JP5442363B2 - X-ray CT system - Google Patents

X-ray CT system Download PDF

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JP5442363B2
JP5442363B2 JP2009197498A JP2009197498A JP5442363B2 JP 5442363 B2 JP5442363 B2 JP 5442363B2 JP 2009197498 A JP2009197498 A JP 2009197498A JP 2009197498 A JP2009197498 A JP 2009197498A JP 5442363 B2 JP5442363 B2 JP 5442363B2
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range
image
subject
projection angle
ray ct
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JP2011045588A (en
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靖浩 今井
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ジーイー・メディカル・システムズ・グローバル・テクノロジー・カンパニー・エルエルシー
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The present invention relates to an X-ray CT (Computed) that modulates the X-ray irradiation output to reduce the X-ray exposure dose of a part of the subject when the subject is subjected to an X-ray CT scan.
Tomography).

  When an X-ray CT scan is performed on the subject, an X-ray irradiation output is set to a predetermined projection angle range (a range in the rotation direction of the scan) in a predetermined range in the body axis direction from a predetermined X-ray irradiation output that is normally set. An X-ray CT apparatus has been proposed that reduces the X-ray exposure dose of a part of the subject, for example, a highly radiation-sensitive part (see, for example, Patent Document 1, Abstract, etc.).

JP 2004-321587 A

  However, no proposal has been made so far for means capable of intuitively grasping the predetermined range in the body axis direction and the predetermined projection angle range in the positional relationship with the subject. Therefore, it is not possible to easily grasp a site where the X-ray exposure dose is reduced by suppressing the X-ray irradiation output, and it is difficult to accurately reduce the X-ray exposure dose for the target site.

  In view of the above circumstances, the present invention performs an X-ray CT scan in which the X-ray irradiation output is smaller than the predetermined X-ray irradiation output in a predetermined projection angle range in a predetermined range in the body axis direction of the subject. An object of the present invention is to provide an X-ray CT apparatus that can intuitively grasp the range in which the X-ray irradiation output is reduced in the positional relationship with the subject.

  In a first aspect, the present invention provides an X-ray irradiation output smaller than a predetermined X-ray irradiation output in a predetermined projection angle range in a predetermined range in the body axis direction when performing X-ray CT scanning of a subject. An X-ray CT apparatus that geometrically shows a front image of the subject, a lateral range of the subject corresponding to the predetermined projection angle range, and a predetermined range in the body axis direction An X-ray CT apparatus is provided that includes display means for displaying them in association with each other.

  Here, the “projection angle” is a rotation angle position of the X-ray focal point of the X-ray tube, and is also referred to as a view angle or a gantry angle.

  Further, the “predetermined X-ray irradiation output” is an X-ray irradiation output based on a scanning condition that does not include a condition that intentionally reduces the X-ray exposure dose of a part of the subject. An X-ray irradiation output determined by a tube voltage and a tube current of the X-ray tube set normally, an X-ray irradiation output at each projection angle at each position in the body axis direction determined by an automatic exposure mechanism, and the like. Note that a part of the subject is, for example, a highly radiation-sensitive part, and specifically, an eyeball, a thyroid gland, a mammary gland, and the like can be considered.

  Further, the “front image of the subject” is an image obtained by photographing the subject in the front-rear direction of the subject, that is, the abdominal back direction (AP direction) or the dorsal abdominal direction (PA direction).

  Further, the “left-right direction” is a direction perpendicular to the body axis direction and the abdominal-dorsal direction or the dorso-abdominal direction of the subject.

  An “image showing the range geometrically” is an image expressed so that the range can be visually understood. For example, an auxiliary line, an arrow provided at the boundary of the range, and the range are covered. The shading provided can be considered.

  Note that, under conditions where the tube voltage of the X-ray tube is constant, the X-ray irradiation output can be increased or decreased by increasing or decreasing the tube current of the X-ray tube.

