JP7370802B2 - Medical image processing equipment and X-ray CT equipment - Google Patents

Description

Embodiments of the present invention relate to a medical image processing device and an X-ray CT device.

During imaging with an X-ray CT device, view and ray errors may occur due to discharge of the X-ray tube, malfunction of the X-ray detector, communication error of the DAS (Data Acquisition System), etc. Projection data may not be collected properly due to missing data at this level.

If there is data missing in the projection data, the quality of the reconstructed image deteriorates, so conventionally, this was handled by interpolating the missing data with normal data near the data location where the missing data was located. was.

JP2015-29913A

However, when data loss in projection data is widespread, it may not be possible to suppress deterioration of image quality only by interpolation using neighboring normal data.

The problem to be solved by the present invention is to improve the image quality of a reconstructed image due to data loss in projection data.

The medical image processing apparatus according to the embodiment includes an acquisition section, a first generation section, a reconstruction section, a second generation section, and a third generation section. The acquisition unit acquires information regarding missing data based on first projection data obtained by scanning the subject. The first generation unit generates second projection data by interpolating missing data in the first projection data based on information regarding the missing data. The reconstruction unit reconstructs the second projection data and generates a first reconstructed image. The second generation unit forward-projects the first reconstructed image and generates third projection data. The third generation unit updates the second projection data based on the third projection data to generate fourth projection data. The reconstruction unit generates a second reconstructed image based on the fourth projection data.

FIG. 1 is a block diagram showing a configuration example of an X-ray CT apparatus, a medical image storage apparatus, and a medical image processing apparatus according to an embodiment. FIG. 2 is a block diagram showing a configuration example of an image generation function within the processing circuit. FIG. 3 is a flowchart illustrating a processing example of the embodiment. FIG. 4A is a diagram illustrating an example of the range of reconstruction for missing rays. FIG. 4B is a diagram illustrating an example of the forward projection range for ray loss. FIG. 5A is a diagram (1) illustrating an example of the range of reconstruction and forward projection for view defects. FIG. 5B is a diagram (2) illustrating an example of the range of reconstruction and forward projection for view defects. FIG. 6 is a flowchart illustrating a processing example of a modification of the embodiment. FIG. 7A is a diagram for explaining a modification of the embodiment. FIG. 7B is a diagram for explaining a modification of the embodiment. FIG. 7C is a diagram for explaining a modification of the embodiment.

Hereinafter, embodiments of a medical image processing device and an X-ray CT device will be described with reference to the drawings. Note that the embodiment is not limited to the following content. Moreover, the content described in one embodiment or modification example is, in principle, similarly applied to other embodiments or modification examples.

The configuration of an X-ray CT apparatus 1 according to an embodiment will be described with reference to FIG. 1. FIG. 1 is a block diagram showing a configuration example of an X-ray CT apparatus 1, a medical image storage apparatus 60, and a medical image processing apparatus 70 according to an embodiment. In FIG. 1, an X-ray CT apparatus 1, a medical image storage apparatus 60, and a medical image processing apparatus 70 are communicably connected to each other via a communication network 5. Note that when the X-ray CT apparatus 1 is used alone, there is no need for connection to the communication network 5, and no need for the medical image storage device 60 or the medical image processing device 70. Furthermore, when processing of projection data and the like is performed in the medical image processing apparatus 70, the function corresponding to the processing can be omitted from the X-ray CT apparatus 1.

The X-ray CT apparatus 1 includes a gantry device 10, a bed device 30, and a console device 40. Although a plurality of gantry devices 10 are depicted in FIG. 1 for convenience of explanation, there is basically one gantry device 10 in the actual configuration. In FIG. 1, the Z-axis direction is the rotation axis of the rotation frame 16 of the gantry device 10 in a non-tilted state or the longitudinal direction of the top plate 33 of the bed device 30. Further, the axial direction that is orthogonal to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction. Further, the axial direction that is orthogonal to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

The gantry device 10 includes an X-ray tube 11, an X-ray detector 15, a rotating frame 16, an X-ray high voltage device 17, a control device 18, a wedge 19, a collimator 20, and a DAS (Data Acquisition System). 21.

The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) toward an anode (target) using a high voltage from an X-ray high voltage device 17. For example, the X-ray tube 11 includes a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons. This embodiment can be applied to both a single-tube type X-ray CT device and a so-called multi-tube type X-ray CT device in which multiple pairs of X-ray tubes and detectors are mounted on a rotating ring. It is. Furthermore, the hardware that generates X-rays is not limited to the X-ray tube 11. For example, instead of the X-ray tube 11, a focus coil that focuses the electron beam generated from an electron gun, a deflection coil that electromagnetically deflects the electron beam, and the deflected electron beam surrounds half the circumference of the subject P and collides with it to emit X-rays. X-rays may be generated using a fifth generation method including a target ring for generating X-rays.

The X-ray high-voltage device 17 has electric circuits such as a transformer and a rectifier, and includes a high-voltage generation circuit that generates a high voltage to be applied to the X-ray tube 11 and a high-voltage generating circuit that generates a high voltage to be applied to the and an X-ray control circuit that controls the output voltage according to the output voltage. The high voltage generation circuit may be of a transformer type or an inverter type. Note that the X-ray high voltage device 17 not only generates high voltage, but also supplies power to the filament, and supplies driving power when the anode is of a rotating type. Further, the X-ray high voltage device 17 may be provided on the rotating frame 16 or may be provided on the fixed frame (not shown) side of the gantry device 10. Note that the fixed frame is a frame that rotatably supports the rotating frame 16.

