Medical information processing device, medical information processing method, and program

Abstract

To efficiently calculate the transmission length of an object substance to be an object of a substance discrimination.SOLUTION: A medical information processing device calculates the transmission length of an object substance to be an object of a substance discrimination within a subject's body using data obtained by imaging the subject with a photon-counting CT scanner and an equation describing X-ray attenuation. The medical information processing device includes a calculation unit. The calculation unit sets two equations on the basis of the count values of X-ray photons counted in each of two energy bins located before and after a K-edge of the object substance under imaging conditions in which the energy width of the two energy bins is set narrower than a predetermined threshold. The calculation unit calculates the transmission length of the object substance by considering the X-ray attenuation in the calibration term, photoelectric absorption term, and Compton scattering term as equivalent, in the two set equations.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments disclosed in the present specification and drawings relate to a medical information processing device, a medical information processing method, and a program. [Background technology]

[0002] In recent years, the field of medical imaging diagnostics has seen the emergence of a new type of photon-counting computed tomography (PCCT) system that uses semiconductor photon-counting detectors. This photon-counting CT system is capable of detecting information containing photon energy, which is expected to further advance functional analyses such as material decomposition, which have been achieved using dual energy technology. K-edge reconstruction is a well-known technique for material decomposition. In K-edge reconstruction, energy bins are placed around the energy of a material's X-ray K absorption edge (called the "K-edge"), and photon counts in these energy bins are used for image reconstruction, enabling targeted imaging (material decomposition) and concentration measurement of the material (called the "K-edge material"). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-067943 Summary of the Invention [Problem to be solved by the invention]

[0004] Photon-counting CT systems can measure photons in any energy range by setting multiple energy bins with a certain energy window in the comparator on the detector side. To improve the accuracy of K-edge reconstruction, it is possible to narrow the energy window of the two energy bins placed before and after the K-edge position. However, narrowing the energy window reduces the number of photons that enter the energy bin, so it is common to have a certain window width (also called "energy width"). On the other hand, if the energy window is widened to a certain extent, a large amount of photon energy attenuated by substances other than the K-edge material will enter, making it difficult to reconstruct the K-edge with high accuracy. This trade-off exists.

[0005] The problem to be solved by the embodiments disclosed in this specification and the drawings is to efficiently calculate the transmission length of a target material that is the subject of material decomposition. However, the problem to be solved by the embodiments disclosed in this specification and the drawings is not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0006] A medical image processing device according to an embodiment calculates the transmission length of a target material that is the target of material decomposition within the body of the subject, using data obtained by imaging the subject using a photon-counting CT scanner and an equation representing X-ray attenuation. The equation includes a calibration term related to calibration, a photoelectric absorption term related to a material that is predominantly photoelectric absorption, a Compton scattering term related to a material that is predominantly Compton scattering, and a target material term related to the target material. The medical image processing device includes a calculation unit. The calculation unit sets the two equations based on count values ​​of X-ray photons counted in each of two energy bins located before and after the K-edge of the target material under imaging conditions in which the energy width between the two energy bins is set to be narrower than a predetermined threshold, and calculates the transmission length of the target material by considering the X-ray attenuation in the calibration term, the photoelectric absorption term, and the Compton scattering term to be equivalent in the two set equations. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing an example of the configuration of a photon-counting CT apparatus 1 according to an embodiment. [Figure 2A] FIG. 1 is a diagram for explaining a method for setting energy bins (normal setting) according to the prior art. [Figure 2B] 10A and 10B are diagrams for explaining a method of setting an energy bin (narrow setting) according to the embodiment. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of a DAS 16 according to the embodiment. [Figure 4] 4 is a flowchart showing an example of image reconstruction processing by the photon-counting CT apparatus 1 according to the embodiment. [Figure 5] 3 is a flowchart showing an example of optimization processing (optimization method 1) by the photon-counting CT apparatus 1 according to the embodiment. [Figure 6] 10 is a flowchart showing another example (optimization method 2) of the optimization process by the photon-counting CT apparatus 1 according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a medical information processing apparatus, a medical information processing method, and a program according to an embodiment will be described with reference to the drawings.

[0009] [Configuration of photon counting CT device] 1 is a diagram showing an example of a photon-counting CT apparatus 1 according to the first embodiment. The photon-counting CT apparatus 1 uses a direct detector such as a semiconductor detector with excellent energy resolution to generate image data that discriminates the material of the object of examination through which X-rays have passed.

[0010] The photon-counting CT apparatus 1 includes, for example, a gantry 10, a bed 30, and a console 40. For convenience of explanation, Fig. 1 shows both a view of the gantry 10 from the Z-axis direction and a view of the gantry 10 from the X-axis direction, but in reality, there is only one gantry 10. In this embodiment, the rotation axis of the rotating frame 17 in a non-tilted state or the longitudinal direction of the tabletop 33 of the bed 30 is defined as the Z-axis direction, an axis perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction, and a direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

[0011] <Mounting device 10> The gantry device 10 includes, for example, an X-ray tube 11, a wedge 12, a collimator 13, an X-ray high voltage device 14, an X-ray detector 15, a data acquisition system (hereinafter referred to as DAS: Data Acquisition System) 16, a rotating frame 17, and a control device 18. The X-ray detector 15 and the DAS 16 constitute a detector module 20.

[0012] The X-ray tube 11 generates X-rays by irradiating thermoelectrons from a cathode (filament) to an anode (target) when a high voltage is applied from the X-ray high voltage device 14. The X-ray tube 11 includes a vacuum tube. For example, the X-ray tube 11 is a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

[0013] The wedge 12 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11 to the subject P. The wedge 12 attenuates the X-rays passing through it so that the distribution of the X-ray dose irradiated from the X-ray tube 11 to the subject P becomes a predetermined distribution. The wedge 12 is also called a wedge filter or a bow-tie filter. The wedge 12 is made by processing aluminum so as to have a predetermined target angle and a predetermined thickness, for example.

