JP5972606B2 - Collimator, X-ray detector unit and X-ray computed tomography apparatus - Google Patents

Description

  Embodiments described herein relate generally to a collimator, an X-ray detector unit, and an X-ray computed tomography apparatus.

  In an X-ray detector such as an X-ray computed tomography apparatus, each detection element is separated from X-rays, and the scattered X-rays are removed by restricting the incident X-ray direction to improve the direct line detection ability A collimator is installed for this purpose. 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 rows (also referred to as segments), typically four rows, 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. A collimator applied to such a two-dimensional array type X-ray detector is assumed to be obtained by bending a lattice plate obtained by punching a soft material plate mixed with X-ray shielding metal powder into a lattice shape.

  However, the collimator having such a structure cannot focus the sights of a plurality of collimated regions partitioned by the grating on the X-ray focal point.

JP 2004-195235 A JP 2010-223836 A JP 2003-149348 A JP 2000-338254 A JP 02-253200 A JP 2008-89341 A

  The purpose is to improve the aiming or focusing of the lattice collimator.

The collimator according to the present embodiment includes a collimator frame having a shape of a part of an annulus, and a plurality of collimators that are supported by the collimator frame and arranged radially along the circumferential direction of the annulus and have a shielding property against radiation. A first partition plate, and a plurality of second partition plates arranged radially in each gap between the first partition plates and having a shielding property against radiation, wherein each of the first partition plates includes the shielding plate and the A resin layer formed on the surface of the shielding plate, and the shielding plate and the resin layer are formed so that a plurality of guide grooves for holding the second partition plate is formed by the resin layer. Provided on the first partition plate, the guide groove passes through the resin layer and reaches the shielding plate, or is formed in the resin layer.

It is a figure which shows the external appearance of the collimator which concerns on this embodiment. It is a figure which shows the structure of the whole X-ray computed tomography apparatus provided with the collimator which concerns on this embodiment. It is a figure which shows the aim of the collimated area | region of FIG. It is a figure which shows the collimate line of FIG. It is the elements on larger scale (plan view) regarding the lattice structure of the channel partition plate and slice partition plate of FIG. It is the elements on larger scale (perspective view) regarding the lattice structure of the channel partition plate and slice partition plate of FIG. It is a figure which shows the arrangement | sequence of the channel partition plate of FIG. It is a figure which shows the arrangement | sequence of the slice partition board of FIG. It is a figure which shows the collimator frame of FIG. FIG. 10 is a view showing guide grooves of an upper / lower frame of the collimator frame of FIG. 9. It is a figure which shows mounting | wearing of the channel partition plate and slice partition plate with which the collimator frame of FIG. 10 is mounted | worn. It is a figure which shows the insertion direction of the slice partition plate with respect to the channel partition plate of FIG. FIG. 10 is a plan view of the channel partition plate of FIG. 9. It is an enlarged view of the guide groove formed in the channel partition plate of FIG. It is a figure which shows the aim of the collimating line of FIG. It is a top view of the slice partition plate of FIG. It is the elements on larger scale (perspective view) regarding the lattice structure of the channel partition plate and slice partition plate of FIG. It is a figure which shows the external appearance of the inner side abutting board which comprises the collimator of this embodiment. In this embodiment, it is a top view which shows the inner side abutting plate and outer side abutting plate which align a channel partition plate and a slice partition plate. In this embodiment, it is a side view which shows the inner side abutting plate and outer side abutting plate which align a channel partition plate and a slice partition plate. It is a top view which shows the other structure of the slice partition plate of FIG. It is sectional drawing of the slice partition board of FIG. It is the elements on larger scale (plan view) regarding the lattice structure of the channel partition plate and slice partition plate of FIG. It is sectional drawing which shows the other structure of the slice partition plate of FIG. It is sectional drawing which shows the other structure of the slice partition plate of FIG.

  The collimator of this embodiment has a collimator frame having a shape of a part of a ring. The collimator frame is instructed with a plurality of channel partition plates having shielding properties against radiation. The plurality of channel partition plates are arranged radially along the circumferential direction of the ring. A plurality of slice partition plates are arranged radially in each gap of the channel partition plates. Each of the channel partition plates has a shielding plate and a resin layer formed on the surface of the shielding plate. A plurality of guide grooves for holding the slice partition plate is formed by the resin layer.

