JP6294008B2 - X-ray computed tomography apparatus, reconstruction processing method, and reconstruction processing program - Google Patents

Description

  Embodiments described herein relate generally to an X-ray computed tomography apparatus, a reconstruction processing method, and a reconstruction processing program.

  The metal embedded in the subject absorbs more X-rays than the tissue in the subject. For this reason, in an X-ray CT (Computed Tomography) scan, X-rays related to rays passing through the metal in the subject reach a X-ray detector in the X-ray computed tomography (CT) apparatus in a sufficient amount that can be detected. do not do. As a result, the projection data becomes insufficient in the image reconstruction process. As a result, metal artifacts occur in the reconstructed image (hereinafter referred to as a reconstructed image). FIG. 5 is a diagram showing metal artifacts in the reconstructed image.

  Conventionally, an X-ray computed tomography (hereinafter referred to as CT) apparatus has a function of performing metal artifact reduction (hereinafter referred to as MAR) processing in order to reduce the metal artifact. . The MPR process is executed together with an image reconstruction process using projection data. By the MAR process, metal artifacts in the reconstructed image are reduced. FIG. 6 is a diagram illustrating a reconstructed image reconstructed by executing the MAR process. MAR processing includes a method involving forward projection and a method using dual energy. The calculation load in the MAR process is large in any method. For this reason, the time required for image reconstruction with MAR processing is longer than the time required for image reconstruction without MAR processing.

  In addition, if the MAR process is always ON, the speed of the reconstruction process is slow, resulting in a problem that the workflow in the image diagnosis is slow. Therefore, generally, the X-ray CT apparatus has an ON / OFF switch related to execution of the MAR process. The operator can arbitrarily select execution of the MAR process by operating the ON / OFF switch.

  However, when a metal such as an artificial joint having a high X-ray absorption amount is present in the subject, the operator can perform reconstruction performed by performing an X-ray CT scan and an image reconstruction process on the subject. It is necessary to determine the presence or absence of metal in the subject from the image. Next, the operator needs to operate the ON / OFF switch related to the execution of the MAR process according to the determination of the presence or absence of metal in the subject. That is, since the presence or absence of execution of the MAR process is executed based on the operator's judgment, there is a problem that the workflow relating to image diagnosis is hindered. In addition, since the MAR process is performed by image reconstruction twice, the workflow has a problem of further delay.

  An object is to provide an X-ray computed tomography apparatus, a reconstruction processing method, and a reconstruction process capable of reconstructing volume data with an artifact reduction process for reducing artifacts caused by an X-ray superabsorber without an operation by an operator. To provide a program.

An X-ray computed tomography apparatus according to this embodiment includes an X-ray generation unit that generates X-rays, an X-ray detection unit that detects X-rays generated from the X-ray generation unit and transmitted through a subject, A projection data generation unit that generates projection data of the subject based on an output from the X-ray detection unit, a projection image generation unit that generates a projection image based on the projection data, and edge detection for the projection image when the pixel value of the edge region in the generated edge image by processing exceeds a predetermined threshold value, and the total number or the total sum of the pixel value exceeding the first threshold value in the projection image exceeds a second threshold, of the subject A determination unit that determines that an X-ray absorption body having an X-ray absorption amount higher than that of the tissue is present in the projection image; and a determination that the projection image includes the X-ray absorption body The X-ray A reconstruction unit that activates an artifact reduction process for reducing artifacts caused by the absorber and reconstructs the volume data of the subject with the artifact reduction process based on the projection data. And

FIG. 1 is a configuration diagram showing a configuration of an X-ray computed tomography apparatus according to the present embodiment. FIG. 2 is a diagram illustrating an example of an X-ray superabsorber (artificial bone head) in a projection image (scanogram) according to the present embodiment. FIG. 3 is a diagram illustrating an example of an X-ray superabsorbent (spine fixing unit) in a projection image different from that in FIG. 2 according to the present embodiment. FIG. 4 is a flowchart illustrating an example of a process procedure related to the artifact reduction process activation function according to the present embodiment. FIG. 5 is a diagram showing metal artifacts in a conventional reconstructed image. FIG. 6 is a diagram illustrating a reconstructed image reconstructed by executing MAR processing according to the related art.

