Computed tomography scanner

Abstract

To provide a computer tomography apparatus which can enhance angular resolution of a projection image without increasing a frame rate of a radiation detector and slowing down a rotational speed of an imaging unit.SOLUTION: A CT apparatus includes: a plurality of imaging units; a rotation mechanism; and a CPU. The rotation mechanism rotates the plurality of imaging units around a body axis of a subject while keeping an arrangement interval. An imaging control unit of the CPU controls operations of the plurality of imaging units and the rotation mechanism. An angle interval determined by a frame rate of the radiation detector and a rotational speed of the imaging unit and prescribing acquisition timing of the projection image based on the radiation is same in the plurality of imaging units. The plurality of imaging units has different phases in a rotation direction, and positions for acquiring the projection images of the plurality of imaging units are different by a preset angle less than the angle interval.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The technology disclosed herein relates to a computed tomography apparatus.

Background Art

[0002] Patent Document 1 describes a computed tomography apparatus (hereinafter referred to as a CT (Computed Tomography) apparatus) for imaging a subject in a supine position. In order to improve the efficiency of acquiring projection images that are the basis of tomographic images, the CT apparatus includes a plurality of imaging units each including a radiation source that emits radiation toward the subject and a radiation detector that detects the radiation transmitted through the subject. The plurality of imaging units are arranged at equal intervals on a gantry that rotates around the body axis of the subject, for example, three at every 120°. The radiation source irradiates a cone beam, and the radiation detector has a configuration in which a plurality of pixels are arranged in a two-dimensional matrix.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the CT apparatus described in Patent Document 1 in which a plurality of imaging units are arranged at equal intervals, in order to improve the angular resolution of projection images (to reduce the rotation angle of the imaging unit required to acquire projection images for one frame), it was necessary to increase the frame rate of the radiation detector and / or slow down the rotation speed of the imaging unit. However, there is a limit to the frame rate of the radiation detector. Also, slowing down the rotation speed of the imaging unit increases the time required for imaging. When imaging takes a long time, the burden on the subject increases, and the possibility of deterioration of the image quality of the tomographic image due to body movement of the subject also increases.

[0005] One embodiment of the technology of this disclosure provides a computed tomography apparatus capable of increasing the angular resolution of a projected image without increasing the frame rate of the radiation detector or slowing down the rotation speed of the imaging unit. [Means for solving the problem]

[0006] The computed tomography apparatus of this disclosure comprises multiple imaging units, each consisting of a radiation source that emits cone-shaped radiation toward a subject and a radiation detector having multiple pixels arranged in two dimensions to detect radiation that has passed through the subject; a rotation mechanism that rotates the multiple imaging units around the body axis of the subject while maintaining the spacing between them; and a processor that controls the operation of the multiple imaging units and the rotation mechanism. The angular interval, which is determined by the frame rate of the radiation detector and the rotation speed of the imaging units, is the same for all multiple imaging units, the rotational phases of the multiple imaging units are different, and the positions for acquiring the projection images of the multiple imaging units differ by a set angle less than the angular interval.

[0007] The set angle is preferably an angle that divides the angle interval into equal parts.

[0008] The processor preferably compensates for deviations in the set angle, including manufacturing errors, by varying the timing of radiation irradiation from the radiation source.

[0009] Preferably, the processor irradiates radiation from all of the multiple imaging units during a pre-set first period, and outputs projected images from all of the multiple imaging units during a pre-set second period following the first period.

[0010] Preferably, the processor irradiates multiple imaging units with radiation at the same time during the first period, and outputs projected images from multiple imaging units at the same time during the second period.

[0011] The first period is preferably longer than the irradiation time from the start to the end of radiation irradiation.

[0012] The processor preferably irradiates radiation from multiple imaging units at different timings within the first period without overlap.

[0013] It is preferable that the multiple imaging units are positioned at angles greater than 90° apart when viewed from the axis of rotation of the multiple imaging units.

[0014] When viewed from the axis of rotation of multiple imaging units, it is preferable that the radiation detectors are positioned at an offset position that is a predetermined angle different from the reference position directly facing the radiation source.

[0015] Preferably, the multiple imaging units are held in a frame, the subject is positioned within the frame, and when viewed from the axis of rotation of the multiple imaging units, the radiation source is located outside the frame and the radiation detector is located inside the frame.

[0016] The subject is preferably positioned in either a standing or sitting position. [Effects of the Invention]

[0017] The technology of this disclosure provides a computed tomography system that can improve the angular resolution of projected images without increasing the frame rate of the radiation detector or slowing down the rotation speed of the imaging unit. [Brief explanation of the drawing]

[0018] [Figure 1] This is a front view of a CT scanner. [Figure 2] This is a side view of a CT scanner. [Figure 3] This diagram shows the configuration of the first and second imaging units. [Figure 4]This is a front view of a CT apparatus showing a state in which a subject in a sitting position on a wheelchair is positioned. [Figure 5] This is a diagram showing an elevating mechanism. [Figure 6] This is a diagram showing a rotating mechanism. [Figure 7] This is a perspective view showing a radiation source, a radiation detector, and radiation. [Figure 8] This is a diagram showing the arrangement positions of the first imaging unit and the second imaging unit. [Figure 9] This is a diagram showing the reference position and offset position of a radiation detector. [Figure 10] This is a block diagram showing a processing unit of a CPU of a control device. [Figure 11] This is a diagram showing the acquisition positions of projection images of the first imaging unit and the second imaging unit. [Figure 12] This is a diagram showing the acquisition positions of projection images of the first imaging unit, the second imaging unit, and all imaging units. [Figure 13] This is a timing chart showing the irradiation timing of radiation from a radiation source and the readout timing of a projection image of a radiation detector. [Figure 14] This is a timing chart showing details of the readout operation of a projection image of a radiation detector. [Figure 15] This is a flowchart showing an imaging procedure by a CT apparatus. [Figure 16] This is a diagram showing the acquisition position of a projection image of an imaging unit when the acquisition positions of projection images of the first imaging unit and the second imaging unit are not made different by a set angle. [Figure 17] This is a diagram for explaining the effect of arranging the second imaging unit at a position separated by an angle greater than 90° from the first imaging unit. [Figure 18] This is a diagram showing a case where the second imaging unit is arranged at a position separated by 125° from the first imaging unit. [Figure 19] This is a diagram showing the effective field of view when a radiation detector is at a reference position. [Figure 20]This diagram shows the effective field of view when the radiation detector is in an offset position. [Figure 21] This figure shows another example of the acquisition positions for the projected images of the first and second imaging units. [Figure 22] This figure shows another example of the acquisition positions for the projected images of the first imaging unit, the second imaging unit, and all imaging units. [Figure 23] This figure shows the case where the set angle is off due to manufacturing tolerances. [Figure 24] This figure shows a method of correcting deviations in the set angle, including manufacturing errors, by varying the timing of radiation irradiation from the radiation source. [Figure 25] This figure shows the case where the timing of radiation exposure from the second radiation source is accelerated. [Figure 26] This diagram illustrates the effect of making the first period longer than the total irradiation time from the start to the end of radiation exposure. [Figure 27] This figure shows a configuration in which radiation is irradiated from multiple imaging units at different times within the first period without overlap. [Figure 28] This diagram shows an example with three shooting units. [Figure 29] This diagram shows the configuration of the first imaging unit, the second imaging unit, and the third imaging unit. [Figure 30] This diagram shows the acquisition positions of the projected images from the first imaging unit, the second imaging unit, and the third imaging unit. [Figure 31] This graph shows the time-dependent change in the frame's rotation speed. [Modes for carrying out the invention]

[0019] As an example, as shown in Figure 1, the CT scanner 10 is a device for obtaining tomographic images of a subject S, and consists of a main unit 11 and a control device 12. The main unit 11 is installed, for example, in the imaging room of a medical facility. The control device 12 is installed, for example, in a control room adjacent to the imaging room. The control device 12 is a desktop personal computer, a notebook personal computer, or a tablet terminal. The control device 12 is operated by an operator of the CT scanner 10, such as a radiological technologist.

