JP2006326175A - Digital x-ray tomography system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve precision in trajectory correction even when precision in installation positioning is low comparatively in a digital X-ray tomography system generating a tomogram of digital X-ray images imaged from a plurality of directions. <P>SOLUTION: The system comprises: an X-ray tube apparatus 30 for housing an X-ray tube 33 rotatably; an X-ray detector apparatus 40 for housing an X-ray detector 43 rotatably; a marker panel 51 on an X-ray tube side mounted to the front face of the X-ray tube apparatus: a marker panel 61 on the X-ray tube mounted to the front face of the X-ray detector apparatus; an image storage part 5 for storing data of the plurality of X-ray images imaged from a plurality of directions; a wide-area position calculation part 13 for calculating a wide-area position of each of the X-ray tube and the X-ray detector of each X-ray image based on the image of the marker 52 on the X-ray tube side and the image of the marker 62 on the side of the X-ray detector in the X-ray image; a local position calculation part 15 for calculating the local position of of the X-ray tube and the X-ray detector of each X-ray image based on the image of the marker 52 on the X-ray tube side and the image of the marker 62 on the side of the X-ray detector in the X-ray image; and an image-forming part 17 for forming a tomogram from the plurality of X-ray images based on the calculated wide-area position and local position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital X-ray tomography apparatus that generates a tomographic image from digital X-ray images taken from a plurality of directions.

  There is digital tomosynthesis as a technique for generating a stereoscopic image using X-ray images taken from several directions (see Non-Patent Document 1).

  A method for taking a tomographic image using this technique is X-ray digital tomography. In digital tomography, it is possible to improve the resolution of an image by calculating the position of the X-ray tube and the detector at the time of each X-ray image acquisition using an X-ray marker and performing an image formation process using it. It is known, and is also described in the above non-patent document 1 as Tuned aperture computed tomography. Here, this technique is called scan trajectory calibration.

  Patent Document 1 discloses an X-ray marker frame for brain surgery and a scan trajectory calibration method using the same for performing tomography with scan trajectory calibration in order to obtain a high resolution image during brain surgery. Are listed. The intraoperative X-ray tomographic imaging apparatus here is configured to be separated into a housing on the X-ray tube side and the detector side, and may be configured to be installed at a predetermined position with respect to the position of the imaging target when used. It is assumed that.

The function of the marker frame is to copy the marker together with the affected part to the X-ray image, measure the focus and detector position at the time of X-ray image shooting, perform position correction, and improve the resolution of the imaging process. A typical configuration of the marker frame is as follows.

-A marker panel with markers on the X-ray tube side and detector side is installed for the affected area.
-About 1.5φ of roughly lead cylinders (or lead spheres) are arranged in a lattice pattern at intervals of several centimeters on the marker panel on the X-ray tube side.
-The marker panel on the detector side has approximately 2x6mm roughly vertical cuboids arranged in a grid at intervals of several centimeters.
The mechanical positional relationship of each marker is fixed, and the positional relationship is made with high accuracy.

  Japanese Patent Application Laid-Open No. H10-228667 describes a scan trajectory calibration method using these marker frames. The outline is as follows. At the time of installation of the apparatus, the X-ray side casing and the detector side casing are installed at predetermined positions. At this time, an installation position guide mechanism using a laser projector (for example) is provided, which is installed at a predetermined position. The position installation accuracy at this time is assumed to be within about 1 cm. Thereafter, when imaging is performed, a plurality of X-ray images are acquired while moving the X-ray tube and the detector. If the predetermined installation position of the apparatus, the arrangement position of the marker, and the scan trajectory of the X-ray tube and the detector are known, it is possible to calculate at which position of the X-ray image the marker is imaged. On the other hand, when a marker position is detected from the acquired X-ray image, there is generally a difference between the calculated marker position and the detected marker position. This is caused by a shift in the installation position, accuracy in manufacturing the apparatus, distortion of an arm that supports and moves the detector and the X-ray tube, and an error in control of moving the detector and the X-ray tube. When the scan trajectory (the focus and the position of the detector in each captured image) is corrected and the deviation is calculated once again, the value becomes different from the previous deviation. Therefore, if the scan trajectory is corrected so that the deviation is minimized, the scan trajectory when the X-ray image is actually taken, that is, the focus and the position of the detector should be able to be estimated.

