JP4405836B2 - Computed tomography equipment - Google Patents

Description

  The present invention relates to an industrial or medical computer tomography apparatus.

  In recent years, in order to inspect small electronic components and the like with high resolution, high-resolution industrial computer tomography apparatuses (hereinafter referred to as CT) have been made.

  For example, in a conventionally known high-resolution CT described in Patent Document 1, a cone-shaped X-ray beam generated from an X-ray tube and transmitted through a subject is detected by a two-dimensional X-ray detector and detected. A transmission image of the subject is generated based on the X-ray intensity.

  When a cross-sectional image is taken with such a conventional high-resolution CT, a scanning method that detects a large number of transmitted images while rotating the subject once between a fixed X-ray tube and an X-ray detector. Is used. In this case, in order to obtain a three-dimensional image which is a large number of cross-sectional images of the subject, a large number of transmission images obtained in this way are reconstructed.

  The scan described above is a scan method called an RR method (rotate / rotate method), which scans only by a rotation operation (rotate / rotate operation).

  For such cone beam image reconstruction, the method described in Non-Patent Document 1 is usually used. This method is a kind of filter-corrected back projection method (FBP (Filtered Back Projection) method), and is three-dimensionally back-projected. An example of reconstruction by this filter-corrected back projection method is used in the invention described in Patent Document 1.

  FIG. 8 is a simple configuration diagram for explaining a general high-resolution CT100. 8A is a plan view, and FIG. 8B is a front view. The high resolution CT 100 includes an X-ray tube 101, an X-ray detector 102, and a rotary table 103. An X-ray beam 104 generated from the X-ray tube 101 passes through a subject 105 placed on a rotatable rotary table 103 and is detected by an X-ray detector 102 facing the X-ray tube 101.

  This high-resolution CT100 is characterized in that the X-ray geometry can be set freely and can be used for measurement of various subjects 105. By disposing the subject 105 and moving the rotary table 103 and the X-ray detector 102 in the x direction, the distance from the X-ray tube 101 having the focal point F can be changed. Thus, the imaging distance FCD (Focus to rotation Center Distance) and the detection distance FDD (Focus to Detector Distance) can be continuously changed, and the imaging magnification (magnification rate) (= (FDD / FCD) can be freely changed.

  Further, the high resolution CT 100 can move the rotary table 103 in the z direction (vertical direction). As described above, by moving the subject 105 in the vertical direction, the imaging region of the subject 105 can be freely changed.

  In FIG. 8, a scan area A (cross-sectional image field) is a circle centered on the rotation center C included in the X-ray beam 104 on the rotation surface, and becomes smaller as the imaging magnification increases. The X-ray beam 104 is an X-ray to be measured, and X-rays that are not measured are emitted outside the X-ray beam 104. This scan area A is an area where sufficient data that can be reconstructed without difficulty is collected, and has a volume with a thickness in the rotation axis direction (z-axis direction). This thickness is a thickness included in the X-ray beam 104 in the rotation axis direction.

  In such a high-resolution CT100, it is preferable to take an image with a magnification as large as possible without getting out of the scan region A according to the size of the subject 105, because a high-resolution cross-sectional image can be obtained.

  Here, when a space measured by the measurement region 106 of the X-ray detector 102 is defined as a measurement field, the measurement field coincides with the spread of the X-ray beam 104. For this reason, the subject 105 that protrudes from the measurement visual field during scanning can be said to be the subject 105 that protrudes from the scan region A. Such an object 105 cannot obtain an entire three-dimensional image by a normal RR method. Therefore, as a technique in this case, Patent Document 2 and Patent Document 3 describe a method of obtaining a large range of three-dimensional images that do not fit in the measurement field of view by rotating a plurality of rotations while continuously shifting the rotation center. However, this method has a complicated image reconstruction process. In addition, there is a problem that it is difficult to accurately move the center of rotation in synchronization with the rotation, which is difficult to implement.

