X-ray CT device

Abstract

Provided is an X-ray CT device capable of suppressing a decrease in image quality of a tomographic image due to attenuation of X-rays on a headrest or a bed plate. This X-ray CT device is provided with: 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 rotation plate that rotates the X-ray source and the X-ray detector around the subject; an image generation unit that generates a tomographic image of the subject on the basis of a detection signal from the X-ray detector; and a control unit for controlling each part, the X-ray CT device being characterized in that the control unit sets the irradiation conditions of the X-rays irradiated from the X-ray source during the rotation of the rotating plate so that the irradiation conditions of the X-rays irradiated from the X-ray source are within the range of the projection angle of the X-rays passing through the headrest or the bed plate, and the irradiation conditions of the X-rays are within the range of the projection angle of the X-rays passing through the headrest or the bed plate. The mode of increasing the irradiation dose from the side where the headrest or the bed board is arranged is changed.

Description

Technical Field

[0001] The present invention relates to an X-ray CT apparatus for capturing tomographic images of an object, and more particularly to a technique for reducing exposure of the object. Background Art

[0002] X-ray CT systems generate tomographic images of a subject using projection data from multiple directions. These projection data are obtained by rotating an X-ray source, which irradiates the subject with X-rays, and an X-ray detector, which detects the X-rays that pass through the subject. The generated tomographic images depict the shapes of organs within the subject and are used for diagnostic imaging.

[0003] While increasing the X-ray dose irradiating the subject improves the quality of the tomographic image, this also increases the subject's exposure. Because this increased exposure can adversely affect the subject, it is important to limit the amount of X-rays irradiated, or the exposure dose, especially to areas of the body that are located on the surface and are highly sensitive to radiation, such as the eyes and breasts.

[0004] Patent Document 1 discloses an X-ray source that rotates around a subject to reduce the irradiation dose when the source is located in front of the subject, which is a site with high radiation sensitivity, compared to when the source is located behind the subject.

[0005] Patent Document 1: U.S. Patent No. 9,867,587

[0006] However, Patent Document 1 does not adequately consider X-ray attenuation caused by the headrest or bed resting the subject's head. This X-ray attenuation by the headrest or bed reduces the amount of X-rays detected by the X-ray detector, thereby degrading the quality of the tomographic image. Furthermore, increasing the irradiation dose to compensate for X-ray attenuation by the headrest or bed increases the subject's exposure. Summary of the Invention

[0007] Therefore, an object of the present invention is to provide an X-ray CT apparatus capable of suppressing degradation of tomographic image quality due to X-ray attenuation on a headrest or a bed board.

[0008] To achieve the above-mentioned object, the X-ray CT apparatus of the present invention comprises: an X-ray source for irradiating an object with X-rays; an X-ray detector for detecting X-rays that have passed through the object; a rotating plate for rotating the X-ray source and the X-ray detector around the object; an image generating unit for generating a tomographic image of the object based on detection signals from the X-ray detector; and a control unit for controlling each unit. The X-ray CT apparatus is characterized in that the control unit changes the irradiation conditions of the X-rays irradiated from the X-ray source during the rotation of the rotating plate in such a manner as to increase the irradiation dose from the side where the headrest or the bed board is arranged within the range of the projection angle of the X-rays passing through the headrest or the bed board.

[0009] Effects of the Invention

[0010] According to the present invention, it is possible to provide an X-ray CT apparatus capable of suppressing degradation in the quality of tomographic images due to X-ray attenuation on a headrest or a bed board. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram showing an example of the overall configuration of the X-ray CT apparatus according to the first embodiment.

[0012] Figure 2 This is a diagram explaining modulation of the irradiation dose.

[0013] Figure 3 This is a diagram showing an example of the processing flow of Example 1.

[0014] Figure 4 This is a diagram showing an example of a screen for selecting a headrest.

[0015] Figure 5 This is a diagram explaining an example of changing X-ray irradiation conditions.

[0016] Figure 6 This is a diagram illustrating another example of changing the X-ray irradiation conditions.

[0017] Figure 7 This is a diagram showing an example of the overall configuration of an X-ray CT apparatus according to the second embodiment.

[0018] Figure 8 This is a diagram showing an example of the processing flow of Example 2.

[0019] Figure 9 This is a diagram showing an example of a camera image.

