JP5085165B2 - X-ray CT system - Google Patents

Description

  The present invention relates to a technique for switching an imageable area in an X-ray CT (Computed Tomography) system.

  In the X-ray CT system, an X-ray generation unit and an X-ray detection unit are provided so as to be rotatable around the body axis of the subject, and projection data (data) obtained by scanning the subject. ) To reconstruct a tomographic image of the subject. In general, the X-ray detection unit includes a plurality of X-ray detection elements arranged in at least the angular direction of rotation, that is, the channel direction, the X-ray focal point of the X-ray generation unit, and the rotation center. The centers of the X-ray detection areas of the X-ray detection unit are arranged in a straight line. According to such an X-ray CT system, a circle that is centered on the rotation center and inscribed in a straight line of two sides forming a fan angle α of the X-ray beam (beam) emitted from the X-ray generator. The region is a region in which a tomographic image can be reconstructed (see Patent Document 1).

JP 2006-320468 A

  By the way, as a situation in which an object is imaged by an X-ray CT system, for example, when an object whose tomographic plane is larger than an assumed size is desired to be imaged, or an object placed on a portable bed in an emergency is used. There is a case where it is desired to take an image as it is without aligning the body axis of the subject and the center of the cavity, without being placed on a dedicated imaging table (table). In order to cope with such a situation, in the conventional X-ray CT system, by increasing the distance between the X-ray generation unit and the X-ray detection unit and increasing the detection range of the X-ray detection unit, An X-ray CT system having a larger imageable area than usual is used.

  However, in the X-ray CT system in which such an imageable area is designed to be larger than usual, there is a problem that the gantry is enlarged and spatially bulky. In addition, if the imageable area remains large, X-ray photon noise in the obtained tomographic image will appear prominently, and the image quality level (level) of the tomographic image with respect to the X-ray dose is also constant. There is a problem of getting worse. That is, to obtain a high-quality tomographic image, the X-ray dose must be increased, and the amount of exposure to the subject increases.

  In view of the circumstances described above, an object of the present invention is to provide an X-ray CT system that can change an imageable region as necessary without changing the size of the system.

  Japanese Patent Laid-Open No. 2005-6772 discloses an X-ray diagnostic apparatus capable of performing high-definition CT imaging of a subject from a relatively small size to a large size with a compact and simple configuration. However, this apparatus is different from the present invention in that a panel detector for detecting X-rays is provided so as to be offset in a predetermined direction.

  In a first aspect, the present invention provides an X-ray generation unit that generates an X-ray beam and an X-ray detection unit in which a large number of X-ray detection elements are arranged one-dimensionally or two-dimensionally. An X-ray CT system that revolves a tomogram of a subject on the basis of projection data obtained by scanning the subject and arranged opposite to each other around an axis, the X-ray detection unit A counter weight disposed at a position facing the X-ray generation unit across the X-ray generation unit, and a relative positional relationship between the X-ray generation unit and the counter weight with respect to the X-ray detection unit A positional relationship in which the center of gravity of the generation unit and the counterweight coincides with the center of rotation, and a straight line passing through the center of rotation and the center of the X-ray detection region of the X-ray detection unit; Before the reference plane formed by the body axis A moving means for moving the X-ray generator and the counterweight so that the X-ray focal point of the X-ray generator may have a first positional relationship and a second positional relationship different from each other. An X-ray CT system is provided.

  In a second aspect, according to the present invention, the first positional relationship is a positional relationship in which the positions of the X-ray generator and the counterweight are on the straight line, and the second positional relationship is the X The X-ray CT system according to the first aspect, wherein the position of the line generator and the counterweight is in a positional relationship deviating from the straight line.

  In a third aspect, the present invention provides the X-ray beam irradiation range in which the moving means has the same position and orientation of the X-ray generation unit and the same fan angle of the X-ray beam from the X-ray generation unit. Provided is the X-ray CT system according to the first aspect or the second aspect, in which the X-ray generation part is moved so as to be in a position and an orientation that substantially coincide with the range of the detection region of the X-ray detection part. To do.

  In a fourth aspect, the present invention provides an X-ray beam irradiation range so that an X-ray beam irradiation range from the X-ray generation unit substantially matches an X-ray detection region range of the X-ray detection unit. The X-ray CT system according to the first aspect or the second aspect, further comprising an X-ray irradiation range control means for controlling the X-ray irradiation range control means.

  In a fifth aspect, the present invention provides the fourth aspect, wherein the X-ray irradiation range control means includes a swing mechanism that changes the direction of the X-ray generation unit along a plane perpendicular to the axis of rotation. An X-ray CT system is provided.

