X-ray CT device and control method

[0026] (First embodiment)

[0027] First, before describing the X-ray CT apparatus according to the first embodiment, the photon counting CT will be described.

[0028] In photon counting CT, the amount of light (X-ray) is measured by counting the number of photons. The more photons per unit time, the stronger the light (X-ray). In addition, although each photon has a different energy, in the photon counting CT, the information of the energy component of the X-ray can be obtained by measuring the energy of the photon. That is, in the photon counting CT, data collected by irradiating X-rays with one tube voltage can be divided into a plurality of energy components and imaged. For example, in photon counting CT, image data that uses the difference in K absorption limit to identify substances can be obtained.

[0029] However, in the photon counting CT, when the amount of incident radiation is large, "pile up" of data accumulated for each photon count occurs. When accumulation occurs, the individual photons cannot be separated, so the occurrence of counting characteristics is not linear "counting undercounting".

[0030] Figure 1A , Figure 1B as well as Figure 1C It is a diagram to illustrate the accumulation. When a photon is incident, the sensor (element) used in the photon-counting detector outputs a 1-pulse electrical signal. When the light is weak, such as Figure 1A As shown, the incident interval of photons becomes sparse, and therefore, each pulse output from the sensor can be distinguished.

[0031] However, when the incident interval of photons becomes shorter due to the increase of light, such as Figure 1B As shown, the pulses output from the sensor are accumulated, and each pulse cannot be distinguished. Specifically, the accumulated multiple pulses are recognized as one pulse in appearance (refer to Figure 1B The dashed waveform shown). As a result, undercounting occurs, and the linearity between the number of photons actually incident on the sensor and the count value (number of pulses) of the pulse output by the sensor is lost. That is, as Figure 1C As shown, as the X-ray intensity becomes higher, the number of pulses is counted as less than the number of photons.

[0032] Therefore, the X-ray CT apparatus according to the first embodiment is configured as follows to reduce the occurrence of undercounting. figure 2 It is a diagram for explaining a configuration example of the X-ray CT apparatus according to the first embodiment. Such as figure 2 As shown, the X-ray CT apparatus according to the first embodiment includes a gantry device 10, a bed device 20, and a console device 30.

[0033] The gantry device 10 is a device that irradiates the subject P with X-rays and collects data related to the X-rays transmitted through the subject P, and has a high-voltage generating unit 11, an X-ray tube 12, a detector 13, and a collection unit 14. , The rotating frame 15 and the frame drive unit 16.

[0034] The rotating frame 15 is supported so that the X-ray tube 12 and the detector 13 face each other across the subject P, and rotates at high speed on a circular orbit centered on the subject P by a gantry drive unit 16 described later Round frame.

[0035] The X-ray tube 12 is a vacuum tube that irradiates the subject P with an X-ray beam by a high voltage supplied from a high-voltage generator 11 described later, and irradiates the subject P with the X-ray beam as the rotating frame 15 rotates.

[0036] The high voltage generator 11 is a device that supplies a high voltage to the X-ray tube 12, and the X-ray tube 12 uses the high voltage supplied from the high voltage generator 11 to generate X-rays. That is, the high-voltage generator 11 adjusts the amount of X-rays irradiated to the subject P by adjusting the tube voltage and the tube current supplied to the X-ray tube 12.

[0037] The gantry driving unit 16 rotates the rotating gantry 15 to rotate the X-ray tube 12 and the detector 13 on a circular orbit centered on the subject P.

[0038] The detector 13 has a first element group that detects the intensity of X-rays transmitted through the subject P and a second element group that counts light (X-ray photons) from the X-rays transmitted through the subject P. The first element group is composed of a plurality of first elements for X-ray intensity detection. The first element is, for example, a light emitting diode. In addition, the second element group is composed of a plurality of second elements as photon counting sensors. The second element is, for example, a cadmium telluride (CdTe)-based semiconductor. That is, the second element is a direct conversion semiconductor that directly converts incident X-rays into light and counts the light from the X-rays. In addition, the present embodiment can also be applied to, for example, a case where the second element is an indirect conversion type composed of a scintillator and a photomultiplier tube.

[0039] In addition, the detector 13 according to the first embodiment is divided into a first area and a second area along the channel direction. In addition, the first element group is arranged in the first area, and the second element group is arranged in the second area. image 3 It is a diagram for explaining an example of the detector according to the first embodiment.

[0040] Such as image 3 As shown, the detector 13 related to the first embodiment will be arranged in the channel direction ( figure 2 The component row in the Y-axis direction in) is along the body axis direction of the subject P ( figure 2 (Shown in the Z-axis direction) are arranged in multiples. And like image 3 As shown, the detector 13 according to the first embodiment is divided into a first area 133 and a second area 134 along the channel direction. In the first region 133, first elements 131 as light-emitting diodes are arranged two-dimensionally. In addition, in the second region 134, the second element 132 as a photon counting sensor is arranged two-dimensionally. The first area 133 and the second area 134 are approximately the same size.

