JP2014045895A - X-ray computer tomography apparatus and method for producing collimator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a two-dimensional collimator having an integral structure, improved in strength and uniformity.SOLUTION: An X-ray computer tomography apparatus includes an X-ray source, an X-ray detector, a collimator and a reconstruction part. In the X-ray detector, a plurality of X-ray detection elements for detecting X-rays generated from an X-ray focus of the X-ray source and transmitted through a subject are arranged in a lattice state in a channel direction orthogonal to a body axis of the subject and in a slice direction along the body axis. The collimator is mounted in the X-ray detector. The reconstruction part reconstructs image data related to the subject on the basis of an output of the X-ray detector. The collimator includes a plurality of channel partition plates and a plurality of slice partition plates. The plurality of channel partition plates are arranged along the channel direction, and have a shielding property against the X-rays. The plurality of slice partition plates are arranged in gaps between the channel partition plates, respectively, have the shielding property against the X-rays, and are welded to the channel partition plates, respectively.

Description

  Embodiments described herein relate generally to a computer tomography apparatus and a collimator manufacturing method.

  In an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus), an X-ray transmitted through a subject while rotating a pair of an X-ray tube and an X-ray detector around the subject. Is detected by a plurality of X-ray detection elements in the X-ray detector. The X-ray detector includes a collimator for separating each X-ray detection element from the X-ray and removing the scattered radiation by limiting the incident X-ray direction to improve the direct ray detection ability. Equipped. The collimator is formed by, for example, a plurality of X-ray shielding plates (partition plates) (hereinafter also referred to as channel partition plates) arranged in the fan angle direction (channel direction) orthogonal to the body axis of the subject. As the partition plate, for example, a molybdenum (Mo) plate can be used.

  In recent years, two-dimensional array type X-ray detectors have been widely used. As this two-dimensional array type X-ray detector, a relatively small number of detection element arrays (also referred to as segments), typically, four arrays are widely used. However, recently, by adopting a solid state detection element that combines a scintillator element and a photodiode element, or a solid state detection element such as selenium that converts X-rays directly into electric charge, the number of columns exceeds 64. Wide-field X-ray detectors have appeared.

  When the number of X-ray detectors is increased, the collimator (one-dimensional collimator) formed only by the channel partition plate described above has a cone angle direction (slice direction) along the body axis direction of the subject. Cannot be removed, causing artifacts and CT value fluctuations. Therefore, a collimator (hereinafter also referred to as a two-dimensional collimator) in which a plurality of X-ray shielding plates (partition wall plates) (hereinafter also referred to as slice partition walls) is disposed also in the cone angle direction is required. That is, the two-dimensional collimator is composed of a channel partition plate and a slice partition plate assembled in a lattice shape facing the X-ray tube (X-ray focal point) from the viewpoint of removing scattered radiation in two directions of fan angle and cone angle. Need to be formed.

  As such a two-dimensional collimator, for example, an integrated structure collimator formed by a number of comb-shaped plates assembled in a lattice shape is known. A two-dimensional collimator having an integral structure manufactured by joining collimator modules that partially cover the visual field is also known.

JP 2001-137234 A

  However, it is difficult to assemble the two-dimensional collimators as described above so as to have high strength. Further, in the case of the latter two-dimensional collimator, stress due to centrifugal force accompanying high-speed rotation is concentrated at the joint portion of each collimator module, and a space is generated, which may reduce the uniformity of sensitivity distribution.

  An object is to provide an X-ray computed tomography apparatus and a collimator manufacturing method capable of realizing a two-dimensional collimator having an integrated structure with improved strength and uniformity.

  The X-ray computed tomography apparatus according to the embodiment includes an X-ray source, an X-ray detector, a collimator, and a reconstruction unit.

  The X-ray detector includes a plurality of X-ray detection elements for detecting X-rays generated from an X-ray focal point of the X-ray source and transmitted through the subject, in a channel direction orthogonal to the body axis of the subject. They are arranged in a lattice pattern in the slice direction along the body axis.

  The collimator is attached to the X-ray detector.

  The reconstruction unit reconstructs image data related to the subject based on the output of the X-ray detector.

  The collimator includes a plurality of channel partition plates and a plurality of slice partition plates.

  The plurality of channel partition plates are arranged along the channel direction and have shielding properties against the X-rays.

  The plurality of slice partition plates are arranged in the gaps of the channel partition plates, have a shielding property against the X-rays, and are welded to the channel partition plates.