  In a second aspect, the present invention provides the left-right direction of the arc corresponding to the predetermined projection angle range on a circumference in which the range in the left-right direction corresponding to the predetermined projection angle range represents the contour of the imaging field of view. An X-ray CT apparatus according to the first aspect of the present invention is provided.

  Here, the “imaging field of view” is an image reconfigurable region determined based on the geometric structure of a data acquisition system including an X-ray source and an X-ray detector, and is a so-called SFOV (Scan Field Of View).

  In a third aspect, the present invention provides that the display means has substantially the same shape as a rectangular region in which the left-right range corresponding to the predetermined projection angle range and the predetermined range in the body axis direction overlap. An X-ray CT apparatus according to the first aspect or the second aspect, which displays an image representing a figure superimposed on a front image of the subject.

  Here, “substantially the same shape as the rectangular region” means that the shape includes a shape similar to the extent that the rectangular region can be specified.

  In a fourth aspect, the present invention receives a change in the position or shape of the displayed image by an operation from an operator, and based on the change in the image, the predetermined range in the body axis direction and the predetermined projection There is provided an X-ray CT apparatus according to any one of the first to third aspects, further comprising changing means for changing at least one of the angle ranges.

  In a fifth aspect, the present invention provides that the display unit further includes a side image of the subject, a range in the front-rear direction of the subject corresponding to the predetermined projection angle range, and a predetermined amount in the body axis direction. Provided is an X-ray CT apparatus according to any one of the first to fourth aspects, in which an image showing a range is geometrically associated and displayed.

  Here, the “side view image of the subject” is an image obtained by photographing the subject in the left-right direction of the subject, and is a so-called lateral image.

  In a sixth aspect, the present invention provides the front-rear direction of an arc corresponding to the predetermined projection angle range on a circumference in which the front-rear direction range corresponding to the predetermined projection angle range represents a contour of the imaging field of view. An X-ray CT apparatus according to the fifth aspect of the present invention is provided.

  In a seventh aspect, the present invention provides the display device having substantially the same shape as a rectangular region in which the front-rear direction range corresponding to the predetermined projection angle range and the predetermined range in the body axis direction overlap. The X-ray CT apparatus according to the fifth aspect or the sixth aspect, which displays an image representing a figure superimposed on a side image of the subject.

  In an eighth aspect, the present invention provides an estimation for estimating a transition angle interval from when the X-ray irradiation output starts to change toward a target output within the predetermined projection angle range until the target output is reached. And an X-ray CT apparatus according to the first to seventh aspects, wherein the display means further displays information indicating the estimated transition angle section.

  In a ninth aspect, the present invention provides a front image of the subject, an image obtained by scout scan of the subject with X-rays, and an X-ray CT scan of the subject. An X-ray CT apparatus according to any one of the first to sixth aspects is provided, which is an acquired image or an image obtained by imaging the subject with an optical imaging apparatus.

  Here, the “scout scan” is a scan performed before the main scan in order to acquire an image used for the scan plan. As the “scout scan”, for example, an X-ray beam (beam) having a lower dose than that of the main scan while moving the subject or the scanning gantry in the body axis direction while keeping the rotation angle position of the X-ray tube, that is, the projection angle constant. A scan in which projection data is collected by irradiating the subject with the object can be considered. Further, for example, a helical scan using an X-ray beam having a dose much lower than that of the main scan can be considered.

  As the “image obtained by X-ray CT scan of a subject”, for example, an image obtained by a main scan performed in the past examination or immediately before the current scan can be considered.

  In addition, as an “image obtained by photographing with an optical photographing apparatus”, for example, an image obtained by a digital camera (digital camera) that receives reflected light from a subject and generates an image is considered. be able to.

