JP2024066111A - Medical image processing device and method - Google Patents

Abstract

To improve accuracy and efficiency of component diagnosis using virtual monochromatic energy.SOLUTION: A medical image processing device according to an embodiment comprises a setting unit, a generation unit, and a display control unit. The setting unit sets a line expressing a composition diagnosis object to a CT image on an analyte. The generation unit generates a characteristic image expressing a change in a CT value with a change in virtual monochromatic energy at each of a plurality of positions included in the line. The display control unit displays the characteristic image on a display apparatus.SELECTED DRAWING: Figure 1

Description

The embodiments disclosed in this specification and the drawings relate to medical image processing devices and methods.

Dual Energy CT and Photon Counting CT allow calculation of virtual monochromatic energy [keV]. The change in CT value associated with the change in virtual monochromatic energy allows for a diagnosis of the composition of human tissue. The change in CT value associated with the change in virtual monochromatic energy is visually perceived as a change in gradation (density or brightness) in a virtual monochromatic X-ray image associated with the change in virtual monochromatic energy. Specifically, by switching between and displaying multiple virtual monochromatic X-ray images corresponding to multiple virtual monochromatic energies in sequence, doctors who interpret images can visually grasp the change in CT value of human tissue as a change in gradation. However, accurate quantitative composition diagnosis cannot be performed through visual perception.

JP 2011-244875 A

One of the problems that the embodiments disclosed in this specification and the drawings attempt to solve is to improve the accuracy and efficiency of composition diagnosis using virtual monochromatic energy. However, the problems that the embodiments disclosed in this specification and the drawings attempt to solve are 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.

The medical image processing device according to the embodiment has a setting unit, a generating unit, and a display control unit. The setting unit sets a line representing a composition diagnosis target in a CT image of a subject. The generating unit generates a characteristic image representing a change in CT value associated with a change in virtual monochromatic energy for each of a plurality of positions included in the line. The display control unit displays the characteristic image on a display device.

FIG. 1 is a diagram showing the arrangement of an X-ray computed tomography apparatus according to this embodiment. FIG. 2 is a diagram showing a procedure for composition diagnosis using virtual monochromatic energy. FIG. 3 is a diagram showing an example of setting a line of interest. FIG. 4 is a diagram showing an example of a first characteristic image based on the line of interest shown in FIG. FIG. 5 is a diagram showing an example of a second characteristic image based on the first characteristic image shown in FIG. FIG. 6 is a diagram showing an example of an image interpretation report. FIG. 7 is a diagram showing an example of a first characteristic image according to the first modification. FIG. 8 is a diagram showing an example of a second characteristic image according to the second modification.

Below, we will explain in detail the embodiments of the medical image processing device and method with reference to the drawings.

The medical image processing device according to this embodiment is a computer that performs image processing on CT images collected by a spectral CT such as a dual energy CT or a photon counting CT. The medical image processing device may be a computer included in an X-ray computed tomography device, or may be a computer independent of the X-ray computed tomography device such as an image processing server or an image viewer, or may be any computer capable of image processing. For the purposes of the following explanation, the medical image processing device according to this embodiment is assumed to be a computer included in an X-ray computed tomography device.

The X-ray computed tomography apparatus according to this embodiment is available in various types, such as third-generation CT and fourth-generation CT, and any of these types can be applied to this embodiment. Here, the third-generation CT is a rotate/rotate type in which the X-ray tube and detector rotate around the subject as a unit. The fourth-generation CT is a stationary/rotate type in which a large number of X-ray detection elements arrayed in a ring shape are fixed and only the X-ray tube rotates around the subject. In addition, the X-ray computed tomography apparatus according to this embodiment can be applied to a single-tube type in which one pair of an X-ray tube and a detector is mounted on a rotating ring, or a multi-tube type in which multiple pairs of an X-ray tube and a detector are mounted on a rotating ring, but in the following explanation, it is assumed to be a single-tube type.

The X-ray computed tomography apparatus according to this embodiment performs spectral CT. Spectral CT according to this embodiment includes dual energy CT and photon counting CT. For the purposes of the following description, the X-ray computed tomography apparatus according to this embodiment performs dual energy CT.

Figure 1 is a diagram showing the configuration of an X-ray computed tomography apparatus 1 according to this embodiment. The X-ray computed tomography apparatus 1 irradiates X-rays from an X-ray tube 11 to a subject P, and detects the irradiated X-rays with an X-ray detector 12. The X-ray computed tomography apparatus 1 generates a CT image of the subject P based on the output from the X-ray detector 12.

As shown in FIG. 1, the X-ray computed tomography apparatus 1 has a gantry 10, a bed 30, and a console 40. For convenience of explanation, the gantry 10 is illustrated in multiple places in FIG. 1, but the number of gantry 10 mounted on the X-ray computed tomography apparatus 1 may be one or multiple. The gantry 10 is a scanning device having a configuration for X-ray CT imaging of the subject P. The bed 30 is a transport device for placing the subject P to be subjected to X-ray CT imaging and positioning the subject P. The console 40 is a computer that controls the gantry 10. For example, the gantry 10 and the bed 30 are installed in a CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The gantry 10, the bed 30, and the console 40 are connected to each other by wire or wirelessly so that they can communicate with each other. The console 40 does not necessarily have to be installed in the control room. For example, the console 40 may be installed in the same room as the gantry 10 and the bed 30. The console 40 may also be incorporated into the gantry 10. The console 40 is an example of a medical image processing device.

As shown in FIG. 1, the gantry 10 has an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a data acquisition circuit (DAS: Data Acquisition System) 18.

