WO2017130657A1 - Dispositif et procédé de tomodensitométrie à rayons x pour le réglage des conditions d'imagerie et programme de réglage des conditions d'imagerie - Google Patents

Dispositif et procédé de tomodensitométrie à rayons x pour le réglage des conditions d'imagerie et programme de réglage des conditions d'imagerie Download PDF

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WO2017130657A1
WO2017130657A1 PCT/JP2017/000262 JP2017000262W WO2017130657A1 WO 2017130657 A1 WO2017130657 A1 WO 2017130657A1 JP 2017000262 W JP2017000262 W JP 2017000262W WO 2017130657 A1 WO2017130657 A1 WO 2017130657A1
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ray
shooting
imaging
map
feature
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PCT/JP2017/000262
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English (en)
Japanese (ja)
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後藤　大雅
高橋　悠
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株式会社日立製作所
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]

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  • the present invention relates to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program, and more particularly to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program for controlling an X-ray dose applied to a specific part of a subject.
  • the X-ray tube While rotating the X-ray tube around the body axis of the subject, the X-ray tube emits X-rays in the form of a fan beam or cone beam, the X-ray transmitted through the subject is detected by the detector, and the obtained projection
  • An X-ray CT apparatus that acquires a reconstructed image inside a subject by back projecting data is known.
  • the rotation angle of the X-ray tube is divided into a plurality of angle ranges, and the X-ray irradiation output is reduced in an angle range where the distance between the X-ray sensitive part and the X-ray focal point is close.
  • an X-ray CT apparatus for reducing the X-ray exposure dose at a site having high X-ray sensitivity is disclosed.
  • Patent Document 2 by moving the bed, moving the subject relative to the X-ray source, and arranging the center of the diagnostic target part at or near the imaging center, An X-ray CT apparatus that suppresses X-ray irradiation on a living tissue is disclosed.
  • the X-ray CT apparatus of Patent Document 2 is not considered at all about reducing the X-ray exposure dose for a part having high X-ray sensitivity. For this reason, when a region having high X-ray sensitivity is included in the imaging range, the X-ray exposure dose may not be sufficiently reduced only by placing the center of the diagnostic target region at or near the imaging center.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to more effectively reduce unnecessary X-ray exposure dose for a portion having high X-ray sensitivity.
  • the present invention provides the following means.
  • One aspect of the present invention includes an X-ray source that circulates around a subject on a bed, and an X-ray detector that detects a dose of X-rays irradiated from the X-ray source and transmitted through the subject,
  • a scanner that acquires projection data, a reconstruction calculation unit that acquires a reconstructed image based on the projection data, a shooting condition setting unit that sets shooting conditions when acquiring the projection data, and projection according to the shooting conditions
  • a shooting feature value map generation unit that generates a shooting feature value map that maps feature values as information indicating features of the reconstructed image generated when data is acquired, and displays the shooting feature value map on a display unit
  • An X-ray CT apparatus including a display control unit is provided.
  • 1 is an external configuration diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention.
  • 1 is a block diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention. It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention.
  • 5 is a flowchart showing operations from acquisition of a positioning image to generation of a reconstructed image in the X-ray CT apparatus according to the first embodiment of the present invention.
  • an X-ray CT apparatus it is explanatory drawing which shows the imaging
  • an X-ray CT apparatus it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the X-ray source trajectory (trajectory) when performing an axial scan.
  • an X-ray CT apparatus it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the track
  • an X-ray CT apparatus a subject placed on a bed is irradiated with X-rays in a fan beam or cone beam shape while rotating an X-ray source around a body axis, and a plurality of detection elements are formed in an arc shape. Imaging is performed by receiving X-rays that have passed through the subject with a detector disposed in the area. Normally, one shooting in the rotation direction is referred to as one view, and about 1000 shootings are performed per one rotation in the rotation direction.
  • the following methods are mainly known as scanning (imaging) methods for performing imaging while rotating the X-ray source in this way.
  • FIG. 7A An imaging method in which the bed moves in the body axis direction after imaging and repeats an axial scan, which is called spiral scan, helical scan, or spiral scan.
  • the bed moves at a constant speed in the body axis direction and the X-ray source becomes the subject.
  • An imaging method (FIG. 7A)
  • FIG. 7B an imaging method in which the bed reciprocates in the body axis direction and the X-ray source circulates around the subject in a spiral orbit ( FIG. 7C) and called variable pitch scan, the bed moves at a variable speed, and the X-ray source orbits around the subject in a spiral orbit.
  • Imaging method, and the like are known as the main scanning method that.
  • an imaging method performed without rotating the X-ray source an imaging method called a scanogram, in which the bed moves with the X-ray source fixed (FIG. 7D) is also known.
