X-ray CT apparatus

Abstract

To provide an X-ray CT apparatus capable of suppressing deterioration in the quality of a tomographic image due to X-ray attenuation in a headrest and a top plate.SOLUTION: An X-ray CT apparatus includes: an X-ray source for irradiating a subject with an X-ray; an X-ray detector for detecting an X-ray transmitting the subject; a rotation plate for rotating the X-ray source and the X-ray detector around the subject; an image generation part for generating a tomographic image of the subject on the basis of a detection signal of the X-ray detector; and a control part for controlling each part. The control part changes an irradiation condition of the X-ray radiated from the X-ray source while the rotation plate rotates so as to increase a radiation quantity from the side where a headrest and a top plate are arranged in the range of a projection angle that the X-ray passes through the headrest and the top plate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an X-ray CT apparatus that captures tomographic images of a subject, and more particularly to a technique for reducing exposure of the subject to radiation. [Background technology]

[0002] X-ray CT systems generate cross-sectional images of a subject using projection data from multiple directions obtained by rotating an X-ray source that irradiates the subject with X-rays and an X-ray detector that detects the X-rays that have passed through the subject around the subject.The generated cross-sectional images depict the shape of the organs inside the subject and are used for diagnostic imaging.

[0003] The higher the dose of X-rays irradiated onto the subject, the better the quality of the tomographic image, but the subject's exposure dose also increases.Since increased exposure has adverse effects on the subject, it is important to limit the exposure dose (the amount of X-rays irradiated), especially to areas located on the surface of the body that are highly sensitive to radiation, such as the eyes and mammary glands.

[0004] Patent Document 1 discloses that when an X-ray source that rotates around a subject is positioned in front of the subject, which is the side of the subject that has high radiation sensitivity, the exposure dose is reduced compared to when the X-ray source is positioned behind the subject. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 9,867,587 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 does not sufficiently consider the attenuation of X-rays caused by the head support on which the subject's head rests and the tabletop on which the subject rests. X-ray attenuation caused by the head support and tabletop reduces the amount of X-rays detected by the X-ray detector, thereby degrading the image quality of the tomographic image. Furthermore, increasing the exposure dose to compensate for the attenuation of X-rays caused by the head support and tabletop increases the subject's exposure dose.

[0007] Therefore, an object of the present invention is to provide an X-ray CT apparatus that can suppress deterioration in image quality of tomographic images due to X-ray attenuation by the headrest or tabletop. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides an X-ray CT device comprising an X-ray source that irradiates an object with X-rays, an X-ray detector that detects X-rays that have passed through the object, a rotating plate that rotates the X-ray source and the X-ray detector around the object, an image generation unit that generates a tomographic image of the object based on the detection signal of the X-ray detector, and a control unit that controls each unit, wherein the control unit changes the irradiation conditions of the X-rays irradiated from the X-ray source while the rotating plate rotates so as to increase the irradiation dose from the side where the headrest or the tabletop is placed, within the range of projection angles at which the X-rays pass through the headrest or the tabletop. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an X-ray CT apparatus that can suppress deterioration in the quality of tomographic images due to X-ray attenuation by the headrest or tabletop. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of the overall configuration of an X-ray CT apparatus according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating modulation of an irradiation dose. [Figure 3] FIG. 1 is a diagram illustrating an example of a processing flow according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing an example of a screen used to select a headrest. [Figure 5] FIG. 10 is a diagram illustrating an example of changing an X-ray irradiation condition. [Figure 6] 10A and 10B are diagrams illustrating another example of changing the X-ray irradiation conditions. [Figure 7] FIG. 10 is a diagram showing an example of the overall configuration of an X-ray CT apparatus according to a second embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of a processing flow according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of a camera image. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of an X-ray CT (Computed Tomography) apparatus according to the present invention will be described below with reference to the accompanying drawings. The X-ray CT apparatus is an apparatus for generating tomographic images as medical images used for diagnosing a subject. In the following description and the accompanying drawings, components having the same functions are designated by the same reference numerals, and redundant description will be omitted. [Example]

[0012] The overall configuration of the X-ray CT apparatus of the first embodiment will be described with reference to Fig. 1. The X-ray CT apparatus includes a scan gantry unit 100 and an operation unit 120. The scan gantry unit 100 is installed in an imaging room surrounded by a shielding material that blocks X-rays, and the operation unit 120 is installed in an operation room outside the imaging room.