[0020] As an example, as shown in Figure 2, the device body 11 comprises a stage 13, three support columns 14A, 14B, and 14C, and a top plate 15. The stage 13 is, for example, an octagonal flat plate (see Figure 6). Casters 16 for transport are attached to the four corners of the underside of the stage 13. The casters 16 are equipped with a rotation locking mechanism (not shown), and after the device body 11 is installed in the installation location, the rotation locking mechanism can be activated to lock the rotation of the casters 16. Alternatively, the casters 16 are removable from the stage 13, and the casters 16 can be removed after the device body 11 is installed in the installation location.

[0021] The support columns 14A to 14C have a rectangular plate shape and are erected at the four corners of the surface of the stage 13. Support columns 14A and 14C are located on the left and right sides of the front of the device body 11 (left and right in front of the subject S). Support column 14B is located in the center of the rear side of the device body 11 (behind the subject S). The top plate 15 is attached to the upper ends of the support columns 14A to 14C. The top plate 15 is, for example, a flat plate with an octagonal shape that follows the shape of the stage 13 (see Figure 6). The top plate 15 has a circular cutout in the center and is C-shaped with a cutout in the front part of the device body 11 between the support columns 14A and 14C. In the following description, unless there is a need to distinguish them, support columns 14A to 14C will be collectively referred to as support column 14.

[0022] A connecting member 17A is connected to column 14A, a connecting member 17B is connected to column 14B, and a connecting member 17C is connected to column 14C. A frame 18 is connected to connecting members 17A to 17C. In other words, columns 14A to 14C and the frame 18 are interconnected via connecting members 17A to 17C. In the following explanation, unless otherwise specified, connecting members 17A to 17C will be collectively referred to as connecting member 17.

[0023] Frame 18 is circular in shape. The subject S is positioned at the center C (see Figure 6) of this circular frame 18. Figures 1 and 2 show the positioning of the subject S in a standing position with both hands raised above his head.

[0024] The support column 14 is provided with a guide rail (not shown) into which the connecting member 17 is fitted. The connecting member 17, and thus the frame 18, can move up and down vertically along the guide rail. That is, the support column 14 holds the frame 18 so that it can move up and down vertically. The frame 18 can also rotate around the body axis of the subject S, with the axis passing vertically through its center C as the axis of rotation RA (see Figure 3). That is, the support columns 14A to 14C hold the frame 18 so that it can rotate around the body axis of the subject S. Hereinafter, the center C may be referred to as the axis of rotation C. The arrow indicated by the symbol RAD indicates the axis direction of rotation of the frame 18. The axis direction RAD is parallel to the vertical direction. Here, the body axis is the axis that passes through the subject S from the top of the head to the tail (anus). When the subject S is in a standing or sitting position (see Figure 4), the body axis is parallel to the vertical direction and the axis direction RAD. "Parallel" refers not only to perfect parallelism, but also to parallelism that includes errors that are generally acceptable in the art to which the disclosed technology belongs, and that do not contradict the spirit of the disclosed technology. Furthermore, the height position of the frame 18 may be changed by extending or retracting the support column 14.

[0025] Frame 18 is equipped with a first radiation source 201 and a second radiation source 202 that irradiate the subject S with radiation R (see Figure 7), such as X-rays and gamma rays, and a first radiation detector 211 and a second radiation detector 212 that detect the radiation R that has passed through the subject S. The first radiation source 201 and the second radiation source 202 are box-shaped, while the first radiation detector 211 and the second radiation detector 212 are rectangular plates.

[0026] As an example, as shown in Figure 3, the first radiation source 201 and the first radiation detector 211 constitute the first imaging unit 301. The second radiation source 202 and the second radiation detector 212 constitute the second imaging unit 302. In other words, the CT scanner 10 has two imaging units: the first imaging unit 301 and the second imaging unit 302. In the following explanation, unless otherwise specified, the first radiation source 201 and the second radiation source 202 will be collectively referred to as radiation source 20. Similarly, the first radiation detector 211 and the second radiation detector 212 will be collectively referred to as radiation detector 21. Furthermore, the first imaging unit 301 and the second imaging unit 302 will be collectively referred to as imaging unit 30.

[0027] Returning to Figures 1 and 2, a screw shaft 22A is provided on support column 14A, a screw shaft 22B is provided on support column 14B, and a screw shaft 22C is provided on support column 14C. The screw shafts 22A to 22C have a height that reaches from the stage 13 to the top plate 15. As the screw shafts 22A to 22C rotate, the connecting members 17A to 17C, and consequently the frame 18, move up and down in the rotation axis direction RAD. In the following description, unless there is a need to distinguish between them, the screw shafts 22A to 22C will be collectively referred to as screw shaft 22.

[0028] A touch panel display 25 is attached to the support column 14A via a movable arm 24. The touch panel display 25 is operated by an operator. The touch panel display 25 also displays various information to the operator.

[0029] Figures 1 and 2 show an example in which a subject S in a standing position with both hands raised above his head is positioned within the frame 18, but this is not the only example. As shown in Figure 4, the CT scanner 10 can also position and photograph a subject S in a seated position in a wheelchair 32 within the frame 18. In both the standing subject S and the seated subject S in the wheelchair 32, the subject S is positioned so that its front faces the support columns 14A and 14C and its back faces the support column 14B.

[0030] As an example, as shown in Figure 5, the lifting mechanism 35 that raises and lowers the connecting member 17, and consequently the frame 18, in the rotation axis direction RAD, is a ball screw mechanism consisting of the aforementioned screw shaft 22, a ball-filled nut 36 that screws onto the screw shaft 22, and a lifting motor 37 that rotates the screw shaft 22. The lifting motor 37 is mounted on the back surface of the stage 13. The height position of the frame 18 is determined from the rotation direction and rotation speed of the lifting motor 37.

[0031] The connecting member 17 has a first connecting portion 38 that connects to the frame 18 and a second connecting portion 39 that connects to the support column 14. The first connecting portion 38 protrudes toward the frame 18, and the second connecting portion 39 protrudes toward the support column 14, so the connecting member 17 as a whole is Z-shaped. A bearing 40 is built into the first connecting portion 38. The bearing 40 is fitted into a guide groove 41 (see also Figure 1, etc.) formed around the entire circumference of the frame 18. The bearing 40 rolls as the frame 18 rotates. A nut 36 is built into the second connecting portion 39.

[0032] As an example, as shown in Figure 6, the rotation mechanism 45 that rotates the frame 18, and by extension the shooting unit 30, around the body axis of the subject S, consists of a rotating belt 46 wrapped around the entire circumference of the frame 18, a rotating motor 47, and a potentiometer 48, etc. The rotating motor 47 is built into the connecting member 17B and is connected to a part of the rotating belt 46 drawn out from the frame 18 via a pulley 49. Driven by this rotating motor 47, the frame 18, and by extension the shooting unit 30, rotates in a clockwise (right) direction CW and a counterclockwise (left) direction CCW. The rotation speed of the shooting unit 30 is, for example, 36° / sec (seconds). In this case, the time required for the shooting unit 30 to complete one rotation (360° rotation) is 10 seconds. The clockwise direction CW and the counterclockwise direction CCW are examples of "directions of rotation" related to the technology of this disclosure.

[0033] The potentiometer 48 is built into the connecting member 17C and is connected to a portion of the rotating belt 46 that extends from the frame 18 via a pulley 50. The potentiometer 48 has a variable resistor whose resistance value changes depending on the rotational position of the frame 18 and outputs a voltage signal corresponding to the rotational position of the frame 18. The rotational position of the frame 18 is determined by this voltage signal from the potentiometer 48. Note that in Figure 6, the photographic unit 30 is omitted from the illustration to avoid complexity.

[0034] As an example, as shown in Figure 7, the radiation source 20 incorporates a radiation tube 55. The radiation tube 55 emits radiation R. Although not shown in the figure, the radiation source 20 also incorporates a field lamp that emits, for example, orange visible light to indicate the irradiation field of radiation R.

[0035] The radiation source 20 has a field limiter 56. The field limiter 56, also called a collimator, defines the field of radiation R directed to the radiation detector 21. The field limiter 56 has an entrance aperture through which radiation R from the radiation tube 55 enters, and an exit aperture through which radiation R exits. Near the exit aperture, for example, four shielding plates are provided. The shielding plates are made of a material that shields radiation R, such as lead. The shielding plates are arranged on each side of a rectangle, in other words, in a checkered pattern, forming a rectangular irradiation aperture that transmits radiation R. The field limiter 56 changes the size of the irradiation aperture by changing the position of each shielding plate, thereby changing the field of radiation R directed to the radiation detector 21. Due to the action of this field limiter 56, a pyramidal area of ​​radiation R is irradiated from the radiation source 20. The radiation angle θ of radiation R when viewed from the rotation axis direction RAD is, for example, 10° to 30°. The radiation angle θ is also called the cone angle.