  Hereinafter, embodiments of the X-ray computed tomography (hereinafter referred to as CT) apparatus (also referred to as X-ray CT apparatus) will be described with reference to the drawings. Note that in the X-ray computed tomography apparatus, an X-ray tube and an X-ray detector are integrated and a Rotate / Rotate-Type in which the periphery of the subject rotates and a large number of X-ray detection elements arrayed in a ring shape are fixed. There are various types such as Stationary / Rotate-Type in which only the X-ray tube rotates around the subject, and any type is applicable to the present embodiment.

  Further, in order to reconstruct an image, projection data for 360 ° around the subject and projection data for 180 ° + fan angle are required for the half scan method. The present embodiment can be applied to any reconfiguration method. In addition, the mechanism for changing incident X-rays to electric charge is based on an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is further converted into electric charges by a photoelectric conversion element such as a photodiode, and by X-rays. The generation of electron-hole pairs in a semiconductor such as selenium and the transfer to the electrodes, that is, the direct conversion type utilizing a photoconductive phenomenon, are the mainstream. Any of these methods may be adopted as the X-ray detection element.

  Furthermore, in recent years, the so-called multi-tube type X-ray computed tomography apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating frame has been commercialized, and the development of peripheral technologies has progressed. Yes. In the present embodiment, either a conventional single-tube X-ray computed tomography apparatus or a multi-tube X-ray computed tomography apparatus can be applied. In the case of the multi-tube type, the plurality of tube voltages applied to the plurality of tube bulbs are different (multi-tube method). Here, a single tube type will be described.

  Further, the X-ray detection element may be a two-layer detection element having a front detection part for detecting low energy X-rays and a back detection part provided on the back surface of the front detector for detecting high energy X-rays. Good. Here, in order to simplify the explanation, it is assumed that the X-ray detector is a single-layer X-ray detection element.

  In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

  FIG. 1 shows a configuration of an X-ray computed tomography apparatus 1 according to this embodiment. The X-ray computed tomography apparatus 1 includes a gantry unit 100, a projection data generation unit 200, a projection image generation unit 300, a determination unit 400, a reconstruction unit 500, a storage unit 600, a display unit 700, an input unit 800, and a control unit 900. Have The X-ray computed tomography apparatus 1 may have an interface (hereinafter referred to as I / F) not shown. The I / F connects the X-ray computed tomography apparatus 1 to an electronic communication line (hereinafter referred to as a network). The network is connected to a radiation department information management system, a hospital information system, other medical image diagnostic apparatuses, etc., not shown.

  The gantry unit 100 accommodates a rotation support mechanism (not shown). The rotation support mechanism includes a rotation frame 101, a frame support mechanism that supports the rotation frame 101 so as to be rotatable about the rotation axis Z, and a rotation drive unit (electric motor) 103 that drives the rotation of the rotation frame 101.

  The rotating frame 101 includes an X-ray generation unit 105 that generates X-rays according to control by a control unit 900 described later, and an X-ray detection unit (hereinafter referred to as an area detector) also referred to as a two-dimensional array type or a multi-column type. ) 115, a data acquisition system (Data Acquisition System: hereinafter referred to as DAS) 121, a non-contact data transmission unit 123, a cooling device and a gantry control device (not shown), and the like.

  The rotation drive unit 103 rotates the rotation frame 101 at a predetermined rotation speed in accordance with a drive signal from the control unit 900 described later.

  The X-ray generation unit 105 includes a high voltage generator 107 and an X-ray tube 109. The high voltage generator 107 supplies the tube voltage applied to the X-ray tube 109 and the X-ray tube 109 using the power supplied via the slip ring 111 under the control of the control unit 900 described later. Tube current. The high voltage generator 107 may be provided outside the gantry unit 100. At this time, the high voltage generator 107 applies a tube voltage to the X-ray tube 109 via the slip ring 111 and supplies a tube current to the X-ray tube 109.

