JP2020096693A - X-ray CT system and processing program - Google Patents

Abstract

To efficiently acquire an image for confirmation for the purpose of confirming an imaging range, etc.SOLUTION: In an X-ray CT system, X-ray energy is periodically changed while an X-ray irradiation unit rotates around a subject once. A data processing unit executes processing including interpolation processing for generating a plurality of first interpolation data sets corresponding to a rotation position where first energy is not irradiated, based on a plurality of first projection data sets collected when an X-ray of the first energy is irradiated, and generating a plurality of second interpolation data sets corresponding to a rotation position where second energy is not irradiated, based on a plurality of second projection data sets collected when an X-ray of the second energy is irradiated. The reconstruction unit reconstructs an image based on composite data sets generated based on the plurality of projection data sets including the processed projection data sets.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to an X-ray CT system and a processing program.

Conventionally, in an X-ray CT (Computed Tomography) system, it is possible to display a confirmation image for confirming the movement of a subject, an imaging range, etc. immediately after scanning. Specifically, the X-ray CT system promptly provides the operator with a confirmation image for confirming whether the CT image data obtained by the scan is collected according to the plan, and the subsequent workflow Enables you to proceed quickly. For example, when the operator refers to the confirmation image displayed immediately after the scan and determines that the images are collected as planned, the operator can quickly lower the subject from the bed apparatus. Further, for example, when the operator determines that the confirmation images are not collected according to the plan, the operator can quickly perform the rescan. Here, the confirmation image is, for example, an image generated without performing image processing such as correction on the projection data collected by scanning.

Further, in the X-ray CT system, a technique for performing dual-energy (DE) acquisition by using X-rays of two different energies in a scan, and an X-ray of three or more different energies in a CT scan. Techniques for performing multi-energy (ME) collection using lines are known. As a result, it is possible to collect projection data corresponding to each energy and distinguish the type, atomic number, density, etc. of the substance contained in the subject by utilizing the fact that the X-ray absorption characteristics differ for each substance. is there. DE collection or ME collection is performed by, for example, the KV switching method in which the energy of X-rays is changed for each irradiation angle of X-rays on the subject. In the KV switching method, for example, the X-ray energy is changed for each one or a plurality of views.

JP, 2016-64043, A Japanese Patent Publication No. 2018-511443

The problem to be solved by the present invention is to efficiently obtain an image for confirmation for the purpose of confirming a shooting range.

The X-ray CT system according to the embodiment includes an X-ray irradiation unit, an X-ray control unit, an X-ray detection unit, a data processing unit, and a reconstruction unit. The X-ray irradiation unit irradiates X-rays while rotating around the subject. The X-ray control unit cyclically changes the energy of the X-rays while the X-ray irradiation unit makes one revolution around the subject. The X-ray detection unit detects the X-rays and collects a projection data set for each rotational position of the X-ray irradiation unit. The data processing unit, based on the plurality of first projection data sets collected when the X-ray of the first energy is emitted, includes a plurality of first projection data sets corresponding to rotational positions where the first energy is not emitted. 1 interpolation data set, corresponding to the rotational position where the second energy was not irradiated, based on the plurality of second projection data sets collected when the second energy X-ray was irradiated. A process including an interpolation process for generating a plurality of second interpolation data sets is executed. The reconstruction unit reconstructs an image based on a composite data set generated based on a plurality of projection data sets including the processed projection data set.

FIG. 1 is a block diagram showing an example of the configuration of the X-ray CT system according to the first embodiment. FIG. 2 is a diagram for explaining processing by the data processing function according to the first embodiment. FIG. 3 is a diagram for explaining the filter processing by the data processing function according to the first embodiment. FIG. 4 is a flowchart for explaining the processing flow of the X-ray CT system according to the first embodiment. FIG. 5 is a diagram for explaining scaling processing by a data processing function according to another embodiment. FIG. 6 is a block diagram showing an example of the configuration of an X-ray CT system according to another embodiment.

Hereinafter, an embodiment of an X-ray CT system and a processing program according to the embodiment will be described in detail with reference to the accompanying drawings. The line CT system and the processing program according to the present application are not limited to the embodiments described below.

(First embodiment)
First, the configuration of the X-ray CT system 1 according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing an example of the configuration of an X-ray CT system 1 according to the first embodiment. As shown in FIG. 1, the X-ray CT system 1 includes a gantry device 10, a bed device 30, and a console device 40. That is, the X-ray CT system 1 according to the first embodiment is also called an X-ray CT apparatus.

In FIG. 1, the longitudinal direction of the rotary shaft of the rotary frame 13 or the top plate 33 of the bed apparatus 30 in the non-tilted state is the Z-axis direction. Further, an axial direction that is orthogonal to the Z-axis direction and is horizontal to the floor surface is the X-axis direction. Further, the Y-axis direction is defined as an axial direction that is orthogonal to the Z-axis direction and is perpendicular to the floor surface. It should be noted that FIG. 1 shows the gantry device 10 drawn from a plurality of directions for the sake of explanation, and shows a case where the X-ray CT system 1 has one gantry device 10.

The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a DAS 18.

The X-ray tube 11 is a vacuum tube having a cathode (filament) that generates thermoelectrons and an anode (target) that generates X-rays upon receiving collision of thermoelectrons. The X-ray tube 11 radiates thermoelectrons from the cathode to the anode by applying a high voltage from the X-ray high-voltage device 14 to generate X-rays for irradiating the subject P. For example, the X-ray tube 11 includes a rotary anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons. The X-ray tube 11 is an example of an X-ray irradiation unit.