[0036] The radiation detector 21 consists of, for example, a scintillator that converts radiation R into visible light, a TFT (Thin Film Transistor) substrate having a detection surface 58 in which multiple pixels 57 that detect radiation R by accumulating charge corresponding to visible light are arranged in a two-dimensional matrix, a signal processing circuit that outputs a voltage signal corresponding to the charge as a projected image, and a housing that houses these components. The detection surface 58 has a size of, for example, 430 mm × 430 mm (17 inches). The SID (Source To Image Distance), which is the distance from the focal point of radiation R (the point from which radiation R is emitted in the radiation tube 55) to the detection surface 58, is, for example, 1200 mm. Note that the radiation detector 21 may be of a type that directly detects radiation R instead of using visible light converted from radiation R.

[0037] The frame rate of the radiation detector 21 is, for example, 15 fps (frames per second). If the rotation speed of the imaging unit 30 is 36° / sec as described above, the radiation detector 21 outputs a projected image 125 (see Figure 13) every 36 / 15 = 2.4° (2.4° / frame). This 2.4° is an example of the "angle interval" related to the technology of this disclosure. The angle interval is determined by the frame rate of the radiation detector 21 and the rotation speed of the imaging unit 30, and defines the timing of acquisition of the projected image 125. The angle interval is the same for the first imaging unit 301 and the second imaging unit 302.

[0038] As an example, as shown in Figure 8, when viewed from the rotation axis direction RAD, if the position of the first radiation source 201 is set to 0°, and the positions in the counterclockwise direction CCW are set to 90°, 180°, and 270°, then the second radiation source 202 is positioned at an angle φ greater than 90° from the first radiation source 201. The first radiation detector 211 and the second radiation detector 212 are positioned according to the positions of the first radiation source 201 and the second radiation source 202. For this reason, the first imaging unit 301 and the second imaging unit 302 have different phases in the rotation direction. In this example, φ is 121.2°.

[0039] The first radiation R1, which is radiation R from the first radiation source 201, and the second radiation R2, which is radiation R from the second radiation source 202, intersect near the rotation center C of the frame 18. The first central axis RCA1 of the radiation beam of the first radiation R1 intersects perpendicularly with the first center point CS1 of the detection surface 58 of the first radiation detector 211. Similarly, the second central axis RCA2 of the radiation beam of the second radiation R2 intersects perpendicularly with the second center point CS2 of the detection surface 58 of the second radiation detector 212. In the following explanation, unless otherwise specified, the first central axis RCA1 and the second central axis RCA2 will be collectively referred to as the central axis RCA. Also, the first center point CS1 and the second center point CS2 will be collectively referred to as the center point CS.

[0040] The first radiation source 201 and the second radiation source 202 are mounted to the frame 18 by attachments 60A and 60B. Similarly, the first radiation detector 211 and the second radiation detector 212 are mounted to the frame 18 by attachments 61A and 61B. These attachments 60A, 60B, 61A, and 61B are secured to the frame 18 with bolts 62. When viewed from the rotation axis direction RAD, the radiation sources 20 are located on the outside of the frame 18, and the radiation detectors 21 are located on the inside of the frame 18.

[0041] The frame 18 is formed by joining two semi-circular members by welding or other means. The attachment 60A is attached so as to cover one of the two opposing joints 63 of the frame 18. By attaching the attachment 60A to the joint 63 in this way, the joint 63, which is a mechanically weak part, can be reinforced with the attachment 60A.

[0042] As an example, as shown in Figure 9, when viewed from the rotation axis direction RAD, the radiation detector 21 is positioned at an offset position that is a predetermined angle different from the reference position directly facing the radiation source 20. Here, the reference position is the position where the central axis RCA of the radiation beam R when the emission aperture of the irradiation field limiter 56 is opened to its maximum extent intersects perpendicularly with the center point CS of the detection surface 58 of the radiation detector 21. In this example, the predetermined angle of the offset position is half the radiation angle θ (θ / 2).

[0043] As an example, as shown in Figure 10, the computer constituting the control device 12 includes storage 95, memory 96, CPU (Central Processing Unit) 97, display 98, and input devices 99, etc.

[0044] Storage 95 is a hard disk drive built into the computer constituting the control unit 12, or connected via cable or network. Alternatively, storage 95 is a disk array consisting of multiple hard disk drives installed in series. Storage 95 stores control programs such as the operating system, various application programs, and various data associated with these programs. A solid-state drive may be used instead of a hard disk drive.

[0045] Memory 96 is work memory for the CPU 97 to execute processing. The CPU 97 loads the program stored in storage 95 into memory 96 and executes processing according to the program. In this way, the CPU 97 comprehensively controls all parts of the computer. CPU 97 is an example of a "processor" related to the technology of this disclosure. Note that memory 96 may be built into the CPU 97.

[0046] The display 98 displays various screens. These screens are equipped with GUI (Graphical User Interface) operation functions. The computer constituting the control unit 12 receives operation instructions from the input device 99 through the various screens. The input device 99 includes a keyboard, mouse, touch panel, and microphone for voice input.

[0047] The operating program 105 is stored in storage 95. The operating program 105 is an application program that enables the computer to function as a control device 12. In addition to the operating program 105, the storage 95 also stores the irradiation condition table 106 and the order-specific irradiation condition information 107, etc.

[0048] When the operation program 105 is started, the CPU 97 of the control device 12 works in cooperation with the memory 96 and other components to function as the reception unit 110, the read / write (hereinafter abbreviated as RW (Read Write)) control unit 111, the shooting control unit 112, the image processing unit 113, and the display control unit 114.

[0049] The reception unit 110 receives various operation instructions input by the operator via the touch panel display 25 and input device 99 of the main unit 11 of the device. For example, the reception unit 110 receives the shooting menu 116. The reception unit 110 outputs the shooting menu 116 to the RW control unit 111.

[0050] The RW control unit 111 receives the imaging menu 116 from the reception unit 110. The RW control unit 111 reads the radiation R irradiation conditions 117 corresponding to the received imaging menu 116 from the irradiation condition table 106. The RW control unit 111 writes the irradiation conditions 117 read from the irradiation condition table 106 to the order-specific irradiation condition information 107.

[0051] The imaging control unit 112 controls the operation of the radiation source 20 (radiation tube 55 and irradiation field limiter 56), the lifting mechanism 35 (lifting motor 37), the rotation mechanism 45 (rotation motor 47 and potentiometer 48), and the radiation detector 21. The imaging control unit 112 reads the irradiation conditions 117 from the order-specific irradiation condition information 107. The imaging control unit 112 drives the irradiation field limiter 56 according to the irradiation conditions 117 to adjust the irradiation field. The control device 12 receives an imaging instruction from the operator through an irradiation switch (not shown). When an imaging instruction is received, the imaging control unit 112 drives the radiation tube 55 according to the irradiation conditions 117 and generates radiation R from the radiation tube 55. The imaging control unit 112 outputs the projection image 125 detected by the radiation detector 21 due to the irradiation of radiation R from the radiation detector 21 to the image processing unit 113.

[0052] The image processing unit 113 receives the projection image 125 from the radiation detector 21. The image processing unit 113 performs various image processing operations on the projection image 125. The image processing unit 113 also performs reconstruction processing on multiple processed projection images 125 to generate a tomographic image. The image processing unit 113 outputs the tomographic image to the display control unit 114.

[0053] The display control unit 114 controls the display of various information on the touch panel display 25 and the display 98. The display control unit 114 receives tomographic images from the image processing unit 113. The display control unit 114 displays the tomographic images on the touch panel display 25 and the display 98.

[0054] The imaging menu 116 includes, for example, the imaging order ID (Identification Data) and the imaging procedure. The imaging order ID is identification information for the imaging order issued by a physician who performs diagnosis using tomographic images. The imaging procedure consists of the posture of the subject S, such as standing or sitting, the imaging area, such as the head, neck, or entire spine, and the attributes of the subject S, such as adult male, adult female, or child.