  According to the X-ray CT apparatus of the present invention, an X-ray CT scan is performed to make the X-ray irradiation output smaller than the predetermined X-ray irradiation output in a predetermined projection angle range in a predetermined range in the body axis direction of the subject. In this case, the front image of the subject is displayed in association with the image in the left-right direction of the subject corresponding to the predetermined projection angle range and the image geometrically indicating the predetermined range in the body axis direction. The range in which the X-ray irradiation output is reduced can be intuitively grasped in the positional relationship with the subject.

1 is a diagram schematically showing a configuration of an X-ray CT apparatus according to a first embodiment. It is a flowchart (flow chart) which shows the flow of the process which concerns on the X-ray CT apparatus of 1st embodiment. It is a figure for demonstrating a scout scan. It is a figure which shows an example of the scan plan screen displayed on a monitor (monitor). It is a figure which shows the example of a display of a tube current reduction setting window (window). It is a figure which shows the relationship between the 1st and 2nd figure, tube current reduction scanning range, and tube current reduction projection angle range by 1st embodiment. In 1st embodiment, it is a figure which shows the 1st and 2nd figure in the case where a tube current reduction projection angle range is set as a range of 3π / 2 to π / 2. It is a figure which shows an example of the relationship between the projection angle and tube current output rate in a tube current reduction scanning range. It is a figure which shows the relationship between the projection angle and tube current output rate in a tube current reduction scanning range when the rotation speed of the rotation part of a scanning gantry is quick. It is a figure which shows the relationship between the 1st and 2nd figure, tube current reduction scanning range, and tube current reduction projection angle range by 2nd embodiment. In 2nd embodiment, it is a figure which shows the 1st figure and 2nd figure in the case where a tube current reduction projection angle range is set as a range of projection angle 3π / 2 to π / 2. It is a figure which shows the other example of a display of a tube current reduction setting window.

  Hereinafter, embodiments of the present invention will be described. Note that the present invention is not limited thereby.

(First embodiment)
FIG. 1 is a diagram schematically showing the configuration of the X-ray CT apparatus according to the first embodiment.

  The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 that receives input from an operator, a central processing unit 3 that performs control of each unit for imaging a subject, data processing for generating an image, and the like, and a scanning gantry 20. A data collection buffer (buffer) 5 for collecting acquired data, a monitor 6 for displaying images, and a storage device 7 for storing programs, data, and the like are provided.

  The imaging table 10 includes a cradle 12 on which the subject 40 is placed and put into and out of the opening B of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10. Here, the body axis direction of the subject 40, that is, the horizontal linear movement direction of the cradle 12 is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

  The scanning gantry 20 includes a rotating unit 15 and a main body 20a that rotatably supports the rotating unit 15. The rotating unit 15 includes an X-ray tube 21, an X-ray controller 22 that controls the X-ray tube 21, and a collimator (collimate) that shapes and collimates the X-ray beam 81 generated from the X-ray tube 21. collimator) 23, an X-ray detector 24 for detecting the X-ray beam 81 transmitted through the subject 40, and a DAS (Data Acquisition System) for converting the output of the X-ray detector 24 into projection data and collecting the data (data acquisition system) 25) and a rotating unit controller 26 that controls the X-ray controller 22, the collimator 23, and the DAS 25. The main body 20 a includes a control controller 29 that communicates control signals and the like with the operation console 1 and the imaging table 10. The rotating part 15 and the main body part 20 a are electrically connected via a slip ring 30.

  The central processing unit 3 and the monitor 6 are examples of display means in the present invention. The central processing unit 3 is an example of a changing unit and an estimating unit in the present invention.

  From this, the flow of the process which concerns on the X-ray CT apparatus of 1st embodiment is demonstrated.

  FIG. 2 is a flowchart showing a flow of processing according to the X-ray CT apparatus of the first embodiment.