The X-ray detector 15 detects the X-rays emitted from the X-ray tube 11 and passed through the subject P, and outputs a signal corresponding to the detected X-ray dose to the DAS 21. The X-ray detector 15 includes, for example, a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction (circling direction) along one circular arc centered on the focal point of the X-ray tube 11. have The X-ray detector 15 has, for example, a structure in which a plurality of X-ray detection element rows in which a plurality of X-ray detection elements are arranged in the channel direction are arranged in the slice direction (column direction, row direction).

Further, the X-ray detector 15 is, for example, an indirect conversion type detector having a grid, a scintillator array, and a photosensor array. A scintillator array has multiple scintillators. The scintillator has a scintillator crystal that outputs light with an amount of photons corresponding to the amount of incident X-rays. The grid is disposed on the X-ray incident side of the scintillator array and has an X-ray shielding plate that absorbs scattered X-rays. Note that the grid is sometimes called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array has a function of converting the amount of light from the scintillator into an electrical signal, and includes optical sensors such as photodiodes and photomultiplier tubes (PMTs). Note that the X-ray detector 15 may be a direct conversion type detector having a semiconductor element that converts incident X-rays into electrical signals.

The rotating frame 16 (mount base) is an annular frame that supports the X-ray tube 11 and the X-ray detector 15 so as to face each other, and allows the X-ray tube 11 and the X-ray detector 15 to be rotated by the control device 18 . For example, the rotating frame 16 is cast from aluminum. Note that, in addition to the X-ray tube 11 and the X-ray detector 15, the rotating frame 16 can also support the X-ray high voltage device 17 and the DAS 21. Additionally, rotating frame 16 may further support various configurations not shown in FIG. Below, in the gantry device 10, the portion that rotates and moves together with the rotating frame 16 and the rotating frame 16 will also be referred to as a rotating section. Although we have described the Rotate/Rotate-Type (third generation CT) in which the X-ray tube 11 and the X-ray detector 15 rotate around the subject P as a unit, there are other types of CT in which the X-ray tube 11 and the X-ray detector 15 are arranged in a ring shape. There are various types such as Stationary/Rotate-Type (4th generation CT) in which a large number of X-ray detection elements are fixed and only the X-ray tube 11 rotates around the subject P, and any type can be applied to this embodiment. Applicable.

Note that the detection data generated by the DAS 21 is transmitted from a transmitter having a light emitting diode (LED) provided in the rotating frame 16 to a photodiode provided in a non-rotating portion of the gantry device 10 by optical communication. and is transferred to the console device 40. Here, the non-rotating portion is, for example, a fixed frame (not shown in FIG. 1) that rotatably supports the rotating frame 16. Note that the method for transmitting detection data from the rotating frame 16 to the non-rotating part of the gantry device 10 is not limited to optical communication, but any method that can transmit data between the rotating part and the non-rotating part can be used. I don't mind if you do.

The control device 18 includes a drive mechanism such as a motor and an actuator, and a circuit that controls this mechanism. The control device 18 receives input signals from the input interface 43, the input interface provided on the gantry device 10, and the like, and controls the operations of the gantry device 10 and the bed device 30. For example, the control device 18 controls the rotation of the rotating frame 16, the tilt of the gantry device 10, the operation of the bed device 30 and the top plate 33, and the like. For example, as a control for tilting the gantry device 10, the control device 18 rotates the rotation frame 16 about an axis parallel to the X-axis direction based on input inclination angle (tilt angle) information. Note that the control device 18 may be provided on the gantry device 10 or may be provided on the console device 40.

The wedge 19 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11. Specifically, the wedge 19 transmits and attenuates the X-rays emitted from the X-ray tube 11 so that the X-rays emitted from the X-ray tube 11 to the subject P have a predetermined distribution. This is a filter that For example, the wedge 19 is a wedge filter or a bow-tie filter, and is formed by processing aluminum or the like to have a predetermined target angle and a predetermined thickness.

The collimator 20 is a lead plate or the like for narrowing down the irradiation range of the X-rays that have passed through the wedge 19, and forms a slit by combining a plurality of lead plates or the like. Note that the collimator 20 is sometimes called an X-ray diaphragm. The aperture and position of the collimator 20 are adjusted by a collimator adjustment circuit (not shown). Thereby, the irradiation range of the X-rays generated by the X-ray tube 11 is adjusted.

The DAS 21 includes an amplifier that performs amplification processing on the electrical signal output from each X-ray detection element of the X-ray detector 15, and an A/D converter that converts the electrical signal into a digital signal. generate. DAS21 is realized by a processor, for example. The detection data generated by the DAS 21 is transferred to the console device 40. Further, the DAS 21 is an example of a data collection unit.