  On the other hand, in addition to the above-described high-resolution CT of the RR method, there is a CT using a scan in the TR method (translate / rotate method) performed by an operation (translate / rotate operation) that combines translation and rotation. Are known. When this TR scan method is employed, a cross-sectional image of the subject that protrudes from the measurement visual field can be obtained.

However, when this TR method is applied to a high-resolution CT, a large subject can be scanned. However, in the case of a small subject, the scan time is longer than the RR method, which easily improves the mechanism accuracy in terms of image quality. There's a problem. In addition, there is a problem that a TR image reconstruction method for obtaining a three-dimensional image in one scan using a cone beam is not known.
JP 2001-330568 A JP 2002-219127 A JP-A-9-164133 L. A. Feldkamp, L.M. C. Davis, J.A. W. Kress, “Practical cone-beam algorithm”, Optical Society of America (USA), Vol. 1, No. 1 6 June 1984, p. 612-619

  In order to solve the above problems, an object of the present invention is to obtain a large three-dimensional image of a subject that does not fit in the measurement visual field by a simple scanning method using a cone-shaped X-ray beam.

In order to solve the above-mentioned problem, the invention according to claim 1 is a two-dimensional resolution radiation detector that detects a cone-shaped radiation beam generated by a radiation source and transmitted through a subject, the subject, and the radiation beam. A three-dimensional image of the subject from a plurality of transmission data obtained by detection by the radiation detector at a plurality of positions while being skinned by an RR method for performing the rotation, While being scanned by the TR method that repeats the parallel movement and the stepwise rotation, the cone beam RR reconstructing means for reconstructing, the parallel moving means for giving a relative translation to the subject and the radiation beam, Cone beam TR reconstruction means for reconstructing a three-dimensional image of the subject from a plurality of transmission data obtained by being detected by the radiation detector at a plurality of positions, Nbimu TR reconstruction means, converts the axial position m of the rotating two-dimensional resolution, orthogonal direction position n, the transmission data by logarithmic transformation into projection data composed of a translational position t and translation number k A logarithmic conversion function, a filter function for applying a high-frequency emphasis filter to the converted projection data in the direction of the translation position t, and a set of the axial position m and the translation position t after being subjected to the high-frequency emphasis filter. and the projection data is the surface data, the radiation beam the each set of surface data in all orthogonal direction position n and translation of times k that backprojection angle viewed from the rotation axis direction is a 180 ° component A back projection function for performing three-dimensional back projection on a virtual three-dimensional lattice representing the subject toward the focal point of the object, and depending on the size of the subject, scanning by the RR method or The gist of the invention is that it is possible to freely select and operate the TR scan.

  According to the first aspect of the present invention having the above-described configuration, it is possible to select either the RR method or the TR method for scanning according to the size of the subject. A wide range of measurements is possible.

According to a second aspect of the present invention, a radiation detector having a two-dimensional resolution that detects a cone-shaped radiation beam generated by a radiation source and transmitted through a subject, and a relative rotation is applied to the subject and the radiation beam. Detected by the radiation detector at a plurality of positions during a rotation scan, a translation device that gives a relative translation to the subject and the radiation beam, and a TR scan that repeats the translation and the stepwise rotation. Cone beam TR reconstructing means for reconstructing a three-dimensional image of the subject from a plurality of transmission data obtained in this manner, and the cone beam TR reconstructing means comprises the rotation of the two-dimensional resolution. a logarithmic conversion function for converting axial position m, orthogonal direction position n, the transmission data by logarithmic transformation into projection data composed of a translational position t and translation number k, the A filter function of multiplying the high-frequency emphasis filter in translation position t direction relative to the projection data conversion, after being frequency emphasis filter seat, the projection data is a set of surface data at an axial position m and translational position t The subject is directed toward the focal point of the radiation beam for each set of plane data at all the orthogonal direction positions n and the number of parallel movements k at which the back projection angle viewed from the rotation axis direction is 180 °. And a back projection function for performing a three-dimensional back projection on a virtual three-dimensional lattice representing the above.

According to the invention according to claim 2 having the above-described configuration, transmission data covering the subject by translation is obtained by scanning the subject that does not fit in the radiation beam by the TR method, and the cone beam. A three-dimensional image can be obtained by the TR reconstruction means.