  In step S1, a scout image of the subject 40 is acquired by performing a scout scan of the subject 40. The scout scan is, for example, by irradiating the subject 40 with an X-ray beam from the X-ray tube 21 while moving the cradle 12 on which the subject 40 is placed horizontally in the z direction while the rotating unit 15 is stationary. 40 projection data are obtained, and a scout image, which is a perspective image of the subject 40, is obtained based on the projection data. Thereby, a scout image obtained by projecting the subject 40 in one direction such as the x direction and the y direction is obtained. A three-dimensional image that is CT volume data (volume data) of the subject 40 obtained by performing a helical scan with an ultra-low dose X-ray beam, or an image obtained by projecting this three-dimensional image in the x direction or the y direction. May be acquired as a scout image. In place of such a scout image, the subject 40 is imaged by an optical imaging device without using a three-dimensional image obtained by scanning the subject 40 during a past examination, a projection image thereof, or X-rays. You may acquire the image obtained by doing. That is, the image to be prepared in this step may be any image as long as it can be used for the scan plan in the next step.

  Here, as shown in FIG. 3, the X-ray focal point f of the X-ray tube 21 is positioned at a projection angle θ = 0 (0 °), which is directly above the subject 40, and the first X-ray beam 81 is irradiated. A scout scan and a second scout scan that irradiates the X-ray beam 81 with the X-ray focal point f of the X-ray tube 21 positioned at a projection angle θ = π / 2 (90 °) that is directly beside the subject 40 are performed. . As a result, a first scout image that is a front image of the subject 40 and a second scout image that is a side image of the subject 40 are acquired.

  In step S2, a scan plan including tube current reduction is set. The scan plan is performed on a scan plan screen displayed on the monitor 6.

  FIG. 4 is a diagram illustrating an example of a scan plan screen displayed on the monitor. In the scan plan screen 51, a “start position” column 61, an “end position” column 62, a “slice thickness” column 63, a “tube voltage” column 64, and a “tube current” column 65 are displayed. . The “start position” field 61 and the “end position” field 62 are fields for inputting the start position and the end position of the scan. The “slice thickness” column 63 is a column for inputting a slice thickness in scanning. The “tube voltage” column 64 and the “tube current” column 65 are columns for inputting a tube voltage and a tube current applied to the X-ray tube 21 at the time of scanning. Further, the scan plan screen has an image area 66, and one of the scout images acquired in step S1 is displayed here. In this example, it is assumed that the second scout image 42 that is a side image of the subject 40 is displayed. The operator proceeds with the scan plan while viewing the second scout image 42 displayed in the image area 66.

  When values are input to the “start position” column 61 and the “end position” column 62, the body axis direction of the subject 40, that is, z, is displayed on the second scout image 42 in the image area 66 based on the input values. A line za indicating the scan start position in the direction and a line zb indicating the scan end position are displayed. Further, when a value is input to the “slice thickness” field 63, based on this input value, the image position that is the center position of each slice of the tomographic image to be imaged is calculated, and within the line za-zb interval. A line zi indicating these image positions is displayed.

  Further, a tube current reduction setting window is opened and displayed on the scan plan screen 51 in accordance with a predetermined operation from the operator. The operator performs tube current reduction setting processing in this tube current reduction setting window.

  Here, the tube current reduction setting process will be described. In the X-ray CT apparatus 100 according to this example, when performing an X-ray CT scan, the tube current of the X-ray tube is smaller than a predetermined tube current that is normally set in a predetermined projection angle range in a predetermined range in the z direction. Thus, the X-ray exposure dose of a part of the subject 40, such as an eyeball, a thyroid gland, a mammary gland, or the like, which has a high radiation sensitivity is reduced. In the tube current reduction setting process, a predetermined range in the z direction (hereinafter referred to as a tube current reduction scan range) and a predetermined projection angle range (hereinafter referred to as a tube current reduction projection angle range) are set. It is processing. The predetermined tube current is a tube current according to a predetermined scan condition set in advance, and is a tube current input in the “tube current” column 65 in this example. Incidentally, when the tube current is modulated in the z direction and further in the projection angle θ direction by the automatic exposure mechanism, the tube current at the time of modulation at each projection angle in each z direction position becomes the predetermined tube current. In this example, the tube current reduction projection angle range is a range on the front side of the subject 40, that is, a range in which the projection angle θ is 3π / 2 to π / 2 and is symmetric in the x direction. It is not limited to.