[0041] The detector 13 according to the first embodiment detects the intensity of X-rays irradiated from the X-ray tube 12 and transmitted through the subject P using a plurality of first elements 131 arranged two-dimensionally. In addition, the detector 13 according to the first embodiment outputs an electric signal through a plurality of second elements 132 arranged two-dimensionally. By using this electrical signal, X-ray photons irradiated from the X-ray tube 12 and transmitted through the subject P can be counted, and the energy of the counted X-ray photons can be measured.

[0042] back to figure 2 , The collection unit 14 collects various information based on the output signal of the detector 13. Such as figure 2 As shown, the collection unit 14 according to the first embodiment has an intensity distribution data collection unit 14a and a counting result collection unit 14b. The intensity distribution data collecting unit 14a collects intensity distribution data of X-rays irradiated from the X-ray tube 12 and transmitted through the subject P. Specifically, the intensity distribution data collecting unit 14a collects intensity distribution data for each phase (tube phase) of the X-ray tube 12.

[0043] In addition, the counting result collecting unit 14b collects the counting result of counting the X-ray photons irradiated from the X-ray tube 12 and transmitted through the subject P. Specifically, the counting result collecting unit 14b uses the incident position (detection position) of the X-ray photon obtained by discriminating and counting the pulses output by the second element 132 and the energy value of the X-ray photon as the counting result, according to the X-ray tube Collect each phase of 12 (tube phase). The counting result collecting unit 14b uses, for example, the position of the second element 132 that outputs the pulse used for counting as the incident position. In addition, the counting result collecting unit 14b calculates the energy value based on, for example, the peak value of the pulse and the response function peculiar to the system. Alternatively, the counting result collecting unit 14b calculates the energy value by integrating the intensity of the pulse, for example.

[0044] The count result is, for example, in the "tube phase "α1", in the second element 132 at the incident position "P11", the count value of photons with energy "E1" is "N1", and the count value of photons with energy "E2" The count value is "N2"" and other information. Or, the count result is, for example, "in the tube phase "α1", in the second element 132 at the incident position "P11", the count value per unit time of the photon with the energy "E1" is "n1" and has energy The count value of the photon of "E2" per unit time is "n2" and other information. In addition, the above-mentioned energy "E1" may be, for example, the energy range "E1 to E2". At this time, the count result becomes information such as "In the second element 132 at the tube phase "α1" and the incident position "P11", the count value of the photon having the energy range "E1 to E2" is "NN1". The energy range becomes an energy discrimination threshold for the counting result collecting unit 14b to discriminate and distribute the value of energy in a coarse-grained region.

[0045] The intensity distribution data collection unit 14a transmits the collected intensity distribution data to the scan control unit 33 (described later) of the console device 30. In addition, the counting result collection unit 14b sends the collected counting results to the preprocessing unit 34 (described later) of the console device 30.

[0046] Here, the intensity distribution data is collected by the first scan for collecting intensity distribution data. Then, after the X-ray dose adjustment based on the intensity distribution data is performed, the count result is collected by the second scan for counting result collection. In addition, the execution method of the first scan and the second scan and the X-ray dose adjustment based on the intensity distribution data will be described in detail later.

[0047] The bed device 20 is a device on which the subject P is placed, and has a top plate 22 and a bed driving device 21. The top plate 22 is a plate on which the subject P is placed, and the bed driving device 21 moves the top plate 22 in the Z-axis direction to move the subject P into the rotating frame 15.

[0048] In addition, the gantry device 10 performs, for example, a spiral scan in which the rotating gantry 15 is rotated while moving the top plate 22 to scan the subject P in a spiral shape. Alternatively, the gantry device 10 performs a regular scan in which the rotating gantry 15 is rotated while the position of the subject P is fixed after the top plate 22 is moved, and the subject P is scanned on a circular orbit.

[0049] The console device 30 is a device that accepts operations performed by the operator on the X-ray CT device, and at the same time uses the counting information collected by the gantry device 10 to reconstruct X-ray CT image data. Such as figure 2 As shown, the console device 30 has an input device 31, a display device 32, a scan control unit 33, a pre-processing unit 34, a projection data storage unit 35, an image reconstruction unit 36, an image storage unit 37, and a system control unit 38.

[0050] The input device 31 has a mouse, a keyboard, and the like used by the operator of the X-ray CT apparatus to input various instructions and various settings, and transfers the instructions and setting information received from the operator to the system control unit 38. For example, the input device 31 receives reconstruction conditions when reconstructing X-ray CT image data, image processing conditions for X-ray CT image data, and the like from the operator.