[0020] Explanation of symbols

[0021] 10-Subject, 100-Scanning gantry unit, 101-X-ray source, 102-Rotating plate, 103-Collimator, 104-Aperture unit, 105-Couch, 106-X-ray detector, 107-Data collection unit, 108-Rotating plate control unit, 109-Couch control unit, 110-X-ray control unit, 111-High voltage generation unit, 120-Operation unit, 121-Input unit, 122-Image generation unit, 123-Storage unit, 124-System control unit, 125-Display unit, 201-Headrest, 202-Couch board, 400-Headrest selection screen, 401-Size setting unit, 402-Material setting unit, 700-Camera. DETAILED DESCRIPTION

[0022] The following describes an embodiment of an X-ray CT (Computed Tomography) apparatus according to the present invention, with reference to the accompanying drawings. An X-ray CT apparatus generates tomographic images as medical images used for diagnosis of subjects. In the following description and drawings, components having the same functions are denoted by the same reference numerals to omit duplicate descriptions.

[0023] [Example 1]

[0024] use Figure 1 The overall structure of the X-ray CT apparatus of Example 1 will be described. The X-ray CT apparatus includes a scanning gantry 100 and an operating unit 120. The scanning gantry 100 is installed in an imaging room surrounded by a shielding material that shields X-rays, and the operating unit 120 is installed in an operating room located outside the imaging room.

[0025] The scanner gantry 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 controller 108, a bed controller 109, an X-ray controller 110, and a high-voltage generator 111. The X-ray source 101 is a device, such as an X-ray tube, that irradiates a subject 10 placed on the bed 105 with X-rays. The collimator 103 is a device that limits the irradiation range of the X-rays. The rotating plate 102 has an opening 104 for the subject 10 placed on the bed 105 to enter. It carries the X-ray source 101 and the X-ray detector 106 and rotates them around the subject 10. The rotation axis of the rotating plate 102 is the Z-axis, the horizontal plane is the ZX plane, and the vertical axis is the Y-axis.

[0026] The X-ray detector 106 is positioned opposite the X-ray source 101 and is equipped with multiple detection elements that detect X-rays, thereby acquiring 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 along the rotation axis of the rotating plate 102. The data acquisition unit 107 collects the spatial distribution of X-rays acquired by the X-ray detector 106 as digital data.

[0027] The rotating plate controller 108 controls the rotation and tilt of the rotating plate 102. The bed controller 109 controls the vertical, horizontal, and forward, backward, and forward movements of the bed 105. The high-voltage generator 111 is a power supply that generates the tube voltage applied to the X-ray source 101 and the tube current supplied to the X-ray source 101. The X-ray controller 110 controls the output of the high-voltage generator 111. The rotating plate controller 108, bed controller 109, and X-ray controller 110 are, for example, microprocessors (MPUs).

[0028] The operation unit 120 includes an input unit 121, an image generator 122, a display unit 125, a storage unit 123, and a system control unit 124. The input unit 121 is a device for inputting 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 generator 122 is a device for generating tomographic images using the digital data collected by the data acquisition unit 107, and is, for example, an MPU or a GPU (Graphics Processing Unit). The display unit 125 is a device for displaying tomographic images generated by the image generator 122, and is, for example, a liquid crystal display or a touch panel. The storage unit 123 is a device for storing digital data collected by the data acquisition unit 107, tomographic images generated by the image generator 122, programs executed by the system control unit 124, and data used by the programs, and is, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The system control unit 124 is a device that controls the rotating plate control unit 108 , the bed control unit 109 , the X-ray control unit 110 and other units, and is, for example, a CPU (Central Processing Unit).

[0029] Based on the imaging conditions set via the input unit 121, the high voltage generator 111 generates a tube voltage and tube current, irradiating the subject 10 with X-rays corresponding to the imaging conditions from the X-ray source 101. The X-ray detector 106 uses multiple detection elements to detect X-rays emitted from the X-ray source 101 and transmitted through the subject 10, acquiring the spatial distribution of the transmitted X-rays. The rotating plate 102 is controlled by the rotating plate controller 108 and rotates based on the imaging conditions input via the input unit 121, particularly the rotation speed. The bed 105 is controlled by the bed controller 109 and moves relative to the rotating plate 102.