The invention according to claim 3 is the computer tomography apparatus according to claim 1 or 2 , further comprising FCD changing means for changing FCD which is a distance between the focal point of the radiation beam and the rotation axis. It is said.

According to the invention of claim 3 having the above-described configuration, the optimum geometric condition can be set by changing the FCD according to the size of the subject, and a high-quality three-dimensional image can be obtained. .

According to a fourth aspect of the present invention, in the computed tomography apparatus according to any one of the first to third aspects, the FDD changing means changes an FDD that is a distance between the focal point of the radiation beam and the radiation detector. And TR scan control means for automatically changing the number of repetitions of the stepwise rotation and parallel movement of the radiation beam divergence angle θ ₀ in accordance with the FDD. Yes.

According to the invention of claim 4 having the above-described configuration, it is possible to set an optimal geometric condition according to the size of the subject, and to obtain a high-quality three-dimensional image. Further, when the FDD is changed, the change in the fan angle .theta.0 is automatically set, and the number of repetitions is automatically determined. Therefore, the FCD can be set without the troublesomeness of setting the number of repetitions.

  As described above, according to the present invention, there is provided a computed tomography apparatus capable of obtaining a three-dimensional image of a large subject that does not fit in a measurement visual field by a simple scanning method using a cone-shaped X-ray beam. Can do.

  The present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram illustrating a high resolution CT 1 according to the first embodiment of the present invention. 1A is a plan view, and FIG. 1B is a front view.

  The high-resolution CT 1 according to the present invention includes an X-ray tube 2, an X-ray detector 3, support frames 4 and 5, a support base 6, an XY movement mechanism 7, a rotation / lifting mechanism 8, a y-direction movement mechanism 9, and an x-direction shift. A mechanism 10, a mechanism control unit 11, a data processing unit 12, an input / output unit 13, an X-ray control unit 14, and a high voltage generator 15 are provided.

  The X-ray tube 2 has a function of generating an X-ray beam 20 and uses a microfocus X-ray tube having a focal point F of several μm. The X-ray detector 3 has a function of detecting the X-ray intensity of the X-ray beam 20 generated from the X-ray tube 2 using an X-ray flat panel detector (FPD) in which a scintillator is bonded to a two-dimensional semiconductor optical sensor. have. The X-ray tube 2 and the X-ray detector 3 are supported by the support frames 4 and 5 so as to face each other.

  The support table 6 is used to place the subject 21, and the X-ray beam 20 generated from the X-ray tube 2 passes through the subject 21 placed on the support table 6 and is used as an X-ray detector. 3 is detected. The support base 6 can be moved in the xy direction (moving in a horizontal plane) by the XY moving mechanism 7.

  The subject 21 is rotated within the X-ray beam 20 by the rotation / elevation mechanism 8 along the imaging surface 22 of the cross-sectional image, and is moved (elevated) in the z direction at right angles to the imaging surface 22. The positional relationship between the rotation center C and the subject 21 is adjusted by moving in the XYz directions by the XY movement mechanism 7 and the rotation / lifting mechanism 8.

  The support base 6 is moved in the y direction in FIG. 1 so as to cross the X-ray beam 20 by operating the y direction moving mechanism 9 together with the rotating shaft 23. Further, the x-direction shift mechanism 10 moves the x-ray tube 2 and the x-ray detector 3 in the x direction, thereby changing the imaging distance FCD.

  The mechanism control unit 11 controls operations on the XY movement mechanism 7, the rotation / lifting mechanism 8, the y-direction movement mechanism 9, and the x-direction shift mechanism 10. The rotation center C is adjusted to be the center of the X-ray beam 20 by movement in the y direction.

  Here, the scan area A is a cylindrical area that is included in the X-ray beam 20 measured around the rotation axis with the rotation axis 23 as the center, and sufficient data that can be reconstructed without difficulty in scanning by the RR method. The area to be collected. The scan area B is a cylindrical area in which the diameter can be arbitrarily set around the rotation axis 23 and the rotation axis direction is included in the X-ray beam 20, and can be reconfigured without difficulty in scanning by the TR method. This is an area where various data is collected.