[0055] The imaging order is transmitted from the Radiology Information System (RIS), which is not shown in the diagram, to the control device 12. The control device 12, under the control of the display control unit 114, displays a list of imaging orders on the display 98. The operator views the list of imaging orders and confirms their contents. The control device 12 then displays the imaging menu corresponding to the imaging order on the display 98 in a configurable format. The operator selects and inputs the imaging menu according to the imaging order by operating the input device 99.

[0056] The irradiation condition table 106 contains irradiation conditions 117 for each imaging procedure. Irradiation conditions 117 include the tube voltage and tube current applied to the radiation tube 55, and the irradiation time of radiation R. Irradiation conditions 117 also include the size of the irradiation field. Irradiation conditions 117 can be finely adjusted by the operator. Alternatively, the tube current-irradiation time product, the so-called mAs value, may be used as irradiation condition 117 instead of tube current and irradiation time.

[0057] The order-specific irradiation condition information 107 contains irradiation conditions 117 for each shooting order ID. The shooting control unit 112 reads the irradiation conditions 117 corresponding to the shooting order ID of the next shooting from the order-specific irradiation condition information 107 and controls the operation of each part according to the read irradiation conditions 117.

[0058] As an example, as shown in Figure 11, the first imaging unit 301 uses 0°, where the first radiation source 201 is located, as its rotation start and end positions, and outputs projected images 125 at 2.4° intervals: 2.4°, 4.8°, 7.2°, ..., 117.6°, 120°, 122.4°, ..., 352.8°, 355.2°, and 357.6°. The second imaging unit 302 uses 121.2°, where the second radiation source 202 is located, as its rotation start and end positions, and outputs projected images 125 at 123.6°, ..., 354°, 356.4°, 358.8°, 1.2° (361.2°), 3.6° (363.6°), 6° (366°), ..., also at 2.4° intervals. The rotation end position is, strictly speaking, the position that makes an angle θ in the counterclockwise direction (CCW) from 0° and 121.2°.

[0059] Because the second radiation source 202 is positioned at 121.2°, the acquisition position of the projected image 125 differs by 1.2°, which is half of the angular interval of 2.4°, between the first imaging unit 301 and the second imaging unit 302. In other words, the first imaging unit 301 and the second imaging unit 302 are arranged so that the acquisition position of their respective projected images 125 differs by 1.2°. Therefore, the second imaging unit 302 can acquire projected images 125 at positions that are not captured by the first imaging unit 301, such as 1.2° between 0° and 2.4°, 3.6° between 2.4° and 4.8°, ..., 354° between 352.8° and 355.2°, and 356.4° between 355.2° and 357.6°. In short, positions that are not captured by the first imaging unit 301 can be interpolated and captured by the second imaging unit 302.

[0060] 1.2° is an example of a "set angle" relating to the technology of this disclosure. The set angle is an angle less than the angle interval, and in this case, it is the angle obtained by dividing the angle interval into two equal parts. Note that "equal division" refers not only to a perfect division, but also to an error that is generally acceptable in the art to which the technology of this disclosure belongs, and that does not contradict the spirit of the technology of this disclosure. The acceptable error is an error that is considered not to cause problems in the reconstruction process when generating a tomographic image by applying a reconstruction process to the projected image 125. Specifically, it is an error within the size of one pixel 57 (e.g., 0.15 mm). Note that when binning readout is performed to read out the charges of multiple adjacent pixels 57 together, the error will be within the size of multiple pixels 57. For example, when binning readout is performed to read out the charges of four 2x2 pixels 57 together, the error will be within the size of two pixels 57 (e.g., 0.15 x 2 = 0.3 mm).

[0061] As an example, as shown in Figure 12, the sector indicated by reference numeral 120 represents a portion of the acquisition position of the projected image 125 of the first imaging unit 301. On the other hand, the sector indicated by reference numeral 121 represents a portion of the acquisition position of the projected image 125 of the second imaging unit 302. The sector indicated by reference numeral 122 represents a portion of the acquisition position of the projected image 125 of all imaging units 30, including the first imaging unit 301 and the second imaging unit 302. Since the acquisition positions of the projected image 125 of the first imaging unit 301 and the second imaging unit 302 differ by 1.2° of the set angle, the number of acquisition positions of the projected image 125 of all imaging units 30 is twice the number of acquisition positions of the projected image 125 of one imaging unit 30. Therefore, the frame rate of the radiation detector 21 is effectively 30 fps.

[0062] Figure 13 is an example of a timing chart showing the irradiation timing of radiation R from the radiation source 20 and the readout timing of the projected image 125 from the radiation detector 21. Prior to imaging, the imaging control unit 112 causes the first radiation detector 211 and the second radiation detector 212 to perform a readout operation. This readout operation is an operation to sweep out unwanted charges such as dark charge accumulated in the pixels 57 during standby, and is also called a reset operation.

[0063] After causing the first radiation detector 211 and the second radiation detector 212 to perform a readout operation to sweep out unwanted charges, the imaging control unit 112 irradiates the first radiation R1 and the second radiation R2 from the first radiation source 201 and the second radiation source 202 under the same irradiation conditions during a preset first period P1. The imaging control unit 112 also causes the first radiation detector 211 and the second radiation detector 212 to perform an accumulation operation during the first period P1. The accumulation operation is the operation of accumulating charges based on the first radiation R1 and the second radiation R2 in the pixel 57. The length of the first period P1 is set to the maximum irradiation time of radiation R.

[0064] During the subsequent second period P2, the imaging control unit 112 causes the first radiation detector 211 and the second radiation detector 212 to perform readout operations and output the projected image 125 from the first radiation detector 211 and the second radiation detector 212. The length of the second period P2 is set to the time required for the readout operation.

[0065] In the first period P1, the imaging control unit 112 irradiates the first radiation R1 and the second radiation R2 from the first radiation source 201 and the second radiation source 202 at the same timing. In the second period P2, the imaging control unit 112 outputs the projected image 125 from the first radiation detector 211 and the second radiation detector 212 at the same timing. The term "same" in "same timing" refers not only to exact identical timing, but also to errors that are generally acceptable in the art to which the present invention belongs, and that do not contradict the spirit of the present invention. Here, since the imaging unit 30 is rotating, there is a slight difference in the position of the imaging unit 30 between the start and end of radiation irradiation, but the position of the imaging unit 30 at the start of radiation irradiation is used as the acquisition position for the projected image 125. Note that 0°, 1.2°, 2.4°, 3.6°, 4.8°, ... 1.2° The rotation of frame 18 may be temporarily stopped at each angular interval, and then radiation R may be irradiated from radiation source 20.

[0066] Figure 14 shows the details of the readout operation of the projection image 125 of the radiation detector 21 during the second period P2. The radiation detector 21 reads out the charge accumulated in the pixels 57 by the accumulation operation, one row at a time, from the first row to the Nth row (where N is a natural number greater than or equal to 2, for example, N=2836). The period from the start of reading out the first row of pixels 57 to the end of reading out the Nth row of pixels 57 is the readout operation period shown in Figure 13. Similarly, the period from the start of accumulation in the Nth row of pixels 57 to the end of accumulation in the first row of pixels 57 is the accumulation operation period shown in Figure 13. The start and end timings of the accumulation operation differ for each row, but the time spent on the accumulation operation (charge accumulation time) is the same for each row.

[0067] Next, the imaging procedure using the CT scanner 10 will be explained using the flowchart shown in Figure 15 as an example. First, the subject S is guided into the main unit 11 by the operator (step ST100). Then, under the control of the imaging control unit 112, the lifting mechanism 35 is operated and the frame 18 is moved to a height position according to the imaging menu 116 (step ST110). After that, the subject S is positioned by the operator (step ST120). At this time, if necessary, the irradiation field lamp built into the radiation source 20 is turned on and the operator determines whether the height position of the frame 18 and the positioning of the subject S are appropriate for imaging. If the height position of the frame 18 and the positioning of the subject S are not appropriate for imaging, the operator adjusts the height position of the frame 18 or readjusts the position of the subject S. If the height position of the frame 18 and the positioning of the subject S are appropriate for imaging, the operator inputs an imaging instruction through the irradiation switch. The imaging instruction is received by the reception unit 110 (YES in step ST130). This allows the imaging unit 30 to take an image (step ST140).