The bed device 30 is a device on which a subject P to be scanned is placed and moved, and includes a base 31, a bed driving device 32, a top plate 33, and a support frame 34. The base 31 is a casing that supports the support frame 34 movably in the vertical direction. The bed driving device 32 is a drive mechanism that moves the top plate 33 on which the subject P is placed in the longitudinal direction of the top plate 33, and includes a motor, an actuator, and the like. The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. In addition to the top plate 33, the bed driving device 32 may move the support frame 34 in the longitudinal direction of the top plate 33. Only the top plate 33 may be moved, or the support frame of the bed device 30 may be moved together. When applied to standing CT, a method may be adopted in which a patient support mechanism corresponding to the top plate 33 is moved. When performing a scan (helical scan, positioning scan, etc.) that involves a relative change in the positional relationship between the gantry device 10 and the top plate 33, the relative change in the positional relationship may be performed by driving the top plate 33. However, it may be performed by moving the gantry device 10, or by a combination of these methods. When applied to dental CT, the bed device 30 and the like are not required.

The console device 40 has a memory 41, a display 42, an input interface 43, and a processing circuit 44. Note that although the console device 40 will be described as being separate from the gantry device 10, the gantry device 10 may include the console device 40 or a part of each component of the console device 40.

The memory 41 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. For example, the memory 41 stores projection data and reconstructed image data. Further, for example, the memory 41 stores a program for a circuit included in the X-ray CT apparatus 1 to realize its function. The memory 41 is also used as a non-transitory hardware storage medium. Note that the storage of projection data and reconstructed image data is not limited to the memory 41 of the console device 40, but may be stored in a medical image storage such as a cloud server that can be connected to the X-ray CT apparatus 1 via a communication network 5 such as the Internet. The storage device 60 may store projection data and reconstructed image data upon receiving a storage request from the X-ray CT apparatus 1.

The display 42 displays various information. For example, the display 42 outputs a medical image (CT image) generated by the processing circuit 44, a GUI (Graphical User Interface) for accepting various operations from an operator, and the like. For example, the display 42 is a liquid crystal display or a CRT (Cathode Ray Tube) display. Further, the display 42 may be provided on the gantry device 10. Further, the display 42 may be of a desktop type, or may be configured with a tablet terminal or the like that can communicate wirelessly with the console device 40 main body.

The input interface 43 receives various input operations from an operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit 44 . For example, the input interface 43 receives from the operator acquisition conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-processed image from a CT image, etc. . For example, the input interface 43 is realized by a mouse, keyboard, trackball, switch, button, joystick, touch panel, or the like. Further, the input interface 43 may be provided in the gantry device 10. Furthermore, the input interface 43 may be configured with a tablet terminal or the like that can communicate wirelessly with the main body of the console device 40.

The processing circuit 44 controls the overall operation of the X-ray CT apparatus 1 . For example, the processing circuit 44 has a scan control function 441, an image generation function 442, a display control function 443, and a control function 444. The processing circuit 44 is realized by, for example, a processor.

For example, the processing circuit 44 reads a program corresponding to the scan control function 441 from the memory 41 and executes it, thereby controlling the X-ray CT apparatus 1 to perform a scan. Here, the scan control function 441 can execute scanning using various methods, such as a conventional scan, a helical scan, and a step-and-shoot method, for example.

Specifically, the scan control function 441 controls the bed driving device 32 to move the subject P into the imaging port of the gantry device 10 . The scan control function 441 also controls the X-ray high voltage device 17 to supply high voltage to the X-ray tube 11 . The scan control function 441 also adjusts the opening degree and position of the collimator 20. Furthermore, the scan control function 441 rotates the rotating section including the rotating frame 16 by controlling the control device 18 . The scan control function 441 also causes the DAS 21 to collect projection data. Note that to reconstruct a CT image, projection data for 360° around the subject P is required, and even in the half-scan method, projection data for 180° + fan angle is required. This embodiment is applicable to any reconstruction method.

For example, the processing circuit 44 reads a program corresponding to the image generation function 442 from the memory 41 and executes it to perform logarithmic conversion processing, offset correction processing, and sensitivity between channels on the detection data output from the DAS 21. Generates data that has undergone preprocessing such as correction processing and beam hardening correction. Note that the data before preprocessing (detection data) and the data after preprocessing may be collectively referred to as projection data. Further, for example, the image generation function 442 generates CT image data. Specifically, the image generation function 442 generates CT image data by performing reconstruction processing on the preprocessed projection data using a filtered back projection method, a successive approximation reconstruction method, or the like. The image generation function 442 also performs processing to improve image quality in response to deterioration in image quality due to missing data in projection data. Details of the processing will be described later. Further, the image generation function 442 converts CT image data into tomographic image data of an arbitrary cross section or three-dimensional image data based on input operations received from the operator via the input interface 43.

Further, for example, the processing circuit 44 displays the CT image on the display 42 by reading a program corresponding to the display control function 443 from the memory 41 and executing it. Further, for example, the processing circuit 44 can perform various functions of the processing circuit 44 based on input operations received from the operator via the input interface 43 by reading out and executing a program corresponding to the control function 444 from the memory 41. control.

Note that although FIG. 1 shows a case where each processing function of the scan control function 441, image generation function 442, display control function 443, and control function 444 is realized by a single processing circuit 44, this embodiment is not applicable. It is not limited to. For example, the processing circuit 44 may be configured by combining a plurality of independent processors, and each processor may implement each processing function by executing each program. Further, each processing function of the processing circuit 44 may be appropriately distributed or integrated into a single processing circuit or a plurality of processing circuits. The processing circuit 44 is not limited to being included in the console device 40, but may be included in an integrated server that collectively processes detection data acquired by a plurality of medical image diagnostic apparatuses. Although the console device 40 has been described as having a single console that executes a plurality of functions, the plurality of functions may be executed by separate consoles. Post-processing may be performed either by the console device 40 or by an external workstation. Further, the processing may be performed by both the console device 40 and the workstation.

