X-ray CT apparatus and medical image processing system

Abstract

An X-ray CT apparatus (10) according to an embodiment comprises: an X-ray control unit (145a) for irradiating a subject with X-rays while switching the energy of the X-rays between a plurality of X-ray energies; an X-ray detection unit (112) that detects the X-rays and outputs an electrical signal; a setting unit (145b) that sets an amplification condition for each of the plurality of X-ray energies; a data collection unit (118) that collects a plurality of projection data sets corresponding to the plurality of X-ray energies by amplifying the electrical signal under the amplification condition and converting the electrical signal into digital data; and an image processing unit (145c) that executes image processing based on the plurality of projection data sets on the basis of the amplification condition.

Description

X-ray CT Apparatus and Medical Image Processing System

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray CT apparatus and a medical image processing system.

[0002] In an examination using an X-ray computed tomography (CT) apparatus, a method of collecting projection data corresponding to each of a plurality of X-ray energies is known. For example, by performing imaging while switching the tube voltage for each one or more views, projection data corresponding to each of the plurality of X-ray energies can be collected.

[0003] Japanese Patent Application Laid-Open No. 2023-108512

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the quality of X-ray CT images collected by kV switching. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above. The problems corresponding to the respective effects of each configuration shown in the embodiments described later can also be regarded as other problems.

[0005] The X-ray CT apparatus according to the embodiment includes an X-ray control unit that irradiates a subject while switching the energy of X-rays among a plurality of X-ray energies, an X-ray detection unit that detects the X-rays and outputs an electrical signal, a setting unit that sets amplification conditions for each of the plurality of X-ray energies, a data collection unit that collects a plurality of projection data sets corresponding to the plurality of X-ray energies by amplifying the electrical signal under the amplification conditions and converting it into digital data, and an image processing unit that performs image processing based on the plurality of projection data sets based on the amplification conditions.

[0006] Figure 1 is a block diagram showing an example of the configuration of an X-ray CT apparatus according to the first embodiment. Figure 2A is a diagram showing an example of dual-energy scanning according to the first embodiment. Figure 2B is a diagram showing an example of dual-energy scanning according to the first embodiment. Figure 3 is a flowchart illustrating a series of processing steps of the X-ray CT apparatus according to the first embodiment. Figure 4 is a diagram showing an overview of the DAS gain setting process according to the first embodiment. Figure 5 is a flowchart illustrating a method for setting the DAS gain according to the first embodiment. Figure 6 is a block diagram showing an example of the configuration of a medical image processing system according to another embodiment.

[0007] The embodiments of the X-ray CT apparatus and medical image processing system will be described in detail below with reference to the attached drawings.

[0008] (First Embodiment) In the first embodiment, the X-ray CT apparatus 10 shown in Figure 1 will be described as an example. Figure 1 is a block diagram showing an example of the configuration of the X-ray CT apparatus 10 according to the first embodiment. For example, the X-ray CT apparatus 10 has a cradle device 110, a patient bed device 130, and a console device 140.

[0009] In Figure 1, the rotation axis of the rotating frame 113 in the non-tilted state or the longitudinal direction of the top plate 133 of the patient device 130 is defined as the Z-axis direction. The Z-axis direction corresponds to the body axis direction of the subject P placed on the top plate 133. The axis direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction. The axis direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction. Note that Figure 1 is a drawing of the gantry device 110 from multiple directions for explanatory purposes, and shows the case where the X-ray CT apparatus 10 has one gantry device 110.

[0010] The mounting device 110 includes an X-ray tube 111, an X-ray detector 112, a rotating frame 113, an X-ray high-voltage device 114, a control device 115, a wedge 116, a collimator 117, and a DAS (Data Acquisition System) 118.

[0011] The X-ray tube 111 is a vacuum tube having a cathode (filament) that generates thermionic electrons and an anode (target) that generates X-rays upon collision with thermionic electrons. The X-ray tube 111 generates X-rays to irradiate the subject P by irradiating thermionic electrons from the cathode to the anode when a high voltage is applied from the X-ray high-voltage device 114. The X-ray tube 111 is an example of an X-ray generating unit.

[0012] Furthermore, the hardware for generating X-rays is not limited to the X-ray tube 111. For example, instead of the X-ray tube 111, a fifth-generation system may be used to generate X-rays, which includes a focus coil for focusing the electron beam generated from the electron gun, a deflection coil for electromagnetic deflection, and a target ring that surrounds half of the subject P and generates X-rays when the deflected electron beam collides with it. In other words, the X-ray generation unit may consist of a focus coil, a deflection coil, and a target ring.

[0013] The X-ray detector 112 detects X-rays irradiated from the X-ray tube 111 that have passed through the subject P, and outputs a signal corresponding to the detected X-ray amount to the DAS 118. The X-ray detector 112 has, for example, multiple arrays of detection elements arranged in the channel direction (channel direction) along a single arc centered on the focal point of the X-ray tube 111. The X-ray detector 112 has, for example, a structure in which multiple arrays of detection elements, each arranged in the channel direction, are arranged in the row direction (slice direction, row direction). The X-ray detector 112 is an example of an X-ray detection unit.

[0014] For example, the X-ray detector 112 is an indirect conversion type detector having a grid, a scintillator array, and a photosensor array. The scintillator array has multiple scintillators. The scintillators have scintillator crystals that output light in a quantity of photons corresponding to the amount of incident X-rays. The grid is arranged on the X-ray incident side of the scintillator array and has an X-ray shielding plate that absorbs scattered X-rays. The grid is sometimes called a collimator (one-dimensional collimator or two-dimensional collimator). The photosensor array has the function of converting the amount of light from the scintillators into an electrical signal, and has a photosensor such as a photodiode. The X-ray detector 112 may also be a direct conversion type detector having semiconductor elements that convert incident X-rays into electrical signals. Alternatively, the X-ray detector 112 may be a photon counting type detector that outputs a signal that can measure the energy value of the incident X-ray photons.

[0015] The rotating frame 113 is an annular frame that supports the X-ray tube 111 and the X-ray detector 112 opposite each other and rotates the X-ray tube 111 and the X-ray detector 112 by the control device 115. For example, the rotating frame 113 is a casting made of aluminum. In addition to the X-ray tube 111 and the X-ray detector 112, the rotating frame 113 can also support an X-ray high-voltage device 114, a wedge 116, a collimator 117, a DAS 118, etc. Furthermore, the rotating frame 113 can also support various configurations not shown in Figure 1. Hereafter, in the mounting device 110, the rotating frame 113 and the part that rotates together with the rotating frame 113 will also be referred to as the rotating part.

[0016] The X-ray high-voltage device 114 includes an electrical circuit such as a transformer and a rectifier, a high-voltage generator that generates a high voltage to be applied to the X-ray tube 111, and an X-ray control device that controls the output voltage according to the X-rays generated by the X-ray tube 111. The high-voltage generator may be of the transformer type or the inverter type. The X-ray high-voltage device 114 may be mounted on the rotating frame 113 or on a fixed frame (not shown).

[0017] The control device 115 includes a processing circuit with a CPU (Central Processing Unit), etc., and a drive mechanism such as a motor and actuator. The control device 115 receives input signals from the input interface 142 and controls the operation of the frame device 110 and the bed device 130. For example, the control device 115 controls the rotation of the rotating frame 113, the tilt of the frame device 110, and the operation of the bed device 130. To give one example, as a control to tilt the frame device 110, the control device 115 rotates the rotating frame 113 around an axis parallel to the X-axis direction based on the input tilt angle information. The control device 115 may be installed on the frame device 110 or on the console device 140.

[0018] The wedge 116 is an X-ray filter used to adjust the amount of X-rays irradiated from the X-ray tube 111. Specifically, the wedge 116 is an X-ray filter that attenuates the X-rays irradiated from the X-ray tube 111 so that the X-rays irradiated from the X-ray tube 111 to the subject P have a predetermined distribution. For example, the wedge 116 is a wedge filter or a bow-tie filter, and is manufactured by processing aluminum or the like to have a predetermined target angle and predetermined thickness.