The X-ray tube 11 irradiates the subject P with X-rays. Specifically, the X-ray tube 11 includes a cathode that generates thermoelectrons, an anode that receives thermoelectrons flying from the cathode and generates X-rays, and a vacuum tube that holds the cathode and anode. The X-ray tube 11 is connected to the X-ray high voltage device 14 via a high-voltage cable. A tube voltage is applied between the cathode and the anode by the X-ray high voltage device 14. Thermoelectrons fly from the cathode to the anode due to the application of the tube voltage. Thermoelectrons fly from the cathode to the anode, causing a tube current to flow. Thermoelectrons fly from the cathode (filament) to the anode (target) due to the application of high voltage and the supply of filament current from the X-ray high voltage device 14, and X-rays are generated when the thermoelectrons collide with the anode. For example, the X-ray tube 11 includes a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

The hardware that generates X-rays is not limited to the X-ray tube 11. For example, instead of the X-ray tube 11, X-rays may be generated using a fifth-generation system. The fifth-generation system includes a focus coil that focuses the electron beam generated from the electron gun, a deflection coil that electromagnetically deflects the beam, and a target ring that surrounds half of the subject P and generates X-rays when the deflected electron beam collides with the target ring.

The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passing through the subject P, and outputs an electrical signal corresponding to the detected X-ray dose to the data acquisition circuit 18. The X-ray detector 12 has a structure in which multiple X-ray detection element rows, each of which has multiple X-ray detection elements arranged in the channel direction, are arranged in the slice direction (row direction). The X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and an optical sensor array. The scintillator array has multiple scintillators. The scintillator outputs a light amount corresponding to the amount of incident X-ray. The grid is arranged on the X-ray incidence surface side of the scintillator array, and has an X-ray shielding plate that absorbs scattered X-rays. The grid may also be called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array converts the light from the scintillator into an electrical signal corresponding to the amount of light. For example, a photodiode is used as the optical sensor. The X-ray detector 12 may be a direct conversion type detector.

The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so that they can rotate around a rotation axis (Z-axis). Specifically, the rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 facing each other. The rotating frame 13 is supported by a fixed frame (not shown) so that it can rotate around the rotation axis. The control device 15 rotates the rotating frame 13 around the rotation axis, thereby rotating the X-ray tube 11 and the X-ray detector 12 around the rotation axis. The rotating frame 13 receives power from a drive mechanism of the control device 15 and rotates around the rotation axis at a constant angular velocity. An image field of view (FOV) is set in an opening 19 of the rotating frame 13.

In this embodiment, the rotation axis of the rotating frame 13 in the non-tilted state or the longitudinal direction of the top plate 33 of the bed 30 is defined as the Z-axis direction, the axis direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction, and the axis direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

The X-ray high voltage device 14 has a high voltage generator and an X-ray control device. The high voltage generator has electrical circuits such as a transformer and a rectifier, and generates a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11. The X-ray control device controls the output voltage according to the X-rays emitted by the X-ray tube 11. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 in the gantry 10, or on a fixed frame (not shown) in the gantry 10.

The wedge 16 adjusts the dose of X-rays irradiated to the subject P. Specifically, the wedge 16 attenuates the X-rays so that the dose of X-rays irradiated from the X-ray tube 11 to the subject P has a predetermined distribution. For example, a metal plate such as aluminum, such as a wedge filter or bow-tie filter, is used as the wedge 16.

The collimator 17 limits the irradiation range of the X-rays that have passed through the wedge 16. The collimator 17 slidably supports multiple lead plates that block X-rays, and adjusts the shape of the slits formed by the multiple lead plates. The collimator 17 is sometimes called an X-ray aperture.

The data collection circuitry 18 reads out an electrical signal from the X-ray detector 12 that corresponds to the X-ray dose detected by the X-ray detector 12. The data collection circuitry 18 amplifies the read electrical signal and integrates the electrical signal over a view period to collect projection data having a digital value that corresponds to the X-ray dose over the view period. The data collection circuitry 18 is realized, for example, by an application specific integrated circuit (ASIC) equipped with circuit elements capable of generating projection data. The digital data is transmitted to the console 40 via a non-contact data transmission device or the like.

The control device 15 controls the X-ray high voltage device 14 and the data acquisition circuit 18 to perform X-ray CT imaging according to the imaging control function 441 of the processing circuit 44 of the console 40. The control device 15 has a processing circuit having a CPU (Central Processing Unit) or MPU (Micro Processing Unit), etc., and a driving mechanism such as a motor and an actuator. The processing circuit has a processor such as a CPU and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory) as hardware resources. The control device 15 may also be realized by an ASIC or a Field Programmable Gate Array (FPGA). The control device 15 may also be realized by another Complex Programmable Logic Device (CPLD) or Simple Programmable Logic Device (SPLD). The control device 15 has a function of receiving an input signal from an input interface 43 (described later) attached to the console 40 or the gantry 10 and controlling the operation of the gantry 10 and the bed 30. For example, the control device 15 receives an input signal and performs control to rotate the rotating frame 13, control to tilt the gantry 10, and control to operate the bed 30 and the tabletop 33. Note that the control to tilt the gantry 10 is realized by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on inclination angle (tilt angle) information input by an input interface attached to the gantry 10. Note that the control device 15 may be provided in the gantry 10 or in the console 40.

The bed 30 comprises a base 31, a support frame 32, a top plate 33, and a bed drive device 34. The base 31 is placed on the floor surface. The base 31 is a housing that supports the support frame 32 so that it can move vertically (Y-axis direction) relative to the floor surface. The support frame 32 is a frame provided on the upper part of the base 31. The support frame 32 supports the top plate 33 so that it can slide along the rotation axis (Z-axis). The top plate 33 is a flexible plate on which the subject P is placed.