[0051] The display device 32 is a display referred to by the operator. Under the control of the system control unit 38, the X-ray CT image data is displayed to the operator, or is used to receive various instructions and various devices from the operator via the input device 31. Fixed GUI (Graphical User Interface).

[0052] The scanning control unit 33 controls the operation of the high-voltage generating unit 11, the gantry drive unit 16, the collection unit 14 and the bed drive device 21 under the control of the system control unit 38 described later to control the counting information in the gantry device 10 Collection and processing.

[0053] Specifically, the scan control unit 33 according to the first embodiment causes the gantry device 10 to perform the first scan, and receives intensity distribution data from the intensity distribution data collection unit 14a. Then, the scan control unit 33 according to the first embodiment determines scan conditions based on the intensity distribution data, and causes the gantry device 10 to execute the second scan. The scan control unit 33 according to the first embodiment performs the first scan using the first element group (a plurality of first elements 131). In addition, the scan control unit 33 according to the first embodiment executes the second scan using the second element group (a plurality of second elements 132). In addition, the control processing performed by the scan control unit 33 according to the first embodiment will be described in detail later.

[0054] The pre-processing unit 34 generates projection data by performing correction processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on the count result sent from the count result collection unit 14b.

[0055] The projection data storage unit 35 stores the projection data generated by the pre-processing unit 34. That is, the projection data storage unit 35 stores projection data for reconstructing X-ray CT image data.

[0056] The image reconstruction unit 36 ​​reconstructs X-ray CT image data by performing back-projection processing on the projection data stored in the projection data storage unit 35, for example. As the back projection processing, for example, back projection processing based on the FBP (Filtered Back Projection) method can be cited. In addition, the image reconstruction unit 36 ​​may perform reconstruction processing by, for example, a successive approximation method. In addition, the image reconstruction unit 36 ​​generates image data by performing various image processing on the X-ray CT image data. The image reconstruction unit 36 ​​stores the reconstructed X-ray CT image data and image data generated by various image processing in the image storage unit 37.

[0057] Here, the projection data generated based on the counting result obtained by the photon counting CT includes information on the energy of the X-rays weakened by passing through the subject P. Therefore, the image reconstruction unit 36 ​​can reconstruct X-ray CT image data of a specific energy component, for example. In addition, the image reconstruction unit 36 ​​can reconstruct X-ray CT image data of each of a plurality of energy components, for example.

[0058] In addition, the image reconstruction unit 36, for example, assigns a hue corresponding to the energy component to each pixel of the X-ray CT image data of each energy component, and can generate image data obtained by superimposing a plurality of X-ray CT image data color-separated according to the energy component. . In addition, the image reconstruction unit 36 ​​can use the K absorption limit inherent to the substance to generate image data capable of identifying the substance. As other image data generated by the image reconstruction unit 36, monochromatic X-ray image data, density image data, effective atom number image data, and the like can be cited.

[0059] The system control unit 38 performs overall control of the X-ray CT apparatus by controlling the operations of the gantry device 10, the bed device 20, and the console device 30. Specifically, the system control unit 38 controls the CT scan performed by the gantry device 10 by controlling the scan control unit 33. In addition, the system control unit 38 controls the image reconstruction process and the image generation process in the console device 30 by controlling the preprocessing unit 34 and the image reconstruction unit 36. In addition, the system control unit 38 performs control so that various image data stored in the image storage unit 37 are displayed on the display device 32.

[0060] In the foregoing, the overall configuration of the X-ray CT apparatus according to the first embodiment has been described. With this configuration, the X-ray CT apparatus according to the first embodiment performs the control process described below by the scan control unit 33 to reduce the occurrence of undercounting.

[0061] First, the intensity distribution data collection unit 14a collects intensity distribution data of X-rays irradiated from the X-ray tube 12 and transmitted through the subject P by the first scan. As described above, in the detector 13 according to the first embodiment, the first element group (a plurality of first elements 131) is two-dimensionally arranged in the first area 133, and the second element group (a plurality of first elements 131) is arranged in the second area 134. The second element 132) is arranged two-dimensionally. Therefore, the scan control unit 33 according to the first embodiment moves the first region 133 in which the plurality of first elements 131 are two-dimensionally arranged to a position facing the X-ray tube 12 when performing the first scan. In other words, when the first scan is executed, the scan control unit 33 moves the first area 133 to the X-ray irradiation range of the X-ray tube 12.