[0019] The collimator 117 is a lead plate or the like used to narrow the irradiation range of X-rays that have passed through the wedge 116, and a slit is formed by combining multiple lead plates or the like. The collimator 117 is sometimes called an X-ray diaphragm. In Figure 1, the wedge 116 is shown to be placed between the X-ray tube 111 and the collimator 117, but the collimator 117 may also be placed between the X-ray tube 111 and the wedge 116. In this case, the wedge 116 transmits and attenuates the X-rays that are irradiated from the X-ray tube 111 and whose irradiation range has been limited by the collimator 117.

[0020] The DAS 118 collects X-ray signals detected by each detection element of the X-ray detector 112. For example, the DAS 118 has an A / D converter that amplifies the electrical signals output from each detection element and converts them into digital signals, thereby generating detection data. The DAS 118 is implemented by a processor such as an Application Specific Integrated Circuit (ASIC). The DAS 118 is an example of a data acquisition unit.

[0021] The amplification process performed by the A / D converter of the DAS118 is carried out according to the amplification conditions set by the setting function 145b. For example, the setting function 145b sets the DAS gain as an amplification condition. The DAS gain allows setting the amplification factor of the photon count input to the DAS118.

[0022] The DAS 118 may be a simultaneous acquisition system or a sequential acquisition system. In the simultaneous acquisition system, the DAS 118 is provided for each detection element of the X-ray detector 112. The simultaneous acquisition system DAS 118 generates detection data by reading out the charge as soon as it is accumulated in the corresponding detection element. In the sequential acquisition system, the DAS 118 is provided for each of the multiple detection elements (group of detection elements). The sequential acquisition system DAS 118 generates detection data by sequentially reading out the charge accumulated in each of the multiple detection elements.

[0023] The data generated by DAS118 is transmitted via optical communication from a transmitter having a light-emitting diode (LED) on the rotating frame 113 to a receiver having a photodiode located on the non-rotating part of the mounting device 110 (for example, a fixed frame, etc., which is not shown in Figure 1), and then transferred to the console device 140. Here, the non-rotating part is, for example, a fixed frame that rotatably supports the rotating frame 113. Note that the method of transmitting data from the rotating frame 113 to the non-rotating part of the mounting device 110 is not limited to optical communication; any non-contact data transmission method or a contact-type data transmission method may be used.

[0024] The examination bed device 130 is a device for placing and moving the subject P to be scanned, and comprises a base 131, an examination bed drive device 132, a top plate 133, and a support frame 134. The base 131 is a housing that supports the support frame 134 so that it can move in the vertical direction. The examination bed drive device 132 is a drive mechanism that moves the top plate 133 on which the subject P is placed in the direction of the long axis of the top plate 133, and includes a motor and actuators. The top plate 133, which is provided on the upper surface of the support frame 134, is a plate on which the subject P is placed. In addition to moving the top plate 133, the examination bed drive device 132 may also move the support frame 134 in the direction of the long axis of the top plate 133.

[0025] The console device 140 includes a communication interface 141, an input interface 142, a display 143, a memory 144, and a processing circuit 145. Although the console device 140 is described separately from the mounting device 110, the mounting device 110 may include the console device 140 or some of its components.

[0026] The communication interface 141 controls the transmission and communication of various data sent and received between the X-ray CT apparatus 10 and other devices and systems connected via the network. Specifically, the communication interface 141 is connected to the processing circuit 145 and outputs data received from other devices and systems to the processing circuit 145, or transmits data output from the processing circuit 145 to other devices and systems. For example, the communication interface 141 can be implemented by a network card, network adapter, NIC (Network Interface Controller), etc.

[0027] The input interface 142 receives various input operations from the user, converts the received input operations into electrical signals, and outputs them to the processing circuit 145. For example, the input interface 142 can be implemented using a mouse, keyboard, trackball, switch, button, joystick, touchpad that performs input operations by touching the operating surface, touchscreen that integrates a display screen and a touchpad, a non-contact input circuit using an optical sensor, an audio input circuit, etc. The input interface 142 may also consist of the X-ray CT apparatus 10 main unit and a tablet terminal that can communicate wirelessly. Furthermore, the input interface 142 may be a circuit that receives input operations from the user via motion capture. For example, the input interface 142 can receive the user's body movements and gaze as input operations by processing signals acquired via a tracker and images collected about the user. Moreover, the input interface 142 is not limited to those equipped with physical operating components such as a mouse or keyboard. 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 X-ray CT apparatus 10 and outputs this electrical signal to a processing circuit 145 is also included as an example of an input interface 142.

[0028] The display 143 displays various types of information. For example, the display 143 displays a GUI (Graphical User Interface) for receiving various instructions and settings from the user via the input interface 142, as well as shooting conditions and collected image data. For example, the display 143 may be a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescent display (OLED), or a plasma display. The display 143 may be a desktop type, or it may be composed of a tablet terminal that can communicate wirelessly with the X-ray CT scanner 10.

[0029] In Figure 1, the X-ray CT apparatus 10 is described as having a display 143, but the X-ray CT apparatus 10 may also have a projector instead of or in addition to the display 143. The projector can project onto a screen, wall, floor, the body surface of the subject P, etc., under the control of the processing circuit 145. For example, the projector can also project onto any plane, object, space, etc., by projection mapping. The display 143 and the projector are examples of display units.

[0030] The memory 144 can be implemented using, for example, semiconductor memory elements such as RAM (Random Access Memory) or flash memory, an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an optical disc. For example, the memory 144 stores programs for the circuits included in the X-ray CT scanner 10 to perform their functions. The memory 144 also stores various collected data obtained by performing scans on the subject P, as well as information such as imaging conditions. The memory 144 may also be implemented using a group of servers (cloud) connected to the X-ray CT scanner 10 via a network NW.

[0031] The processing circuit 145 controls the operation of the entire X-ray CT apparatus 10 by executing a control function 145a, a setting function 145b, an image processing function 145c, and an output function 145d. The control function 145a is an example of an X-ray control unit. The setting function 145b is an example of a setting unit. The image processing function 145c is an example of an image processing unit.

[0032] For example, the processing circuit 145 reads a program corresponding to the control function 145a from the memory 144 and executes it to perform a scan on the subject P. For example, the control function 145a supplies high voltage to the X-ray tube 111 by controlling the X-ray high-voltage device 114. As a result, the X-ray tube 111 generates X-rays to irradiate the subject P. The control function 145a also moves the subject P into the imaging port of the pallet device 110 by controlling the bed drive device 132. The control function 145a also controls the distribution of X-rays irradiated on the subject P by adjusting the position of the wedge 116 and the aperture and position of the collimator 117. The control function 145a also rotates the rotating part by controlling the control device 115. While the scan is being performed by the control function 145a, the DAS 118 collects electrical signals output from each detection element in the X-ray detector 112 and generates detection data.

[0033] Furthermore, the control function 145a performs preprocessing on the detection data output from the DAS 118. For example, the control function 145a performs preprocessing on the detection data output from the DAS 118, such as logarithmic transformation, offset correction, inter-channel sensitivity correction, and beam hardening correction. The data after preprocessing is also referred to as raw data. The detection data before preprocessing and the raw data after preprocessing are collectively referred to as projection data.

[0034] Here, the control function 145a controls the X-ray high-voltage device 114 to switch the energy of the X-rays emitted from the X-ray tube 111 during scanning between multiple X-ray energies. This allows the DAS 118 to collect multiple projection datasets corresponding to multiple X-ray energies. In other words, the control function 145a performs a dual-energy scan using two types of X-ray energies, or a dual-energy scan using three or more types of X-ray energies, by kV switching. Details of the X-ray control by the control function 145a will be described later.

