JP6359268B2 - X-ray CT system - Google Patents

Description

  Embodiments described herein relate generally to an X-ray CT (Computed Tomography) apparatus.

  When the tube voltage of the X-ray tube changes in the X-ray CT apparatus, the energy spectrum of the X-ray irradiated to the subject changes. For example, an X-ray CT apparatus configured to perform so-called dual energy imaging can perform imaging while switching the X-ray tube voltage between a low voltage (for example, 80 kV) and a high voltage (for example, 140 kV) at high speed during scanning. Do. According to the X-ray CT apparatus configured to be capable of dual energy imaging, it is possible to acquire an image of an X-ray beam having different energy spectra, so that the difference in the constituent elements of the subject can be visualized. For example, a calcified tissue part and a blood vessel image by a contrast medium can be separated.

  In view of this, a technique has been proposed for acquiring rough X-ray energy information for each view when performing dual energy imaging in an X-ray CT apparatus configured to be able to perform this type of dual energy imaging. In this technology, a general scintillator type (product-sum type) detector or CdTe that combines a scintillator and a photodiode while irradiating X-rays by switching the tube voltage to 80 kV and 140 kV for one or a plurality of views. X-ray energy information is roughly acquired for each view by the photon counting semiconductor detector used.

  Specifically, threshold values that are divided into three threshold values of 80 kV, 140 kV, and intermediate kV are provided as X-ray energy threshold values, and whether X-ray energy information is 80 kV, 140 kV, or intermediate kV for each view. To get to. According to this technique, in dual energy imaging, it is possible to grasp whether the X-ray projection data of each view is 80 kV data, 140 kV data, or transient kV data accompanying switching of the X-ray tube voltage.

JP 2009-201885 A

  By the way, it is difficult to keep the tube voltage constant in the first place. For this reason, when performing X-ray imaging of a subject in an X-ray CT apparatus, the tube voltage of the X-ray tube often fluctuates due to various factors, even if dual energy imaging is not performed. When the tube voltage varies, the energy spectrum of X-rays irradiated to the subject varies. When the X-ray energy spectrum changes, the X-ray absorption rate of the subject also changes. For this reason, it is important to know what kind of energy spectrum is actually irradiated when X-ray imaging of a subject is performed. However, in the conventional technique for acquiring X-ray energy information roughly for each view, the X-ray projection data of each view in dual energy imaging is 80 kV data, 140 kV data, or X-ray tube voltage switching. It is difficult to grasp the energy spectrum of the X-rays actually irradiated to the subject for each view.

  In order to solve the above-described problems, an X-ray CT apparatus according to an embodiment of the present invention includes a first X-ray detection unit that detects X-rays that have been irradiated from an X-ray tube and transmitted through a subject, a scintillator, and silicon A photomultiplier that detects X-rays incident from the X-ray tube as photons, and outputs a signal corresponding to the energy of the incident X-rays; and a second X-ray detection unit An energy spectrum acquisition unit that obtains the relationship between the intensity and intensity of X-rays incident on the second X-ray detection unit based on the output signal, and obtains the energy spectrum of X-rays emitted from the X-ray tube based on the obtained relationship. And.

1 is a block diagram showing a configuration example of an X-ray CT apparatus according to an embodiment of the present invention. The external appearance perspective view which shows the example of 1 structure of a 2nd X-ray detection part. It is explanatory drawing which shows one structural example of an APD chip. (A) is explanatory drawing which shows one structural example in the case of using the photon counting type | mold semiconductor detector (henceforth CdTe detector) using the conventional CdTe as an electrode incident type detector, (b), Explanatory drawing which shows one structural example in the case of using the conventional CdTe detector as an element incidence type detector. The schematic block diagram which shows the structural example of the function implementation part by CPU of a main control part. Explanatory drawing which shows an example of the relationship (detection relationship) between the energy and intensity | strength of the X-ray detected by the 2nd X-ray detection part. Explanatory drawing which shows an example of the relationship between a detection relationship and a prior measurement spectrum. Explanatory drawing which shows an example of the relationship between a detection relationship, a prior measurement spectrum, and a prior detection relationship.

  Embodiments of an X-ray CT apparatus according to the present invention will be described with reference to the accompanying drawings.

