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

Abstract

The goal is to enable the determination of the respiratory phase suitable for respiratory-gated imaging. [Solution] The medical image processing method of the embodiment involves a computer acquiring monitoring data of the respiratory movements of a subject during imaging using a medical image diagnostic device, determining a reference phase in which the amplitude of respiration is minimized in each of a plurality of respiratory cycles included in the respiratory waveform based on the acquired monitoring data, and determining a respiratory phase to be used for reconstructing a respiratory-gated image based on the determined reference phase.

Description

[Technical Field]

[0001] Embodiments disclosed herein and in the drawings relate to medical image processing methods, medical image processing apparatuses, and programs. [Background technology]

[0002] Traditionally, as a form of medical imaging diagnosis, examinations using PET-CT scanners, which combine PET (Positron Emission Tomography) imaging and X-ray CT (Computed Tomography) imaging, have been performed. Furthermore, in examinations using these PET-CT scanners, a technique called respiratory gating (hereinafter referred to as "respiratory gated PET-CT examination") is employed to reduce image blur caused by organ movement associated with the subject's respiration.

[0003] In respiratory-gated PET-CT scans, the respiratory state of the subject is monitored to generate a respiratory waveform, and only the data corresponding to a specific reference phase is extracted for image reconstruction. As the reference phase, for example, the resting phase (e.g., the expiratory phase) in which the respiratory movement is minimized in each respiratory cycle included in the respiratory waveform is used. This resting phase is determined by defining the point where the respiratory amplitude reaches its upper limit peak in the respiratory waveform as a reference (hereinafter referred to as the "trigger"), and assuming that the center between these triggers is the center of the resting phase. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-233896 [Overview of the project] [Problems that the invention aims to solve]

[0005] The respiratory waveform used in respiratory-gated PET-CT scans changes depending on the subject's respiratory state, with variations in the length and amplitude of the respiratory cycle. As a result, the length of the resting and moving phases changes with each respiratory cycle. Conventional methods assume the center of the resting phase as the center of the trigger interval, and use respiratory phases (phase points) that are estimated to have symmetrical amplitudes before and after this center of the resting phase as a reference for reconstruction. Therefore, if the subject's respiratory state is unstable, it may not be possible to determine a respiratory phase suitable for respiratory gating, resulting in noise and blurring in the generated reconstructed image.

[0006] The problem that the embodiments disclosed herein and in the drawings aim to solve is to enable the determination of a respiratory phase suitable for respiratory-gated imaging. However, the problems that the embodiments disclosed herein and in the drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0007] The medical image processing method of the embodiment involves a computer acquiring monitoring data of the respiratory motion of a subject during imaging using a medical imaging diagnostic device, determining a reference phase in which the amplitude of respiration is minimized in each of a plurality of respiratory cycles included in the respiratory waveform based on the acquired monitoring data, and determining a respiratory phase to be used for reconstructing a respiratory-gated image based on the determined reference phase. [Brief explanation of the drawing]

[0008] [Figure 1] A configuration diagram showing an example of a PET-CT apparatus 1 according to the first embodiment. [Figure 2] A flowchart showing an example of respiratory synchronization processing (first method) by the PET-CT apparatus 1 according to the first embodiment. [Figure 3] A diagram illustrating the overview of respiratory synchronization processing in conventional methods. [Figure 4]A diagram illustrating the phase point determination process based on the respiratory synchronization process of the first method according to the first embodiment. [Figure 5] A flowchart showing an example of respiratory synchronization processing (second method) by the PET-CT apparatus 1 according to the second embodiment. [Figure 6A] A diagram illustrating how the stationary phase MQ (center of the stationary phase MQ) is determined in the second embodiment. [Figure 6B] A diagram illustrating how the stationary phase MQ (center of the stationary phase MQ) is determined in the second embodiment. [Figure 7] A flowchart showing an example of respiratory synchronization processing (third method) by the PET-CT apparatus 1 according to the third embodiment. [Figure 8] A flowchart showing an example of respiratory synchronization processing (fourth method) by the PET-CT apparatus 1 according to the fourth embodiment. [Modes for carrying out the invention]

[0009] The medical image processing method, medical image processing apparatus, and program of the embodiment will be described below with reference to the drawings. The medical image processing apparatus is, for example, a PET apparatus, a PET-CT apparatus, a PET-MR (Magnetic Resonance) apparatus, a CT apparatus, an MR apparatus, etc. In the following description, the case in which the medical image processing apparatus is a PET-CT apparatus will be used as an example.

[0010] <First Embodiment> [PET-CT system configuration] Figure 1 is a configuration diagram showing an example of a PET-CT apparatus 1 according to the first embodiment. The PET-CT apparatus 1 comprises a PET imaging mechanism and a CT imaging mechanism. The PET imaging mechanism detects radiation emitted by radioactive substances contained in a radiopharmaceutical administered to a subject, determines the tendency of radiopharmaceutical accumulation from the detected radiation dose, and generates an image corresponding to the detected radiation dose (hereinafter referred to as "PET image"). The CT imaging mechanism detects X-rays transmitted through the subject from an X-ray tube and generates an image corresponding to the amount of X-rays detected (hereinafter referred to as "CT image"). The PET-CT apparatus 1 generates an image (hereinafter referred to as "PET-CT image") by superimposing the PET image and CT image thus generated. This allows the person performing the PET-CT examination (doctor, technician, etc.) to visually confirm whether or not there is a lesion in the subject's body (and if so, the location, shape, size, etc.).