  The data processing unit 12 has a function of performing processing for constructing a transmission image from the X-ray intensity detected by the X-ray detector 3 and a function of reconstructing a three-dimensional image from the transmission image. Software for reconstructing a scan sequence, a three-dimensional image (cross-sectional image), and the like are stored. In response to an operation command from the data processing unit 12, the mechanism control unit 11 performs an operation. The data processing unit 12 performs RR scanning and TR scanning, and RR reconstruction that creates a three-dimensional image (cross-sectional image) as an RR scanning unit 12a, TR scanning unit 12c that controls scanning, as software functional blocks Part 12b and TR reconstructing part 12d.

  Further, the input / output unit 13 has a function of inputting various operation instructions for operating the high resolution CT 1 and a function of outputting a processing result processed by the data processing unit 12. For example, input is performed using a mouse or a keyboard, and the result is output to a display or the like.

  The data processing unit 12 and the input / output unit 13 are ordinary computers and include a CPU, a memory, a disk, a keyboard, an interface, and the like. The operator uses the input / output unit 13 to perform menu selection, condition setting, manual operation of the mechanism unit, start of scanning, status reading of the apparatus, and the like. The input / output unit 13 displays a three-dimensional image (cross-sectional image) obtained by the operation.

  The X-ray control unit 14 is connected to a high voltage generator 15 that generates a high voltage, and has a function of controlling the tube voltage and tube current of the X-ray tube 2. Although not shown, there is an X-ray shielding box that houses a portion including the X-ray tube 2, the X-ray detector 3, and the subject 21.

  The tube voltage and tube current can be freely changed according to the subject 21. An encoder (not shown) is attached to the x-direction shift mechanism 10, the y-direction movement mechanism 9, etc., and FCD value, FDD value, y value, etc. are read, and the data processing unit is respectively connected via the mechanism control unit 11. 12 is input.

  The flow of the high-resolution CT processing according to the first embodiment of the present invention will be described. First, when a scanning method is selected and input from the input / output unit 13 such as a mouse or a keyboard by the operator, the data processing unit 12 scans by the RR method or the TR method according to the input of the selected operation instruction. Is started.

  Note that “transmission image”, “detection intensity”, and “projection data” in the following examples are names at the processing stage, and are included in “transmission data” described in the claims.

<Process when scanning by RR method>
First, the flow of processing when the RR method is selected as the scanning method will be described. Generally, this RR method is a method used when measuring a relatively small subject 21. The operator first sets the FCD and FDD by placing the subject 21 on the support base 6 and operating the x-direction shift mechanism 10. Thereafter, the XY movement mechanism 7 is operated so that the subject 21 enters the scan area A.

  In the example shown in FIG. 1, the subject 21 is drawn so as to protrude from the scan area A for convenience of explanation. However, the subject 21 is usually placed so that the subject 21 does not protrude from the scan area A so that the image quality does not deteriorate.

  When the scan is started, the data processing unit 12 controls the scan by the RR scan unit 12a, and the RR reconstruction unit 12b reconstructs the three-dimensional image of the scan area A from the transmission image obtained by the X-ray detector 3. Constitute.

  The scan by the RR method is performed only by the rotation operation with respect to the rotation shaft 23, and a three-dimensional image of the scan area A is obtained. Image reconstruction in this case is described in Feldkamp et al. It is done by the method. An outline of the image reconstruction method will be described with reference to FIGS.

  The flowchart shown in FIG. 2 is a diagram for explaining the flow of RR image reconstruction processing using cone beams. FIG. 3 is a diagram for explaining back projection in this case. Here, x ′, y ′, and z ′ are coordinates fixed to the subject 21, and the rotation axis 23 is the z ′ axis. Here, the transmission data generated from the X-ray intensity obtained by the X-ray detector 3 is transmitted by the transmission data I (m, n, φ).