  An X-ray CT apparatus according to an embodiment of the present invention includes a detection unit for acquiring an X-ray energy spectrum, and the detection unit includes a scintillator and a silicon photomultiplier (Geiger mode APD (Avalanche Photo Diode), (Hereinafter referred to as Si-PM) and a photon counting detector.

  In addition, the X-ray detection unit for collecting image generation data according to the present embodiment may be configured with a scintillator type (product-sum type) detector, or a photon counting type semiconductor using CdTe or the like. It may be constituted by a detector, or may be constituted by a photon counting type detector including a scintillator and Si-PM as in the correction detection unit.

  In addition, the X-ray CT apparatus according to the present embodiment is configured to be capable of dual energy imaging by generating X-rays having a plurality of energy spectra corresponding to a plurality of tube voltages at a predetermined time by an X-ray generator. May be.

  FIG. 1 is a block diagram showing a configuration example of an X-ray CT apparatus 10 according to an embodiment of the present invention.

  The X-ray CT apparatus 10 according to one embodiment of the present invention includes a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and an X-ray detector are integrally rotated around a subject, and a ring shape. There are various types such as a stationary / rotating type in which a large number of detection elements are arrayed and only the X-ray tube rotates around the subject, and the present invention can be applied to any type. In the following description, the rotation / rotation type will be described.

  In recent years, the so-called multi-tube type X-ray CT apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has been advanced. The X-ray CT apparatus 10 according to the present embodiment can be applied to either a single-tube type X-ray CT apparatus or a multi-tube type X-ray CT apparatus. Here, a single tube X-ray CT apparatus will be described.

  As shown in FIG. 1, the X-ray CT apparatus 10 includes a scanner device 11 and an image processing device 12. The scanner device 11 of the X-ray CT apparatus 10 is usually installed in an examination room, and generates X-ray transmission data of the subject P. The image processing apparatus 12 is normally installed in a control room adjacent to the examination room, and generates projection data from transmission data to generate and display a reconstructed image.

  The scanner device 11 of the X-ray CT apparatus 10 includes an X-ray tube 21, an aperture 22, an X-ray detection unit 23, a DAS (Data Acquisition System) 24, a rotation unit 25, a high-voltage power supply 26, an aperture drive device 27, and a rotation drive device 28. , A top plate 30, a top plate driving device 31, and a controller 32.

  The X-ray tube 21 generates X-rays when a voltage (hereinafter referred to as tube voltage) is applied from a high-voltage power supply 26. X-rays generated by the X-ray tube 21 are irradiated toward the subject P as fan beam X-rays or cone beam X-rays.

  The diaphragm 22 is controlled by the controller 32 via the diaphragm driving device 27 to adjust the irradiation range in the slice direction of the X-rays irradiated from the X-ray tube 21.

  The X-ray detection unit 23 includes a first X-ray detection unit 231 for acquiring image generation data, and a second X-ray detection unit 232 for acquiring an X-ray energy spectrum.

  The first X-ray detection unit 231 detects X-rays emitted from the X-ray tube 21 and transmitted through the subject P. The first X-ray detection unit 231 may be composed of a scintillator type (product-sum type) detector, a photon counting type semiconductor detector using CdTe, or the like, or a second X-ray detection. Similarly to the unit 232, the photon counting detector may include a scintillator and Si-PM.

  In the case of the multi-slice type, the first X-ray detection unit 231 may be one in which a plurality of rows of X-ray detection elements having a plurality of channels in the channel direction (X axis) are arranged in the slice direction (Z axis). In the case of a two-dimensional array type, the X-ray detection unit 23 is configured by a plurality of X-ray detection elements that are densely distributed in both the channel direction (X axis) and the slice direction (Z axis). Can do.

  The second X-ray detector 232 is composed of a photon counting detector including a scintillator and Si-PM, detects X-rays emitted from the X-ray tube 21 as photons, and outputs a signal corresponding to the energy of the photons. Output.