[0014] The collimator 13 is a mechanism for narrowing the irradiation range of the X-rays that have passed through the wedge 12. The collimator 13 narrows the irradiation range of the X-rays, for example, by forming a slit using a combination of multiple lead plates. The collimator 13 is sometimes called an X-ray aperture. The narrowing range of the collimator 13 may be mechanically drivable.

[0015] The X-ray high voltage device 14 includes, for example, a high voltage generator (not shown) and an X-ray control device (not shown). The high voltage generator has an electric circuit including a transformer, a rectifier, etc., and generates a high voltage to be applied to the X-ray tube 11. The X-ray control device controls the output voltage of the high voltage generator according to the X-ray dose to be generated by the X-ray tube 11. The high voltage generator may be one that boosts voltage using the above-mentioned transformer, or one that boosts voltage using an inverter. The X-ray high voltage device 14 may be provided on the rotating frame 17, or may be provided on the side of the fixed frame (not shown) of the gantry device 10.

[0016] The X-ray detector 15 detects the intensity of X-rays that are generated by the X-ray tube 11 and that have passed through the subject P and are incident thereon. The X-ray detector 15 outputs an electrical signal (which may be an optical signal, etc.) corresponding to the intensity of the detected X-rays to the DAS 16. The X-ray detector 15 has, for example, multiple X-ray detection element rows. Each of the multiple X-ray detection element rows has multiple X-ray detection elements arranged in the channel direction along an arc centered on the focal point of the X-ray tube 11. The multiple X-ray detection element rows are arranged in the slice direction (column direction, row direction).

[0017] The X-ray detector 15 is, for example, a direct detection detector. An example of an applicable X-ray detector 15 is a semiconductor diode with electrodes attached to both ends of a semiconductor. An X-ray photon incident on the semiconductor is converted into an electron-hole pair. The number of electron-hole pairs generated by the incidence of one X-ray photon depends on the energy of the incident X-ray photon. The electrons and holes are attracted to a pair of electrodes formed on both ends of the semiconductor. The pair of electrodes generates an electric pulse having a peak value corresponding to the charge of the electron-hole pair. One electric pulse has a peak value corresponding to the energy of the incident X-ray photon.

[0018] The DAS 16 collects count data (count values) indicating the number of counts of X-ray photons detected by the X-ray detector 15 for a plurality of energy bins in accordance with, for example, a control signal from the control device 18. The count values ​​for the plurality of energy bins correspond to an energy spectrum of the X-rays incident on the X-ray detector 15, which has been modified in accordance with the response characteristics of the X-ray detector 15.

[0019] FIG. 2A is a diagram illustrating a conventional energy bin setting method (normal setting). In FIG. 2A, graph LN shows the energy characteristics of a specific reference material (also referred to as a "K-edge material"). Examples of K-edge materials include iodine, gadolinium, barium, gold, bismuth, and calcium. The horizontal axis represents the energy of X-ray photons, and the vertical axis represents the X-ray attenuation coefficient. In the conventional technology, for example, multiple energy bins with a predetermined fixed energy range (e.g., 20 to 30 keV) are set. In the example shown in FIG. 2A, energy bins are set for the purpose of distinguishing K-edge materials having an X-ray K absorption edge (K edge) near e2 keV. In this example, three energy bins are set: a first energy bin bin1 (e1 to e2 keV), a second energy bin2 (e2 to e3 keV), and a third energy bin3 (e3 to e4 keV). Here, by using the photon count values ​​in the first energy bin bin1 and the second energy bin bin2 located before and after the K-edge for image reconstruction, the K-edge material can be discriminated.

[0020] On the other hand, FIG. 2B is a diagram for explaining the energy bin setting method (narrow setting) according to this embodiment. Similar to FIG. 2A, in FIG. 2B, graph LN shows the energy characteristics of a specific reference material (K-edge material). The horizontal axis represents the energy of the X-ray photon, and the vertical axis represents the X-ray attenuation coefficient. In the energy bin setting method according to this embodiment, the energy width of the energy bins located before and after the K-edge is set narrow. In the example shown in FIG. 2B, energy bins are set for the purpose of discriminating K-edge materials having a K-edge around E2 keV. In this example, three energy bins are set: a first energy bin 1 (E1 to E2 keV), a second energy bin 2 (E2 to E3 keV), and a third energy bin 3 (E3 to E4 keV). Here, the energy widths of the first energy bin 1 and the second energy bin 2 located before and after the K-edge are set narrow. The energy width (E1 to E2 keV) of the first energy bin bin1 and the energy width (E2 to E3 keV) of the second energy bin2 in FIG. 2B are each set narrower than the energy width (e1 to e2 keV) of the first energy bin bin1 and the energy width (e2 to e3 keV) of the second energy bin2 in FIG. 2A.

[0021] Returning to FIG. 1 , the DAS 16 outputs projection data based on the digital signal to the console device 40. The projection data is a digital count value identified by the channel number and column number of the X-ray detection element that generated the data, and a view number indicating the acquired view. The view number is a number that changes according to the rotation of the rotating frame 17, for example, a number that is incremented according to the rotation of the rotating frame 17. Therefore, the view number is information that indicates the rotation angle of the X-ray tube 11. The view period is the period that falls between the rotation angle corresponding to a certain view number and the rotation angle corresponding to the next view number.

[0022] The DAS 16 may detect the view switching by a timing signal input from the control device 18, by an internal timer, or by a signal acquired from a sensor (not shown). When a full scan is performed and X-rays are continuously emitted by the X-ray tube 11, the DAS 16 collects a group of projection data for the entire circumference (360 degrees). When a half scan is performed and X-rays are continuously emitted by the X-ray tube 11, the DAS 16 collects projection data for half the circumference (180 degrees + fan angle). The DAS 16 processes the projection data detected by the semiconductor detector.