  In a sixth aspect, the present invention provides the above X-ray irradiation range control means, wherein the X-ray irradiation range control means includes a collimator that forms a slit that limits the irradiation range of the X-ray beam from the X-ray generation unit. The X-ray CT system according to the fourth aspect or the fifth aspect is provided.

  In a seventh aspect, the present invention allows the moving means to continuously move the X-ray generator and the counterweight while maintaining a positional relationship in which the center of gravity coincides with the center of rotation. An X-ray CT system according to any one of the fourth to sixth aspects is provided.

  In an eighth aspect, the present invention provides the moving means, wherein the X-ray focal point of the X-ray generator is perpendicular to the X-ray focal point in the first positional relationship and the axis of rotation, and the center of rotation. The X-ray CT system according to the seventh aspect, wherein the X-ray generation unit is moved so as to move along the circumference of a circle passing through both end points of the X-ray detection unit on a plane including To do.

  Here, the X-ray generator is not only an X-ray source that generates X-rays, but also moves accompanying the X-ray source, for example, if there is a collimator, moves accompanying the X-ray generator. Including. Further, the counterweight is a kind of weight, and for example, a main component may be a metal or a stone.

  The center of gravity of the X-ray generation unit and the counterweight means a total center of gravity when the X-ray generation unit and the counterweight are considered as one body. That is, the center of gravity of the X-ray generation unit and the counterweight is a point on a line segment connecting the center of gravity of the X-ray generation unit and the center of gravity of the counterweight, and the weight of the X-ray generation unit and the center of gravity of the X-ray generation unit The value obtained by multiplying the distance from the counter weight and the value obtained by multiplying the weight of the counterweight by the distance from the center of gravity of the counterweight are equal.

  Therefore, the counterweight is rotated based on the weight of the X-ray generation unit, the position of the center of gravity, and the position of the center of rotation, in the first and second positional relationships. The shape, arrangement, and arrangement for determining the weight and the center of gravity are designed so as to coincide with the center of the image.

  The fan angle means an irradiation angle in the channel direction of the X-ray beam generated from the X-ray generation unit.

  Details of a mechanism for changing the size of a reconfigurable region of a tomographic image by shifting the position of the X-ray generation unit is disclosed in Japanese Patent Application No. 2006-316100 by the present applicant.

  According to the X-ray CT system of the present invention, the reconfigurable region of the tomographic image can be changed only by changing the relative positional relationship between the X-ray generator and the counterweight with respect to the X-ray detector by the moving means. The imageable area can be changed as needed without changing the size of the system. In the first and second positional relationships, the center of gravity of the X-ray generation unit and the counterweight is coincident with the center of rotation thereof, so that the weight balance (weight balance) is maintained even if the X-ray generation unit is moved. ) Is maintained, the rotation is stable, and high-speed rotation is also possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)

  FIG. 1 is a diagram showing a configuration of an X-ray CT system in the present embodiment. Here, the horizontal direction in the drawing is the x-axis direction, the vertical direction in the drawing is the y-axis direction, and the direction perpendicular to the drawing is the z-axis direction.

  As shown in the figure, this system performs X-ray irradiation on a subject (patient) and X-rays transmitted through the subject, and various operation settings are performed on the gantry 100 and is output from the gantry 100. The operation console 200 includes a console 200 that reconstructs and outputs (displays) a tomogram based on the received data.

  The gantry 100 has the following configuration including a main controller 10 that controls the entire gantry 100.

  That is, the gantry 100 aligns the subject lying on the interfaces (interfaces) 11 and 12 and the table (table) 14 for communicating with the operation console 200 in the z-axis direction (generally in the direction of the patient's body axis). A rotating part 13 having a hollow part for conveying in the direction).

  Inside the rotating unit 13 are an X-ray tube 15, a collimator 17 having an opening for limiting the X-ray irradiation range, and an opening control motor for adjusting the opening width of the collimator 17 in the x-axis direction and the z-axis direction. (Motor) 18, a position control motor 20 for adjusting the positions of the collimator 17 in the x-axis direction and the z-axis direction, an X-ray tube movement control motor 30 for moving the X-ray tube 15, and the X-ray tube 15 are moved. A plurality of X-ray beams (for example, 1,000) for detecting X-ray beams from the X-ray tube movement guide (guide) 31, the collimator 17 and the X-ray tube 15 passing through the cavity. X-ray detection elements 22, which are arranged opposite to the X-ray tube 15 across the cavity, and based on the outputs from the X-ray detection elements of the X-ray detection section 22 Data A data collection unit 23 to collect, a counter weight 28 disposed opposite to the X-ray tube 15 across the X-ray detection unit 22, a counter weight movement control motor 33 for moving the counter weight 28, and a counter weight 28 A counterweight movement guide 34 is provided for determining the position and orientation that can be taken by the movement of the counterweight.