[0030] As the rotating plate 102 rotates, X-ray irradiation by the X-ray source 101 and X-ray detection by the X-ray detector 106 are repeated, and projection data, which are X-ray projection images of the subject 10, are measured at various projection angles. The projection data is associated with a view (View) representing each projection angle, and a channel (ch) number and a column number, which are the detection element numbers of the X-ray detector 106. The measured projection data is sent to the image generator 122. The image generator 122 generates a tomographic image by back-projecting the plurality of projection data. The generated tomographic image is displayed as a medical image on the display 125 or stored in the storage unit 123.

[0031] In an X-ray CT scanner, as the amount of X-rays irradiating the subject 10, or the irradiation dose, increases, the quality of the generated tomographic images improves. However, this also increases the exposure of the subject 10. Because this increased exposure adversely affects the subject 10, it is necessary to suppress the irradiation dose. In particular, to reduce exposure to areas of the body surface that are highly sensitive to radiation, such as the eyes and breasts, the irradiation dose to the subject 10 is sometimes modulated during the rotation of the rotating plate 102.

[0032] use Figure 2 , the irradiation dose modulated during the rotation of the rotating plate 102 is described. Figure 2 The upper part shows an X-ray source 101 that rotates around the head of the subject 10. In addition, the imaging part of the subject 10 is not limited to the head. When the rotation angle θ of the X-ray source 101 is within the range of θ1 to θ2, the X-rays irradiate the eyes, which are parts with high radiation sensitivity. Therefore, in order to reduce the exposure of the eyes, the irradiation dose is modulated according to the rotation angle 0. In addition, the rotation angle 0 is equivalent to the projection angle. And, in Figure 2 In the figure, the negative direction of the Y axis is set to θ=0.

[0033] exist Figure 2In the lower part of the figure, a solid line shows an example of a modulation pattern of the irradiation dose. The vertical axis is the irradiation dose, and the horizontal axis is the rotation angle θ. For comparison, the irradiation dose before modulation is shown by a dotted line. In addition, since the X-ray source 101 rotates at a predetermined speed, the rotation angle θ is proportional to time. Figure 2 In the modulation pattern illustrated in , when θ12 < θ < θ21, D_L is set to be less than the pre-modulation dose D_0, thereby reducing the exposure dose when θ1 < θ < θ2. Furthermore, to compensate for the reduction in the irradiation dose when θ12 < θ < θ21, D_H is set to be greater than the pre-modulation dose D_0 when θ < θ11 and θ22 < θ. Furthermore, when θ11 < θ < θ12, the irradiation dose is changed from D_H to D_L, and when θ21 < θ < θ22, it is changed from D_L to D_H.

[0034] The headrest 201 resting on the head of the subject 10 and the bed 202 resting on the subject 10 attenuate the X-rays that reach the subject 10. This X-ray attenuation caused by the headrest 201 and bed 202 reduces the amount of X-rays detected by the X-ray detector 106, thereby increasing noise in the tomographic images and degrading image quality. Therefore, in Example 1, the irradiation dose is adjusted to compensate for the X-ray attenuation caused by the headrest 201 and bed 202. Specifically, within the range of the projection angle of X-rays passing through the headrest 201 or bed 202, the irradiation dose from the side where the headrest 201 or bed 202 is located is increased, thereby suppressing degradation in tomographic image quality.

[0035] use Figure 3 , an example of the processing flow of Example 1 is described according to each step.

[0036] (S301)

[0037] The operator selects the type of the headrest 201 to be placed under the head of the subject 10 through the operation unit 120. In selecting the type of the headrest 201, for example, Figure 4 The headrest selection screen 400 is shown. The headrest selection screen 400 is displayed on the display unit 125 and includes a size setting unit 401 and a material setting unit 402.

[0038] In the size setting unit 401, the size of the headrest 201 is set. Figure 4 In the example of the size setting unit 401, Medium is selected from the three options of Large, Middle, and Small, and a size corresponding to Medium is set. The sizes corresponding to Large, Middle, and Small are stored in the storage unit 123 in advance.

[0039] In the material setting unit 402, the material of the headrest 201 is set. Figure 4In the material setting unit 402 shown in the example, 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.

[0040] (S302)

[0041] The operator sets the X-ray irradiation conditions, that is, the conditions for irradiating the subject 10 with the X-ray amount from the X-ray source 101, via the operation unit 120. Figure 2 As shown by the dotted line in the graph of , a predetermined irradiation dose D_0 is set at all rotation angles θ, or as shown by the solid line in the graph, the irradiation dose to the part with high radiation sensitivity is set to be lower than the irradiation dose to other parts. In addition, the irradiation dose can be set so that the irradiation dose at each rotation angle θ falls within a predetermined range. Figure 2 The case of X-ray irradiation conditions as shown by the solid line in the graph will be described.