The X-ray detector 12 detects 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 18. The X-ray detector 12 has, for example, a plurality of detection element arrays in which a plurality of detection elements are arranged in the channel direction along one arc centered on the focal point of the X-ray tube 11. The X-ray detector 12 has, for example, a structure in which a plurality of detection element rows in which a plurality of detection elements are arranged in the channel direction are arranged in the row direction (slice direction, row direction). Further, the X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and an optical sensor array. The scintillator array has a plurality of scintillators. The scintillator has a scintillator crystal that outputs a photon amount of light according to the incident X-ray dose. The grid has an X-ray shield plate arranged on the X-ray incident side surface of the scintillator array and absorbing scattered X-rays. The grid may be called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array has a function of converting into an electric signal according to the amount of light from the scintillator, and has, for example, an optical sensor such as a photodiode. The X-ray detector 12 may be a direct conversion type detector having a semiconductor element that converts an incident X-ray into an electric signal. The X-ray detector 12 is an example of an X-ray detector.

The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so as to face each other, and causes the controller 15 to rotate the X-ray tube 11 and the X-ray detector 12. For example, the rotating frame 13 is a casting made of aluminum. In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 can further support the X-ray high-voltage device 14, the wedge 16, the collimator 17, the DAS 18, and the like. Further, the rotating frame 13 can further support various configurations not shown in FIG. In the following, in the gantry device 10, the rotating frame 13 and a portion that rotates together with the rotating frame 13 are also referred to as a rotating portion.

The X-ray high-voltage device 14 has an electric circuit such as a transformer and a rectifier, and a high-voltage generator that generates a high voltage to be applied to the X-ray tube 11, and an X-ray generated by the X-ray tube 11. And an X-ray controller for controlling the output voltage according to the above. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 or a fixed frame (not shown).

The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and a drive mechanism such as a motor and an actuator. The control device 15 receives an input signal from the input interface 43 and controls the operation of the gantry device 10 and the bed device 30. For example, the control device 15 controls the rotation of the rotary frame 13, the tilt of the gantry device 10, the operations of the bed device 30 and the top plate 33, and the like. As an example, the control device 15 rotates the rotating frame 13 about an axis parallel to the X-axis direction based on the input tilt angle (tilt angle) information as control for tilting the gantry device 10. The control device 15 may be provided in the gantry device 10 or the console device 40.

The wedge 16 is a filter for adjusting the X-ray dose emitted from the X-ray tube 11. Specifically, the wedge 16 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. It is a filter to do. For example, the wedge 16 is a wedge filter or a bow-tie filter, and is a filter obtained by processing aluminum or the like so as to have a predetermined target angle and a predetermined thickness.

The collimator 17 is a lead plate or the like for narrowing down the irradiation range of the X-rays that have passed through the wedge 16, and a slit is formed by a combination of a plurality of lead plates or the like. The collimator 17 may be called an X-ray diaphragm. Further, although FIG. 1 shows a case where the wedge 16 is arranged between the X-ray tube 11 and the collimator 17, it is a case where the collimator 17 is arranged between the X-ray tube 11 and the wedge 16. Good. In this case, the wedge 16 transmits the X-rays which are emitted from the X-ray tube 11 and whose irradiation range is limited by the collimator 17, and attenuate the X-rays.

The DAS 18 collects X-ray signals detected by the respective detection elements included in the X-ray detector 12. For example, the DAS 18 includes an amplifier that amplifies an electric signal output from each detection element and an A/D converter that converts the electric signal into a digital signal, and generates detection data. The DAS 18 is realized by, for example, a processor. In addition, below, the detection data generated by DAS may be described as projection data.

Here, the DAS 18 may be a sequential acquisition type DAS that sequentially collects X-ray signals detected by a plurality of detection elements, or it may simultaneously detect X-ray signals detected by a plurality of detection elements. It may be the case where the simultaneous collection type DAS for collecting is used.

The data generated by the DAS 18 is transmitted from a transmitter having a light emitting diode (LED) provided on the rotating frame 13 by optical communication to a non-rotating portion of the gantry device 10 (for example, a fixed frame. In FIG. 1). (Not shown in the figure), and is transmitted to the console device 40. Here, the non-rotating portion is, for example, a fixed frame or the like that rotatably supports the rotating frame 13. The method of transmitting data from the rotating frame 13 to the non-rotating portion of the gantry device 10 is not limited to optical communication, and any non-contact data transmission method may be adopted. You can use it.

The bed device 30 is a device for placing and moving the subject P to be scanned, and includes a base 31, a bed driving device 32, a top plate 33, and a support frame 34. The base 31 is a housing that supports the support frame 34 so as to be movable 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 long axis 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. The bed driving device 32 may move the support frame 34 in the long axis direction of the top plate 33 in addition to the top plate 33.

The console device 40 has a memory 41, a display 42, an input interface 43, and a processing circuit 44. Although the console device 40 is described as a separate body 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 device such as a flash memory, a hard disk, an optical disk, or the like. The memory 41 stores, for example, projection data and CT image data. In addition, for example, the memory 41 stores a program for a circuit included in the X-ray CT system 1 to realize its function. The memory 41 may be realized by a server group (cloud) connected to the X-ray CT system 1 via a network.