  The X-ray tube 109 receives the application of the tube voltage from the high voltage generator 107 and the supply of the tube current, and emits X-rays from the X-ray focal point. A collimator (not shown) is provided in the X-ray emission window on the front surface of the X-ray tube 109. The collimator has a plurality of collimator plates. The plurality of collimator plates shape X-rays emitted from the X-ray focal point in the X-ray tube 109 into, for example, a cone beam shape (pyramidal shape). Specifically, the plurality of collimator plates are driven by a control unit 900 described later in order to obtain a cone angle for obtaining projection data for actual measurement of a preset slice thickness. Further, at least two collimator plates (hereinafter referred to as cone angle collimators) among the plurality of collimator plates are independently driven under control of the control unit 900 with respect to the opening width related to the cone angle.

  The radiation range of X-rays is indicated by a dotted line 113 in FIG. The X axis is a straight line perpendicular to the rotation axis Z and upward in the vertical direction. The Y axis is a straight line orthogonal to the X axis and the rotation axis Z.

  The area detector 115 detects X-rays that have passed through the subject. The area detector 115 is attached to the rotating frame 101 at a position and an angle facing the X-ray tube 109 with the rotation axis Z interposed therebetween. The area detector 115 has a plurality of X-ray detection elements. Here, it is assumed that a single X-ray detection element constitutes a single channel. The plurality of channels are perpendicular to the rotation axis Z and centered on the focal point of the radiated X-ray, and the arc direction (channel) having a radius from this center to the center of the light receiving portion of the X-ray detection element for one channel. Direction) and the slice direction. The two-dimensional array is configured by arranging a plurality of channels arranged one-dimensionally along the channel direction in a plurality of rows in the slice direction.

  The area detector 115 having such a two-dimensional X-ray detection element array may be configured by arranging a plurality of the above-described modules arranged in a one-dimensional shape in a substantially arc direction in a plurality of rows in the slice direction. Further, the area detector 115 may be composed of a plurality of modules in which a plurality of X-ray detection elements are arranged in a line. At this time, the modules are arranged one-dimensionally in a substantially arc direction along the channel direction. Hereinafter, the number of X-ray detection elements arranged in the slice direction is referred to as the number of columns.

  During a scan related to X-ray imaging or X-ray computed tomography (hereinafter referred to as CT scan) on the subject, the subject is placed in a cylindrical imaging region 117 between the X-ray tube 109 and the area detector 115. It is placed on the top plate 119 and inserted. To the output of the area detector 115, a data acquisition circuit (Data Acquisition System: hereinafter referred to as DAS) 121 is connected.

  Specifically, before the CT scan for the subject, a scan for setting the imaging range (CT scan start position and end position) in the CT scan and setting the imaging conditions in the CT scan (hereinafter referred to as positioning scan). Is called). In the positioning scan, the rotating frame 101 is fixed in order to fix the X-ray tube 109 at the position of the X-ray tube 109, that is, a predetermined view angle. The positioning scan is a scan that is performed on a subject that is placed on the top plate 119 and moves within the imaging region 117 while the position of the X-ray tube 109 is fixed.

  After the positioning scan, a CT scan (hereinafter referred to as a main scan) is executed. Prior to execution of the main scan, an imaging range, imaging conditions, and the like of the main scan are input via the input unit 800 described later. During the main scan, the subject is placed on the top 119 and moved into the imaging region 117.

  The DAS 121 includes an IV converter that converts a current signal of each channel of the area detector 115 into a voltage, an integrator that periodically integrates the voltage signal in synchronization with an X-ray exposure cycle, An amplifier for amplifying the output signal of the integrator and an analog / digital converter for converting the output signal of the amplifier into a digital signal are attached to each channel. The DAS 121 changes the integration interval in the integrator according to the scan under the control of the control unit 900 described later. Data (pure raw data) output from the DAS 121 passes through a non-contact data transmission unit 123 using magnetic transmission / reception or optical transmission / reception, and a projection data generation unit (also referred to as pre-processing unit) 200 described later. Is transmitted.