[0035] Furthermore, for example, the processing circuit 145 sets various imaging conditions by reading and executing a program corresponding to the setting function 145b from the memory 144. For example, the setting function 145b sets the scan range, X-ray irradiation conditions such as tube voltage and tube current, and X-ray detection conditions such as signal amplification conditions in the DAS 118. Details of setting imaging conditions using the setting function 145b will be described later.

[0036] Furthermore, for example, the processing circuit 145 performs various image processing based on projection data by reading and executing a program corresponding to the image processing function 145c from the memory 144. For example, the image processing function 145c performs reconstruction processing based on projection data, noise reduction processing targeting projection data, noise reduction processing targeting the reconstructed X-ray CT image (volume data), and material discrimination processing. Here, the image processing function 145c performs image processing based on projection data based on the signal amplification conditions in the DAS 118. Details of the image processing by the image processing function 145c will be described later.

[0037] Furthermore, for example, the processing circuit 145 outputs various types of data by reading and executing a program corresponding to the output function 145d from the memory 144. For example, the output function 145d controls the display on the display 143. Also, for example, the output function 145d transmits the collected projection data and X-ray CT images to another device via the communication interface 141, for storage in that other device, or for display on that other device.

[0038] In the X-ray CT apparatus 10 shown in Figure 1, each processing function is stored in memory 144 in the form of a program that can be executed by a computer. The processing circuit 145 is a processor that realizes the function corresponding to each program by reading and executing the program from memory 144. In other words, the processing circuit 145, when a program has been read, has the function corresponding to the read program.

[0039] In Figure 1, the control function 145a, setting function 145b, image processing function 145c, and output function 145d are described as being realized by a single processing circuit 145. However, the processing circuit 145 may be configured by combining multiple independent processors, and each processor may realize the functions by executing a program. Furthermore, each processing function of the processing circuit 145 may be appropriately distributed or integrated across one or more processing circuits. Also, in Figure 1, an example is shown in which the programs corresponding to each processing function are stored in a single memory 144. However, the programs corresponding to each processing function may be distributed and stored in multiple memories, and each program may be read and executed from each memory.

[0040] Furthermore, the processing circuit 145 may also implement its functions by utilizing the processor of an external device connected via a network NW. For example, the processing circuit 145 reads and executes programs corresponding to each function from the memory 144, and also utilizes a group of servers (cloud) connected to the X-ray CT apparatus 10 via a network NW as computing resources to implement the functions shown in Figure 1.

[0041] The above describes an example configuration of the X-ray CT apparatus 10. Under this configuration, the X-ray CT apparatus 10 improves the quality of the X-ray CT images acquired by kV switching through the process described below.

[0042] First, we will describe the CT scan performed on the subject P under the control of the control function 145a. In this embodiment, we will describe an example of performing a dual-energy scan using kV switching.

[0043] For example, first, the setting function 145b is used to set various imaging conditions, such as the two types of X-ray energies to be used in dual-energy scanning and the signal amplification conditions in the DAS 118.

[0044] For example, the setting function 145b sets the high tube voltage Vh and the low tube voltage Vl as two types of X-ray energies used in dual-energy scanning. During the scan execution, the control function 145a can irradiate the subject P with X-rays while switching the X-ray energy by alternately switching the tube voltage applied to the X-ray tube 111 between Vh and Vl. The X-ray energy may be automatically set by the setting function 145b based on a shooting protocol or the like set for each imaging target site, or may be manually set by a user such as a doctor via the input interface 142.

[0045] The switching of the X-ray energy during the scan is performed for each one or more views. A view is a collection unit of projection data in the time direction. For example, the time width (view period) per view corresponds to the sampling period of digital data by the A / D converter included in the DAS 118. In a CT scan, projection data is collected for each view while sequentially changing the imaging angle as the rotating part rotates.

[0046] An example of dual-energy scanning will be described using FIG. 2A. The horizontal axis in FIG. 2A indicates the view number. The horizontal axis in FIG. 2A can also be rephrased as a time axis. FIG. 2A shows a range for "12 views" from view ️1 to view 12.

[0047] FIG. 2A shows an example of switching the X-ray energy every "5 views". That is, the control function 145a irradiates the X-rays with the high tube voltage Vh from view 1 to view 5, irradiates the X-rays with the low tube voltage Vl from view 6 to view 10, and irradiates the X-rays with the high tube voltage Vh again after view 11.

[0048] Also, in FIG. 2A, the DAS gain is set to the high tube voltage for any view. Conventionally, when performing dual-energy scanning by kV switching, due to hardware constraints, a fixed DAS gain was often used without following the switching of the X-ray energy.

[0049] When the DAS118 amplifies an electrical signal and converts it into digital data, if the amplification factor is insufficient, only a portion of the dynamic range can be used, resulting in a decrease in resolution regarding signal strength. On the other hand, if the amplification factor is too high, it exceeds the maximum value of the dynamic range. In other words, if the amplification factor is too high, an overflow occurs, and when converted to digital data, information from electrical signals above a certain intensity is lost. It is preferable to set the DAS gain so as not to cause overflow while making maximum use of the dynamic range.

[0050] When performing a dual-energy scan with a constant DAS gain, the DAS gain for high tube voltage is set to account for the overflow problem. This is because high-tube-voltage X-rays have higher transmittance compared to low-tube-voltage X-rays, allowing more X-ray photons to reach the X-ray detector 112. In other words, if the DAS gain is the same, overflow is more likely to occur when irradiating with high-tube-voltage X-rays, so the DAS gain is set to prevent overflow even when irradiated with high-tube-voltage X-rays.

[0051] In recent years, as shown in Figure 2B, it has become possible to switch the DAS gain during scanning and follow the switching of X-ray energy. For example, the DAS 118 includes a gain switch, an A / D converter for high tube voltage, and an A / D converter for low tube voltage. The gain switch switches the output destination from the detection element between the A / D converter for high tube voltage and the A / D converter for low tube voltage. For example, in views 1 to 5 of Figure 2B, the DAS 118 inputs the electrical signal output from the X-ray detector 112 to the A / D converter for high tube voltage via the gain switch and amplifies it with the DAS gain for high tube voltage. Also, in views 6 to 10 of Figure 2B, the DAS 118 inputs the electrical signal output from the X-ray detector 112 to the A / D converter for low tube voltage via the gain switch and amplifies it with the DAS gain for high tube voltage.

[0052] The processing circuit 145 according to this embodiment not only switches the DAS gain during scanning, but also sets the DAS gain for high tube voltage and the DAS gain for low tube voltage, respectively, in order to maximize the use of the dynamic range while preventing overflow. Furthermore, the processing circuit 145 performs image processing such as reconstruction processing and noise reduction processing based on the DAS gain for high tube voltage and the DAS gain for low tube voltage.

[0053] The following describes the series of processes performed by the processing circuit 145, following the flowchart in Figure 3. Steps S11 and S15 in Figure 3 correspond to the control function 145a, steps S12, S13, and S14 correspond to the setting function 145b, steps S16 and S17 correspond to the image processing function 145c, and step S18 corresponds to the output function 145d. Figure 3 is a flowchart illustrating the series of processes of the X-ray CT apparatus 10 according to the first embodiment.

[0054] First, the processing circuit 145 performs a scan on the subject P placed on the top plate 133 (step S11) and collects a scan image. The scan image is an image collected before the main scan is performed to collect diagnostic images, for purposes such as positioning the subject P. In the flowchart of Figure 3, the dual-energy scan performed in step S15 is the main scan. The main scan is usually performed using a higher dose of X-rays than during the scan.

[0055] For example, the processing circuit 145 rotates the rotating part while irradiating the subject P with a low dose of X-rays and reconstructs a three-dimensional scan image from the projection data collected by the DAS 118. The processing circuit 145 also sets the scan range of the main scan based on the scan image. For example, the processing circuit 145 identifies the position of the area to be inspected in a coordinate system based on the top plate 133 based on the scan image and sets the scan range of the main scan to include the area to be inspected.