  • the X-ray CT apparatus when imaging is performed while rotating the X-ray source as described above, fan-shaped fan beam-shaped or conical cone-beam-shaped X-rays are emitted from the X-ray source.
  • the number (period) of irradiation with X-rays varies depending on the region of the subject. That is, for example, the number of times (period) of X-ray irradiation differs between the vicinity of the body axis center of the subject and the body surface of the subject.
  • the period during which X-rays are irradiated differs for each region (image position) of the subject.
  • the period during which X-rays are irradiated (the rotation angle width at which the pixel position is imaged) is longer at the rotation center position. That is, projection data that can be used for reconstruction is collected over many angular widths at the rotation center, but is collected from a small angular width at positions away from the rotation center. Therefore, as shown in FIGS.
  • the angular width (back projection phase width) of projection data that can be used for reconstruction is related to the pixel position and the bed movement speed, and X
  • the imaging redundancy at each position of the subject differs depending on the trajectory of the radiation source, and in general spiral scanning, dose unevenness of 1.5 to 2 times can occur depending on the position. The same applies to the image noise, and unevenness such as the image noise ratio map in the spiral scan shown in FIGS. 10 and 11 occurs.
  • the X-ray irradiation amount can vary 1.5 to 2 times depending on the trajectory of the X-ray source. Even if it is half, depending on the trajectory of the X-ray source, the dose may be doubled. That is, if the trajectory of the X-ray source is not taken into account, the X-ray exposure dose cannot always be reduced.
  • the trajectory of the X-ray source can change depending on the imaging start angle (position) of the X-ray source, as will be described below.
  • FIG. 12A shows the case where the image is taken from 250 degrees from the image taking start angle 0 degree and FIG. 12B is from the image taking start angle 180 degree.
  • a, b, and c show the positions of the subjects. ing.
  • FIG. 12A shows that the points a, b, and c are both irradiated with fan beam-shaped X-rays from the X-ray source and photographed for 250 degrees.
  • each pixel considering with a parallel beam, it is considered that the image is taken over 180 degrees at the point b and 270 degrees or more at the point c.
  • FIG. 12B shows that points a, b, and c are irradiated with fan beam-shaped X-rays from the X-ray source and imaged over 250 degrees as in FIG. 12A.
  • FIG. 12B when viewed from each pixel (considering a parallel beam), it is considered that the image is taken over 180 degrees at the point c and over 270 degrees at the point b.
  • the shooting time (shooting angle range with a fan beam) is the same, the angle range when viewed with a parallel beam is different for each pixel, and these relationships change according to the shooting start angle.
  • the trajectory of the X-ray source changes according to the imaging start angle. That is, it can be seen that the X-ray exposure dose of the subject, the noise distribution in the axial plane, and the temporal resolution distribution change according to the imaging start angle.
  • 13A and 13B show the relationship between the imaging start angle and the source trajectory.
  • the position where data is collected does not depend on the shooting start angle.
  • the angle range for shooting that is, the position where data is collected, changes according to the shooting start angle.
  • the body axis direction position of the X-ray source may be varied when imaging the same range of the subject. it can. Therefore, in the case of step scan, the angle range to be imaged can be changed by the body axis direction position of the X-ray source to be imaged in addition to the imaging start angle.
  • the X-ray exposure dose of the subject depends on the trajectory of the X-ray source, and the trajectory of the X-ray source varies depending on the scanning method, the imaging start angle, and the like. For this reason, in order to reduce the X-ray exposure dose for a part having high X-ray sensitivity, it is necessary to set imaging conditions such as an X-ray source trajectory including an imaging start angle in accordance with the scanning method.
  • the present invention aims to more effectively reduce the unnecessary X-ray exposure dose for a specific part of a subject such as a part having high X-ray sensitivity under such a background.
  • the X-ray CT apparatus 1 according to the present embodiment can be applied to, for example, a multi-slice CT apparatus, and for example, a rotation-rotation system (third generation) can be adopted as a scanning system.
  • a rotation-rotation system third generation
  • the X-ray CT apparatus 1 includes a scanner 10, an operation unit 20, and a bed 30.
  • the scanner 10 performs a scan process on the subject placed on the bed 30 in accordance with an instruction from the operation unit 20.
  • the scanner 10 includes an X-ray generator 5 as an X-ray source, a high voltage generator 6, an X-ray controller 7, a collimator 8, a collimator controller 9, a detector 11, a central controller 12, a scanner controller 13, and a bed.
  • a control device 14, a couch movement measuring device 15, a driving device 16, a preamplifier 17, and an A / D converter 18 are provided.
  • the X-ray generator 5 generates X-rays by the high voltage applied to the high-voltage generator 6 while circling around the subject placed on the bed by the driving device 16 to be described later. Irradiate.