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

The input interface 43 receives various input operations from the operator, converts the received input operations into electric signals, and outputs the electric signals to the processing circuit 44. For example, the input interface 43 allows the operator to acquire the acquisition conditions when acquiring projection data, the reconstruction conditions when reconstructing CT image data, the image processing conditions when generating a CT image from CT image data, and the like. Accept. For example, the input interface 43 includes a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad for performing an input operation by touching an operation surface, a touch screen in which a display screen and a touch pad are integrated, and an optical sensor. It is realized by the used non-contact input circuit, voice input circuit and the like. The input interface 43 may be provided in the gantry device 10. Further, the input interface 43 may be configured with a tablet terminal or the like that can wirelessly communicate with the console device 40 main body. Further, the input interface 43 is not limited to the one including physical operation parts such as a mouse and a keyboard. For example, an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the console device 40 and outputs the electric signal to the processing circuit 44 is also an example of the input interface 43. included.

The processing circuit 44 controls the operation of the entire X-ray CT system 1. For example, the processing circuit 44 executes the system control function 441, the data processing function 442, the preprocessing function 443, the reconstruction function 444, and the output function 445. That is, the processing circuit 44 controls the operation of the entire X-ray CT system 1 by reading out and executing the programs corresponding to the respective functions from the memory 41. The system control function 441 is an example of an X-ray controller. The data processing function 442 is an example of a data processing unit. The reconstruction function 444 is an example of a reconstruction unit.

In the X-ray CT system 1 shown in FIG. 1, each processing function is stored in the memory 41 in the form of a program executable by a computer. The processing circuit 44 is a processor that realizes a function corresponding to each program by reading the program from the memory 41 and executing the program. In other words, the processing circuit 44 in the state where each program is read has a function corresponding to the read program.

2 shows the case where each processing function of the system control function 441, the data processing function 442, the preprocessing function 443, the reconstruction function 444, and the output function 445 is realized by the single processing circuit 44. The embodiment is not limited to this. For example, the processing circuit 44 may be configured by combining a plurality of independent processors, and each processor may realize each processing function by executing each program. Further, each processing function of the processing circuit 44 may be implemented by being appropriately dispersed or integrated into a single or a plurality of processing circuits.

The system control function 441 controls various processes in the X-ray CT system 1 based on the input operation received from the operator via the input interface 43. For example, the system control function 441 controls the bed driving device 32, the collimator 17, the control device 15, the X-ray high voltage device 14 and the like in the X-ray CT system 1 to execute the positioning scan and the main scan.

Here, the system control function 441 controls the "shooting by Dual Energy" by the "Rapid kV switching method". Specifically, the system control function 441 transmits a control signal for switching between a high voltage and a low voltage to the X-ray high-voltage device 14 so that the high-voltage from the X-ray high-voltage device 14 to the X-ray tube 11 becomes high. Control the application of low voltage. Further, the system control function 441 transmits the control signal to the DAS 18 so that the detected data detected is from high voltage X-ray irradiation or low voltage X-ray irradiation. Control so that it is identified.

The data processing function 442 generates projection data for generating an image for confirmation by performing various processes on the projection data collected by “imaging by Dual Energy” by “Rapid kV switching method”. .. Specifically, the data processing function 442 generates projection data for generating a confirmation image by performing scaling processing or the like on the detection data (projection data) generated by the DAS 18. For example, the data processing function 442 may process at least one of the projection data of the first tube voltage (for example, high voltage) and the projection data of the second tube voltage (for example, low voltage). , Generating projection data for generating an image for confirmation. The projection data generated by the data processing function 442 is stored in the memory 41. The details of the processing by the data processing function 442 will be described later. Further, below, the projection data of each tube voltage collected while alternately switching the tube voltage by the "Rapid kV switching method" is referred to as a projection data set.

The pre-processing function 443 performs logarithmic conversion processing, correction processing such as offset correction, sensitivity correction, and beam hardening correction on the detection data (projection data) transmitted from the DAS 18 to obtain post-processing post-projection data. To generate. For example, the pre-processing function 443 generates a pre-processed projection data set from the detection data (projection data) of the first tube voltage (for example, high voltage). Further, the preprocessing function 443 generates a preprocessed projection data set from the detection data (projection data) of the second tube voltage (for example, low voltage).

In addition, the pre-processing function 443 uses two types of projection data sets to determine two or more predetermined reference substances (water, iodine, calcium, hydroxyapatite, fat, etc.) that are present in the target region for imaging. To separate. Then, the pre-processing function 443 generates post-processing projection data sets of two or more types of monochromatic X-rays corresponding to each of the two or more reference substances. For example, the pre-processing function 443 generates water and iodine monochromatic X-ray pre-processed projection data sets from the high-energy pre-processed projection data set and the low-energy pre-processed projection data set, respectively. The pre-processed projection data set generated by the pre-processing function 443 is stored in the memory 41.

The reconstruction function 444 generates various images from the preprocessed projection data set stored in the memory 41, and stores the generated images in the memory 41. For example, the reconstruction function 444 reconstructs the post-processing post-projection data by various reconstruction methods (for example, a back projection method such as FBP (Filtered Back Projection), a successive approximation method, or the like) to generate CT image data. The reconstructed CT image data is stored in the memory 41. Further, the reconstruction function 444 performs various image processing to generate a CT image such as an MPR image from the CT image data, and stores the generated CT image in the memory 41.