[0062] To perform this control, in the first embodiment, as an example, a moving mechanism (not shown) for moving the detector 13 in the circumferential direction is provided inside the rotating frame 15. Figure 4 It is a diagram for explaining the first scan according to the first embodiment. For example, the gantry drive unit 16 drives the moving mechanism in accordance with the instruction of the scan control unit 33 to move the detector 13 to a position where the first area 133 faces the X-ray tube 12. That is, as Figure 4 As shown, the detector 13 moves along the circumferential direction of the rotating frame 15 to a position where the first area 133 faces the X-ray tube 12.

[0063] And like Figure 4 As shown, the scan control unit 33 performs X-ray irradiation on the entire periphery of the subject P to execute the first scan. That is, the first scan is performed with the first area 133 maintained at a position opposed to the X-ray tube 12. The first scan for intensity measurement is IS (Intensity Scan). In addition, the X-ray dose (D0) irradiated from the X-ray tube 12 in the first scan may be, for example, the X-ray dose corresponding to the imaging conditions set by the operator, or may be initially set for the first scan. The amount of X-rays.

[0064] In this way, the intensity distribution data collecting unit 14a collects intensity distribution data of the entire surrounding area. In addition, the scan control unit 33 estimates the amount of X-rays capable of distinguishing each X-ray photon passing through the subject P based on the intensity distribution data. Specifically, the scan control unit 33 estimates the X-ray amount of each tube phase as a result of the collection count based on the intensity distribution data of the entire surrounding amount collected by the first scan. Figure 5 It is a diagram for explaining the scan control unit according to the first embodiment.

[0065] For example, such as Figure 5 As shown, the scan control unit 33 estimates the amount of X-rays irradiated from the X-ray tube 12 by the “tube phase: α1” of the second scan based on the “intensity distribution data: I1” of the “tube phase: α1” as “D1 ". For example, the scan control unit 33 determines the maximum X-ray intensity "I1(max)" from "intensity distribution data: I1". In addition, the scan control unit 33 compares "I1(max)" with the threshold value "Ith". For example, "Ith" is the upper limit threshold set in advance based on the physical characteristics of the first element 131 and the second element 132, and the second element 132 can avoid the accumulation of the largest amount of X-rays. The X-ray intensity when the specimen P is incident on the first element 131. "Ith" is, for example, a value obtained by calibrating the X-ray CT apparatus before imaging, at the time of periodic inspection, or at the time of shipment.

[0066] Also, when "I1(max)" is greater than "Ith", for example, the scan control unit 33 estimates as "D1=D0×(I1(max)/Ith)". In addition, when "I1(max)" is equal to or less than "Ith", for example, the scan control unit 33 estimates "D1=D0". In this way, the scan control unit 33 uses the output pulse of the second element group in the "tube phase: α1" collected by the second scan to estimate the X of each X-ray photon transmitted through the subject P. The amount of radiation "D1". Through the same treatment, such as Figure 5 As shown, the scan control unit 33 estimates the amount of X-rays irradiated from the X-ray tube 12 in the second scan of the "tube phase: α2" based on the "intensity distribution data: I2" of the "tube phase: α2" as " D2". By performing this processing, the scan control unit 33 can estimate the X-ray dose (optimal X-ray dose) in all tube phases required for the imaging conditions set for photon counting CT.

[0067] The amount of X-rays irradiated from the X-ray tube 12 in each tube phase is not necessarily constant. Therefore, when performing full reconstruction to reconstruct a tomographic image based on the projection data of the "360-degree range" (counting result), it is preferable to collect intensity distribution data of the entire surrounding amount. However, the scan control unit 33 may estimate the minimum value of the optimum X-ray dose estimated for each tube phase as the optimum X-ray dose for all tube phases, for example. In addition, when performing semi-reconstruction to reconstruct the tomographic image based on the projection data (count result) of "180 degrees + α (range of sector angle)", intensity distribution data of the amount of "180 degrees + α" may also be collected.

[0068] Then, the scan control unit 33 irradiates the subject P with X-rays of the estimated X-ray dose from the X-ray tube 12 to perform the second scan for photon counting CT. The scan control unit 33 according to the first embodiment moves the second area 134 in which the plurality of second elements 132 are two-dimensionally arranged to a position facing the X-ray tube 12 when performing the second scan. In other words, the scan control unit 33 moves the second area 134 within the X-ray irradiation range of the X-ray tube 12 when performing the second scan. Image 6 It is a diagram for explaining the second scan according to the first embodiment. For example, the gantry drive unit 16 drives the above-mentioned moving mechanism in accordance with the instruction of the scan control unit 33, so as Image 6 As shown, the detector 13 is moved to a position where the second area 134 faces the X-ray tube 12. That is, as Image 6 As shown, the detector 13 moves along the circumferential direction of the rotating frame 15 to a position where the second area 134 faces the X-ray tube 12.