[0042] (S303)

[0043] The system control unit 124 calculates the range of projection angles of X-rays passing through the headrest 201 or the bed board 202. The projection angle of X-rays passing through the headrest 201 or the bed board 202 refers to the projection angle when a line connecting the X-ray focal point of the X-ray source 101 and the central channel of the X-ray detector 106 intersects at least one of the headrest 201 and the bed board 202. This range of projection angles is calculated based on the size of the headrest 201 or the size of the bed board 202 set in S301.

[0044] exist Figure 5 In the upper portion of FIG, a solid line shows an example of the range of the projection angle of X-rays passing through the headrest 201 or the bed board 202. That is, 0≤θ_HR1, θ_HR2-π≤θ≤θ_HR1+π, and θ_HR2≤θ are the ranges of the projection angle.

[0045] (S304)

[0046] 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 bed 202 is arranged increases due to X-ray attenuation in the headrest 201 or the bed 202 within the projection angle range calculated in S303 .

[0047] exist Figure 5The lower part of the figure illustrates an X-ray irradiation condition in which the irradiation dose is increased due to the attenuation of X-rays in the headrest 201, etc., within the range of projection angles of θ≤θ_HR1 and θ_HR2≤θ, where X-rays irradiated from the side where the headrest 201 or the bed board 202 are arranged pass through the headrest 201, etc. The attenuation of X-rays in the headrest 201 or the bed board 202 is calculated for each projection angle based on the length of the line connecting the X-ray focus of the X-ray source 101 and the central channel of the X-ray detector 106 passing through the headrest 201, etc. and the X-ray attenuation coefficient of the headrest 201, etc. The changed X-ray irradiation condition is not limited to Figure 5 .

[0048] use Figure 6 Another example of the modified X-ray irradiation conditions will be described. If the irradiation dose of X-rays irradiated from the side where the headrest 201 is located is increased within the range of the projection angle through which the headrest 201 is located, the exposure of the subject 10 increases. Therefore, the X-ray irradiation conditions are modified so that the irradiation dose from the opposite side is reduced by an amount corresponding to the increase in the irradiation dose from the side where the headrest 201 is located.

[0049] exist Figure 6 In the upper part of the figure, the solid line indicates the range of projection angles for increasing the irradiation dose, and the dotted line indicates the range of projection angles for decreasing the irradiation dose. Figure 6 The lower part of the diagram illustrates an X-ray irradiation condition in which the irradiation dose is increased in the projection angle range θ≤θ_HR1 and θ_HR2≤θ on the side where the headrest 201 and the like are arranged, and the irradiation dose is reduced in the projection angle range θ_HR2-π≤θ≤θ_HR1+π on the opposite side. Figure 6 The lower part is indicated by a dotted line. Figure 5 The solid line at the bottom shows the X-ray irradiation conditions. Figure 3 Description.

[0050] (S305)

[0051] The system control unit 124 images the subject 10 using the X-ray irradiation conditions changed in S304, and uses the projection data obtained by the imaging to generate a tomographic image of the subject 10. 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.

[0052] According to use Figure 3 The processing flow described above changes the X-ray irradiation conditions in a manner that compensates for the X-ray attenuation on the headrest 201 or the bed plate 202, thereby suppressing the degradation of the tomographic image quality. Figure 6As shown, by reducing the irradiation dose from the opposite side according to the amount of X-ray attenuation by the compensation headrest 201 , the exposure dose of the subject 10 can be suppressed.

[0053] [Example 2]

[0054] In the first embodiment, the X-ray irradiation conditions are changed according to the type of the headrest 201 selected by the operator. In the second embodiment, the X-ray irradiation conditions are changed according to the type of the headrest 201 estimated from a camera image or the like.

[0055] use Figure 7 , the overall structure of the X-ray CT apparatus of Example 2 is described. Figure 1 The difference is that the camera 700 is added, so the description of other structures is omitted.

[0056] The camera 700 is a device installed on the ceiling of the imaging room that images the subject 10 placed on the bed 105 together with the bed 105 or the headrest 201 from above. The camera image captured by the camera 700 is sent to the system control unit 124 and used to estimate the size and material of the headrest 201.