[0023] Fig. 3 is a diagram showing an example of the configuration of the DAS 16 according to the embodiment. The DAS 16 has readout channels, the number of which corresponds to the number of X-ray detection elements. These multiple readout channels are implemented in parallel in an integrated circuit such as an ASIC. Fig. 3 shows the configuration of only one readout channel, DAS 16-1.

[0024] The DAS 16-1 includes a preamplifier circuit 61, a waveform shaping circuit 63, a plurality of pulse height discriminator circuits 65, a plurality of counter circuits 67, and an output circuit 69. The preamplifier circuit 61 amplifies the detected electrical signal DS (current signal) from the connected X-ray detection element. For example, the preamplifier circuit 61 converts the current signal from the connected X-ray detection element into a voltage signal having a voltage value (peak value) proportional to the amount of charge of the current signal. A waveform shaping circuit 63 is connected to the preamplifier circuit 61. The waveform shaping circuit 63 shapes the waveform of the voltage signal from the preamplifier circuit 61. For example, the waveform shaping circuit 63 reduces the pulse width of the voltage signal from the preamplifier circuit 61.

[0025] A number of counting channels corresponding to the number of energy bands (energy bins) are connected to the waveform shaping circuit 63. When n energy bins are set, n counting channels are provided in the waveform shaping circuit 63. Each counting channel has a pulse height discrimination circuit 65-n and a counting circuit 67-n.

[0026] Each of the pulse height discrimination circuits 65-n discriminates the energy of the X-ray photons detected by the X-ray detection elements, which is the pulse height value of the voltage signal from the waveform shaping circuit 63. For example, the pulse height discrimination circuit 65-n has a comparison circuit 653-n. The voltage signal from the waveform shaping circuit 63 is input to one input terminal of each of the comparison circuits 653-n. A reference signal TH (reference voltage value) corresponding to a different threshold value is supplied from the control device 18 to the other input terminal of each of the comparison circuits 653-n.

[0027] For example, the comparison circuit 653-1 for energy bin B1 is supplied with a reference signal TH-1, the comparison circuit 653-2 for energy bin B2 is supplied with a reference signal TH-2, and the comparison circuit 653-n for energy bin Bn is supplied with a reference signal TH-n. Each of the reference signals TH has an upper reference value and a lower reference value. Each of the comparison circuits 653-n outputs an electrical pulse signal when the voltage signal from the waveform shaping circuit 63 has a peak value corresponding to the energy bin corresponding to each of the reference signals TH. For example, the comparison circuit 653-1 outputs an electrical pulse signal when the peak value of the voltage signal from the waveform shaping circuit 63 is the peak value corresponding to energy bin B1 (when it is between reference signals TH-1 and TH-2). On the other hand, the comparison circuit 653-1 for energy bin B1 does not output an electrical pulse signal when the peak value of the voltage signal from the waveform shaping circuit 63 is not the peak value corresponding to energy bin B1. Also, for example, the comparison circuit 653-2 outputs an electrical pulse signal when the peak value of the voltage signal from the waveform shaping circuit 63 is the peak value corresponding to energy bin B2 (when it is between reference signals TH-2 and TH-3).

[0028] The counter circuit 67-n counts the electrical pulse signals from the pulse-height discriminator circuit 65-n at a readout period that coincides with the view switching period. For example, the counter circuit 67-n receives a trigger signal TS from the control device 18 at the timing of each view switching. The counter circuit 67-n, triggered by the supply of the trigger signal TS, increments the count number stored in its internal memory each time an electrical pulse signal is input from the pulse-height discriminator circuit 65-n. The counter circuit 67-n reads out the count number data (i.e., the count value) stored in its internal memory and supplies it to the output circuit 69 when the next trigger signal is supplied. The counter circuit 67-n also resets the count number stored in its internal memory to its initial value each time the trigger signal TS is supplied. In this manner, the counter circuit 67-n counts the count number for each view.

[0029] The output circuit 69 is connected to counting circuits 67-n for multiple readout channels mounted on the X-ray detector 15. The output circuit 69 integrates count values ​​from the counting circuits 67-n for multiple readout channels for each of multiple energy bins to generate count values ​​for multiple readout channels for each view. The count value for each energy bin is a collection of data with a count number defined by the channel, segment (column), and energy bin. The count value for each energy bin is transmitted to the console device 40 on a view-by-view basis. The count value for each view is called a count data set CS. Furthermore, the output circuit 69 transmits data detected for each pixel detected by the X-ray detector 15 to the console device 40. The projection data includes at least one of the data detected for each pixel and the count value for each energy bin.

[0030] Returning to FIG. 1 , the rotating frame 17 is an annular member that supports the X-ray tube 11, wedge 12, collimator 13, and X-ray detector 15 in opposing positions. The rotating frame 17 is supported by a fixed frame so as to be rotatable around the subject P introduced inside. The rotating frame 17 also supports the DAS 16. Projection data output by the DAS 16 is transmitted by optical communication from a transmitter having a light-emitting diode (LED) provided on the rotating frame 17 to a receiver having a photodiode provided on a non-rotating portion of the gantry device 10 (e.g., the fixed frame), and then transferred to the console device 40 by the receiver. Note that the method of transmitting projection data from the rotating frame 17 to the non-rotating portion is not limited to the above-mentioned method using optical communication, and any non-contact transmission method may be adopted. The rotating frame 17 is not limited to an annular member, and may be an arm-like member as long as it can support and rotate the X-ray tube 11, etc.

[0031] The photon counting CT device 1 is, for example, a rotate / rotate-type X-ray CT device (third generation CT) in which both the X-ray tube 11 and the X-ray detector 15 are supported by a rotating frame 17 and rotate around the subject P, but is not limited to this and may also be a stationary / rotate-type X-ray CT device (fourth generation CT) in which multiple X-ray detection elements arranged in a circular ring are fixed to a fixed frame and the X-ray tube 11 rotates around the subject P.