[0069] Then, the scan control unit 33 notifies the high-voltage generator 11 of the control value (for example, the tube voltage or the tube current) that becomes the optimum X-ray dose in each tube phase. In this way, the high-voltage generator 11 supplies the X-ray tube 12 with the tube voltage and the tube current that become the optimum amount of X-rays in each tube phase. Thus, as Image 6 As shown, the scan control unit 33 performs X-ray irradiation on the entire periphery of the subject P to execute the second scan. That is, the second scan is performed in a state where the second area 134 is maintained at a position opposed to the X-ray tube 12. In addition, in Image 6 , Shows the second scan when performing full reconstruction. The second scan for photon counting CT is called PCS (Photon Counting Scan).

[0070] In this way, the scan control unit 33 causes the first scan and the second scan to be executed alternately and continuously once on the same track. For example, when reconstructing X-ray CT image data of one axial section through a normal scan, the scan control unit 33 executes the second scan on the same track as the first scan after performing the first scan.

[0071] In addition, since the detector 13 is an area detector, the X-ray CT apparatus can reconstruct a plurality of axial sections through regular scanning. Therefore, the X-ray CT apparatus can reconstruct the three-dimensional X-ray CT image data of the subject P by moving the position of the top plate 22 at regular intervals to perform a static intensity modulation method for regular scanning. In the static intensity modulation method, whenever the position of the top plate 22 is moved, after the first scan is executed, the scan control unit 33 executes the second scan on the same track as the first scan.

[0072] In addition, in recent years, “helical shuttle scanning” has been performed in which the X-ray tube 12 is continuously rotated on a circular orbit centered on the subject P and the top plate 22 is continuously reciprocated. In the "helical shuttle scan", if the forward scan and the return scan can be controlled to be on the same track, the forward scan is set as the first scan, and the multiple scan is set as the second scan, so that the above control processing can be applied to the spiral scan.

[0073] Next, use Figure 7 The processing of the X-ray CT apparatus according to the first embodiment will be described. Figure 7 It is a flowchart for explaining an example of processing of the X-ray CT apparatus according to the first embodiment. In addition, in Figure 7 The shown flowchart illustrates the processing when the static intensity modulation method is performed.

[0074] Such as Figure 7 As exemplified, the system control unit 38 of the X-ray CT apparatus according to the first embodiment determines whether or not an imaging start request has been received from the operator (step S101). Here, when the imaging start request is not accepted (step S101: No), the system control unit 38 waits until the imaging start request is accepted.

[0075] On the other hand, when the imaging start request is accepted (step S101 affirmative), the scan control unit 33 controls the gantry drive unit 16, the high voltage generator 11, etc., to execute the first scan (step S102). Then, the intensity distribution data collecting unit 14a collects intensity distribution data (step S103). Then, the system control unit 38 estimates that no undercounted X-ray dose has occurred based on the intensity distribution data (step S104), and executes the second scan (step S105).

[0076] Then, the counting result collecting unit 14b collects counting results (step S106), and the image reconstruction unit 36 ​​reconstructs X-ray CT image data (step S107). Then, the scan control unit 33 determines whether or not the imaging in all the scan areas has ended (step S108). Here, when the imaging in all the scanning areas is not finished (step S108 is negative), the scanning control unit 33 controls the bed driving device 21 to move the top plate 22 to the next scanning area (step S109), returns to step S102, and executes the next step. The first scan in a scan area.

[0077] On the other hand, when the imaging in all the scan areas is completed (step S108: Yes), the scan control unit 33 ends the processing.

[0078] As described above, in the first embodiment, the X-ray intensity is measured in advance by the first scan (IS) to estimate the amount of X-rays capable of distinguishing each X-ray photon, and the second scan (PCS) is executed. Therefore, in the first embodiment, since X-rays are excessively incident, it is possible to reduce the probability that each photon cannot be identified. Therefore, in the first embodiment, the occurrence of undercounting can be reduced. In addition, in the first embodiment, the amount of X-rays is optimized, and therefore, unnecessary X-ray radiation during the execution of the second scan can be avoided.

[0079] In addition, in order to avoid an increase in the processing load of the console device 30, the scan control unit 33 may stop the data output from the counting result collection unit 14b when the first scan is executed, and may stop the data output from the intensity distribution when the second scan is executed. The data output of the data collection unit 14a is stopped. In addition, in order to avoid an increase in the processing load of the collection unit 14, the scan control unit 33 may cut off the output path from the second element group to the collection unit 14 when the first scan is executed, and cut off the output path from the second scan when the second scan is executed. The output of one element group to the output path of the collection unit 14 stops. As an example, the scan control unit 33 stops the operation of the readout circuit of the output signal of the second element group during the execution of the first scan, and causes the readout circuit of the output signal of the first element group to operate during the execution of the second scan. The action stops.