For example, the reconstruction function 444 reads the pre-processed projection data set of the monochromatic X-ray of the reference substance stored in the memory 41, and reconstructs the reference substance image data (reference substance emphasized image data). As an example, the reconstruction function 444 reconstructs the reference material image data of the water component based on the preprocessed projection data set with the water component emphasized, and the preprocessed projection data set with the iodine component emphasized. The reference substance image data of the iodine component is reconstructed based on the above. The reconstruction function 444 also performs image processing on the reference material image data of the water component and the reference material image data of the iodine component to generate the reference material image of the water component and the reference material image of the iodine component. To do. In addition, the reconstruction function 444 generates various images such as a monochromatic X-ray image at a predetermined energy, a density image, an effective atomic number image, etc. by performing a weighting calculation process using the two reference substance image data. You can

Further, for example, the reconstruction function 444 reads the high-energy preprocessed projection data set and the low-energy preprocessed projection data set stored in the memory 41, and reads the CT image data from each preprocessed projection data set. To reconstruct each. Then, the reconstruction function 444 can also generate a multicolor X-ray image corresponding to high energy and a multicolor X-ray image corresponding to low energy from the CT image data.

Further, the reconstruction function 444 reconstructs the projection data set generated by the data processing function 442 by various reconstruction methods (for example, a backprojection method such as FBP (Filtered Back Projection) or a successive approximation method). Thus, the CT image data is reconstructed, and the reconstructed CT image data is stored in the memory 41. Further, the reconstruction function 444 performs various image processing to generate a confirmation image from the CT image data, and stores the generated confirmation image in the memory 41.

The output function 445 causes the display 42 to display the CT image generated by the reconstruction function 444, the image for confirmation, and the like.

The overall configuration of the X-ray CT system 1 according to this embodiment has been described above. With such a configuration, the X-ray CT system 1 according to the present embodiment makes it possible to efficiently obtain a confirmation image for the purpose of confirming the imaging range. Specifically, the X-ray CT system 1 makes it possible to promptly provide a confirmation image with a constant image quality even when imaging with a plurality of different energies by the "Rapid kV switching method".

As described above, in the imaging by the "Rapid kV switching method", the X-ray energy is changed for each one or a plurality of views, so that projection data of different energies are mixed. Therefore, the amount of X-ray transmission in the projection data corresponding to each energy is different. For example, when the energy is high, the amount of X-rays transmitted is higher than when the energy is low. Therefore, if an image for confirmation is generated using such a projection data set, an artifact may occur, which may not be used for confirmation. Further, for example, it is possible to generate a confirmation image using only the projection data set corresponding to one energy, but in this case, since the data is thinned out and part of the data is lost, an artifact is generated. In some cases, it cannot be used for confirmation.

Therefore, in the X-ray CT system 1 according to the present embodiment, an interpolation data set that interpolates a defective portion in the projection data sets acquired by different energies is generated, and the generated interpolation data set and the actually acquired projection data set are generated. By performing a combining process for combining, a confirmation image with reduced artifacts is generated.

The data processing function 442, based on the plurality of first projection data sets collected when the first energy X-rays are irradiated, includes a plurality of first positions corresponding to the rotational positions where the first energy is not irradiated. 1 corresponding to the rotational position where the second energy was not irradiated, based on the plurality of second projection data sets collected when the 1 interpolation data set was generated and the X-ray of the second energy was irradiated. Processing including interpolation processing for generating the second interpolation data set of Then, the data processing function 442 generates a first combined data set by combining the first projection data set corresponding to the rotation position of the X-ray tube 11 and the second interpolation data set, and the second projection corresponding to the rotation position. A second combined data set is generated by combining the data set and the first interpolation data set.

FIG. 2 is a diagram for explaining processing by the data processing function 442 according to the first embodiment. Here, in FIG. 2, a part of the projection data collected by “imaging by Dual Energy” by the “Rapid kV switching method” is shown. That is, the high-energy rectangle and the low-energy rectangle shown in FIG. 2 collect X-rays emitted by the X-ray detector 12 while switching between high energy and low energy for each one or a plurality of views, and the DAS 18 The projection data sets output from are shown respectively.

For example, as shown in FIG. 2, the data processing function 442 separates a projection dataset in which high energy data and low energy data are mixed into a projection dataset of high energy data and a projection dataset of low energy data. .. Then, as shown in FIG. 2, the data processing function 442 generates the data of the defective portion by the interpolation process for each of the high energy data projection data set and the low energy data projection data set.

For example, the data processing function 442 uses a plurality of high-energy projection data sets to generate an interpolation data set of a defective portion (rotational position where high-energy X-rays are not irradiated). Similarly, the data processing function 442 uses a plurality of low energy projection data sets to generate an interpolation data set of a defective portion (rotational position where low energy X-rays are not irradiated). That is, the data processing function 442 generates a high-energy interpolation data set for the rotation position irradiated with the low-energy X-rays, and a low-energy interpolation data set for the rotation position irradiated with the high-energy X-rays. To generate.

The interpolation processing method executed by the data processing function 442 may be any interpolation method such as linear interpolation, Lagrange interpolation, and sigmoid as long as the interpolation data set can be generated from the projection data set. It may be used.

Then, the data processing function 442 generates a combined data set in which the actually collected projection data set and the generated interpolation data set are combined for each rotational position. For example, the data processing function 442, as shown in FIG. 2, generates a combined data set “(HD1) & (LID1)” that combines the high energy data (HD1) and the low energy interpolation data (LID1). Further, as shown in FIG. 2, the data processing function 442 generates a combined data set “(HID1) & (LD1)” that combines the high energy interpolation data (HID1) and the low energy data (LD1). Similarly, the data processing function 442 generates a synthetic data set by synthesizing the actually collected projection data set and the generated interpolation data set.