[0011] The PET-CT apparatus 1 comprises, for example, a PET stand 10, a CT stand 20, a patient table 30, and a console 40. Note that in Figure 1, for illustrative purposes, both views of the PET stand 10 and CT stand 20 from the Z-axis direction and from the X-axis direction are shown; however, in reality, the PET-CT apparatus 1 comprises only one PET stand 10 and one CT stand 20. In this embodiment, the central axis of the frame 13 and the rotating frame 27 in the non-tilted state, or the longitudinal direction of the top plate 33 of the patient table 30, is defined as the Z-axis direction, the axis perpendicular to the Z-axis direction and horizontal to the floor is defined as the X-axis direction, and the direction perpendicular to the Z-axis direction and perpendicular to the floor is defined as the Y-axis direction. The PET-CT apparatus 1 and / or console 40 is an example of a "medical image processing apparatus" within the claims.

[0012] (PET stand device) The PET rig device 10 includes, for example, a radiation detector 11, a data acquisition system (hereinafter referred to as "DAS: Data Acquisition System") 12, a frame 13, and a PET control device 14.

[0013] The radiation detector 11 detects radiation, such as gamma rays, emitted from the subject P (more specifically, the radioactive drug administered to the subject P). The radiation detector 11 outputs an electrical signal (which may also be an optical signal, etc.) to the DAS 12 corresponding to the amount of radiation detected (radiation dose). The radiation detector 11 is formed in a cylindrical shape and is arranged to surround the imaging aperture formed in the PET mount device 10. The radiation detector 11 has, for example, multiple PET detection elements 110 arranged in the circumferential direction and the central axis direction. Each PET detection element 110 detects radiation emitted into the surroundings from the subject P located inside the imaging aperture. The radiation detector 11 outputs an electrical signal to the DAS 12 corresponding to the radiation dose detected by each PET detection element 110.

[0014] DAS12 includes, for example, an amplifier, an integrator, and an A / D converter. The amplifier performs amplification processing on the electrical signals output by each PET detection element 110 of the radiation detector 11. The integrator integrates the amplified electrical signals at predetermined time intervals. The A / D converter converts the electrical signals representing the integration result by the integrator into digital signals. DAS12 outputs acquired data (scan data) based on the digital signals to the console device 40. The acquired data is, for example, a digital value representing the radiation dose collected for each position within the radiation detector 11 where the PET detection elements 110 are located.

[0015] Frame 13 is an annular member that supports the radiation detector 11 and DAS 12. Frame 13 is not limited to an annular member; it may be an arm-like member, as long as it can support the radiation detector 11 and DAS 12.

[0016] The PET control device 14 includes a processing circuit having a processor such as a CPU (Central Processing Unit). The PET control device 14 receives input signals from an input interface 43 attached to the console device 40 or the PET stand device 10 and controls the operation of the PET stand device 10 and the patient bed device 30. For example, the PET control device 14 tilts the PET stand device 10 or moves the top plate 33 of the patient bed device 30. When tilting the PET stand device 10, the PET control device 14 tilts the frame 13 about an axis parallel to the Z-axis direction based on the tilt angle input to the input interface 43. The PET control device 14 knows the tilt angle of the frame 13 by the output of a sensor (not shown), etc. The PET control device 14 also provides the tilt angle of the frame 13 to the console device 40 as needed. The PET control device 14 may be installed on the PET stand device 10 or on the console device 40.

[0017] (CT stand device) The CT stand device 20 includes, for example, an X-ray tube 21, a wedge 22, a collimator 23, an X-ray high-voltage device 24, an X-ray detector 25, a DAS 26, a rotating frame 27, and a CT control device 28.

[0018] The X-ray tube 21 generates X-rays by irradiating thermionic electrons from the cathode (filament) to the anode (target) when a high voltage is applied from the X-ray high-voltage device 24. The X-ray tube 21 includes a vacuum tube. For example, the X-ray tube 21 is a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermionic electrons.

[0019] The wedge 22 is a filter for adjusting the amount of X-rays irradiated onto the subject P from the X-ray tube 21. The wedge 22 attenuates the X-rays that pass through it so that the distribution of the X-ray dose irradiated onto the subject P from the X-ray tube 21 becomes a predetermined distribution. The wedge 22 is made of aluminum, for example, processed to have a predetermined target angle and a predetermined thickness.

[0020] The collimator 23 is a mechanism for narrowing the irradiation area of ​​X-rays that have passed through the wedge 22. The collimator 23 narrows the irradiation area of ​​X-rays by forming a slit, for example, by combining multiple lead plates.

[0021] The X-ray high-voltage device 24 includes, for example, a high-voltage generator and an X-ray control device. The high-voltage generator has an electrical circuit including a transformer and a rectifier, etc., and generates a high voltage to be applied to the X-ray tube 21. The X-ray control device controls the output voltage of the high-voltage generator according to the amount of X-rays to be generated in the X-ray tube 21. The high-voltage generator may perform voltage boosting using the transformer described above, or it may perform voltage boosting using an inverter. The X-ray high-voltage device 24 may be installed on the rotating frame 27, or it may be installed on the side of the fixed frame (not shown) of the CT stand device 20.

[0022] The X-ray detector 25 detects the intensity of X-rays generated by the X-ray tube 21 and incident after passing through the subject P. The X-ray detector 25 outputs an electrical signal (or optical signal, etc.) corresponding to the detected X-ray intensity to the DAS 26. The X-ray detector 25 has, for example, multiple rows of X-ray detection elements. Each of the multiple rows of X-ray detection elements has multiple X-ray detection elements arranged in the channel direction along an arc centered on the focal point of the X-ray tube 21. The multiple rows of X-ray detection elements are arranged in the slice direction (column direction, row direction). The X-ray detector 25 is, for example, an indirect type detector having a grid, a scintillator array, and a photosensor array. The X-ray detector 25 may also be a direct conversion type detector having semiconductor elements that convert incident X-rays into electrical signals.