[0080] In addition, in the above, the case where the position of the detector 13 is moved in the circumferential direction in order to change the relative positional relationship between the X-ray tube 12 and the detector 13 in the first scan and the second scan has been described. However, in the first embodiment, in order to change the relative positional relationship between the X-ray tube 12 and the detector 13 in the first scan and the second scan, the position of the X-ray tube 12 is moved in the circumferential direction.

[0081] (Second embodiment)

[0082] In the second embodiment, a case where the detector 13 is configured differently from the first embodiment will be described. In addition, the X-ray CT apparatus according to the second embodiment has the same configuration as the X-ray CT apparatus according to the first embodiment described using FIG. 1 except for the detector 13.

[0083] In the detector 13 according to the second embodiment, the plurality of first elements 131 constituting the first element group and the plurality of second elements 132 constituting the second element group are arranged two-dimensionally dispersed. Figure 8A as well as Figure 8B It is a diagram for explaining an example of the detector according to the second embodiment. For example, such as Figure 8A As shown, the first element 131 and the second element 132 are respectively arranged in a element row along the body axis direction in the detector 13. And like Figure 8A As shown, the element rows of the first element 131 and the element rows of the second element 132 are alternately arranged along the channel direction.

[0084] With this structure, in the second embodiment, as Figure 8B As shown, in a state where the relative positions of the X-ray tube 12 and the detector 13 are fixed, the first scan and the second scan can be performed. That is, in the second embodiment, it is possible to perform the first scan and the second scan without providing the movement mechanism of the detector 13 required in the first embodiment.

[0085] Here, in the second embodiment, if the relative position of the detector 13 with respect to the X-ray tube 12 can be fixed in the first scan and the second scan, the detector 13 can also be configured in various ways. For example, in the second embodiment, the first element 131 and the second element 132 may be arranged in element rows along the channel direction, and the element rows of the first element 131 and the second element 132 may be along the body axis direction. Alternate arrangement. In the second embodiment, for example, the first element 131 and the second element 132 may be alternately arranged in the two directions of the channel direction and the body axis direction.

[0086] Among them, for example, when the element rows of the first element 131 and the element rows of the second element 132 are alternately arranged, in order to avoid a decrease in the spatial resolution of the X-ray image data captured by the second scan, it is preferable to arrange it as densely as possible. The element row of the first element 131 is determined. Or, for example, when the first element 131 and the second element 132 are alternately arranged in the channel direction and the body axis direction, in order to avoid a decrease in the spatial resolution, it is preferable to set the size of the first element 131 as much as possible. The ground is small.

[0087] In addition, the content described in the first embodiment is described in the second embodiment, except for the point that the detector 13 is configured so that the relative position of the detector 13 with respect to the X-ray tube 12 can be fixed in the first scan and the second scan. It can also be applied in the method.

[0088] (Third Embodiment)

[0089] In the third embodiment, for the case of performing control processing for reducing radiation caused by the first scan, use Picture 9 Be explained. Picture 9 It is a diagram for explaining the first scan according to the third embodiment.

[0090] In addition, the X-ray CT apparatus according to the third embodiment has the same configuration as the X-ray CT apparatus according to the first embodiment described using FIG. 1, but the first scan and the first scan executed under the control of the scan control unit 33 The implementation is different. Hereinafter, the first scan executed in the third embodiment will be described.

[0091] The scan control unit 33 according to the third embodiment performs X-ray irradiation on the half circumference of the subject P to execute the first scan. That is, as Picture 9 As shown, the scan control unit 33 only performs X-ray irradiation in the range "from 0 degrees to 180 degrees." In other words, the first scan performed in the third embodiment is a half scan.

[0092] In addition, the scan control unit 33 according to the third embodiment uses the intensity distribution data of each tube phase in the half-periphery amount collected by the first scan as the intensity distribution data of the opposing tube phase to obtain the entire surrounding Quantity of intensity distribution data. That is, the scanning control unit 33 rearranges the intensity distribution data "from 0 degrees to 180 degrees" in a rotationally symmetrical geometric position centered on the rotation center of the rotating frame 15 to obtain "from 180 degrees to 360 degrees" Quantity of intensity distribution data. In addition, the scan control unit 33 according to the third embodiment estimates the X-ray dose of each tube phase based on the acquired intensity distribution data of the entire surrounding volume.

[0093] Here, in order to further reduce the radiation caused by the first scan, the scan control unit 33 according to the third embodiment intermittently performs X-ray irradiation around the subject P to execute the first scan. That is, the scan control unit 33 does not perform the first scan of the half scan by continuously irradiating X-rays, but performs it by intermittent X-ray irradiation (pulsed X-ray irradiation). In addition, the scan control unit 33 according to the third embodiment estimates the intensity distribution data of the tube phases that were not collected in the first scan by interpolation processing using the collected intensity distribution data of each tube phase.