  The X-ray tube 15, the opening control motor 18, the position control motor 20, the X-ray tube movement control motor 30, and the counterweight movement control motor 33 are respectively an X-ray tube controller 16, an opening control motor driver (motor driver) 19, and a position. Driving is controlled by the control motor driver 21, the X-ray tube movement control motor driver 29, and the counterweight movement control motor driver 32.

  The rotating unit 13 is configured to rotate around the cavity while maintaining the positional relationship. The rotating unit 13 includes other components of the entire rotating unit 13 except for the X-ray tube 15, the collimator 17 associated therewith, and the counterweight 28 (strictly, including a part of members that support them). Is designed so that its center of gravity coincides with the center of rotation of the rotating unit 13. The rotation unit 13 is rotated by a rotation motor 25 driven by a drive signal from a rotation motor driver 24. Further, the table 14 on which the subject is placed is transported in the z-axis direction, and is driven by a table motor 26 driven by a drive signal from the table motor driver 27.

  The main controller 10 analyzes various commands received via the interface 11, and based on the analysis, the X-ray tube controller 16, the aperture control motor driver 19, the position control motor driver 21, the rotation motor driver 24, and the table motor driver. 27, various control signals are output to the data collection unit 23, the X-ray tube movement control motor driver 29, and the counterweight movement control motor driver 32.

  The data collected by the data collection unit 23 is sent to the operation console 200 via the interface 12.

  On the other hand, the operation console 200 is a so-called workstation, and as shown in the figure, functions as a main storage device, a CPU 51 that controls the entire apparatus, a ROM 52 that stores a boot program (boot program), and the like. Including the RAM 53, the following configuration is provided.

  The HDD 54 is a hard disk device for giving various instructions to the gantry 100 and executing tomographic image reconstruction and display based on data received from the gantry 100 in addition to the OS. The image processing program is stored. The VRAM 55 is a memory that develops image data to be displayed, and can be displayed on a monitor 56 by developing the image data or the like. Reference numerals 57 and 58 denote a keyboard and a mouse for making various settings, respectively. Reference numerals 59 and 60 denote interfaces for communicating with the gantry 100 and are connected to the interfaces 11 and 12 of the gantry 100, respectively.

  The X-ray tube 15 and the collimator 17 are an example of the X-ray generation unit in the present invention, and the X-ray detection unit 22 is an example of the X-ray detection unit in the present invention, and the X-ray tube movement control motor driver 29, X The tube movement control motor 30, the X-ray tube movement guide 31, the counter weight movement control motor driver 32, the counter weight movement control motor 33, and the counter weight movement guide 34 are examples of moving means in the present invention.

  The configuration of the X-ray CT system in this embodiment is generally as described above. Next, the X-ray tube 15, collimator 17, X-ray detection unit 22, counter weight 28, X-ray tube movement guide 31, counter weight movement guide The structure 34 will be described in more detail with reference to FIG.

  FIG. 2 is a schematic configuration diagram of the gantry rotating unit 13, specifically, the X-ray tube 15, the collimator 17, the X-ray detection unit 22, the counter weight 28, the X-ray tube moving guide 31, and the counter weight moving guide 34. The principal part structure is shown.

  These components are supported by a predetermined base portion of the rotating portion 13 and have a positional relationship as illustrated. As the base, for example, a metal disk having a doughnut shape as shown in the figure can be considered. However, the base can support the above-described components and can rotate around the cavity. It can be anything.

  As described above, the X-ray tube 15 and the X-ray detection unit 22 are disposed to face each other with the cavity portion interposed therebetween. The collimator 17 is arranged between the X-ray tube 15 and the cavity, and the X-ray beam Bc from the X-ray tube 15 is adjusted by the collimator 17 with the fan angle α in the channel direction and the irradiation angle in the slice direction. The X-ray detection area of the line detection unit 22 is irradiated.

  The X-ray detection unit 22 has a plurality of X-ray detection elements arranged two-dimensionally, that is, arranged in a matrix in the channel direction and the slice direction. Note that the X-ray detection unit 22 may include a plurality of X-ray detection elements arranged one-dimensionally, that is, arranged in a line in the channel direction.

  The X-ray tube movement guide 31 and the counterweight movement guide 34 have a rail shape bent so as to draw an arc (not limited to a strict arc) on the xy plane. The X-ray tube movement guide 31 is disposed on the back of the X-ray tube 15, and the counterweight movement guide 34 is disposed on the opposite side of the cavity with respect to the X-ray detection unit 22.