Here, the data processing function 442 weights the actually collected projection data set rather than the interpolation data set in order to use more information of the actually collected projection data and performs the combining process. For example, the data processing function 442 generates the composite data set “(HD1) & (LID1)” by the expression “(Wb×HD1)+(1-Wb)×LID1” using the weight “Wb”. , And the weight is “Wb=0.75”. As a result, the information amount of the high energy data (HD1) in the combined data set “(HD1) & (LID1)” increases. The data processing function 442 similarly performs a synthesis process in which the actually collected projection data set is weighted more than the interpolation data set when other synthetic data sets are generated.

The reconstruction function 444 generates a confirmation image by performing reconstruction processing or the like on the projection data set (a plurality of combined data sets) after the combining processing by the data processing function 442. The output function 445 causes the display 42 to display the confirmation image generated by the reconstruction function 444.

As described above, in the X-ray CT system 1 according to the first embodiment, the interpolation data set of the defective portion is generated, and the synthesis process is performed on the collected projection data set to reduce the artifact. Image can be generated.

Here, in the above-described embodiment, a case has been described in which after the interpolation data set is generated, it is combined with the actually collected projection data set. However, the embodiment is not limited to this, and the confirmation image may be generated using the projection data set in which the defective portion is interpolated. As an example, a confirmation image may be generated using the projection data set after interpolation shown in the third row of FIG. In such a case, the reconstruction function 444 generates a confirmation image using the high energy projection data set in which the interpolation data is interpolated or the low energy projection data set in which the interpolation data is interpolated.

Here, the X-ray CT system 1 according to the first embodiment can further execute processing for reducing artifacts. Specifically, the data processing function 442 further reduces the artifact by further filtering the projection data set after the synthesis processing.

FIG. 3 is a diagram for explaining filter processing by the data processing function 442 according to the first embodiment. Here, in FIG. 3, the projection data set (plurality of composite data sets) after the composite processing shown in FIG. 2 is shown.

For example, the data processing function 442 applies different filters to the plurality of projection data sets, and then synthesizes the plurality of applied projection data sets. As an example, as shown in FIG. 3, the data processing function 442 duplicates the projection data set after the combining process and applies a smoothing filter and a high pass filter to each projection data set. Then, the data processing function 442 synthesizes the filtered projection data sets to generate a filtered projection data set.

As an example, the data processing function 442 synthesizes the synthesized data set “(HD1) & (LID1)” to which the smoothing filter has been applied and the synthesized data set “(HD1) & (LID1)” to which the high pass filter has been applied. The combined data set “(HD1) & (LID1)” is generated. Similarly, the data processing function 442 also generates a composite data set that combines the composite data set to which the smoothing filter has been applied and the composite data set to which the high-pass filter has been applied, for the composite data sets at other rotational positions.

Here, the data processing function 442 can also generate a composite data set in which information in the composite data set to which the smoothing filter has been applied and information in the composite data set to which the high-pass filter has been applied are evenly included in the above-described composition processing. However, one of the pieces of information can be weighted. That is, the data processing function 442 can also perform the combining process so as to include more information of either one of the smoothing-filtered combined data set and the high-pass filtered combined data set.

When the information in the synthesized data set subjected to the smoothing filter and the information in the synthesized data set subjected to the high-pass filter are equally included, for example, the data processing function 442 may use the data processing function 442 to synthesize the smoothed-filtered synthesized data set and the high-pass filtered synthesis data. A weight "0.5" is applied to each of the data sets to synthesize them. On the other hand, when performing the combining process so as to include more information of either one, the data processing function 442 applies to either the smoothing-filtered combined data set or the high-pass filtered combined data set. The value is increased and the weight is combined.

This can reduce some streak-like artifacts that may remain in the combined data set before filtering. Note that, in the above-described example, the case of performing the filter processing using both the smoothing filter and the high-pass filter has been described, but the case where the filter processing using either one of the filters may be performed.

Next, an example of a processing procedure by the X-ray CT system 1 will be described with reference to FIG. FIG. 4 is a flowchart for explaining the processing flow of the X-ray CT system 1 according to the first embodiment. Here, FIG. 4 shows a case where the filtering process is performed after the combining process. In addition, FIG. 4 illustrates a case where a confirmation image in “shooting by Dual Energy” is displayed.

Step S101 is a step realized by the processing circuit 44 reading and executing a program corresponding to the system control function 441. Steps S102 to S108 are steps realized by the processing circuit 44 reading and executing the program corresponding to the data processing function 442. Step S109 is a step realized by the processing circuit 44 reading and executing the program corresponding to the reconstruction function 444. Step S110 is a step realized by the processing circuit 44 reading and executing a program corresponding to the output function 445.

First, the processing circuit 44 collects high energy data and low energy data by the "Rapid kV switching method" (step S101). Next, the processing circuit 44 separates the data into high energy data and low energy data (step S102). Then, the processing circuit 44 generates interpolation data for high energy data and interpolation data for low energy data, respectively (steps S103 and S104).

After that, the processing circuit 44 performs weighted addition so that more information of the actually collected projection data set is included (step S105), and the smoothing filtering process and the high pass filtering process are performed on the projection data set after the addition. Is executed (steps S106 and 107). Then, the processing circuit 44 executes weighted addition so that more desired information is included (step S108). After that, the processing circuit 44 generates a confirmation image using the generated projection data set (step S109), and displays the confirmation image on the display 42 (step S110).