On the other hand, the medical image storage device 60 includes a memory 61, a display 62, an input interface 63, and a processing circuit 64. The processing circuit 64 has a database function 641 and a control function 642.

The memory 61 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. For example, the memory 61 stores projection data and reconstructed image data. Further, for example, the memory 61 stores a program for a circuit included in the medical image storage device 60 to realize its function. The memory 61 is also used as a non-transitory hardware storage medium.

The display 62 displays various information. For example, the display 62 outputs a GUI (Graphical User Interface) for accepting various operations from an operator. For example, the display 62 is a liquid crystal display or a CRT (Cathode Ray Tube) display.

The input interface 63 accepts various input operations from an operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit 64 . For example, the input interface 63 receives medical image storage conditions and the like from the operator. For example, the input interface 63 is realized by a mouse, keyboard, trackball, switch, button, joystick, touch panel, or the like.

The processing circuit 64 controls the overall operation of the medical image storage device 60. For example, the processing circuit 64 has a database function 641 and a control function 642. The processing circuit 64 is realized by, for example, a processor.

For example, the processing circuit 64 inputs, stores, and outputs medical images by reading out and executing a program corresponding to the database function 641 from the memory 61.

Further, for example, the processing circuit 64 reads a program corresponding to the control function 642 from the memory 61 and executes it, thereby controlling various functions of the processing circuit 64 based on input operations received from the operator via the input interface 63. control.

Although FIG. 1 shows a case where each processing function of the database function 641 and the control function 642 is realized by a single processing circuit 64, the embodiment is not limited to this. For example, the processing circuit 64 may be configured by combining a plurality of independent processors, and each processor may implement each processing function by executing each program. Further, each processing function of the processing circuit 64 may be appropriately distributed or integrated into a single processing circuit or a plurality of processing circuits.

On the other hand, the medical image processing device 70 includes a memory 71, a display 72, an input interface 73, and a processing circuit 74. The processing circuit 74 has an image generation function 741, a display control function 742, and a control function 743.

The memory 71 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. For example, the memory 71 stores projection data and reconstructed image data. Further, for example, the memory 71 stores a program for a circuit included in the medical image processing device 70 to realize its function. The memory 71 is also used as a hardware non-transitory storage medium. Note that the projection data and reconstructed image data are obtained directly from the X-ray CT apparatus 1 or via the medical image storage apparatus 60. Although it is assumed that the projection data is acquired after being preprocessed, it may be obtained without being preprocessed. If preprocessing has not been completed, preprocessing is performed on the medical image processing device 70 side.

The display 72 displays various information. For example, the display 72 outputs a medical image (CT image) generated by the processing circuit 74, a GUI (Graphical User Interface) for accepting various operations from an operator, and the like. For example, the display 72 is a liquid crystal display or a CRT (Cathode Ray Tube) display.

The input interface 73 accepts various input operations from an operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit 74 . For example, the input interface 73 receives from the operator reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-processed image from a CT image, and the like. For example, the input interface 73 is realized by a mouse, keyboard, trackball, switch, button, joystick, touch panel, or the like.

The processing circuit 74 controls the overall operation of the medical image processing apparatus 70 . For example, the processing circuit 74 has an image generation function 741, a display control function 742, and a control function 743. The processing circuit 74 is realized by, for example, a processor.

For example, the processing circuit 74 generates CT image data by reading a program corresponding to the image generation function 741 from the memory 71 and executing it. Furthermore, when generating CT image data, the image generation function 741 performs processing to improve image quality against image quality deterioration due to missing data in projection data. Details of the processing will be described later. Further, the image generation function 741 converts CT image data into tomographic image data of an arbitrary cross section or three-dimensional image data based on input operations received from the operator via the input interface 73.

Further, for example, the processing circuit 74 displays the CT image on the display 72 by reading out a program corresponding to the display control function 742 from the memory 71 and executing it. Further, for example, the processing circuit 74 reads out and executes a program corresponding to the control function 743 from the memory 71, thereby controlling various functions of the processing circuit 74 based on input operations received from the operator via the input interface 73. control.

Although FIG. 1 shows a case in which the image generation function 741, display control function 742, and control function 743 are realized by a single processing circuit 74, the embodiment is not limited to this. do not have. For example, the processing circuit 74 may be configured by combining a plurality of independent processors, and each processor may implement each processing function by executing each program. Moreover, each processing function that the processing circuit 74 has may be realized by being appropriately distributed or integrated into a single processing circuit or a plurality of processing circuits.

The term "processor" used in the above explanation refers to, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (for example, It means a circuit such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), or a field programmable gate array (FPGA). The processor realizes functions by reading and executing programs stored in the memories 41, 61, and 71. Note that instead of storing the program in the memories 41, 61, and 71, the program may be directly incorporated into the circuit of the processor. In this case, the processor realizes its functions by reading and executing a program built into the circuit. Note that each processor of this embodiment is not limited to being configured as a single circuit for each processor, but may also be configured as a single processor by combining multiple independent circuits to realize its functions. good.