[0094] For example, the scan control unit 33 Picture 9 Pulse X-rays are irradiated at angles of "0 degrees, A, B, C, D, E, 90 degrees, F, G, H, I, J, 180 degrees" as shown. As a result, the intensity distribution data collection unit 14a collects the intensity distribution data of "0 degrees, A, B, C, D, E, 90 degrees, F, G, H, I, J, and 180 degrees" and sends them to the scan control unit 33 send. In addition, the scanning control unit 33 uses the intensity distribution data of "A, B, C, D, E, 90 degrees, F, G, H, I, J" as Picture 9 The intensity distribution data of "A', B', C', D', E', 270 degrees, F', G', H', I', J'" are shown.

[0095] In addition, the scan control unit 33 estimates the intensity distribution data of the tube phase between "0 degree" and "A" by interpolation processing using the intensity distribution data of "0 degree" and the intensity distribution data of "A", for example. In this way, the scan control unit 33 obtains intensity distribution data "from 0 degrees to 180 degrees". In addition, the scan control unit 33 uses the estimated intensity distribution data of "5 degrees" as the intensity distribution data of "185 degrees", for example. In this way, the scan control unit 33 obtains intensity distribution data of "from 180 degrees to 360 degrees".

[0096] Then, the scan control unit 33 executes the optimal X-ray dose for each tube phase, and executes the second scan.

[0097] In addition, the content described in the first embodiment and the second embodiment can also be applied to the third embodiment in addition to the difference in the first scanning method.

[0098] As described above, in the third embodiment, if the X-ray transmission paths are the same, the X-ray intensity at the opposed positions is substantially the same, and the first scan is performed by the half scan. Therefore, in the third embodiment, the amount of radiation due to the execution of the first scan can be reduced. In addition, in the third embodiment, on the premise that the intensity distribution data of the tube phase before and after the tube phase can be used to estimate the intensity distribution data of the uncollected tube phase through interpolation processing, the intermittent scanning is used. Perform the first scan. Therefore, in the third embodiment, the amount of radiation due to the execution of the first scan can be further reduced.

[0099] In addition, in the third embodiment, the first scan of the half scan may be performed by continuously irradiating X-rays. In addition, in the third embodiment, the first scan may be executed by a full scan based on pulsed X-ray irradiation. In either case, compared with the case of performing a full scan based on continuous X-ray irradiation, the amount of radiation can be reduced.

[0100] In addition, in the first to third embodiments, when the same subject is subjected to multiple photon counting CT inspections of the same part in a short period of time, it is estimated by borrowing intensity distribution data collected from the first scan of the previous time. If the optimal X-ray dose is obtained, the second scan is performed. At this time, the first scan is not performed, and the second scan can be performed with the possibility of accumulation reduced. Therefore, the radiation dose can be greatly reduced.

[0101] In addition, in the first to third embodiments, as described below, in order to expand the dynamic range of the photon counting sensor, the second element group as a plurality of photon counting sensors may be configured by the modification described below. In this modification, the second element group 132 is composed of multiple types of elements having different sensitivity to X-ray dose.

[0102] Here, the “sensitivity to the amount of X-rays” refers to the “count rate characteristics with respect to the amount of X-rays”. That is, the second element group included in the detector 13 according to the present modification example is constituted by "a plurality of types of detection elements having different output numbers of electrical signals per unit time even if the same amount of X-rays are incident." Hereinafter, a case where the second element group is composed of two types of second detection elements (a high-sensitivity element and a low-sensitivity element) having different sensitivities to the X-ray dose will be described. However, this modification can also be applied to the case where the second element group is constituted by three or more second detection elements having different sensitivity to X-ray dose. Picture 10 as well as Picture 11 It is a diagram for explaining a modified example.

[0103] Picture 10 An example in which this modification is applied to the detector 13 described in the first embodiment is shown. Such as Picture 10 As illustrated, the detection unit 13 according to this modification example is divided into a first area 133 and a second area 134 along the channel direction, similarly to the above-mentioned first embodiment. And like Picture 10 As illustrated, in the first region 133, as in the first embodiment, the first elements 131 that are light-emitting diodes for IS are arranged two-dimensionally. And, in this modification, as Picture 10 As an example, in the second region 134, as a photon counting sensor for PCS, a plurality of low-sensitivity elements 132L and a plurality of high-sensitivity elements 132H are alternately arranged two-dimensionally.