  Each of these guides may be assumed to be designed such that, for example, both end points in the longitudinal direction of the guide correspond to the positions of the X-ray tube 15 and the counterweight 28 in the first and second positional relationships. Of course, a predetermined position other than the end point on the guide may be designed to correspond to each of these positions. Further, the relative positional relationship between the guides and the ones moving along the guides (X-ray tube 15 and counterweight 28) is not particularly limited to these.

  The counterweight 28 has a rectangular shape here, but is not limited to such a shape. For example, it may be spherical, cylindrical, cubic, or the like. The counter weight 28 may be, for example, a metal made of copper, lead, iron or the like, or a box filled with an aqueous solution. However, any counter weight may be used. May be.

  The X-ray tube 15 and the collimator 17 are coupled by a member (not shown), and both are supported so as to be movable along the X-ray tube moving guide 31. The counterweight 28 is supported so as to be movable along the counterweight movement guide 34. The counterweight movement guide 34 may be supported by the X-ray detection unit 22 instead of the base of the rotation unit 13.

  In the figure, an X-ray tube 15 has a structure in which a cathode sleeve containing a focusing electrode and a filament, and a rotating target are accommodated in a housing. Radiate a line. The X-rays radiated from the X-ray tube 15 pass through the slit S formed by the collimator 17, thereby forming a cone beam (corn beam) Bc having a predetermined X-ray irradiation angle (fan angle). .

  The X-ray detection unit 22 described above forms a detector in a row with a plurality of, for example, 1000 X-ray detection elements (detection channels), and this detector is in the z-axis direction (coincides with the transport direction of the table 14). A plurality of rows, for example, 8 rows, are arranged. The fan angles of the cone beam in the x-axis direction and the z-axis direction are adjusted so that the X-ray irradiation range substantially coincides with the detection range of the X-ray detection unit 22, that is, the detection surface. As a result, a so-called multi-slice multi-slice X-ray CT is realized.

  In the above configuration, the width of the slit S formed by the collimator 17 in the x-axis direction and the z-axis direction (hereinafter simply referred to as the opening width), and the position of the collimator 17 in the x-axis direction and the z-axis direction respectively perform mechanical operations. It can be adjusted by doing. As the structure of the collimator 17, for example, the structure of a collimator described in JP-A-2005-46199 can be applied.

  The X-ray tube movement guide 31 and the counterweight movement guide 34 respectively support the X-ray tube 15 and the counterweight 28 so as to be movable. As such guides, for example, an LM guide series (manufactured by THK) ( For example, a guide series or other bearing type can be used. The X-ray tube 15 and the counterweight 28 can travel on these guides and stop at a plurality of predetermined positions, thereby changing the size of the reconfigurable region of the tomographic image. Details will be described later.

  In the X-ray CT system having such a configuration, collection of projection data is performed as follows, for example.

  First, the position in the z-axis direction is fixed in a state where the subject is positioned in the cavity of the rotating unit 13, and the subject 70 is irradiated with the X-ray beam from the X-ray tube 15 (projection of X-rays). The transmitted X-ray is detected by the X-ray detector 22. The transmission X-rays are detected by rotating the X-ray tube 15 and the X-ray detection unit 22 around the subject 70, that is, while changing the projection angle (view angle). For example, 360 degrees is performed in the view direction of N = 1,000).

  Each detected transmission X-ray is converted into a digital value by the data acquisition unit 23 and transferred to the operation console 200 via the interface 12 as projection data. A series of these processes is called one scan as one unit. Then, the scan position is sequentially moved by a predetermined amount in the z-axis direction, and the next scan is performed. Such a scanning method is called an axial scan method, and the table 14 is continuously moved in accordance with the rotation of the gantry rotating unit 13 (the X-ray tube 15 and the X-ray detecting unit 22 are covered). A helical scan method that collects projection data (which spirals around the specimen) may be used.

  The operation console 200 stores the projection data transferred from the gantry 100 in the HDD 54, performs a convolution operation with a predetermined reconstruction function, and reconstructs a tomographic image by back projection processing. Here, the operation console 200 can reconstruct a tomogram in real time from projection data sequentially transferred from the gantry 100 during the scan process, and always display the latest tomogram on the monitor 56. It is. Furthermore, it is also possible to call up the projection data stored in the HDD 54 and perform image reconstruction again.

  Here, it will be described that the reconfigurable region of the tomographic image changes depending on the positional relationship between the X-ray tube 15 and the counterweight 28.

  FIG. 3 is a diagram showing the positional relationship before and after the movement of the X-ray tube 15 and the counterweight 28 in the present embodiment.