  The second X-ray detection unit 232 is preferably provided at a position where X-rays transmitted through only the atmosphere region without passing through the subject P are irradiated. For example, as shown in FIG. The detection unit 231 may be provided adjacent to an end portion in the rotation direction, or may be provided in the vicinity of the end portion. Further, as long as the position does not block the X-ray beam irradiated to the first X-ray detection unit 231 from the X-ray tube 21 via the subject P, the X-ray tube 21 may be provided in the vicinity of the X-ray tube 21, for example. In addition, when the first X-ray detection unit 231 is configured with a photon counting detector including a scintillator and Si-PM as with the second X-ray detection unit 232, the second X-ray detection unit 232 is the first X-ray detection unit. 231 may be a part.

As shown in FIG. 1, when the second X-ray detector 232 is provided adjacent to the end of the first X-ray detector 231 in the rotational direction, the X-ray tube 21 and the X-ray detector 23 are mounted on the top plate 30. The rotating unit 25 supports the object P so as to be opposed to the placed object P.
Here, the second X-ray detection unit 232 will be described in detail.

  FIG. 2 is an external perspective view showing a configuration example of the second X-ray detection unit 232. As shown in FIG. 2, the second X-ray detection unit 232 includes a plurality of APD chips 42 provided so as to be spread on the printed wiring board 41, and a scintillator 43 provided on each APD chip 42. X-ray photons incident on the scintillator 43 are converted into visible light photons and detected as photons by the APD chip 42. As a result, the APD chip 42 outputs a signal corresponding to the energy of the X-ray incident on the second X-ray detection unit 232 (energy possessed by the X-ray photon).

  FIG. 3 is an explanatory diagram showing a configuration example of the APD chip 42. As shown in FIG. 3, the APD chip 42 is formed by arranging a plurality of Geiger mode APD cells 44 in an array. A quenching resistor is connected to each APD cell 44. The plurality of APD cells 44 are electrically connected in parallel. The output signals of each APD cell 44 are bundled into one, waveform-shaped and output to one readout channel.

  FIG. 4A is an explanatory diagram showing a configuration example when a conventional photon counting semiconductor detector (hereinafter referred to as a CdTe detector) 101 using CdTe is used as an electrode incident type detector. ) Is an explanatory diagram showing a configuration example when the conventional CdTe detector 101 is used as an element incidence type detector.

  The CdTe detector 101 is configured to move a hole electron pair generated by X-rays incident on the CdTe element 102 by an applied electric field, extract it from the electrode 103, and output it through a waveform shaping circuit (analog ASIC). .

  However, when the CdTe detector 101 is used as an electrode incident type detector as shown in FIG. 4A, the CdTe element 102 is used to increase the flight distance in the X-ray CdTe element 102 so that X-rays can be reliably captured. It is necessary to thicken. However, the hole mobility of the CdTe element 102 is much smaller than the electron mobility. For this reason, when the CdTe element 102 is formed thick, the probability that the next X-rays are incident before the holes reach the electrode 103 increases, and the collection efficiency decreases.

  4B, when the CdTe detector 101 is used as an element incident type detector, the CdTe element 102 can be formed thin, but a plurality of CdTe detectors 101 are provided (tiled). ), A dead zone is formed in the adjacent CdTe element 102 by the electrode 103, and the collection efficiency is also lowered.

  Photon counting semiconductor detectors such as the CdTe detector 101 are expensive, and due to the occurrence of polarization, the output characteristics drift as the energization time of the detector becomes longer and the energy peak moves. It has been known. For this reason, when the imaging time exceeds 10 minutes, the output of the photon counting semiconductor detector has an output characteristic different from the original characteristic, which is very difficult to handle.

  Also, as shown in FIG. 4, the photon counting semiconductor detector is difficult to tile, such as the direction in which the electrode 103 is attached.

  On the other hand, the second X-ray detection unit 232 according to the present embodiment is not angry at a decrease in collection efficiency due to the arrangement direction unlike the photon counting semiconductor detector, and has higher collection efficiency than the photon counting semiconductor detector. Further, since the APD chip 42 can be produced by an existing CMOS production process, the second X-ray detection unit 232 can be mass-produced by effectively using existing equipment, and can be produced at low cost. Further, the second X-ray detection unit 232 does not change the output characteristics in principle only by the energization time. In addition, as shown in FIG. 2, the second X-ray detection unit 232 may be connected to the substrate 41 with one surface as a photon incident surface and the other surface as a signal extraction surface, so that tiling is easy.