[0032] The control device 18 includes a processing circuit having a processor such as a CPU (Central Processing Unit). The control device 18 receives input signals from an input interface attached to the console device 40 or the gantry device 10 and controls the operations of the gantry device 10, the bed device 30, and the DAS 16. For example, the control device 18 rotates the rotating frame 17 or tilts the gantry device 10. When tilting the gantry device 10, the control device 18 rotates the rotating frame 17 around an axis parallel to the Z-axis direction based on the tilt angle (tilt angle) input to the input interface. The control device 18 determines the rotation angle of the rotating frame 17 based on the output of a sensor (not shown) or the like. The control device 18 also controls the energy bin (reference signal TH) of the DAS 16. The control device 18 may be provided in the gantry device 10 or the console device 40.

[0033] <Bed Device 30> The bed device 30 is a device on which the subject P to be scanned is placed, moved, and introduced into the rotating frame 17 of the gantry device 10. The bed device 30 includes, for example, a base 31, a bed driving device 32, a top plate 33, and a support frame 34. The base 31 includes a housing that supports the support frame 34 so that the support frame 34 can move in the vertical direction (Y-axis direction). The bed driving device 32 includes a motor and an actuator. The bed driving device 32 moves the top plate 33 in the longitudinal direction of the top plate 33 (Z-axis direction) along the support frame 34. The bed driving device 32 also moves the top plate 33 in the vertical direction (Y-axis direction). The top plate 33 is a plate-shaped member on which the subject P is placed.

[0034] The bed driving device 32 may move not only the tabletop 33 but also the support frame 34 in the longitudinal direction of the tabletop 33. Alternatively, conversely to the above, the gantry device 10 may be movable in the Z-axis direction, and the movement of the gantry device 10 may be controlled so that the rotating frame 17 comes around the subject P. Alternatively, both the gantry device 10 and the tabletop 33 may be configured to be movable. The photon-counting CT apparatus 1 may be an apparatus in which the subject P is scanned in a standing or sitting position. In this case, the photon-counting CT apparatus 1 has a subject support mechanism instead of the bed device 30, and the gantry device 10 rotates the rotating frame 17 around an axial direction perpendicular to the floor surface.

[0035] <Console Device 40> The console device 40 includes, for example, a memory 41, a display 42, an input interface 43, a network connection circuit 44, and a processing circuit 50. In this embodiment, the console device 40 is described as being separate from the gantry device 10, but the gantry device 10 may include some or all of the components of the console device 40.

[0036] The memory 41 is realized by, for example, a semiconductor memory element such as a RAM (Random Access Memory), a flash memory, a hard disk, an optical disk, etc. The memory 41 stores, for example, energy bin setting data, projection data, reconstructed image data (photon-counting CT image data), information data related to the subject P, imaging condition data, etc. The memory 41 stores, for example, count values ​​related to a plurality of energy bins transmitted from the gantry device 10. These data may be stored in an external memory with which the photon-counting CT device 1 can communicate, instead of (or in addition to) the memory 41. The external memory is controlled by, for example, a cloud server that manages the external memory, by the cloud server accepting a read / write request.

[0037] The display 42 displays various types of information. For example, the display 42 displays medical images (photon-counting CT images) generated by a processing circuit, GUI (Graphical User Interface) images that accept various operations by an operator such as a doctor or technician, etc. The display 42 is, for example, a liquid crystal display, a CRT (Cathode Ray Tube), an organic EL (Electroluminescence) display, etc. The display 42 may be provided on the gantry device 10. The display 42 may be a desktop type, or may be a display device (for example, a tablet terminal) that can wirelessly communicate with the main body of the console device 40. The display 42 is an example of a "display device."

[0038] The input interface 43 accepts various input operations by an operator and outputs an electrical signal indicating the content of the accepted input operation to the processing circuitry 50. For example, the input interface 43 accepts input operations such as energy bin setting conditions, acquisition conditions when acquiring projection data, reconstruction conditions when reconstructing CT images, and image processing conditions when generating post-processed images from CT images. For example, the input interface 43 is realized by a mouse, keyboard, touch panel, drag ball, switch, button, joystick, camera, infrared sensor, microphone, etc.

[0039] The input interface 43 may be provided in the gantry device 10. Alternatively, the input interface 43 may be realized by a display device (e.g., a tablet terminal) capable of wireless communication with the main body of the console device 40. Note that, in this specification, the input interface is not limited to one equipped with physical operation components such as a mouse and a keyboard. For example, an example of the input interface also includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs this electrical signal to a control circuit.

[0040] The network connection circuit 44 includes, for example, a network card having a printed circuit board, a wireless communication module, etc. The network connection circuit 44 implements an information communication protocol according to the type of the network to be connected.

[0041] The processing circuitry 50 controls the overall operation of the photon-counting CT apparatus 1, the operation of the gantry device 10, and the operation of the bed device 30. The processing circuitry 50 executes, for example, a system control function 51, a preprocessing function 52, a reconstruction function 53, an image processing function 54, a scan control function 55, a display control function 56, and the like. The reconstruction function 53 includes, for example, an acquisition function 53-1, a calculation function 53-2, an optimization function 53-3, and the like. These components are realized, for example, by a hardware processor (computer) executing a program (software) stored in the memory 41. The hardware processor refers to a circuit such as a CPU, a GPU (Graphics Processing Unit), an ASIC, a programmable logic device (for example, a Simple Programmable Logic Device (SPLD) or a Complex Programmable Logic Device (CPLD), or a Field Programmable Gate Array (FPGA)).