  Hereinafter, setting and display in the tube current reduction setting window will be described.

  FIG. 5 is a view showing a display example of the tube current reduction setting window. In this tube current reduction setting window 68, the first scout image 41 and the second scout image 42 are displayed side by side. On these scout images, a line za indicating the scan start position, a line zb indicating the scan end position, and a line zi indicating the image position are displayed in an overlapping manner.

  Appropriate ranges are initially set for the tube current reduction scan range Rz and the tube current reduction projection angle range Rθ, respectively.

  On the first scout image 41, the ranges Rx and Rz, which are geometrically images of the x-direction range Rx and the tube current reduction scan range Rz corresponding to the tube current reduction projection angle range Rθ, are shown in shape. The first graphic F1 is displayed so as to be associated with the first scout image 41 in a positional manner. In addition, on the second scout image 42, the ranges Ry and Rz, which are images geometrically showing the range Ry in the y direction and the tube current reduction scan range Rz corresponding to the tube current reduction projection angle range Rθ, are formed. A second figure F2 indicated by is superimposed on the second scout image 42 and displayed in an overlapping manner.

  Although details will be described later, the operator changes the position or shape of the displayed first graphic F1 or second graphic F2 to interactive using the mouse or the like constituting the input device 2. can do. When the position or shape of the first figure F1 or the second figure F2 is changed, the tube current reduction scan range Rz and the tube current reduction projection angle range Rθ are changed to the first figure F1 or the second figure after the change. The range is changed to the range indicated by the position or shape of the figure F2.

  A relationship between the shapes of the first graphic F1 and the second graphic F2 and the tube current reduction scan range Rz and the tube current reduction projection angle range Rθ will be described.

  FIG. 6 is a diagram showing the relationship between the shapes of the first graphic and the second graphic and the tube current reduction scan range and the tube current reduction projection angle range. In FIG. 6, IC is an iso-center that is the rotation center of the rotating unit 15, and the coordinate values of the IC in the x and y directions are set to zero.

  Here, the tube current reduction scan range Rz is a range of coordinates z1 to z2 (za ≦ z1 ≦ zb, za ≦ z2 ≦ zb, z1 <z2) in the z direction, and the tube current reduction projection angle range Rθ is the projection angle 2π. It is assumed that the range is −θ1 to θ1 (0 <θ1 ≦ π / 2).

  The first graphic F1 is displayed as a graphic having substantially the same shape as a rectangular area where the x-direction (left-right direction) range Rx corresponding to the tube current reduction projection angle range Rθ and the tube current reduction scan range Rz overlap. . That is, the range in the z direction (vertical direction in FIG. 6) of the first graphic F1 represents the tube current reduction scan range Rz, and the range in the x direction (horizontal direction in FIG. 6) of the first graphic F1 is the tube current reduction. A range Rx in the x direction corresponding to the projection angle range Rθ is represented.

  The second graphic F2 is displayed as a graphic having substantially the same shape as the rectangular area where the range Ry in the y direction (front-rear direction) corresponding to the tube current reduction projection angle range Rθ and the tube current reduction scan range Rz overlap. Is done. That is, the range in the z direction (horizontal direction in FIG. 6) of the second graphic F2 represents the tube current reduction scan range Rz, and the range in the y direction (vertical direction in FIG. 6) of the second graphic F2 is the tube current reduction. A y-direction range Ry corresponding to the projection angle range Rθ is represented.