As described above, according to the first embodiment, the X-ray tube 11 emits X-rays while rotating around the subject. The system control function 441 periodically changes the energy of X-rays while the X-ray tube 11 makes one revolution around the subject. The X-ray detector 12 detects X-rays and collects a projection data set for each rotational position of the X-ray irradiation unit. The data processing function 442, based on the plurality of first projection data sets collected when the first energy X-rays are irradiated, includes a plurality of first positions corresponding to the rotational positions where the first energy is not irradiated. 1 corresponding to the rotational position where the second energy was not irradiated, based on the plurality of second projection data sets collected when the 1 interpolation data set was generated and the X-ray of the second energy was irradiated. Processing including interpolation processing for generating the second interpolation data set of The reconstruction function 444 reconstructs an image based on a composite data set generated based on a plurality of projection data sets including the processed projection data set. Therefore, the X-ray CT system 1 according to the first embodiment is for confirmation in which artifacts are reduced by generating a projection data set that interpolates a defective portion in the projection data set acquired by the “Rapid kV switching method”. Image can be generated, and it is possible to efficiently obtain a confirmation image for the purpose of confirming the shooting range.

The present embodiment can be applied to both a system that switches the tube voltage for each view and a system that switches the tube voltage for each of a plurality of views, and generates an image for confirmation in which artifacts are reduced. be able to. In particular, in a system in which the tube voltage is switched for each of a plurality of views, the rotation angle collected with the same energy becomes large, so that the artifact generated in the confirmation image becomes remarkable. Therefore, the present embodiment is more effective when applied to a system that switches such a tube voltage for each of a plurality of views.

Further, according to the first embodiment, the composite data set is generated by applying different filters to the plurality of projection data sets, and then combining the plurality of applied projection data sets. Therefore, the X-ray CT system 1 according to the first embodiment makes it possible to further reduce artifacts.

Further, according to the first embodiment, the data processing function 442 generates a first combined data set by combining the first projection data set and the second interpolation data set corresponding to the rotational position of the X-ray tube 11. , And generates a second combined data set by combining the second projection data set corresponding to the rotation position and the first interpolation data set. The reconstruction function 444 reconstructs an image using the first composite data set and the second composite data set. Therefore, the X-ray CT system 1 according to the first embodiment can interpolate the defective portion more accurately, and further reduce the artifact.

Further, according to the first embodiment, the data processing function 442 performs weighting so that the ratio of the first projection data set and the second projection data set is high, and the first composite data set and the second composite data set. Respectively. Therefore, the X-ray CT system 1 according to the first embodiment makes it possible to generate a confirmation image that further includes information on the collected data.

(Other embodiments)
Although the first embodiment has been described so far, it may be implemented in various different forms other than the first embodiment described above.

In the above-described first embodiment, a case has been described in which the collected projection data set is subjected to interpolation processing to be combined. However, the embodiment is not limited to this, and may be processed so as to reduce the difference in the amount of energy transmission before the synthesis. Specifically, in the X-ray CT system 1 according to the other embodiment, a correction image is generated according to the difference in the amount of transmission at different energies to generate a confirmation image with reduced artifacts. Specifically, in the X-ray CT system 1, the processing of the data processing function 442 reduces the difference in transmission amount. In the following, processing for reducing the difference in transmission amount will be referred to as scaling processing.

In such a case, the data processing function 442 may include the plurality of first projection data sets collected when the first energy X-ray is emitted and the plurality of first projection data sets collected when the second energy X-ray is emitted. A process including a correction process is performed on at least one of the plurality of second projection data sets according to a difference in transmission amount between the X-ray of the first energy and the X-ray of the second energy. .. Specifically, the data processing function 442 includes a plurality of first projection data sets and a plurality of first projection data sets so as to reduce the difference in the amount of transmission between the first energy X-rays and the second energy X-rays. The correction process is performed on at least one of the second projection data sets.

FIG. 5 is a diagram for explaining scaling processing by the data processing function 442 according to another embodiment. For example, the data processing function 442 executes a correction process of multiplying the plurality of first projection data sets or the plurality of second projection data sets by a coefficient based on the difference in transmission amount. As an example, the data processing function 442 multiplies each high-energy projection data set (high-energy data in the figure) by a “coefficient a”, as shown in the lower left diagram of FIG. That is, the data processing function 442 multiplies the value of the projection data in each view included in the high-energy projection data set by the “coefficient a”. Here, the “coefficient a” is calculated based on the difference in the transmission amount, and the transmission amount of X-rays in the high energy projection data set is converted into the transmission amount of X-rays in the low energy projection data set. It is a coefficient for approximation.

Alternatively, for example, the data processing function 442 multiplies each low-energy projection data set (low-energy data in the figure) by a “coefficient b”, as shown in the lower center diagram of FIG. That is, the data processing function 442 multiplies the value of the projection data in each view included in the low energy projection data set by the “coefficient b”. Here, the “coefficient b” is calculated on the basis of the difference in the transmission amount, and the transmission amount of X-rays in the low energy projection data set is converted into the transmission amount of X-rays in the high energy projection data set. It is a coefficient for approximation.

Here, the above-mentioned “coefficient a” and “coefficient b” are calculated in advance and stored in the memory 41. For example, high energy data and low energy data are collected in advance, and the difference in the X-ray transmission amount is calculated. Then, a coefficient is calculated from the calculated difference in transmission amount and stored in the memory 41. Such a coefficient is stored in the memory 41 for each energy combination, and the data processing function 442 reads a coefficient corresponding to the currently used energy combination from the memory 41 and performs scaling processing.

