JP2015205065A - X-ray computer tomography apparatus and scan schedule setting support apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set tube current modulation in detail, in good accuracy and in good operability.SOLUTION: An X-ray computer tomography apparatus includes: an X-ray tube device 101; a high-voltage generation part 109; an X-ray detector 103; a bed device 111 and a rotary mechanism. Volume data is reconstituted by a reconstitution processing part 118 on the basis of the projection data generated from the output of the X-ray detector. A plurality of organ regions are extracted from the volume data by an extraction processing part 123. A plurality of doses relating to the plurality of extracted organ regions are calculated in accordance with the scan condition of a real scan by a dose calculation part 124. The plurality of doses are displayed on a display part.

Description

  Embodiments described herein relate generally to an X-ray computed tomography apparatus (X-ray CT) and a scan plan setting support apparatus.

  Due to recent advances in low-dose imaging technology, the main scan used for diagnosis is being reduced in dose. At the scan planning stage, an image for positioning is taken in order to set the scan position and range of the main scan, the determination of the reconstruction position and range, the tube voltage, the tube current, and the like. As shown in FIG. 7, the positioning image is obtained by moving the top plate at a constant speed by fixing the X-ray tube at a position of 0 °, that is, a position in front of the subject lying on the top plate, for example. Photographing is performed by intermittently repeating photographing while intermittently moving or in synchronization with the top plate moving / stopping. Positioning images may be collected from two directions of the side direction (90 °) in addition to the front direction (0 °), and from any direction, but the display direction cannot be changed after shooting.

  As described above, since the positioning image is currently acquired by stopping the rotation of the X-ray tube, information in only one direction, at most two directions, can be obtained, and it is only a projection image. Therefore, it does not have CT value information. Therefore, the organ of the subject cannot be accurately recognized, and dose management for each organ cannot be performed. The exposure dose is also managed only by CTDI (Computed Tomography Dose Index) and DLP (Dose Length Product).

Japanese Patent Laid-Open No. 7-23946

  The purpose is to achieve high-accuracy dose management for each organ in the scan plan.

  An X-ray computed tomography apparatus according to this embodiment includes an X-ray tube apparatus, a high voltage generation unit that generates a tube voltage to be applied to the X-ray tube apparatus, an X-ray detector, and a subject. And a projection mechanism generated from the output of the X-ray detector, and a rotation mechanism for rotatably supporting the periphery of the subject. A storage unit, a reconstruction processing unit that reconstructs volume data based on the projection data, an extraction processing unit that extracts a plurality of organ regions from the volume data, and a plurality of extracted organ regions, respectively. A dose calculation unit that calculates a plurality of doses according to the scan conditions of the main scan; and a display unit that displays the calculated plurality of doses.

FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus according to this embodiment. FIG. 2 is a flowchart showing the processing procedure of the entire CT examination according to this embodiment. FIG. 3 is a diagram showing a helical scan in step S11 of FIG. FIG. 4 is a diagram showing the non-helical scan in step S11 of FIG. FIG. 5 is a diagram showing an example of a scan plan setting screen configured by the scan expert system of FIG. FIG. 6 is an enlarged view of the dose list display portion of FIG. FIG. 7 is a diagram showing a projection image (positioning image) in one direction acquired by a conventional photographing method.

  The X-ray computed tomography apparatus and scan plan setting support apparatus according to the present embodiment will be described below with reference to the drawings. Volume data reconstructed from projection data collected by a scan (called positioning scan) that collects data for the positioning image used in the scan plan before the main scan with the same dose as conventional imaging of the positioning image By using it, it becomes possible to obtain three-dimensional information of the subject. The amount of information obtained can be greatly increased as compared with the conventional projection image (positioning image) taken from one or two directions, and sufficient information can be given for the scan planning of the main scan. Since the range and position of the organ of the subject in the scan range can be accurately grasped in three dimensions, how much dose is applied to which part at the time of the scan plan before the main scan, and the exposure for each organ after the examination Dose management can be performed more accurately.

  FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus according to this embodiment. The X-ray computed tomography apparatus includes an X-ray tube apparatus 101 and an X-ray detector 103 as one body, a rotation / rotation (ROTATE / ROTATE) type in which the periphery of a subject rotates around a rotation axis, and a ring shape. There are various types such as a fixed / rotation (STATIONARY / ROTATE) type in which a large number of detection elements are arrayed and only the X-ray tube apparatus 101 rotates around the subject, and any type is applicable. Here, the rotation / rotation type that currently occupies the mainstream will be described. Further, to reconstruct one slice of tomographic image data, projection data for about 360 ° around the subject and about 360 ° is required, and projection data for 180 ° + fan angle is also required in the half scan method. . The present invention can be applied to any reconstruction method. In addition, the mechanism for converting incident X-rays into electric charges 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. The generation of electron-hole pairs in semiconductors and their transfer to the electrode, that is, the direct conversion type utilizing a photoconductive phenomenon, is the mainstream. Any of these methods may be employed as the X-ray detection element, but here, the former indirect conversion type will be described. In recent years, the so-called multi-tube X-ray computed tomography apparatus in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has progressed. Yes. The present invention can be applied to both a conventional single-tube X-ray computed tomography apparatus and a multi-tube X-ray computed tomography apparatus. Here, a single tube type will be described.

  The X-ray computed tomography apparatus of this embodiment has a gantry 100. The gantry 100 has an annular rotating frame 102. The rotating frame 102 constitutes a rotating mechanism together with the gantry driving unit 107. The rotating frame 102 is driven by the gantry driving unit 107 and rotates around the rotation axis RA. An X-ray tube device 101 and an X-ray detector 103 are mounted on the rotating frame 102 so as to face each other. During scanning, a subject placed on the top plate of the bed apparatus 111 is inserted between the X-ray tube apparatus 101 and the X-ray detector 103. The top plate is moved back and forth along the longitudinal direction by a drive unit (not shown) provided in the bed apparatus 111.

  The X-ray tube apparatus 101 receives an application of a tube voltage and a filament current from the high voltage generator 109 via the slip ring 108 and generates X-rays. The X-ray detector 103 includes a plurality of X-ray detection elements that detect X-rays that have passed through the subject and output electrical signals that reflect the dose of incident X-rays. The plurality of X-ray detection elements are arranged in a two-dimensional form of, for example, 320 columns × 912 channels.

  The data collection circuit 104 collects a signal output from the X-ray detector 103 and converts it into a digital signal (referred to as raw data). The data collection circuit 104 is connected to a preprocessing device 106 via a non-contact data transmission device 105. The pre-processing device 106 performs processing such as sensitivity correction and logarithmic conversion on the pure raw data to generate projection data. The projection data is stored in the storage device 112. The scan control unit 110 controls each operation of the gantry driving unit 107, the high voltage generation device 109, and the bed device 111 in order to execute a scan according to scan plan information described later.

  The image reconstruction unit 117 is provided for reconstructing image data with relatively low noise based on projection data collected by scanning with low-dose X-rays that is comparable to the conventional two-dimensional positioning image capturing. . As the reconstruction method by the image reconstruction unit 117, an arbitrary method having a relatively high applicability for noise reduction is used. For example, an image reconstruction method using the successive approximation method (sequential approximation method applied image reconstruction method) is used. Here, the image reconstruction unit 117 is described below as reconstructing volume data by the successive approximation method applied image reconstruction method, but is not limited to the successive approximation method applied image reconstruction method as described above. .

  The image reconstruction unit 117 reconstructs image data, here volume data, based on the projection data stored in the storage device 112, for example, by an algorithm based on a successive approximation applied reconstruction method. Volume data is stored in the storage device 112. The successive approximation applied reconstruction process is used to reconstruct volume data used for the scan plan before the main scan, or to reconstruct image data (tomographic image data, volume data) based on projection data collected by the main scan. Is also selectively applied to other types of reconstruction processing provided in the reconstruction processing unit 118 described later.