  The X-ray tube 15 and the collimator 17 (hereinafter collectively referred to as the X-ray generation unit 15 ′) and the counter weight 28 are relative to each other with respect to the X-ray detection unit 22. Is a positional relationship in which the center of gravity of the X-ray generation unit 15 ′ and the counterweight 28 coincides with the rotation center IC, and a straight line L passing through the rotation center IC and the center DC of the X-ray detection region of the X-ray detection unit 22. And the vertical component of the X-ray focal point F of the X-ray tube 15 from the reference plane formed by the body axis A of the subject 70 move so as to be able to take different first and second positional relationships. . In the present embodiment, the first positional relationship is such that the positions of the X-ray generation unit 15 ′ and the counterweight 28 are on a straight line L passing through the rotation center IC and the center DC of the X-ray detection region of the X-ray detection unit 22. The second positional relationship is a positional relationship in which the positions of the X-ray generator 15 'and the counterweight 28 deviate from the straight line L. However, the second positional relationship is such that the angle of deviation from the first positional relationship is less than 90 degrees, and the X-ray focal point F of the X-ray tube 15 is outside the irradiation space of the cone beam Bc in the first positional relationship. It is a serious positional relationship.

  T1, F1, and W1 represent the center of gravity of the X-ray generator 15 ', the X-ray focal point of the X-ray tube 15, and the center of gravity of the counterweight 28 in the first positional relationship, respectively. , The center of gravity of the X-ray generator 15 ′, the X-ray focal point of the X-ray tube 15, and the position of the center of gravity of the counterweight 28 in the second positional relationship, respectively. D1 and D2 represent both end points of the X-ray detection unit 22 on a plane perpendicular to the rotation axis IC and including the rotation center IC.

  Although the collimator 17 is not shown here, its opening is fixed. Therefore, the fan angle of the cone beam from the X-ray tube 15 is always constant, and the irradiation direction changes according to the orientation of the X-ray tube 15 on the xy plane.

  The X-ray tube moving guide 31 has the same X-ray beam with the same position and orientation of the X-ray generator 15 ′ and the same fan angle of the X-ray beam from the X-ray tube 15 in both the first and second positional relationships. The X-ray generation unit 15 ′ is moved so that the irradiation range is substantially the same as the X-ray detection region of the X-ray detection unit 22. That is, the X-ray generation unit 15 ′ moves only to a predetermined position corresponding to the first and second positional relationships along the X-ray tube moving guide 31, and the X-ray beam irradiation range is adjusted by the collimator 17. None, it automatically matches the range of the X-ray detection area of the X-ray detection unit 22. Therefore, the movement of the X-ray generation unit 15 ′ here is not a simple rotational movement in terms of geometry.

  When the X-ray generation unit 15 ′ and the counter weight 28 are in the first positional relationship (standard state), the X-ray tube 15 irradiates the cone beam Bc 1 toward the X-ray detection unit 22. In this case, when the rotation unit 13 is rotated, the range in which the projection data of each view corresponding to the rotation angle of 180 degrees necessary for reconstruction of the tomogram is obtained is centered on the rotation center IC, and the X-ray focal point F1. A circular region P1 having a radius r1 inscribed in a straight line connecting the end points D1 or D2. Accordingly, the reconfigurable area in this case is the circular area P1.

  On the other hand, when the X-ray tube 15 and the counterweight 28 are in the second positional relationship, the X-ray tube 15 irradiates the cone beam Bc2 toward the X-ray detection unit 22. In this case, when the rotation unit 13 is rotated, the range in which the projection data of each view corresponding to the rotation angle of 180 degrees necessary for the reconstruction of the tomographic image is obtained is centered on the rotation center IC, and the X-ray focal point F2. A circular region P2 having a radius r2 inscribed in a straight line connecting the end point D1 is formed. Therefore, the reconfigurable area in this case is a circular area P2. That is, in the second positional relationship, the size of the reconfigurable area is larger than that in the first positional relationship.

  For the circular region P1, a tomographic image can be reconstructed by half scan (half scan) in which the rotating unit 13 is rotated by 180 degrees + fan angle α of the X-ray beam, but for the circular region P2, the rotating unit 13 is used. A tomographic image can be reconstructed by a full scan by rotating 360 degrees.

  In this way, by switching the positional relationship between the X-ray generation unit 15 ′ and the counterweight 28, the area in which the tomographic image can be reconstructed, that is, the imageable area can be switched.

  Next, the operation of the X-ray CT system according to the present embodiment will be described.

  FIG. 4 is a flowchart illustrating an example of a series of processes in the X-ray CT system according to the present embodiment. The program corresponding to this flowchart is included in the image processing program stored in the hard disk 54 of the operation console 200, loaded into the RAM 53 after being powered on, and executed by the CPU 51.

  First, a scan plan is made (step S1). For example, in the operation console 200 provided by the image processing program, the slice thickness, the scan start / end position, the size of the imaging region, the current value applied to the X-ray tube 15, the gantry rotation unit 13, via the GUI. Scan conditions such as rotation speed are set. The set scan conditions are stored in the RAM 53.