  • the high voltage generator 6 supplies a high voltage to the X-ray generator 5 in accordance with a control signal from the X-ray controller 7.
  • the collimator 8 is controlled by the collimator control device 9 and controls an X-ray irradiation region irradiated by the X-ray generator according to a control signal from the collimator control device 9.
  • the detector 11 is disposed facing the X-ray generator 5, detects X-rays irradiated from the X-ray generator 5 and transmitted through the subject, and outputs the detection result to the preamplifier 17 as a current value.
  • a single-row detector or a multi-row detector can be applied.
  • the multi-row detector has an advantage that a plurality of single-row detectors are arranged in the direction of the rotation axis, and as a whole, a wider range than that of the single detector can be photographed.
  • the preamplifier 17 amplifies the detection result received from the detector 11 and outputs it to the A / D converter 18.
  • the analog current value amplified by the preamplifier 17 is converted into digital data, further LOG-converted, calibrated, and output as projection data to an arithmetic unit 22 described later.
  • the X-ray generator 5, the collimator 8, the detector 11, the preamplifier 17, and the like are arranged on a disk (not shown), and the X-ray generator 5 is driven around the subject by driving the disk by the driving device 16. It is designed to go around.
  • the scanner control device 13 controls the drive device 16 and the collimator control device 9 for driving the disk on which the X-ray generation device 5 as the X-ray source is mounted in accordance with a control signal from the central control device 12 described later.
  • the couch controller 14 controls the moving speed and the like of the couch 30 according to the control signal from the central controller 12.
  • the bed 30 is measured for movement speed and distance by the bed movement measuring device 15.
  • the central control device 12 controls the above-described X-ray control device 7, scanner control device 13, and bed control device 14 based on an instruction input from the operation unit 20.
  • the operation unit 20 performs operations by the user, generation of reconstructed images, display of images, and the like, and includes an input / output device 21 and an arithmetic device 22.
  • the input / output device 21 includes a display control device 23 for displaying on the display device 29 a reconstructed image generated by the arithmetic device 22 and a photographing feature amount map, which will be described later, an input device 24 for inputting photographing conditions and reconstruction conditions, It includes a storage device 25 that stores input conditions and images to be displayed.
  • a display device 29 that displays various images in accordance with instructions from the display control device 23 is connected to the display control device 23.
  • a display device such as a liquid crystal display can be applied, and as the input device 24, one or more of a mouse, a keyboard, a touch panel, and the like can be applied.
  • the storage device 25 a drive device such as a hard disk or various storage media can be applied.
  • Examples of photographing conditions input from the input device 24 by the user include a bed moving speed, tube current, tube voltage, and slice position.
  • imaging methods such as axial scan and spiral scan, imaging start angle, imaging range in the body axis direction, beam pitch, tube current, tube voltage, etc., and settings such as X-ray exposure control (AEC) are also performed. .
  • the reconstruction conditions input from the input device 24 by the user include, for example, a reconstruction method, an image slice thickness, a backprojection phase width, a view weight slope width, a region of interest, a reconstructed image matrix size, and a reconstruction filter function. And the position of the reference point.
  • the computing device 22 includes a reconstruction computing device 26 that generates a reconstructed image based on projection data collected by the scanner, an image processing device 27 that performs necessary image processing on the reconstructed image, and a reconstructed image.
  • a shooting feature value map generation device 28 that maps the shooting feature values is included.
  • the function of each device included in the arithmetic device 22 can be realized as software by a CPU (not shown) included in the arithmetic device 22 reading and executing a program stored in a memory such as a ROM in advance. Also, some or all of the operations executed by each device included in the arithmetic device 22 can be realized by ASIC (application specific integrated circuit) or FPGA (field-programmable gate array).
  • the reconstruction calculation device 26 can reconstruct the acquired projection data by various methods.
  • the reconstruction calculation device 26 can be reconstructed by a known method such as so-called fan beam reconstruction or so-called parallel beam reconstruction.
  • the backprojection phase range used for reconstruction is determined for each reconstruction pixel. They may be different or in the same range.
  • the image processing device 27 performs necessary image processing on the reconstructed image reconstructed by the reconstruction computing device 26 so that the reconstructed image is in an optimum form for display on the display device 29.
  • the shooting feature amount map generation device 28 maps feature amounts as information indicating the features of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24. A photographed feature map is generated. Details of the shooting feature map will be described later.
  • the imaging process and the reconstruction process in the X-ray CT apparatus configured as described above are performed as follows.
  • a shooting start signal is generated and input from the operation unit 20 to the central controller 12.
  • the central control device 12 receives the input imaging start signal, and sends a control signal necessary for imaging to the X-ray control device 7, the scanner control device 13, and the bed control device 14, and starts imaging.