  Hereinafter, the collimator according to the present embodiment will be described with reference to the drawings. The collimator according to this embodiment constitutes an X-ray detector unit together with an X-ray detector and other components. The X-ray detector unit constitutes an X-ray computed tomography apparatus together with other components.

  As shown in FIG. 1, the collimator 13 according to this embodiment includes a single collimator frame 16 having a shape of a part of a ring. A plurality of channel partition plates 31 are supported on the collimator frame 16. The plurality of channel partition plates 31 are arranged radially along the circumferential direction (channel direction) of the ring of the collimator frame 16.

  In each of the gaps between the arranged channel partition plates 31, a plurality of slice partition plates 33 are arranged radially along a curved direction that approximates the slice direction. The slice partition plate 33 typically has a trapezoidal strip shape. The slice partition plate 33 may have a rectangular strip shape. The trapezoidal strip shape exhibits higher convergence and scattered radiation removal performance than the rectangular strip shape. All the slice partition plates 33 have the same shape.

  The collimator 13 according to the present embodiment constitutes an X-ray detector unit together with the X-ray detector. The X-ray detector unit is a component part of the X-ray computed tomography apparatus.

  As shown in FIG. 2, the X-ray computed tomography apparatus is equipped with a two-dimensional array type X-ray detector. 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 system 104 generally called DAS (data acquisition system). The data acquisition system 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 period. 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 unit 106 is connected to the data collection system 104 via a non-contact data transmission device 105. The pre-processing unit 106 corrects non-uniform sensitivity between channels for the projection data detected by the data acquisition system 104, and extremely reduces signal strength due to an X-ray strong absorber, mainly a metal part. Alternatively, preprocessing such as correction of signal dropout is executed. The projection data corrected by the preprocessing unit 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 to stably rotate the rotating ring 102 at a constant speed in order to perform a projection data collecting operation, that is, a scan, and from the X-ray tube 101 during the scan period. The high voltage generator 109 is controlled to generate X-rays, and control related to scanning such as controlling the data acquisition system 104 and the like in synchronization with X-ray generation is integrated.

  The two-dimensional array type X-ray detector 11 has a plurality of X-ray detection elements. The plurality of X-ray detection elements are two-dimensionally arranged with respect to the channel direction and the slice direction. A collimator 13 is provided on the X-ray source side of the two-dimensional array type X-ray detector 11. The collimator 13 optically separates the plurality of detection elements individually and provides incident directivity to each of the plurality of detection elements. As a result, scattered radiation is removed, and direct line detection ability is improved. The collimator 13 has a plurality of X-ray shielding plates assembled in a lattice shape in two directions of the slice direction and the channel direction.

  Here, the conventional collimator has a plurality of collimator modules having the same structure. The plurality of collimator modules are arranged in a polygonal shape around the X-ray focal point. Each module covers a partial matrix (assuming n × m channels here). m is the number of channels in the slice direction, and n is the number obtained by dividing the total number N of channels in the slice direction of the X-ray detector 11 by the number of collimator modules. Each module has (n + 1) plate-shaped channel partition plates to separate the detection elements in the channel direction. The (n + 1) channel partition plates are arranged on the module frame while changing the mounting angle little by little along the channel direction. Each module has (m + 1) slice partition plates to separate the detection elements in the slice direction. Each slice partition plate has a comb shape that covers the sensitivity width for n channels, and is inserted into (n + 1) channel partition plates in common. Therefore, the (n × m) collimated regions surrounded by the channel partition plate and the slice partition plate are aimed at the X-ray focal point in the central channel, but many other collimated regions are off the X-ray focal point. End up. This defect becomes more pronounced as the number of channels in the slice direction increases. In addition, there is a concern that sensitivity is reduced at the joint portion of the collimator module, and stress due to centrifugal force due to high-speed rotation concentrates on the joint portion of the collimator module and the sensitivity distribution becomes non-uniform. In the present embodiment, it is possible to eliminate such a problem.

  The collimator 13 is not a module in which a plurality of individually assembled modules are arranged in an arc shape as in the prior art, but can be assembled as a whole in accordance with the X-ray fan angle. Moreover, the collimator 13 has a structure capable of giving a constant curvature in two directions, that is, the channel direction and the slice direction. This structure realizes that all of the plurality of collimated regions are accurately aimed at the X-ray focal point F as shown in FIG. As shown in FIG. 4, the collimating region refers to each region surrounded by vertical and horizontal partition plates that constitute the collimator 13. A line connecting the center of one end face of the collimated region and the center of the other end face is called a collimate line. The collimate line indicates the directivity of the collimated region.