  The projection data generation unit 200 generates projection data based on the pure raw data output from the DAS 121. Specifically, the projection data generation unit 200 performs preprocessing on pure raw data. The preprocessing includes, for example, sensitivity non-uniformity correction processing between channels, X-ray strong absorber, processing for correcting signal signal drop or signal loss due to extreme metal intensity mainly. Data immediately before reconstruction processing output from the projection data generation unit 200 (referred to as raw data or projection data, here referred to as projection data) is associated with a view angle when data is collected. Then, it is stored in a storage unit 600 having a magnetic disk, a magneto-optical disk, or a semiconductor memory.

  Here, for convenience of explanation, a set of projection data having the same view angle collected and interpolated almost simultaneously in one shot and having a plurality of channels defined by the cone angle is referred to as a projection data set. Also, the view angle is an angle in a range of 360 °, with each position of the circular orbit around which the X-ray tube 109 circulates about the rotation axis Z, for example, the uppermost portion of the circular orbit vertically upward from the rotation axis Z being 0 °. It is represented by. The projection data for each channel of the projection data set is identified by the view angle, cone angle, and channel number.

  The projection image generation unit 300 generates a projection image based on the projection data (projection data set) generated by the projection data generation unit 200 in the positioning scan. The projection image corresponds to the position of the X-ray tube, that is, a plane transmission image from a predetermined view angle. Projection image generation unit 300 outputs the generated projection image to determination unit 400 and display unit 700 described later. The projected image is also called, for example, a scanogram, a scano, a scout view, or a fluoroscopic image.

  The determination unit 400 determines the presence or absence of an X-ray high absorber in the projection image based on a plurality of pixel values respectively corresponding to a plurality of pixels in the projection image. The X-ray superabsorber has an X-ray absorption amount higher than that of the tissue of the subject. Specifically, the X-ray superabsorber is, for example, a metal. The X-ray superabsorber in the projected image is, for example, an artificial bone head, a plate, a screw, a rod, a spinal fixation unit, or the like formed of metal (titanium, titanium alloy, cobalt chrome alloy, etc.). The luminance value of the X-ray superabsorber (metal) is very high compared to the luminance value of the surrounding pixels in the projection image.

  Specifically, the determination unit 400 counts the number of pixels having a pixel value exceeding the first threshold in the projection image. For example, in the projection image, the first threshold value is set to a value larger than the pixel value of any tissue of the subject and smaller than the pixel value of any X-ray superabsorber. That is, the total number (total) of pixel values counted by the determination unit 400 corresponds to a region where the X-ray high-absorber exists in the projection image. Note that the determination unit 400 may count the area of pixels having a pixel value exceeding the first threshold in the projection image.

  Next, the determination unit 400 determines whether or not the counted number of pixels exceeds the second threshold value. The second threshold is, for example, the number of pixels corresponding to the smallest projected image among the projected images with respect to the X-ray superabsorber of any form. The determination unit 400 determines whether or not the counted area exceeds the second threshold value. At this time, the second threshold value is, for example, an area corresponding to the smallest projected image among the projected images with respect to the X-ray superabsorber of any form.

  When the counted number of pixels or the counted area exceeds the second threshold value, the determination unit 400 determines that there is an X-ray high absorber on the projection image (hereinafter referred to as “high absorber presence determination”). ). When the counted number of pixels or the counted area is equal to or smaller than the second threshold, the determination unit 400 determines that there is no X-ray high absorber on the projection image (hereinafter referred to as “no high absorber determination”). . The determination unit 400 outputs a determination result corresponding to the presence or absence of the superabsorber on the projection image to the reconstruction unit 500 described later.