[0023] The DAS26 includes, for example, an amplifier, an integrator, and an A / D converter. The amplifier performs amplification processing on the electrical signals output by each X-ray detection element of the X-ray detector 25. The integrator integrates the amplified electrical signals over the view period. The A / D converter converts the electrical signals showing the integration result into a digital signal. The DAS26 outputs detection data based on the digital signal to the console device 40. The detection data is a digital value of X-ray intensity identified by the channel number, column number, and view number of the generating X-ray detection element, and the collected view. The view number is a number that changes according to the rotation of the rotating frame 27, for example, a number that is incremented according to the rotation of the rotating frame 27. Therefore, the view number is information indicating the rotation angle of the X-ray tube 21. The view period is the period that falls between the rotation angle corresponding to a certain view number and the rotation angle corresponding to the next view number.

[0024] The rotating frame 27 is an annular member that supports the X-ray tube 21, wedge 22, and collimator 23, and the X-ray detector 25 in opposition to each other. The rotating frame 27 is supported by a fixed frame so as to be rotatable around the subject P introduced inside. The rotating frame 27 further supports the DAS 26. Detection data (scan data) output by the DAS 26 is transmitted by optical communication from a transmitter having a light-emitting diode (LED) provided on the rotating frame 27 to a receiver having a photodiode provided on the non-rotating part (e.g., the fixed frame) of the CT stand device 20, and is then transferred by the receiver to the console device 40. Note that the method of transmitting detection data from the rotating frame 27 to the non-rotating part is not limited to the optical communication method described above, but any non-contact transmission method may be used. The rotating frame 27 is not limited to an annular member, but may be an arm-like member, as long as it can support and rotate the X-ray tube 21, etc.

[0025] The CT control device 28 includes, for example, a processing circuit having a processor such as a CPU, and a drive mechanism including a motor and actuators. The CT control device 28 receives input signals from an input interface 43 attached to the console device 40 or the CT stand device 20, and controls the operation of the CT stand device 20 and the patient bed device 30. For example, the CT control device 28 rotates the rotating frame 27, tilts the CT stand device 20, or moves the top plate 33 of the patient bed device 30. When tilting the CT stand device 20, the CT control device 28 rotates the rotating frame 27 around an axis parallel to the Z-axis direction based on the tilt angle input to the input interface 43. The CT control device 28 knows the rotation angle of the rotating frame 27 by the output of a sensor (not shown), etc. The CT control device 28 also provides the rotation angle of the rotating frame 27 to the console device 40 as needed. The CT control device 28 may be installed on the CT stand device 20 or on the console device 40.

[0026] (Bed equipment) The patient table device 30 is a device that places and moves the subject P to be scanned and introduces it into the frames of the PET stand device 10 and the CT stand device 20. The patient table device 30 comprises, for example, a base 31, a patient table drive device 32, a top plate 33, and a support frame 34. The base 31 includes a housing that supports the support frame 34 so as to be movable in the vertical direction (Y-axis direction). The patient table drive device 32 includes a motor and an actuator. The patient table drive device 32 moves the top plate 33 on which the subject P is placed along the support frame 34 in the longitudinal direction (Z-axis direction) of the top plate 33. The top plate 33 is a plate-shaped member on which the subject P is placed.

[0027] The patient bed drive device 32 may move not only the tabletop 33 but also the support frame 34 in the longitudinal direction of the tabletop 33. Alternatively, the PET stand device 10 and the CT stand device 20 may be movable in the Z-axis direction, and their movement may be controlled so that each frame is positioned around the subject P. Alternatively, both the PET stand device 10 and the CT stand device 20 and the tabletop 33 may be movable. Furthermore, the PET-CT device 1 may be a device in which the subject P is scanned in a standing or sitting position. In this case, the PET-CT device 1 has a subject support mechanism instead of the patient bed device 30, and the PET stand device 10 and the CT stand device 20 move their respective frames in a direction perpendicular to the floor surface.

[0028] (Console device) The console device 40 includes, for example, a memory 41, a display 42, an input interface 43, a network connection circuit 44, and a processing circuit 50. In this embodiment, the console device 40 is described as being separate from the PET stand device 10 and the CT stand device 20, but the PET stand device 10 and / or the CT stand device 20 may include some or all of the components of the console device 40.

[0029] Memory 41 can be implemented using semiconductor memory elements such as ROM (Read Only Memory), RAM (Random Access Memory), or flash memory, or by a hard disk drive (HDD), optical disc, etc. Memory 41 stores data such as acquired data output by DAS12 or DAS26, sinograms generated based on the acquired data, and reconstructed images (PET images, CT images, PET-CT images) generated based on the sinograms.

[0030] These data may be stored not in memory 41 (or in addition to memory 41) but in external memory that the PET-CT device 1 can communicate with. The external memory is controlled by a cloud server, for example, by a cloud server that manages the external memory and accepts read / write requests. The external memory is implemented by a system called PACS (Picture Archiving and Communication Systems). PACS is a medical image management system that systematically stores images taken by various imaging diagnostic devices.

[0031] The display 42 displays various types of information. For example, the display 42 displays reconstructed images (PET images, CT images, PET-CT images) generated by the processing circuit 50, or GUI (Graphical User Interface) images that accept various operations from the operator (doctor, technician, etc.) of the PET-CT device 1. The display 42 can be, for example, a liquid crystal display (LCD), a CRT (Cathode Ray Tube) display, or an organic EL (Electroluminescence) display. The display 42 may be provided on the PET stand device 10 and / or the CT stand device 20. The display 42 may be a desktop type, or it may be a display device (e.g., a tablet terminal) that can communicate wirelessly with the main body of the console device 40.