  In the above description, it has been stated that the installation accuracy of the apparatus is assumed to be about 1 cm or less, because the marker panel is arranged at equal intervals and the pattern is periodic, If the installation position of the device deviates from the predetermined position by more than half of the cycle, the scan trajectory is estimated at one (or more) cycle of the cycle, and the estimation is incorrect. Since there is no means for knowing, there is a problem that an image forming process is performed using the calibration result, and as a result, an erroneous image is generated.

As described above, conventionally, the positioning (installation positioning) at the time of installation of the apparatus is required to have high accuracy. On the other hand, it is necessary to adjust the installation position with high positional accuracy. This results in increased time and reduced usability.
James T Dobbins III and Devon J Godfrey: Digital x-ray tomosynthesis: current state of the art and clinical potential, PHYSICS IN MEDICINE AND BIOLOGY (Phys. Med. Biol.) 48 (2003) R65-R106 JP 2005-021345 A

  An object of the present invention is to improve the accuracy of scan trajectory calibration even when the accuracy of installation positioning is relatively low.

  A digital X-ray tomography apparatus according to the present invention includes an X-ray tube device that rotatably accommodates an X-ray tube, an X-ray detector device that rotatably accommodates an X-ray detector, and the X-ray tube device. An X-ray tube side marker panel having a plurality of X-ray tube side markers attached to the front surface and having X-ray high absorbency, and a plurality of X-ray detector devices attached to the front surface of the X-ray detector device An X-ray detector side marker panel having an X-ray detector side marker, and an image storage unit for storing data of a plurality of X-ray images taken from a plurality of imaging directions by the X-ray tube and the X-ray detector And the wide area of each of the X-ray tube and the X-ray detector for each X-ray image based on the X-ray tube side marker image and the X-ray detector side marker image in the X-ray image. A wide-area position calculation unit for calculating a correct position, and the X-ray tube side macro in the X-ray image. A local position calculation unit that calculates a local position of each of the X-ray tube and the X-ray detector for each X-ray image based on an image of a mosquito and an image of the X-ray detector side marker; An imaging unit configured to form a tomographic image from the plurality of X-ray images based on the calculated wide-area position and local position.

  According to the present invention, it is possible to improve the accuracy of scan trajectory calibration even if the accuracy of installation positioning is relatively low.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIGS. 1, 2, and 3, the digital X-ray tomography apparatus according to the present embodiment includes an X-ray tube device 30 and an X-ray detector device 40. The X-ray tube device 30 and the X-ray detector device 40 are physically separated from each other and configured as separate bodies. The X-ray tube device 30 is portable due to a stand 31 with casters 32. The stand 31 is mounted with a housing 34 that houses the X-ray tube 33. The X-ray tube 33 is supported by an X-ray tube rotation mechanism (not shown) so as to be rotatable about the imaging center axis SC in a state where the X-ray center axis is inclined with respect to the imaging center axis SC. The X-ray detector device 40 is portable by a stand 41 with casters 42. The stand 41 is equipped with a housing 44 that houses the X-ray detector 43. As the X-ray detector 43, a flat panel detector having a plurality of solid-state detection elements arranged in a two-dimensional manner is employed. The X-ray detector 43 is supported by a detector rotation mechanism (not shown) so as to be rotatable about the imaging center axis SC.

  An X-ray tube side marker panel 51 is mounted on the front surface of the housing 34 of the X-ray tube device 30. As shown in FIG. 4A, the X-ray tube side marker panel 51 absorbs X-rays higher than the substrate 53 on a substrate 53 formed in a circular shape with, for example, acrylic resin having relatively high X-ray transmission. A plurality of markers (X-ray tube side markers) 52 that are typically made of lead as a material having a ratio and typically spherical in the same predetermined shape are embedded or pasted. Since the marker 52 has clearly different shadows on the X-ray image, the image of the marker 52 can be easily extracted from the captured image by threshold processing in the alignment process described later.