The bed drive device 34 is housed within the housing of the bed 30. The bed drive device 34 is a motor or actuator that generates power to move the support frame 32 on which the subject P is placed and the tabletop 33. The bed drive device 34 operates under the control of the console 40, etc.

The console 40 has a memory 41, a display 42, an input interface 43, and a processing circuit 44. Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via a bus. Note that although the console 40 is described as being separate from the gantry 10, the gantry 10 may include the console 40 or some of the components of the console 40.

The memory 41 is a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit storage device that stores various information. The memory 41 stores, for example, projection data and reconstructed image data. In addition to an HDD or SSD, the memory 41 may be a portable storage medium such as a CD (Compact Disc), DVD (Digital Versatile Disc), or flash memory. The memory 41 may be a drive device that reads and writes various information between the memory 41 and a semiconductor memory element such as a flash memory or a RAM (Random Access Memory). The storage area of the memory 41 may be in the X-ray computed tomography apparatus 1 or in an external storage device connected via a network. The memory 41 stores a database, which will be described later.

The display 42 displays various information. For example, the display 42 outputs CT images generated by the processing circuit 44, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. As the display 42, various arbitrary displays can be used as appropriate. For example, as the display 42, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OELD), or a plasma display can be used. The display 42 may also be provided on the stand 10. The display 42 may also be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the console 40 main body.

The input interface 43 accepts various input operations from the operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuit 44. For example, the input interface 43 accepts from the operator the collection conditions for collecting projection data, the reconstruction conditions for reconstructing CT images, and the image processing conditions for generating post-processed images from CT images. As the input interface 43, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, a touch panel display, and the like can be used as appropriate. In this embodiment, the input interface 43 is not limited to one having physical operation parts such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, and a touch panel display. For example, 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 the electrical signal to the processing circuit 44 is also included as an example of the input interface 43. The input interface 43 may also be provided on the pedestal 10. The input interface 43 may also be configured as a tablet terminal or the like capable of wireless communication with the console 40 main body.

The processing circuit 44 controls the operation of the entire X-ray computed tomography apparatus 1 in response to the electrical signals of the input operations output from the input interface 43. The processing circuit 44 generates image data based on the electrical signals output from the X-ray detector 12. For example, the processing circuit 44 has a processor such as a CPU, MPU, or GPU, and a memory such as a ROM or RAM, as hardware resources. The processing circuit 44 executes an imaging control function 441, a reconstruction function 442, a setting function 443, a characteristic image generation function 444, a display control function 445, and a pasting function 446, etc., by a processor that executes a program expanded in the memory. Each of the functions 441 to 446 is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each of the functions 441 to 446.

In the imaging control function 441, the processing circuitry 44 controls the X-ray high voltage device 14, the control device 15, and the data acquisition circuitry 18 to perform a dual energy CT scan on the subject P. In a dual energy CT scan, the X-ray high voltage device 14 alternately applies a first tube voltage and a second tube voltage lower than the first tube voltage to the X-ray tube 11, and the data acquisition circuitry 18 alternately acquires projection data corresponding to the first tube voltage and projection data corresponding to the second tube voltage. Here, the first tube voltage is called the high tube voltage, and the second tube voltage is called the low tube voltage.

In the reconstruction function 442, the processing circuitry 44 generates a CT image of the subject P based on the projection data output from the data acquisition circuitry 18. The CT image represents the spatial distribution of CT values that evaluate the attenuation coefficient of the substance contained in each pixel. The processing circuitry 44 converts the CT image into a cross-sectional image of an arbitrary cross section or a rendering image of an arbitrary viewpoint direction. The conversion is performed based on an input operation received from the operator via the input interface 43. For example, the processing circuitry 44 performs three-dimensional image processing such as volume rendering, surface volume rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing on the CT image to generate rendering image data of an arbitrary viewpoint direction.

In dual energy CT, various CT images can be generated. For example, the processing circuitry 44 can generate a CT image corresponding to a high tube voltage based on projection data when a high tube voltage is applied, and generate a CT image corresponding to a low tube voltage based on projection data when a low tube voltage is applied. These CT images are CT images collected by imaging with polychromatic X-rays having an energy spectrum with an X-ray photon energy corresponding to the tube voltage value at its approximate maximum value, and are also called polychromatic X-ray images. In addition, the processing circuitry 44 generates a virtual monochromatic X-ray image relating to any virtual monochromatic energy based on projection data when a high tube voltage is applied and projection data when a low tube voltage is applied. A virtual monochromatic X-ray image is a CT image that can be collected by imaging with monochromatic X-rays having any single X-ray photon energy (virtual monochromatic energy). The virtual monochromatic energy means a single X-ray photon energy assumed by a virtual monochromatic X-ray image.

The procedure for generating a virtual monochromatic X-ray image is, for example, as follows. First, the processing circuitry 44 generates a first reference material image representing the spatial distribution of the density value of the first reference material, a second reference material image representing the spatial distribution of the density value of the second reference material, and a third reference material image representing the spatial distribution of the density value of the third reference material based on the projection data when a high tube voltage is applied and the projection data when a low tube voltage is applied. Next, the processing circuitry 44 acquires the attenuation coefficients of the first reference material, the second reference material, and the third reference material in the virtual monochromatic energy to be generated. A table in which the attenuation coefficients of the first reference material, the second reference material, and the third reference material for each virtual monochromatic energy are registered is stored in advance in the memory 41 or the like. When the virtual monochromatic energy to be generated is set, the processing circuitry 44 reads out the attenuation coefficients of the first reference material, the second reference material, and the third reference material corresponding to the virtual monochromatic energy from the table. The processing circuit 44 then generates a virtual monochromatic X-ray image corresponding to the virtual monochromatic energy to be generated based on the attenuation coefficients of the first reference material, the second reference material, and the third reference material corresponding to the read virtual monochromatic energy, and the first reference material image, the second reference material image, and the third reference material image. A combination of the first reference material, the second reference material, and the third reference material is called a reference material pair. The types of the first reference material, the second reference material, and the third reference material are not particularly limited, but in the following embodiment, it is assumed that the first reference material is fat, the second reference material is soft tissue, and the third reference material is iodine.