[0057] use Figure 8 , an example of the processing flow of Example 2 is explained according to each step.

[0058] (S801)

[0059] The system control unit 124 estimates the size and material of the headrest 201 based on the camera image captured by the camera 700. In estimating the size and material of the headrest 201, for example, Figure 9 The camera image shown. In addition, the shape of the bed plate 202 is different in the direction of the rotation axis of the rotating plate 102, so the size of the bed plate 202 that changes according to the imaging part can be recognized by the camera 700. Moreover, in the case where there is an X-ray shielding object around the subject 10, the X-ray shielding object can also be recognized by the camera 700 in the same way as the bed plate 202. In addition, instead of the camera image, an X-ray fluoroscopic image, i.e., a positioning image, acquired before CT imaging can be used to estimate the size and material of the headrest 201. In addition, in the estimation process of the headrest 201, AI (Artificial Intelligence) that is pre-generated by learning multiple camera images or positioning images and the size and X-ray attenuation coefficient of the headrest 201 as training data can also be used. By using AI, the accuracy of the estimation process can be improved.

[0060] (S802)

[0061] As in S302 , the operator sets the X-ray irradiation conditions, which are the conditions for the amount of X-rays irradiated from the X-ray source 101 to the subject 10 , via the operation unit 120 .

[0062] (S803)

[0063] The system control unit 124 calculates the range of projection angles of X-rays passing through the headrest 201 or the bed board 202. The range of projection angles is calculated based on the size of the headrest 201 or the size of the bed board 202 estimated in S801.

[0064] (S804)

[0065] 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 bed 202 is arranged increases due to X-ray attenuation in the headrest 201 or the bed 202 within the projection angle range calculated in S803 .

[0066] (S805)

[0067] The system control unit 124 images the subject 10 using the X-ray irradiation conditions changed in S804, and uses the projection data obtained by the imaging to generate a tomographic image of the subject 10. 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.

[0068] According to use Figure 8 The processing flow described above changes X-ray irradiation conditions to compensate for X-ray attenuation on the headrest 201 or bed 202, thereby minimizing degradation in tomographic image quality. Furthermore, since the size and material of the headrest 201 are estimated based on camera images, the burden on the operator is reduced.

[0069] The above describes the embodiments of the present invention. The present invention is not limited to the above embodiments, and the components can be modified and specified within the scope of the present invention. In addition, multiple components disclosed in the above embodiments can be appropriately combined. Moreover, some components can be deleted from all the components shown in the above embodiments.

Claims

1. An X-ray CT apparatus comprising: an X-ray source for irradiating an object with X-rays; an X-ray detector for detecting X-rays that have passed through the object; a rotating plate for rotating the X-ray source and the X-ray detector around the object; an image generator for generating a tomographic image of the object based on detection signals from the X-ray detector; and a control unit for controlling each unit. The X-ray CT apparatus is characterized in that: The control unit changes the irradiation conditions of the X-rays irradiated from the X-ray source during the rotation of the rotating plate so as to increase the irradiation dose from the side where the headrest or the bed board is arranged within a range of a projection angle of the X-rays passing through the headrest or the bed board.

2. The X-ray CT apparatus according to claim 1, wherein: The control unit changes the irradiation condition so that the irradiation dose from the side opposite to the side where the headrest or the bed board is arranged is reduced according to the amount of the irradiation dose from the side where the headrest or the bed board is arranged.

3. The X-ray CT apparatus according to claim 1, wherein: The control unit performs the following calculations: Calculating a range of projection angles of the X-ray passing through the headrest or the bed board according to the size of the headrest or the bed board; and The amount of increase in irradiation dose from the side where the headrest or the bed board is arranged is calculated based on the length of the X-rays that pass through the headrest or the bed board and the X-ray attenuation coefficient of the headrest or the bed board.

4. The X-ray CT apparatus according to claim 3, wherein: The size and X-ray attenuation coefficient of the headrest are set according to selections made on a selection screen for selecting the type of the headrest.

5. The X-ray CT apparatus according to claim 3, wherein: The control unit estimates the size and the X-ray attenuation coefficient of the headrest based on a camera image or a locator image captured by a camera that captures the subject from above.

6. The X-ray CT apparatus according to claim 5, characterized in that: The control unit uses AI generated in advance by learning a plurality of camera images or positioning images, 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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