  • a control signal is transmitted from the X-ray controller 7 to the high voltage generator 6, a high voltage is applied to the X-ray generator 5, and the subject is irradiated with X-rays from the X-ray generator 5. Is done.
  • a control signal is transmitted from the scanner control device 13 to the drive device 16, and the X-ray generator 5, the detector 11, the preamplifier 17, etc. circulate around the subject 4 by rotating the disk.
  • the bed 30 on which the subject is placed moves still (normal scan) or translates in the body axis direction of the subject (spiral scan).
  • X-rays irradiated by the X-ray generator are limited in irradiation area by the collimator 6, absorbed (attenuated) in each tissue in the subject, transmitted through the subject, and detected by the detector 11.
  • the X-rays detected by the detector 11 are converted into current, amplified by a preamplifier 19, converted to digital data by an A / D converter 20, LOG converted, calibrated, and subjected to calibration as an arithmetic unit 22 as projection data. Is input.
  • the reconstruction calculation device 26 performs a reconstruction process based on the projection data input to the calculation device 32 to generate a reconstructed image.
  • the generated reconstructed image is stored in the storage device 25 and displayed as a CT image by the display device 29.
  • the image processing device 27 the image is displayed as a CT image by the display device 29.
  • the shooting feature amount map generation device 28 generates a shooting feature amount map in which feature amounts as information indicating features of the reconstructed image are mapped.
  • the generated reconstructed image is stored in the storage device 25 and displayed on the display device 29 as shown in FIGS.
  • the shooting feature amount map generation device 28 is information indicating the characteristics of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24.
  • a shooting feature amount map in which the feature amount is mapped is generated.
  • the X-ray exposure amount when acquiring the projection data and the re-generation generated from the acquired projection data is defined as a feature amount.
  • the shooting feature value map generation device 28 maps this feature value, that is, generates a map expressed on the image as a shooting feature value map.
  • the imaging feature amount map for example, an irradiation dose ratio map, an image noise ratio map, a time resolution ratio map, a spatial resolution ratio map, and the like can be generated.
  • the shooting feature amount map generation device 28 generates a shooting feature amount map and displays it on the display device 29.
  • the shooting feature amount map generation device 28 acquires a positioning image, generates a shooting feature amount map corresponding to the positioning image, and displays it on the display device 29 together with the positioning image.
  • FIG. 3 and 4 show an example of the display screen of the display device 29.
  • FIG. 3 In the display screen shown in FIG. 3, an area for setting two shooting feature amount maps, a reconstructed image, and shooting conditions are displayed together with the positioning image.
  • FIG. 4 together with the positioning image, two imaging feature quantity maps having different cross-sectional directions, an area for setting imaging conditions, and an imaging start angle and imaging feature quantity (irradiation dose) which are one of the imaging conditions. , Graphs (curves) representing the relationship with image noise, time resolution) are displayed.
  • the user can grasp the X-ray exposure dose and the degree of noise from the imaging feature map.
  • the display device 29 by causing the display device 29 to display the imaging feature amount map together with the positioning image, the user grasps in which part of the subject an area where the X-ray exposure amount or noise increases may occur. can do.
  • an imaging feature map for example, an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, a body axis resolution ratio map, and the like can be used. Can be created.
  • the irradiation dose ratio map can be acquired, for example, by performing a back projection process using a tube current / time product (mAs) per view as a projection value. In this case, it can be expressed as the following formulas (1) and (2) using fan beam back projection.
  • DSRM is a dose ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector in fan beam projection.
  • N view is the number of views
  • mA is the tube current modulation function [mA] in the view direction
  • T scan is the scan speed [s]
  • ⁇ 1 is the back projection start view with the fan beam
  • ⁇ 2 is the fan beam
  • the backprojection end view at x, y, z is the pixel index.
  • image noise ratio map The image noise (SD) ratio map can be expressed as the following formulas (3) and (4) using, for example, fan beam back projection.
  • an image noise ratio map may be generated as shown in the following formulas (5) and (6).
  • an image noise ratio map may be created by actually measuring the volume image.
  • SDRM is an image noise ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector row in fan beam projection.
  • N view is the number of views
  • W f is a view weight function
  • mA is a tube current modulation function [mA] in the view direction
  • T scan is a scan speed [s]
  • G is logarithmically converted when creating a projection value.
  • Pe is the projection data of the subject estimated from the positioning image and the imaging data for positioning image
  • Pa is the projection data of the Bowtie filter and the X-ray filter obtained by Air cal imaging
  • ⁇ 1 backprojection startup view of a fan beam beta 2 backprojection ends view of a fan-beam
  • x, y, z are the pixel It is an index.
  • positioning imaging data and forward projection data of the obtained positioning image can be used as Pe.
  • a projection value estimated based on the object model obtained from the projection value distribution of the scanogram may be used as Pe.