  In addition, since the second X-ray detection unit 232 uses Si-PM, the signal intensity is much higher than that of the photon counting semiconductor detector. For this reason, the photon counting semiconductor detector requires a special ASIC for handling a weak signal, and it is difficult to extract the signal, whereas the second X-ray detector 232 can extract the signal very easily. .

  The output signal of the second X-ray detection unit 232 is given to the DAS 24 in the same manner as the output signal of the first X-ray detection unit 231.

  The DAS 24 shown in FIG. 1 amplifies the output signal of the first X-ray detection unit 231 and the output signal of the second X-ray detection unit 232 of the X-ray detection unit 23, converts them into digital signals, and outputs them. The output data of the DAS 24 is given to the image processing device 12 via the controller 32 of the scanner device 11.

  The rotating unit 25 integrally holds the X-ray tube 21, the diaphragm 22, the X-ray detection unit 23, and the DAS 24. When the rotation unit 25 is controlled and rotated by the controller 32 via the rotation drive device 28, the X-ray tube 21, the diaphragm 22, the X-ray detection unit 23, and the DAS 24 rotate around the subject P as a unit.

  The high voltage power supply 26 is controlled by the controller 32 to supply the X-ray tube 21 with power necessary for X-ray irradiation. Information about the timing and period during which the X-ray tube 21 generates X-rays and the tube current and tube voltage to be applied to the X-ray tube 21 are supplied from the image processing device 12 to the controller 32.

  The aperture driving device 27 is controlled by the controller 32 to adjust the irradiation range in the X-ray slice direction by adjusting the aperture of the aperture 22.

  The rotation driving device 28 is controlled by the controller 32 to rotate the rotating unit 25 around the cavity.

  The top plate 30 is configured so that the subject P can be placed thereon. The top board drive device 31 is controlled by the controller 32 to move the top board 30 up and down in the Y-axis direction. Further, the top plate driving device 31 is controlled by the controller 32 to transfer the top plate 30 along the Z-axis direction to the X-ray irradiation field at the opening of the central portion of the rotating unit 25.

  The controller 32 includes a storage medium such as a CPU, a RAM, and a ROM, and in accordance with a program stored in the storage medium, the X-ray detection unit 23, the DAS 24, the high-voltage power supply 26, the aperture driving device 27, and the rotation driving device. The scanning is executed by controlling the 28 and the top plate driving device 31. The RAM of the controller 32 provides a work area for temporarily storing programs and data executed by the CPU. The storage medium such as the ROM of the controller 32 stores a startup program for the scanner device 11, a control program for the scanner device 11, and various data necessary for executing these programs.

  The storage medium such as the ROM of the controller 32 has a configuration including a recording medium readable by the CPU, such as a magnetic or optical recording medium or a semiconductor memory, and programs and data in these storage media. A part or all of these may be downloaded via an electronic network.

  The controller 32 also includes a photon including at least information on energy (keV) of X-rays incident on the second X-ray detection unit 232, information on intensity, and information on detection time based on the output signal of the second X-ray detection unit 232. The detection information is collected and given to the image processing apparatus 12.

  On the other hand, the image processing apparatus 12 of the X-ray CT apparatus 10 is configured by a personal computer, for example, and can transmit and receive data to and from a network such as a hospital basic local area network (LAN).

  As illustrated in FIG. 1, the image processing apparatus 12 includes an input unit 51, a display unit 52, a network connection unit 53, a storage unit 54, and a main control unit 55.

  The input unit 51 is configured by a general input device such as a keyboard, a trackball, a touch panel, and a numeric keypad, and outputs an operation input signal corresponding to a user operation to the main control unit 55. For example, when a scan plan is set by the user via the input unit 51, the main control unit 55 determines, for example, the X-ray irradiation timing and period and the tube current to be applied to the X-ray tube 21 based on the scan plan. And instructs the controller 32 on the tube voltage. Then, the controller 32 instructs the high-voltage power supply 26 to supply power to the X-ray tube 21 at the instructed tube current and tube voltage at the irradiation timing and irradiation period instructed by the main control unit 55.