[0032] The input interface 43 receives various input operations from the operator of the PET-CT device 1 and outputs an electrical signal indicating the content of the received input operation to the processing circuit 50. For example, the input interface 43 receives input operations such as acquisition conditions when collecting scan data, generation conditions when generating a sinogram, reconstruction conditions when reconstructing an image, and image processing conditions when generating a post-processed image. The input interface 43 includes, for example, a mouse, keyboard, trackball, switch, button, joystick, touch panel, etc. The input interface 43 may also be a user interface that accepts audio input, such as a microphone. If the input interface 43 is a touch panel, the input interface 43 may also have the display function of the display 42.

[0033] Furthermore, in this specification, the term "input interface" 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 located separately from the device and outputs this electrical signal to a control circuit is also included as an example of an input interface.

[0034] The network connection circuit 44 includes, for example, a network card having a printed circuit board, or a wireless communication module. The network connection circuit 44 implements an information communication protocol according to the type of network to be connected. The network includes, for example, a LAN (Local Area Network), a WAN (Wide Area Network), the Internet, a cellular network, a dedicated line, etc.

[0035] The processing circuit 50 controls the overall operation of the PET-CT device 1. The processing circuit 50 performs, for example, system control functions 51, acquisition functions 52, judgment functions 53, respiratory synchronization control functions 54, reconstruction functions 55, display control functions 56, etc. The processing circuit 50 realizes these functions, for example, by having a hardware processor execute a program (software) stored in memory 41.

[0036] A hardware processor refers to circuits such as CPUs, GPUs (Graphics Processing Units), Application Specific Integrated Circuits (ASICs), and programmable logic devices (e.g., Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field Programmable Gate Arrays (FPGAs)). Instead of storing the program in memory 41, the hardware processor may be configured to directly embed the program within its circuitry. In this case, the hardware processor performs its functions by reading and executing the program embedded within the circuitry. A hardware processor is not limited to being configured as a single circuit; it may also be configured as a single hardware processor by combining multiple independent circuits to implement each function. Furthermore, multiple components may be integrated into a single hardware processor to implement each function. Alternatively, multiple components may be incorporated into a single dedicated LSI to implement each function. Here, the program (software) may be stored in advance in a storage device that constitutes memory 41, such as ROM, RAM, HDD, or flash memory (a storage device equipped with a non-transient storage medium), or it may be stored in a removable storage medium (a non-transient storage medium) such as a DVD or CD-ROM, and installed in the storage device of the console device 40 when the storage medium is inserted into a drive device provided in the console device 40. Alternatively, the program (software) may be downloaded in advance from another computer device via a network connected by the network connection circuit 44 and installed in the storage device of the console device 40.

[0037] Each component of the console device 40 or the processing circuit 50 may be distributed and implemented by multiple hardware components. The processing circuit 50 may not be implemented by the console device 40, but by a processing unit that can communicate with the console device 40. The processing unit is, for example, a workstation connected to one PET-CT device, or a device (e.g., a cloud server) connected to multiple PET-CT devices that performs processing equivalent to that of the processing circuit 50 described below in a batch. In other words, the configuration of this embodiment can also be implemented as a PET-CT examination system in which a PET-CT device and other processing units are connected via a network. In this case, other processing units such as workstations are examples of "medical image processing units" in the claims.

[0038] The system control function 51 controls various functions of the processing circuit 50, for example, based on input operations received by the input interface 43. The system control function 51 also controls various functions by issuing instructions to the DAS 12, PET control device 14, DAS 26, CT control device 28, and bed drive device 32, for example, based on input operations received by the input interface 43.

[0039] The acquisition function 52 acquires scan data of the subject P obtained by imaging using the PET-CT device 1 (medical imaging diagnostic device) from the PET stand device 10 and / or CT stand device 20. The acquisition function 52 also acquires monitoring data of the subject P's respiratory activity during imaging from the respiratory sensor 60. The acquisition function 52 is an example of the "acquisition unit" in the claims.

[0040] The determination function 53 generates a respiratory waveform (respiratory motion waveform) of the subject P during imaging based on the acquired monitoring data, and determines each of the multiple respiratory cycles based on the peak of the upper limit of the amplitude of the subject P's respiration in the generated respiratory waveform. The determination function 53 is an example of the "determination unit" in the claims.

[0041] The respiratory synchronization control function 54 determines a reference phase (resting phase) in which the respiratory amplitude is minimized in each of the multiple respiratory cycles included in the respiratory waveform based on the acquired monitoring data, and determines the respiratory phase to be used for reconstructing the respiratory-synchronized image based on the determined reference phase. The resting phase indicates the phase in which the respiratory amplitude is minimized in each of the multiple respiratory cycles, that is, the phase with the least respiratory movement. The resting phase corresponds to, for example, the expiratory phase. The respiratory synchronization control function 54 determines the respiratory phase included in a preset first phase width based on the reference phase as the respiratory phase to be used for reconstructing the respiratory-synchronized image. Furthermore, the respiratory synchronization control function 54 adjusts the reference phase based on a preset phase offset (phase adjustment value), and determines the respiratory phase to be used for reconstructing the respiratory-synchronized image based on the adjusted reference phase. The respiratory synchronization control function 54 is an example of a "respiratory synchronization control unit" in the claims.

[0042] The reconstruction function 55 performs predetermined preprocessing on the scan data output by DAS12, performs predetermined reconstruction processing to generate a PET image, and stores the generated PET image in memory 41. The reconstruction function 55 also performs predetermined preprocessing on the scan data output by DAS26, performs predetermined reconstruction processing to generate a CT image, and stores the generated CT image in memory 41. Existing methods such as iterative reconstruction are used as the image reconstruction algorithm. The reconstruction function 55 is an example of the "reconstruction unit" in the claims.