  • This object model can be acquired by using a method of estimating the object shape from the scanogram by AEC or the like.
  • the time resolution ratio map (total time width map) can be obtained, for example, by weighted backprojection processing using the imaging time ⁇ T scan per view as a projection value, as shown in the following formula (7). it can.
  • the effective time width map when used, it can be obtained by performing weighted backprojection using the imaging time ⁇ T scan per view as a projection value, as shown in the following formula (8).
  • TRRM is a temporal resolution ratio map
  • ⁇ is a view index in fan beam projection
  • N view is the number of views
  • W f is a view weight function
  • T scan is a scan speed [s]
  • ⁇ 1 is back projection with a fan beam.
  • the start view, ⁇ 2 is the back projection end view with the fan beam, and x, y, and z are pixel indices.
  • the spatial resolution ratio map can be obtained, for example, by performing a weighted back projection process on the value of the beam width in the channel direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as the following formulas (9) and (10) using fan beam back projection.
  • SRRM is a spatial resolution ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector row in fan beam projection.
  • N view is the number of views [view]
  • W f is the view weight function
  • D sid is the source-detector element distance [mm]
  • L is the source-pixel distance [mm]
  • ⁇ dcs is the channel direction detection.
  • the element size [mm] ⁇ 1 is a back projection start view with a fan beam
  • ⁇ 2 is a back projection end view with a fan beam
  • x, y, and z are pixel indexes.
  • the body axis resolution ratio map can be obtained, for example, by performing weighted back projection processing on the value of the beam width in the body axis direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as follows using fan beam back projection.
  • ZRRM is a body axis resolution ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector array in fan beam projection.
  • N view is the view number [view]
  • W f is the view weight function
  • D sid is the source-detector element distance [mm]
  • L is the source-pixel distance [mm]
  • ⁇ drs is the column direction.
  • ⁇ 1 is a back projection start view with a fan beam
  • ⁇ 2 is a back projection end view with a fan beam
  • x, y, and z are pixel indexes.
  • an imaging feature map an example of a method for generating an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, and a body axis resolution ratio map has been described.
  • the feature amount map based on other feature amounts indicating the features of the image can be applied to the shooting feature amount map, and other known methods can be used for the above-described feature amount map generation method. Can be used.
  • the above-described shooting feature amount map is generated as a three-dimensional image, and when the positioning image is volume data generated by a spiral scan, it is preferably displayed in accordance with the display of the positioning image. At that time, the same cross section is displayed side by side, the shooting feature map is colored and displayed superimposed on the positioning image, the value for the position selected by the cursor is displayed by referring to the shooting feature map, the positioning image The average value, maximum value, and minimum value of a predetermined area such as a circle or rectangle can be calculated and displayed.
  • the imaging feature map may display a plurality of surfaces such as an axial surface.
  • a three-dimensional image that is a shooting feature map may be projected in the same direction as the scanogram shooting to create and display a scanogram of the shooting feature map.
  • a cross section that passes through the rotation center of the three-dimensional image that is the imaging feature amount map or a cross section that becomes the center of the subject may be displayed. The subject center cross section at this time can be estimated from the positioning image.
  • the arithmetic unit 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S11), and the positioning image according to the imaging condition set. Is sent to the scanner 10 (step 12).
  • the setting of the imaging condition of the positioning image and the imaging of the positioning image can be performed by a known method. For example, scanogram imaging or low-dose spiral scanning can be applied.
  • the imaging conditions and reconstruction conditions in the actual imaging are set by the user based on the positioning image.
  • the arithmetic unit 22 receives the set various conditions via the input device 24 (step S13).
  • the image reconstruction method can be set as a reconstruction condition.
  • imaging conditions an imaging method such as an axial scan and a spiral scan, an imaging start angle, an imaging range in the body axis direction, a beam pitch, a tube current, a tube voltage, and X-ray exposure control (AEC) are also set.
  • AEC X-ray exposure control
  • the type of shooting feature value to be calculated is also selected in the shooting condition setting area 50.
  • the shooting feature value map generating device 28 In the next step S14, the shooting feature value map generating device 28 generates a shooting feature value map from the shooting conditions set and input by the user in the previous step S13. At this time, the shooting feature value map generation device 28 calculates the feature value according to any one of the above-described formulas (1) to (12) according to the type of the feature value selected in the previous step, and the shooting feature value map. And the generated shooting feature amount map is transmitted to the display control device 23. The display control device 23 causes the display device 29 to display a shooting feature amount map together with the positioning image.
  • the shooting feature amount map displayed on the display device 29 is confirmed, and an input of whether or not the user needs to change the shooting conditions is accepted via the input device 24 (step S15).