  Next, it is determined based on the input of the keyboard 57 or the mouse 58 whether or not a scan start instruction has been made (step S2). When a scan start instruction is given, a scan start command using the scan condition set in step S2 as a parameter is transmitted to the gantry 100 (step S3).

  Then, the main controller 10 of the gantry 100 determines the size of the set imaging region based on the received parameter (step S4). If it is determined in step S4 that the imaging region is small, the main controller 10 issues a command to the X-ray tube movement control motor driver 31 and the counter weight position control motor driver 33, and the X-ray generation unit 15 'and the counter weight. 28 is moved to the first positional relationship (standard state), and the imaging region is set to the circular region P1 (step S5). If it is already in the first positional relationship, it is left as it is. On the other hand, if it is determined in step S4 that the imaging region is large, the main controller 10 issues a command to the X-ray tube movement control motor driver 31 and the counterweight position control motor driver 33, and the X-ray generation unit 15 'and The counter weight 28 is moved to the second positional relationship, and the photographing area is set to the circular area P2 (step S6). If it is already in the second positional relationship, it is left as it is.

  The main controller 10 transmits a command to each controller and each driver based on the received parameters, and scans the subject under the set scan conditions.

  The operation console 200 receives the data obtained by the scan from the gantry 100 (step S7), and monitors whether or not the processing for the received data has been completed (step S8).

  The following processing is performed until all processing for received data is completed.

  Predetermined preprocessing such as reference correction, beam hardening correction, and correction of physical characteristics of the X-ray detector is performed on the received data (step S9). These pretreatments are selectively performed as necessary. In addition, you may perform a scattered ray correction after such a pre-processing.

  Then, image reconstruction processing is performed using the X-ray projection data preprocessed in step S9 to generate an X-ray tomographic image of the subject (step S10), and the X-ray tomographic image is displayed on the monitor 56. The display is output (step S11).

  According to the present embodiment described above, the area where the tomographic image can be reconstructed is changed only by changing the relative positional relationship between the X-ray generator 15 'and the counterweight 28 with respect to the X-ray detector 22 by the moving means. The area that can be photographed can be changed as needed, with little change in the size of the system. In the first and second positional relationships, since the center of gravity of the X-ray generator 15 'and the counterweight 28 coincides with these rotation centers IC, the weight balance is maintained even if the X-ray tube 15 is moved. Is maintained, the rotation is stable, and high-speed rotation is also possible.

In addition, according to the present embodiment, the X-ray tube moving guide 31 constituting the moving means has the same X-ray tube 15 position and orientation with the same fan angle of the X-ray beam from the X-ray tube 15. Since the X-ray tube 15 is moved so that the X-ray tube 15 is moved to a position and orientation that substantially match the X-ray detection region range of the X-ray detection unit 22 Therefore, it is possible to easily switch the shootable area.
(Second Embodiment)

  The X-ray CT system according to the present embodiment is basically the same as the first embodiment except for the features described below. Therefore, description of the configuration, structure, main functions of each component, etc. is omitted here.

  FIG. 5 is a diagram showing the positional relationship before and after the movement of the X-ray generator 15 ′ and the counterweight 28 in the present embodiment.

  In the present embodiment, the X-ray tube movement guide 31 constituting the moving means has the X-ray focal point of the X-ray tube 15 as the X-ray focal point F1 in the first positional relationship and the rotation axis IC of the X-ray detection unit 22. An X-ray generation unit composed of an X-ray tube and a collimator 17 so as to move along the circumference of a circle Ctd that passes through both end points D1 and D2 of the X-ray detection unit 22 on a vertical plane including the rotation center IC The X-ray irradiation range is adjusted by the swing mechanism 35 or the collimator 17 of the X-ray generator 15 'as necessary. The swing mechanism 35 changes the direction of the X-ray generator 15 'along a plane perpendicular to the rotation axis IC.

  In the present embodiment, the X-ray tube moving guide 31 and the counterweight moving guide 34 that constitute the moving means, the X-ray generator 15 'and the counterweight 28 have a positional relationship in which their centers of gravity coincide with the rotation center IC. The second positional relationship can be continuously obtained by such continuous movement.

  T1, F1, and W1 represent the positions of the center of gravity of the X-ray generation unit 15 ′, the X-ray focal point, and the center of gravity of the counterweight 28 in the first positional relationship, respectively, and T2, F2, and W2 represent the second position. The positions of the center of gravity of the X-ray generation unit 15 ′, the X-ray focal point, and the center of gravity of the counterweight 28 in the relationship are shown. D1 and D2 represent both end points of the X-ray detection unit 22 on a plane perpendicular to the rotation axis IC of the X-ray detection unit 22 and including the rotation center IC.