In addition, as another process for applying the coefficient, for example, the data processing function 442 applies a coefficient based on the difference between the first energy and the third energy to the plurality of first projection data sets, and then performs the plurality of first projection data sets. A correction process of multiplying the two projection data sets by a coefficient based on the difference between the second energy and the third energy is executed. That is, the data processing function 442 multiplies the projection data set of each energy by a coefficient so as to approximate the amount of X-ray transmission at one target energy. The third energy is, for example, energy between the first energy and the second energy.

As an example, the data processing function 442 multiplies each of the high energy data by the “coefficient c” and the “energy d” of each of the low energy data, as shown in the lower right diagram of FIG. Multiply by. That is, the data processing function 442 multiplies the value of the projection data in each view included in the high-energy projection data set by the “coefficient c” to obtain the value of the projection data in each view included in the low-energy projection data set. Is multiplied by "coefficient d". Here, the "coefficient c" is a coefficient for approximating the X-ray transmission amount in the high-energy projection data set to the X-ray transmission amount at the target energy. The “coefficient d” is a coefficient for approximating the X-ray transmission amount in the low energy projection data set to the X-ray transmission amount in the target energy.

Here, the scaling processing using the above-mentioned “coefficient c” and “coefficient d” can be executed by applying the processing in the beam hardening correction. For example, in the beam hardening correction, the correction processing is performed on the collected projection data so as to approximate the transmission amount of the target monochromatic energy. Therefore, the data processing function 442 performs a correction process on the high energy projection data set and the low energy projection data set so as to approximate the transmission amount of the target monochromatic energy. Thereby, the transmission amount in the high energy projection data set and the transmission amount in the low energy projection data set are close to the transmission amount of the target monochromatic energy, and the mutual transmission amounts are also close to each other.

In addition, in the above-described embodiment, the case where the coefficient used for the scaling process is calculated from the difference in the actual transmission amount and the coefficient used for the beam hardening correction is applied to the coefficient of the scaling process has been described. However, the embodiment is not limited to this, and a theoretically calculated value may be used. For example, the X-ray transmission amount at the first energy and the X-ray transmission amount at the second energy may be logically calculated, and the coefficient may be calculated from the difference between the calculated transmission amounts.

As described above, the data processing function 442 executes the correction process of multiplying the plurality of first projection data sets or the plurality of second projection data sets by the coefficient based on the difference in transmission amount. Thereby, the X-ray CT system 1 can reduce the difference in the X-ray transmission amount in the projection data set in which different energies are mixed.

In the X-ray CT system 1 according to the other embodiment, for example, the above-described scaling processing is executed before the combining processing in the first embodiment to generate a confirmation image in which artifacts are further reduced. be able to. In such a case, the data processing function 442 separates the projection data set after the above-described scaling processing into projection data sets for each energy, interpolates the defective portion, and then performs the combining processing. Note that, for example, the reconstruction function 444 should generate a confirmation image with reduced artifacts, regardless of which data of the three projection data sets multiplied by the coefficient shown in the lower part of FIG. 5 is used. You can

In addition, in the above-described first embodiment, (imaging by Dual-Energy) is described as an example. However, the embodiment is not limited to this, and even when applied to a projection data set collected by using X-rays of three or more different energies (imaging by Multi-Energy). Good.

The X-ray CT system 1 according to the first embodiment has been described as a system (X-ray CT apparatus) in which the gantry device 10, the bed device 30, and the console device 40 are mutually connected. However, the embodiment is not limited to this, and for example, the X-ray CT system of the present application may be configured such that a part of the above-described processing is distributed and performed by the devices on the network. ..

FIG. 6 is a block diagram showing an example of the configuration of an X-ray CT system 100 according to another embodiment. It should be noted that the X-ray CT system 100 according to another embodiment is different from the X-ray CT system 1 shown in FIG. 1 in that it has the image processing server 2, and the X-ray CT apparatus has the communication interface 45. It is different in that it is connected to the image processing server 2 via the network NW. Hereinafter, points having the same configurations as those described in the first embodiment will be denoted by the same reference numerals as those in FIG. 1, and description thereof will be omitted.

The communication interface 45 is connected to the processing circuit 44 and controls transmission and communication of various data with the image processing server 2 connected via the network NW. For example, the communication interface 45 is realized by a network card, a network adapter, a NIC (Network Interface Controller), or the like. As an example, the communication interface 45 transmits the projection data set generated by the DAS 18 to the image processing server 2. The communication interface 45 also receives the processed projection data set from the image processing server 2 and outputs it to the processing circuit 44.

The image processing server 2 has a communication interface 21, a memory 22, and a processing circuit 23.

The communication interface 21 is connected to the processing circuit 23 and controls transmission and communication of various data with the X-ray CT apparatus connected via the network NW. For example, the communication interface 21 is realized by a network card, network adapter, NIC (Network Interface Controller), or the like. As an example, the communication interface 21 receives the projection data set from the X-ray CT apparatus and outputs it to the processing circuit 23. The communication interface 21 also outputs the processed projection data set processed by the processing circuit 23 to the X-ray CT apparatus.

The memory 22 is connected to the processing circuit 23 and stores various data. For example, the memory 22 is realized by a semiconductor memory device such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like. For example, the memory stores a projection data set or the like received from the X-ray CT apparatus. Further, the memory 22 stores a program corresponding to each processing function executed by the processing circuit 23.