  First, the transmission data I (m, n, φ) is converted into projection data P (m, n, φ) by logarithmic conversion (S11). Since this logarithmic conversion is a method usually used in CT, description thereof is omitted. Next, the obtained projection data P (m, n, φ) is subjected to high-frequency emphasis filtering in the orthogonal direction (n direction) (S12). This filter is a | ω | filter similar to the filter generally used in CT.

After the high frequency enhancement filter is applied, as shown in FIG. 3, the projection data is converted into projection data P (m, n) which is a set of plane data described by the rotation axis direction position m and the orthogonal direction position n. ), Three-dimensional backprojection is performed on the virtual three-dimensional lattice representing the subject 21 toward the focal point F (S13). That is, the data of the point _GP on the corresponding measurement region 30 is added to all the grid points G. When this back projection is performed for one rotation of φ, a three-dimensional image of the scan area A of the subject 21 is obtained.

  The three-dimensional image of the subject 21 reconstructed in this way by the RR reconstruction unit 12b is displayed on the input / output unit 13 such as a display.

<TR scan method>
Next, the flow of processing when the TR method is selected as the scanning method will be described. First, the operator places the subject 21 on the support base 6 in the same manner as in the RR scan. Subsequently, by operating the x-direction shift mechanism 10, FCD and FDD are set. When FCD and FDD are set, the center of the subject 21 is aligned with the rotation axis 23 by operating the XY movement mechanism 7. Thereafter, the scan area B is set. The setting of the scan area B is performed, for example, by inputting the diameter of the scan area B as a mm value.

When a scan operation instruction is given after setting the scan region B, the scan is started by the operation of the TR scan unit 12c. At this time, the fan angle θ ₀ that is the spread angle of the X-ray beam 20 is changed by FDD. In order to cope with this change, the number of times of translation K is automatically set in accordance with the fan angle θ ₀ by the TR scanning unit 12c before the scan is started. Specifically, the translation count K is
Minimum integer K such that K · θ ₀ > π
As required.

Thereafter, the TR scanning unit 12c controls scanning, and scanning is started. As in the well-known TR method, scanning is performed by repeating y-direction movement (translation operation) and step rotation of the fan angle θ ₀ with respect to the rotating shaft 23. The scanning is performed so that the X-ray beam 20 completely traverses the diameter of B, and the scanning is completed after K times of y movement.

  Next, based on the transmission data obtained by the X-ray detector 3 by the scanning operation, a three-dimensional image of the subject 21 in the scan region B is reconstructed by the TR reconstruction unit 12d.

  The outline of this image reconstruction method will be described with reference to FIGS. The flowchart shown in FIG. 4 is a diagram for explaining the flow of TR image reconstruction processing using cone beams. FIG. 5 is a diagram for explaining back projection in this case. Here, x ′, y ′, and z ′ are coordinates fixed to the subject, and the rotation axis 23 is the z ′ axis.

  The transmission data generated from the X-ray intensity detected by the X-ray detector 3 is the rotation axis direction position m, the orthogonal direction position n, the y direction movement position t, and the y direction movement number of the measurement region 30 of the X-ray detector 3. Is described as transparent data I (m, n, t, k).

  First, transmission data I (m, n, t, k), which is a detection intensity proportional to the X-ray intensity, is logarithmically converted into projection data P (m, n, t, k) (S21). Thereafter, a high frequency enhancement filter is applied to the projection data P (m, n, t, k) in the t direction (S22). This filter is a | ω | filter generally used in CT. Since the logarithmic conversion and the high frequency emphasis filter are the same techniques as those in the prior art, the description is omitted.

When the high-frequency emphasis filter is applied, as shown in FIG. 5, the projection data P (m) is a set of plane data described by the rotation axis direction position m and the y-direction movement position t. , T), three-dimensional backprojection is performed on the virtual three-dimensional lattice representing the subject 21 toward the focal point F (S23). At this time, the focal point F moves according to the y-direction moving position t (F miracle 33). Therefore, when viewed from the direction of the rotation axis 23, the backprojection direction is parallel and forms an angle ψ with respect to the y ′ axis. Here, ψ is an angle determined by the orthogonal position n and the number of translations k. Further, the back projection is to add the data of the corresponding point _GP on the mt plane 34 to all the lattice points G. Note that G _P generally does not coincide with the data point, so interpolation calculation is performed (by the neighboring four points). When this back projection is performed at all orthogonal position n and the number of translations k (for 180 ° of ψ), a three-dimensional image of the scan region B of the subject 21 is obtained.