  • the arithmetic unit 22 receives a signal indicating that the shooting conditions are not changed from the input device 24, proceeds to the next step S16, and is set. An instruction is transmitted to the scanner 10 to perform the main photographing under the photographing conditions.
  • the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, returns to step S13, and accepts the input of the reset shooting condition. Then, the shooting feature value map generation device 28 creates a shooting feature value map again according to the reset shooting conditions (step S14).
  • the irradiation dose ratio is selected in the imaging condition setting region 50 by the user, and the imaging feature value map generation device 28 uses the irradiation dose as the imaging feature value map.
  • a ratio map is generated and displayed on the display device 29.
  • the user can grasp
  • the user adjusts the imaging start angle as an imaging condition so that X-ray irradiation to highly sensitive X-ray parts such as the spleen, the lens, and the thyroid gland is reduced.
  • the photographing start angle can be adjusted by a slide bar displayed on the display screen of the display device 29 as shown in FIG. 3, or can be directly designated by a user's manual input.
  • a variable pitch scan it may be adjusted to increase the bed moving speed in a highly sensitive X-ray sensitive region such as the spleen, the lens or the thyroid gland.
  • the X-ray exposure amount increases.
  • the position in the body axis direction of the X-ray generator 5 can also be adjusted so that the joint of imaging shifts from a portion having high X-ray sensitivity.
  • a tomographic image is generated by reconstructing the projection data collected by the main imaging performed in step S16, and displayed on the display device 29.
  • the imaging feature amount map selected by the user is displayed side by side with the tomographic image, the imaging feature amount map is colored and displayed over the tomographic image, or the cursor It is also possible to display the value for the position selected by referring to the shooting feature map, or to calculate and display the average value, maximum value, or minimum value of the area surrounded by a circle or rectangle on the positioning image.
  • the X-ray generator as an X-ray source is circulated around the subject by the scanner, and the X-ray dose irradiated from the X-ray generator and transmitted through the subject is detected by the X-ray detector.
  • the detected projection data is acquired, and the projection data is reconstructed by a reconstruction calculation device to obtain a reconstructed image.
  • imaging conditions for acquiring projection data are set according to the subject. Then, when projection data is acquired by the scanner according to the set shooting conditions, a shooting feature amount map is generated by mapping feature amounts as information indicating features in the obtained reconstructed image, and this is displayed on the display device. .
  • the feature amount of the generated reconstructed image can be presented to the user, and the user confirms the displayed imaging feature amount map to thereby display the reconstructed image in the reconstructed image.
  • the feature amount of the image can be grasped. Therefore, the user can set the imaging conditions again as necessary. For example, when it is desired to reduce the X-ray irradiation to the X-ray sensitive parts such as the spleen, the lens and the thyroid gland, The starting angle and the like can be adjusted. Thereby, the trajectory of the X-ray source is changed, and the X-ray exposure amount can be reduced by reducing the X-ray irradiation period for the site having high X-ray sensitivity.
  • an irradiation dose ratio map corresponding to the imaging start angle as an imaging feature amount map
  • the user can obtain an X-ray irradiation dose for a site of interest such as a site with high X-ray sensitivity of the subject. It can be determined whether it is appropriate.
  • the irradiation dose ratio map when the X-ray irradiation dose to a part having high X-ray sensitivity is large, the X-ray sensitivity is changed by changing the trajectory of the X-ray generator by changing the imaging start angle. The X-ray exposure dose for high sites can be reduced.
  • an imaging feature amount map to be generated and displayed by appropriately selecting any one of a time resolution ratio map, an image noise ratio map, etc., the image of interest has good image noise, time resolution, spatial resolution,
  • An imaging condition that can generate a reconstructed image having a desired imaging feature amount, that is, a tomographic image, in the region of interest can be set.
  • FIG. 7A shows the trajectory of the X-ray generator during normal scanning
  • FIG. 7B shows the trajectory of the X-ray generator during helical scanning.
  • the data obtained by the spiral orbit as shown in FIG. 7B is corrected to the circular orbit data as shown in FIG. 7A by using data interpolation, and then the filter correction two-dimensional backprojection is performed.
  • the degree of artifact is determined by the degree of discontinuity in the X-ray source locus, that is, the degree of artifact varies depending on the moving speed of the subject.
  • the present embodiment after the shooting conditions are set, when the projection data is acquired according to the shooting conditions set by displaying the desired shooting feature amount map and the reconstructed image is generated, the degree of the artifact is increased. You can present what will happen. Therefore, the user can reset the photographing conditions as necessary, and can improve the quality of the acquired reconstructed image.
  • the X-ray CT apparatus sets a region of interest, that is, a ROI (Region of Interest) in the positioning image, and optimizes a feature amount in the set ROI.