[0042] Instead of storing a program in memory 41, the program may be directly embedded in the circuit of the hardware processor. In this case, the hardware processor realizes its functions by reading and executing the program embedded in the circuit. The hardware processor is not limited to being configured as a single circuit, but may be configured as a single hardware processor by combining multiple independent circuits to realize each function. Furthermore, multiple components may be integrated into a single hardware processor to realize each function.

[0043] Each component of the console device 40 or the processing circuitry 50 may be distributed and realized by multiple pieces of hardware. The processing circuitry 50 may not be a component of the console device 40, but may be realized by a processing device capable of communicating with the console device 40. The processing device is, for example, a workstation connected to one photon-counting CT device, or a device (e.g., a cloud server) connected to multiple photon-counting CT devices and collectively executing processing equivalent to that of the processing circuitry 50 described below. The photon-counting CT device 1, the console device 40, the workstation, the cloud server, or a combination thereof is an example of a "medical information processing device."

[0044] The system control function 51 controls various functions of the processing circuit 50 based on input operations received by the input interface 43. The system control function 51 performs, for example, setting of energy bins, and setting of the tube voltage and tube current of the X-ray tube 11. The system control function 51 outputs the setting conditions of the set energy bins to the control device 18.

[0045] The pre-processing function 52 performs pre-processing such as offset correction, inter-channel sensitivity correction, and beam hardening correction on the projection data output by the DAS 16 .

[0046] The reconstruction function 53 reconstructs a photon-counting CT image of the subject P based on the projection data (count values). The reconstruction function 53 calculates the X-ray absorption amount for each of multiple reference materials based on the count values ​​for multiple energy bins, the energy spectrum of X-rays incident on the subject P, and a response function representing the detector response characteristics stored in the memory 41. This process of obtaining the X-ray absorption amount for each reference material is also called material decomposition. The reconstruction function 53 reconstructs a photon-counting CT image representing the spatial distribution of the reference material to be imaged among the multiple reference materials based on the calculated X-ray absorption amount for each of the multiple reference materials, and stores the generated CT image data in the memory 41. The reconstruction function 53 can also generate image data similar to conventional CT images using combined data of count values ​​for multiple energy bands (energy bins).

[0047] The acquisition function 53-1 acquires imaging data obtained by imaging the subject P. The acquisition function 53-1 acquires, for example, count values ​​for each of a plurality of energy bins. The acquisition function 53-1 is an example of an "acquisition unit."

[0048] The calculation function 53-2 sets two equations indicating the attenuation of X-rays based on the count values ​​of X-ray photons counted in each of two energy bins located before and after the K-edge of the K-edge material (target material) under imaging conditions in which the energy width of the two energy bins located before and after the K-edge of the K-edge material (target material) is set narrower than a predetermined threshold, and calculates the transmission length (also called the "path length") of the target material by considering the X-ray attenuation in the calibration term, photoelectric absorption term, and Compton scattering term to be equivalent in the two set equations. The calculation function 53-2 is an example of a "calculation unit." Details of the processing of the calculation function 53-2 will be described later.

[0049] The optimization function 53-3 optimizes the calculated transmission length of the target substance based on the transmission length of the target substance calculated by the calculation function 53-2 and data obtained by imaging the subject P. The optimization function 53-3 is an example of an "optimization unit." Details of the processing of the optimization function 53-3 will be described later.

[0050] The image processing function 54 converts the CT image data into three-dimensional image data or cross-sectional image data of an arbitrary cross section by a known method based on the input operation received by the input interface 43. The conversion into three-dimensional image data may be performed by the pre-processing function 52.

[0051] The scan control function 55 controls the collection process of projection data in the gantry device 10 by issuing instructions to the X-ray high voltage device 14, the DAS 16, the control device 18, and the bed driving device 32. The scan control function 55 controls the operation of each part when taking images to collect positioning images and when taking images to be used for diagnosis.

[0052] The display control function 56 displays, on the display 42, medical images (photon-counting CT images) generated by the processing circuit, GUI images that accept various operations by an operator such as a doctor or technician, etc. The display control function 56 is an example of a "display control unit."

[0053] With the above configuration, the photon-counting CT apparatus 1 scans the subject P in a scan mode such as helical scan, conventional scan, or step-and-shoot. Helical scan is a mode in which the rotating frame 17 is rotated while the top 33 is moved, thereby scanning the subject P in a spiral shape. Conventional scan is a mode in which the rotating frame 17 is rotated while the top 33 is stationary, thereby scanning the subject P in a circular orbit. Step-and-shoot is a mode in which the position of the top 33 is moved at regular intervals, and conventional scans are performed in multiple scan areas.

[0054] [Processing flow] Next, a series of steps in the image reconstruction process of the photon-counting CT apparatus 1 will be described, focusing on the processing of the console device 40. Fig. 4 is a flowchart showing an example of the image reconstruction process by the photon-counting CT apparatus 1 according to this embodiment. The image reconstruction process shown in Fig. 4 is started when the operator inputs a command to start the process via the input interface 43, for example, when executing a scan on the subject P.

[0055] First, the system control function 51 sets energy bins based on an input operation by the operator received by the input interface 43, and outputs the setting conditions of the set energy bins to the control device 18 (step S101). In setting the energy bins here, the energy widths of two energy bins located before and after the K-edge of the K-edge material to be subjected to material decomposition are set to be narrow. For example, as described with reference to FIG. 2B , the energy widths of the first energy bin bin1 and the second energy bin2 located before and after the K-edge of the target K-edge material are set to be narrow, and further, a third energy bin bin3, which is in a higher energy band than the second energy bin bin2, is set as another energy bin. The energy width of the third energy bin bin3 is arbitrary. For example, the energy width of the other energy bin (the third energy bin bin3) may be set wider than the energy bins located before and after the K-edge (the first energy bin bin1 and the second energy bin2). Furthermore, additional energy bins may be set.