  The three-dimensional image of the subject 21 whose image has been reconstructed in this way by the TR reconstruction unit 12d is displayed on the input / output unit 13 such as a display.

  As a method of selecting FCD and FDD, it is preferable to increase the enlargement ratio in both the above-described RR method and TR method, but the resolution is improved, but the thickness of the scan region is reduced. Further, when the magnification is the same, an image with less noise can be obtained by reducing the FCD as much as possible, but interference between the subject and the mechanism occurs. Therefore, in practice, the geometric setting is performed according to the subject and the examination purpose in consideration of such a situation.

  According to the present invention according to the first embodiment, since a single CT can be used by switching between the TR scan method and the RR scan method, various subjects can be measured regardless of the size. is there.

  For example, by selecting the TR scan method, it is possible to easily obtain a three-dimensional image even for a large subject that does not fit in the measurement visual field. In addition, by selecting the RR scan method, in the case of a small subject that can be accommodated in the measurement field of view, it is possible to perform the scan only by rotating, thereby reducing the scan time and improving the mechanism accuracy. It is possible to obtain a high-quality three-dimensional image.

  In addition, since FCD, FDD, and the like are variable, it is possible to set an optimal geometric condition such as an enlargement ratio in accordance with the subject, and a high-quality three-dimensional image can be obtained.

  Furthermore, since a two-dimensional detector is used, a transmission image can be easily obtained.

Further, in the TR scan, the number of translations K is automatically determined by automatically setting the change in the fan angle θ ₀ accompanying the change in the FDD. Therefore, it is not necessary to change the number of translations K, which is bothersome. FDD can be set without any changes.

Regarding the image reconstruction when scanning is performed by the above-described TR method of the present invention, it is also possible to reconstruct using ψ with overlapping data exceeding π. In this case, an overlapping portion at the end of the collected data range K · θ ₀ is used. However, when there are few overlapping portions, one translation may be added. Then, the obtained projection data P (m, t, ψ) is back-projected by applying a weight W (ψ) as shown in FIG.

  As shown in FIG. 6A, W (ψ) is a weight having an inclined portion that linearly changes from 0 to 1 in the overlapping section 2 · α at the front end and the rear end. This weight should be smoothly shifted from 0 to 1 at the front end of ψ, and from 1 to 0 at the rear end, and W (ψ) + W (ψ + π) = 1, and the weight W ′ in FIG. A curve may be formed as in (ψ). By this weighting, artifacts due to data seams at both ends of the data range can be reduced, and image reconstruction can be completed when scanning is performed using the cone beam TR method. This weighting may be performed before or after filtering.

  Although omitted in the description of the above-described TR image reconstruction, normally, the projection data P (m, n, t, k) is averaged by bundling in the n direction before back projection to reduce the number of data. is doing. By bundling in this way, the number of back projections with respect to ψ can be reduced, and reconstruction can be performed at high speed.

  In addition, when used without bundling, the number of directions in ψ becomes excessive in the case of TR scan. When the setting of the three-dimensional lattice pitch for reconstruction is made coarse, the respective directions of the rotational axis direction position m, the orthogonal direction position n, and the Y direction movement position t may be bundled accordingly. Bundling may be performed before logarithmic conversion.

  Furthermore, in both the RR scan and the TR scan, it is possible to obtain a wide three-dimensional image by connecting the three-dimensional images obtained by scanning a plurality of times while changing the lift position in the z direction. At this time, the three-dimensional images can be overlapped to adjust the position error by fitting, and the overlapping portions can be averaged with weights to create a three-dimensional image that is smoothly connected.