[0013] The scan gantry unit 100 includes an X-ray source 101, a rotating plate 102, a collimator 103, an X-ray detector 106, a data acquisition unit 107, a bed 105, a rotating plate control unit 108, a bed control unit 109, an X-ray control unit 110, and a high-voltage generation unit 111. The X-ray source 101 is a device that irradiates X-rays onto a subject 10 placed on the bed 105, and is, for example, an X-ray tube device. The collimator 103 is a device that limits the X-ray irradiation range. The rotating plate 102 has an opening 104 through which the subject 10 placed on the bed 105 enters, and is equipped with the X-ray source 101 and the X-ray detector 106, and rotates the X-ray source 101 and the X-ray detector 106 around the subject 10. The rotation axis of the rotating plate 102 is defined as the Z-axis, the horizontal plane as the ZX plane, and the vertical axis as the Y-axis.

[0014] The X-ray detector 106 is disposed opposite the X-ray source 101 and is equipped with a plurality of detection elements for detecting X-rays, thereby obtaining the spatial distribution of X-rays. The detection elements of the X-ray detector 106 are arranged two-dimensionally in the direction of rotation and the direction of the rotation axis of the rotating plate 102. The data collection unit 107 is a device that collects the spatial distribution of X-rays obtained by the X-ray detector 106 as digital data.

[0015] The rotating plate control unit 108 is a device that controls the rotation and tilt of the rotating plate 102. The bed control unit 109 is a device that controls the up / down, forward / backward, and left / right movement of the bed 105. The high voltage generation unit 111 is a power source that generates a tube voltage that is a voltage applied to the X-ray source 101 and a tube current that is a current supplied to the X-ray source 101. The X-ray control unit 110 is a device that controls the output of the high voltage generation unit 111. The rotating plate control unit 108, the bed control unit 109, and the X-ray control unit 110 are, for example, MPUs (Micro-Processing Units) or the like.

[0016] The operation unit 120 includes an input unit 121, an image generation unit 122, a display unit 125, a storage unit 123, and a system control unit 124. The input unit 121 is a device used to input examination data such as the name of the subject 10, the examination date and time, and imaging conditions, and is, for example, a keyboard, a pointing device, or a touch panel. The image generation unit 122 is a device that generates a tomographic image using digital data collected by the data collection unit 107, and is, for example, an MPU or a GPU (Graphics Processing Unit). The display unit 125 is a device that displays the tomographic image generated by the image generation unit 122, and is, for example, a liquid crystal display or a touch panel. The storage unit 123 is a device that stores the digital data collected by the data collection unit 107, the tomographic image generated by the image generation unit 122, a program executed by the system control unit 124, data used by the program, and is, for example, a hard disk drive (HDD) or a solid state drive (SSD). The system control unit 124 is a device that controls each unit such as the rotating plate control unit 108, the bed control unit 109, and the X-ray control unit 110, and is, for example, a CPU (Central Processing Unit).

[0017] Based on the imaging conditions set via the input unit 121, the high voltage generation unit 111 generates a tube voltage and a tube current, and X-rays according to the imaging conditions are irradiated from the X-ray source 101 to the subject 10. The X-ray detector 106 detects the X-rays irradiated from the X-ray source 101 and transmitted through the subject 10 with a large number of detection elements, and acquires the spatial distribution of the transmitted X-rays. The rotating plate 102 is controlled by a rotating plate control unit 108 and rotates based on the imaging conditions, particularly the rotation speed, etc., input from the input unit 121. The bed 105 is controlled by a bed control unit 109 and moves relative to the rotating plate 102.

[0018] The irradiation of X-rays by the X-ray source 101 and the detection of X-rays by the X-ray detector 106 are repeated as the rotating plate 102 rotates, thereby measuring projection data, which is an X-ray projection image of the subject 10, at various projection angles. The projection data is associated with a view, which indicates each projection angle, and a channel (ch) number and a column number, which are the numbers of the detecting elements of the X-ray detector 106. The measured projection data is transmitted to an image generation unit 122. The image generation unit 122 generates a tomographic image by performing back projection processing on the multiple projection data. The generated tomographic image is displayed on a display unit 125 as a medical image or stored in a memory unit 123.

[0019] In an X-ray CT apparatus, the higher the exposure dose, which is the amount of X-rays irradiated onto the subject 10, the better the image quality of the generated tomographic image, but the higher the amount of radiation exposure to the subject 10. Since an increase in the amount of radiation exposure has an adverse effect on the subject 10, it is necessary to suppress the exposure dose. In particular, to reduce the amount of radiation exposure to areas located on the body surface that are highly sensitive to radiation, such as the eyes and mammary glands, the exposure dose to the subject 10 may be modulated while the rotating plate 102 is rotating.