[0043] The display control function 56 controls the display mode of the display 42. For example, the display control function 56 controls the display 42 to display PET-CT images generated by the processing circuit 50, GUI images that accept various operations from the operator of the PET-CT device 1, etc. The display control function 56 is an example of a "display control unit" in the claims.

[0044] (Respiration sensor) The respiratory sensor 60 transmits monitoring data, which monitors the respiratory movements of the subject P, to the console device 40. The respiratory sensor 60 is, for example, a pressure sensor attached to the chest or abdomen of the subject P to collect changes in chest pressure in response to the subject P's respiratory movements. Alternatively, the respiratory sensor 60 may be a non-contact sensor that collects the respiratory cycle of the subject P by measuring the amount of displacement of the subject P's body surface using infrared light or a camera.

[0045] In this embodiment, a device-based respiratory synchronization process using a respiratory sensor 60 is described as an example, but a device-less respiratory synchronization process that automatically extracts body movement information from the collected data itself and performs respiratory synchronization may also be implemented.

[0046] <Respiratory synchronization processing (first method)> Next, the respiratory synchronization process in the PET-CT device 1 will be described. Figure 2 is a flowchart showing an example of the respiratory synchronization process (first method) by the PET-CT device 1 according to the first embodiment. The process shown in Figure 2 is started when the respiratory sensor 60 is attached to the subject P to be examined and placed on the examination table device 30, and an input operation (scan start operation) is performed by the operator via the input interface 43.

[0047] First, while the PET and / or CT scans are being performed on subject P, the acquisition function 52 acquires monitoring data of subject P's respiratory activity from the respiratory sensor 60 (step S101). During this time, the acquisition function 52 also acquires scan data acquired by the PET stand 10 and / or CT stand 20. The acquisition function 52 stores the acquired monitoring data and scan data in the memory 41.

[0048] Subsequently, after the scan of subject P is completed (or in parallel with the scan), the determination function 53 generates a respiratory waveform using the acquired monitoring data and performs trigger determination (respiratory cycle determination) based on the generated respiratory waveform (step S103). A trigger indicates the start or end point of the respiratory cycle. For example, a trigger corresponds to the peak of the upper limit of the respiratory amplitude.

[0049] Next, the respiratory synchronization control function 54 focuses on one of the respiratory cycles determined above (the first respiratory cycle) and determines the waveform minimum point M, which is the phase in which the amplitude of respiration is minimized. min The determination is made (step S105). Furthermore, the determination function 53 determines the minimum point M of this waveform. min The stationary phase M Q It is determined that (M Q =M min )(Step S107).

[0050] Waveform minimum point M by respiratory synchronization control function 54 minThe determination process will be described in detail. FIG. 3 is a diagram for explaining a respiratory waveform showing an irregular respiratory motion and an overview of the respiratory synchronization process in the conventional method. As shown in FIG. 3, in the conventional method, the peak of the upper limit of the amplitude in the respiratory waveform is used as a trigger (T1 to T7) for determination, and the interval between adjacent triggers is determined as one respiratory cycle (one respiratory cycle). Further, the midpoint on the horizontal axis (time axis) between adjacent triggers is determined as the reference phase CP (rest phase), and the phase points symmetrically located with this reference phase CP as the reference (center) are determined as the synchronized phase points for respiration and used for the subsequent image reconstruction process. For example, for the first respiratory cycle (the first trigger T1 to the second trigger T2), the midpoint on the horizontal axis (time axis) of both triggers is determined as the reference phase CP1, and the respiratory phases (phase points included in a predetermined phase width SP, for example, phase points PP1a, PP1b, etc.) symmetrically located with this reference phase CP1 as the reference are determined. When the respiratory waveform maintains left-right symmetry with the reference phase CP1 as the reference as in the first respiratory cycle, appropriate phase points can be determined even with this conventional method. However, for example, for the sixth respiratory cycle (the sixth trigger T6 to the seventh trigger T7), when left-right symmetry is not maintained with the reference phase CP6, which is the midpoint on the horizontal axis (time axis) of both triggers, respiratory phases (phase points included in the phase width NSP, for example, phase points PP6a, PP6b, etc.) that are not suitable for respiratory synchronization are determined.

[0051] On the other hand, FIG. 4 is a diagram for explaining the determination process of phase points based on the respiratory synchronization process of the first method according to the first embodiment. In this embodiment, instead of using the midpoint on the horizontal axis (time axis) between adjacent triggers as the reference phase CP, the phase at which the amplitude of respiration is minimum is determined as the waveform minimum point M min and used as the rest phase. For example, for the first respiratory cycle (the first trigger T1 to the second trigger T2), the waveform minimum point M min1 at which the amplitude of respiration is minimum in this cycle is determined as the rest phase. Also, for example, for the sixth respiratory cycle (the sixth trigger T6 to the seventh trigger T7), the waveform minimum point M min6 at which the amplitude of respiration is minimum in this cycle is determined as the rest phase.

[0052] Returning to Figure 2, next, the respiratory synchronization control function 54 has a phase offset M offset Using the stationary phase M Q The adjusted version is the reference phase M phase This is determined (step S109). The phase offset is a phase adjustment value used to adjust the position of the reference phase. The phase offset is set in advance by the operator or the like. For example, the respiratory synchronization control function 54 determines the reference phase M based on the following equation (1). phase Determine.

[0053] M phase =M Q +M offset ...Formula (1)

[0054] As shown in Figure 4, for example, when this phase offset is set, the waveform minimum point M occurs in the second respiratory cycle. min2 After this is determined, the minimum point M of this waveform min2 (= resting phase M) Q ) with phase offset M offset The result of adding this to the reference phase M phase2 This is determined. The phase offset is set to be applied similarly to all respiratory cycles. Note that the phase offset does not need to be set (phase offset M offset =0).