  Note that the determination of the presence or absence of the X-ray superabsorber on the projection image by the determination unit 400 is not limited to the method using the total number or area of the pixel values. That is, any determination method may be used for determining the presence or absence of the X-ray superabsorber on the projection image by the determination unit 400. The determination unit 400 has a memory (not shown). The memory stores a first threshold value and a second threshold value. The memory may store a program for determining the presence or absence of an X-ray superabsorber in the projection image.

  FIG. 2 is a diagram showing an example of an X-ray superabsorber (artificial bone head) in a projection image (scanogram). FIG. 3 is a diagram illustrating an example of an X-ray superabsorbent (spine fixing unit) in a projection image different from that in FIG. 2. As shown in FIGS. 2 and 3, in the projection image, the X-ray high-absorber has a higher pixel value (luminance value) than the pixel value (luminance value) of the pixel related to the tissue of the subject. For this reason, in the projection image, it is possible to determine the presence or absence of an X-ray high absorber.

  When the determination result determined by the determination unit 400 is the determination that there is no superabsorbent, the reconstruction unit 500 reconstructs the volume corresponding to the imaging range of the subject as follows.

  The reconstruction unit 500 uses a Feldkamp method or a cone beam reconstruction method based on a projection data set having a view angle in the range of 360 ° or 180 ° + fan angle to form a substantially cylindrical three-dimensional image related to the reconstruction region. It has a function of reconfiguring (volume data). The reconstruction unit 500 has a function of reconstructing a two-dimensional image (tomographic image) by, for example, a fan beam reconstruction method (also referred to as a fan beam convolution back projection method) or a filtered back projection method. The Feldkamp method is a reconstruction method when a projection ray intersects the reconstruction surface like a cone beam. The Feldkamp method is an approximate image reconstruction method in which convolution is performed by assuming that the cone angle is small, and processing is performed as a fan projection beam, and back projection is processed along a ray at the time of scanning. The cone beam reconstruction method is a reconstruction method that corrects projection data in accordance with the angle of the ray with respect to the reconstruction surface, as a method that suppresses cone angle errors more than the Feldkamp method.

  The reconstruction unit 500 generates volume data corresponding to the imaging range for the subject based on the determination result by the determination unit 400 and the projection data set related to the main scan. Specifically, when the determination result determined by the determination unit 400 is a determination that there is a high absorber, the reconstruction unit 500 reconstructs the volume corresponding to the imaging range of the subject as follows.

  The reconstruction unit 500 activates an artifact reduction process for reducing artifacts caused by the X-ray high absorber. The artifact reduction process is, for example, a metal artifact reduction (hereinafter referred to as MAR) process that reduces metal artifacts caused by an X-ray high-absorber such as metal. The reconstruction unit 500 reconstructs volume data with MAR processing based on the projection data set related to the main scan.

  Specifically, for example, the reconstruction unit 500 reconstructs volume data based on the projection data set. The reconstruction unit 500 specifies an area related to the X-ray high-absorber in the volume data (hereinafter referred to as a high-absorber voxel area) by the MAR process. The reconstruction unit 500 generates forward projection data by performing forward projection on the volume data. Based on the superabsorber voxel region, the reconstruction unit 500 identifies a superabsorber region in the forward projection data (hereinafter referred to as a superabsorber forward projection region). The reconstruction unit 500 corrects the forward projection data of the superabsorber forward projection region based on the projection data included in the region near the superabsorber forward projection region (hereinafter referred to as the neighborhood region). In this correction, the forward projection data of the superabsorber forward projection region may be replaced with the projection data of the nearby region, or may be replaced by appropriate interpolation using the projection data of the nearby region. The reconstruction unit 500 reconstructs the volume data again using the corrected forward projection data set. Note that the reconstruction process with the MAR process may be repeatedly executed as appropriate.

  The reconstruction unit 500 is based on the volume data reconstructed with the MAR processing, for example, an arbitrary cross section (for example, three orthogonal cross sections (axial image, sagittal image, coronal image), MPR (MultiPlanar Reconstruction) image of an arbitrary cross section, ) To generate a reconstructed image. The reconstruction unit 500 outputs the generated reconstruction image to the display unit 700 described later.