In the setting function 443, the processing circuitry 44 sets a line representing the composition diagnosis target in the CT image generated by the reconstruction function 442. The line representing the composition diagnosis target is called a line of interest. The line of interest is a straight line or a curved line. The CT image in which the line of interest is set may be a polychromatic X-ray image or a virtual monochromatic X-ray image.

In the characteristic image generating function 444, the processing circuit 44 generates a characteristic image showing the change in CT value associated with the change in virtual monochromatic energy for each of the multiple positions included in the line of interest set by the setting function 443. The characteristic image includes a first characteristic image and a second characteristic image. The first characteristic image is a two-dimensional image in which the first axis is defined as the virtual monochromatic energy and the second axis is defined as a position on the line of interest. Each pixel of the first characteristic image is assigned a virtual monochromatic CT value, or a gradation value or color value corresponding to the virtual monochromatic CT value. The virtual monochromatic CT value means the CT value assigned to the virtual monochromatic X-ray image. The second characteristic image is a two-dimensional image including multiple CT value change curves corresponding to multiple positions on the line of interest. Each of the multiple CT value change curves is drawn on a graph in which the first axis is defined as the virtual monochromatic energy and the second axis is defined as the virtual monochromatic CT value.

In the display control function 445, the processing circuitry 44 displays various information on the display 42. As an example, the processing circuitry 44 displays CT images such as polychromatic X-ray images and virtual monochromatic X-ray images, and characteristic images such as a first characteristic image and a second characteristic image.

In the pasting function 446, the processing circuitry 44 pastes the characteristic image generated by the characteristic image generating function 444 onto the image interpretation report for the subject P. The pasted characteristic image is the first characteristic image and/or the second characteristic image.

Below, we will explain an example of the operation of the medical image processing device 40 for composition diagnosis using virtual monochromatic energy.

Figure 2 is a diagram showing the processing procedure for composition diagnosis using virtual monochromatic energy. Before the start of the processing in Figure 2, a dual energy CT scan is performed on the subject P by the imaging control function 441, projection data when a high tube voltage is applied and projection data when a low tube voltage is applied are collected, and a CT image of the diagnostic cross section is generated by the reconstruction function 442. A dual energy CT scan is performed on the subject P into which iodine has been injected. The iodine is labeled with a drug that specifically accumulates in malignant tumors. In other words, there is a positive correlation between the concentration of iodine accumulation and the probability of a malignant tumor.

2, the processing circuitry 44 displays a CT image of a diagnostic target section by implementing the display control function 445 (step S1). The diagnostic target section may be set to a section including a target organ for composition diagnosis. As an example, the diagnostic target section may be set according to an instruction from an operator via the input interface 43. The operator is assumed to be a medical professional such as a radiologist. As another example, the diagnostic target section may be set according to a predetermined algorithm by extracting a target organ from a three-dimensional CT image (volume data) generated by the reconstruction function 442 by arbitrary image processing, and an arbitrary section including the extracted target organ may be set. As the CT images to be displayed, a polychromatic X-ray image corresponding to a high tube voltage, a polychromatic X-ray image corresponding to a low tube voltage, a fat density image which is a reference material image representing the spatial distribution of the density value of fat as a first reference material, a soft tissue density image which is a reference material image representing the spatial distribution of the density value of soft tissue as a second reference material, an iodine density image which is a reference material image representing the spatial distribution of the density value of iodine as a third reference material, a virtual monochromatic X-ray image relating to an arbitrary virtual monochromatic energy, etc. may be displayed. In the case of the liver, the soft tissue corresponds to the liver parenchyma. The type of CT image to be displayed may be selected by the operator via the input interface 43. The processing circuitry 44 displays the CT image on the display 42.

When step S1 is performed, the processing circuitry 44 sets a line of interest in the CT image by implementing the setting function 443 (step S2). The line of interest is set as the target for composition diagnosis.

Figure 3 is a diagram showing an example of setting the line of interest I13. As shown in Figure 3, an image region of a target organ (hereafter, target organ region) I11 is drawn on a CT image I1. The target organ region includes an image region of a target site for composition diagnosis (hereafter, target site region) I12. The target organ is not particularly limited, but is assumed to be the liver. In addition, the target site is assumed to be a tumor occurring in the liver parenchyma.

The processing circuit 44 sets a line of interest I13 so that it passes through the target area I12. The line of interest I13 is set as a straight line connecting the starting point PS and the ending point PE. The line of interest I13 may be set manually by the operator via the input interface 43, or may be set automatically by image processing. The width of the line of interest is set to one pixel. The line of interest I13 is not limited to a straight line, and may be a curved line. If it is a curved line, it may be a closed curve or an open curve. The above various setting parameters related to the line of interest can be arbitrarily set by the operator via the input interface 43.

The line of interest I13 includes multiple positions. As an example, the positions refer to anatomically divided regions. As shown in FIG. 3, the line of interest I13 includes positions RA, RB, and RC. Position RA corresponds to an image region outside the target organ. Position RB corresponds to the hepatic parenchyma of the liver, which is the target organ. Position RC corresponds to a tumor, which is a target site of composition diagnosis in the target organ.