  • a region of interest that is, a ROI (Region of Interest)
  • the optimization refers to, for example, an average value, a maximum value, a minimum value, etc. as an index value for the imaging feature amount in the entire ROI, and the imaging conditions so that the index value related to the imaging feature amount is the best. It means to decide.
  • the imaging feature amount is an irradiation dose ratio
  • the imaging is performed such that an index value (average value, maximum value, integral value, etc. of the irradiation dose ratio) related to the irradiation dose ratio in the ROI is low. It can be optimized by determining the conditions.
  • the imaging condition is determined so that the index value (average value, minimum value, integral value, etc.) of the time resolution in the ROI becomes high. Can be optimized.
  • the imaging conditions are determined so that an index value (average value, minimum value, integrated value, etc.) of the spatial resolution ratio in the ROI is high. It can be optimized by doing.
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and the ROI, and at the same time, sets the value of the shooting feature value corresponding to the ROI position for each shooting start angle. And a shooting start angle-feature amount curve is generated. Then, the shooting feature value generation device 28 automatically sets an appropriate shooting start angle as an optimum shooting condition from the shooting start angle-feature value curve.
  • the imaging feature value generation device 28 starts imaging so that the average value or integral value of the imaging start angle-feature amount curve corresponding to the ROI range is optimized from the imaging start angle-feature value curve. Determine the angle.
  • the positioning image acquisition method, imaging condition setting, and image reconstruction method can be appropriately selected from various methods.
  • the arithmetic device 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S21), and the positioning image is obtained according to the imaging condition set. An instruction for photographing is transmitted to the scanner 10 (step S22).
  • the arithmetic unit 22 sets a region of interest in the positioning image set and input by the user in the input device 24 as the ROI 51. (Step S23).
  • shooting conditions and reconstruction conditions in the main shooting are set by the user based on the positioning image, and the arithmetic device 22 Accepts various set conditions via the input device 24 (step S24).
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and ROI, and transmits the generated shooting feature value map to the display device 29.
  • the shooting feature value map generation device 28 calculates the value of the shooting feature value corresponding to the ROI position for each shooting start angle, and is a graph showing the relationship between the shooting start angle and the feature value. -Generate a feature curve.
  • the shooting feature amount map generation device 28 transmits the generated shooting start angle-feature amount curve to the display control device 23, and causes the display device 29 to display the shooting start angle-feature amount curve as shown in FIG.
  • the imaging feature amount a graph showing the relationship between the irradiation start, the image noise, and the time resolution with the imaging start opening angle is generated.
  • the shooting feature value map generation device 28 considers the priority for each of these three shooting start angle-feature value curves, and the value of the feature value to be prioritized is closest to the target value, that is, the best. Is calculated as a candidate and displayed on the display device 29. In the arithmetic device 22, when there is one candidate, the photographing start angle which is the candidate is automatically determined (step S26).
  • the shooting feature amount with the highest priority is determined.
  • the imaging start angle is determined so as to be the best within the ROI.
  • the shooting start angle with the second highest shooting feature value in the ROI is determined as a candidate. If there are a plurality of candidate shooting start angles even when the second highest priority shooting feature amount is used, the third highest priority shooting feature amount is the best shooting start angle in the ROI. Are determined as candidates.
  • the shooting feature amount is first set to be the best (maximum value) when it is 1 and is most defective (minimum value) when it is 0.
  • the shooting start angle is determined so that the sum of values obtained by multiplying each shooting feature value by the respective priority coefficient is the highest.
  • a value obtained by subtracting the shooting feature value from 1 Can be used as candidates for the imaging feature amount.
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the previously input shooting conditions and the shooting start angle automatically determined in step S26, and displays it together with the positioning image. It is displayed on the device 29.
  • step S28 when it is determined that the user needs to change the shooting condition, and the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, the process returns to step S24 to reset the shooting condition by the user. Then, the input of the reset imaging conditions is accepted. Then, the shooting feature amount map generation device 28 calculates again the shooting start angle-feature amount curve according to the reset shooting conditions (step S25), and again determines the best shooting start angle (step S26). Then, a shooting feature amount map is created (step S27).
  • step S28 If it is determined in step S28 that the user does not need to change the shooting condition, the arithmetic unit 22 receives a signal indicating that the shooting condition is not changed from the input device 24, and proceeds to the next step S29 to set the set shooting condition. An instruction is transmitted to the scanner 10 so as to perform actual photographing under conditions. Then, by reconstructing the obtained projection data, a tomographic image as a reconstructed image is generated and displayed on the display device 29 (step S30).
  • the imaging feature amount in the case of the helical scan fluctuates with the period of the beam pitch in the body axis direction
  • the entire ROI may not be a desired imaging feature amount. Therefore, when the ROI body axis size is large, it is desirable to automatically correct the beam pitch in the ROI region using variable pitch scanning, and such information may be presented to the user. Alternatively, a correction candidate for the shooting condition may be proposed to the user.