  When the X-ray CT apparatus 10 is configured to be capable of dual energy imaging, the main control unit 55 outputs a second voltage (for example, 140 kV) after outputting a first voltage (for example, 80 kV) for the first period. The high voltage power supply 26 is controlled via the controller 32 so as to repeat the output for the second period. As a result, the X-ray tube 21 is alternately applied with the first voltage and the second voltage, and alternately generates X-rays having an energy spectrum corresponding to the applied tube voltage.

  The display unit 52 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, for example, and displays an X-ray CT image and an energy spectrum shape of each view under the control of the main control unit 55. Various images such as are displayed. When the first X-ray detection unit 231 is configured with a photon counting detector, the X-ray CT image may be an image for each energy bin, for example.

  The network connection unit 53 implements various information communication protocols according to the network form. The network connection unit 53 connects the image processing apparatus 12 and other electrical devices such as an image server according to these various protocols. For this connection, an electrical connection via an electronic network can be applied.

  Here, the electronic network means an entire information communication network using telecommunications technology. In addition to a wireless / wired LAN such as a hospital backbone LAN and an Internet network, a telephone communication line network, an optical fiber communication network, a cable communication network, Includes satellite communications networks.

  The storage unit 54 includes a recording medium that can be read and written by the CPU of the main control unit 55, such as a magnetic or optical recording medium or a semiconductor memory. The storage unit 54 stores data collected by the scanner device 11. The storage unit 54 may store an X-ray energy spectrum (hereinafter referred to as a pre-measurement spectrum) corresponding to each of a plurality of tube voltages measured in advance. In addition, by irradiating the X-ray tube 21 to the second X-ray detection unit 232 with each of a plurality of tube voltages in advance, the relationship between the energy and intensity of X-rays (hereinafter referred to as a pre-detection relationship) is changed to a plurality of tubes. It may be acquired for each of the voltages, and the prior detection relationship may be stored in the storage unit 54 in advance.

  The main control unit 55 includes a storage medium such as a CPU, a RAM, and a ROM, and controls the controller 32 of the scanner apparatus 11 according to the scanner apparatus control program stored in the storage medium.

  The CPU of the main control unit 55 loads an energy spectrum acquisition program stored in a storage medium such as a ROM and data necessary for the execution of the program into the RAM, and X irradiates the subject according to the program. A process for obtaining the energy spectrum of the line is executed.

  The RAM of the main control unit 55 provides a work area for temporarily storing programs and data executed by the CPU. The storage medium such as the ROM of the main control unit 55 stores an energy spectrum acquisition program and various data necessary for executing the program.

  A storage medium such as a ROM has a configuration including a recording medium readable by a CPU, such as a magnetic or optical recording medium or a semiconductor memory, and a part of programs and data in the storage medium. Or you may comprise so that all may be downloaded via an electronic network.

  FIG. 5 is a schematic block diagram illustrating a configuration example of a function realization unit by the CPU of the main control unit 55. In addition, this function realization part may be comprised by hardware logics, such as a circuit, without using CPU.

  As shown in FIG. 5, the CPU of the main control unit 55 performs at least a scan control unit 61, a transmission data acquisition unit 62, a reconstruction unit 63, a correction data acquisition unit 64, and an energy spectrum acquisition unit 65 by an energy spectrum acquisition program. And functions as the correction unit 66. Each of the units 61 to 66 uses a required work area of the RAM as a temporary storage location for data.

  The scan control unit 61 receives a scan plan execution instruction from the user via the input unit 51 and controls the scanner device 11 via the controller 32 based on the scan plan, thereby detecting the X-ray tube 21 and the X-ray detection. The unit 23 is rotated around the subject P, and projection data is collected while changing the projection angle, that is, the view angle.

  As a result, X-ray information (projection data) transmitted through the subject P based on the output signal of the first X-ray detection unit 231 is given to the transmission data acquisition unit 62. Further, photon detection information including at least information on energy (keV) of X-rays incident on the second X-ray detection unit 232 based on an output signal of the second X-ray detection unit 232, information on intensity, and information on detection time is correction data. This is given to the acquisition unit 64.

  The transmission data acquisition unit 62 acquires the projection data and supplies it to the reconstruction unit 63 and the correction unit 66.