[0020] The exposure dose modulated during rotation of the rotating plate 102 will be described using Figure 2. The upper part of Figure 2 shows the X-ray source 101 rotating around the head of the subject 10. Note that the imaging region of the subject 10 is not limited to the head. When the rotation angle θ of the X-ray source 101 is in the range of θ1 to θ2, X-rays are irradiated onto the eyes, which are highly sensitive to radiation. Therefore, in order to reduce the amount of exposure to the eyes, the exposure dose is modulated according to the rotation angle θ. Note that the rotation angle θ corresponds to the projection angle. In Figure 2, the negative direction of the Y-axis is taken as θ=0.

[0021] The lower part of Figure 2 shows an example of an exposure dose modulation pattern using a solid line. The vertical axis represents the exposure dose, and the horizontal axis represents the rotation angle θ. For comparison, the exposure dose before modulation is shown using a dotted line. Note that because the X-ray source 101 rotates at a constant speed, the rotation angle θ is proportional to time. In the modulation pattern shown in Figure 2, a lower exposure dose D_L than D_0 before modulation is set when θ12<θ<θ21 so that the exposure dose when θ12<θ<θ21 is reduced. Note that to compensate for the reduced exposure dose when θ12<θ<θ21, a higher exposure dose D_H than D_0 before modulation is set when θ<θ11 and θ22<θ. Furthermore, the exposure dose changes from D_H to D_L when θ11<θ<θ12, and from D_L to D_H when θ21<θ<θ22.

[0022] Incidentally, the head rest 201 on which the head of the subject 10 is placed and the tabletop 202 on which the subject 10 is placed attenuate the X-rays irradiated to the subject 10. X-ray attenuation by the head rest 201 and the tabletop 202 reduces the amount of X-rays detected by the X-ray detector 106, increasing noise in the tomographic image and degrading image quality. Therefore, in the first embodiment, the irradiation dose is adjusted to compensate for the X-ray attenuation by the head rest 201 and the tabletop 202. Specifically, within the range of projection angles in which the X-rays pass through the head rest 201 and the tabletop 202, the irradiation dose from the side where the head rest 201 and the tabletop 202 are placed is increased to suppress degradation in image quality of the tomographic image.

[0023] An example of the processing flow of the first embodiment will be described step by step with reference to FIG.

[0024] (S301) The operator selects the type of head rest 201 to be placed under the head of the subject 10 via the operation unit 120. To select the type of head rest 201, for example, a head rest selection screen 400 shown in Fig. 4 is used. The head rest selection screen 400 is displayed on the display unit 125, and has a size setting section 401 and a material setting section 402.

[0025] The size setting unit 401 sets the size of the head rest 201. In the size setting unit 401 illustrated in Fig. 4, Middle is selected from three options of Large, Middle, and Small, and the size corresponding to Middle is set. The sizes corresponding to Large, Middle, and Small are stored in advance in the storage unit 123.

[0026] The material setting unit 402 sets the material of the head rest 201. In the material setting unit 402 shown in Fig. 4, "Soft" is selected from "Hard" and "Soft", and a material corresponding to "Soft" is set. The materials corresponding to "Hard" and "Soft" are stored in advance in the storage unit 123 together with the X-ray attenuation coefficient of each material.

[0027] (S302) The operator sets, via the operation unit 120, X-ray irradiation conditions, which are conditions for the amount of X-rays irradiated from the X-ray source 101 to the subject 10. The X-ray irradiation conditions may be, for example, a constant irradiation dose D_0 at all rotation angles θ as shown by the dotted line in the graph of FIG. 2, or may be set so that the irradiation dose to areas with high radiation sensitivity is lower than the irradiation dose to other areas as shown by the solid line in the graph. Alternatively, the irradiation dose may be set so that the transmission dose at each rotation angle θ falls within a predetermined range. In the following, a case where the X-ray irradiation conditions as shown by the solid line in the graph of FIG. 2 are set will be described.

[0028] (S303) The system control unit 124 calculates the range of the projection angle at which the X-rays pass through the head rest 201 and the tabletop 202. The projection angle at which the X-rays pass through the head rest 201 and the tabletop 202 is the projection angle at which the line connecting the X-ray focal point of the X-ray source 101 and the central channel of the X-ray detector 106 crosses at least one of the head rest 201 and the tabletop 202. The range of the projection angle is calculated based on the size of the head rest 201 and the size of the tabletop 202 set in S301.