FIG. 2 is a block diagram showing a configuration example of the image generation functions 442 and 741 in the processing circuits 44 and 74, and is a configuration example for processing to improve image quality against image quality deterioration due to missing data in projection data. be. In FIG. 2, the image generation functions 442 and 741 include an acquisition unit 81, a generation unit (interpolation unit) 82, a reconstruction unit 83, a generation unit (forward projection unit) 84, a projection data update unit 85, and an end It includes a control section 86 and an output section 87.

The acquisition unit 81 has a function of inputting projection data D1 and imaging-related information D2 generated when the subject P is scanned by the X-ray CT apparatus 1, and acquiring information D3 regarding missing data. The projection data D1 and the photographing related information D2 are an example of first projection data. The photographing related information D2 includes discharge information, communication error information, and the like. The discharge information is information regarding the discharge of the X-ray tube 11. The communication error information is information regarding a communication error between the DAS 21 and the processing circuit 44 on the console device 40 side. In addition, there is information on failure of the X-ray detector 15. For example, this information is recorded in such a manner that events and occurrence times are associated with each other.

The information D3 regarding the missing data includes missing location information, interpolated normal location information, reconstruction and forward projection ranges, and the like. The missing location information is information indicating the position of missing data included in the projection data D1. The position of data is represented by channel (ch), slice (sl), view, etc. The interpolation normal location information is information indicating the position of normal data that can be used for interpolating missing data. The range of reconstruction and forward projection is information on the range of reconstruction and forward projection that is executed for processing to improve image quality against image quality deterioration due to missing data in projection data. In other words, the reconstruction and forward projection performed for processing to improve image quality only need to be performed in the range that affects the missing data, and by limiting the range to be processed, processing time can be expected to be shortened.

The generation unit 82 has a function of interpolating the missing data portion of the projection data D1 based on the missing part information and the interpolation normal part information of the information D3 regarding the missing data, and generating projection data D4 after interpolation. There is. The generation unit 82 is an example of a first generation unit. The projection data D4 is an example of second projection data.

The reconstruction unit 83 has a function of performing reconstruction (back projection) from the projection data D4 and generating reconstructed image data D5 based on the reconstruction range of the information D3 regarding the missing data. Furthermore, the reconstruction unit 83 has a function of performing reconstruction from projection data D7, which will be described later, to generate reconstructed image data D5, based on the reconstruction range of information D3 regarding missing data. The reconstructed image data D5 is an example of the first reconstructed image or the second reconstructed image.

The generation unit 84 has a function of performing forward projection from the reconstructed image data D5 to generate projection data D6 based on the forward projection range of the information D3 regarding missing data. The generation unit 84 is an example of a second generation unit. Projection data D6 is an example of third projection data.

The projection data updating unit 85 has a function of generating updated projection data D7 from the projection data D4 and the projection data D6. After the projection data D7 is generated, the previous projection data D7 may be used for updating. The projection data update section 85 is an example of a third generation section. Projection data D7 is an example of fourth projection data.

The termination control unit 86 has a function of determining whether to repeat or terminate the process after the reconstruction performed by the reconstruction unit 83 to improve the image quality, and to control the process. If the end control unit 86 determines that the reconstruction unit 83 should repeat the process subsequent to the reconstruction to improve the image quality, the termination control unit 86 causes the reconstruction unit 83 to repeat the process subsequent to the reconstruction to improve the image quality. . Further, when the termination control unit 86 determines that the process should be terminated, the termination control unit 86 causes the reconfiguration unit 83 to perform reconfiguration for output. Note that the determination as to whether to repeat the reconstruction or to end it is determined that the reconstruction is completed when the preset number of repetitions (in the case of 1, the reconstruction is performed only once and is not repeated), and also when the projection data D6 It can be determined that the process is finished when the difference from the previous time in the projection data D7 is less than a predetermined threshold value and the values have converged.

Reconstructed image data D5 obtained by reconstruction from projection data D4 that has been interpolated with respect to projection data D1 that includes missing data is reconstructed from projection data D1 that has not been interpolated. The image quality has improved compared to the previous case. However, since the image is reconstructed from data interpolated in a cut-and-paste manner, the image remains unnatural. In this regard, in this embodiment, projection data D6 is generated from the reconstructed image data D5 by forward projection, and the most recent projection data D4, etc. are updated with this projection data D6, and this is repeated as necessary to create the final projection data D6. Since the reconstructed image data D5 is obtained from the projection data D7, a high-quality reconstructed image without any unnaturalness can be obtained.

The output unit 87 outputs the final reconstructed image data D5 generated by the output reconstruction as reconstructed image data D8, and also outputs the latest projection data D7 that is the source thereof as projection data D9. It has a function.

FIG. 3 is a flowchart illustrating a processing example of the embodiment. In FIG. 3, when the scan control function 441 of the processing circuit 44 of the X-ray CT apparatus 1 performs imaging (scanning) of the subject P (step S1), projection data D1 and imaging related information D2 are generated. .