  The X-ray tube side marker 52 is classified into a first X-ray tube side marker 52-1 and a second X-ray tube side marker 52-2 from the viewpoint of arrangement. The plurality of first X-ray tube side markers 52-1 are regularly arranged at equal intervals in the vertical and horizontal directions (the interval is 4 · d, where d is a unit distance). A plurality of (here, four) second X-ray tube side markers 52-2 are arranged at positions deviating from the arrangement rule of the first X-ray tube side markers 52-1. Specifically, (A) of the second X-ray tube side marker 52-2 is on the right side at a distance d with respect to the first X-ray tube side marker 52-1 located on the right side with respect to the center line SC. It is arranged at a position adjacent to. (B) of the second X-ray tube side marker 52-2 is located at a position adjacent to the upper side at a distance d with respect to the first X-ray tube side marker 52-1 located on the upper side with respect to the center line SC. Be placed. (C) of the second X-ray tube side marker 52-2 is adjacent to the left side at a distance d with respect to the first X-ray tube side marker 52-1 located on the left side with respect to the center line SC. Be placed. (D) of the second X-ray tube side marker 52-2 is adjacent to the lower side at a distance d with respect to the first X-ray tube side marker 52-1 located below the center line SC. Placed in position. With such an arrangement of the plurality of second X-ray tube side markers 52-2, at least four second X-ray tube side markers 52-2 are included in the X-ray field (X-ray bundle) regardless of the tube position. One X-ray tube side marker panel 51 is included depending on the relative positions of the one second X-ray tube side marker 52-2 and the first X-ray tube side marker 52-1 adjacent thereto. The focal position of the X-ray tube 33 in the whole can be specified for each image.

  Similarly, the X-ray detector side marker panel 61 is also mounted on the front surface of the housing 44 of the X-ray detector device 40. As shown in FIG. 4B, the X-ray detector side marker panel 61 has an X-ray higher than the substrate 63 on a substrate 63 formed in a circular shape with, for example, acrylic resin having relatively high X-ray transparency. A plurality of markers (X-ray tube side markers) 62 that are typically formed in a cylindrical shape as a predetermined shape that is different from the X-ray tube side marker 52 are typically embedded as lead as an absorptive material. Or it is pasted. Since the marker 62 has a clearly different shadow on the X-ray image, the image of the marker 62 can be easily extracted from the photographed image by threshold processing in the alignment process described later. Further, since the markers 52 and 62 have clearly different shapes from each other, they can be easily distinguished on the X-ray image.

  The X-ray detector side marker 62 is classified into a first X-ray detector side marker 62-1 and a second X-ray detector side marker 62-2 from the viewpoint of the arrangement. The plurality of first X-ray detector side markers 62-1 are regularly arranged at equal intervals in the vertical and horizontal directions (interval is 4 · g, g is a unit distance). A plurality of (here, four) second X-ray detector side markers 62-2 are arranged at positions deviating from the arrangement rule of the first X-ray detector side markers 62-1. Specifically, (A) of the second X-ray detector side marker 62-2 has a distance 2 on the right side with respect to the first X-ray detector side marker 62-1 located on the right side of the center line SC. -It is g and it adjoins in the position of the distance g on the upper side. (B) of the second X-ray tube side marker 62-2 has a distance 2 · g on the upper side with respect to the first X-ray detector side marker 62-1 located on the upper side of the center line SC, Adjacent to the left side at a distance g. (C) of the second X-ray detector side marker 62-2 has a distance of 2 · g on the left side with respect to the first X-ray detector side marker 62-1 located on the left side of the center line SC. Adjacent to each other at a distance g. (D) of the second X-ray detector side marker 62-2 has a distance of 2 · g below the first X-ray detector side marker 62-1 located below the center line SC. It is adjacent to the right side at the position of distance g. That is, with the arrangement of the plurality of second X-ray detector side markers 62-2, four second X-ray detector side markers in the detection surface of the detector 43 regardless of the position of the detector 43. At least one of the second X-ray detector-side markers 62-2 and the relative position of the first X-ray detector-side marker 62-1 adjacent thereto, The position of the detector 43 in the entire X-ray detector side marker panel 61 can be specified for each image.