[0056] In other words, scan images are also collected in general inspection procedures for positioning the main scan. The processing circuit 145 uses such scan images for setting the DAS gain.

[0057] Next, the processing circuit 145 acquires a water model based on the scan image (step S12). For example, as shown in Figure 4, the processing circuit 145 acquires a water model W1 based on the scan image I1. Figure 4 is a diagram illustrating the overview of the DAS gain setting process.

[0058] The water model W1 calculates the equivalent water length for each position of the subject P in the body axis direction (Z axis direction), assuming that the entire object being photographed is water. For example, the processing circuit 145 calculates the equivalent water length based on the shape of the subject P. To give one example, the processing circuit 145 acquires the shape of the cross-section (axial cross-section) at each position in the Z axis direction based on the scan image I1. Since the cross-sections of the chest and head are close to elliptical in shape, the processing circuit 145 can acquire the shortest line segment (minor axis) that can be set within the cross-section as the equivalent water length. That is, the processing circuit 145 calculates the equivalent water length based on the scan image collected from the subject P before collecting the projection dataset in step S15.

[0059] Furthermore, the processing circuit 145 may determine the equivalent water length by taking the composition into consideration. For example, after calculating the short axis as described above, the processing circuit 145 can obtain the equivalent water length by multiplying it by a coefficient greater than "1" if there are high-density areas such as bone in the cross-section, and by multiplying it by a coefficient less than "1" if there are low-density areas such as lungs.

[0060] Next, the processing circuit 145 sets the Automatic Exposure Control (AEC) conditions (step S13). Specifically, the processing circuit 145 sets the tube current value [mA] at each position in the Z-axis direction.

[0061] AEC is a process that controls the amount of X-rays irradiated to reduce the radiation dose to the subject P and suppress variations in image quality. Generally, at locations with a large equivalent water length, X-rays are greatly attenuated, and the amount of X-rays reaching the X-ray detector 112 decreases. Therefore, when imaging is performed with a constant amount of X-rays irradiated from the X-ray tube 111, the dose may be insufficient at locations with a large equivalent water length, or excessive radiation exposure may occur at locations with a small equivalent water length. To address this, the processing circuit 145 sets the AEC conditions so that the tube current value [mA] is increased at locations with a large equivalent water length to obtain the necessary image quality, and the tube current value [mA] is decreased at locations with a small equivalent water length to suppress the radiation dose.

[0062] For example, AEC setting information is created in advance and recorded in memory 144. The AEC setting information is, for example, information that defines the correspondence between the equivalent length of water and the pipe current value [mA]. ​​In such AEC setting information, the correspondence is set so that the pipe current value [mA] increases as the equivalent length of water increases. For example, the AEC setting information is set so that the pipe current value [mA] increases in proportion to the equivalent length of water. Then, the processing circuit 145 sets the pipe current value [mA] at each position in the Z-axis direction by comparing the equivalent length of water at each position shown in the water model W1 in Figure 4 with the AEC setting information.

[0063] Next, the processing circuit 145 sets the DAS gains for high tube voltage and low tube voltage, respectively (step S14). That is, the processing circuit 145 sets different amplification conditions for each X-ray energy. For example, the processing circuit 145 switches the X-ray energy between a first X-ray energy and a second X-ray energy lower than the first X-ray energy, and sets a first amplification condition corresponding to the first X-ray energy and a second amplification condition corresponding to the second X-ray energy. The details of step S13 will be explained below with reference to Figure 5. Figure 5 is a flowchart for explaining the method of setting the DAS gain according to the first embodiment.

[0064] First, the processing circuit 145 obtains the minimum value of the calculated equivalent water length (minimum equivalent water length) (step S101). For example, in the water model W1 shown in Figure 4, the equivalent water length at position Z1 on the Z axis is the minimum equivalent water length.

[0065] Furthermore, the processing circuit 145 acquires an LUT (Look Up Table) corresponding to the tube voltage (step S102). For example, an LUT is created in advance, linking the count obtained when X-rays are irradiated to the equivalent length of water, tube current, and tube voltage, and is recorded in the memory 144. For example, the LUT can be created by actually scanning the water phantom while changing conditions such as the tube voltage. The processing circuit 145 then acquires an LUT corresponding to the high tube voltage Vh and an LUT corresponding to the low tube voltage Vl, respectively.

[0066] Next, the processing circuit 145 sets "n" as the DAS gain for the high tube voltage (step S103). Here, "n" may be an identification number of a preset DAS gain, a multiplier of the amplified signal strength to the signal strength before amplification, or a value in decibels (dB). In any case, "n" is set such that the larger the value of "n", the greater the amplification factor. The same applies to "m" and "l", which will be described later. Furthermore, it is preferable that the initially set "n" is a small value such that no overflow occurs regardless of the settings of the imaging conditions, including the tube voltage.

[0067] Next, the processing circuit 145 determines whether or not an overflow will occur when amplification processing is performed with a DAS gain of "n" based on the minimum equivalent water length obtained in step S102, the high tube voltage Vh, the LUT obtained in step S102 according to the high tube voltage Vh, and other imaging conditions such as the tube current (step S104). The tube current here is the tube current value [mA] set for the position Z1 where the equivalent water length is minimum, among the AEC conditions in step S13. That is, the processing circuit 145 sets the AEC conditions based on the equivalent water length and sets the amplification conditions based on the minimum equivalent water length and the AEC conditions. If it is determined that no overflow will occur (negation in step S104), the processing circuit 145 replaces "n" with "n+1" (step S105) and proceeds back to step S103. In other words, if it is determined that no overflow will occur, the processing circuit 145 increases the amplification factor by one step and determines again whether or not an overflow will occur.

[0068] On the other hand, if it is determined that an overflow will occur (step S104 affirmative), the processing circuit 145 determines the DAS gain for the high tube voltage (step S106). For example, the processing circuit 145 determines the DAS gain "n-1" as the DAS gain for the high tube voltage. That is, the processing circuit 145 determines the DAS gain for the high tube voltage to be one step lower than the amplification factor at which it was determined that an overflow would occur. In this way, the processing circuit 145 sets the amplification conditions so that no overflow occurs and the amplification factor is maximized. That is, the processing circuit 145 sets the amplification conditions so that no overflow occurs when the electrical signal is amplified and converted into digital data and the amplification factor is maximized.

[0069] The DAS gain for low tube voltage can be set in the same way. For example, the processing circuit 145 sets "m" as the DAS gain for low tube voltage (step S107). Next, the processing circuit 145 determines whether or not an overflow will occur when amplification processing is performed with the DAS gain "m" based on the minimum equivalent water length obtained in step S102, the low tube voltage Vl, the LUT obtained in step S102 according to the low tube voltage Vl, and other imaging conditions such as the tube current (step S108). If it is determined that no overflow will occur (step S108 negative), the processing circuit 145 replaces "m" with "m+1" (step S109) and proceeds back to step S107. On the other hand, if it is determined that an overflow will occur (step S108 positive), the processing circuit 145 determines the DAS gain for low tube voltage (step S110).

[0070] The DAS gain "m" determined in step S110 is greater than the DAS gain "n" determined in step S106. In other words, the DAS gain for low tube voltage is set to have a higher amplification factor than the DAS gain for high tube voltage. This is because X-rays attenuate more easily at lower tube voltages, resulting in a smaller amount of X-rays detected by the X-ray detector 112. That is, in the case of low tube voltage, even if a higher amplification factor is set than the DAS gain for high tube voltage, the amount of X-rays detected by the X-ray detector 112 is correspondingly smaller, thus avoiding overflow.