[0055] Returning to Figure 2, next, the respiratory synchronization control function 54 is set to reference phase M phase Phase point M based on PhPoints The determination is made (step S111). For example, the respiratory synchronization control function 54 determines the phase point M based on the following equation (2). PhPoints Determine.

[0056] M PhPoints =M phase -W to M phase +W…Formula (2)

[0057] In equation (2) above, W represents a predetermined phase width (first phase width). The phase width W is set in advance by the operator or other person. As shown in Figure 4, for the first respiratory cycle (first trigger T1 to second trigger T2), the reference phase Mphase1 Based on this, the phase points included in the phase range W before and after that point on the horizontal axis (time axis) are determined. Furthermore, for the 6th respiratory cycle (6th trigger T6 to 7th trigger T7), the reference phase M phase6 Based on this, the phase points included in the phase width W before and after that point on the horizontal axis (time axis) are determined. By determining the phase points in this way, it becomes possible to determine a phase point suitable for respiratory synchronization even for respiratory waveforms where symmetry is not maintained when the midpoint on the horizontal axis (time axis) of both triggers is determined as the reference phase (for example, the 6th respiratory cycle).

[0058] Returning to Figure 2, the respiratory synchronization control function 54 then determines whether the processing of the last respiratory cycle in the respiratory waveform has been completed (whether processing for all respiratory cycles has been completed) (step S113). If the respiratory synchronization control function 54 determines that the processing of the last respiratory cycle has not been completed, it returns to step S105 and performs processing for the unprocessed respiratory cycles. On the other hand, if the respiratory synchronization control function 54 determines that the processing of the last respiratory cycle has been completed, it terminates the processing in this flowchart.

[0059] Subsequently, the reconstruction function 55 reconstructs the PET-CT image using the scan data corresponding to the phase point determined as described above during each respiratory cycle. The display control function 56 displays the reconstructed PET-CT image on the display 42. This allows the operator to confirm the respiratory-synchronized PET-CT image displayed on the display 42.

[0060] According to the first embodiment described above, it becomes possible to determine a respiratory phase suitable for respiratory-gated imaging. As a result, by reconstructing the image using the data corresponding to the determined respiratory phase, it becomes possible to improve the image quality of the final medical image.

[0061] <Second Embodiment> Next, a second embodiment will be described. The second embodiment differs from the first embodiment in its method for determining the stationary phase. In the following description, components and functions identical to those in the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0062] <Respiratory synchronization processing (second method)> Figure 5 is a flowchart showing an example of respiratory synchronization processing (second method) by the PET-CT apparatus 1 according to the second embodiment. Since the processing from steps S101 to S105 is the same as in the first embodiment described above, a detailed explanation is omitted.

[0063] The respiratory synchronization control function 54 controls the waveform minimum point M in step S105. min After determining this, the minimum point M of this waveform min Based on the amplitude symmetry in the vicinity, the stationary phase M Q The determination is made (step S207). For example, the respiratory synchronization control function 54 determines the resting phase M based on the following equation (3). Q Determine.

[0064] Rest phase M Q =MIN(|A(M min -W Q )|-|A(M min +W Q )|)…Formula (3)

[0065] In equation (3) above, W Q This indicates a predetermined stationary phase width (second phase width). Stationary phase width W Q This is set in advance by the operator, etc. Static phase width W Q For example, it is narrower than the phase width W mentioned above. A represents the amplitude. The equation within the MIN function (minimization function) represents the waveform minimum point M. min The horizontal axis (time axis) before and after the reference point (center) W Q This shows the difference in amplitude D at the position.

[0066] Figures 6A and 6B show the stationary phase M in the second embodiment. Q (Still phase M) QThis diagram illustrates how the center of the waveform is determined. As shown in Figure 6A, the minimum waveform point M determined in step S105 min Using this as the reference point (center), the horizontal axis (time axis) is before and after W Q If the amplitudes at the phase position are amplitude PP1 and amplitude PP2, the difference D1 between amplitude PP1 and amplitude PP2 is calculated by the following equation (4).

[0067] D1=|A(M min -W Q )|-|A(M min +W Q )|)…Formula (4)

[0068] In the process of step S207 described above, the respiratory synchronization control function 54 controls the waveform minimum point M determined in step S105. min Move (adjust) it on the horizontal axis (time axis) to find the waveform minimum point M that minimizes the above difference D. min We search for the minimum waveform point M in Figure 6A, as shown in Figure 6B. min (The minimum waveform point M determined in step S105) min When the waveform is moved in the negative direction of the horizontal axis (time axis), the minimum waveform point M after the movement is obtained. min Using this as the reference point (center), the horizontal axis (time axis) is before and after W Q If the amplitudes at the phase positions are denoted as amplitude PP1' and amplitude PP2', the difference D2 between amplitude PP1' and amplitude PP2' is calculated by the following equation (5).

[0069] D2=|A(M min -W Q )|-|A(M min +W Q )|)…Formula (5)

[0070] Comparing the difference D1 in Figure 6A with the difference D2 in Figure 6B, it can be seen that the difference D2 is smaller than the difference D1. Thus, the respiratory synchronization control function 54 determines the minimum waveform point M within a predetermined phase width (first phase width). min Move the waveform on the horizontal axis (time axis) and find the minimum waveform point M that minimizes the above difference D. min The search is conducted to find the minimum waveform point M. minThe stationary phase M Q This is the conclusion.