Next, the acquisition unit 81 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 inputs the projection data D1 generated at the time of scanning and the information related to the time of imaging D2, and removes the missing data. information D3 is obtained (step S2). The acquisition unit 81 specifies the position of the missing data based on the information on the missing location in the information D3 related to the missing data, based on the discharge information, X-ray detector failure information, communication error information, etc. in the imaging related information D2. Note that the acquisition unit 81 may specify the position of the missing data since the data includes an abnormal value.

Regarding the interpolation normal location information, in the case of a defect at the ray level, for example, the acquisition unit 81 obtains the normal data of a channel or slice adjacent to the channel of the missing data within the same view, or the normal data of the view adjacent to the slice. Identify the normal data of the corresponding channel. Furthermore, in the case of a loss at the view level, the acquisition unit 81 identifies, for example, normal data in a view adjacent to the view of the missing data, or normal data in a view adjacent to the view on the slice.

Furthermore, the acquisition unit 81 specifies the reconstruction range and the forward projection range based on the position of missing data in the projection data. FIG. 4A is a diagram illustrating an example of the range of reconstruction for missing rays. In FIG. 4A, if missing data c exists in a part of the projection data b acquired by the X-rays emitted from the X-ray source a, the missing data c is covered in the reconstructed image d corresponding to the subject. The range e to be reconstructed may be set as the range for reconstruction. Further, FIG. 4B is a diagram illustrating an example of the range of forward projection for ray loss. In FIG. 4B, if missing data c exists in a part of the projection data b acquired by the X-rays irradiated from the X-ray source a, the range f that covers the missing data c may be set as the range of forward projection. .

FIG. 5A is a diagram illustrating an example of the range of reconstruction and forward projection for a view defect, in the case where a view defect occurs in the range g when scanning is performed on multiple slices using the step-and-shoot method. It shows. In this case, the acquisition unit 81 sets range g or a wider range including range g as the reconstruction range. Further, FIG. 5B is a diagram showing another example of the range of reconstruction and forward projection for a view loss, and shows a case where a view loss occurs in a range h when helical scanning is performed. . In this case, the acquisition unit 81 sets the range h or a wider range including the range h as the reconstruction range.

Returning to FIG. 3, next, the generation unit 82 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 generates data based on the missing part information and the interpolated normal part information of the information D3 regarding the missing data. , the missing data portion is interpolated for the projection data D1, and the interpolated projection data D4 is generated (step S3).

Next, the reconstruction unit 83 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 performs reconstruction ( (back projection) to generate reconstructed image data D5 (step S4).

Next, the generation unit 84 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 performs forward projection from the reconstructed image data D5 based on the forward projection range of the information D3 regarding the missing data. is performed to generate projection data D6 (step S5).

Next, the projection data update unit 85 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 generates updated projection data D7 from the projection data D4 and the projection data D6 ( Step S6). After the projection data D7 is generated, the previous projection data D7 may be used for updating.

If the projection data D4 estimated by interpolation is LI (ch, sl, view) and the projection data D6 obtained by the n-th forward projection is FPJ (ch, sl, view, n), then after the n-th update The projection data D7 is, for example,
eproj(ch,sl,view,n)=LI(ch,sl,view)*(1.0-w(n))+FPJ(ch,sl,view,n)*w(n)
It is expressed as Note that ch is a channel, sl is a slice, view is a view, and w(n) is a monotonically increasing function that can take a value from 0.0 to 1.0. w(n) need not start with a value of 0.0 at the beginning of n, and need not end with a value of 1.0 at the end of n.

Next, the termination control unit 86 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 determines whether to repeat or terminate the reconstruction by the reconstruction unit 83, and controls the process. (Step S7). Here, if the termination control unit 86 determines that the reconstruction unit 83 should repeat the reconstruction to improve the image quality (No in step S7), the termination control unit 86 causes the reconstruction unit 83 to repeat the reconstruction to improve the image quality. to be returned (steps S4 to S6).

Further, when the termination control unit 86 determines to terminate (Yes in step S7), the termination control unit 86 causes the reconfiguration unit 83 to perform reconfiguration for output, and the reconfiguration unit 83 determines the range of reconfiguration of the information D3 regarding the missing data. However, the initial range specified by the user is reconstructed to generate reconstructed image data D5 (step S8).

Next, the output unit 87 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 converts the final reconstructed image data D5 generated by the reconstruction for output into a reconstructed image. At the same time, the latest projection data D7, which is the source thereof, is output as projection data D9 (step S9).

The order of processing in the flowchart described in FIG. 3 may be changed within a range that does not essentially affect the results. Furthermore, processing may be performed in parallel as long as it does not essentially affect the results.

Step S1 shown in FIG. 3 is a step corresponding to the scan control function 441 of the X-ray CT apparatus 1. Step S1 is a step in which the processing circuit 44 of the X-ray CT apparatus 1 reads and executes a program corresponding to the scan control function 441 from the memory 41, thereby realizing the scan control function 441.

Steps S2 to S9 are steps corresponding to the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70. In steps S2 to S9, the processing circuit 44 of the X-ray CT apparatus 1 or the processing circuit 74 of the medical image processing apparatus 70 reads and executes a program corresponding to the image generation function 442 or the image generation function 741 from the memory 41 or the memory 71. This is a step in which the image generation function 442 or the image generation function 741 is realized.