  The successive approximation applied reconstruction method is an application of the successive approximation method. As is well known, the successive approximation method is a method for reconstructing an image while repeating the correction by comparing the difference between the actual measurement value and the calculation value for the projection data. The successive approximation applied reconstruction method is a method in which a process for reducing noise on projection data and a process for reducing noise in the reconstructed image data are added in the image reconstruction cycle of the successive approximation method. . The algorithm of the successive approximation applied reconstruction method reduces noise by using a statistical noise model and a scanner model for the collected projection data. Furthermore, using an anatomical model, in the image reconstruction domain, identify which is noise and which is true projection data, extract only the noise component, and repeat this work to remove and reduce noise with high accuracy. To do. The successive approximation applied reconstruction method is a reconstruction method that achieves both low-dose imaging and low noise high image quality.

  The reconstruction processing unit 118 is different from the successive approximation applied image reconstruction method in the image reconstruction unit 117 based on projection data within a range of 360 ° or 180 ° + fan angle, for example, the Feldkamp method, or Volume data is reconstructed by cone beam reconstruction. The Feldkamp method is a reconstruction method when the projection ray intersects the reconstruction surface like a cone beam, and it is treated as a fan projection beam when convolved on the assumption that the cone angle is small. Back projection is an approximate image reconstruction method that processes along a ray during scanning. The cone beam reconstruction method is a reconstruction method in which projection data is corrected according to the angle of the ray with respect to the reconstruction surface, as a method of suppressing the cone angle error more than the Feldkamp method. Volume data is stored in the storage device 112.

  In order to reconstruct volume data from the projection data collected in the positioning scan, for example, the successive approximation applied reconstruction method having high applicability to noise reduction is applied, while the volume data is reconstructed from the projection data collected in the main scan. The successive approximation reconstruction method, the Feldkamp method, and the cone beam reconstruction method are arbitrarily selected.

  The display device 116 is provided mainly for displaying an image generated from the volume data and for displaying a scan plan support screen constructed by the scan expert system 120. The input device 115 includes a keyboard, a mouse, and the like for inputting an operator's instruction.

  The three-dimensional image processing unit 121 has a function of generating three-dimensional image data from volume data stored in the storage device 112 by volume rendering processing, and axial / sagittal / coronal or arbitrary from volume data by cross-section conversion processing (MPR processing). It has a function of generating cross-sectional image data relating to the oblique cross-section of each. The projection image generation processing unit 122 generates projection image data as a positioning image from the projection data stored in the storage device 112. For example, when an arbitrary view angle is selectively specified from, for example, 0 °, 45 °, and 90 ° on the scan plan support screen, the X-ray tube apparatus 101 is positioned at the view angle under the control of the scan expert system 120. Sometimes collected projection data is read from the storage device 112. The view angle is a position expressed in angle on the rotational trajectory of the X-ray tube apparatus 101 at the time of projection data collection. 0 ° indicates that the X-ray tube apparatus 101 is at the top position on the rotation trajectory. The projection image generation processing unit 122 arranges the read projection data of the same view angle according to the respective top plate positions, and synthesizes them into one sheet, thereby generating positioning image data equivalent to the conventional one.

  The part extraction processing unit 123 extracts a plurality of organ regions included in the scan range from the volume data stored in the storage device 112, typically using threshold processing and pattern recognition together. In particular, the region extraction processing unit 123 extracts regions such as “testis”, “ovary”, “spinal cord”, and “eyeball (lens)” with high X-ray sensitivity from the volume data according to the threshold value and shape pattern applied to each organ. To do. The extracted organ region information is supplied to the scan expert system 120.

  The dose calculation processing unit 124 individually determines an effective dose (mSv) and an equivalent dose (mSv) for each extracted organ region based on, for example, the tube current, tube voltage, slice thickness, and scan time of the main scan planned for the scan. Calculate The effective dose (mSv) of each organ is obtained by multiplying the equivalent dose of each organ by the tissue weighting factor. The equivalent dose of each organ is obtained by multiplying the absorbed dose for each organ by the radiation weighting factor for each organ. The absorbed dose is calculated from the X-ray condition by the tube voltage and tube current, the scan time, etc., and the absorbed dose for each organ is calculated as the sum of the volumes of each organ. In addition, the method of calculating | requiring the effective dose of each organ, the equivalent dose of each organ, the absorbed dose for every organ can be used arbitrarily. Since volume data can be collected in the positioning scan before the main scan, the organ region can be accurately extracted in three dimensions, and the dose can be calculated with high accuracy.