  In this example, as shown in FIG. 6, the x-direction range Rx corresponding to the tube current reduction projection angle range Rθ (projection angles 2π−θ1 to θ1, 0 <θ1 ≦ π / 2) is centered on the isocenter IC. The range of the arc VB in the x direction (coordinates x1 to -x1) corresponding to the tube current reduction projection angle range Rθ on the circumference of the radius r representing the contour of the imaging field of view SFOV. Further, the y-direction range Ry corresponding to the tube current reduction projection angle range Rθ is the y-direction range (coordinates y1 to r) of the arc VB as shown in FIG.

  The first figure F1 and the second figure F2 are close to a virtual representation of an X-ray protection shield formed of bismuth or the like, and are familiar to the operator's senses. easy.

  The operator translates the displayed first figure F1 in the z direction by using a drag and drop function by the pointer 67 or the like, and the upper and lower sides of the first figure F1 are The range (width) of the figure in the z direction can be changed by moving each independently in the z direction. Further, the left end side and the right end side of the first figure F1 can be moved in the x direction while maintaining the left-right symmetry, and the range (width) of the figure in the x direction can be changed. Similarly, the second figure F2 can be translated in the z direction, or the lower end side of the second figure F2 can be moved in the y direction to change the range (width) of the figure in the y direction. Further, the left end side and the right end side of the second figure F2 can be independently moved in the z direction to change the range (width) of the figure in the z direction.

  When the range of the first figure F1 in the x direction or the range of the second figure F2 in the y direction is changed, the range of the arc VB corresponding to these ranges is obtained, and the obtained arc VB is further obtained. A corresponding angular range in the rotational direction is determined. Then, the obtained angle range is set as the tube current reduction projection angle range Rθ.

  Similarly, when the range in the z direction of the first graphic F1 or the range in the z direction of the second graphic F2 is changed, the changed range in the z direction is set as the tube current reduction scan range Rz.

  Thereby, the tube current reduction scan range Rz and the tube current reduction projection angle range Rθ can be set to desired ranges, respectively. When the position or shape of one of the first figure F1 and the second figure F2 is changed to change the tube current reduction scan range Rz or the tube current reduction projection angle range Rθ, the position of the other figure The display is changed in conjunction with the shape.

  FIG. 7 is a diagram showing a first graphic and a second graphic when the tube current reduction projection angle range is set as a projection angle range of 3π / 2 to π / 2.

  The above is the description of the setting / display in the tube current reduction setting window 68. When it is desired to perform tube current reduction setting for a plurality of ranges in the set scan range, the first and second scout images are displayed. The first and second graphics F1 and F2 may be displayed on 41 and 42 by the number of the ranges, and the positions and shapes of these graphics may be set while changing.

  In step S3, scanning is performed according to scanning conditions including tube current reduction set by the scanning plan in step S2, and projection data of the subject 40 is collected. The scan is, for example, a full scan or a helical scan of an axial scan from the scan start position za to the scan end position zb, and collects projection data of about 1000 views per rotation. To do.

  FIG. 8 is a diagram showing an example of the relationship between the projection angle θ and the tube current output rate k in the tube current reduction scan range Rz. The tube current output rate k is the tube current when the tube current reduction setting is turned on when the tube current is normally set, that is, the tube current when the tube current reduction setting is turned off under the set scan conditions is 1. Is a value indicating the ratio of. In the tube current reduction projection angle range Rθ, that is, in the range where the projection angle θ is 2π−θ1 to θ1, the tube current output rate k is k1 (for example, 0.5) smaller than 1, and in other projection angle ranges, The tube current output rate k is 1. The tube current output rate k1 may be constant as shown in the figure, or may be changed according to the projection angle θ.

  In step S4, an image is reconstructed based on the collected projection data, and a tomographic image of the subject 40 is obtained.

  In step S5, the reconstructed tomographic image is displayed on the monitor 6.