  As shown in FIG. 5, the digital X-ray tomography apparatus according to the present embodiment includes a control unit 1, an interface 3, an image storage unit 5, a logarithmic calculation unit 7, It has a computer device in which a marker extraction unit 9, a global position calculation unit 13, a local position calculation unit 15, a reconstruction unit 17, an image processing unit 19, and a display unit 21 are connected. The image storage unit 5 stores data of a plurality of X-ray images output from the X-ray detector 43 and subjected to logarithmic calculation by the logarithmic calculation unit 7. The plurality of X-ray images are different from each other in at least one of the position of the X-ray tube 33, the position of the X-ray detector 43, and the direction of the X-ray tube 33 at the time of imaging. Note that the X-ray image includes images of the plurality of markers 52 and 62 together with the image of the subject. The marker extraction unit 9 has a function of extracting the image areas of the markers 52 and 62 for each X-ray image by threshold processing. The wide-area position calculation unit 13 determines the X-ray tube side marker panel 51 based on the relative positions of the second X-ray tube side marker 52-2 and the first X-ray tube side marker 52-1. The wide-area position of the focal point of the X-ray tube 33 in the whole is specified for each image. That is, it is specified for each image whether the second X-ray tube side marker 52-2 shown in the image is A, B, C, or D. The wide-area position calculation unit 13 detects the X-rays based on the relative positions of the second X-ray detector side marker 62-2 and the first X-ray detector side marker 62-1 adjacent thereto. The wide-area position of the X-ray detector 43 in the entire device side marker panel 61 is specified. That is, the second X-ray detector side marker 62-2 shown in the image is identified as A, B, C, or D. Details of the local position calculation process will be described later.

  The local position calculation unit 15 includes the wide-area position of the X-ray tube 33 and the wide-area position of the X-ray detector 43, the image of the first X-ray tube side marker 52, and the first Based on the deviation from the image of the X-ray detector side marker 62, the local position of the focal point of the X-ray tube 33 and the local position of the X-ray detector 43 are calculated for each image. Details of the wide area position calculation process will be described later.

  Based on the local position of the focal point of the X-ray tube 33 calculated for each X-ray image by the position calculation units 13 and 15 and the position of the X-ray detector 43, the reconstruction unit 17 performs single determination from a plurality of X-ray images. Alternatively, multi-stage tomographic image data (volume data) is reconstructed. The image processing unit 19 generates a two-dimensional image for display, for example, a tomographic image having an arbitrary cross section, from the reconstructed tomographic image. The generated tomographic image or the like is displayed on the display of the display unit 21.

  The position calculation process by the position calculation unit 11 will be described below. For example, the positional relationship of the markers 52 attached to the marker panel 51 on the X-ray tube 33 side is stored in a computer-readable form by preparing the following table in advance.

Arrangement table of first X-ray tube side marker 52-1
Marker # 1: x1 y1 z1
Marker # 2: x2 y2 z3
Marker # 3: x3 y3 z3
...
Marker #N: xN yN zN
Arrangement table of second X-ray tube side marker 52-2
Marker A: xA yA zA
Marker B: xB yB zB
Marker C: xC yC zC
Marker D: xD yD zD
(xi, yi, zi) (i = 1..N) is the coordinate value of the i-th marker 52-1. These numerical values are created by reading the origin at a suitable and easy-to-understand position (such as the center of the marker panel 51) on the design drawing. Similarly, a marker arrangement table on the detector 43 side is created in the same manner.

  During imaging, generation of X-ray pulses is repeated while the X-ray tube 33 rotates around the center line SC continuously or intermittently under the control of the control unit 1. Under the control of the control unit 1, the X-ray detector 43 synchronizes with the generation of X-ray pulses while continuously or intermittently rotating around the center line SC in synchronization with the rotation of the X-ray tube 33. Then, charge accumulation / signal readout / reset is repeated.

  Images of the markers 52 and 62 are extracted by the marker extraction unit 9 from each captured image. FIG. 6 shows an example of a circular marker and a line segment marker shown in an X-ray image. In the image of FIG. 6, second markers 52-2 and 62-2 having wide-area position information arranged at non-equal intervals are imaged at positions indicated by arrows. By applying the following processing to this image, two types of markers (circular X-ray tube side marker 52-2 image, rectangular X-ray detector side marker 62-2) are distinguished, and each marker in the image The position can be determined.