  Here, the straight line F2D1 and the straight line F2D2 are cone beams necessary for making the X-ray irradiation range coincide with the detection surface of the X-ray detection unit 22 when the X-ray generation unit 15 ′ is in the second positional relationship. It matches the outline of Bc21. Further, as described above, the X-ray focal point F2 in the second positional relationship is on the circumference of the circle Ctd passing through the three points F1, D1, and D2, and therefore, the angle D1F2D2 is always constant according to the circumference angle theorem. It becomes. Accordingly, the fan angle of the cone beam Bc21 to be irradiated is always constant no matter where the X-ray generator 15 ′ moves.

  On the other hand, the X-ray beam emitted from the X-ray tube 15 when the X-ray generator 15 'is in the second positional relationship becomes a cone beam Bc20 as shown in the figure, and the cone beam Bc21 to be actually emitted. Are not completely matched, and the deviation increases as the X-ray focal point F2 becomes farther from the X-ray focal point F1.

  Therefore, since the fan angle of the cone beam Bc21 to be irradiated is always constant, when the above-described deviation in the irradiation direction of the X-ray beam is negligible, or in advance so that it can be ignored. When the range is set to be slightly wider than the detection surface of the X-ray detection unit 22, the X-ray beam can be adjusted without adjusting the irradiation range of the X-ray beam regardless of the position of the X-ray generation unit 15 ′. Can be made to substantially coincide with the range of the X-ray detection region of the X-ray detection unit 22, and the region in which the tomographic image can be reconstructed can be continuously changed.

  However, when the above-described deviation in the irradiation direction of the X-ray beam cannot be ignored, means for controlling the irradiation range of the X-ray beam is necessary.

  FIG. 6 is a diagram illustrating a state in which the X-ray generation unit 15 ′ is provided with a swing mechanism 35 and the X-ray tube 15 is changed in direction on the xy plane to correct a deviation in the irradiation direction of the X-ray beam. FIG. 7 is a diagram showing how the X-ray beam irradiation direction is corrected by changing the opening of the collimator 17.

  If there is a means for controlling the irradiation range of the X-ray beam, the X-ray beam irradiation range is changed to the X-ray detection region of the X-ray detection unit 22 regardless of the position of the X-ray generation unit 15 ′. The tomographic region can be reconstructed continuously.

  According to the present embodiment described above, the size of the reconfigurable region of the tomographic image can be continuously changed within a predetermined range, so the size of the imaging region is set to a necessary and sufficient size. Therefore, it is possible to perform imaging in which the amount of exposure to the subject and the image quality of the tomographic image are balanced.

  In the present embodiment, the X-ray tube moving guide 31 is a circle in which the X-ray focal point of the X-ray tube 15 passes through the X-ray focal point F1 in the first positional relationship and the end points D1 and D2 of the X-ray detection unit 22. Although the X-ray generator 15 'is moved so as to move along the circumference of Ctd, the X-ray generator 15' may be moved on a different curve or straight line. In this case, if the means for controlling the irradiation range of the X-ray beam is a combination of the swing mechanism 35 and the collimator 17 of the X-ray generator 15 ', the X-ray generator 15' can be moved to any position. The irradiation range of the X-ray beam can be made substantially coincident with the detection surface of the X-ray detection unit 22, and the reconfigurable region of the tomographic image can be continuously changed.

  In the present embodiment, the moving means is an electric type using a motor and its driver. However, for example, the moving means is a mechanical device, and the operator sets the X-ray generator 15 ′ and the counter weight 28. It is good also as what can move a position manually. In this case, it is desirable that the positions of the X-ray generator 15 'and the counterweight 28 be designed so that they can be easily switched by a lever or the like.

  In the present embodiment, the counter weight 28 corresponding to the X-ray generator 15 'is provided, and the X-ray generator 15 so that the center of gravity of the X-ray generator 15' and the counter weight 28 coincides with the rotation center IC. 'And the counter weight 28 are moved. As another method, for example, a correction weight for correcting a shift in the center of gravity of the entire rotation unit 13 that occurs when the X-ray generation unit 15' is moved, and this correction weight. May be provided so that when the X-ray generator 15 ′ is moved, the correction weight is moved to a position where the deviation of the center of gravity is corrected. That is, in this case, the center of gravity of the X-ray generation unit 15 ′ and the correction weight does not necessarily coincide with the rotation center IC, and it is only necessary that the center of gravity of the entire rotation unit 13 coincides with the rotation center IC.

  In addition, these embodiment is an example of the best form for implementing this invention, and this invention is not limited to these embodiment. That is, the present invention can be changed, added, or combined in any manner without departing from the spirit of the present invention.