  • the shooting start angle with the best feature amount is automatically determined by the calculation device from the shooting start angle-feature amount curve.
  • the present invention is not limited to this. Can be performed manually by a user who has confirmed the shooting start angle-feature amount curve.
  • the X-ray CT apparatus determines the imaging start angle in consideration of a plurality of feature amounts. Therefore, as shown in FIG. 4, priority coefficients indicating priorities to be considered are set for a plurality of feature amounts, and a shooting start angle-feature amount curve is created for each feature amount. Then, the shooting start angle is determined so that the value calculated from the product of the shooting feature value and the priority coefficient is the best.
  • one shooting start angle-feature amount curve obtained by combining a plurality of types of shooting start angle-feature amount curves based on the priority coefficient may be generated in consideration of the priority coefficient. The user can manually determine the shooting start angle based on the plurality of displayed shooting start angle-feature amount curves.
  • the synthesis of the shooting start angle-feature amount curve is performed as follows. For example, in the case where a plurality of shooting feature amounts are set and priority coefficients are set for the respective shooting feature amounts, first, each shooting feature amount is best when it is 1, and is lowest when it is 0. Thus, it is standardized in advance. After that, by creating a function of the sum of values obtained by multiplying each shooting feature value by the priority coefficient with respect to the shooting start angle, one shooting start angle-feature amount curve synthesized from a plurality of shooting start angle-feature amount curves is created. can do.
  • the X-ray CT apparatus determines an imaging start angle in consideration of feature quantities in a plurality of ROIs.
  • a plurality of ROIs are set in the positioning image, and an imaging start angle-feature amount curve at each ROI position is generated and displayed.
  • the candidate for the shooting start angle is determined so that the sum of the product of the feature amount with respect to the shooting start angle and the priority coefficient is the best based on the priority coefficient set in each ROI.
  • a shooting start angle-feature amount curve at each ROI position may be synthesized, and one obtained shooting start angle-feature amount curve may be used.
  • the fifth embodiment of the present invention will be described below.
  • the X-ray CT apparatus according to this embodiment is a so-called two-tube CT apparatus, and the imaging start angle is determined in consideration of the feature amount in the two-tube CT apparatus.
  • imaging system two sets of X-ray tube and detector pairs (imaging system) are arranged at different angles in the rotation direction (the difference between the two angles is ⁇ ) (imaging system A, imaging system).
  • System B In the two-tube CT, the imaging systems A and B rotate at the same speed, and the beam pitch at the time of spiral imaging is the same in each imaging system.
  • different X-ray filters can be used for the imaging systems A and B, and the X-rays output from the X-ray tubes can be made different.
  • a single tomographic image is generated by combining data obtained by the two imaging systems.
  • the X-ray filter and the imaging dose are different between the imaging systems A and B, and the trajectory of the X-ray generator at the time of spiral scanning is also different.
  • a feature amount map and a shooting start angle-feature amount curve are obtained.
  • two shooting feature value maps can be displayed separately, and from the viewpoint of improving visibility, a composite map obtained by adding the two shooting feature value maps is used. It is desirable to use it.
  • a shooting start angle-feature amount curve is also obtained from a composite map, or a combined curve obtained by adding two shooting start angle-feature amount curves is used. Then, this composite curve can be used when automatically determining the photographing start angle candidates.

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Abstract

Afin de réduire plus efficacement l'exposition inutile aux rayons X d'une région présentant une grande sensibilité aux rayons X, la présente invention concerne un dispositif de tomodensitométrie à rayons X comportant : une source de rayons X voisine de la périphérie d'un sujet installé sur un lit ; un scanner pour l'acquisition des données de projection, le scanner comprenant un détecteur de rayons X pour détecter la dose de rayons X émis par la source de rayons X et traversant le sujet ; une unité de calcul de reconstruction pour l'acquisition d'une image de reconstruction sur la base des données de projection ; une unité de réglage des conditions d'imagerie pour le réglage des conditions d'imagerie durant l'acquisition des données de projection ; une unité de génération d'une carte des valeurs des caractéristiques d'imagerie pour la génération d'une carte des valeurs des caractéristiques d'imagerie dans laquelle la valeur d'une caractéristique est cartographiée sous la forme d'une information indiquant une caractéristique de l'image de reconstruction générée lorsque les données de projection sont acquises conformément aux conditions d'imagerie ; et une unité de commande d'affichage pour amener la carte des valeurs des caractéristiques d'imagerie à s'afficher sur une unité d'affichage.
PCT/JP2017/000262 2016-01-29 2017-01-06 Dispositif et procédé de tomodensitométrie à rayons x pour le réglage des conditions d'imagerie et programme de réglage des conditions d'imagerie WO2017130657A1 (fr)

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