  According to the first embodiment, the tube current reduction setting window 68 allows the operator to set the tube current reduction projection angle range Rθ and the tube current reduction scan range Rz in the positional relationship with the subject 40. Setting and checking can be performed while intuitively grasping. As a result, it is possible to easily grasp the portion where the X-ray exposure dose is reduced by suppressing the X-ray irradiation output, and it is possible to accurately reduce the X-ray exposure dose for the target portion.

(Second embodiment)
FIG. 9 is a diagram showing the relationship between the projection angle and the tube current output rate in the tube current reduction scan range when the rotation speed of the rotating part of the scanning gantry is fast. In FIG. 9, a solid line K represents an ideal tube current output rate, and a broken line K ′ represents an actual tube current output rate.

  There is a limit to the response speed in controlling the tube current of the X-ray tube 21. For this reason, when the rotation speed of the rotation unit 15 of the scanning gantry 20 increases, the angle section (hereinafter referred to as the rotation unit 15) rotates from when the tube current starts to change toward the target tube current until it reaches the target tube current. Sθ) (referred to as transition angle section) becomes large and cannot be ignored. Therefore, as shown in FIG. 9, the timing for changing the tube current is adjusted so that the transition angle section Sθ does not deviate from the set tube current reduction projection angle range Rθ. In such a case, in the transition angle section Sθ, that is, in the section where the actual tube current output rate k is not ideal in the tube current reduction projection angle range Rθ, the tube current is not sufficiently reduced, and the X-ray exposure dose is reduced. Reduction cannot be performed sufficiently. Therefore, the operator needs to grasp this point and set the tube current reduction projection angle range Rθ.

  Therefore, in the second embodiment, the transition angle section Sθ is estimated on the basis of the rotational speed of the rotating unit 15 in consideration of the response speed in the control of the tube current of the X-ray tube 21, and information indicating the transition angle section Sθ is obtained. Is attached to the first and second graphics F1, F2.

  FIG. 10 is a diagram showing the relationship between the shapes of the first graphic and the second graphic, the tube current reduction scan range, and the tube current reduction projection angle range according to the second embodiment. In this example, as shown in FIG. 10, a region F1b corresponding to the transition angle section Sθ in the first graphic F1 and a region F2b corresponding to the transition angle section Sθ in the second graphic F2 Displayed in a different color or pattern from the other areas F1a and F2a.

  FIG. 11 is a diagram showing a first graphic and a second graphic when the tube current reduction projection angle range is set as a projection angle range of 3π / 2 to π / 2 in the second embodiment.

  According to such a second embodiment, the operator can grasp the transition angle section Sθ in the positional correspondence relationship with the subject, and consider the part where the X-ray exposure dose is not sufficiently reduced. Thus, the tube current reduction projection angle range Rθ can be set appropriately. For example, when the transition angle section Sθ is larger than expected, the tube current reduction projection angle range Rθ is set slightly larger so that the X-ray exposure dose can be sufficiently reduced.

  In each of the above-described embodiments, in the tube current reduction setting window 68, a rectangle that overlaps these ranges as a figure indicating the range Rx in the x direction corresponding to the tube current reduction projection angle range Rθ and the tube current reduction scan range Rz. A first figure F1 having substantially the same shape as the area is displayed, but a figure showing a range Rx in the x direction corresponding to the tube current reduction projection angle range Rθ, and a figure showing a tube current reduction scan range Rz May be displayed separately. For example, as shown in FIG. 12, auxiliary lines F1′a to F1′d corresponding to both ends of each of the x-direction range Rx corresponding to the tube current reduction scan range Rz and the tube current reduction projection angle range Rθ are provided. You may make it display. Similarly, instead of the substantially rectangular second shape F2, the auxiliary line F2 corresponding to both ends in the respective ranges of the tube current reduction scan range Rz and the y direction range Ry corresponding to the tube current reduction projection angle range Rθ. 'A to F2'd may be displayed.