  The scan expert system 120 selects a plurality of scan plan candidates suitable for the examination purpose, the examination target organ, the age and sex of the subject, etc. included in the examination request information in order to assist the user in setting the scan plan. Then, the scan plan support screen is constructed together with the contents of the inspection request with the list of scan plan candidates. As illustrated in FIG. 5, the scan plan support screen includes a positioning image and a three-dimensional image of the entire positioning scan range. The scan range of the main scan is overlaid on the positioning image as a rectangular auxiliary frame line.

  The scan expert system 120 superimposes the organ regions extracted by the part extraction processing unit 123 on the positioning image and the three-dimensional image on the scan plan support screen in the assigned colors. In particular, areas such as “testis”, “ovary”, “spinal cord”, and “eyeball (lens)” that are highly sensitive to X-rays are assigned, for example, red as a warning color, and are superimposed on the positioning image and the three-dimensional image.

  The scan expert system 120 includes an effective dose (mSv) and an equivalent dose (mSv) of each of the plurality of organ regions individually calculated by the dose calculation processing unit 124 for the plurality of organ regions extracted by the region extraction processing unit 123. Are arranged in a list in a predetermined area on the scan plan support screen. The scan expert system 120 extracts the effective dose and equivalent dose of each of the plurality of organ regions individually calculated by the dose calculation processing unit 124 from each organ region on the three-dimensional image or positioning image on the scan plan support screen. Overlay via line.

  When the effective dose (mSv) and equivalent dose (mSv) calculated for each organ by the dose calculation processing unit 124 exceed the upper limit value prescribed in advance for each organ, the scan expert system 120 notifies that fact. A message for alerting is displayed on the scan plan support screen.

  In addition, a scan position, a scan range, a reconstruction position, a reconstruction range, a tube voltage, a slice thickness, a reconstruction function, and the like are designated on the scan plan support screen. The scan expert system 120 generates scan plan information according to the confirmed scan plan. The scan plan information is sent to the scan control unit 110, and the main scan is executed according to the scan plan information under the control of the scan control unit 110.

  FIG. 2 shows a processing procedure of the entire CT examination from the low-dose positioning scan in the scan planning stage according to the present embodiment to the final image display through the main scan. In the scan planning stage, first, the scan control unit 110 controls the helical scan method illustrated in FIG. 3 at a lower dose than the main scan, or the entire scan of the subject, such as the entire chest, abdomen, and the entire upper body. The positioning scan is executed by the non-helical scan method illustrated in FIG. In the helical scan method, the X-ray tube device 101 and the X-ray detector 103 continuously rotate around the subject, and the X-ray detector 103 repeatedly detects the transmitted X-rays of the subject. The top plate on which the subject is placed is continuously moved. In the case of the non-helical scan method, projection data for one round is collected with the top plate stopped, and then the top plate is moved a predetermined distance according to the cone spread angle, and projection data for one round at that position. Are collected and such operations are repeated. 360 ° projection data over a wide range along the body axis of the subject is collected by the positioning scan (S11). Volume data is reconstructed by the image reconstruction unit 117 based on the projection data collected by this positioning scan (S12). Volume data is stored in the storage device 112.

  Of the projection data for the entire circumference collected by the positioning scan, projection data collected by the X-ray tube apparatus 101 at an angle arbitrarily selected via the input device 115 from 0 °, 45 °, and 90 °, for example. The data is read from the storage device 112 to the projection image generation processing unit 122. As shown in FIGS. 3 and 4, the read projection data is arranged according to the top plate position (position in the body axis direction) and synthesized into one sheet. Thereby, data of a positioning image (projected image) viewed from one direction is generated. Initially, a positioning image of 0 ° is generated and displayed on the scan plan support screen as shown in FIG. When another 45 ° or 90 ° projection direction is selected via the input device 115, the selected other 45 ° or 90 ° positioning image is generated and switched to the display. An auxiliary frame line of the scan range is overlaid on the positioning image on the scan plan support screen.