Note that the processing circuit 44 of the X-ray CT apparatus 1 or the processing circuit 74 of the medical image processing apparatus 70 determines the size of an area constituted by at least one missing data and the number of consecutive areas in the view direction. Depending on the situation, the processes of steps S3 to S8 described above are performed, or the missing data portion is interpolated for the projection data D1 to generate the interpolated projection data D10, and the reconstructed image is generated from the projection data D10. It is also possible to switch whether or not to perform the process of generating the data D11. Details of such a modification will be explained.

In the description of the modified example, an area composed of at least one piece of missing data includes an area composed of one piece of missing data, and an area composed of two or more consecutive pieces of missing data. is included.

FIG. 6 is a flowchart illustrating a processing example of a modification of the embodiment. Note that in the flowchart shown in FIG. 6, the same processes as the processing example shown in FIG. 3 are given the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 6, the generation unit 82 determines the size of an area constituted by at least one piece of missing data in the projection data D1, and the size of this area based on the missing part information of the information D3 regarding missing data. It is determined whether the number of consecutive images in the view direction is smaller than a threshold value (step S10).

A specific example of the determination in step S10 will be explained. For example, the generation unit 82 specifies the size of an area made up of at least one piece of missing data based on the missing location information of the information D3 regarding missing data. Furthermore, the generation unit 82 specifies the number of consecutive regions in the view direction based on the missing location information of the information D3 regarding missing data.

FIG. 7A is a diagram for explaining a modification of the embodiment. FIG. 7A shows a region 90 made up of missing data in which only one missing data exists in the channel direction and 80 pieces are consecutively arranged in the slice direction in the projection data D1. Here, an example will be described in which the number of consecutive areas 90 in the view direction is "1000".

In the case shown in FIG. 7A, the generation unit 82 sets the maximum number of missing data in the channel direction in the area 90 to "1" as the size of the area 90 made up of consecutive missing data, and , the maximum number "80" of consecutive missing data in the slice direction within the region 90 is specified. Furthermore, the generation unit 82 specifies the number “1000” in which the regions 90 are continuous in the view direction.

Then, the generation unit 82 determines whether the function min(ch_number, sl_number, view_number) is smaller than a predetermined threshold α. Here, "ch_number" indicates the maximum number of consecutive missing data in the channel direction within the region 90. Further, "sl_number" indicates the maximum number of consecutive missing data in the slice direction within the region 90. Note that when there is only one missing data in each of the channel direction and the slice direction, the maximum number of consecutive missing data is "1". Further, "view_number" indicates the number of consecutive regions 90 in the view direction. Further, the function min(ch_number, sl_number, view_number) indicates the minimum value among "ch_number", "sl_number", and "view_number". That is, in the case shown in FIG. 7A, "min(1,80,1000)=1".

In addition, the predetermined threshold value α is, for example, the maximum number of consecutive missing data in the channel direction when the user can tolerate deterioration in image quality even when interpolation is performed, and the maximum number of consecutive missing data in the slice direction. This is the value obtained by adding "1" to the maximum value of the maximum number of consecutive missing data and the maximum number of consecutive missing data in the view direction.

In this way, the generation unit 82 calculates the maximum number of consecutive missing data in the channel direction within the specified region 90, the maximum number of consecutive missing data in the slice direction within the specified region 90, and Among the number of consecutive areas 90 in the view direction, the minimum value is specified. The generation unit 82 then determines whether the identified minimum value is smaller than a predetermined threshold α. The predetermined threshold value α is, for example, “2”.

If the identified minimum value is smaller than the predetermined threshold α (Yes in step S10), the missing data within the area 90 can be addressed by interpolation. Therefore, when the identified minimum value is smaller than the predetermined threshold α (Yes in step S10), the generation unit 82 generates projection data D1 based on the missing part information and the interpolated normal part information of the information D3 regarding missing data. The missing data portion is interpolated for the data, and projection data D10 after interpolation is generated (step S11). The projection data D10 is an example of the fifth projection data.

For example, in the case shown in FIG. 7A, in step S11, the missing data portion is interpolated for the projection data D1 using normal data adjacent to the region 90 in the channel direction, and the interpolated projection data D10 is generated. do.

Here, with reference to FIG. 7B, another example of the process of step S11 will be described. FIG. 7B is a diagram for explaining a modification of the embodiment. FIG. 7B shows a region 91 in the projection data D1 that includes one piece of missing data in the channel direction and only one piece of missing data in the slice direction. Here, an example will be described in which the number of consecutive areas 91 in the view direction is "1000".

In the case shown in FIG. 7B, "min(1,1,1000)" is smaller than the predetermined threshold α. Therefore, in step S11, the generation unit 82 uses normal data adjacent to the region 91 in the channel direction or normal data adjacent to the region 91 in the slice direction to generate a missing data portion for the projection data D1. interpolation is performed to generate projection data D10 after interpolation.

Next, the reconstruction unit 83 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 performs reconstruction ( (back projection) to generate reconstructed image data D11 (step S12). The reconstructed image data D11 is an example of the third reconstructed image.

Next, in step S9, the output unit 87 of the image generation function 442 of the X-ray CT apparatus 1 or the image generation function 741 of the medical image processing apparatus 70 outputs the final reconstructed image data D11 generated by the reconstruction for output. At the same time, the latest projection data D10 that is the source thereof is output.