The processing circuit 23 executes a data processing function 231 and a reconstruction function 232. That is, the processing circuit 23 controls the operation of the image processing server by reading out and executing a program corresponding to each function from the memory 22. Specifically, the data processing function 231 executes the same processing as the data processing function 442 described above. Further, the reconfiguration function 232 executes the same processing as the reconfiguration function 444 described above. The data processing function 231 is an example of a data processing unit. The reconfiguration function 232 is an example of a reconfiguration unit.

In the image processing server 2 shown in FIG. 6, each processing function is stored in the memory 22 in the form of a program executable by a computer. The processing circuit 23 is a processor that realizes a function corresponding to each program by reading the program from the memory 22 and executing the program. In other words, the processing circuit 23 in the state where each program is read has the function corresponding to the read program.

Although FIG. 6 shows the case where each processing function of the data processing function 231 and the reconstruction function 232 is realized by the single processing circuit 23, the embodiment is not limited to this. For example, the processing circuit 23 may be configured by combining a plurality of independent processors, and each processor may realize each processing function by executing each program. Further, each processing function of the processing circuit 23 may be implemented by being appropriately dispersed or integrated in a single or a plurality of processing circuits.

The word "processor" used in the above description is, for example, a CPU, a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device ( A circuit such as a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). The processor realizes the function by reading and executing the program stored in the memory 41 or the memory 22.

Note that, in FIG. 1, the single memory 41 has been described as storing a program corresponding to each processing function. Further, in FIG. 6, it has been described that the single memory 22 stores the program corresponding to each processing function. However, the embodiment is not limited to this. For example, the plurality of memories 41 may be arranged in a distributed manner, and the processing circuit 44 may read the corresponding program from the individual memories 41. Further, for example, the plurality of memories 22 may be arranged in a distributed manner, and the processing circuit 23 may read the corresponding programs from the individual memories 22. Further, instead of storing the program in the memory 41 or the memory 22, the program may be directly incorporated in the circuit of the processor. In this case, the processor realizes the function by reading and executing the program incorporated in the circuit.

Each component of each device according to the above-described embodiment is functionally conceptual, and does not necessarily have to be physically configured as illustrated. That is, the specific form of distribution/integration of each device is not limited to that shown in the figure, and all or a part of the device may be functionally or physically distributed in arbitrary units according to various loads or usage conditions. It can be integrated and configured. Furthermore, all or arbitrary parts of the processing functions performed by each device may be realized by a CPU and a program that is analyzed and executed by the CPU, or may be realized as hardware by a wired logic.

Further, the processing program described in the above-described embodiment can be realized by executing a processing program prepared in advance on a computer such as a personal computer or a workstation. This processing program can be distributed via a network such as the Internet. Further, this processing program can also be executed by being recorded in a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, or a DVD, and being read from the recording medium by the computer.

According to at least one embodiment described above, it is possible to efficiently obtain a confirmation image for the purpose of confirming the shooting range.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof, as well as included in the scope and spirit of the invention.

1, 100 X-ray CT system 11 X-ray tube 12 X-ray detector 23, 44 Processing circuit 441 System control function 231, 442 Data processing function 232, 444 Reconstruction function

Claims (5)

An X-ray irradiation unit that irradiates X-rays while rotating around the subject,
An X-ray control unit that periodically changes the energy of the X-rays while the X-ray irradiation unit makes one revolution around the subject;
An X-ray detection unit that detects the X-rays and collects a projection data set for each rotational position of the X-ray irradiation unit;
Based on the plurality of first projection data sets collected when the first energy X-rays are irradiated, a plurality of first interpolation data sets corresponding to the rotational positions where the first energy is not irradiated are generated. A plurality of second interpolations corresponding to rotational positions that were not irradiated with the second energy, based on a plurality of second projection data sets that were generated and collected when the second energy X-ray was irradiated. A data processing unit that executes a process including an interpolation process for generating a data set,
A reconstruction unit that reconstructs an image based on a composite data set generated based on a plurality of projection data sets including the processed projection data set;
X-ray CT system equipped with. The X-ray CT system according to claim 1, wherein the composite data set is generated by applying different filters to the plurality of projection data sets and then combining the plurality of applied projection data sets. The data processing unit generates a first combined data set by combining a first projection data set corresponding to the rotation position of the X-ray irradiation unit and a second interpolation data set, and a second projection data set corresponding to the rotation position. Generate a second combined data set by combining the data set and the first interpolated data set,
The X-ray CT system according to claim 1, wherein the reconstruction unit reconstructs an image using the first synthetic data set and the second synthetic data set. The data processing unit weights the first projection data set and the second projection data set so as to have a high ratio and generates the first composite data set and the second composite data set, respectively. The X-ray CT system according to item 3. A processing program that uses projection data sets collected for each rotational position by periodically changing the energy of X-rays while rotating once around the subject,
Based on the plurality of first projection data sets collected when the first energy X-rays are irradiated, a plurality of first interpolation data sets corresponding to the rotational positions where the first energy is not irradiated are generated. A plurality of second interpolations corresponding to rotational positions that were not irradiated with the second energy, based on a plurality of second projection data sets that were generated and collected when the second energy X-ray was irradiated. A data processing function for executing processing including interpolation processing for generating a data set,
A reconstruction function for reconstructing an image based on a composite data set generated based on a plurality of projection data sets including the processed projection data set,
A processing program for making a computer realize.

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