  The storage unit 600 stores medical images reconstructed by the reconstructing unit 500 (hereinafter referred to as reconstructed images), a plurality of projection data sets, and the like. The storage unit 600 stores information such as operator instructions, image processing conditions, and imaging conditions input by an input unit 800 described later. The storage unit 600 stores a control program for controlling the gantry unit 100, the bed, and the like for X-ray computed tomography.

  The display unit 700 inputs a medical image reconstructed by the reconstruction unit 500, a projection image (scano image), scan conditions set for X-ray computed tomography, reconstruction conditions regarding reconstruction processing, and the like. Display the input screen. The display unit 700 displays an imaging range in the main scan on the projection image.

  The input unit 800 captures various instructions, commands, information, selections, and settings from the operator into the X-ray computed tomography apparatus 1. The various instructions / commands / information / selections / settings that have been taken in are output to the control unit 900, which will be described later. Although not shown, the input unit 800 includes a trackball, a switch button, a mouse, a keyboard, and the like for setting a region of interest (ROI). The input unit 800 inputs the imaging range of the main scan with respect to the displayed projection image generated by imaging (positioning scan) for determining the scan start position and imaging conditions for the subject.

  The input unit 800 detects the coordinates of the cursor displayed on the display screen, and outputs the detected coordinates to the control unit 900. Note that the input unit 800 may be a touch panel provided to cover the display screen. In this case, the input unit 800 detects coordinates touched by the operator on the basis of coordinate reading principles such as electromagnetic induction, electromagnetic distortion, and pressure sensitive, and outputs the detected coordinates to the control unit 900.

  The bed not shown includes a top plate 119, a support frame (not shown) that supports the top plate 119 so as to be movable along the Z direction, and a drive unit (not shown) that drives the top plate 119 and the bed. Have. The drive unit moves the bed up and down in response to an input by an operator's instruction. The drive unit moves the top board 119 along the Z direction according to the photographing plan input by the input unit 800.

  The control unit 900 functions as the center of the X-ray computed tomography apparatus 1. The control unit 900 includes a CPU (Central Processing Unit) (not shown) and a memory. The control unit 900 controls the high voltage generator 107, the gantry unit 100, and the like for X-ray computed tomography of the subject based on examination schedule data and a control program stored in a memory (not shown). . Specifically, the control unit 900 temporarily stores an operator instruction or the like sent from the input unit 800 or the like in a memory (not shown). The control unit 900 controls the high voltage generator 107, the gantry unit 100, and the like based on information temporarily stored in the memory. The control unit 900 reads out a control program for executing predetermined image generation / display and the like from the storage unit 600 and develops it on its own memory, and executes calculations / processings and the like regarding various processes.

(Artifact reduction processing start function)
The artifact reduction processing activation function determines the presence or absence of an X-ray superabsorber in the projection image based on the pixel value of the projection image generated by the positioning scan. This is a function for reconfiguring the volume data by starting the processing. Hereinafter, processing related to the artifact reduction processing activation function will be described.

FIG. 4 is a flowchart illustrating an example of a process procedure related to the artifact reduction process activation function.
A projected image is generated by the positioning scan (step Sa1). The projected image is displayed on the display unit 700. In the displayed projection image, an imaging range in the main scan is input (step Sa2). Based on the pixel value in the projection image, the presence or absence of the X-ray superabsorber is determined (step Sa3).

  If there is an X-ray superabsorber in the projected image (step Sa4), the MAR process is activated (step Sa5). Next, the main scan is executed (step Sa6). At this time, a projection data set relating to the main scan is generated. Based on the projection data set, volume data is reconstructed with MAR processing (step Sa7).

  If there is no X-ray superabsorber in the projected image (step Sa4), the MAR process is not started. Next, the main scan is executed (step Sa8). At this time, a projection data set relating to the main scan is generated. Based on the projection data set, the volume data is reconstructed without the MAR process (step Sa9).