[0029] 5, solid lines show an example of the range of projection angles in which X-rays pass through the headrest 201 and the tabletop 202. That is, the range of projection angles is θ≦θ_HR1, θ_HR2−π≦θ≦θ_HR1+π, and θ_HR2≦θ.

[0030] (S304) The system control unit 124 changes the X-ray irradiation conditions set in S302 so that the irradiation dose from the side where the headrest 201 or the tabletop 202 is placed within the range of the projection angle calculated in S303 is increased in accordance with the X-ray attenuation in the headrest 201 or the tabletop 202.

[0031] The lower part of Fig. 5 illustrates X-ray irradiation conditions in which the irradiation dose is increased according to the X-ray attenuation in the head rest 201, etc., within the range of projection angles θ≦θ_HR1 and θ_HR2≦θ, where the X-rays irradiated from the side where the head rest 201 and the tabletop 202 are placed pass through the head rest 201, etc. The X-ray attenuation in the head rest 201 and the tabletop 202 is calculated for each projection angle based on the length of the line connecting the X-ray focal point of the X-ray source 101 and the central channel of the X-ray detector 106 that crosses the head rest 201, etc., and the X-ray attenuation coefficient of the head rest 201, etc. Note that the changed X-ray irradiation conditions are not limited to those shown in Fig. 5.

[0032] Another example of the changed X-ray irradiation conditions will be described with reference to Fig. 6. If the irradiation dose is increased within the range of projection angles where the X-rays irradiated from the side where the headrest 201 etc. are placed pass through the headrest 201 etc., the exposure dose of the subject 10 increases. Therefore, the X-ray irradiation conditions are changed so that the irradiation dose from the opposite side is reduced by the amount of the increase in the irradiation dose from the side where the headrest 201 etc. is placed.

[0033] In the upper part of Fig. 6, the range of projection angles for increasing the exposure dose is shown by a solid line, and the range of projection angles for decreasing the exposure dose is shown by a dotted line. Furthermore, in the lower part of Fig. 6, examples of X-ray irradiation conditions are shown in which the exposure dose is increased in the projection angle ranges θ≦θ_HR1 and θ_HR2≦θ on the side where the head support 201 etc. are arranged, and the exposure dose is decreased in the projection angle range θ_HR2-π≦θ≦θ_HR1+π on the opposite side. Note that in the lower part of Fig. 6, the X-ray irradiation conditions shown by solid lines in the lower part of Fig. 5 are shown by dotted lines. Returning to the explanation of Fig. 3.

[0034] (S305) The system control unit 124 images the subject 10 using the X-ray irradiation conditions changed in S304, and generates a tomographic image of the subject 10 using the projection data obtained by the imaging. The generated tomographic image is displayed on the display unit 125 or stored in the storage unit 123 for use in image diagnosis of the subject 10.

[0035] 3, the X-ray irradiation conditions are changed to compensate for the X-ray attenuation at the headrest 201 and the tabletop 202, thereby suppressing degradation of the image quality of the tomographic image. Furthermore, as shown in FIG. 6, by compensating for the X-ray attenuation at the headrest 201, the radiation dose from the opposite side is reduced, thereby suppressing the radiation exposure dose of the subject 10. [Example]

[0036] In the first embodiment, it has been described that the X-ray irradiation conditions are changed according to the type of headrest 201 selected by the operator. In the second embodiment, it will be described that the X-ray irradiation conditions are changed according to the type of headrest 201 estimated from a camera image or the like.

[0037] The overall configuration of the X-ray CT apparatus of the second embodiment will be described with reference to Fig. 7. The difference from Fig. 1 is that a camera 700 is added, and therefore, description of the other components will be omitted.

[0038] The camera 700 is a device that photographs the subject 10 placed on the bed 105 from above together with the bed 105 and the headrest 201, and is installed on the ceiling of the imaging room. The camera image taken by the camera 700 is transmitted to the system control unit 124 and used to estimate the size and material of the headrest 201.

[0039] An example of the processing flow of the second embodiment will be described step by step with reference to FIG.

[0040] (S801) The system control unit 124 estimates the size and material of the headrest 201 based on the camera image captured by the camera 700. The camera image shown in FIG. 9 is used to estimate the size and material of the headrest 201, for example. Because the shape of the tabletop 202 is not uniform in the direction of the rotation axis of the rotating plate 102, the size of the tabletop 202, which varies depending on the imaging region, may be recognized by the camera 700. Even if an X-ray shield is present around the subject 10, the X-ray shield may be recognized by the camera 700 in the same way as the tabletop 202. Instead of a camera image, a positioning image, which is an X-ray fluoroscopic image acquired prior to CT imaging, may be used to estimate the size and material of the headrest 201. The estimation process for the headrest 201 may also use artificial intelligence (AI) generated in advance by learning from multiple camera images, positioning images, the size of the headrest 201, and the X-ray attenuation coefficient as training data. The use of AI can improve the accuracy of the estimation process.