When step S2 is performed, the processing circuitry 44 generates a first characteristic image by implementing the characteristic image generation function 444 (step S3). The first characteristic image represents the distribution of virtual monochromatic CT values in a two-dimensional plane defined by the line of interest axis and the virtual monochromatic energy axis. The processing circuitry 44 generates the first characteristic image based on the line of interest set in step S2 and multiple virtual monochromatic X-ray images that respectively correspond to multiple virtual monochromatic energies related to the subject P.

Figure 4 is a diagram showing an example of a first characteristic image I2 based on the line of interest I13 shown in Figure 3. As shown in Figure 4, the first characteristic image I2 is a two-dimensional image whose horizontal axis is defined as the virtual monochromatic energy [keV] and whose vertical axis is defined as the position on the line of interest, and each pixel is assigned a virtual monochromatic CT value, or a gradation value or color value corresponding to the virtual monochromatic CT value. As an example, the lower end of the first characteristic image II2 is set to the starting point PS of the line of interest I13, and the upper end is set to the end point PE of the line of interest I13.

The procedure for generating the first characteristic image I2 is, for example, as follows. First, the processing circuitry 44 prepares a template map for the first characteristic image I2. A virtual monochromatic CT value is not assigned to each pixel of the template map. The number of pixels on the vertical axis of the template map (first characteristic image I2) is, for example, proportional to the number of pixels constituting the line of interest. Next, the processing circuitry 44 identifies the virtual monochromatic CT value of the same position in the multiple virtual monochromatic X-ray images for each position of the line of interest I13. When multiple pixels are included in each position, the average, maximum, minimum, intermediate, or other statistical value of the virtual monochromatic CT values of the multiple pixels is characterized as the virtual monochromatic CT value of the position. Then, the processing circuitry 44 assigns the identified virtual monochromatic CT value to the corresponding pixel in the template map. This generates the first characteristic image I12. In order to display the first characteristic image, in addition to the virtual monochromatic CT value, each pixel may be assigned a gradation (density) corresponding to the virtual monochromatic CT value.

The number of pixels on the vertical axis of the first characteristic image I2 does not need to be proportional to the number of pixels along the line of interest I13. In other words, the number of pixels on the vertical axis (trace width) of the image area in the first characteristic image I2 corresponding to one position on the line of interest I13 can be set to any number of pixels. For example, even if the length of each position on the line of interest I13 (the number of pixels along the line of interest I13) is different, the trace width of each position in the first characteristic image I2 may be standardized to the same width.

As shown in FIG. 4, the first characteristic image I2 can represent the change in the virtual monochromatic CT value associated with the change in virtual monochromatic energy at each position on the line of interest. Specifically, for position RA on the line of interest, the virtual monochromatic CT value is constant regardless of the change in virtual monochromatic energy. For position RB on the line of interest, the virtual monochromatic CT value decreases as the virtual monochromatic energy increases, but the rate of decrease gradually becomes gentler. For position RC on the line of interest, the virtual monochromatic CT value increases as the virtual monochromatic energy decreases. The change in the virtual monochromatic CT value associated with the change in virtual monochromatic energy for each substance is known as empirical knowledge. Therefore, an operator, etc. can estimate the substance present at each position on the line of interest by observing the first characteristic image I2.

When step S3 is performed, the processing circuitry 44 generates a second characteristic image by implementing the characteristic image generation function 444 (step S4). The second characteristic image is a graph of the virtual monochromatic CT value associated with the change in virtual monochromatic energy for each position on the line of interest. The processing circuitry 44 generates the second characteristic image based on the first characteristic image generated in step S3.

Figure 5 is a diagram showing an example of a second characteristic image I3 based on the first characteristic image I2 shown in Figure 4. As shown in Figure 5, the second characteristic image I3 is a two-dimensional image representing a plurality of CT value change curves respectively corresponding to a plurality of positions on the line of interest. Each of the plurality of CT value change curves is drawn on a graph whose horizontal axis is defined as the virtual monochromatic energy [keV] and whose second axis is defined as the virtual monochromatic CT value. Note that in Figure 5, a CT value curve corresponding to position RB and a CT value change curve corresponding to position RC are drawn.

The procedure for generating the second characteristic image I3 is, for example, as follows. First, the processing circuit 44 reads out a graph in which the first axis is defined as the virtual monochromatic energy and the second axis is defined as the virtual monochromatic CT value. A CT value change curve has not yet been assigned to the graph. Next, the processing circuit 44 identifies the virtual monochromatic CT value for each virtual monochromatic energy for each position in the first characteristic image. Then, the processing circuit 44 assigns the identified virtual monochromatic CT value for each virtual monochromatic energy to the graph. The second characteristic image I3 is generated. Note that the CT value change curve may be a curve that has been subjected to moving average processing with respect to the virtual monochromatic energy axis.

As shown in FIG. 5, the second characteristic image I3 can graphically represent CT value change curves associated with changes in virtual monochromatic X-ray energy corresponding to each position on the line of interest. Specifically, the CT value change curve at position RB represents a decrease in the virtual monochromatic CT value as the virtual monochromatic energy increases, and the CT value change curve at position RC represents an increase in the virtual monochromatic CT value as the virtual monochromatic energy decreases. Therefore, by observing the second characteristic image I3, an operator or the like can estimate the substance present at each position on the line of interest.

Compared to the first characteristic image, the second characteristic image is in a graph format, so it is possible to intuitively grasp the change in virtual monochromatic CT value associated with the change in virtual monochromatic X-ray energy. On the other hand, compared to the second characteristic image, the first characteristic image is a two-dimensional image defined by the line of interest axis and the virtual monochromatic energy axis, so it is possible to grasp the change in virtual monochromatic CT value associated with the change in virtual monochromatic X-ray energy, as well as the spatial relationship between each position of interest.