1. Filtering
2. Threshold processing, connected area labeling processing
3. Calculation of area, circularity, aspect ratio, density
4. Marker discrimination processing based on each calculated value (circular marker 52-2 and line segment marker 62-2 are distinguished in this process)
5. Marker position calculation processing (As a result, the position information of each marker is obtained numerically)
First, the wide area position information extraction process will be described. Here, only the circular marker (image of the X-ray tube side marker 52-2) will be described as an example, but the same applies to the case of the line segment marker (X-ray detector side marker 62-2).

  Based on the position information of each marker 52, first, the second markers 52-2 that are not regularly arranged at regular intervals at a distance of 4 · d are extracted. For this purpose, the distance from one detected marker 52 to another marker 52 is calculated, and this is the distance 4 · d (the distance corresponding to the distance 4 · d on the actual image, but for convenience of explanation) It is determined whether it is a possible distance from the marker arrangement, such as an integer multiple of the distance 4 · d). Here, if the interval between all the markers 52 is an interval of 4 · d, all the markers 52 are periodically arranged, but there are markers 52-2 that are not arranged at regular positions. In this case, the distance from the marker 52-2 to the other marker 52-1 should be d, not the distance 4 · d. Therefore, the marker 52-2 deviating from the interval 4 · d with respect to the other marker 52 is selected, the marker 52-2 is excluded, and the determination based on the inter-marker interval is performed again. If these are repeated, all the markers 52-1 will eventually have an appropriate interval. In this process, the excluded marker 52-2 is determined to be the second marker 52-2 which is not located at equal intervals.

  Next, as shown in FIG. 7, for each of the markers 52-2 that are not located at equal intervals, the vertical and horizontal intervals with respect to other nearby markers 52 are examined. In FIG. 7, the unit distance d is omitted. When the reference interval of the marker 52-1 is 4 · d, the horizontal distance from the marker 52-2 (A) to the marker 52-1 is 3, 7, 11, −1, −5 , -9, -13 (· d). The distances from B, C, D to the other equally spaced markers 52-1 should be as shown in FIG. Note that the markers 52-2 that are not evenly spaced all have different patterns in the vertical or horizontal spacing from the equally spaced markers 52-1. Therefore, by comparing the table interval with the calculated interval, it can be determined whether each marker 52-2 corresponds to any one of A, B, C, and D, and the actual marker. It is possible to specify which of the markers 52-2 corresponds to A, B, C, or D on the arrangement. The position of the image of the extraction marker 52-2 for which one of A, B, C, and D is specified has wide-area position information.

  In order to extract the wide-area position information described above, the arrangement of the non-uniformly spaced markers 52-2 is not limited to four, and the arrangement positions may not be as described above. That should be easy to guess.

Next, local position calculation will be described. Prior to the description of the wide-area position calculation process, the coordinate system and their relationship are defined in FIG.
The Xs coordinate system is a coordinate system in which a certain point (designed focus rotation center) of the X-ray tube housing 34 is taken as the origin.
The fi coordinate system is a coordinate system that is translated with respect to the Xs coordinate system, and is different for each projection (for each photographing).
TfiXs is an affine transformation matrix representing the amount of translation.
r0fi is a vector representing the focal position in the fi coordinate system in each projection.
The Xm coordinate system is a coordinate system with the origin of the marker panel reference point of the circular marker.
TXsXm is an affine transformation matrix that represents the position of the marker panel in the X-ray generator housing.
The G coordinate system is a coordinate system whose origin is a virtual reference point in the imaging region.
TXmG is an affine transformation matrix representing the positional relationship between the Xm coordinate system and G.
The Ds coordinate system is a coordinate system with the origin of rotation of the detector in the detector housing as the origin.
The Dm coordinate system is a coordinate system with the origin of the marker panel reference point of the line segment marker.
TDmDs is an affine transformation matrix representing the positional relationship between the Ds coordinate system and the Dm coordinate system.
The Di coordinate system is a coordinate system with the center position of the detector as the origin, and is different for each projection.

    TDsDi is an affine transformation matrix that represents the positional relationship between the Ds coordinate system and the Di coordinate system.

If the above affine transformation matrixes TfiXs, TDsDi, TXsXm, TXmG, TGDm, and TDmDs are determined, the X-ray markers 52-2 arranged at non-uniform intervals arranged on the marker panel 51 are projected onto the detectors. (Designed marker coordinates P _k ) can be calculated.