[0071] As explained above, the processing circuit 145 can set the DAS gain for high tube voltage and the DAS gain for low tube voltage by repeatedly determining whether or not an overflow occurs when amplification processing is performed at a given amplification factor while changing the amplification factor. In other words, the processing circuit 145 sets amplification conditions for each of the multiple X-ray energies by repeatedly determining whether or not an overflow occurs when amplification processing is performed at a given amplification factor while changing the amplification factor of the electrical signal. In Figure 5, the DAS gain for high tube voltage and the DAS gain for low tube voltage are set sequentially, but these settings may be performed in parallel. That is, the processing in steps S103 to S106 and the processing in steps S107 to S110 may be performed in parallel.

[0072] Alternatively, instead of the processing in steps S107 to S110, the DAS gain for the low tube voltage may be set based on the DAS gain for the high tube voltage determined in step S106. For example, if "n" is set as the DAS gain for the high tube voltage, the processing circuit 145 sets "m = n + 1" as the DAS gain for the low tube voltage. That is, the processing circuit 145 may calculate the DAS gain for the high tube voltage based on the LUT, etc., and set the DAS gain for the low tube voltage to an amplification factor one step higher than the DAS gain for the high tube voltage.

[0073] Furthermore, Figure 5 illustrates an example in which the amplification factor is gradually increased while sequentially determining whether or not an overflow occurs. However, the embodiments are not limited to this. For example, the processing circuit 145 may set the DAS gain by gradually decreasing the amplification factor while sequentially determining whether or not an overflow occurs.

[0074] For example, the processing circuit 145 sets "l" as the DAS gain for high tube voltage. It is preferable that the value of "l" set here is large enough to cause overflow regardless of the settings of the imaging conditions, including the tube voltage. Next, the processing circuit 145 determines whether or not overflow will occur when amplification processing is performed with the DAS gain "l" based on the LUT, etc. If it is determined that overflow will occur, the processing circuit 145 replaces "l" with "l-1" and repeats the process of determining whether or not overflow will occur. Then, the processing circuit 145 determines the DAS gain "l" at the point in time when it is determined that no overflow will occur as the DAS gain for high tube voltage.

[0075] As explained above, the processing circuit 145 sets various imaging conditions such as the high tube voltage Vh and low tube voltage Vl, the DAS gain for the high tube voltage and the DAS gain for the low tube voltage, and the AEC conditions. Then, under the set imaging conditions, the processing circuit 145 performs a dual energy scan (step S15).

[0076] During dual-energy scanning, projection data is collected under high-voltage conditions for high-voltage views. Specifically, a high-voltage Vh is applied to the X-ray tube 111 to irradiate it with high-energy X-rays. The irradiated X-rays are converted into electrical signals by the X-ray detector 112, and the DAS 118 amplifies the electrical signals with a DAS gain for high-voltage to collect projection data. Furthermore, as the X-ray irradiation position moves in the Z-axis direction, the tube current is changed according to the AEC conditions. A set of projection data collected for each view under high-voltage conditions is also referred to as the high-voltage projection dataset. Similarly, a set of projection data collected for each view under low-voltage conditions is also referred to as the low-voltage projection dataset.

[0077] Next, the processing circuit 145 performs reconstruction processing based on the projection data collected by the dual-energy scan (step S16). For example, the processing circuit 145 generates a high-tube-voltage X-ray CT image (high-tube-voltage image) based on a high-tube-voltage projection dataset and generates a low-tube-voltage X-ray CT image (low-tube-voltage image) based on a low-tube-voltage projection dataset.

[0078] Alternatively, the processing circuit 145 may perform material discrimination processing using a high-tube voltage projection dataset and a low-tube voltage projection dataset, and generate a material discrimination image by reconstruction processing. Alternatively, the processing circuit 145 may generate a material discrimination image by performing material discrimination processing using a high-tube voltage image and a low-tube voltage image. Examples of material discrimination images include a reference material image that emphasizes the reference material used in the material discrimination processing, a virtual monochromatic X-ray image (monochromatic image) at an arbitrary energy, a density image, an effective atomic number image, and the like.

[0079] While not limited to reconstruction methods, examples include successive reconstruction methods such as Filtered Back Projection (FBP) and Model-Based Iterative Reconstruction (MBIR), as well as AI-based reconstruction methods such as Deep-Learning Reconstruction (DLR).

[0080] In various reconstruction methods, the reconstruction parameters are adjusted according to the characteristics of the noise contained in the projection data. For example, in the FBP method, the type and settings of the preprocessing filter and reconstruction filter are adjusted as reconstruction parameters. In the successive reconstruction method, the type and settings of the filter, the number of subsets, and the number of iterations are adjusted as reconstruction parameters.

[0081] Here, each projection dataset collected by dual-energy scanning contains noise corresponding to the DAS gain. Specifically, the electrical signal output from the X-ray detector 112 contains noise components such as dark current and circuit noise, regardless of whether it is a high-voltage or low-voltage view. Furthermore, when the DAS 118 amplifies the electrical signal, the noise contained in the electrical signal is also amplified. As mentioned above, the DAS gain for low-voltage is set to have a higher amplification factor than the DAS gain for high-voltage. Therefore, low-voltage projection datasets typically contain more noise than high-voltage projection datasets.

[0082] The processing circuit 145 performs the reconstruction process in step S16 based on the amplification conditions. Here, different amplification conditions are set for each projection dataset, such as DAS gain for high tube voltage and DAS gain for low tube voltage. Therefore, the processing circuit 145 performs the reconstruction process with different reconstruction conditions for each projection dataset. That is, as image processing based on multiple projection datasets, the processing circuit 145 sets reconstruction conditions according to the amplification conditions for each of the multiple projection datasets and performs the reconstruction process. For example, the processing circuit 145 performs the reconstruction process using different reconstruction parameters depending on the DAS gain.

[0083] For example, the processing circuit 145 uses a ramp filter to perform reconstruction processing based on a high-tube voltage projection dataset, and uses a high-pass filter such as Shepp & Logan to perform reconstruction processing based on a low-tube voltage projection dataset. Since noise is often contained in high-frequency components, the processing circuit 145 employs a high-pass filter as the reconstruction filter, enabling it to generate noise-reduced X-ray CT images from low-tube voltage projection datasets that contain a lot of noise. Furthermore, the processing circuit 145 can generate sharp X-ray CT images from high-tube voltage projection datasets with less noise without excessively removing high-frequency components.

[0084] Furthermore, in the MBIR method, for example, there is an adaptive process that estimates the statistical weight and changes the noise reduction intensity accordingly. Specifically, in the MBIR method, the higher the statistical weight, the lower the noise reduction intensity is adjusted. For example, the processing circuit 145 sets the reconstruction parameters so that the statistical weight increases as the amplification factor of the DAS gain decreases, and then performs the reconstruction process using the MBIR method.

[0085] Furthermore, in the DLR method, for example, noise is estimated for both the projection data and the X-ray CT image, and adaptive noise reduction processing is performed, which changes depending on the noise, before inputting it to the DNN (Deep Neural Network). The processing circuit 145 performs reconstruction processing using the DLR method with different estimation parameters corresponding to the DAS gains of the high tube voltage and low tube voltage, respectively.

[0086] For example, a DNN is trained using multiple projection data sets with different noise levels as input data and high-quality data as output data. Each of the multiple projection data sets is labeled with noise level information. High-quality data can be prepared, for example, by performing high-dose scans or executing high-precision reconstruction processes that are computationally intensive, such as the MBIR method. The processing circuit 145 then inputs the projection dataset, along with noise level information estimated from the DAS gain, into the DNN, and can perform reconstruction processing using the DLR method under estimated parameters adjusted according to the DAS gain.

[0087] Alternatively, multiple DNNs are trained for each level of noise in the projection data used as input data. For example, a DNN for high-noise data and a DNN for low-noise data are trained separately. Then, the processing circuit 145 inputs the projection dataset to a DNN selected according to the noise level estimated from the DAS gain, and can perform reconstruction processing using the DLR method under estimated parameters corresponding to the DAS gain.