[0104] In this way, by combining the low-sensitivity element 132L and the high-sensitivity element 132H having different sensitivities to the X-ray dose to form the second element group, a signal output with a large dynamic range to the X-ray dose can be obtained. Picture 11 The curve H shown represents the response characteristic of the count rate with respect to the X-ray dose of the high-sensitivity element 132H. In addition, Picture 11 The curve L shown represents the response characteristic of the count rate with respect to the X-ray dose of the low sensitivity element 132L. In addition, Picture 11 The "n" shown represents the count rate corresponding to noise.

[0105] When comparing Picture 11 In the curve H and the curve L shown, the X-ray dose (X1) at the count rate of the noise level in the high-sensitivity element 132H is smaller than the X-ray dose (X2) at the count rate of the noise level in the low-sensitivity element 132L. In addition, Picture 11 The curve H shown indicates that when the X-ray dose exceeds X2, the number of photons due to accumulation in the high-sensitivity element 132H is undercounted. In addition, Picture 11 The curve L shown indicates that when the amount of X-rays exceeds X3, the low-sensitivity element 132L causes undercounting of the number of photons due to accumulation.

[0106] In addition, Picture 11 The curve H shown, for example, shows that the count rate characteristic of the high-sensitivity element 132H is approximately linear in "X1 to X2". That is, the dynamic range when the second element group is composed of only the high-sensitivity element 132H becomes "X1 to X2". In addition, Picture 11 The curve L shown, for example, indicates that the count rate characteristic of the low sensitivity element 132L is approximately linear in "X2 to X3". That is, the dynamic range when the second element group is composed of only the low-sensitivity element 132L is "X2 to X3".

[0107] In contrast, in this modification example, the high-sensitivity element 132H and the low-sensitivity element 132L constitute the second element group. Therefore, the dynamic range in the PCS of the detector 13 is expanded to “X1 to X3”. That is, in this modification example, the second element group is constituted by a plurality of types of elements having different sensitivities to X-ray doses, thereby constituting the detector 13 with a large dynamic range capable of reducing the occurrence of accumulation. In addition, the structure of this modification can also be applied to Figure 8A The detector 13 according to the second embodiment shown.

[0108] In addition, in this modification, the scan control unit 33 estimates the optimal X-ray dose for PCS based on the intensity distribution data obtained from IS. For example, in this modified example, as "Ith" described in the first embodiment, for example, the scan control unit 33 uses "X3" to estimate the optimal X-ray dose for each tube phase. In addition, the IS performed in this modification example may be the IS described in the first embodiment or the IS described in the third embodiment.

[0109] Here, when reconstructing X-ray CT image data in this modification, for example, the counting result collecting unit 14b compares the count value (count rate) obtained by the high sensitivity element 132H and the count value (count rate) obtained by the low sensitivity element 132L ( At least one of the count rate) is corrected to the count value (count rate) of the same sensitivity level. This correction process is performed based on the shape of the curve H and the shape of the curve L, for example.

[0110] Assume that the slope of “X2 to X3” of the curve H is “dH”, and the slope of “X1 to X2” of the curve L is “dL”. The count result collection unit 14b corrects the count value obtained by the low sensitivity element 132L to be a count value of a high sensitivity level by multiplying "dH/dL", for example. Alternatively, the counting result collecting unit 14b corrects the count value of the low sensitivity level by, for example, multiplying the count value obtained by the high sensitivity element 132H by "dL/dH".

[0111] However, this correction process is only an example. The above-mentioned correction processing may be performed, for example, by applying a method of statistically estimating the true count value from the count value obtained when the accumulation occurs. In addition, the above-mentioned correction processing may be performed in combination with interpolation processing. For example, in the case of PCS in "X1 to X2", the count result collection unit 14b estimates the low sensitivity element 132L by interpolation processing using the count value obtained from the high sensitivity element 132H located around the low sensitivity element 132L. The count value at the location. In addition, in the case of the PCS of "X2 to X3", the count result collection unit 14b estimates the count of the high sensitivity element 132H by interpolation processing using the count value obtained from the low sensitivity element 132L located around the high sensitivity element 132H value. In addition, the counting result collecting unit 14b corrects the estimated value obtained by the interpolation process to a value of the same sensitivity level. In addition, the correction processing of various count values ​​performed in this modification example may be performed by the gantry device 10 or the console device 30.

[0112] As described above, in this modification example, the second element group is composed of a plurality of types of elements having different sensitivities to X-ray doses, so that the occurrence of undercounting can be reduced.

[0113] In addition, the control methods described in the first to third embodiments and the modified examples are realized by executing a control program prepared in advance by a computer such as a personal computer or a workstation. This control can be issued via a network such as the Internet. In addition, the control program can be recorded on a computer-readable recording medium such as a hard disk, a floppy disk (FD), CD-ROM, MO, DVD, etc., and executed by being read from the recording medium by a computer.

[0114] As described above, according to the first to third embodiments and modifications, it is possible to reduce the occurrence of undercounting.