・ Designed marker coordinates P _k (k = 1, 2,..., N _m )
N _m is the number of X-ray markers 52 arranged. P _k is represented by a marker frame coordinate system (in this case, represents the coordinates of the markers 52-2 at non-uniform intervals).

On the other hand, the marker 52 shown in the photographed X-ray image is extracted by image processing to obtain its position.
Extracted marker coordinates q ^′ _ik (i = 1, 2,..., N _p )
N _p is the number of projections. In the following description, the subscript i always represents the projection number. (k = 1, 2, ... N _e (i))
N _e (i) is the number of X-ray markers extracted from the image of projection i.
q ^′ _ik is represented by the detector coordinate system (here, the extracted marker coordinates are arranged at non-uniform intervals).

Assuming that the focal point and the position of the detector 43 when actually photographed are exactly the same as the designed position, the marker 52 at the position _Pk attached to the marker panel 51 is the detection surface 43 in the projection i. The square error from the extracted marker position q ^′ _ik projected to the upper position P ^′ _ik

(The square error s is the mean square value of the distance on the detection surface between the projected marker position and the detected marker) is zero. Note that the x and y coordinates of P ^′ _ik and q ^′ _ik are the coordinate values in the horizontal and vertical directions on the detector 43. However, in actuality, there is an error in the position of the focus and the detector, and there is also a manufacturing error in the arrangement of the marker 52. Therefore, the square error is calculated as a value reflecting the average shift distance.

In the fitting process in the wide-area alignment, first, the design marker coordinates _Pk are calculated using the design values as TfiXs, TDsDi, TXsXm, TXmG, TGDm, and TDmDs, and the marker 52 is actually photographed. A square error s with the marker position q ^′ _ik extracted from the obtained image is calculated.

  Next, a fitting process for correcting TXsXm, TXmG, TGDm, and TDmDs is performed so that the square error s becomes as small as possible. For this processing, a generally known optimization method can be used. In this process, TfiXs and TDsDi are constants. The finally obtained TXsXm, TXmG, TGDm, TDmDs and constants TfiXs, TDsDi are the focal point and the position of the detector with respect to both marker panels 51, and the X-ray tube housing 34 and the detector housing. This indicates the positional relationship between the position 44 and 44.

Next, the local alignment process will be described. In the process of local alignment, the X-ray focus and detector 43 in each projection is obtained by using the extraction result of the marker 52 including only the equally spaced marker 52-1 or the non-equally spaced marker 52-2. Is estimated. Here, the designed marker coordinates P _k and the extracted marker coordinates q ^′ _ik represent the coordinates of the markers 52 including the equally spaced markers 52-1 or the non-equally spaced markers 52-2.

In the process of fitting by local alignment, first, marker coordinates P _k are calculated using the values obtained by wide-range alignment as TfiXs, TDsDi, TXsXm, TXmG, TGDm, and TDmDs. The square error s with the marker position q ^′ _ik extracted from the image taken is calculated.

  Next, a fitting process for correcting TfiXs and TDsDi is performed so that the square error s becomes as small as possible. For this processing, a generally known optimization method can be used. In this process, TXsXm, TXmG, TGDm, and TDmDs are constants. The finally obtained TXsXm, TXmG, TGDm, and TDmDs and constants TfiXs and TDsDi represent the positions of the focus and the detector 43 in each projection.

Here, the alignment process is performed ignoring the erroneously detected marker. This alignment process is basically the same as the above-described fitting process. However, when calculating the square error, only when the distance between q ^′ _ik and P ^′ _ik is smaller than a certain distance D, the calculation result of the square error is The only difference is that a calculation method that reflects the position of is used. For example, the calculation formula is as follows.

  When a large value is used as D, the fitting process is substantially the same as the fitting process in the previous section and the previous section. This alignment process is not indispensable in the present invention. However, in addition to (or replacing) the previous section and the previous section, if this section fitting was performed, it was excessively extracted in the marker extraction process. Even if a marker exists, such a marker does not affect the value of the above calculation formula as long as it is a small percentage of the whole. Therefore, this method has an effect that the fitting result is not easily affected by an error in the marker extraction process.