[0088] An example of adjusting reconstruction parameters based on amplification conditions has been described, but the processing circuit 145 may also select a reconstruction method according to the amplification conditions. For example, as mentioned above, the projection dataset at low tube voltages is collected at a higher amplification factor than the dataset at high tube voltages and contains more noise. Therefore, the processing circuit 145 may perform reconstruction processing on the projection dataset at low tube voltages while removing noise using a reconstruction method with a high processing load, such as the MBIR method, and perform reconstruction processing on the projection dataset at high tube voltages using a reconstruction method with a low processing load, such as the FBP method.

[0089] Next, the processing circuit 145 performs noise reduction processing on the X-ray CT image (step S17). Here, the processing circuit 145 performs the noise reduction processing in step S17 based on the amplification conditions.

[0090] For example, the processing circuit 145 first estimates the noise contained in the X-ray CT image. For example, the processing circuit 145 estimates the noise in both the high-voltage and low-voltage images, assuming that higher amplification factors contain more noise. Furthermore, the processing circuit 145 may also estimate the noise by considering the reconstruction parameters and reconstruction methods used when reconstructing each X-ray CT image. Then, the processing circuit 145 performs adaptive noise reduction processing, changing the noise reduction intensity according to the estimated noise. That is, as image processing based on multiple projection datasets, the processing circuit 145 sets a noise reduction intensity according to the amplification conditions for each of the multiple X-ray CT images reconstructed based on the multiple projection datasets and performs noise reduction processing. This makes it possible to sufficiently remove noise from the X-ray CT image without smoothing the image due to excessive noise reduction processing.

[0091] Next, the processing circuit 145 performs display based on the X-ray CT image (step S18). Specifically, the processing circuit 145 generates a display image based on the X-ray CT image and displays it on the display 143. Examples of processing for generating the display image include, but are not limited to, volume rendering, surface volume rendering, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing.

[0092] The above explains the series of processes shown in Figure 3. Of course, the flowchart in Figure 3 is just one example, and various modifications are possible.

[0093] For example, in Figure 3, after the reconstruction process in step S16, noise reduction processing is performed on the X-ray CT image in step S17. However, the embodiment is not limited to this. For example, noise reduction processing may be performed on projection data before the reconstruction process in step S16. For example, the processing circuit 145 may perform noise reduction processing as image processing based on multiple projection datasets by setting a noise reduction intensity according to the amplification conditions for each of the multiple projection datasets. Specifically, the processing circuit 145 may set a noise reduction intensity according to the amplification conditions for each of the projection datasets with high tube voltage and low tube voltage, and perform noise reduction processing on these projection datasets. In this case, the processing circuit 145 can perform reconstruction processing on the projection dataset after noise reduction processing.

[0094] As described above, the X-ray CT apparatus 10 according to the first embodiment includes a control function 145a, an X-ray detector 112, a setting function 145b, a DAS 118, and an image processing function 145c. The control function 145a irradiates the subject P with X-rays while switching the X-ray energy between a plurality of X-ray energies. The X-ray detector 112 detects X-rays and outputs an electrical signal. The setting function 145b sets amplification conditions for each of the plurality of X-ray energies. The DAS 118 collects a plurality of projection data sets corresponding to the plurality of X-ray energies by amplifying the electrical signal under the amplification conditions set by the setting function 145b and converting it into digital data. The image processing function 145c performs image processing based on the plurality of projection data sets based on the amplification conditions. With this configuration, the X-ray CT apparatus 10 can improve the quality of X-ray CT images collected by kV switching.

[0095] Specifically, when scanning an object with the same tube current but different tube voltages, a higher tube voltage yields a greater number of photon counts. The X-ray CT apparatus 10 takes these characteristics corresponding to tube voltage into consideration, sets appropriate amplification conditions for each tube voltage, and performs dual-energy scanning using kV switching to maximize the dynamic range while preventing overflow. This allows the X-ray CT apparatus 10 to include more information in the acquired projection data and improve the quality of the reconstructed X-ray CT image.

[0096] Furthermore, image processing such as reconstruction and noise reduction can be maximized by optimizing various parameters. The X-ray CT apparatus 10 can improve the quality of X-ray CT images by setting different amplification conditions for each tube voltage and then executing various image processing operations with parameters that take these amplification conditions into account.

[0097] (Other Embodiments) Figure 2B shows an example where the X-ray energy is switched every "5 views," but the number of views for which the X-ray energy is switched can be arbitrarily changed. For example, the control function 145a may switch the X-ray energy every "1 view."

[0098] Furthermore, the number of views required for switching may differ for each X-ray energy. For example, the control function 145a may irradiate with X-rays at a high tube voltage Vh for "5 views" to switch the X-ray energy, and then irradiate with X-rays at a low tube voltage Vl for "7 views".

[0099] Furthermore, in Figure 2B, views 1 to 5 are described as high tube voltage views, and the view switches to a low tube voltage view from view 6 onwards. However, when switching tube voltages, a rise or fall period occurs, albeit for a short time. For example, when switching from a low tube voltage Vl to a high tube voltage Vh, a rise period is necessary, and during this time, X-rays are irradiated at a tube voltage different from both the low tube voltage Vl and the high tube voltage Vh.

[0100] The setting function 145b may further set amplification conditions corresponding to such transition states. For example, the setting function 145b sets view 6 shown in Figure 2B as the view of the transition state, and sets the DAS gain for the transition state as the amplification condition for the electrical signal collected in that view. In this case, the DAS 118 can collect a projection dataset of the transition state by performing amplification processing with the DAS gain for the transition state, in addition to the projection dataset of the high tube voltage and the projection dataset of the low tube voltage. Furthermore, image processing based on the projection dataset of the transition state is performed based on the DAS gain for the transition state.

[0101] Alternatively, the transition state view may follow either the DAS gain for high tube voltage or the DAS gain for low tube voltage. For example, if the DAS gain for high tube voltage is used in the transition state view, at least overflow will be avoided.

[0102] Furthermore, the first embodiment described above illustrates an example of performing a dual-energy scan. However, the embodiments are not limited to this, and the same can be applied to multi-energy scans using three or more types of X-ray energies.

[0103] For example, the control function 145a irradiates the subject P while switching the tube voltage supplied to the X-ray tube 111 between a first tube voltage, a second tube voltage, and a third tube voltage. The setting function 145b sets amplification conditions for each of the first, second, and third tube voltages. The DAS 118 then amplifies the electrical signal and converts it into digital data under the amplification conditions set by the setting function 145b, thereby collecting projection datasets corresponding to the first tube voltage, the second tube voltage, and the third tube voltage. The image processing function 145c then performs image processing based on these projection datasets, according to the amplification conditions set for each projection dataset.

[0104] Furthermore, in the first embodiment described above, an example was given in which the minimum water equivalent length is obtained using a scan image. However, the embodiments are not limited to this. For example, the setting function 145b may estimate the body thickness of the subject P from an optical image taken of the subject P with an optical camera, and obtain the minimum water equivalent length based on the estimation result. Alternatively, the setting function 145b may use medical images acquired in another examination. For example, separate from the series of examinations shown in Figure 3, three-dimensional volume data such as X-ray CT images or MRI images may be collected from the subject P, and anatomical landmarks may be extracted from the three-dimensional volume data. In this case, the setting function 145b can obtain the minimum water equivalent length using the three-dimensional volume data with anatomical landmarks.

[0105] Furthermore, Figure 5 illustrates an example in which overflow determination in steps S104 and S108 is performed based on the minimum equivalent water length and the AEC condition (pipe current value [mA]) at position Z1 where the equivalent water length is minimized. However, the embodiment is not limited to this. For example, the overflow determination in steps S104 and S108 may be performed for each position in the Z-axis direction. For example, the setting function 145b selects an arbitrary position in the Z-axis direction as the determination target, performs an overflow determination based on the equivalent water length and AEC condition (pipe current value [mA]) at that position, and sets the DAS gain for that position. The setting function 145b also sets the DAS gain similarly for each position in the Z-axis direction while changing the position of the determination target. The setting function 145b then sets the minimum value of the DAS gain set for each position as the amplification condition used in this scan. By setting the amplification condition in this way, it is possible to ensure that no overflow occurs at any position in the Z-axis direction when this scan is performed while AEC is being performed.