  The TR scan described above is a half scan for obtaining a three-dimensional image from 180 ° transmission data, but it is easy to use a 360 ° full scan, a 720 ° double full scan, or the like. Understandable. These scans are known from JP-A-11-108857. In this case, back projection may be performed 360 ° and 720 ° with respect to ψ. In the case of the double full scan, the surface data P (m, t) separated by 360 ° is averaged to obtain surface data P (m, t) for 360 ° and then backprojected.

  The RR scan is not a normal scan (360 ° rotation), but a known half scan (180 ° + fan angle rotation), overscan (360 ° + α rotation), helical scan (spiral rotation), and offset scan. It can be easily understood that (center shift) may be used.

  Even when used only for TR scanning (only for TR), it is possible to obtain a large range of three-dimensional images that do not fit in the measurement field of view.

  Moreover, although the use of a microfocus X-ray tube has been described above, the present invention is not limited to microfocus X-rays.

  Furthermore, in the above description, X-rays are used as radiation. However, the present invention is not limited to this, and it is obvious that other transmissive radiation may be used.

  Moreover, although it mentioned above using FPD as a two-dimensional X-ray detector, naturally it is not restricted to FPD.

Modified example

  If the operation of each mechanism of CT is relatively equivalent to the operation described in the first embodiment, the present invention can be applied to other mechanism systems. For example, in the method described in the first embodiment, the rotation is performed by rotating the subject 21 side. However, the same thing can be said even if the X-ray tube 2 and the X-ray detector 3 are rotated together instead of rotating the subject 21 side. Similarly, the movement in the y direction is the same when the X-ray tube 2 and the X-ray detector 3 are moved together.

  FIG. 7 is a configuration diagram for explaining a part of a high-resolution CT50 which is a modification according to the present invention. The high-resolution CT 50 shown in FIG. 7 includes an X-ray tube 51, an X-ray detector 52, an x-direction shift mechanism 53, a y-direction movement mechanism 54, a rotation mechanism 55, a floor 56, and an XYZ mechanism 57.

  The X-ray tube 51 and the X-ray detector 52 are provided to face the x-direction shift mechanism 53. The x-direction shift mechanism 53 is provided on the y-direction movement of the y-direction movement mechanism 54. Further, the y-direction moving mechanism 54 is provided on the rotation of the rotating mechanism 55. The rotation mechanism 55 is supported by the floor 56 by a support portion (not shown). The y direction is a direction perpendicular to the paper surface. An XYZ mechanism 57 is provided below the rotary shaft 60 on the floor 56.

  The subject 61 is supported on the floor 56 by the XYZ mechanism 57 and can be moved in three directions in the XYZ directions with respect to the X-ray beam 62. Although details of the operation are not described, the high-resolution CT50 shown in FIG. 7 is also scanned in the RR method or the TR method in the same manner as described in the first embodiment, and image reconstruction is performed to obtain a three-dimensional image. Is possible.

The block diagram of CT of one Example concerning this invention. The figure explaining the flow of the image reconstruction process of the RR system using a cone beam. The figure explaining the back projection in the RR system image reconstruction process using a cone beam. The figure explaining the flow of the image reconstruction process of TR system using a cone beam. The figure explaining the back projection in the image reconstruction process of TR system using a cone beam. The figure explaining the weight in the image reconstruction of TR system using a cone beam. The block diagram of CT of the other Example concerning this invention. A simple configuration diagram of a general high-resolution CT.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... CT, 2 ... X-ray tube, 3 ... X-ray detector, 4, 5 ... Support frame, 6 ... Support stand, 7 ... XY moving mechanism, 8 ... Rotation / lifting mechanism, 9 ... Y direction moving mechanism, 10 ... x-direction shift mechanism, 11 ... mechanism control unit, 12 ... data processing unit, 12a ... RR scan unit, 12b ... RR reconstruction unit, 12c ... TR scan unit, 12d ... TR reconstruction unit, 13 ... input / output unit, DESCRIPTION OF SYMBOLS 14 ... X-ray control part, 15 ... High voltage generator, 20 ... X-ray beam, 21 ... Subject, 22 ... Imaging surface, 23 ... Rotating axis, 30 ... Measurement area, 33 ... F miracle, 34 ... mt surface, 50 ... CT, 51 ... X-ray tube, 52 ... X-ray detector, 53 ... x-direction shift mechanism, 54 ... y-direction movement mechanism, 55 ... rotation mechanism, 56 ... floor, 57 ... XYZ mechanism, 60 ... rotation shaft, 61 ... Subject, 62 ... X-ray beam, 100 ... CT, 101 ... X-ray tube, 102 ... X Detector, 103 ... rotary table, 104 ... X-ray beam, 105 ... object, 106 ... measured region