  Since the region extraction processing unit 123 obtains volume data of CT values from the volume data stored in the storage device 112, an organ region such as an examination target is extracted by threshold processing, or by matching processing with a standard anatomical model An organ region can be identified by organ segmentation (S13). In particular, when regions such as “testis”, “ovary”, “spinal cord”, “eyeball (lens)” with high X-ray sensitivity and high risk of exposure are extracted, those organ regions are important. The extracted organ region information is supplied to the scan expert system 120.

  The scan plan support screen includes a scan plan, scan start time, pause time, scan start position, scan end position, scan mode, number of scans, tube voltage (kV), tube current (mA), scan range (C-FOV). The recommended values such as the reconstruction range (D-FOV), scan speed (total time), imaging slice thickness, movement range, post-scan movement amount, and scan time are individually expressed as numerical values, and the user arbitrarily sets ( S14).

  Effective dose (mSv) and equivalent dose (mSv) based on scan conditions such as tube current, tube voltage, slice thickness, scan time, etc., related to the main scan set in the scan plan individually for the extracted organ region Is calculated by the dose calculation processing unit 124 (S15). First, the absorbed dose is calculated from the tube voltage, tube current, scan time, etc. within the scan conditions of the main scan, and the absorbed dose for each organ is calculated as the sum of the volumes of each organ. The equivalent dose of each organ can be obtained by multiplying the absorbed dose for each organ by the radiation weighting factor for each organ. The effective dose of each organ is calculated by multiplying the equivalent dose of each organ by the respective tissue weighting factor.

  The calculated effective dose or equivalent dose of each organ is displayed on the scan plan support screen by the scan expert system 120. Whether to display the effective dose or the equivalent dose can be selected at any time by the user. For example, as shown in FIG. 6, the effective dose (or equivalent dose) for all the organs in the extracted scan range is displayed together with the organ name in a list, and all the organs in the scan range or a part of the organs are displayed. The effective dose (or equivalent dose) is displayed on the three-dimensional image together with the organ name via the lead line (S16). Some organs include the organ to be examined and the highly sensitive organ. Of the organ names and effective doses displayed in the list, the organ names and effective doses related to the organ to be examined are displayed in a mode different from the organ names and effective doses related to other organs, for example, in a specific color (blue). The organ name and effective dose for sensitive organs are displayed in a specific color, for example, red, which is clearly different from the organ names and effective dose for other organs. The remaining organs are displayed in white or black, for example.

  The dose calculation processing unit 124 or the scan expert system 120 holds the dose limit data for all the organs. When the calculated effective dose or equivalent dose of each organ exceeds the respective dose limit, the display mode of the organ name and effective dose, etc. for that organ is changed from steady display to flashing display to alert Prompt. The calculated effective dose and equivalent dose data of each organ is stored in the storage device 112. The dose calculation processing unit 124 receives, for example, effective dose and equivalent dose data for the past subject from the storage device 112 and accumulates them for each organ. As a result, the annual cumulative effective dose and the annual cumulative equivalent dose for each organ are calculated. These annual cumulative effective dose and annual cumulative equivalent dose are displayed on the scan plan support screen in accordance with user instructions. When at least one of the annual cumulative effective dose and the annual cumulative equivalent dose exceeds the respective upper limit value, in order to call attention, the organ and its annual cumulative effective dose or annual cumulative equivalent dose are set to the upper limit values. At the same time, it is forcibly displayed on the scan plan support screen.

  By clicking the “Confirm” button in the scan plan support screen, the scan plan and the scan conditions therein are confirmed (S18). Thereby, a scan position, a scan range, a reconstruction position, a reconstruction range, and the like are determined, and the presence / absence of tube current modulation and a modulation setting such as a modulation section are determined.

  When the scan plan is confirmed, the scan expert system 120 generates scan plan information according to the confirmed scan plan, and the main scan is executed under the control of the scan control unit 110 according to the scan plan information (S19).

  Based on the projection data collected by the main scan, volume data is reconstructed by, for example, cone beam reconstruction, and a three-dimensional image is generated by the three-dimensional image processing unit 121 and displayed on the display device 116 (S20).