[0106] Furthermore, in the first embodiment described above, an example was given in which common AEC conditions are set for multiple X-ray energies, such as high tube voltage Vh and low tube voltage Vl. However, the embodiment is not limited to this, and AEC conditions may be set for each X-ray energy.

[0107] For example, AEC setting information corresponding to the X-ray energy is created in advance and recorded in memory 144. For example, as AEC setting information, information defining the correspondence between the equivalent length of water, the tube current value [mA], and the tube voltage value [kV] is created in advance. Such setting information can be created, for example, by actually scanning a water phantom. To give one example, setting information corresponding to the tube voltage value [kV] can be created by keeping the tube voltage value [kV] constant and adjusting the tube current value [mA] so that a constant amount of X-rays is detected when the equivalent length of water is changed.

[0108] The processing circuit 145 then obtains setting information corresponding to the high tube voltage Vh from the memory 144 and sets the AEC conditions on the high tube voltage Vh side by comparing the equivalent water length at each position shown in the water model W1 in Figure 4 with the setting information. Similarly, the processing circuit 145 obtains setting information corresponding to the low tube voltage Vl from the memory 144 and sets the AEC conditions on the low tube voltage Vl side by comparing the equivalent water length at each position shown in the water model W1 in Figure 4 with the setting information.

[0109] Furthermore, in the first embodiment described above, an example of setting amplification conditions based on the equivalent length of water was explained. For example, in the first embodiment, an example was described in which the equivalent length of water is determined for each position in the axial direction of the subject, and amplification conditions are set for each of the multiple X-ray energies based on the minimum value of the obtained equivalent length of water. However, the embodiments are not limited to this. For example, any reference substance other than water may be set, and the equivalent length when all the imaging targets are assumed to be that reference substance may be determined and used to set the amplification conditions.

[0110] Furthermore, Figure 1 illustrates a single-tube type device equipped with one pair of X-ray tubes 111 and X-ray detectors 112. However, the embodiment is not limited to this, and the X-ray CT apparatus 10 may be a multi-tube type device equipped with multiple pairs of X-ray tubes 111 and X-ray detectors 112.

[0111] Furthermore, Figure 1 illustrates a Rotate / Rotate-Type device in which the X-ray tube 111 and the X-ray detector 112 rotate together around the subject P. This type of system is also called a third-generation CT. However, the embodiments are not limited to this. For example, the X-ray CT apparatus 10 may be a so-called fourth-generation CT. A fourth-generation CT is a Stationary / Rotate-Type device in which a large number of X-ray detection elements are fixed in a ring-shaped array, and only the X-ray tube 111 rotates around the subject P.

[0112] Furthermore, in Figure 1, the processing circuit 145 of the X-ray CT apparatus 10 was described as having an image processing function 145c. However, the embodiment is not limited to this. That is, image processing such as reconstruction processing and noise reduction processing may be performed on a device other than the X-ray CT apparatus 10.

[0113] An example of performing image processing using a device different from the X-ray CT scanner 10 will be explained with reference to Figure 6. Figure 6 is a block diagram showing an example of the configuration of a medical image processing system 1 according to another embodiment. The medical image processing system 1 includes an X-ray CT scanner 10, a medical image processing device 20, and an image storage device 30.

[0114] As shown in Figure 6, the X-ray CT scanner 10, the medical image processing device 20, and the image storage device 30 are connected via a network NW. Here, the network NW may consist of a closed local network within the hospital, or it may be a network via the internet.

[0115] The image storage device 30 stores projection data and X-ray CT images collected by the X-ray CT scanner 10. The image storage device 30 may also be a data server that stores data collected by multiple modality devices, including the X-ray CT scanner 10. For example, the image storage device 30 is a PACS (Picture Archiving and Communication System) server.

[0116] For example, the medical image processing device 20 includes a communication interface 21, an input interface 22, a display 23, a memory 24, and a processing circuit 25, as shown in Figure 6. The communication interface 21, input interface 22, display 23, and memory 24 can be configured in the same way as the communication interface 141, input interface 142, display 143, and memory 144 shown in Figure 1, so their explanation is omitted.

[0117] The processing circuit 25 controls the operation of the entire medical image processing device 20 by executing an acquisition function 25a, an image processing function 25b, and an output function 25c. The acquisition function 25a is an example of an acquisition unit. The image processing function 25b is an example of an image processing unit.

[0118] The acquisition function 25a acquires projection datasets collected by the X-ray CT apparatus 10 using dual-energy scanning or multi-energy scanning with kV switching. Alternatively, the acquisition function 25a acquires X-ray CT images reconstructed from projection datasets collected by the X-ray CT apparatus 10 using dual-energy scanning or multi-energy scanning with kV switching. For example, projection datasets or X-ray CT images collected by the X-ray CT apparatus 10 are stored in the image storage device 30. In this case, the acquisition function 25a can acquire projection datasets or X-ray CT images from the image storage device 30 via a network NW. Alternatively, the acquisition function 25a may acquire projection datasets or X-ray CT images directly from the X-ray CT apparatus 10 without going through the image storage device 30.

[0119] Here, the acquisition function 25a acquires the projection dataset or X-ray CT image along with the amplification conditions that were set during the scan. For example, the amplification conditions are attached to the projection dataset or X-ray CT image as supplementary information.

[0120] Image processing function 25b has the same function as image processing function 145c, and performs image processing based on projection datasets based on amplification conditions set for each projection dataset. For example, acquisition function 25a acquires projection datasets for high tube voltage and low tube voltage, along with DAS gains for high tube voltage and low tube voltage. Then, image processing function 25b performs reconstruction processing and noise reduction processing according to the DAS gain of each projection dataset. Alternatively, for example, acquisition function 25a acquires high tube voltage images and low tube voltage images, along with DAS gains for high tube voltage and low tube voltage. Then, image processing function 25b performs noise reduction processing according to the DAS gain of each X-ray CT image.

[0121] Output function 25c has the same function as output function 145d and performs display based on X-ray CT images. Specifically, output function 25c generates a display image based on the X-ray CT image and displays it on display 23.

[0122] In the medical image processing device 20 shown in Figure 6, each processing function is stored in memory 24 in the form of a program that can be executed by a computer. The processing circuit 25 is a processor that realizes the function corresponding to each program by reading and executing the program from memory 24. In other words, the processing circuit 25, when a program has been read, has the function corresponding to the read program.

[0123] In Figure 6, the acquisition function 25a, image processing function 25b, and output function 25c are described as being realized by a single processing circuit 25. However, the processing circuit 25 may be configured by combining multiple independent processors, and each processor may realize the functions by executing a program. Furthermore, each processing function of the processing circuit 25 may be appropriately distributed or integrated across one or more processing circuits. Also, in Figure 6, an example is shown in which the programs corresponding to each processing function are stored in a single memory 24. However, the programs corresponding to each processing function may be distributed and stored in multiple memories, and each program may be read and executed from each memory.

[0124] Furthermore, the processing circuit 25 may also implement its functions by utilizing the processor of an external device connected via a network NW. For example, the processing circuit 25 reads and executes programs corresponding to each function from the memory 24, and also utilizes a group of servers (cloud) connected to the medical image processing device 20 via a network NW as computing resources to implement the functions shown in Figure 6.