  Further, in each of the above embodiments, the tube current reduction setting window 68 corresponds to a figure indicating the tube current reduction scan range Rz and the tube current reduction projection angle Rθ for both the front image and the side image of the subject 40. However, such a display may be performed only on the front image of the subject 40. In other words, the first scout image 41 and the first graphic F1 may be displayed, and the second scout image 42 and the second graphic F2 may not be displayed.

  Further, in each of the above embodiments, the tube current of the X-ray tube 21 is changed in accordance with the projection angle in the scan in order to reduce the X-ray exposure amount of a highly radiation-sensitive part. It may be realized. For example, the tube voltage of the X-ray tube 21 may be changed according to the projection angle. Further, for example, a filter having a variable X-ray absorption rate may be installed on the path of the X-ray beam 81, and the dose of the X-ray beam 81 may be changed by controlling this filter.

  The above embodiments are all related to the X-ray CT apparatus, but the present invention is also applicable to a PET-CT apparatus, a SPECT-CT apparatus, or the like that combines the X-ray CT apparatus and PET or SPECT. Is possible.

DESCRIPTION OF SYMBOLS 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 15 Rotating part 20 Scanning gantry 21 X-ray tube 22 X-ray controller 23 Collimator 24 X-ray detector 25 DAS
26 Rotating unit controller 29 Control controller 30 Slip ring 40 Subject 41 First scout image 42 Second scout image 68 Tube current reduction setting window 81 X-ray beam 100 X-ray CT apparatus F1 First figure F2 Second figure

Claims (9)

  1. An X-ray CT apparatus for making an X-ray irradiation output smaller than a predetermined X-ray irradiation output in a predetermined projection angle range in a predetermined range in the body axis direction when performing X-ray CT scanning on a subject,
    Display means for displaying the front image of the subject in association with an image that geometrically shows a range in the left-right direction of the subject corresponding to the predetermined projection angle range and a predetermined range in the body axis direction An X-ray CT apparatus comprising:
  2.   The range in the left-right direction corresponding to the predetermined projection angle range is the range in the left-right direction of an arc corresponding to the predetermined projection angle range on the circumference representing the contour of the imaging field of view. X-ray CT system.
  3.   The display means displays an image representing a figure having substantially the same shape as a rectangular area where the range in the left-right direction of the arc and the predetermined range in the body axis direction overlap with the front image of the subject. The X-ray CT apparatus according to claim 1 or 2.
  4.   Changing means for receiving a change in the position or shape of the displayed image by an operation from an operator and changing at least one of the predetermined range in the body axis direction and the predetermined projection angle range based on the change in the image The X-ray CT apparatus according to any one of claims 1 to 3, further comprising:
  5.   The display means further includes a side image of the subject and an image geometrically showing a range in the front-rear direction of the subject and a predetermined range in the body axis direction corresponding to the predetermined projection angle range. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus displays the information in association with each other.
  6.   The range in the front-rear direction corresponding to the predetermined projection angle range is a range in the front-rear direction of an arc corresponding to the predetermined projection angle range on a circumference representing an outline of the imaging field of view. X-ray CT system.
  7.   The display means displays an image representing a figure having a shape substantially the same as a rectangular region in which the range in the front-rear direction corresponding to the predetermined projection angle range and the predetermined range in the body axis direction overlap. The X-ray CT apparatus according to claim 5, wherein the X-ray CT apparatus displays the image superimposed on a side image.
  8. An estimation means for estimating a transition angle interval from when the X-ray irradiation output starts to change toward the target output within the predetermined projection angle range until reaching the target output;
    The display means, X-rays CT apparatus according to any one of claims 1 to 7 which further displays information indicating the estimated transition angle interval.
  9.   The front image of the subject is an image obtained by performing a scout scan of the subject with X-rays, an image obtained by performing an X-ray CT scan of the subject, or applying the subject to an optical imaging apparatus. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is an image obtained by imaging.
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