  A program for causing a computer to function as the X-ray CT system of the present invention or each means thereof is also an example of an embodiment of the present invention. This program may be supplied by downloading, distributing, etc. via a network such as the Internet, or supplied by recording this program on a computer-readable recording medium. You may make it do.

The figure which shows the structure of the X-ray CT system by 1st Embodiment. Schematic configuration diagram of gantry rotating part The figure which shows the positional relationship before and behind the movement of the X-ray tube and counterweight in 1st Embodiment. The flowchart which shows the example of a series of processes in the X-ray CT system by 1st Embodiment. The figure which shows the positional relationship before and behind the movement of the X-ray tube and counterweight in 2nd Embodiment. The figure which showed a mode that the shift | offset | difference of the irradiation direction of X-rays was correct | amended by the X-ray tube swing mechanism The figure which showed a mode that the shift | offset | difference of the irradiation direction of X-rays was corrected with a collimator

Explanation of symbols

10 Main controller 11, 12 Interface 13 Rotating unit 14 Table 15 X-ray tube (X-ray generating unit)
16 X-ray tube controller 17 Collimator (X-ray generator, collimator)
DESCRIPTION OF SYMBOLS 18 Opening control motor 19 Opening control motor driver 20 Position control motor 21 Position control motor driver 22 X-ray detection part (X-ray detection part)
23 Data Collection Unit 24 Rotary Motor Driver 25 Rotary Motor 26 Table Motor 27 Table Motor Driver 28 Counter Weight (Counter Weight)
29 X-ray tube movement control motor driver (moving means)
30 X-ray tube movement control motor (moving means)
31 X-ray tube movement guide (moving means)
32 Counterweight movement control motor driver (moving means)
33 Counterweight movement control motor (moving means)
34 Counterweight movement guide (moving means)
35 Swing mechanism (swing mechanism)
51 CPU
52 ROM
53 RAM
54 HDD
55 VRAM
56 monitor 57 keyboard 58 mouse 59, 60 interface 70 subject 100 gantry 200 operation console

Claims (8)

An X-ray generation unit that generates an X-ray beam and an X-ray detection unit in which a number of X-ray detection elements are arranged one-dimensionally or two-dimensionally can be rotated around each other about the body axis of the subject. An X-ray CT system for reconstructing a tomographic image of a subject based on projection data obtained by scanning the subject,
A counterweight disposed at a position facing the X-ray generation unit across the X-ray detection unit;
The relative positional relationship between the X-ray generation unit and the counterweight with respect to the X-ray detection unit is a positional relationship in which the center of gravity of the X-ray generation unit and the counterweight coincides with the center of rotation, The vertical components of the X-ray focal point of the X-ray generation unit from the reference plane formed by the straight line passing through the center of rotation and the center of the X-ray detection region of the X-ray detection unit and the body axis of the subject are different from each other. An X-ray CT system comprising: the X-ray generator and a moving means for moving the counterweight so that the first positional relationship and the second positional relationship can be obtained. The first positional relationship is a positional relationship in which the positions of the X-ray generation unit and the counterweight are on the straight line,
2. The X-ray CT system according to claim 1, wherein the second positional relationship is a positional relationship in which positions of the X-ray generation unit and the counterweight deviate from the straight line.   The moving means sets the position and orientation of the X-ray generation unit so that the fan angle of the X-ray beam from the X-ray generation unit is the same, and the irradiation range of the X-ray beam is within the detection region range of the X-ray detection unit. The X-ray CT system according to claim 1 or 2, wherein the X-ray generation unit is moved so as to have a position and an orientation that substantially match each other.   X-ray irradiation range control means for controlling the X-ray beam irradiation range so that the X-ray beam irradiation range from the X-ray generation unit substantially matches the X-ray detection region range of the X-ray detection unit. The X-ray CT system according to claim 1 or 2, further comprising:   The X-ray CT system according to claim 4, wherein the X-ray irradiation range control means includes a swing mechanism that changes the direction of the X-ray generation unit along a plane perpendicular to the axis of rotation.   6. The X-ray CT system according to claim 4, wherein the X-ray irradiation range control means includes a collimator that forms a slit that limits an irradiation range of the X-ray beam from the X-ray generation unit.   The said moving means can move the said X-ray generation part and the said counter weight continuously, maintaining the positional relationship in which the said gravity center corresponds to the center of the said rotation. The X-ray CT system according to any one of the above.   The moving means includes the X-ray detection unit on a plane in which an X-ray focal point of the X-ray generation unit is perpendicular to the X-ray focal point in the first positional relationship and includes the center of rotation. The X-ray CT system according to claim 7, wherein the X-ray generation unit is moved so as to move along a circumference of a circle passing through both end points.

Images