1 is a block diagram of an X-ray computed tomography apparatus according to an embodiment. FIG. 3 is a structural diagram of a collimator in the same embodiment. It is a top view of the slice partition plate in the same embodiment. It is a figure which shows the focusing of the collimating area | region in the embodiment. It is a figure which shows the collimate line in the same embodiment. It is a figure which shows the arrangement | sequence of the channel partition plate in the same embodiment. It is a figure which shows the arrangement | sequence of the slice partition board in the same embodiment. It is a figure which shows the collimator frame in the same embodiment. It is a figure which shows the guide groove of the collimator frame in the embodiment. It is a flowchart for demonstrating the manufacturing method of the collimator in the embodiment. It is a perspective view for demonstrating the welding of the partition plate in the embodiment. It is a top view for demonstrating the welding of the partition plate in the embodiment. It is a perspective view for demonstrating the welding of the partition plate in the embodiment. It is a top view for demonstrating the welding of the partition plate in the embodiment. It is a structural diagram of a conventional collimator.

  Hereinafter, an X-ray computed tomography apparatus and a collimator manufacturing method according to an embodiment will be described with reference to the drawings.

  FIG. 1 is a block diagram of an X-ray computed tomography apparatus according to an embodiment. The X-ray computed tomography apparatus has a gantry 100 (also referred to as a gantry) as a main structure. The gantry unit 100 includes a rotating ring 102, and the cone beam X-ray tube 101 and the X-ray detector 11 are arranged to face the rotating ring 102. A collimator 13 is attached to the X-ray detector 11. Details of the collimator 13 will be described later. The X-ray tube 101 receives the high voltage pulse periodically generated from the high voltage generator 109 and generates X-rays. The X-ray detector 11 is composed of an ionization chamber type detector box or a semiconductor detector. In the case of a semiconductor X-ray detector, a plurality of X-ray detection elements are arranged in an arc shape around the apex of the cone beam (X-ray focal point F), and this X-ray detection element array is connected to the rotation axis of the rotary ring 102. A plurality are arranged in parallel along a substantially parallel direction. The X-ray detector 11 is connected to a data acquisition circuit 104 generally called a DAS (data acquisition system). The data acquisition circuit 104 includes an IV converter that converts a current signal of each channel of the X-ray detector 11 into a voltage, and periodically integrates the voltage signal in synchronization with an X-ray exposure cycle. An integrator, an amplifier that amplifies the output signal of the integrator, and an analog / digital converter that converts the output signal of the preamplifier into a digital signal are provided for each channel. A pre-processing device 106 is connected to the data collection circuit 104 via a non-contact data transmission device 105. The pre-processing device 106 corrects non-uniform sensitivity between channels for the projection data detected by the data acquisition circuit 104, and extremely reduces the signal strength due to the strong X-ray absorber, mainly metal parts. Alternatively, preprocessing such as correction of signal dropout is executed. The projection data corrected by the preprocessing device 106 is stored in the storage device 112. The reconstruction processing unit 118 reconstructs volume data representing a three-dimensional distribution of CT values based on projection data stored by an arbitrary cone beam image reconstruction algorithm. A typical example of a cone beam image reconstruction algorithm is the weighted Feldkamp method. This Feldkamp method is an approximate reconstruction method based on the fan beam convolution and back projection method, and the convolution process assumes that the cone angle is relatively small and regards the data as fan projection data. Done. However, the back projection process is performed along an actual ray.

  In an image processing unit (not shown), the volume data is converted into image data expressed in a two-dimensional coordinate system by a rendering process or a cross-section conversion process (MPR). The image data is displayed on the display device 116. The host controller 110 controls the gantry driving unit 107 in order to stably rotate the rotating ring 102 at a constant speed in order to perform projection data collection operation, that is, scan, according to the operation of the input device 115 by the operator, and scan The high voltage generator 109 is controlled to generate X-rays from the X-ray tube 101 during the period, and control related to scanning such as controlling the data acquisition circuit 104 in synchronization with X-ray generation is integrated. .

  As shown in FIG. 1, the two-dimensional array type X-ray detector 11 typically includes a plurality of X-ray detection elements arranged in a line in an arc shape around the X-ray focal point. A plurality of rows are juxtaposed along the Z-axis direction (slice direction). The arrangement direction of the detection elements in the X-ray detection element array is referred to as a channel direction.

  On the X-ray source side of the two-dimensional array type X-ray detector 11, a plurality of detection elements are individually optically separated, and the scattered radiation is removed by limiting the incident direction to provide direct line detection ability. In order to improve, a collimator 13 in which an X-ray shielding plate (partition plate) is welded in a lattice shape in two directions of a slice direction and a channel direction is provided.