[0056] In this embodiment, a narrow energy width of an energy bin means, for example, that the energy width is smaller than a predetermined threshold. For example, the threshold is set to a value smaller than the standard energy width (20 to 30 keV) in conventional technology. In this embodiment, the narrow energy width is, for example, about 5 keV. Alternatively, a narrow energy width of an energy bin means, for example, that the energy width is narrow enough that, in the equation showing X-ray attenuation described below, the energy responses of two energy bins located before and after the K-edge, as well as the detector responses of each energy bin and each detector element, can be considered equivalent.

[0057] Under the energy bin conditions set as described above, a photon-counting CT image is reconstructed based on data (count values) acquired by imaging the subject P placed on the bed. First, the calculation function 53-2 calculates the transmission length of the K-edge material based on the acquired data (count values) (step S103). Furthermore, the calculation function 53-2 uses the calculated transmission length of the K-edge material to calculate the transmission lengths of the material dominated by photoelectric absorption and the material dominated by Compton scattering (step S105).

[0058] (Calculation of transmission length of K-edge material) The process of calculating the transmission length of the K-edge material will be explained below. First, Equation (1) showing the attenuation of X-rays in a certain detector element of a certain energy bin is defined as follows.

[0059]

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[0060] In the above formula (1), N b indicates the data (count value) measured in one energy bin, and N0 indicates the data (count value) of the reference detector (Ref detector). E_max indicates the tube voltage of the incident X-ray, and E_min indicates the minimum detection energy in the photon-counting detector. φb (E) shows the energy response for each energy bin, and D b (E) shows the detector response for each energy bin and detector element. b (E) and D b (E) is a calibration term calculated before image reconstruction. Here, as the material to be discriminated, a general material with dominant photoelectric absorption (linear attenuation coefficient: μ ph , transmission length: l ph ), the dominant material for Compton scattering (linear attenuation coefficient: μ co , transmission length: l co ), the K-edge material (linear attenuation coefficient: μ k , transmission length: l k ) will be explained using the following three substances as examples.

[0061] Assuming that the specimen P is composed of the above three materials, the transmission length of each material is calculated. The dominant interactions in the CT X-ray energy range are the photoelectric effect and Compton scattering, which are the basis for conventional Dual Energy technology. In this embodiment, one more material is added to define three materials in order to discriminate K-edge materials in the CT X-ray energy range.

[0062] For the three energy bins set in step S101 above, if the first energy bin bin1 is b1δ, the second energy bin bin2 is b1δ', and the third energy bin bin3 is b2, the following three equations can be set based on the above equation (1):

[0063]

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[0064] Here, the first energy bin bin1 (b1δ) and the second energy bin bin2 (b1δ′) have a narrow energy range and are adjacent to each other. Therefore, the energy response φ of the first energy bin bin1 is b1δ (E) is the energy response φ of the second energy bin bin2 b1δ’(E) can be considered equivalent to (φ b1δ (E)≒φ b1δ’ (E)). Also, the detector response D b1δ (E) is the detector response D for the second energy bin bin2 b1δ’ (D) can be considered equivalent to (E) b1δ (E)≒D b1δ’ (E)). Therefore, for the calibration term, the term relating to the material that dominates photoelectric absorption, and the term relating to the material that dominates Compton scattering, which are set in the integrals of the above equations (2) and (3), the following equation (5) can be set:

[0065]

number

[0066] Using φ′ expressed by the above equation (5), the above equations (2) and (3) can be rewritten as the following equations (6) and (7).

[0067]

number

[0068] Using equations (6) and (7) expressed above, the transmission length l of the K-edge material is k The calculated transmission length of the K-edge material, l k , l k Let's say ^(hat).

[0069] (Calculation of transmission length for materials where photoelectric absorption is dominant and materials where Compton scattering is dominant) Next, based on the formula (8) which sums the count values ​​of the formulas (2) and (3), the transmission length l of the material where photoelectric absorption is dominant is calculated. ph and the penetration length l of the material where Compton scattering is dominant co Calculate.

[0070]

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[0071] The reason for setting the formula (8) which sums the count values ​​of the formulas (2) and (3) is that using the formula (2) alone or the formula (3) alone is susceptible to noise. b1 (E) and D b1 (E) is a calibration term calculated before image reconstruction.

[0072] Here, the calculated transmission length l of the K-edge material is added to the above equations (4) and (8). k By substituting ^(hat) and solving the simultaneous equations, the transmission length l of the material that dominates photoelectric absorption can be obtained. ph and the penetration length l of the material where Compton scattering is dominant co Calculate.

[0073] That is, the equation showing the attenuation of X-rays includes a calibration term related to the calibration, a photoelectric absorption term related to the material having the dominant photoelectric absorption, a Compton scattering term related to the material having the dominant Compton scattering, and a target material term related to the target material. In addition to formulas (2) and (3) set based on the count values ​​of two energy bins located before and after the K-edge, calculation function 53-2 sets formula (4) based on the count values ​​of X-ray photons counted in other energy bins, and calculates the transmission length l of the material having the dominant photoelectric absorption based on the two formulas (2) and (3), the other formula (3), and the calculated transmission length of the K-edge material (target material). ph and the penetration length l of the material where Compton scattering is dominant co The calculation function 53-2 also calculates the calculated transmission length l of the target substance by adding the two equations (2) and (3) to the equation (8) and the other equation (4). k By substituting ^(hat), the transmission length l of the material where photoelectric absorption is dominant is obtained. ph and the penetration length l of the material where Compton scattering is dominant co Calculate.

[0074] The transmission length l of the K-edge material calculated above k ^ (hat) is an approximate solution. Therefore, an optimization process may be required to optimize (fine-tune) the transmission length of the K-edge material. Therefore, the optimization function 53-3 executes an optimization process for the calculated transmission length of the K-edge material (step S107). As the optimization process, the following two methods will be described. Note that such an optimization process does not have to be performed. In this case, the transmission length calculated in step S105 may be used to perform image reconstruction in step S109, which will be described later.