[0068] During imaging, the rotation mechanism 45 is operated under the control of the imaging control unit 112, and the frame 18 is rotated 360°, for example, in a counterclockwise direction (CCW). Meanwhile, under the control of the imaging control unit 112, radiation R is continuously irradiated from the radiation source 20 under the same irradiation conditions, and a projected image 125 is output from the radiation detector 21 each time. More specifically, the first radiation R1 and the second radiation R2 are irradiated from the first radiation source 201 and the second radiation source 202 at the same time, and the projected image 125 is output from the first radiation detector 211 and the second radiation detector 212 at the same time.

[0069] After the imaging is completed, the image processing unit 113 generates a tomographic image from the obtained projection image 125 (step ST150). Then, under the control of the display control unit 114, the tomographic image is displayed on the display 98 or the like for the operator to view (step ST150).

[0070] As described above, the CT scanner 10 comprises multiple imaging units 30, a rotation mechanism 45, and a CPU 97. Each imaging unit 30 consists of a radiation source 20 that emits pyramidal radiation R toward the subject S, and a radiation detector 21 in which multiple pixels 57 that detect radiation R transmitted through the subject S are arranged in two dimensions. The rotation mechanism 45 rotates the multiple imaging units 30 around the body axis of the subject S while maintaining their spacing. The imaging control unit 112 of the CPU 97 controls the operation of the multiple imaging units 30 and the rotation mechanism 45. The angular interval, which is determined by the frame rate of the radiation detector 21 and the rotation speed of the imaging units 30, and defines the timing of acquiring the projection image 125 based on the radiation R, is the same for all multiple imaging units 30. The multiple imaging units 30 have different phases in the rotation direction, and the positions where the projection image 125 is acquired by the multiple imaging units 30 differ by a set angle less than the angular interval. Therefore, it is possible to increase the angular resolution of the projected image 125 without increasing the frame rate of the radiation detector 21 or slowing down the rotation speed of the imaging unit 30.

[0071] Figure 16 shows the case where the position of the second radiation source 202 is 120° instead of 121.2° as in this example, that is, the acquisition positions of the projected images 125 from the multiple imaging units 30 are not differed by the set angle. In this case, as shown by sectors 120 and 121, the acquisition positions of the projected images 125 from the first imaging unit 301 and the second imaging unit 302 are the same. Therefore, the acquisition positions of the projected images 125 from all imaging units 30 are halved compared to the case in this example shown in Figure 12, as shown by sector 122. This confirms that the angular resolution of the projected image 125 can be increased according to the technology of this disclosure.

[0072] As shown in Figure 7, the radiation source 20 emits pyramidal radiation R, and the radiation detector 21 has a configuration in which multiple pixels 57 for detecting radiation R are arranged in two dimensions. Therefore, compared to conventional CT scanners that emit fan-shaped radiation R from the radiation source and detect radiation R with a radiation detector whose pixels are arranged in one dimension, imaging can be completed in a shorter time. Note that conical radiation R may be emitted instead of pyramidal radiation R.

[0073] The set angle is an angle that divides the angular interval into equal parts. Therefore, there is no angular bias in the acquisition position of the projected image 125, making it easier to generate a tomographic image from the projected image 125.

[0074] As shown in Figure 13, the imaging control unit 112 irradiates radiation R from all of the imaging units 30 during a preset first period P1, and outputs a projection image 125 from all of the imaging units 30 during a preset second period P2 following the first period P1. Therefore, imaging can be completed in a shorter time compared to when the imaging units 30 are made to take images sequentially. The burden on the subject S can be reduced, and the risk of deterioration of the image quality of the tomographic image due to the movement of the subject S can be reduced.

[0075] Furthermore, as shown in Figure 13, the imaging control unit 112 irradiates multiple imaging units 30 with radiation R at the same timing during the first period P1, and outputs projected images 125 from multiple imaging units 30 at the same timing during the second period P2. As a result, projected images 125 with equivalent image quality can be acquired from multiple imaging units 30. In addition, the occurrence of band-shaped artifacts in the projected image 125, which will be described later in Figure 25, can be suppressed.

[0076] As shown in Figure 8, the multiple imaging units 30 are positioned at angles greater than 90° apart when viewed from the rotation axis RAD. Therefore, as an example shown in Figure 17, the second radiation detector 212 can be positioned to avoid the region BA which is particularly strongly affected by the backscattered radiation of the first radiation R1.

[0077] If the angle φ is 90° or less, for example, if the angle φ = 90°, the edge of the second radiation detector 212 will fall into region BA, as shown by the dashed line. In this example, since the first radiation R1 and the second radiation R2 are irradiated at the same time, the projected image 125 obtained by the second radiation detector 212 will contain noise from the backscattered radiation of the first radiation R1. However, in this example, since the multiple imaging units 30 are positioned at angles φ greater than 90° apart, the risk of the backscattered radiation of the first radiation R1 appearing as noise in the projected image 125 obtained by the second radiation detector 212 can be reduced. The backscattered radiation referred to here is the scattered radiation caused by the arrangement of the radiation source 20 and the radiation detector 21. However, by positioning the radiation detector 212 in a location that avoids region BA, the influence of scattered radiation caused by the subject S can also be reduced.

[0078] Furthermore, the effects of scattered radiation may be reduced by providing a grid in front of the radiation detector 21. Alternatively, a technique may be applied, such as the one described in Japanese Patent No. 6006193, which achieves the same image quality improvement effect as when a grid is used, through image processing without actually using a grid.

[0079] There is an upper limit to the angle φ. For example, as shown in Figure 18 when the angle φ is 125°, the edge of the second radiation detector 212 must not be visible in the projection image 125 obtained by the first imaging unit 301. For this reason, it is preferable that the angle φ is greater than 90° and less than or equal to the limit angle at which the edge of the second radiation detector 212 is visible in the projection image 125 obtained by the first imaging unit 301. Note that φ is not limited to the example of 121.2°, but may also be 91.2°, etc.

[0080] By reducing the size of the radiation detector 21, it is possible to avoid the radiation detector 21 appearing in the projected image, as shown in Figure 18, even if the angle φ is increased. However, the effective field of view sFOV (Scan Field Of View, see Figure 19) will decrease as the size of the radiation detector 21 is reduced. Alternatively, the angle φ can be increased by increasing the rotation radius of the radiation detector 21 (the distance between the rotation center C and the center point CS of the detection surface 58 of the radiation detector 21). However, in this case as well, the effective field of view sFOV will decrease because the radiation detector 21 moves away from the subject S. For this reason, it is preferable to ensure a relatively wide effective field of view sFOV by setting the ratio of the rotation radius of the radiation source 20 (the distance between the rotation center C and the focal point of the radiation R of the radiation source 20) to the rotation radius of the radiation detector 21 to approximately 2:1 (for example, rotation radius of the radiation source 20 = 800 mm, rotation radius of the radiation detector 21 = 400 mm).

[0081] Alternatively, by increasing the size of the frame 18 and lengthening the SID, the angle φ can be increased without moving the radiation detector 21 away from the subject S. However, this requires a high-power rotation motor 47 to match the larger and heavier frame 18, and thicker support columns 14 to increase rigidity. Also, the power of the radiation R needs to be increased as the SID lengthens. For these reasons, it is preferable that the angle φ be around 120°, as in this example.

[0082] Here, as shown in Figure 19, if the radiation detector 21 is positioned at the reference position, the scanning area does not change with a 360° rotation, so the effective field of view (sFOV) remains relatively small, as indicated by the hatching. In contrast, as shown in Figure 20, if the radiation detector 21 is positioned at an offset position, the scanning area changes with a 360° rotation, so the effective field of view (sFOV) becomes relatively large, as indicated by the hatching. Therefore, as shown in Figure 9, when viewed from the rotation axis direction RAD, by positioning the radiation detector 21 at an offset position that is a predetermined angle different from the reference position directly facing the radiation source 20, the effective field of view (sFOV) can be widened compared to when the radiation detector 21 is positioned at the reference position. Also, the angle φ can be made somewhat larger compared to when the radiation detector 21 is positioned at the reference position.