  As shown in FIG. 2, the collimator 13 includes a plurality of channel partition plates 31 arranged along the channel direction, and a plurality of slice partitions arranged in the gaps between the channel partition plates 31 and welded to the channel partition plates 31. And a plate 33. Each slice partition plate 33 is provided perpendicular to the channel partition plate 31. The channel partition plates 31 and the slice partition plates 33 are preferably arranged radially so as to face the X-ray focal point F of the X-ray source.

  Each channel partition plate 31 is cut into a rectangle from a material having X-ray shielding properties. The material having X-ray shielding properties is, for example, a thin molybdenum plate. All the channel partition plates 33 have the same shape and the same size.

  As shown in FIG. 3, each slice partition plate 33 is a thin plate having a trapezoidal strip shape molded from a material having X-ray shielding properties. The material having X-ray shielding properties is, for example, a thin molybdenum plate. All the slice partition plates 33 have the same shape and the same size.

  As shown in FIGS. 4 and 5, the collimator 13 has a structure in which a certain curvature is provided in two directions of the channel direction and the slice direction so that all of the plurality of collimated regions are accurately focused on the X-ray focal point F. Also good. The collimating region is a region surrounded by the vertical and horizontal partition plates 31 and 33 constituting the collimator 13, and a line connecting the center of one end surface of the collimating region and the center of the other end surface is referred to as a collimating line. The collimate line indicates the directivity of the collimated region.

  Here, as shown in FIG. 6, the channel partition plates 31 are arranged so that the spread angle Δθ <b> 1 defined as an angle formed by the collimating lines adjacent in the channel direction is constant.

  As shown in FIG. 7, each slice partition plate 33 is arranged so that the spread angle Δθ <b> 2 defined as the angle formed between the collimating lines adjacent in the slice direction is constant.

  Each channel partition plate 31 defines a plurality of pyramidal collimated regions together with each slice partition plate 33. Each collimated region corresponds to each detection element. Each collimating line corresponding to each collimating region is focused on one point (X-ray focal point F). This focusing property significantly reduces the scattered radiation incident on each of the plurality of channels, and makes it possible to dramatically improve the diagnostic image accuracy.

  This convergence can be achieved by welding the channel partition plate 31 having a flat plate shape and each slice partition plate 33 having a trapezoidal strip shape. Further, the focusing property can be obtained not by a configuration in which the collimator 13 is a combination of a plurality of modules but by an integrated configuration. Therefore, there is no inconvenience such as excessive distortion applied to the module joint, etc., causing partial distortions, and the scattered radiation removal accuracy greatly changes at the module joint, and the sensitivity in both the channel direction and the slice direction. Distribution uniformity can be obtained.

  The collimator 13 has a collimator frame 16. As shown in FIG. 8, the collimator frame 16 has an upper frame 17 and a lower frame 19. The upper frame 17 has a partial shape of an annular plate. The lower frame 19 has the same shape as the upper frame 17. The radius of the ring of the upper / lower frames 17 and 19 is the distance between the collimator frame 16 mounted on the rotating ring 102 and the X-ray focal point F of the cone beam X-ray tube 101. Is almost equivalent to The upper frame 17 and the lower frame 19 are held in parallel by the side frames 21 and 23. The distance between the upper frame 17 and the lower frame 19 is substantially equivalent to the length of a channel partition plate guide groove to be described later, more specifically, the sensitivity width in the slice direction of the X-ray detector 11.

  As shown in FIG. 9, a plurality of guide grooves (referred to as channel partition plate guide grooves) 25 are formed in the lower frame 19. The plurality of channel partition plate guide grooves 25 are formed radially with respect to the channel direction around the X-ray focal point F at regular intervals. In other words, the plurality of channel partition plate guide grooves 25 are formed along the radial direction of the ring centered on the X-ray focal point F, and are arranged so that the above-described divergence angle Δθ1 is constant. Similarly, a plurality of channel partition plate guide grooves 27 are also formed in the upper frame 17.

  Each channel partition plate 31 is supported by such channel partition plate guide grooves 25 and 27 and fixed with an epoxy adhesive. Each channel partition plate 31 is provided perpendicular to the frames 17 and 19.

  Next, a manufacturing method of the collimator 13 as described above will be described with reference to FIGS. Here, the process of producing the integral structure of each channel partition plate 31 and each slice partition plate 33 in the collimator 13 by a welding apparatus will be mainly described. As the welding apparatus, for example, an apparatus having a positioning mechanism to be welded and a welding machine 40 such as a laser welding machine capable of fine processing can be used as appropriate.