  A reconstructed image is generated based on the volume data. The generated reconstructed image is displayed on the display unit 700 (step Sa10).

(Modification)
A difference from the present embodiment is that a determination method of the presence or absence of the X-ray superabsorber in the determination unit 400 is different. Since the configuration of this modification is the same as that of the embodiment, the configuration diagram of this modification is omitted.

  The determination unit 400 performs edge detection processing on the projection image. The edge detection processing is, for example, filter processing using various edge detection operators (difference operators) such as a Laplacian operator, a Sobel operator, a gradient operator, and a Laplacian Gaussian operator. It is. The determination unit 400 generates an edge image in the projection image by using these operators related to edge detection. The determination unit 400 determines whether or not the pixel value (in the edge region) exceeds a predetermined threshold in the edge image.

  When the pixel value in the edge image exceeds a predetermined threshold, the determination unit 400 determines that there is a superabsorbent. When the pixel value in the edge image does not exceed the predetermined threshold value, the determination unit 400 determines that there is no superabsorbent. The determination unit 400 outputs a determination result (determination that there is a high absorber or a determination that there is no high absorber) to the reconstruction unit 500.

  The processing related to the artifact reduction processing activation function and the artifact reduction processing activation function according to the present modification is the same as in the embodiment, and thus the description thereof is omitted.

  According to this embodiment and this modification, it is possible to determine the presence or absence of an X-ray superabsorber (metal) in a projection image generated by a positioning scan, that is, to detect the X-ray superabsorber on the projection image. it can. The determination or detection is processing for confirming (detecting) the presence or absence of the X-ray superabsorber (metal), not extracting the region corresponding to the X-ray superabsorber (metal) on the projection image. For this reason, in this embodiment and a modification, a very simple design with a high degree of freedom is possible.

  In general, the X-ray superabsorber (metal) in a projection image (scanogram image) is: Very high brightness value, 2. It has two characteristics of sharply changing edges. The determination unit 400 according to the present embodiment and the modification example is configured as described in 1. above. And 2. The image analysis processing for detecting the X-ray superabsorber can be arbitrarily designed in accordance with the features of

  In the present embodiment, the presence / absence of the X-ray superabsorber is determined using the characteristic of the luminance value of 1 described above being very high. Further, in this modification, the presence or absence of an X-ray superabsorber is determined using the characteristic that the above-mentioned two edges absorb. The above 1. And 2. By using both of these characteristics, it is possible to improve robustness with respect to the determination of the presence or absence of the X-ray superabsorber in the projection image. Moreover, the process which detects an X-ray superabsorber in a projection image is not limited to the said embodiment and the said modification, What kind of method may be used if an X-ray superabsorber (metal) can be detected.

According to the configuration described above, the following effects can be obtained.
According to the X-ray computed tomography apparatus 1 in the present embodiment, volume data can be reconstructed with an artifact reduction process for reducing artifacts caused by the X-ray superabsorber without any operation by the operator. Specifically, in the present embodiment, ON / OFF of an artifact reduction process such as a MAR process can be automatically determined based on a projection image generated by a positioning scan without an operator's instruction. . In the case where it is determined that there is an X-ray superabsorber on the projection image, the present embodiment can reconstruct the volume data with the MAR process. That is, according to the present embodiment, the presence or absence of an X-ray superabsorber on the projection image is determined based on the pixel value of the projection image. Data can be reconstructed.

  For these reasons, in the present embodiment and this modification, it is possible to perform imaging and reconfiguration without requiring the operator to specify ON / OFF of the MAR process. From the above, according to the present embodiment, the workflow relating to imaging and reconstruction is simplified, and the diagnostic efficiency is improved.

  In addition, each function according to the embodiment can also be realized by installing a reconfiguration processing program for executing the processing in a computer such as a workstation and developing the program on a memory. At this time, a program capable of causing the computer to execute the method is stored in a storage medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. It can also be distributed.