When step S4 is performed, the processing circuitry 44 displays the first characteristic image and the second characteristic image by implementing the display control function 445 (step S5). In step S5, the processing circuitry 44 displays the first characteristic image and the second characteristic image on the display 42. The processing circuitry 44 may display the first characteristic image and the second characteristic image side by side, or may display them one by one in sequence. Displaying the first characteristic image and the second characteristic image enables composition diagnosis using virtual monochromatic energy. In addition to the first characteristic image and the second characteristic image, the processing circuitry 44 may display a CT image on which a line of interest is drawn. Furthermore, the processing circuitry 44 may display only one of the first characteristic image and the second characteristic image.

According to this embodiment, by simply displaying the first characteristic image and/or the second characteristic image, the change in CT value associated with the change in virtual monochromatic energy of the target area on the line of interest can be visually grasped. Therefore, according to this embodiment, the operator's time and effort in diagnosing the composition of the target area can be reduced compared to image scrolling, which switches between and displays multiple virtual monochromatic X-ray images corresponding to multiple virtual monochromatic energies in sequence.

When step S5 is performed, the processing circuitry 44 pastes the first characteristic image and the second characteristic image into the image interpretation report by implementing the pasting function 446 (step S6). It is assumed that the image interpretation report is created for the target area for composition diagnosis. The image interpretation report is displayed on the display 42 by implementing the display control function 445 by the processing circuitry 44.

Figure 6 is a diagram showing an example of an image interpretation report I4. As shown in Figure 6, image interpretation report I4 includes a CT image I41 and a findings section I42. A representative image that is determined to be effective for interpretation of the target area is selected as the CT image I41. As an example, a CT image I41 is assumed in which the liver, which is the target organ, and the tumor, which is the target area, are depicted, as in Figure 3. Findings are input by an operator or the like and displayed in the findings section I42. As an example, a finding statement regarding the target area, such as "suspected cancer in the liver," is input and displayed.

As shown in FIG. 6, the CT image I43 in which the line of interest was set in step S2, the first characteristic image I44 generated in step S3, and the second characteristic image I45 generated in step S4 are attached to the image interpretation report I4. The CT image I43, the first characteristic image I44, and the second characteristic image I45 may be attached via an instruction from an operator or the like via the input interface 43. The attached CT image I43, the first characteristic image I44, and the second characteristic image I45 are displayed on the image interpretation report I4. By attaching the CT image I43, the first characteristic image I44, and the second characteristic image I45 to the image interpretation report I4, they function as the basis for the findings, improving the reliability of the image interpretation report I4 and making it easier to store the measurement results.

It is not necessary for all of the CT image I43, the first characteristic image I44, and the second characteristic image I45 to be attached to the image reading report I4; it is sufficient for either the first characteristic image I44 or the second characteristic image I45 to be attached. Also, instead of displaying the first characteristic image I44 and/or the second characteristic image I45 in step S5, the image reading report I4 to which the CT image I43, the first characteristic image I44, and the second characteristic image I45 have been attached may be displayed. Also, the attachment process in step S6 does not need to be performed in cases where an image reading report is not created, etc.

Once step S6 is performed, the composition diagnosis according to this embodiment is completed.

The composition diagnosis shown in FIG. 2 is an example, and various additions, modifications, and/or deletions are possible without changing the gist of this embodiment.

(Variation 1)
The first characteristic image according to the first modification expresses that, for each of a plurality of positions included in the line of interest, a change in the virtual monochromatic CT value is positively correlated or negatively correlated with a change in the virtual monochromatic energy. Hereinafter, the first modification will be described.

7 is a diagram showing an example of the first characteristic image I5 according to the first modification. As shown in FIG. 7, the first characteristic image I5 is a two-dimensional image in which the horizontal axis is defined as the virtual monochromatic energy [keV] and the vertical axis is defined as the position on the line of interest, and each pixel is assigned the difference between each virtual monochromatic CT value and the virtual monochromatic CT value corresponding to the reference value I50 of the virtual monochromatic energy, or the gradation value or color value corresponding to the difference. The virtual monochromatic energy characteristic of the first characteristic image I5 is assumed to be the same as the virtual monochromatic energy characteristic of the first characteristic image I2 shown in FIG. The reference value I50 may be set to any virtual monochromatic energy, but as an example, it is preferable to set it from 20 keV to 160 keV, which is highly usable in clinical practice. In this embodiment, it is assumed that the reference value I50 is set to 40 keV. A difference equal to or greater than the threshold and a positive value means that there is a positive correlation between the change in virtual monochromatic CT value and the change in virtual monochromatic energy, and a difference equal to or greater than the threshold and a negative value means that there is a negative correlation between the change in virtual monochromatic CT value and the change in virtual monochromatic energy. A difference less than the threshold means that there is no correlation between the change in virtual monochromatic CT value and the change in virtual monochromatic energy.

The processing circuit 44 visually distinguishes between pixels with positive correlation and pixels with negative correlation. Specifically, pixels with positive correlation are assigned a color value, for example, blue, and pixels with negative correlation are assigned a color value different from the color value assigned to pixels with positive correlation, for example, red. Pixels with no correlation may be assigned a color value different from the color values assigned to pixels with positive correlation and pixels with negative correlation, for example, gray. Color values may also be set so that the color becomes darker according to the difference value. For example, image regions I51 and I53 below the reference value I50 at position RB are negatively correlated and displayed in red, as can be seen by comparing with the CT change curve at position RB in FIG. 5, and image regions I52 and I54 above the reference value I50 are uncorrelated and displayed in gray. Image region I55 at position RC is positively correlated and displayed in blue, as can be seen by comparing with the CT change curve at position RC in FIG. 5.