  The reconstruction unit 63 performs preprocessing and beam hardening correction processing on the projection data, generates a reconstructed image by filtered back projection, and displays the reconstructed image on the display unit 52.

  The correction data acquisition unit 64 acquires photon detection information including at least X-ray energy (keV) information, intensity information, and detection time information, and supplies the photon detection information to the energy spectrum acquisition unit 65.

  FIG. 6 is an explanatory diagram showing an example of a relationship 71 (hereinafter referred to as a detection relationship) between the energy and intensity of X-rays detected by the second X-ray detection unit 232.

  The energy spectrum acquisition unit 65 includes photon detection including at least information on energy (keV) of X-rays incident on the second X-ray detection unit 232 based on an output signal of the second X-ray detection unit 232, information on intensity, and information on detection time. Based on the information, a relationship (detection relationship) 71 between the energy and intensity of the X-rays detected by the second X-ray detection unit 232 is obtained. The energy spectrum acquisition unit 65 acquires the energy spectrum of the X-rays emitted from the X-ray tube 21 based on the detection relationship 71.

  The energy spectrum acquisition unit 65 may display the acquired X-ray energy spectrum on the display unit 52. For example, the energy spectrum acquisition unit 65 may acquire an X-ray energy spectrum for each view, for example, and display it on the display unit 52. This display may be in real time, or may be called up and displayed according to an instruction from the user after the view image is displayed.

  In the case of real-time display, the user can easily grasp the fluctuation of the energy spectrum during the scan via the display unit 52. In addition, when called up and displayed afterwards, the energy spectrum acquisition unit 65 stores the X-ray energy spectrum information in the storage unit 54 in association with the X-ray projection data or the reconstructed image for each view. It is good to leave.

  As shown in FIG. 6, the relationship (detection relationship) 71 between the energy and intensity of X-rays detected by the second X-ray detection unit 232 reflects the shape of the energy spectrum of X-rays emitted from the X-ray tube 21. Have a different shape. For this reason, the energy spectrum acquisition unit 65 may acquire the detection relationship 71 itself as the energy spectrum of the X-rays emitted from the X-ray tube 21.

  FIG. 7 is an explanatory diagram showing an example of the relationship between the detection relationship 71 and the prior measurement spectrum 72.

  The energy spectrum acquisition unit 65 according to the present embodiment can also use an X-ray energy spectrum (pre-measurement spectrum) 72 corresponding to each of a plurality of tube voltages, which is measured in advance. The prior measurement spectrum 72 may be stored in the storage unit 54 in advance, or may be acquired from the network via the network connection unit 53.

  In this case, the energy spectrum acquisition unit 65 compares the plurality of pre-measured spectra 72 and the detection relationship 71 to calculate the similarity. As the similarity, a normalized correlation value or other statistics indicating the distance between other multidimensional data can be used.

  The energy spectrum acquisition unit 65 extracts the pre-measurement spectrum 72 having the highest similarity, and acquires the pre-measurement spectrum 72 as the energy spectrum of the X-rays irradiated from the X-ray tube 21 at the detection time of the detection relationship 71. Can do. Further, the energy spectrum acquisition unit 65 may obtain a more accurate energy spectrum by interpolating using a plurality of prior measurement spectra 72 having a high degree of similarity.

  Further, the energy spectrum acquisition unit 65 may obtain the tube voltage corresponding to the extracted pre-measurement spectrum 72 as the tube voltage applied to the X-ray tube 21 at the detection time of the detection relationship 71. When the X-ray energy spectrum is obtained by interpolation, the tube voltage may be obtained accurately by interpolating the similarity. Further, the energy spectrum acquisition unit 65 may cause the display unit 52 to display tube voltage information.

  This display may be in real time, or may be called up and displayed according to an instruction from the user after the view image is displayed. In the case of real-time display, the user can easily grasp the fluctuation of the tube voltage during the scan through the display unit 52. In addition, when called up and displayed after the fact, the energy spectrum acquisition unit 65 may store the tube voltage information in the storage unit 54 in association with the X-ray projection data or the reconstructed image for each view. .