[0083] Multiple imaging units 30 are held within a frame 18, and the subject S is positioned within the frame 18. As shown in Figure 8, when viewed from the RAD in the rotation axis direction, the radiation source 20 is positioned outside the frame 18, and the radiation detector 21 is positioned inside the frame 18. The effective field of view sFOV increases as the radiation source 20 moves away from the subject S and the radiation detector 21 moves closer to the subject S. Therefore, by positioning the radiation source 20 outside the frame 18 in which the subject S is positioned and the radiation detector 21 inside, the effective field of view sFOV can be widened.

[0084] As shown in Figures 1, 2, and 4, the subject S is positioned in either a standing or sitting position. This allows for the observation of soft tissues such as the lungs in their natural state under gravity, or the observation of joints such as the hip joint under gravity and load. Alternatively, a CT scanner that images the subject S in a supine position may also be used.

[0085] Note that the set angle only needs to be less than the angle interval, and does not necessarily have to be an angle that divides the angle interval equally. For example, as shown in Figure 21, if the angle range is 2.4°, the same as the example shown in Figure 11, the set angle may be set to 0.6° by positioning the second radiation source 202 at an angle of 120.6° from the first radiation source 201 (φ=120.6°). In this case, the second imaging unit 302 uses 120.6°, where the second radiation source 202 is positioned, as the rotation start position and rotation end position, and outputs the projected image 125 at 123°, ..., 353.4°, 355.8°, 358.2°, 0.6° (360.6°), 3° (363°), 5.4° (365.4°), ...

[0086] Figure 22 shows some of the acquisition positions of the projection images 125 for the first imaging unit 301, the second imaging unit 302, and the entire imaging unit 30 in the case of Figure 21. Although there is an angular bias in the acquisition positions of the projection images 125, the number of acquisition positions of the projection images 125 for the entire imaging unit 30 is twice the number of acquisition positions of the projection images 125 for one imaging unit 30, as in the example shown in Figure 12. Therefore, in this case as well, it is possible to improve the angular resolution of the projection images 125 without increasing the frame rate of the radiation detector 21 or slowing down the rotation speed of the imaging unit 30.

[0087] [Second Embodiment] Ideally, the set angle should be as per the design value, but since the assembly of the radiation source 20 and other components is done by humans, manufacturing errors may inevitably cause the set angle to differ from the design value. Therefore, in the second embodiment, the deviation in the set angle, including manufacturing errors, is corrected by varying the irradiation timing of the radiation R from the radiation source 20.

[0088] As an example, as shown in Figure 23, consider the case where, as in the first embodiment described above, the angle φ = 121.2 and the set angle should be the design value of 1.2°, but due to manufacturing errors, φ = 121.12°, resulting in a shift of 0.08° in the clockwise direction CW. In this case, as an example, as shown in Figure 24, a margin period MP is provided in the first period P1, making the first period P1 longer than the irradiation time from the start to the end of irradiation of radiation R. Then, the imaging control unit 112 corrects the shift in the set angle, including manufacturing errors, by delaying the irradiation timing of the second radiation R2 of the second radiation source 202 in the first period P1 by time TΔ. If the shift in the set angle is 0.08° as exemplified and the rotation speed of the imaging unit 30 is 36° / sec as described above, then time TΔ is 0.08 / 36 ≈ 2.22 msec.

[0089] The deviation of the set angle from the design value is measured when the CT scanner 10 is manufactured and shipped. Then, time TΔ is calculated based on the measurement result and stored in storage 95. When taking an image, time TΔ is provided to the imaging control unit 112, and the imaging control unit 112 controls the irradiation timing of radiation R according to time TΔ.

[0090] The length of the margin period MP is set according to the upper limit of the manufacturing tolerance for the set angle. For example, if the upper limit of the manufacturing tolerance for the set angle is 0.6°, the length of the margin period MP will be 0.6 / 36 ≈ 16.7 msec. Conversely to the above example, if the set angle deviates from the design value in the counterclockwise direction (CCW), the irradiation timing of the first radiation R1 of the first radiation source 201 in the first period P1 will be delayed.

[0091] Thus, in the second embodiment, the imaging control unit 112 corrects deviations in the set angle, including manufacturing errors, by varying the irradiation timing of the radiation R from the radiation source 20. Therefore, deviations in the set angle, including manufacturing errors, can be easily corrected. The assembly of the first radiation source 201 and the second radiation source 202 can be carried out with a certain degree of roughness.

[0092] Furthermore, by providing a margin period MP in the first period P1, the following effects can be obtained. As an example, as shown in Figure 25, consider the case where, in an embodiment where no margin period MP is provided in the first period P1, the irradiation start timing of the second radiation R2 by the second radiation source 202 is advanced for some reason. In this case, the second radiation R2 is irradiated during the accumulation period of the latter half of the pixel 57 rows of the previous frame, such as the N-1th row and the Nth row, so a band-shaped artifact occurs in the projected image 125 obtained from the first radiation detector 211. Although not shown in the figure, a similar band-shaped artifact occurs in the projected image 125 if the timing of the readout operation of the projected image 125 by the radiation detector 21 is shifted among multiple imaging units 30.

[0093] In contrast, a margin period MP is provided in the first period P1, and the system is controlled to irradiate with the first radiation R1 and the second radiation R2 from the first radiation source 201 and the second radiation source 202 at a point midway through the first period P1. In this way, as shown in Figure 26 as an example, even if the start timing of irradiation of the second radiation R2 by the second radiation source 202 is earlier than intended, if the difference between the start timing of irradiation of the first radiation R1 by the first radiation source 201 and the second radiation R2 is within the margin period MP, the second radiation R2 will not be irradiated during the accumulation period of the row of pixels 57 in the latter half of the previous frame, and therefore no band-shaped artifacts will occur in the projected image 125 obtained from the first radiation detector 211. In this way, by providing a margin period MP in the first period P1 and making the first period P1 longer than the irradiation time from the start to the end of irradiation of radiation R, the occurrence of band-shaped artifacts in the projected image 125 can be prevented.

[0094] [Third Embodiment] In the first embodiment described above, the first radiation R1 and the second radiation R2 are irradiated from the first radiation source 201 and the second radiation source 202 at the same time during the first period P1, but this is not limited to this. As an example, as shown in Figure 27, the first radiation R1 and the second radiation R2 may be irradiated from the first radiation source 201 and the second radiation source 202 at different timings within the first period P1 without overlap. More specifically, the imaging control unit 112 irradiates with the first radiation R1 from the first radiation source 201 in the first half of the first period P1, and after the irradiation of the first radiation R1 is completed, irradiates with the second radiation R2 from the second radiation source 202 in the second half of the first period P1.

[0095] Thus, in the third embodiment, the imaging control unit 112 irradiates the multiple imaging units 30 with radiation R at different timings within the first period P1 without overlap. For this reason, the voltage generator that generates the tube voltage supplied to the radiation tube 55 can be common to all multiple imaging units 30, and the destination of the tube voltage can be switched using a switch or the like. When multiple imaging units 30 irradiate with radiation R at the same timing, it was necessary to prepare a voltage generator for each of the multiple imaging units 30, but the device configuration can be simplified compared to that configuration. In addition, since one imaging unit 30 is not affected by the backscatter of radiation R from the other imaging unit 30, a projection image with relatively good image quality can be obtained.

[0096] However, because the irradiation timing of radiation R from multiple imaging units 30 is different, imaging takes longer than when radiation R is irradiated from multiple imaging units 30 at the same time. Therefore, the radiation irradiation time itself may be shortened by increasing the intensity of radiation R per unit time.

[0097] [Fourth Embodiment] In the embodiments described above, examples of two imaging units 30, a first imaging unit 301 and a second imaging unit 302, were shown, but the number of imaging units 30 is not limited to these. As an example, as shown in Figures 28 and 29, the system may have three imaging units 30, a first imaging unit 301, a second imaging unit 302, and a third imaging unit 303.

[0098] In this case, when viewed from the RAD in the rotational axis direction, the second radiation source 202 is positioned 120.8° away from the first radiation source 201. The third imaging unit 303 consists of a third radiation source 203 that emits third radiation R3 and a third radiation detector 213. When viewed from the RAD in the rotational axis direction, the third radiation source 203 is positioned 241.6° away from the first radiation source 201 (120.8° away from the second radiation source 202). The first radiation detector 211, the second radiation detector 212, and the third radiation detector 213 are all positioned at the offset positions shown in Figure 9.