  As shown in FIGS. 5 and 6, the collimator 13 includes a plurality of channel partition plates 31 and a plurality of slice partition plates 33 having shielding properties against radiation, here X-rays. The channel partition plate 31 includes a shielding plate 42 having X-ray shielding properties and a guide rail 41. The slice partition plate 33 having X-ray shielding properties is supported by the guide rail 41 of the channel partition plate 31. The channel partition plate 31 optically separates the detection elements of the X-ray detector 11 in the channel direction. The slice partition plate 33 optically separates the detection elements of the X-ray detector 11 in the slice direction. The channel partition plate 31 and the slice partition plate 33 are assembled in a lattice shape.

  As shown in FIG. 7, the plurality of channel partition plates 31 are arranged radially with respect to the channel direction around the X-ray focal point F at regular intervals. As shown in FIG. 8, the plurality of slice partition plates 33 are arranged in the slice direction. The attachment angle of the slice partition plate 33 is individually determined so as to aim at the X-ray focal point F. The attachment angle of the slice partition plate 33 is determined so that the angle (Δθ2) between adjacent slice partition plates 33 is constant.

  FIG. 9 shows a perspective view of the collimator frame 16. The collimator frame 16 includes an upper frame 17, a lower frame 19, and side frames 21 and 23. The upper frame 17 has a partial ring shape. 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 set to be equivalent to The side frames 21 and 23 connect the upper frame 17 and the lower frame 19. The connected upper frame 17 and lower frame 19 are parallel. 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. 10, a plurality of guide grooves (referred to as channel partition plate guide grooves) 25 are formed in the lower frame 19. The plurality of guide grooves 25 are formed radially about the X-ray focal point F at regular intervals. The plurality of guide grooves 25 are arranged along the radial direction of the ring centered on the X-ray focal point F. The plurality of guide grooves 25 are arranged in an orderly manner so that the divergence angle Δθ1 defined as the angle formed between the collimating lines adjacent in the channel direction is constant. Similarly, a plurality of guide grooves 27 are formed in the upper frame 17.

  As shown in FIG. 11, a plurality of channel partition plates 31 are fitted in the plurality of guide grooves 25 and 27 and fixed with an epoxy adhesive. The channel partition plate 31 is provided perpendicular to the frames 17 and 19. Each channel partition plate 31 is disposed along a plane formed by a radius of an annulus centering on the X-ray focal point F and a parallel line to the slice axis.

  As described above, the channel partition plate 31 includes the rectangular shielding plate 42 and the plurality of guide rails 41 attached to the surface of the shielding plate 42. The shielding plate 42 of the channel partition plate 31 is cut into a rectangle from a thin molybdenum original plate having X-ray shielding properties. A plurality of guide rails 41 are formed on the surface of the shielding plate 42 cut out from the molybdenum original plate.

  As shown in FIGS. 12, 13, and 14, the pair of guide rails 41 form one guide groove 35. The pair of guide rails 41 are arranged in parallel with a predetermined interval corresponding to the thickness of the slice partition plate 33. The plurality of guide grooves 35 all have the same shape and the same size. As shown in FIG. 15, the plurality of guide grooves 35 are formed radially about the X-ray focal point F. The guide rail 41 is preferably made of a resin that is transparent to X-rays. The guide rail 41 is formed by printing a resin material directly on the surface of the channel partition plate 31. The outermost rail is used as a stopper rail 39 for the frames 17 and 19 (see FIG. 5).

  As shown in FIG. 16, the slice partition plate 33 is a thin plate having a trapezoidal strip shape made of a material having X-ray shielding properties. The slice partition plate 33 is cut out of a thin, for example, molybdenum original plate having X-ray shielding properties. All the slice partition plates 33 have the same shape and the same size.

  A plurality of slice partition plates 33 are arranged in each gap between adjacent channel partition plates 31. The slice partition plate 33 is fitted into the guide groove 35 of the channel partition plate 31, and is fixed by an epoxy adhesive or laser welding. The slice partition plate 33 is provided perpendicular to the channel partition plate 31.

