon counting X-ray CT apparatus according to claim 8 , wherein the generation unit generates a plurality of the addition count data. The generation unit generates, as the approximate count data, additional count data obtained by adding the number of photons of the same count data as the position of the X-ray tube and the detection element over the entire energy band, A photon counting X-ray CT apparatus according to claim 1 . The generation unit, as the approximate count data, all of the product of the number of photons of the count data and the energy of the energy band in which the number of the photons is counted, where the position of the X-ray tube and the detection element are the same as the detection element. The photon counting X-ray CT apparatus according to claim 1 , wherein a total sum over an energy band of the photon is calculated.