[0075] (Optimization method 1) Optimization method 1 uses the calculated transmission length l of the K-edge material. k The transmission length is optimized based on the comparison result between an image reconstructed based on ^ (hat) and a CT image (normal CT image) containing various substances reconstructed based on the combined data of each energy bin acquired by imaging the subject P. Fig. 5 is a flowchart showing an example of optimization processing (optimization method 1) by the photon-counting CT apparatus 1 according to this embodiment.

[0076] First, the optimization function 53-3 calculates the transmission length l of the calculated K-edge material. k ^ (hat) is set as a reference transmission length (referred to as a "reference transmission length"), and a transmission length (referred to as a "comparison transmission length") obtained by varying this reference transmission length within a predetermined range is set (step S201). For example, the optimization function 53-3 sets the reference transmission length l k One or more comparative transmission lengths (for example, 10 comparative transmission lengths) are set within the range of ^ (hat) ± Δ (arbitrary).

[0077] Next, the calculation function 53-2 calculates the transmission length l of the dominant material of photoelectric absorption for each of the set comparative transmission lengths. ph and the penetration length l of the material where Compton scattering is dominant co For example, the calculation function 53-2 substitutes each of the set comparative transmission lengths into the above equations (4) and (8) to solve the simultaneous equations, thereby recalculating the transmission length l of the material that is dominant in photoelectric absorption. phand the penetration length l of the material where Compton scattering is dominant co Recalculate.

[0078] Next, the reconstruction function 53 generates a reference material image of the K-edge material based on each of the set reference transmission length and comparison transmission length, and a transmission length l of the material that is dominant in photoelectric absorption calculated based on each of the reference transmission length and comparison transmission length. ph The reference material image of the material that is dominant in photoelectric absorption based on the above, and the transmission length l of the material that is dominant in Compton scattering calculated based on each of the reference transmission length and the comparison transmission length. ph (Step S205). Furthermore, the reconstruction function 53 may generate a virtual monochromatic X-ray image (VMI image) based on a combination of the reference material images of the K-edge material, the material dominant in photoelectric absorption, and the material dominant in Compton scattering under each condition. In the following, an example in which a virtual monochromatic X-ray image is generated will be described.

[0079] Next, the reconstruction function 53 reconstructs a normal CT image based on the sum of the data (count values) of each energy bin acquired by imaging the subject P (step S207).

[0080] Next, the optimization function 53-3 compares each of the virtual monochromatic X-ray images with the normal CT image (step S209). Then, the optimization function 53-3 determines an optimal transmission length based on the comparison result and optimizes the transmission length (step S211).

[0081] For example, the optimization function 53-3 instructs the display control function 56 to display a comparison screen. The display control function 56 displays each of the virtual monochromatic X-ray images and the conventional CT image on the display 42 in a manner that allows comparison. The operator selects, via the input interface 43, a virtual monochromatic X-ray image that is visually closest to the conventional CT image from among the virtual monochromatic X-ray images displayed on the display 42. The optimization function 53-3 determines, as optimized transmission lengths, the transmission length of the K-edge material, the transmission length of the material predominant in photoelectric absorption, and the transmission length of the material predominant in Compton scattering that correspond to the base virtual monochromatic X-ray image selected based on the operator's instruction in this way.

[0082] Alternatively, the optimization function 53-3 determines the virtual monochromatic X-ray image with the smallest difference by scoring the difference between each virtual monochromatic X-ray image and the normal CT image using an evaluation function, and determines the transmission length of the K-edge material, the transmission length of the material dominated by photoelectric absorption, and the transmission length of the material dominated by Compton scattering corresponding to the determined virtual monochromatic X-ray image as the optimized transmission lengths.

[0083] That is, the optimization function 53-3 optimizes the calculated transmission length of the target substance based on the comparison result between an image reconstructed based on the calculated transmission length of the target substance and an image reconstructed based on the count values ​​of all energy bins obtained by imaging the subject P.

[0084] (Optimization method 2) Optimization method 2 uses the calculated K-edge material transmission length l k The transmission length is optimized based on a comparison result between projection data (sinogram) calculated based on ^ (hat) and projection data (sinogram) acquired by imaging the subject P. Fig. 6 is a flowchart showing another example (optimization method 2) of the optimization process by the photon-counting CT apparatus 1 according to this embodiment.

[0085] First, the acquisition function 53-1 acquires actual projection data (sinogram) of each energy bin acquired by imaging the subject P (step S301).

[0086] Next, the reconstruction function 53 calculates the calculated K-edge material transmission length l k ^(hat), the transmission length l of the material that dominates photoelectric absorption ph , and the penetration length l of the material where Compton scattering is dominant co The calculation function 53-2 calculates projection data (sinogram) by forward projecting the reconstructed image (step S303).

[0087] Next, the optimization function 53-3 compares the actual projection data acquired in step S301 with the projection data calculated in step S303, and calculates the difference between them (step S305).

[0088] Next, the optimization function 53-3 determines whether the calculated difference is equal to or less than a preset threshold (step S307). If the optimization function 53-3 determines that the calculated difference is equal to or less than the threshold (step S307; YES), it determines the calculated transmission length of the K-edge material, the transmission length of the material predominant in photoelectric absorption, and the transmission length of the material predominant in Compton scattering as optimized transmission lengths (step S309).

[0089] On the other hand, if the optimization function 53-3 determines that the calculated difference is not less than the threshold value (step S307; NO), it fine-tunes (changes and resets) the transmission length of the K-edge material (step S311), returns to step S303, and repeats the subsequent processing (iteratively updates the transmission length of the K-edge material to obtain the optimal solution).

[0090] For example, in the case of the first energy bin A with an energy width of E1 to E2, the optimization function 53-3 calculates the difference (Δ) between the calculated count value and the actual detector value (count value) as shown in the following equation (9), and optimizes the difference so that it becomes smaller. k is updated iteratively.