[0071] In other words, the respiratory synchronization control function 54 adjusts the reference phase based on the symmetry of the respiratory amplitude corresponding to the respiratory phase included in a preset second phase width with respect to the reference phase, before and after the reference phase, and determines the respiratory phase to be used for reconstructing the respiratory-synchronized image based on the adjusted reference phase.

[0072] Next, the respiratory synchronization control function 54 determines the resting phase M as described above. Q Phase offset M offset The adjusted version is the reference phase M phase The system determines this and then executes the subsequent processing. Since the processing from steps S109 to S113 is the same as in the first embodiment described above, a detailed explanation is omitted.

[0073] According to the second embodiment described above, it becomes possible to determine the respiratory phase suitable for respiratory-gated imaging. By reconstructing the image using the data corresponding to the determined respiratory phase, it is possible to improve the image quality of the final medical image. Furthermore, the waveform minimum point M min Based on the amplitude symmetry in the vicinity, the stationary phase M Q (Still phase M) Q By determining the center of the respiratory phase, it becomes possible to determine a respiratory phase that is more suitable for respiratory synchronization.

[0074] <Third Embodiment> Next, a third embodiment will be described. The third embodiment differs from the second embodiment in its method for determining the respiratory phase (phase point). In the following description, components and functions identical to those in the second embodiment will be denoted by the same reference numerals, and detailed explanations will be omitted.

[0075] <Respiratory synchronization processing (third method)> Figure 7 is a flowchart showing an example of respiratory synchronization processing (third method) by the PET-CT apparatus 1 according to the third embodiment. Since the processing in steps S101 to S105, S207, S109, and S113 is the same as in the second embodiment described above, a detailed explanation is omitted.

[0076] The respiratory synchronization control function 54 controls the reference phase M in step S109. phase After determining the reference phase M phase Within a predetermined phase width (first phase width) with the reference (center) as the reference phase M phase Phase point M with an amplitude close to PhPoints The determination is made (step S311). For example, the respiratory synchronization control function 54 determines the phase point M based on the following equations (6) to (8). PhPoints Determine.

[0077] PhDiff[M] = |A(M) - A(M) phase )|)…Formula (6) PhDiff sorted =sort(PhDiff)…Formula (7) M PhPoints =Ph Diff sorted [1:2W]…Formula (8)

[0078] According to equation (6) above, the reference phase M phase The amplitude of each phase point within a predetermined phase width (first phase width) with the reference (center) as the reference, and the reference phase M phase The difference PhDff between the amplitude and the signal is calculated. Then, the difference PhDiff is sorted according to equation (7) above. Furthermore, according to equation (8) above, a predetermined number of phase points are selected from the sorted phase points in order of increasing difference PhDiff.

[0079] In other words, the respiratory synchronization control function 54 determines the respiratory phase to be used for reconstructing the respiratory-synchronized image based on the difference between the respiratory amplitude corresponding to the reference phase and the respiratory amplitude corresponding to each respiratory phase included in a preset first phase width based on the reference phase, for each respiratory cycle.

[0080] Next, the respiratory synchronization control function 54 repeats the above process for each respiratory cycle. Since the process of step S113 is the same as that of the second embodiment described above, detailed description thereof will be omitted.

[0081] As described above, according to the third embodiment, it is possible to determine a respiratory phase suitable for respiratory synchronized imaging. By reconstructing an image using data corresponding to the respiratory phase thus determined, it is possible to improve the image quality of the finally obtained medical image. Further, based on the symmetry of the amplitude near the waveform minimum point M min it is possible to determine the stationary phase M Q (the center of the stationary phase M Q ), and thus it is possible to determine a respiratory phase more suitable for respiratory synchronization. Further, within a predetermined phase width (first phase width) with the reference phase M phase as a reference (center), by determining the phase point M phase having an amplitude close to the reference phase M PhPoints , it is possible to automatically determine a respiratory phase even more suitable for respiratory synchronization.

[0082] <Fourth Embodiment> Next, the fourth embodiment will be described. In the fourth embodiment, the method for determining the respiratory phase is different from that of the second embodiment. In the following description, the same components and functions as those of the second embodiment are denoted by the same reference numerals as those of the second embodiment, and detailed description thereof will be omitted.

[0083] <Respiratory Synchronization Process (Fourth Method)> FIG. 8 is a flowchart showing an example of the respiratory synchronization process (fourth method) by the PET-CT apparatus 1 according to the fourth embodiment. Since the processes of steps S101 to S105, S207, S109, and S113 are the same as those of the second embodiment described above, detailed description thereof will be omitted.

[0084] After determining the reference phase M phase in step S109, the respiratory synchronization control function 54 determines the reference phase M phase and the reference phase M phaseDetermine the difference in amplitude from the phase points within a predetermined phase width (first phase width) centered on

[0085] idx = M × r length + r… Equation (9) PhDiff[idx] = |A(M) - A(M center )|… Equation (10)

[0086] The above Equation (9) indicates the phase index. In the above Equation (10), M center represents the center of the reference phase M phase . The difference in amplitude at each phase index is calculated by the above Equation (10).

[0087] Next, the respiration synchronization control function 54 determines whether the processing of the last respiration cycle in the respiration waveform has been completed (whether the processing for all respiration cycles has been completed) (step S113). If the respiration synchronization control function 54 determines that the processing of the last respiration cycle has not been completed, it returns to step S105 and executes the processing for the next respiration cycle.

[0088] On the other hand, if the respiration synchronization control function 54 determines that the processing of the last respiration cycle has been completed, it determines the phase point M phase having an amplitude close to the reference phase M PhPoints_ALL in all respiration cycles (step S415). For example, the respiration synchronization control function 54 determines the phase point M PhPoints_ALL based on the following Equations (11) to (13).