[0099] As an example, as shown in Figure 30, the first imaging unit 301, similar to the first embodiment described above, uses 0°, where the first radiation source 201 is located, as the rotation start position and rotation end position, and outputs projected images 125 at angular intervals of 2.4°, such as 2.4°, 4.8°, 7.2°, ..., 117.6°, 120°, 122.4°, ..., 352.8°, 355.2°, and 357.6°. The second imaging unit 302 uses 120.8°, where the second radiation source 202 is located, as its rotation start and end positions, and outputs projected images 125 at 123.2°, ..., 353.6°, 356°, 358.4°, 0.8° (360.8°), 3.2° (363.2°), 5.6° (365.6°), ..., also at angular intervals of 2.4°. Furthermore, the third imaging unit 303 uses 241.6°, where the third radiation source 203 is located, as its rotation start and end positions, and outputs projected images 125 at 244°, ..., 354.4°, 356.8°, 359.2°, 1.6° (361.6°), 4° (364°), 6.4° (366.4°), ..., also at angular intervals of 2.4°.

[0100] Because the second radiation source 202 is positioned at 120.8°, the acquisition position of the projected image 125 differs by 0.8°, which is one-third of the angular interval of 2.4°, between the first imaging unit 301 and the second imaging unit 302. In other words, the acquisition position of the respective projected image 125 differs by 0.8° between the first imaging unit 301 and the second imaging unit 302. Furthermore, the first imaging unit 301 and the third imaging unit 303 are positioned at 120.8°, 203 Because it is positioned at 241.6°, the acquisition position of the projected image 125 differs by 1.6°, which is 2 / 3 of the angular interval of 2.4°. In other words, the first imaging unit 301 and the third imaging unit 303 are positioned such that the acquisition position of their respective projected images 125 differs by 1.6°. For this reason, projected images 125 at positions such as 0.8° and 1.6° between 0° and 2.4°, 3.2° and 4° between 2.4° and 4.8°, ..., 353.6° and 354.4° between 352.8° and 355.2°, and 356° and 356.8° between 355.2° and 357.6°, which are not captured by the first imaging unit 301, can be acquired by the second imaging unit 302 and the third imaging unit 303. Here, 0.8° and 1.6° are angles obtained by dividing the angular interval of 2.4° into three equal parts, and are examples of "set angles" related to the technology of this disclosure.

[0101] Thus, even when using three imaging units 30, it is possible to improve the angular resolution of the projected image 125 without increasing the frame rate of the radiation detector 21 or decreasing the rotation speed of the imaging units 30. In this case, the frame rate of the radiation detector 21 is effectively 45 fps.

[0102] Furthermore, frame 18 has a considerable weight. Adding multiple shooting units 30 further increases the weight of frame 18, thus increasing its moment of inertia. Therefore, in reality, as shown in the graph in Figure 31 as an example, the acceleration period AP from the start of rotation to constant speed rotation, and the deceleration period DP from constant speed rotation to rotation stop, each take T1-T0 and T3-T2 times. For example, when rotating frame 18 one full rotation (360°), during the constant speed period CSP, assuming a 360° rotation of frame 18, the acceleration period AP and deceleration period DP are completed in 20° increments. Therefore, in reality, frame 18 is rotated 400°.

[0103] Frame 18 does not have a mechanism like a slip ring, and power is supplied by wiring. Therefore, frame 18 There is a limit to the rotation angle depending on the wiring length. Therefore, as a safety measure, it is preferable to provide a mechanical switch that forcibly cuts off the power supply to the rotating motor 47 when the rotation angle of the frame 18 in one direction reaches the limit rotation angle. As shown in Figure 31, if the frame 18 is actually rotated 400° to rotate 360°, a rotation angle converter that converts 400° rotation to 360° rotation should be connected to the potentiometer 48 of the rotating mechanism 45.

[0104] For example, when photographing a relatively wide area such as the whole body, you may raise and lower frame 18 two or more times and take the picture in two or more separate shots.

[0105] A lifting mechanism may be provided in at least one of the multiple imaging units 30, allowing it to move up and down in the rotation axis direction (RAD).

[0106] A mechanism for moving the radiation source 20 and radiation detector 21 along the circumferential direction of the frame 18 may be provided, and the position of the radiation source 20 and radiation detector 21 may be changed. In this way, the radiation source 20 and radiation detector 21 that interfere with the guidance of the subject S into the main body 11 can be moved to a position where they do not interfere.

[0107] The support columns 14 may consist of four or five columns. Alternatively, the rotating motor 47 may be a stepping motor, and the rotational position of the frame 18 may be determined by the number of pulses supplied to the rotating motor 47. Furthermore, the frame 18 is not limited to a ring shape, but may also be a polygonal ring shape.

[0108] The hardware configuration of the computer constituting the control device 12 can be modified in various ways. For example, the control device 12 can be composed of multiple computers separated as hardware, in order to improve processing power and reliability. For example, the functions of the reception unit 110, RW control unit 111, and display control unit 114, and the functions of the shooting control unit 112 and image processing unit 113 can be distributed among two computers. In this case, the control device 12 is composed of two computers.

[0109] Thus, the hardware configuration of the computer in the control device 12 can be appropriately modified according to the required performance, such as processing power, safety, and reliability. Furthermore, not only the hardware but also application programs such as the operating program 105 can, of course, be duplicated or distributed and stored on multiple storage devices for the purpose of ensuring safety and reliability.

[0110] In each of the above embodiments, for example, the hardware structure of the Processing Unit that performs various processes such as the reception unit 110, RW control unit 111, shooting control unit 112, image processing unit 113, and display control unit 114 can be the following types of processors. The types of processors include a CPU 97, which is a general-purpose processor that executes software (operation program 105) and functions as various processing units, as well as a Programmable Logic Device (PLD), which is a processor whose circuit configuration can be changed after manufacturing, such as an FPGA (Field Programmable Gate Array), and / or a dedicated electrical circuit, which is a processor with a circuit configuration specifically designed to perform a particular process, such as an ASIC (Application Specific Integrated Circuit).

[0111] A single processing unit may consist of one of these various processors, or it may consist of a combination of two or more processors of the same or different types (for example, a combination of multiple FPGAs, and / or a combination of a CPU and an FPGA). Alternatively, multiple processing units may be composed of a single processor.

[0112] Examples of configuring multiple processing units with a single processor include, firstly, a configuration where one or more CPUs and software combine to form a single processor, which then functions as multiple processing units, as exemplified by client and server computers. Secondly, a configuration using a processor that realizes the functions of the entire system, including multiple processing units, on a single IC (Integrated Circuit) chip, as exemplified by System-on-a-Chip (SoC). Thus, various processing units are configured, in terms of hardware structure, using one or more of the above-mentioned processors.

[0113] Furthermore, the hardware structure of these various processors can more specifically utilize electrical circuits (Circuitry) that combine circuit elements such as semiconductor elements.

[0114] From the above description, the technology described in the following supplementary information can be understood.