In this way, according to the first modification, the amount of change in the virtual monochromatic CT value is color coded. This allows the operator to easily grasp the correlation of the changes in the virtual monochromatic CT value by color. In addition, since the amount of change in the virtual monochromatic CT value is color coded, it is possible to distinguish the composition of tissues by color. For example, in a liver composition diagnosis, it is clear that the part displayed in red is iodine, i.e., a tumor, and the part displayed in blue is fat. Furthermore, by providing not only positive correlation and negative correlation, but also uncorrelated areas, it is possible to focus on the parts with strong correlation. It is also possible to determine the composition of the part that belongs to the uncorrelated area, for example, that it is liver parenchyma.

(Variation 2)
The second characteristic image according to the second modification includes a standard CT value change curve of a healthy subject for the target organ in addition to a plurality of CT value change curves respectively corresponding to a plurality of positions included in the line of interest.

8 is a diagram showing an example of the second characteristic image I6 according to the second modification. As shown in FIG. 8, in addition to the CT value change curve at the position RB and the CT value change curve at the position RC, the second characteristic image I6 displays the CT value change curve of the liver parenchyma, which is the soft tissue of the liver, which is the target organ of the healthy person. The memory 41 stores a plurality of CT value change curves corresponding to a plurality of parts of the healthy person that have been collected in advance, and the processing circuit 44 can select and display the CT value change curve of the healthy person for any part according to an instruction by an operator or the like via the input interface 43. The CT value change curve of the healthy person to be displayed is not limited to one part, and CT value change curves for two or more parts may be displayed. In this way, by displaying the CT value change curve of the healthy person in addition to the CT value change curve of the subject, it becomes possible to compare the target organ or target part with that of the healthy person.

(Variation 3)
In the above embodiment, the width of the line of interest is one pixel. The width of the line of interest in the first modification is set to multiple pixels. In this case, each pixel of the first characteristic image may be assigned a statistical value such as a maximum value, a minimum value, an average value, or a median value of multiple virtual monochromatic CT values assigned to multiple pixels in the width direction of the line of interest. This makes it possible to reduce noise. The width may be set to a constant value regardless of the position of the line of interest, or may be set to a different width depending on the position. The width of the line of interest may also be set depending on the type and/or size of the target organ or target site.

(Variation 4)
In the above embodiment, each position on the line of interest is an anatomically divided region. However, this embodiment is not limited to this. Each position on the line of interest according to the fourth modification may correspond to one pixel or multiple pixels that constitute the line of interest.

(Variation 5)
In the above embodiment, the reference material pair is three types, namely, fat, soft tissue, and iodine, but the present embodiment is not limited to this. The reference material pair may be two types, for example, water and iodine. It is known that a virtual monochromatic X-ray image corresponding to any virtual monochromatic energy can be generated from two types of reference material images.

(Variation 6)
Although the above embodiment has been described using liver cancer as a clinical example, the present embodiment can be applied to any other disease. For example, the present embodiment may be applied to diagnosing the degree of gout. In diagnosing the degree of gout, uric acid and calcium may be set as the reference substances. The first characteristic image and/or the second characteristic image may be generated by a method similar to that of the above embodiment. It is expected that the degree of gout can be grasped by observing the change in CT value associated with the change in virtual monochromatic energy in the first characteristic image or the second characteristic image.

(Variation 7)
The spectral CT according to the above embodiment is a dual energy CT. However, this embodiment is not limited to this. The spectral CT according to the seventh modification is a photon counting CT. The seventh modification will be described below.

In photon-counting CT, X-rays are irradiated with one arbitrary tube voltage. A photon-counting type X-ray detector is used as the X-ray detector 12. The DAS 18 collects data of count values of X-ray photons corresponding to multiple energy bins as projection data for each view. The energy bin represents the energy band of X-ray photons incident on each detection element of the X-ray detector 12, and corresponds to virtual monochromatic energy. The processing circuitry 44 reconstructs multiple virtual monochromatic X-ray images corresponding to multiple energy bins based on multiple projection data corresponding to multiple energy bins by implementing the reconstruction function 442. The processing circuitry 44 can also generate one projection data for the entire energy band based on multiple projection data corresponding to multiple energy bins, and generate a polychromatic X-ray image based on the projection data.

As in the above embodiment, a line of interest is set for a polychromatic X-ray image or a virtual monochromatic X-ray image, and a first characteristic image and/or a second characteristic image is generated based on a plurality of virtual monochromatic X-ray images corresponding to a plurality of energy bins, respectively. The process of setting the line of interest by the setting function 443, the process of generating characteristic images by the characteristic image generating function 444, the display process by the display control function 445, and the process of pasting by the pasting function 446 are the same as in the above embodiment, and therefore will not be described.

(Summary)
The medical image processing apparatus according to this embodiment includes a processing circuitry 44. The processing circuitry 44 sets a line of interest representing a composition diagnosis target in a CT image relating to a subject by implementing a setting function 443. The processing circuitry 44 generates a characteristic image representing a change in CT value associated with a change in virtual monochromatic energy for each of a plurality of positions included in the line of interest by implementing a characteristic image generation function 444. The processing circuitry 44 displays the characteristic image on the display 42 by implementing a display control function 445.

According to the above configuration, by observing the characteristic image, it is possible to visually evaluate the virtual monochromatic energy characteristics for the line of interest set in the CT image. This improves the accuracy and efficiency of composition diagnosis compared to the case of image forwarding.