Claims (4)

A radiation detector having a two-dimensional resolution for detecting a cone-shaped radiation beam generated by a radiation source and transmitted through a subject;
Rotating means for providing relative rotation between the subject and the radiation beam;
Cone beam RR reconstruction means for reconstructing a three-dimensional image of the subject from a plurality of transmission data obtained by being detected by the radiation detector at a plurality of positions while being skinned by the RR method for performing this rotation. When,
Translation means for providing a relative translation between the subject and the radiation beam;
While scanning by the TR method that repeats the parallel movement and the stepwise rotation, a three-dimensional image of the subject is reconstructed from a plurality of transmission data obtained by being detected by the radiation detector at a plurality of positions. Cone beam TR reconfiguring means
The cone beam TR reconstructing means logarithmically converts the transmission data composed of the rotational axial position m, the orthogonal direction position n, the parallel movement position t, and the number of parallel movements k of the two-dimensional resolution to obtain projection data. A logarithmic conversion function for converting the converted projection data, a filter function for applying a high-frequency emphasis filter to the converted projection data in the direction of the parallel movement position t, and an axial position m and a parallel movement position t after applying the high-frequency emphasis filter. A set of projection data , which is a set of plane data, is formed for each set of plane data at all the orthogonal direction positions n and the number of parallel movements k at which the back projection angle viewed from the rotation axis direction is 180 °. A backprojection function for three-dimensional backprojection onto a virtual three-dimensional lattice representing the subject toward the focal point of the radiation beam;
A computed tomography apparatus capable of freely selecting and operating the RR scan or the TR scan according to the size of the subject. A radiation detector having a two-dimensional resolution for detecting a cone-shaped radiation beam generated by a radiation source and transmitted through a subject;
Rotating means for providing relative rotation between the subject and the radiation beam;
Translation means for providing a relative translation between the subject and the radiation beam;
A cone that reconstructs a three-dimensional image of the subject from a plurality of transmission data obtained by detection by the radiation detector at a plurality of positions during a TR scan that repeats the parallel movement and the stepped rotation. Beam TR reconstruction means,
The cone beam TR reconstructing means logarithmically converts the transmission data composed of the rotational axial position m, the orthogonal direction position n, the parallel movement position t, and the number of parallel movements k of the two-dimensional resolution to obtain projection data. A logarithmic conversion function for converting the converted projection data, a filter function for applying a high-frequency emphasis filter to the converted projection data in the direction of the translation position t, and an axial position m and a translation position t after applying the high-frequency emphasis filter. A set of projection data , which is a set of plane data, is formed for each set of plane data at all the orthogonal direction positions n and the number of parallel movements k at which the back projection angle viewed from the rotation axis direction is 180 °. What is claimed is: 1. A computed tomography apparatus comprising a back projection function for performing three-dimensional back projection on a virtual three-dimensional lattice representing a subject toward a focal point of a radiation beam. The computed tomography apparatus according to claim 1 or 2,
A computed tomography apparatus comprising FCD changing means for changing an FCD which is a distance between a focal point of the radiation beam and the rotation axis. The computed tomography apparatus according to any one of claims 1 to 3,
FDD changing means for changing FDD which is a distance between the focal point of the radiation beam and the radiation detector;
TR scan control means for automatically changing the number of repetitions of the stepwise rotation and translation of the radiation beam divergence angle θ ₀ according to the FDD,
A computer tomography apparatus characterized by comprising:

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