  Next, in the imaging process, various pre-processes are applied to the X-ray image, the image obtained as a result of these processes, and the position of the X-ray tube and detector for each calculated / corrected X-ray image frame The imaged image is calculated based on the orientation information and the range information designating the imaged region.

  In the above description, in the extraction of the wide-area position information, the correspondence relationship of the markers 52-1 other than the non-equally spaced markers 52-2 is also specified, and the wide-area alignment is performed using all the specified markers 52. To do.

  First, in the projection in which any of A, B, C, and D of the marker 52-2 is extracted, the marker 52-2 whose correspondence is specified is registered as an already specified marker. Next, the marker 52-1 closest to the specified marker 52-2 is selected from the markers 52-1 other than the specified marker 52-2, and the vertical alignment between the marker 52-1 and the specified marker 52-2 is selected. The correspondence between the selected marker 52 and the actual marker 52 is specified based on how many times the distance in the direction and the lateral direction is approximately the reference distance d. Hereinafter, the identified marker 52 is treated as an already specified marker. Furthermore, the closest non-specified marker 52 is selected from these specified markers 52, and the same processing is repeated until the correspondence of all the markers 52 is specified.

  According to the present embodiment, since the number of markers used for wide-area alignment increases, the alignment accuracy can be improved. If the above marker correspondence specification processing can be performed for all projections, the global alignment processing is omitted, and the local alignment processing is directly performed using the specified correspondence relationship. You can also

  FIG. 9 shows another marker arrangement example of the marker panel 51. The marker panel 51 includes a plurality of (in this case, four) subsets 55 each including a predetermined number of markers arranged at equal intervals 2 · d vertically and horizontally. The four subsets 55 are typically 1 / n (n is an integer of 2 or more) as a different distance from the interval 2 · d of the markers 52 in the subset 55, where n = 2 and vertically and horizontally at an interval d. Be placed.

  When the marker panel 51 having the marker arrangement of FIG. 9 is used to perform marker extraction, wide-area position information is obtained. At that time, the correspondence relationship of the markers 52 is specified by the following rule. The vertical distance between the marker 52 on the region A adjacent to the marker 52 of the adjacent subset 55 and the other marker 52 is approximately 2, 4, 6,. -3, -5, ... The vertical distance between the marker 52 on the region B adjacent to the marker 52 of the adjacent subset 55 and the other marker 52 is approximately 1, 3, 5,. 4 or -6. The horizontal distance between the marker 52 on the region C adjacent to the marker 52 of the adjacent subset 55 and the other marker 52 is approximately 2, 4, 6,. One of 3, -5, ... The vertical distance between the area D marker 52 adjacent to the marker 52 of the adjacent subset 55 and the other marker 52 is approximately 1, 3, 5,..., −2, −4, One of -6.

  If the above rule is used, A, B, C, and D markers can be extracted from the marker 52. In general, there are a plurality of (for example) A markers extracted in this way. The correspondence between the plurality of A markers and the actual marker can be individually specified by the distance in the lateral direction from the C or D marker. The same applies to the B marker. The correspondence between the C and D markers can be specified by the distance from the A marker and the B marker in the vertical direction.

  As illustrated in this embodiment, in order to specify the correspondence between the extracted marker and the actual marker, not only the method of arranging another marker that is not equally spaced, but also the purpose of the marker is devised. can do.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is an external view of an imaging mechanism of a digital X-ray tomography apparatus according to an embodiment of the present invention. The figure which shows the marker panel of each of the X-ray tube apparatus and detector apparatus of FIG. FIG. 2 is a schematic internal view of each of the X-ray tube device and the detector device of FIG. 1. The figure which shows the marker arrangement | sequence of the marker panel of FIG. The block diagram of the signal processing apparatus of the digital X-ray tomography apparatus of this embodiment. The figure which shows the image on the image of the 2nd marker of FIG. The figure which shows the vertical and horizontal arrangement | positioning space | center centering on the 2nd marker of FIG. The figure which shows the coordinate system used by the position calculation process by the position calculation part of FIG. The figure which shows the other marker arrangement | sequence of the marker panel of FIG.