  The method of comparing the plurality of prior measurement spectra 72 and the detection relationship 71 is suitable when the resolution of the second X-ray detection unit 232 is not high. Even when the resolution of the second X-ray detection unit 232 is not so high and the detection relationship 71 is a curvy curve compared to the actual spectrum shape, it is more accurate based on the plurality of pre-measured spectra 72. Energy spectrum can be obtained. FIG. 7 shows an example of a detection relationship 71 having a shape that is less than that of FIG.

  FIG. 8 is an explanatory diagram illustrating an example of the relationship among the detection relationship 71, the prior measurement spectrum 72, and the prior detection relationship 73.

  The energy spectrum acquisition unit 65 according to the present embodiment can also use the prior detection relationship 73. The prior detection relationship 73 is acquired in advance by irradiating the second X-ray detection unit 232 with X-rays from the X-ray tube 21 at each of a plurality of tube voltages. The prior detection relationship 73 may be stored in the storage unit 54 in advance, or may be acquired from the network via the network connection unit 53. Moreover, when the energy spectrum acquisition part 65 can utilize both the prior measurement spectrum 72 and the prior detection relationship 73, the data corresponding to the same tube voltage are linked | related with the prior measurement spectrum 72 and the prior detection relationship 73. FIG. Good.

  In this case, the energy spectrum acquisition unit 65 compares the plurality of pre-detection relationships 73 and the detection relationships 71 and calculates the similarity. As the similarity, a normalized correlation value or other statistics indicating the distance between other multidimensional data can be used.

  Then, the energy spectrum acquisition unit 65 interpolates (interpolates) using a plurality of pre-detection relationships 73 having a high degree of similarity, and calculates the energy spectrum of the X-rays irradiated from the X-ray tube 21 at the detection time of the detection relationship 71. get. At this time, the tube voltage applied to the X-ray tube 21 at the detection time of the detection relationship 71 may be obtained by interpolating the similarity. As for the tube voltage, the tube voltage corresponding to the prior detection relationship 73 having the highest similarity may be the tube voltage applied to the X-ray tube 21 at the detection time of the detection relationship 71.

  Furthermore, when the pre-measurement spectrum 72 and the pre-detection relationship 73 are associated with data corresponding to the same tube voltage, the energy spectrum acquisition unit 65 extracts the pre-detection relationship 73 having the highest similarity, A pre-measured spectrum 72 associated with the same tube voltage as the extracted pre-detection relation 73 may be acquired as an X-ray energy spectrum. Further, in this case, the energy spectrum acquisition unit 65 performs interpolation (interpolation) using a plurality of pre-measurement spectra 72 associated with the same tube voltage as each of the plurality of pre-detection relationships 73 having a high degree of similarity. A more accurate energy spectrum may be obtained.

  The method of comparing the prior detection relationship 73, the prior measurement spectrum 72, and the detection relationship 71 is also suitable when the resolution of the second X-ray detection unit 232 is not high. FIG. 8 also shows an example of a detection relationship 71 having a shape that is less than that of FIG.

  The correcting unit 66 corrects data used for generating a reconstructed image by the reconstructing unit 63 based on the information of the X-ray energy spectrum acquired by the energy spectrum acquiring unit 65. For example, when the reconstruction unit 63 includes a calculation that uses information about the energy of X-rays in the reconstructed image generation process, the correction unit 66 converts the information about the energy of X-rays used for this calculation into an energy spectrum acquisition unit. You may correct | amend with the information of the energy spectrum of the X-ray acquired by 65.

  Further, the correction unit 66 receives information on the tube voltage from the energy spectrum acquisition unit 65, and performs control for keeping the tube voltage constant via the scan control unit 61 using the information on the tube voltage. Good. Further, when the X-ray CT apparatus 10 is configured to be capable of dual energy imaging, the correction unit 66 gives the information on the tube voltage received from the energy spectrum acquisition unit 65 to the reconstruction unit 63. In this case, the reconstruction unit 63 determines whether the X-ray projection data of each view in dual energy imaging is data of the first voltage (for example, 80 kV), data of the second voltage (for example, 140 kV), or the X-ray tube. It is possible to easily grasp whether the data is transient kV associated with voltage switching.