[0115] [Additional note 1] Multiple imaging units, each comprising a radiation source that emits cone-shaped radiation toward a subject, and a radiation detector having multiple pixels arranged in a two-dimensional manner to detect the radiation that has passed through the subject, A rotation mechanism that rotates multiple of the aforementioned shooting units around the body axis of the subject while maintaining their spacing, A processor that controls the operation of multiple imaging units and the rotation mechanism, Equipped with, The angular interval is determined by the frame rate of the radiation detector and the rotation speed of the imaging unit, and the angular interval defining the timing for acquiring the projection image based on the radiation is the same for multiple imaging units. Multiple of the aforementioned imaging units have different phases in the direction of rotation. The positions at which the projection images are acquired by the multiple imaging units differ by a set angle less than the angular interval. Computed tomography scanner. [Additional note 2] The computed tomography apparatus described in Appendix 1, wherein the setting angle is an angle obtained by dividing the angle interval into equal parts. [Additional note 3] The aforementioned processor, A computed tomography apparatus according to Appendix 1 or Appendix 2, which corrects deviations in the set angle, including manufacturing errors, by varying the irradiation timing of the radiation from the radiation source. [Additional note 4] The aforementioned processor, During a predetermined first period, the radiation is irradiated from all of the multiple imaging units. A computed tomography apparatus according to any one of the appendices 1 to 3, wherein the projection image is output from all of the multiple imaging units during a predetermined second period following the first period. [Additional note 5] The aforementioned processor, During the first period, the radiation is irradiated from multiple imaging units at the same time. The computed tomography apparatus according to Appendix 4, which outputs the projection images from multiple imaging units at the same time during the second period. [Additional note 6] The computed tomography apparatus according to Appendix 4 or Appendix 5, wherein the first period is a period longer than the irradiation time from the start to the end of irradiation. [Additional note 7] The aforementioned processor, The computed tomography apparatus according to Appendix 4, which irradiates the radiation from multiple imaging units without overlap at different timings within the first period. [Additional note 8] Computed tomography apparatus according to any one of Appendix 1 to Appendix 7, wherein the plurality of imaging units are arranged at positions that are more than 90° apart when viewed from the axis of rotation of the plurality of imaging units. [Additional note 9] A computed tomography apparatus according to any one of Appendix 1 to Appendix 8, wherein, when viewed from the rotation axis direction of the multiple imaging units, the radiation detector is positioned at an offset position that is different by a predetermined angle from a reference position directly facing the radiation source. [Additional Note 10] Multiple of the aforementioned shooting units are held in a frame, and the subject is positioned within the frame. A computed tomography apparatus according to any one of Appendix 1 to Appendix 9, wherein, when viewed from the axis of rotation of the multiple imaging units, the radiation source is located outside the frame and the radiation detector is located inside the frame. [Additional Note 11] The subject is positioned in either a standing or sitting position, and the computed tomography apparatus is as described in any one of the appendices 1 to 10.

[0116] The technology of this disclosure can be appropriately combined with the various embodiments and / or variations described above. Furthermore, it is understood that various configurations can be adopted without departing from the spirit of the invention, and the invention is not limited to the embodiments described above. Moreover, the technology of this disclosure extends not only to programs but also to storage media for storing programs non-temporarily.

[0117] The descriptions and illustrations presented above are detailed explanations of the technical aspects of this disclosure and are merely examples of the technical aspects. For example, the above descriptions of the structure, function, operation, and effect are examples of the structure, function, operation, and effect of the technical aspects of this disclosure. Therefore, it goes without saying that you may delete unnecessary parts, add new elements, or replace elements in the descriptions and illustrations presented above, as long as you do not deviate from the essence of the technical aspects of this disclosure. Furthermore, in order to avoid confusion and facilitate understanding of the technical aspects of this disclosure, explanations of common technical knowledge and the like that do not require special explanation to enable the implementation of the technical aspects of this disclosure have been omitted from the descriptions and illustrations presented above.

[0118] In this specification, "A and / or B" is synonymous with "at least one of A and B." That is, "A and / or B" means that it may be A alone, or B alone, or a combination of A and B. Furthermore, in this specification, the same concept as "A and / or B" applies when expressing three or more things linked by "and / or."

[0119] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference. [Explanation of symbols]

[0120] 10. Computed Tomography Scanning Equipment (CT scanner) 11. Main unit of the device 12 Control device 13 stages 14, 14A~14C pillar 15 Top plate 16 casters 17, 17A~17C Connecting Members 18 frames 20 Radiation source 21 Radiation detectors 22, 22A~22C Screw shaft 24 movable arms 25 Touch panel display 30 shooting units 32 wheelchairs 35 Lifting mechanism 36 nuts 37 Lifting motor 38. First connection section 39 Second connection section 40 bearings 41 Guide groove 45 Rotation mechanism 46 Rotating Belts 47 Rotary motors 48 Potentiometers 49, 50 Pulley 55 Radiation tubes 56 Irradiation field limiter 57 pixels 58 Detection surface 60A, 60B, 61A, 61B Attachments 62 volts 63 Joint 95 storage 96 memory 97 CPU 98 displays 99 Input Devices 105 Operating Program 106 Irradiation Conditions Table 107 Irradiation Conditions Information by Order 110 Reception Department 111 Read / Write Control Unit (RW Control Unit) 112 Imaging Control Unit 113 Image Processing Unit 114 Display Control Unit 116 Shooting Menu 117 Irradiation conditions 120 Sector indicating the acquisition position of the projection image of the first imaging unit. 121 Sector indicating the acquisition position of the projected image of the second imaging unit. 122 Sector shape indicating the acquisition position of the projected image of all imaging units 125 Projection Image 201 1st radiation source 202 Second radiation source 203 Third radiation source 211 First Radiation Detector 212 Second Radiation Detector 213 Third Radiation Detector 301 First Shooting Unit 302 Second Shooting Unit 303 3rd Shooting Unit AP acceleration period Regions particularly affected by backscatter radiation (BA) C-frame center (rotation center) CCW (Counterclockwise direction) Center point of the detection surface of the CS radiation detector CS1 First center point of the detection surface of the first radiation detector CS2 Second center point of the detection surface of the second radiation detector CSP constant speed period CW (Clockwise direction) DP deceleration period MP margin period P1 Period 1 P2 Second Period R radiation R1 First Radiation R2 2nd radiation R3 Third Radiation RA rotation axis RAD (Radius) axis direction RCA radiation beam central axis RCA1: First central axis of the radiation beam of the first radiation. RCA2 Second central axis of the radiation beam of the second radiation S Subject sFOV (effective field of view) ST100, ST110, ST120, ST130, ST140, ST150 Step T0~T3, TΔ time θ: Radiation angle φ Angle of the positions of the first and second radiation sources

Claims

1. Multiple imaging units, each comprising a radiation source that emits cone-shaped radiation toward a subject, and a radiation detector having multiple pixels arranged in a two-dimensional manner to detect the radiation that has passed through the subject, A rotation mechanism that rotates multiple of the aforementioned shooting units around the body axis of the subject while maintaining their spacing, A processor that controls the operation of multiple imaging units and the rotation mechanism, Equipped with, The angular interval is determined by the frame rate of the radiation detector and the rotation speed of the imaging unit, and the angular interval defining the timing for acquiring the projection image based on the radiation is the same for multiple imaging units. Multiple of the aforementioned imaging units have different phases in the direction of rotation. The positions at which the projection images are acquired by the multiple imaging units differ by a set angle less than the angular interval. Computed tomography scanner.

2. The computed tomography apparatus according to claim 1, wherein the setting angle is an angle obtained by dividing the angle interval into equal parts.

3. The aforementioned processor, The computed tomography apparatus according to claim 1, wherein deviations in the set angle, including manufacturing errors, are corrected by varying the irradiation timing of the radiation from the radiation source.

4. The aforementioned processor, During a predetermined first period, the radiation is irradiated from all of the multiple imaging units. The computed tomography apparatus according to claim 1, wherein the projection image is output from all of the plurality of imaging units during a predetermined second period following the first period.

5. The aforementioned processor, During the first period, the radiation is irradiated from multiple imaging units at the same time. The computed tomography apparatus according to claim 4, wherein, during the second period, the projection images are output from a plurality of imaging units at the same time.

6. The computed tomography apparatus according to claim 4, wherein the first period is a period longer than the irradiation time from the start to the end of irradiation of the radiation.

7. The aforementioned processor, The computed tomography apparatus according to claim 4, wherein radiation is irradiated from multiple imaging units at different timings within the first period without overlap.

8. The computed tomography apparatus according to claim 1, wherein the plurality of imaging units are arranged at positions that are more than 90° apart when viewed from the axis of rotation of the plurality of imaging units.

9. The computed tomography apparatus according to claim 1, wherein, when viewed from the rotation axis direction of the multiple imaging units, the radiation detector is positioned at an offset position that is different by a predetermined angle from a reference position directly facing the radiation source.

10. Multiple of the aforementioned shooting units are held in a frame, and the subject is positioned within the frame. The computed tomography apparatus according to claim 1, wherein, when viewed from the axis of rotation of the multiple imaging units, the radiation source is located outside the frame and the radiation detector is located inside the frame.

11. The computed tomography apparatus according to claim 1, wherein the subject is positioned in either a standing or sitting position.

Images