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

  DESCRIPTION OF SYMBOLS 1 ... X-ray computed tomography apparatus, 100 ... Mount part, 101 ... Rotating frame, 103 ... Rotation drive part (electric motor), 105 ... X-ray generation part, 107 ... High voltage generator, 109 ... X-ray tube, 111 ... Slip ring, 113 ... X-ray emission range, 115 ... X-ray detector (area detector), 117 ... Imaging region, 119 ... Top plate, 121 ... Data acquisition circuit (DAS), 123 ... Non-contact data transmitter, DESCRIPTION OF SYMBOLS 200 ... Projection data generation part (preprocessing part), 300 ... Projection image generation part, 400 ... Determination part, 500 ... Reconstruction part, 600 ... Memory | storage part, 700 ... Display part, 800 ... Input part, 900 ... Control part

Claims (6)

An X-ray generator for generating X-rays;
An X-ray detector that detects X-rays generated from the X-ray generator and transmitted through the subject;
A projection data generation unit that generates projection data of the subject based on an output from the X-ray detection unit;
A projection image generator for generating a projection image based on the projection data;
Exceeds the threshold pixel value of a predetermined edge area of the generated edge image by the edge detection process on the projection image, and the total number or the total sum of the pixel value exceeding the first threshold value exceeds a second threshold value in the projection image A determination unit for determining that an X-ray superabsorber having an X-ray absorption amount higher than an X-ray absorption amount of the tissue of the subject is in the projection image ;
When it is determined that the X-ray superabsorber is present in the projection image, an artifact reduction process for reducing artifacts caused by the X-ray superabsorber is started, and the artifact reduction process is performed based on the projection data. A reconstruction unit for reconstructing the volume data of the subject,
An X-ray computed tomography apparatus comprising: The X-ray superabsorber is a metal,
The artifact reduction process is a process of reducing metal artifacts caused by the metal;
The X-ray computed tomography apparatus according to claim 1. The projection image generator is
Based on the projection data generated by the positioning scan for positioning the imaging range of the main scan with respect to the subject, the projection image is generated,
The reconstruction unit includes:
Reconstructing the volume data based on projection data generated by the main scan on the subject;
The X-ray computed tomography apparatus according to claim 1 or 2. The reconstruction unit includes:
If it is determined that the X-ray superabsorber is not present on the projection image, the subject based on the projection data is not started without starting an artifact reduction process for reducing the artifact caused by the X-ray superabsorber. Reconfiguring the volume data of
The X-ray computed tomography apparatus according to any one of claims 1 to 3. A projected image is generated by a positioning scan for positioning the imaging range of the main scan with respect to the subject,
Exceeds the threshold pixel value of a predetermined edge area of the generated edge image by the edge detection process on the projection image, and the total number or the total sum of the pixel value exceeding the first threshold value exceeds a second threshold value in the projection image when determines that the X-ray superabsorbent having a high X-ray absorption than the X-ray absorption of the tissue of the subject is in the projected image,
When it is determined that the X-ray superabsorber is present in the projection image, an artifact reduction process for reducing artifacts caused by the X-ray superabsorber is started.
Generating projection data by the main scan on the subject;
Reconstructing the subject volume data with the artifact reduction processing based on the projection data;
A reconstruction processing method comprising: On the computer,
A projected image is generated by a positioning scan for positioning the imaging range of the main scan with respect to the subject,
Exceeds the threshold pixel value of a predetermined edge area of the generated edge image by the edge detection process on the projection image, and the total number or the total sum of the pixel value exceeding the first threshold value exceeds a second threshold value in the projection image when, by judging that the X-ray superabsorbent having a high X-ray absorption than the X-ray absorption of the tissue of the subject is in the projected image,
When it is determined that the X-ray superabsorber is present in the projection image, an artifact reduction process for reducing artifacts caused by the X-ray superabsorber is started,
Generating projection data by the main scan for the subject;
Reconstructing the volume data of the subject with the artifact reduction processing based on the projection data;
A reconfiguration processing program comprising:

Images