Here, an example of the determination process in step S10 will be described with reference to FIG. 7C. FIG. 7C is a diagram for explaining a modification of the embodiment. FIG. 7C shows, in the projection data D1, a region 92 formed by three pieces of missing data consecutively arranged in the channel direction and three pieces successively arranged in the slice direction. Here, an example will be described in which the number of consecutive areas 92 in the view direction is "1000".

In the case shown in FIG. 7C, “min(3,3,1000)” is greater than the predetermined threshold α. Therefore, in step S3, the generation unit 82 performs processing to generate projection data D4. Then, in step S4, the reconstruction unit 83 performs processing to generate reconstructed image data D5. Then, in step S5, the generation unit 84 performs processing to generate projection data D6.

Then, in step S6, the projection data update unit 85 generates projection data D7. Thereafter, in step S7, when the end control unit 86 determines that the reconstruction is to be completed (Yes in step S7), the reconstruction unit 83 performs a process of generating reconstructed image data D5 in step S8.

Next, in step S9, the output unit 87 outputs the final reconstructed image data D5 generated by the reconstruction for output as reconstructed image data D8, and also outputs the latest projection data D7 that is the source thereof. It is output as projection data D9.

As described above, the processing circuit 44 of the X-ray CT apparatus 1 or the processing circuit 74 of the medical image processing apparatus 70 determines the size of the area constituted by at least one piece of missing data and the direction in which this area is located. Depending on the consecutive numbers, the processes of steps S3 to S8 described above are performed, or the process of generating projection data D10 after interpolation and the process of generating reconstructed image data D11 from projection data D10 are performed. or switch.

This modification has been explained. According to this modification, the processing circuit 44 or the processing circuit 74 determines whether interpolation can be performed in step S10. Note that "a case where interpolation is possible" refers to a case where the user can tolerate deterioration in image quality even if interpolation is performed. If the processing circuit 44 or the processing circuit 74 can handle interpolation, the processing load is reduced compared to the processing load of steps S3 to 8 instead of the processing of steps S3 to 8. The processing of lower steps S10 to S12 is performed to generate reconstructed image data D11. Therefore, according to the modification, the processing load can be reduced compared to the embodiment described above.

According to at least one embodiment and modification described above, it is possible to improve the image quality of a reconstructed image due to data loss in projection data.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

1 X-ray CT device 40 Console device 44 Processing circuit 442 Image generation function 70 Medical image processing device 74 Processing circuit 741 Image generation function 81 Acquisition unit 82 Generation unit 83 Reconstruction unit 84 Generation unit 85 Projection data update unit 86 Termination control unit 87 Output section

Claims (7)

an acquisition unit that acquires information regarding missing data based on first projection data obtained by scanning the subject;
a first generation unit that generates second projection data by interpolating missing data in the first projection data based on information regarding the missing data;
a reconstruction unit that reconstructs the second projection data and generates a first reconstructed image;
a second generation unit that forward projects the first reconstructed image and generates third projection data;
a third generation unit that updates the second projection data based on the third projection data to generate fourth projection data,
The reconstruction unit generates a second reconstructed image based on the fourth projection data,
Based on the size of an area constituted by at least one missing data in the first projection data and the number of consecutive areas in the view direction, processing of the first generation unit and processing of the reconstruction unit processing, the processing of the second generation unit, and the processing of the third generation unit, or the first generation unit executes the processing of the first projection data based on information regarding the missing data. Switching between performing a process of generating fifth projection data by interpolating missing data and a process of generating a third reconstructed image by reconstructing the fifth projection data by the reconstruction unit. further comprising:
Medical image processing device. The reconstruction unit specifies a range for reconstructing the second projection data based on information regarding the missing data, and generates the first reconstructed image based on the specified range.
The medical image processing device according to claim 1. The second generation unit specifies a range for forward projection of the first reconstructed image based on information regarding the missing data, and generates the third projection data based on the specified range.
The medical image processing device according to claim 1 or 2. The information regarding the missing data is based on a discharge of the X-ray tube device, a failure of the X-ray detector, or a communication error between the DAS and the processing circuit on the console device side.
A medical image processing apparatus according to any one of claims 1 to 3. repeating the processing of the reconstruction unit, the second generation unit, and the third generation unit;
A medical image processing apparatus according to any one of claims 1 to 4. The process is repeated until the process reaches a predetermined number of times or the process result converges.
The medical image processing device according to claim 5. an acquisition unit that acquires information regarding missing data based on first projection data obtained by scanning the subject;
a first generation unit that generates second projection data by interpolating missing data in the first projection data based on information regarding the missing data;
a reconstruction unit that reconstructs the second projection data and generates a first reconstructed image;
a second generation unit that forward projects the first reconstructed image and generates third projection data;
a third generation unit that updates the second projection data based on the third projection data to generate fourth projection data,
The reconstruction unit generates a second reconstructed image based on the fourth projection data,
Based on the size of an area constituted by at least one missing data in the first projection data and the number of consecutive areas in the view direction, the processing of the first generation unit and the processing of the reconstruction unit are performed. processing, the processing of the second generation unit, and the processing of the third generation unit, or the first generation unit executes the processing of the first projection data based on information regarding the missing data. Switching between performing a process of generating fifth projection data by interpolating missing data and a process of generating a third reconstructed image by reconstructing the fifth projection data by the reconstruction unit. further comprising:
X-ray CT device.

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