  Conventionally, an X-ray tube is not rotated, but X-rays are usually emitted while being fixed in the 0 ° direction, and at the same time, a positioning image for determining a scanning range is taken by moving the bed in the Z direction. In the scan planning, the scan range or the like is only set from the positioning image in one direction and the positioning image in two directions at most. In this embodiment, the projection data in the 360 ° direction is collected while rotating the X-ray tube in the same manner as in the normal scan, and a three-dimensional image is generated using the obtained projection data in the entire circumferential direction. The three-dimensional structure can be confirmed and organ regions can be extracted. Thereby, the dose can be calculated with high accuracy for each organ. When the dose calculated for each organ exceeds the upper limit prescribed in advance for each organ, a message for alerting the user can be displayed. Scan conditions such as current can be corrected.

  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 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 their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 100 ... Gantry, 101 ... X-ray tube, 102 ... Rotating frame, 103 ... X-ray detector, 104 ... Data acquisition circuit, 105 ... Non-contact data transmission apparatus, 106 ... Pre-processing apparatus, 107 ... Base drive part, 108 ... Slip ring 109 ... High voltage generator 110 ... Host controller 112 ... Storage device 115 ... Input device 116 ... Display device 120 ... Scan expert system 121 ... 3D image processing unit 122 ... Projected image generation processing , 123... Site extraction processing unit, 124... Dose calculation processing unit.

Claims (12)

An X-ray tube device;
A high voltage generator for generating a tube voltage to be applied to the X-ray tube device;
An X-ray detector;
A bed apparatus for placing a subject;
A rotation mechanism that rotatably supports the X-ray tube apparatus and the X-ray detector around the subject;
A storage unit for storing projection data generated from the output of the X-ray detector;
A reconstruction processing unit for reconstructing volume data based on the projection data;
An extraction processing unit for extracting a plurality of organ regions from the volume data;
A dose calculator that calculates a plurality of doses respectively corresponding to the extracted plurality of organ regions according to the scan conditions of the main scan;
An X-ray computed tomography apparatus comprising: a display unit configured to display the plurality of calculated doses.   The X-ray computed tomography apparatus according to claim 1, wherein the plurality of doses are displayed so as to be superimposed on a three-dimensional image or a cross-sectional image generated from the volume data.   The X-ray computed tomography apparatus according to claim 1, wherein the extracted organ region is displayed so as to be superimposed on a projection image generated from the volume data.   When the extracted organ region includes “testis”, “ovary”, “spinal cord”, and “lens” regions having high X-ray sensitivity, the region having high X-ray sensitivity has a unique color as a warning color. The X-ray computed tomography apparatus according to claim 3, wherein   The X-ray computed tomography apparatus according to claim 1, wherein the reconstruction processing unit reconstructs the volume data from the projection data by successive approximation reconstruction or another reconstruction method.   A positioning scan is executed before the main scan, and in the positioning scan, the X-ray tube device and the X-ray detector rotate while the X-ray is lower in dose than the main scan and extends around the subject. The X-ray computed tomography apparatus according to claim 1, wherein projection data is collected.   The X-ray computed tomography apparatus according to claim 1, wherein the dose calculation unit compares the calculated plurality of doses with respective upper limit values.   8. The X-ray computed tomography apparatus according to claim 7, wherein the dose exceeding the upper limit is assigned a unique color as an alert color together with an organ name.   The X-ray computed tomography apparatus according to claim 1, wherein the dose calculation unit accumulates the calculated multiple doses for each past dose and organ related to the subject.   The X-ray computed tomography apparatus according to claim 9, wherein the dose calculation unit compares the accumulated dose with respective upper limit values.   11. The X-ray computed tomography apparatus according to claim 10, wherein a cumulative color exceeding the upper limit value is assigned a unique color as an alert color together with an organ name. An extraction processing unit for extracting a plurality of organ regions from the volume data collected by the X-ray computed tomography apparatus;
A dose calculator that calculates a plurality of doses respectively corresponding to the extracted plurality of organ regions from the scan conditions of the main scan;
A scan plan setting support apparatus, comprising: a display unit configured to display the plurality of calculated doses.