  As shown in FIG. 17, the channel partition plate 31 and the slice partition plate 33 are assembled in a lattice shape. More specifically, a plurality of channel partition plates 31 having a flat plate shape are arranged, and a plurality of slice partition plates 33 having a flat plate shape are arranged in a gap between adjacent channel partition plate 31. This structure can achieve improving the aiming ability to the focus F. Since the channel partition plate 31 and the slice partition plate 33 do not require mechanical processing such as bending, bending, twisting, and welding, strength reduction and stress concentration caused by them can be eliminated. In addition, distortion, bending and twisting can be greatly reduced. Further, the aiming property can be obtained by an integrated configuration, not by the collimator 13 being configured by a combination of a plurality of modules. There are no problems such as excessive distortion applied to the module joint, etc., causing partial distortion, and the scattered radiation removal accuracy changes greatly at the module joint. You can gain continuity.

  FIG. 18 shows the appearance of the inner abutting plate. On the outer surface of the inner abutting plate 52, grooves 51 for receiving the channel partition plate 31 and the slice partition plate 33 are formed vertically and horizontally. The inner abutting plate 52 is made of, for example, a curved acrylic resin plate that is transparent to X-rays. As shown in FIGS. 19 and 20, the inner abutting plate 52 is fixed to the collimator frame 16 with screws or an adhesive. The inner abutting plate 52 supports and aligns the channel partition plate 31 and the slice partition plate 33 assembled in a lattice shape from the inside. The outer abutting plate 53 has a similar shape to the inner abutting plate 52. The outer abutment plate 53 supports and aligns the channel partition plate 31 and the slice partition plate 33 assembled in a lattice shape from the outside. The inner abutting plate 52 and the outer abutting plate 53 maintain the lattice structure of the channel partition plate 31 and the slice partition plate 33. The inner abutting plate 52 and the outer abutting plate 53 may be removed during the assembly process. In that case, the completed collimator 13 is not equipped with the inner abutting plate 52 and the outer abutting plate 53. In the manufacturing process, first, the inner abutting plate 52 is fixed inside the collimator frame 16 by an adhesive and screwing. Next, the channel partition plate 31 is inserted into the channel partition plate guide groove 25 and fitted into the groove 51 of the inner abutting plate 52. The channel partition plate 31 is fixed to the collimator frame 16 and the inner abutting plate 52 with an adhesive, for example. The slice partition plate 33 is inserted into the slice partition plate guide groove 35 of the channel partition plate 31 fixed to the collimator frame 16. The slice partition plate 33 is pressed from the outside by the outer abutment plate 53. Thereby, the slice partition plate 33 is aligned. The slice partition plate 33 is fixed to the channel partition plate 31, the inner abutment plate 52, and the outer abutment plate 53 with an adhesive, for example. Finally, the outer abutment plate 53 is fixed to the collimator frame 16 by screwing.

  The channel partition plate 31 described above includes a shielding plate 42 and a plurality of guide rails 41. The guide groove 35 is formed by a pair of guide rails 41. The guide groove 35 may be formed with a structure other than the guide rail.

  FIG. 21 shows a plan view of a channel partition plate 32 having another structure. FIG. 22 shows an AA cross-sectional view of FIG. FIG. 23 shows a lattice structure of the channel partition plate 32 and the slice partition plate 33. The channel partition plate 32 has a three-layer structure of a shielding plate 42 made of, for example, molybdenum and a resin layer 43 formed on both surfaces of the shielding plate 42. The resin layer 43 is formed of, for example, polyimide or araldide that is transparent to X-rays. The resin layer 43 is precisely applied or bonded to the surface of the shielding plate 42 by screen printing or tape bonding.

  The guide groove 35 is formed by etching the resin layer 43 with a guide groove pattern. The etching process is arbitrarily selected from chemical etching, gas etching, and ion beam etching. At the time of chemical etching, an anticorrosive agent is applied to the surface of the resin layer 43 in a guide groove pattern, and the guide groove 35 is formed by dipping in a corrosive solution. A corrosive solution is selected that is corrosive to polyimide or araldide and not corrosive to molybdenum. The guide groove 35 formed by the etching process penetrates the resin layer 43 and reaches the shielding plate 42. The shielding plate 42 is exposed. The bottom of the guide groove 35 is formed by a shielding plate 42. A side wall of the guide groove 35 is formed by the resin layer 43.

  The guide groove 35 may be formed on the resin layer 43 by a cutting process, a blasting process, or a laser processing process. Note that the blasting process is a technique in which a workpiece called a projection material is made to collide with a workpiece to process the workpiece.