Explanation of symbols

  30 ... X-ray tube device, 40 ... X-ray detector device, 31 ... Stand, 33 ... X-ray tube, 34 ... Housing, 41 ... Stand, 43 ... X-ray detector, 44 ... Housing, 51 ... X-ray Tube side marker panel, 52 ... X-ray tube side marker, 61 ... X-ray detector side marker panel, 62 ... X-ray detector side marker.

Claims (12)

An X-ray tube device that rotatably accommodates the X-ray tube;
An X-ray detector device for rotatably accommodating the X-ray detector;
An X-ray tube side marker panel attached to the front surface of the X-ray tube device and having a plurality of X-ray tube side markers having high X-ray absorption;
An X-ray detector side marker panel attached to the front surface of the X-ray detector device and having a plurality of X-ray detector side markers having high X-ray absorption;
An image storage unit that stores data of a plurality of X-ray images captured from a plurality of imaging directions by the X-ray tube and the X-ray detector;
Wide-range positions of the X-ray tube and the X-ray detector for each X-ray image based on the X-ray tube side marker image and the X-ray detector side marker image in the X-ray image. A global position calculation unit for calculating
Local positions of the X-ray tube and the X-ray detector for each X-ray image based on the X-ray tube side marker image and the X-ray detector side marker image in the X-ray image. A local position calculation unit for calculating
A digital X-ray tomography apparatus comprising: an imaging unit that forms a tomographic image from the plurality of X-ray images based on the calculated wide-area position and local position. The plurality of X-ray tube side markers are a plurality of first X-ray tube side markers arranged at equal intervals in the vertical and horizontal directions, and a plurality of first X-ray tube side markers arranged at positions deviated from the first X-ray tube side markers. The digital X-ray tomography apparatus according to claim 1, comprising two X-ray tube side markers. The plurality of X-ray tube side markers are individually different in relative position with respect to the plurality of first X-ray tube side markers arranged at equal intervals in the vertical and horizontal directions and the first X-ray tube side marker in the vicinity. The digital X-ray tomography apparatus according to claim 1, comprising a plurality of second X-ray tube side markers. The X-ray tube side marker is arranged so that a wide-area position in the entire X-ray tube side marker panel is specified from a positional relationship between a plurality of adjacent X-ray tube side markers. The digital X-ray tomography apparatus according to claim 1. The X-ray tube side markers are divided into a plurality of subsets composed of a predetermined number of X-ray tube side markers arranged at equal intervals in the vertical and horizontal directions, and the four subsets are intervals of the X-ray tube side markers in the subsets. The digital X-ray tomography apparatus according to claim 1, wherein the digital X-ray tomography apparatus is arranged at an interval of 1 / n (n is an integer of 2 or more). The plurality of X-ray detector side markers are arranged at positions separated from the plurality of first X-ray detector side markers arranged at equal intervals in the vertical and horizontal directions and the first X-ray detector side marker. The digital X-ray tomography apparatus according to claim 1, comprising a plurality of second X-ray detector side markers. The plurality of X-ray detector side markers are individually positioned relative to a plurality of first X-ray detector side markers arranged at equal intervals in the vertical and horizontal directions and a nearby first X-ray detector side marker. The digital X-ray tomography apparatus according to claim 1, further comprising a plurality of second X-ray detector side markers different from each other. The X-ray detector side marker is arranged so that a position in the entire X-ray detector side marker panel is specified from a positional relationship among a plurality of adjacent X-ray detector side markers. The digital X-ray tomography apparatus according to claim 1. The X-ray detector side marker is divided into a plurality of subsets each including a predetermined number of X-ray detector side markers arranged at equal intervals in the vertical and horizontal directions, and the four subsets are arranged on the X-ray detector side in the subset. 2. The digital X-ray tomography apparatus according to claim 1, wherein the digital X-ray tomography apparatus is arranged at an interval of 1 / n (n is an integer of 2 or more) of an interval between markers. The digital X-ray tomography apparatus according to claim 1, wherein the X-ray tube side marker has a shape different from that of the X-ray detector side marker. The digital X-ray tomography apparatus according to claim 1, wherein the X-ray tube side marker has a spherical shape, and the X-ray detector side marker has a cylindrical shape. The digital X-ray tomography apparatus according to claim 1, wherein the X-ray tube side marker has a spherical shape, and the X-ray detector side marker has a cylindrical shape.

Images