[0125] In the above description, the term "processor" refers to circuits such as CPUs, GPUs (Graphics Processing Units), ASICs, and programmable logic devices (e.g., Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field Programmable Gate Arrays (FPGAs)). When the processor is a CPU, for example, it realizes its functions by reading and executing programs stored in memory circuits. On the other hand, when the processor is an ASIC, for example, instead of storing programs in memory circuits, the functions are directly incorporated as logic circuits within the processor's circuitry. In addition, each processor in the embodiment is not limited to being configured as a single circuit; multiple independent circuits may be combined to form a single processor and realize its functions. Furthermore, multiple components in each figure may be integrated into a single processor to realize its functions.

[0126] Each component of the apparatus according to the above-described embodiment is a functional concept and does not necessarily have to be physically configured as shown in the illustration. That is, the specific form of distribution and integration of each apparatus is not limited to that shown in the illustration, and all or part of it can be functionally or physically distributed and integrated in any unit according to various loads and usage conditions. Furthermore, each processing function performed by each apparatus can be implemented in whole or in any part by a CPU and a program that is analyzed and executed by the CPU, or by hardware using wired logic.

[0127] Furthermore, the medical image processing method described in the above-mentioned embodiments can be implemented by executing a pre-prepared program on a computer such as a personal computer or workstation. This program can be distributed via a network such as the Internet. Alternatively, this program can be recorded on a computer-readable non-transient recording medium such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and executed by reading it from the recording medium by a computer.

[0128] With respect to the above embodiments, the following appendices are disclosed as aspects of the invention and selective features. (Appendix 1) An X-ray CT apparatus comprising: an X-ray control unit that irradiates a subject with X-rays while switching the energy of X-rays between a plurality of X-ray energies; an X-ray detection unit that detects the X-rays and outputs an electrical signal; a setting unit that sets amplification conditions for each of the plurality of X-ray energies; a data acquisition unit that collects a plurality of projection data sets corresponding to the plurality of X-ray energies by amplifying the electrical signal with the amplification conditions and converting it into digital data; and an image processing unit that performs image processing based on the plurality of projection data sets based on the amplification conditions. (Appendix 2) The image processing unit may, as image processing, set reconstruction conditions according to the amplification conditions for each of the plurality of projection data sets and perform reconstruction processing. (Appendix 3) The image processing unit may, as image processing, set noise reduction intensity according to the amplification conditions for each of the plurality of projection data sets and perform noise reduction processing. (Note 4) The image processing unit may perform noise reduction processing as image processing by setting a noise reduction intensity corresponding to the amplification conditions for each of the multiple X-ray CT images reconstructed based on the multiple projection datasets. (Note 5) The setting unit may set the amplification conditions for each of the multiple X-ray energies by repeatedly determining whether or not an overflow occurs when amplification processing is performed at the amplification ratio while changing the amplification ratio of the electrical signal. (Note 6) The setting unit may set the amplification conditions as the conditions in which no overflow occurs when the electrical signal is amplified and converted into digital data and the amplification ratio is the largest. (Note 7) The setting unit may determine the equivalent water length for each position in the axial direction of the subject and set the amplification conditions for each of the multiple X-ray energies based on the minimum value of the obtained equivalent water length. (Note 8) The setting unit may determine the equivalent water length based on the scan image collected from the subject before collecting the projection dataset.(Note 9) The setting unit may set the AEC conditions based on the equivalent length of water, and set the amplification conditions based on the minimum value of the equivalent length of water and the AEC conditions. (Note 10) The X-ray control unit may switch the energy of the X-rays between a first X-ray energy and a second X-ray energy lower than the first X-ray energy, and the setting unit may set a first amplification condition corresponding to the first X-ray energy and a second amplification condition corresponding to the second X-ray energy. (Note 11) The setting unit may further set amplification conditions corresponding to the transition states that occur when switching the energy of the X-rays between the plurality of X-ray energies. (Note 12) A medical image processing system comprising: an X-ray CT apparatus comprising: an X-ray control unit that irradiates a subject with X-rays while switching the energy of X-rays between a plurality of X-ray energies; an X-ray detection unit that detects the X-rays and outputs an electrical signal; a setting unit that sets amplification conditions for each of the plurality of X-ray energies; and a data acquisition unit that collects a plurality of projection data sets corresponding to the plurality of X-ray energies by amplifying the electrical signal with the amplification conditions and converting it into digital data; and a medical image processing apparatus comprising: an acquisition unit that acquires the amplification conditions set for each of the plurality of X-ray energies and the plurality of projection data sets; and an image processing unit that performs image processing based on the plurality of projection data sets based on the amplification conditions.

[0129] According to at least one embodiment described above, the quality of X-ray CT images acquired by kV switching can be improved.

[0130] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of 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 variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

An X-ray control unit that irradiates a subject with X-rays while switching between multiple X-ray energy levels, An X-ray detection unit that detects the aforementioned X-rays and outputs an electrical signal, A setting unit for setting amplification conditions for each of the aforementioned plurality of X-ray energies, A data acquisition unit that collects multiple projection data sets corresponding to multiple X-ray energies by amplifying the electrical signal under the amplification conditions and converting it into digital data, An image processing unit that performs image processing based on the plurality of projection datasets based on the amplification conditions, An X-ray CT scanner equipped with [a specific feature]. 　 The X-ray CT apparatus according to claim 1, wherein the image processing unit performs reconstruction processing by setting reconstruction conditions corresponding to the amplification conditions for each of the plurality of projection datasets as the image processing. 　 The X-ray CT apparatus according to claim 1, wherein the image processing unit performs noise reduction processing by setting a noise reduction intensity corresponding to the amplification conditions for each of the plurality of projection datasets as the image processing. 　 The X-ray CT apparatus according to claim 1, wherein the image processing unit performs noise reduction processing by setting a noise reduction intensity corresponding to the amplification conditions for each of the plurality of X-ray CT images reconstructed based on the plurality of projection datasets as the image processing. 　 The X-ray CT apparatus according to claim 1, wherein the setting unit sets the amplification conditions for each of the plurality of X-ray energies by repeatedly determining whether or not an overflow occurs when amplification processing is performed at the amplification rate while changing the amplification rate of the electrical signal. 　 The X-ray CT apparatus according to claim 1, wherein the setting unit sets the amplification condition to the condition that does not cause an overflow when the electrical signal is amplified and converted into digital data and has the greatest amplification factor. 　 The X-ray CT apparatus according to claim 1, wherein the setting unit determines the equivalent water length for each position in the axial direction of the subject, and sets the amplification conditions for each of the plurality of X-ray energies based on the minimum value of the determined equivalent water length. 　 The X-ray CT apparatus according to claim 7, wherein the setting unit determines the equivalent water length based on the scan image collected from the subject before collecting the projection dataset. 　 The X-ray CT apparatus according to claim 7, wherein the setting unit sets the AEC conditions based on the equivalent water length, and sets the amplification conditions based on the minimum value of the equivalent water length and the AEC conditions. 　 The X-ray control unit switches the energy of the X-rays between a first X-ray energy and a second X-ray energy lower than the first X-ray energy. The X-ray CT apparatus according to claim 1, wherein the setting unit sets a first amplification condition corresponding to the first X-ray energy and a second amplification condition corresponding to the second X-ray energy. 　 The X-ray CT apparatus according to claim 1, wherein the setting unit further sets amplification conditions corresponding to transition states that occur when switching the X-ray energy between the plurality of X-ray energies. 　 An X-ray CT apparatus comprising: an X-ray control unit that irradiates a subject with X-rays while switching the energy between multiple X-ray energies; an X-ray detection unit that detects the X-rays and outputs an electrical signal; a setting unit that sets amplification conditions for each of the multiple X-ray energies; and a data acquisition unit that collects multiple projection data sets corresponding to the multiple X-ray energies by amplifying the electrical signal with the amplification conditions and converting it into digital data. A medical image processing apparatus comprising: an acquisition unit that acquires the amplification conditions set for each of the plurality of X-ray energies and the plurality of projection datasets; and an image processing unit that performs image processing based on the plurality of projection datasets based on the amplification conditions. A medical image processing system equipped with [the following features].

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