  The X-ray CT apparatus 10 according to the present embodiment receives the output signal of the second X-ray detection unit 232 including a photon counting detector including a scintillator and Si-PM simultaneously with the collection of the projection data of the subject P. Basically, the energy spectrum of X-rays irradiated from the X-ray tube 21 can be acquired. For this reason, the fluctuation | variation of the X-ray energy spectrum by fluctuation | variation of a tube voltage etc. can be grasped | ascertained easily.

  In addition, correction of data used for generating a reconstructed image can be performed using the acquired energy spectrum. Therefore, even if the energy spectrum of irradiated X-rays changes due to fluctuations in the tube voltage or the like, changes in the X-ray absorption rate of the subject P accompanying this change can be corrected, and fluctuations in CT values and the like are suppressed. Can do.

  In addition, the X-ray CT apparatus 10 according to the present embodiment can easily acquire accurate tube voltage information. For this reason, for example, it is possible to perform control for maintaining the tube voltage constant via the scan control unit 61 using the tube voltage information.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 X-ray CT apparatus 21 X-ray tube 23 X-ray detection part 231 1st X-ray detection part 232 2nd X-ray detection part 43 Scintillator 65 Energy spectrum acquisition part 66 Correction | amendment part 71 Detection relation 72 Prior measurement spectrum 73 Prior detection relation

Claims (8)

A first X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the subject;
A second X-ray detector configured by a scintillator and a silicon photomultiplier, and detecting a X-ray incident from the X-ray tube as a photon, thereby outputting a signal corresponding to the energy of the incident X-ray;
Based on the output signal of the second X-ray detector, the relationship between the energy and intensity of the X-rays incident on the second X-ray detector is obtained, and the X-rays irradiated from the X-ray tube are obtained based on the obtained relationship. An energy spectrum acquisition unit for acquiring an energy spectrum;
With
The energy spectrum acquisition unit
An X-ray pre-measurement energy spectrum corresponding to each of a plurality of pre-measured tube voltages is acquired, and the similarity between the X-ray energy and the intensity is the highest among the pre-measurement energy spectra. Obtaining a pre-measured energy spectrum as an energy spectrum of the X-rays irradiated from the X-ray tube;
X-ray CT system. The energy spectrum acquisition unit
Obtaining an energy spectrum of the X-ray by interpolating using a plurality of prior measured energy spectra having a high degree of similarity among each of the previously measured energy spectra;
The X-ray CT apparatus according to claim 1 . The energy spectrum acquisition unit
By irradiating the X-ray tube from the X-ray tube to the second X-ray detection unit in advance with each of a plurality of tube voltages, a pre-detection relationship that is a relationship between the energy and intensity of the X-rays is obtained. And the prior measurement energy spectrum corresponding to the same tube voltage is associated with the prior detection relationship, and the priorities having the highest similarity between the relationship between the energy and intensity of the X-ray Extracting a detection relationship, and obtaining the pre-measured energy spectrum associated with the extracted pre-detection relationship as an energy spectrum of the X-rays irradiated from the X-ray tube;
The X-ray CT apparatus according to claim 1 . The energy spectrum acquisition unit
A plurality of pre-detection relationships having a high degree of similarity between the relationship between the energy and intensity of the X-ray are extracted, and interpolation is performed using a plurality of pre-measurement energy spectra associated with the plurality of pre-detection relationships having a high degree of similarity. To obtain an energy spectrum of the X-rays irradiated from the X-ray tube.
The X-ray CT apparatus according to claim 3 . The energy spectrum acquisition unit
Obtaining a tube voltage applied to the X-ray tube based on the relationship between the energy and intensity of the X-ray;
The X-ray CT apparatus according to any one of claims 1 to 4 . Correction for correcting data generated based on the X-rays detected by the first X-ray detection unit using the energy spectrum of the X-rays irradiated from the X-ray tube acquired by the energy spectrum acquisition unit Part,
The X-ray CT apparatus according to any one of claims 1 to 5 , further comprising: The first X-ray detector is composed of a product-sum type X-ray detector,
X-ray CT apparatus according to any one of claims 1 to 6. The X-ray tube is
X-rays having a plurality of energy spectra corresponding to a plurality of tube voltages are generated every predetermined time.
X-ray CT apparatus according to any one of claims 1 to 7.

Images