[0091]

number

[0092] That is, the optimization function 53-3 optimizes the calculated transmission length of the target material based on the comparison result between the projection data calculated based on the calculated transmission length of the target material and the projection data acquired by imaging the subject.

[0093] 4, the reconstruction function 53 reconstructs the reference material image using the optimized and calculated transmission length of the K-edge material, the transmission length of the material predominant in photoelectric absorption, and the transmission length of the material predominant in Compton scattering, and discriminates the targeted K-edge material (step S109). This completes the processing of this flowchart.

[0094] According to the embodiment described above, the transmission length of a target material can be efficiently calculated under imaging conditions where the energy width of two energy bins located before and after the K-edge of the target material to be material decomposed is set narrower than a predetermined threshold. Narrowing the energy width offers advantages in calculating the transmission length of the K-edge material. Narrowing the energy width unifies the calibration term and attenuation due to photoelectric absorption and Compton scattering for the two energy bins. Conversely, this allows only the difference in attenuation at the K-edge to be clearly discerned. Based on this concept, a calculation flow can be implemented in which the path length of the target material (K-edge material) is first calculated, and then the path length of attenuation due to photoelectric absorption and Compton scattering is calculated. This allows for a calculation method that takes advantage of the energy window width and detection count, which have previously been considered a trade-off. This technology alleviates this trade-off and improves the discrimination accuracy of K-edge materials.

[0095] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0096] 1...photon counting CT device, 10...mounting device, 11...X-ray tube, 12...wedge, 13...collimator, 14...X-ray high voltage device, 15...X-ray detector, 16...data acquisition system, 17...rotating frame, 18...control device, 20...detector module, 30...bed device, 31...base, 32...bed driving device, 33...top plate, 34...support frame, 40...console device, 41...memory, 42...display, 43...input interface, 44...network connection circuit, 50...processing circuit, 51...system control function, 52...preprocessing function, 53...reconstruction function, 53-1...acquisition function, 53-2...calculation function, 53-3...optimization function, 54...image processing function, 55...scan control function, 56...display control function

Claims

1. 1. A medical information processing device that calculates a transmission length of a target material that is a target of material decomposition within a body of a subject, using data obtained by imaging the subject with a photon-counting CT device and an equation showing attenuation of X-rays, comprising: the formula includes a calibration term related to calibration, a photoelectric absorption term related to a material that is predominant in photoelectric absorption, a Compton scattering term related to a material that is predominant in Compton scattering, and a target material term related to the target material, The medical information processing device includes: a calculation unit that sets the two equations based on count values ​​of X-ray photons counted in each of two energy bins located before and after a K-edge of the target material under imaging conditions in which the energy width of the two energy bins located before and after the K-edge of the target material is set narrower than a predetermined threshold, and calculates the transmission length of the target material by regarding X-ray attenuation in the calibration term, the photoelectric absorption term, and the Compton scattering term as equivalent in the two set equations; Medical information processing equipment.

2. the calculation unit further sets another equation based on count values ​​of X-ray photons counted in energy bins other than the two energy bins, and calculates the transmission length of the material dominant in photoelectric absorption and the transmission length of the material dominant in Compton scattering based on the two equations, the other equation, and the calculated transmission length of the target material. The medical information processing device according to claim 1 .

3. The calculation unit calculates the transmission length of the material dominant in photoelectric absorption and the transmission length of the material dominant in Compton scattering by substituting the calculated transmission length of the target material into an equation obtained by adding the two equations together and into the other equation. The medical information processing device according to claim 2 .

4. an optimization unit that optimizes the calculated transmission length of the target substance based on the calculated transmission length of the target substance and data obtained by imaging the subject; The medical information processing device according to claim 1 .

5. the optimization unit optimizes the calculated transmission length of the target substance based on a comparison result between an image reconstructed based on the calculated transmission length of the target substance and an image reconstructed based on count values ​​of all energy bins acquired by imaging the subject. The medical information processing device according to claim 4 .

6. the optimization unit optimizes the calculated transmission length of the target material based on a comparison result between projection data calculated based on the calculated transmission length of the target material and projection data acquired by imaging the subject. The medical information processing device according to claim 4 .

7. 1. A medical information processing method for calculating a transmission length of a target material that is a target of material decomposition within a body of a subject, using data obtained by imaging the subject with a photon-counting CT device and an equation showing attenuation of X-rays, comprising: the formula includes a calibration term related to calibration, a photoelectric absorption term related to a material that is predominant in photoelectric absorption, a Compton scattering term related to a material that is predominant in Compton scattering, and a target material term related to the target material, The medical information processing method includes: the two equations are set based on count values ​​of X-ray photons counted in each of two energy bins located before and after the K-edge of the target material under imaging conditions in which the energy width of the two energy bins is set narrower than a predetermined threshold, and the transmission length of the target material is calculated by regarding the attenuation of X-rays in the calibration term, the photoelectric absorption term, and the Compton scattering term as equivalent in the two set equations; Medical information processing method.

8. A program for calculating a transmission length of a target material that is a target of material decomposition within a body of a subject, using data obtained by imaging the subject with a photon-counting CT device and an equation showing attenuation of X-rays, the program comprising: the formula includes a calibration term related to calibration, a photoelectric absorption term related to a material that is predominant in photoelectric absorption, a Compton scattering term related to a material that is predominant in Compton scattering, and a target material term related to the target material, The program is configured to: the two equations are set based on count values ​​of X-ray photons counted in each of two energy bins located before and after the K-edge of the target material under imaging conditions in which the energy width of the two energy bins is set narrower than a predetermined threshold, and the transmission length of the target material is calculated by regarding the attenuation of X-rays in the calibration term, the photoelectric absorption term, and the Compton scattering term as equivalent in the two set equations; program.

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