  FIG. 24 is a sectional view showing the guide groove 35 formed by the cutting process. The guide groove 35 is formed by cutting the resin layer 43 according to the guide groove pattern. The cutting depth is adjusted to be less than the thickness of the resin layer 43. Both the side wall and the bottom of the guide groove 35 are formed by the resin layer 43. If the cutting reaches the shielding plate 42, the shielding plate 42 may be deformed and warped due to stress generated in the cutting process on the shielding plate 42 having a hardness higher than that of the resin layer 43. In order to suppress the occurrence of warping, the cutting depth is adjusted to be less than the thickness of the resin layer 43. Therefore, when the guide groove 35 is formed by cutting, the resin layer 43 is not penetrated and the shielding plate 42 is not exposed. This is the same even when the guide groove 35 is formed by blast processing or laser processing. In the case where the guide groove 35 is formed by the etching process, mechanical stress is not generated in principle, so that warping can be prevented, which is advantageous compared to cutting.

  FIG. 25 shows a cross-sectional view of the channel partition plate 32 in which the guide groove 35 is directly formed in the shielding plate 42. Typically, the guide groove 35 is formed in the shielding plate 42 by a cutting process. As described above, in order to reduce the warping of the shielding plate 42 due to mechanical stress, it is necessary to give the shielding plate 42 a certain thickness compared to the example of FIG.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the 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 their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 11 ... X-ray detector, 13 ... Collimator, 15 ... X-ray tube, 31 ... Channel partition plate, 33 ... Slice partition plate, 25 ... Channel partition plate guide groove, 35 ... Slice partition plate guide groove

Claims (6)

A collimator frame having a shape of a part of an annulus;
A plurality of first partition plates supported by the collimator frame, arranged radially along the circumferential direction of the ring, and having shielding properties against radiation;
A collimator comprising a plurality of second partition plates arranged radially in the gaps of the first partition plates and having a shielding property against the radiation ,
Each of the first partition plates has a shielding plate and a resin layer formed on the surface of the shielding plate, and a plurality of guide grooves for holding the second partition plate is formed by the resin layer. The shielding plate and the resin layer are provided on the first partition plate,
The guide groove penetrates the resin layer and reaches the shielding plate or is formed in the resin layer.
Collimator.   The collimator according to claim 1, wherein the second partition plate has a trapezoidal strip shape.   The collimator according to claim 1, wherein the second partition plates have the same shape.   The collimator according to claim 1, wherein the first partition plates have the same shape. An X-ray detector in which a plurality of X-ray detection elements for detecting X-rays are arranged in the channel direction and the slice direction;
In an X-ray detector unit comprising a collimator attached to the X-ray detector and providing incident directivity to the plurality of X-ray detection elements,
The collimator is
A collimator frame having a shape of a part of an annulus;
A plurality of first partition plates supported by the collimator frame, arranged radially along the channel direction, and having shielding properties against X-rays;
Along said slice direction are arranged radially, have a plurality of second partition plate having a shielding property to the X-ray in a gap each of the first partition plate,
Each of the first partition plates has a shielding plate and a resin layer formed on the surface of the shielding plate, and a plurality of guide grooves for holding the second partition plate is formed by the resin layer. The shielding plate and the resin layer are provided on the first partition plate,
The guide groove penetrates the resin layer and reaches the shielding plate or is formed in the resin layer.
X-ray detector unit. An X-ray source;
An X-ray detector in which a plurality of X-ray detection elements for detecting X-rays generated from the X-ray source and transmitted through the subject are arranged in the channel direction and the slice direction;
A collimator attached to the X-ray detector and providing incident directivity to the plurality of X-ray detection elements;
In an X-ray computed tomography apparatus comprising a reconstruction unit that reconstructs image data relating to the subject based on the output of the X-ray detector,
The collimator is
A collimator frame having a shape of a part of an annulus;
A plurality of first partition plates supported by the collimator frame, arranged radially along the channel direction, and having shielding properties against X-rays;
Along said slice direction are arranged radially, have a plurality of second partition plate having a shielding property to the X-ray in a gap each of the first partition plate,
Each of the first partition plates has a shielding plate and a resin layer formed on the surface of the shielding plate, and a plurality of guide grooves for holding the second partition plate is formed by the resin layer. The shielding plate and the resin layer are provided on the first partition plate,
The guide groove penetrates the resin layer and reaches the shielding plate or is formed in the resin layer.
X-ray computed tomography apparatus.

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