[0041] (S802) As in S302, the operator sets, via the operation unit 120, the X-ray irradiation conditions, which are conditions for the amount of X-rays irradiated from the X-ray source 101 to the subject 10.

[0042] (S803) The system control unit 124 calculates the range of the projection angle through which the X-rays pass through the headrest 201 and the tabletop 202. The range of the projection angle is calculated based on the size of the headrest 201 and the size of the tabletop 202 estimated in S801.

[0043] (S804) The system control unit 124 changes the X-ray irradiation conditions set in S802 so that the irradiation dose from the side where the headrest 201 or the tabletop 202 is placed within the range of the projection angle calculated in S803 is increased in accordance with the X-ray attenuation in the headrest 201 or the tabletop 202.

[0044] (S805) The system control unit 124 images the subject 10 using the X-ray irradiation conditions changed in S804, and generates a tomographic image of the subject 10 using the projection data obtained by the imaging. The generated tomographic image is displayed on the display unit 125 or stored in the storage unit 123 for use in image diagnosis of the subject 10.

[0045] 8, the X-ray irradiation conditions are changed to compensate for the X-ray attenuation in the headrest 201 and the tabletop 202, thereby suppressing degradation in the image quality of the tomographic image. In addition, the size and material of the headrest 201 are estimated from camera images, etc., which reduces the burden on the operator.

[0046] The embodiments of the present invention have been described above. The present invention is not limited to the above embodiments, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, multiple components disclosed in the above embodiments may be combined as appropriate. Furthermore, some components may be deleted from all the components shown in the above embodiments. [Explanation of symbols]

[0047] 10: subject, 100: scan gantry, 101: X-ray source, 102: rotating plate, 103: collimator, 104: opening, 105: bed, 106: X-ray detector, 107: data acquisition unit, 108: rotating plate control unit, 109: bed control unit, 110: X-ray control unit, 111: high voltage generation unit, 120: operation unit, 121: input unit, 122: image generation unit, 123: memory unit, 124: system control unit, 125: display unit, 201: head support, 202: top plate, 400: head support selection screen, 401: size setting unit, 402: material setting unit, 700: camera.

Claims

1. An X-ray CT apparatus comprising: an X-ray source that irradiates a subject with X-rays; an X-ray detector that detects X-rays that have passed through the subject; a rotating plate that rotates the X-ray source and the X-ray detector around the subject; an image generating unit that generates a tomographic image of the subject based on a detection signal from the X-ray detector; and a control unit that controls each unit, The control unit changes the irradiation conditions of the X-rays emitted from the X-ray source while the rotating plate rotates so as to increase the irradiation dose from the side where the headrest or the tabletop is placed within the range of projection angles at which the X-rays pass through the headrest or the tabletop.

2. 2. The X-ray CT apparatus according to claim 1, The control unit changes the irradiation conditions so that the irradiation dose from the side where the head support or the tabletop is placed is increased by the amount that the irradiation dose from the side opposite the side where the head support or the tabletop is placed is reduced.

3. 2. The X-ray CT apparatus according to claim 1, The control unit calculates a range of projection angles at which the X-rays pass through the headrest and the tabletop based on the size of the headrest and the tabletop, An X-ray CT device characterized by calculating the amount of increase in the radiation dose from the side where the head rest or the tabletop is placed based on the length that the X-rays cross the head rest or the tabletop and the X-ray attenuation coefficient of the head rest or the tabletop.

4. 4. The X-ray CT apparatus according to claim 3, An X-ray CT device characterized in that the size of the headrest and the X-ray attenuation coefficient are set based on a selection made on a selection screen for selecting the type of headrest.

5. 4. The X-ray CT apparatus according to claim 3, The control unit estimates the size of the head support and the X-ray attenuation coefficient based on a camera image or a positioning image taken by a camera that photographs the subject from above.

6. 6. The X-ray CT apparatus according to claim 5, The control unit is an X-ray CT device characterized in that it uses AI generated in advance by learning a large number of camera images or positioning images and the size of the headrest and the X-ray attenuation coefficient as training data to estimate the size of the headrest and the X-ray attenuation coefficient.

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