  In the welding apparatus, as shown in FIGS. 10 and 11, one of the channel partition plates 31 among the channel partition plates 31 is a welding target, and each slice partition plate 33 is welded to the channel partition plate 31 to be welded. The machine 40 sequentially welds (ST1). In step ST1, the welding machine 40 welds the channel partition plate 31 to be welded and each slice partition plate 33 from one direction. Specifically, for example, as shown in FIG. 12, the welding machine 40 is opposed to the slice partition plate 33 other than the welding target on the central axis 41 that substantially divides the angle formed by the partition plates 31 and 33 to be welded. The partition plates 31 and 33 are welded along one direction 42 facing the partition plates 31 and 33 to be welded from a position where the welding is not performed.

  Next, in the welding apparatus, as shown in FIG. 13 and FIG. 14, with the back surface of the new channel partition plate 31 in contact with the other end of each slice partition plate 33 welded at one end (ST2), The welding machine 40 sequentially welds each new slice partition plate 33 to the surface of the new channel partition plate 31 (ST3). In step ST3, welding is performed from one direction 42 facing the front surface, so that welding on the front surface and welding on the other end in contact with the back surface are performed simultaneously. Supplementally, when the channel partition plate 31 to be welded is the second or later, the welding machine 40 also welds the partition plates 31 and 33 located on the back surface portion 44 to the weld portion 43 on the front surface at the same time. The simultaneous welding of the front surface and the back surface utilizes a phenomenon in which the brazing material of the welding portion 43 on the front surface oozes out to the back surface portion 44.

  Thereafter, by repeatedly executing steps ST2 and ST3, the integral partition wall plates 31 and 33 welded in a lattice shape are manufactured. The integral partition plates 31 and 33 are fixed in the frames 17, 19, 21 and 23. Thereby, the collimator 13 is produced.

  As described above, according to the present embodiment, the plurality of channel partition plates 31 are arranged along the channel direction, and the plurality of slice partition plates 33 are arranged in the gaps of the channel partition plates 31, A two-dimensional collimator having an integrated structure with improved strength and uniformity can be realized by the welded configuration.

  Supplementally, as shown in FIG. 15, the conventional one-dimensional collimator has only the channel partition plate 31 arranged in the fan angle direction and cannot remove scattered rays from the cone angle direction.

  On the other hand, in the present embodiment, as shown in FIG. 2, the scattered rays from the fan angle and cone angle directions can be removed, and by using an integrated structure by welding, a plurality of collimators are different from the conventional one. A collimator having higher strength and a more uniform sensitivity distribution can be realized without generating a singular point such as a joint portion of the module.

  In addition, according to the present embodiment, a new channel partition plate 31 is resurfaced with the back surface of the new channel partition plate 31 in contact with the other end of each slice partition plate 33 welded at one end. The welding machine 40 sequentially welds each slice partition plate 33. At this time, the welding is performed from one direction 42 facing the surface, and the phenomenon that the brazing material of the welded portion 43 on the surface oozes out to the back surface portion 44 is used to weld the surface and contact the back surface. Welding with the other end can be performed simultaneously.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof in the same manner as included in the scope and gist of the invention.

  DESCRIPTION OF SYMBOLS 11 ... X-ray detector, 13 ... Collimator, 15 ... X-ray tube, 31 ... Channel partition plate, 33 ... Slice partition plate

Claims (3)

An X-ray source;
A plurality of X-ray detection elements for detecting X-rays generated from an X-ray focal point of the X-ray source and transmitted through the subject are sliced along a channel direction perpendicular to the body axis of the subject and the body axis An X-ray detector arranged in a grid pattern in a direction;
A collimator mounted on the X-ray detector;
A reconstruction unit that reconstructs image data relating to the subject based on the output of the X-ray detector;
The collimator is
A plurality of channel partition plates arranged along the channel direction and having shielding properties against the X-rays;
An X-ray computed tomography apparatus comprising: a plurality of slice partition plates arranged in each gap of the channel partition plates, having shielding properties against the X-rays and welded to the channel partition plates. The X-ray computed tomography apparatus according to claim 1,
The X-ray computed tomography apparatus according to claim 1, wherein the channel partition plates and the slice partition plates are arranged radially so as to face the X-ray focal point of the X-ray source. A collimator manufacturing method for manufacturing a collimator in which a plurality of channel partition plates and a plurality of slice partition plates are arranged in a grid pattern,
A first welding step in which one of the channel partition plates is a welding target, and a welding machine sequentially welds each of the partition partition plates to the channel partition plate to be welded;
The welding machine sequentially puts each new slice partition plate on the surface of the new channel partition plate in a state where the back surface of the new channel partition plate is brought into contact with the other end of each slice partition plate welded at one end. A second welding process for welding,
The second welding step performs the welding on the front surface and the welding on the other end in contact with the back surface simultaneously by performing the welding from one direction facing the front surface. Production method.

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