[0089] PhDiff sorted = sort(PhDiff) … Equation (11) N Points = 2 × W × r… Equation (12) M PhPoints_ALL = PhDiff sorted [1:N Points … Equation (13)

[0090] According to equation (11) above, the amplitude differences PhDiff[idx] for all respiratory cycles determined in step S411 above are sorted. Furthermore, according to equations (12) and (13) above, a predetermined number of phase points are selected from the sorted phase points in ascending order of their PhDiff differences. This completes the processing of this flowchart.

[0091] In other words, the respiratory synchronization control function 54 calculates the difference between the respiratory amplitude corresponding to the reference phase and the respiratory amplitude corresponding to each respiratory phase included in a preset first phase width based on the reference phase, and determines the respiratory phase to be used for reconstructing the respiratory-synchronized image based on the comparison result of the magnitude of the difference in all respiratory cycles included in the respiratory waveform.

[0092] According to the fourth embodiment described above, it becomes possible to determine the respiratory phase suitable for respiratory-gated imaging. By reconstructing the image using the data corresponding to the determined respiratory phase, it is possible to improve the image quality of the final medical image. Furthermore, the waveform minimum point M min Based on the amplitude symmetry in the vicinity, the stationary phase M Q (Still phase M) Q By determining the center of the respiratory phase, it becomes possible to determine a respiratory phase more suitable for respiratory synchronization. Furthermore, throughout the entire respiratory cycle, the reference phase M phase Phase point M with an amplitude close to PhPoints By determining this, it becomes possible to automatically determine a more suitable respiratory phase through respiratory synchronization.

[0093] While several embodiments of the present invention 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 carried out in a variety of other forms, and various omissions, substitutions, and modifications 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. [Explanation of Symbols]

[0094] 1…PET-CT scanner, 10…PET stand, 11…Radiation detector, 12…Data acquisition system (DAS), 13…Frame, 14…PET control unit, 20…CT stand, 21…X-ray tube, 22…Wedge, 23…Collimator, 24…X-ray high voltage device, 25…X-ray detector, 26…DAS, 27…Rotating frame, 28…CT control unit, 30…Clinic table, 31…Base, 32…Clinic table drive unit, 33…Tabletop, 34…Support frame, 40…Console unit, 41…Memory, 42…Display, 43…Input interface, 44…Network connection circuit, 50…Processing circuit, 51…System control function, 52…Acquisition function, 53…Determination function, 54…Respiratory synchronization control function, 55…Reconstruction function, 56…Display control function

Claims

1. Computers We acquire monitoring data of the subject's respiratory movements during imaging using a medical imaging diagnostic device. Based on the acquired monitoring data, a reference phase is determined for each of the multiple respiratory cycles included in the respiratory waveform, where the respiratory amplitude is minimized. Based on the determined reference phase, the respiratory phase to be used for reconstructing the respiratory-gated image is determined. Medical image processing methods.

2. Furthermore, in the respiratory waveform, each of the plurality of respiratory cycles is determined based on the peak of the upper limit of the amplitude of the subject's respiration. The medical image processing method according to claim 1.

3. The respiratory phase included in a preset first phase width based on the aforementioned reference phase is determined to be the respiratory phase used for reconstructing the respiratory-gated image. The medical image processing method according to claim 1.

4. Based on a preset phase adjustment value, the reference phase is adjusted. Based on the adjusted reference phase, the respiratory phase to be used for reconstructing the respiratory-gated image is determined. The medical image processing method according to claim 1.

5. Based on the symmetry of the amplitude of respiration corresponding to the respiration phase included in a preset second phase width with respect to the aforementioned reference phase, before and after the reference phase, the reference phase is adjusted. Based on the adjusted reference phase, the respiratory phase to be used for reconstructing the respiratory-gated image is determined. The medical image processing method according to claim 1.

6. In each of the respiratory cycles, the respiratory phase to be used for reconstructing the respiratory-synchronized image is determined based on the difference between the respiratory amplitude corresponding to the reference phase and the respiratory amplitude corresponding to each of the respiratory phases included in a preset first phase width based on the reference phase. The medical image processing method according to claim 1.

7. In each of the respiratory cycles, the difference between the respiratory amplitude corresponding to the reference phase and the respiratory amplitude corresponding to each respiratory phase included in a preset first phase width based on the reference phase is calculated. Based on the comparison of the magnitude of the difference in the entire respiratory cycle included in the respiratory waveform, the respiratory phase to be used for reconstructing the respiratory-gated image is determined. The medical image processing method according to claim 1.

8. Computers We acquire monitoring data of the subject's respiratory movements during imaging using a PET-CT (Positron Emission Tomography-Computed Tomography) device. Based on the acquired monitoring data, a reference phase is determined for each of the multiple respiratory cycles included in the respiratory waveform, where the respiratory amplitude is minimized. Based on the determined reference phase, the respiratory phase to be used for reconstructing the respiratory-gated PET-CT image is determined. Medical image processing methods.

9. An acquisition unit that acquires monitoring data of the respiratory movements of a subject during imaging using a medical imaging diagnostic device, A respiratory synchronization control unit determines a reference phase in which the respiratory amplitude is minimized in each of the multiple respiratory cycles included in the respiratory waveform based on the acquired monitoring data, and determines the respiratory phase to be used for reconstructing the respiratory synchronization image based on the determined reference phase. A medical image processing device equipped with [a specific feature].

10. On the computer, During imaging using a medical imaging diagnostic device, monitoring data of the subject's respiratory movements is acquired. In each of the multiple respiratory cycles included in the respiratory waveform based on the acquired monitoring data, the reference phase in which the respiratory amplitude is minimized is determined. Based on the determined reference phase, the respiratory phase to be used for reconstructing the respiratory-gated image is determined. program.

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