Here, this embodiment is compared with a comparative example in which virtual monochromatic energy characteristics within an image region (ROI) surrounded by a closed curve are evaluated. In the comparative example, the operator needs to set the position and size of the ROI to a constant value in order to perform a quantitative evaluation, but this is difficult. Since the ROI must have a certain size, it is not possible to set the ROI only on the minute object, and the ROI includes the minute object and its surrounding tissue. Therefore, only the virtual monochromatic energy characteristics averaged between the minute object and the surrounding tissue can be evaluated, and the virtual monochromatic energy characteristics of the minute object cannot be accurately evaluated. In addition, since the ROI cannot be set only on the boundary portion, the virtual monochromatic energy characteristics of the boundary portion cannot be accurately evaluated. Compared to the comparative example, according to this embodiment, a straight or curved line of interest is set on the CT image, so there is no need to adjust the size, and it is expected that the quantitativeness will be superior. In addition, since it is sufficient to set the line of interest so that it intersects with the minute object, it is possible to accurately evaluate the virtual monochromatic energy characteristics of the minute object compared to the comparative example. In addition, by setting the line of interest so that it intersects or overlaps the boundary, it becomes possible to more accurately evaluate the virtual monochromatic energy characteristics of the boundary compared to the comparative example.

According to at least one of the embodiments described above, it is possible to improve the accuracy and efficiency of composition diagnosis using virtual monochromatic energy.

The term "processor" used in the above description means, for example, a CPU, a GPU, or an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)), and other circuits. The processor realizes its function by reading and executing a program stored in a memory circuit. Instead of storing a program in a memory circuit, the processor may be configured to directly incorporate the program into the circuit. In this case, the processor realizes its function by reading and executing a program incorporated in the circuit. On the other hand, when the processor is, for example, an ASIC, instead of storing the program in a memory circuit, the function is directly incorporated as a logic circuit in the processor circuit. In addition, each processor in this embodiment is not limited to being configured as a single circuit for each processor, and may be configured as a single processor by combining multiple independent circuits to realize its function. Furthermore, multiple components in FIG. 1 may be integrated into a single processor to achieve the functions.

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, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1 X-ray computed tomography apparatus 10 Stand 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 Data acquisition circuit (DAS: Data Acquisition System)
19 Opening 30 Bed 31 Base 32 Support frame 33 Top plate 34 Bed driving device 40 Medical image processing device (console)
41 Memory 42 Display 43 Input interface 44 Processing circuit 441 Shooting control function 442 Reconstruction function 443 Setting function 444 Characteristic image generation function 445 Display control function 446 Pasting function

Claims (13)

A setting unit that sets a line representing a composition diagnosis target on a CT image of a subject;
a generating unit that generates a characteristic image representing a change in CT value associated with a change in virtual monochromatic energy for each of a plurality of positions included in the line;
a display control unit that displays the characteristic image on a display device;
A medical image processing device comprising: the characteristic image is a two-dimensional image including a plurality of CT value change curves respectively corresponding to the plurality of positions,
Each of the plurality of CT value change curves is plotted on a graph in which a first axis is defined as a virtual monochromatic energy and a second axis is defined as a virtual monochromatic CT value.
2. The medical image processing apparatus according to claim 1. The medical image processing device according to claim 1, wherein the characteristic image is a two-dimensional image in which a first axis is defined as virtual monochromatic energy and a second axis is defined as a position on the line, and each pixel is assigned a virtual monochromatic CT value or a gradation value or color value corresponding to the virtual monochromatic CT value. The medical image processing device according to claim 1, wherein the characteristic image represents that for each of the multiple positions, the change in virtual monochromatic CT value is positively or negatively correlated with the change in virtual monochromatic energy. The medical image processing device according to claim 4, wherein the change in the virtual monochromatic CT value is defined as the difference between each virtual monochromatic CT value and a virtual monochromatic CT value corresponding to a reference value of the virtual monochromatic energy. The medical image processing device according to claim 4, wherein the display control unit displays the positive correlation and the negative correlation in a visually distinct manner. The medical image processing device according to claim 4, wherein the display control unit visually distinguishes between pixels in which the change in the virtual monochromatic CT value is large and small compared to a threshold value. The medical image processing device according to claim 2, wherein the characteristic image includes, in addition to the multiple CT value change curves, a standard CT value change curve for a healthy subject with respect to the target organ. The medical image processing device according to claim 1, wherein the line is a straight line or a curved line. The medical image processing device according to claim 1, wherein the CT image is a polychromatic X-ray image or a virtual monochromatic X-ray image. The medical image processing device according to claim 1, further comprising an attachment unit that attaches the characteristic image to an image interpretation report relating to the subject. the characteristic images include a first characteristic image and a second characteristic image;
the first characteristic image is a two-dimensional image in which a first axis is defined as a virtual monochromatic energy and a second axis is defined as a position on the line, and each pixel is assigned a virtual monochromatic CT value or a gradation value or color value corresponding to the virtual monochromatic CT value;
the second characteristic image is a two-dimensional image including a plurality of CT value change curves respectively corresponding to the plurality of positions, each of the plurality of CT value change curves being plotted on a graph having a first axis defined as a virtual monochromatic energy and a second axis defined as a virtual monochromatic CT value;
the generating unit generates the first characteristic image based on the line, and generates the second characteristic image based on the first characteristic image.
2. The medical image processing apparatus according to claim 1. A line representing a composition diagnostic target is set on a CT image of the subject;
generating a characteristic image representing a change in CT value associated with a change in virtual monochromatic energy for each of a plurality of positions included in the line;
displaying the characteristic image on a display device;
A medical image processing method comprising the steps of: