JP2009036660A - Tomogram system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tomogram system capable of surely measuring a rotation shake and of correcting a rotation shake generated by the run out measured, when a tomogram image is photographed. <P>SOLUTION: The tomogram system comprises a rotation unit 15 for rotating at least one of an object to be inspected, a radiation source, and a radiation detector; an optical axis for connecting the radiation source and radiation detector; a variable unit 16 for varying a lamino-angle formed with a rotation axis; a calculation unit 19 for determining the amount of run out from transmission data which is detected by a radiation detector for each predetermined rotational-angle, when the object is controlled by the rotation unit over one revolution, in a state where the lamino-angle is set at 0° and the object used for measuring the amount of the run out is mounted on a table; and a correction unit 20 for correcting the amount of the run out, by giving the table or the optical axis a movement for canceling the amount of the amount of the run out, in response to the rotation angle of this rotation, when the object is rotation-controlled by the rotation unit in the detection of the transmission data of the object by the radiation detector, when the lamino-angle is set at a value other than 0°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circular orbit type tomography apparatus that changes a radiation irradiation direction of a subject along a cone.

  One type of tomography device is a tomosynthesis device or Laminograph that obtains transmission data (tomographic images) of a subject while controlling a circular orbit (conical orbit) with respect to radiation (hereinafter referred to as “conical orbit”). Type of tomography device ").

  In such a conical orbit type tomography apparatus, the subject is rotated around the rotation axis inclined with respect to the optical axis of the radiation, or the subject is rotated around the rotation axis inclined with respect to the optical axis of the radiation. Without rotating the radiation source and radiation detector, the circular orbit (conical orbit) is controlled, and the tomographic image and 3D data of the subject are obtained from the two-dimensional transmission data obtained by the radiation detector during rotation. It has been reconfigured.

  As described above, the cone trajectory type tomography apparatus needs to control rotation (circular orbit), and this rotation is required to be centered on the stationary rotation axis. It may cause problems such as blurring in images and 3D data.

  In order to solve the problem of rotational shake that occurs in such a conical orbit type tomography apparatus, the rotational shake is measured from the image of the subject obtained by the X-ray detector, and the rotational shake is canceled using the measured rotational shake. There is also a tomographic apparatus that acquires transmission data after moving a rotating mechanism in a direction (see, for example, Patent Document 1).

  In addition, Patent Document 1 describes a technique for determining rotational shake using a rotation table that is a perfect circle and a sensor that detects the outer peripheral surface of the rotary table in addition to obtaining rotational shake from an image as a method for measuring rotational shake. Yes.

Furthermore, Patent Document 1 describes a technique for correcting shake for an image (transmission data) obtained by a radiation detector, in addition to moving the rotating mechanism in a direction to cancel the rotational shake as a method for correcting the rotational shake. Yes.
JP 2005-106515 A

  When measuring rotational shake using an image (transmission data) of an object detected by a radiation detector as described in Patent Document 1, even if the fluoroscopic direction of the object changes due to rotation, The feature point must always be fixed to one point of the subject. However, in the transmission image, the feature point is rarely fixed at one point on the subject, and in the actual transmission image, the clear feature point is rarely fixed on the subject. It is difficult to measure an accurate rotational shake by a measurement method using an image.

  Moreover, when measuring rotational shake using a sensor as described in Patent Document 1, it is difficult to generate the outer peripheral surface of the table in a perfect circle, and unreliable rotational shake is measured. There is. In addition, a sensor is used because the accuracy of rotational shake measured is inferior due to minute scratches generated on the outer peripheral surface of the table, deformation of the table due to heat, or distortion generated when the subject is placed on the table. It is difficult to measure an accurate rotational runout with a measuring method.

  In view of the above problems, an object of the present invention is to provide a tomographic apparatus that can reliably measure rotational shake and can accurately correct rotational shake that occurs during tomographic imaging due to the measured rotational shake.

In order to achieve the above object, the invention according to claim 1 is characterized in that the transmission data obtained by detecting the radiation generated from the radiation source and transmitted through the subject placed on the table by the radiation detector, A tomography apparatus that reconstructs a tomographic image of a subject, wherein the subject, the radiation source, or the radiation source or the radiation are in a relative rotational relationship with respect to a predetermined rotation axis. The radiation source or the radiation detection so as to change a lamino angle formed by a rotating means for rotating at least one of the radiation detector, an optical axis connecting the radiation source and the radiation detector, and the rotation axis. A variable means for moving at least one of the vessels or tilting the rotation axis, and a reference object used for measuring the amount of rotation while the lamino angle is set to 0 ° are placed on the table. In the state, when the rotation means performs control over one rotation, the calculation means for obtaining the rotation shake amount from the transmission data detected by the radiation detector for each predetermined rotation angle, and the lamino angle is other than 0 ° When the rotation detector controls the rotation when the transmission data of the subject is detected by the radiation detector, the amount of shake of the rotation on the table or the optical axis depends on the rotation angle of the rotation. And a correction means for correcting a shake of rotation by giving a movement that cancels the rotation.

  As shown in FIG. 1A, in the tomography apparatus 1 a according to claim 1, the radiation 31 irradiated from the radiation source 10 passes through the subject 32 and is detected by the radiation detector 12 with two-dimensional resolution. . The rotating means 15 rotates the table 11 on which the subject 32 is placed around a rotation axis RA inclined from the optical axis L by a lamino angle α. Alternatively, the rotating unit 15 may rotate the subject 32 and the radiation 31 relatively by rotating the radiation source 10 and the radiation detector 12 together instead of the table 11. The variable means 13 changes the lamino angle α by tilting the optical axis L or tilting the rotation axis RA.

  In the tomography apparatus 1a, first, prior to tomography, the lamino angle α = 0 ° is set as shown in FIG. 1B, and the reference object 33 placed on the table 11 is moved to the vicinity of the rotation axis RA. Thus, transmission data (transmission image) is obtained at a predetermined rotation angle every predetermined angle step over one rotation. The calculation means 19 calculates the image shake of the transmission image of the reference object 33 for each rotation angle from the obtained transmission data, divides the image shake by the enlargement factor, and obtains and stores the rotation shake amount. Here, the rotation angle means a rotation angle (position of rotation) from the origin of the table, not a step angle.

  Further, in the tomography apparatus 1a, at the time of tomography, the lamino angle α ≠ 0 ° is set, and the subject 32 is placed on the table 11 and imaged. At this time, the correction unit 14 relatively gives the radiation 31 and the subject 32 a movement that cancels out the shake amount of the rotation of the corresponding rotation angle calculated by the calculation unit 19 for each rotation angle. That is, the correction unit 14 corrects the movement of the subject 32 or the optical axis L so as to cancel out the rotational shake. The reconstruction unit 18 generates a tomographic image of the subject 32 from the transmission data obtained by correcting the rotation shake at a plurality of rotation angles (rotation positions) over one rotation.

  Thus, the tomographic apparatus 1a according to claim 1 can obtain a good tomographic image by correcting the shake with respect to reproducible rotational shake.

According to a second aspect of the present invention, a tomographic image of the subject is obtained from transmission data obtained by detecting radiation emitted from a radiation source and transmitted through the subject placed on a table by a radiation detector. A tomographic apparatus for reconfiguring the subject, the radiation source, or the radiation detector so that the subject and the radiation are in a relative rotational relationship with respect to a predetermined rotational axis. At least one of the radiation source and the radiation detector so as to change a lamino angle formed by a rotating means for rotating at least one of the light source, an optical axis connecting the radiation source and the radiation detector, and the rotation axis. The rotating hand in a state in which the variable object for moving the rotation axis or the tilting axis of the rotating object and the reference object used for measuring the rotational shake amount are set on the table and the lamino angle is set to 0 °. , When performing control over one rotation, calculation means for obtaining a rotational shake amount from transmission data detected by the radiation detector for each predetermined rotation angle, and the lamino angle is set to a value other than 0 ° and the radiation When detecting the transmission data of the subject with the detector, if the rotation means controls the rotation, the rotation data is detected with respect to the transmission data detected by the radiation detector according to the rotation angle for detecting the transmission data. The gist of the present invention is to have correction means for performing correction to cancel out the shake amount.

  As shown in FIG. 2 (a), the tomography apparatus 1b according to claim 2 differs from the tomography apparatus 1a according to claim 1 described above in FIG. Although it differs in the point provided, other structures are the same.

  Also in the tomography apparatus 1b, first, prior to tomography, as shown in FIG. 2 (b), the calculation means 19 uses the transmission data obtained by using the reference object 33 for each rotation angle as in the case of the tomography apparatus 1a. The rotation amount of rotation is obtained and stored.

  Also in the tomography apparatus 1b, at the time of tomography, the lamino angle α ≠ 0 ° is set, the subject 32 is placed on the table 11, and transmission data of the subject 32 is obtained. At this time, the correction unit 20 corrects the obtained transmission data by shifting the rotation amount of the corresponding rotation angle calculated by the calculation unit 19. The reconstruction unit 18 generates a tomographic image of the subject 32 from the transmission data obtained at a plurality of rotation angles over one rotation as described above and corrected for rotation shake.

  Thus, the tomographic apparatus 1b according to claim 2 can obtain a good tomographic image by correcting the shake with respect to the reproducible rotational shake.

  According to the present invention, it is possible to reliably measure the rotational shake with reproducibility, and to accurately correct the rotational shake that occurs during tomographic imaging by the measured rotational shake.

  Hereinafter, the tomography apparatus according to each embodiment of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals and the description thereof is omitted, and similar parts are described by using similar symbols.

<First Embodiment>
A tomography apparatus 2a according to the first embodiment described with reference to FIG. 3 is a tomography apparatus that images a tomographic image of a subject using X-rays as radiation. As shown in FIG. 3, the tomography apparatus 2a includes an X-ray tube 10, a table 11, an X-ray detector 12, an XY mechanism 14, a rotating mechanism 15, an xz mechanism 16, a detector moving mechanism 13, a mechanism control unit 17, A reconstruction unit 18 and a calculation unit 19 are provided.

  The X-ray tube 10 is a radiation source that generates an X-ray beam 30. The X-ray tube 10 is a transmission type microfocus X-ray tube, and has a minute X-ray focal point F of about 1 μm. A part of the X-ray beam 30 (X-ray beam 31) generated from the X-ray tube 10 passes through the subject 32 placed on the table 11 and is detected by the X-ray detector 12.

  The X-ray detector 12 is a radiation detector that detects X-rays with a two-dimensional resolution on the detection surface 12a, and is a combination of an X-ray II (X-ray image intensifier) and a television camera, or an FPD (flat) Panel type detector). The X-ray detector 12 is moved and set by the detector moving mechanism 13 within the detector tilting surface S shown on the paper surface in FIG. The X-ray detector 12 is moved in the xd direction by the detector moving mechanism 13 and is swing-controlled so that the detection surface 12a always faces the X-ray focal point F. The detector moving mechanism 13 may move the X-ray detector 12 linearly or in an arc shape.

  By moving the X-ray detector 12 within the range of the X-ray beam 30 by the detector moving mechanism (variable means) 13, the lamino angle α that is an angle formed by the rotation axis RA and the X-ray optical axis L is 0. It can be varied in the range of ° to about 70 °. The X-ray optical axis L is a straight line FD connecting the X-ray focal point F serving as an X-ray source and the center D of the detection surface 12a. When the lamino angle α is changed, the subject 32 (and the rotational axis RA) is moved by the xz mechanism 16 so that the X-ray optical axis L intersects the rotational axis RA at one point (point C) in the subject. The

  The XY mechanism 14 moves the table 11 in the xy direction. The XY mechanism 14 can move a desired examination region of the subject 32 on the rotation axis RA by moving the table 11 in the xy direction. Further, in the tomography apparatus 2a, the XY mechanism 14 moves the table 11 in the xy direction, so that the correction of rotational shake intended in the present invention can be realized.

  The rotation mechanism 15 rotates the table 11 around the rotation axis RA. The rotation mechanism 15 changes the inclination direction of the inclination angle (perspective angle) α by rotating the table 11 when performing fluoroscopy, and performs a conical orbit scan by rotating the subject 32 during tomography.

  The xz mechanism 16 moves the table 11 together with the rotation axis RA in the xz direction. The xz mechanism 16 moves the table 11 in the xz direction to set the examination magnification (magnification rate) or the examination area of the subject 32 on the X-ray optical axis L when the inclination angle α is changed. The field of view is corrected so as not to deviate.

  The mechanism control unit 17 supplies power to the detector moving mechanism 13, the XY mechanism 14, the rotating mechanism 15, and the xz mechanism 16 and controls the mechanisms 13 to 16.

  The reconstruction unit 18 generates a tomographic image of the subject 32 using the transmission data of the subject 32 detected by the X-ray detector 12. Specifically, when the lamino angle α ≠ 0 °, the reconstruction unit 18 transmits the subject 32 at every predetermined angle step over one rotation centered on the rotation axis RA obtained by the X-ray detector 12. Data (transmission image) is input, and a tomographic image of the subject 32 is generated from the transmission data.

  The calculation unit 19 calculates a rotation shake amount used to correct the rotation shake. Specifically, when the lamino angle α = 0 °, the calculation unit 19 obtains a rotational shake amount for each step of a predetermined angle over one rotation from the transmission data of the reference object obtained by the X-ray detector 12. , Stored in advance in a memory (not shown). Further, the calculation unit 19 outputs the amount of rotation shake for each rotation angle stored in the memory to the mechanism control unit 17.

  When the table 11 is rotated by the rotation mechanism 15 during tomography, the mechanism control unit 17 controls the XY mechanism 14 using the amount of rotation shake for each rotation angle input from the calculation unit 19 to set the table in the xy direction. 11 is moved to correct the rotational shake caused by the rotation.

  In the tomography apparatus 2a, in addition to the above-described configuration, normal tomography such as a housing (not shown) for fixing the X-ray tube 10, the xz mechanism 16, the detector moving mechanism 13 and the like and shielding X-rays is used. The equipment has the necessary configuration.

<Calculation of runout>
FIG. 4A shows the state of the tomography apparatus 2a when the calculation unit 19 calculates the rotational shake, and FIG. 4B shows the reference object 33 imaged in the state of FIG. 4A. A transmission image P is shown. FIG. 5 is a diagram for explaining the relationship between the focal point F and the X-ray detector 12 when the reference subject 33 is in the state shown in FIG. 4A in the tomography apparatus 2a.

  In the tomography apparatus 2a, prior to tomography of the subject 32, the lamino angle α = 0 ° is set as shown in FIG. 4A, and the reference subject 33 is placed in the vicinity of the rotation axis RA instead of the subject 32. (Preferably on the rotation axis RA), and transmission data of the reference object 33 by rotating the table 11 (reference object 33) around the rotation axis RA in one rotation, that is, a step of a predetermined angle over 360 °. (Transparent image) is obtained.

  For example, as shown in FIG. 4A, the reference object 33 is obtained by bonding a metal ball 33b that hardly transmits X-rays on a plate 33a that easily transmits X-rays. The metal ball 33b is placed close to the rotation axis RA (preferably on the rotation axis RA), and close to the X-ray tube 10 to increase the measurement accuracy, and the imaging magnification (fdd / fcd) is increased. To do. By allowing the metal ball 33b to be positioned on the rotation axis RA, as shown in FIG. 4B, a transmission image of the metal ball 33b is detected at the center D of the detection surface 12a.

The calculation unit 19 calculates the image shake of the transmission image of the reference object 33 for each rotation angle Φ from the transmission data of the reference object 33. Specifically, the calculation unit 19 obtains the center of gravity O ₁ of the metal ball 33b included in the transmission image P shown in FIG. 4B, and the metal ball from the center C _{1 of the} transmission image P set as the reference position. The image blur of the center of gravity O ₁ of 33b is obtained. That is, when there is no rotational shake, the transmission image of the metal ball 33b is detected at the center D on the detection surface 12a, so the center of gravity O ₁ should be at the center C ₁ . However, as shown in FIG. 5, a transmission image of the metal ball 33b is not detected at the center D of the detection surface 12a. Therefore, when the center of gravity O ₁ is not in the center C _1, the deviation from the center C ₁ to the center of gravity O ₁ becomes the image blur caused by a shake rotation.

Since this image blur is obtained in units of pixels, the calculation unit 19 multiplies the obtained image blur by the size (mm / pixel) of one pixel on the detection surface 12a, thereby causing the image blur on the detection surface 12a. Δx ₀ , Δy ₀ (mm) can be obtained. Thereafter, the calculation unit 19 divides the image shake by the enlargement ratio (fdd / fcd) to obtain shake amounts Δx (Φ) and Δy (Φ) for each rotation angle Φ, and calculates the rotation shake amount as the rotation shake vector S ( (Φ) is stored in the memory.

<< Tomographic image photography >>
In the tomography apparatus 2a, the tomography of the subject 32 is performed after the rotational shake vector S (Φ) is obtained as described above.

  At the time of tomography, first, when the detector moving mechanism 13 sets the lamino angle α ≠ 0 ° and the subject 32 is placed, the XY mechanism 14 moves the examination region of the subject 32 on the rotation axis RA. Then, the enlargement ratio is set and the field of view is adjusted by the xz mechanism 16, and then tomography is started while the table 11 is rotated by the rotation mechanism 15.

  The mechanism control unit 17 controls the XY mechanism 14 by using the rotational shake amount (rotational shake vector S (Φ)) input from the calculation unit 19 at each angle step (rotational angle Φ) at the time of tomographic imaging. Each time the angle is rotated, the subject 32 is moved in the direction opposite to the rotational shake vector S (Φ) of the corresponding rotational angle (−S (Φ)) to cancel the rotational shake.

  In the tomography apparatus 2a, transmission data of the subject 32 detected by the X-ray detector 12 after the subject 32 has been moved so as to cancel the rotational shake is used as a transmission image used for reconstruction of the tomographic image.

《Reconstruction of tomographic image》
In the tomography apparatus 2a, Feldkamp's cone beam CT reconstruction algorithm (LAFeldkamp, LCDavis and JWKress, Practical cone-beam algorithm, J. Opt. Soc.Am.A / Vol.1, No.6 / June 1984).

  A method for reconstructing a tomographic image using Feldkamp's cone beam CT reconstruction algorithm will be briefly described with reference to FIG.

  The reconstruction unit 18 logarithmically converts a large number of transmission images collected on the detection surface 12a for each rotation angle Φ, and performs a spatial filter process on each logarithmically converted transmission image P (Φ). The spatial filter processing performs high-cut processing in the direction v along the detector tilting surface S and high-frequency enhancement processing (Ramachandran & Lakshminarayanan filter processing used in CT, etc.) in the orthogonal direction u.

  Thereafter, as shown in FIG. 7A, the reconstruction unit 18 directs the transmission image P (Φ) subjected to the spatial filter to the matrix 40 on the xy plane passing through the point C toward the X-ray focal point F. Are projected back to the point A2 three-dimensionally at each rotation angle Φ to generate a transmission image Pc (Φ) (centering image).

  More specifically, the generation of the centering image is performed by obtaining projection points A1 on the detection surface 12a for each point (A2) for all points on the two-dimensional matrix 40, and four points closest to the projection point A1. The transmission image value P (Φ) interpolated at the data point is set as the value of the projection image Pc (Φ) at one point (A2). The centering image is created with a smaller matrix size than the final tomographic image.

  Next, as shown in FIG. 7B, the reconstruction unit 18 rotates the description coordinates of the transmission image Pc (Φ) from x, y to x ′, y ′ by an angle Φ. That is, the transmission image Pr (Φ) is generated by converting the data points of the transmission image Pc (Φ) into the matrix 41 along the coordinates x ′ and y ′ fixed to the subject 32. Further, a point in the direction toward or away from the focal point F along the X-ray path, to the three-dimensional matrix 42 along the coordinates x ′, y ′, z ′ with the transmission image Pr (Φ) fixed to the subject 32. A2 is backprojected three-dimensionally to the point A3, and the tomogram (three-dimensional image) of the subject 32 is obtained by integrating each other with respect to the angle Φ.

More specifically, this backprojection obtains a projection point (A2) on the two-dimensional matrix 41 for each point (A3) for every point on the three-dimensional matrix 42, and the nearest neighbor of the projection point (A2). The transmission image value Pr (Φ) of one data point (or the nearest four interpolation values) is integrated to one point (A3). Further, when the back projection, to Pr ([Phi), as the correction backprojection density, the distance between F-A3 as R, of the weight 1 / R ² is multiplied.

  As described above, in the tomography apparatus 2a according to the first embodiment of the present invention, the transmission image of the reference subject is taken for each rotation angle at the lamino angle α = 0 °, and the rotational shake amount is obtained. When the tomographic image is stored with the lamino angle α ≠ 0 °, the stored rotational shake amount is used to move and correct the subject for each rotation angle. As a result, the shake of the center of gravity of the metal ball is measured by vertical fluoroscopy, so that the tomography apparatus 2a provides a tomography apparatus that can more reliably measure reproducible rotation shake and enables accurate rotation shake correction. can do.

  Further, in the tomographic apparatus 2a according to the first embodiment, rotational shake correction can be performed without measuring rotational shake during tomographic imaging regardless of the enlargement ratio and the lamino angle α.

<Second Embodiment>
A tomography apparatus 2b according to the second embodiment of the present invention will be described with reference to FIG. In the second embodiment, a tomographic apparatus 2b that captures a tomographic image of a subject using X-rays as radiation will be described. As shown in FIG. 7, the tomography apparatus 2 b is different in that it includes a correction unit 20 in addition to the configuration included in the tomography apparatus 2 a described above in the first embodiment.

  In the tomography apparatus 2b as well as the tomography apparatus 2a, the calculation unit 19 uses the reference object 33 in advance to obtain a rotation shake amount (vector S (Φ)) for each step (rotation angle Φ) of a predetermined angle. , Previously stored in the memory.

  In the tomography apparatus 2b, the correction unit 20 uses the shake vector S (Φ) of rotation of the corresponding rotation angle input from the calculation unit 19 for each step of the predetermined angle (rotation angle Φ). ) Is corrected. Specifically, as shown in FIG. 8, the correction unit 20 cancels a vector (vector Sg (Φ)) obtained by projecting the rotational shake vector S (Φ) onto the detection surface 12 a of the X-ray detector 12 (vector Sg (Φ)). The transmission data is corrected by shifting the transmission data to -Sg (Φ)).

  The reconstruction unit 18 generates a tomographic image of the subject 32 from the transmission data corrected by the correction unit 20 by the method described above in the first embodiment.

  That is, in the tomography apparatus 2a according to the first embodiment, the rotational shake is corrected by physically moving the table 11 in the xy direction before acquiring transmission data, but the tomography according to the second embodiment. In the imaging device 2b, the rotational shake is corrected by correcting the acquired transmission data instead of moving the table 11.

  According to the tomographic apparatus 2b according to the second embodiment described above, rotational shake correction can be performed without measuring rotational shake at the time of tomographic imaging, regardless of the magnification ratio or the lamino angle α.

  Further, according to the tomography apparatus 2b according to the second embodiment described above, since the transmission data is corrected by shifting rather than mechanical correction, a minute rotational shake can be corrected accurately.

<First Modification>
Tomograph 2a described above, in 2b, when determining the rotation shake on the transmitted image, as a reference position a center C ₁ of the transmitted image P as shown in FIG. 4 (b), the image blur from the center C ₁ of the image As described in the obtained example, the reference position may not be the center C ₁ of the image. For example, a point on a circle (reference circular orbit) drawn in synchronization with the rotation can be used as the reference point. As the reference circular orbit, for example, a circular orbit in which the sum of squares of the trajectory for one revolution from a circular orbit having a predetermined radius can be obtained and selected by the least square method. This is an ideal method that can minimize the correction amount.

FIG. 9 is an explanatory diagram for obtaining a rotational shake vector S ₀ ′ (Φ) that is a minimized rotational shake amount in the first modification. The trajectory 51 is a trajectory drawn by the center of gravity of the metal ball 33b on the transmission image P. The trajectory 51 is also a trajectory drawn by the rotational shake vector S ₀ (Φ) with reference to the measured center C _{1 of} the screen.

The reference circular trajectory 52 is a trajectory drawn by the reference point (reference vector R ₀ (Φ)), and is determined by the circle center coordinates (xc, yc), radius (r), and phase (Φ ₀ ). Specifically, the vector R ₀ (Φ) that is the reference circular orbit 52 is expressed by dividing the x component and the y component as shown in the equations (1) and (2).

Further, the rotational shake vector S ₀ ′ (Φ) is expressed by Expression (3) using the reference vector R ₀ (Φ) according to Expression (1) and Expression (2).

Incidentally, the reference vector R ₀ (Φ) needs to be selected so as to minimize the rotational shake vector S ₀ ′ (Φ). For this reason, a reference circular trajectory R ₀ (Φ) that minimizes the sum of one rotation of the square of the absolute value of the rotational shake vector S ₀ ′ (Φ) is selected by the method of least squares. Specifically, from equation (3), the sum of squares of the absolute value of rotational shake vector S ₀ ′ is represented by equation (4).

When the expressions (1) and (2) are substituted into the expression (4), the sum of squares of the absolute value of the rotational shake vector S ₀ ′ is expressed as a function of xc, yc, r, Φ ₀ . Here, xc, yc, r, and Φ ₀ that minimize the sum of squares of the absolute value of the rotational shake vector S ₀ ′ are obtained by using a normal equation by a well-known general method of least squares. Can be sought. Thus, R ₀ (Φ), which is the reference circular orbit 52 that minimizes S ₀ ′ (Φ), is determined, and the minimized rotational shake vector S ₀ ′ (Φ) is obtained using Equation (3). Can do.

In this way, the rotational shake vector S ₀ ′ (Φ) obtained with the predetermined circular orbit as a reference is used instead of the rotational shake vector S ₀ (Φ) obtained with the center C ₁ of the image as a reference. Alternatively, the correction amount corrected by the correction unit 20 can be minimized.

In the above description, the reference circular trajectory R ₀ (Φ) is selected so that the sum of one square of the absolute value of S ₀ ′ (Φ) is minimized. Is not limited to the method of minimizing the value, and for example, it may be selected so that the sum of the first round of the absolute value of S ₀ ′ (Φ) is minimized. In this case, the expression (4) is changed, but is the same in other points such as the expressions (1) to (3).

<Second Modification>
In the tomography apparatus 2b described above, the correction unit 20 corrects the rotational shake for the transmission data before reconstruction, but may correct the transmission data during reconstruction.

  When correcting the transmission data in the middle of reconstruction, the correction unit 20 corrects, for example, the transmission image P (Φ) after logarithmic conversion or after spatial filter processing. In this case, the reconstruction unit 18 outputs the transmission image in the middle of processing to the correction unit 20, and the correction unit 20 cancels the shake vector Sg (Φ) on the detection surface 12a as in the case of correction before reconstruction. Then, the data is output to the reconstruction unit 18 again. The reconstruction unit 18 continues the reconstruction process using the transmission image in which the rotational shake is corrected.

  Further, the correcting means 20 may correct the transmitted image Pc (Φ) (centering image) being processed. In this case, the reconstruction unit 18 outputs the transmission image Pc (Φ) to the correction unit 20. The correction unit 20 cancels the shake vector S (Φ) on the xy plane using the rotation vector S (Φ) of the rotation angle corresponding to the transmission image Pc (Φ) being processed from the calculation unit 19. Thus, after correcting the shift (by −S (Φ)), the data is output to the reconstruction unit 18 again. The reconstruction unit 18 continues the reconstruction process using the corrected transmission image.

<Third Modification>
In the tomography apparatuses 2a and 2b described above, the detector moving mechanism 13 moves the X-ray detector 12 to make the lamino angle variable. However, the laminar angle variable is limited to the movement of the X-ray detector 12. I can't. In other words, the variable means described in the claims can be configured so that the X-ray optical axis L can be tilted by moving either one or both of the X-ray focal point F and the X-ray detector 12. It is also possible to change the lamino angle α by tilting RA.

  In the above-described tomography apparatuses 2a and 2b, the rotation mechanism 14 rotates the rotation table 11 (subject 32) while performing the step rotation for each predetermined angle at the time of image capturing. It is not limited to the rotation. At least one of the subject 32, the X-ray tube 10 (X-ray focal point F), or the X-ray detector 12 is rotated so that the subject 32 and the X-ray beam 31 have a relative rotational relationship with respect to the rotation axis RA. Thus, equivalent transmission data can be obtained. For example, the rotary table 11 is fixed, and the X-ray tube 10 (X-ray focal point F) and the X-ray detector 12 are rotated around the rotation axis RA by rotating means (not shown in FIGS. 3 and 7). May be. In this case, since the radiation 31 and the subject 32 are relatively in the same relationship as when the rotary table 11 is rotated, the same transmission data as when the rotary table 11 is rotated can be obtained.

  Further, in the tomography apparatus 2a described above, the subject 32 is moved by the XY mechanism 14 disposed on the rotation mechanism 15 so as to cancel the amount of rotation shake calculated by the calculation unit 19, and the rotation shake is detected only by the XY movement. Although it is corrected, it is not limited to the correction by the XY mechanism 14. For example, a correction moving mechanism that corrects rotational shake may be disposed under the rotation mechanism 15 and the rotational shake may be corrected by the correction moving mechanism. Alternatively, the correction may be made by moving either or both of the X-ray tube 10 and the X-ray detector 12 to move the optical axis L so as to cancel the rotational shake amount.

<Fourth modification>
In the tomography apparatuses 2a and 2b described above, the rotation may be step rotation or continuous smooth rotation. However, in either case, transmission data is collected every step of a predetermined angle.

  Transmission data collection in the case of continuous rotation collects transmission data at the timing of the encoder pulse of the rotation mechanism while continuing the continuous rotation. Further, in the case of continuous rotation, the correction means 14 corrects the rotational shake by continuously giving a movement that cancels the shake amount S (Φ) according to the rotational angle Φ to the table 11 while continuing the continuous rotation. .

Further, the angle step for collecting transmission data may be different at the time of shake amount calculation and tomography. In this case, the amount of shake S (Φ ₁ ) and S (Φ ₂ ) at the two closest rotation angles is interpolated with the rotation angle Φ at the time of tomography, and S (Φ) is obtained and used for correction.

  Also, the angle step for collecting transmission data need not be strictly constant.

1 is a conceptual diagram of a tomography apparatus according to claim 1 of the present invention. It is a conceptual diagram of the tomography apparatus which concerns on Claim 2 of this invention. 1 is a conceptual diagram of a tomography apparatus according to a first embodiment of the present invention. It is a figure explaining calculation of the amount of image shake in the tomography apparatus of FIG. FIG. 6 is another diagram for explaining calculation of an image shake amount in the tomography apparatus of FIG. 3. It is a figure explaining the reconstruction of the image in the tomography apparatus of FIG. It is a conceptual diagram of the tomography apparatus which concerns on the 2nd Embodiment of this invention. It is a figure explaining the correction | amendment of the image blurring in the tomography apparatus of FIG. It is a figure explaining calculation of the image shake in the tomography apparatus concerning the 1st modification.

Explanation of symbols

1a, 1b, 2a, 2b ... Tomography apparatus 10 ... X-ray tube (radiation source)
11 ... Table 12 ... X-ray detector (radiation detector)
12a: Detection surface 13: Detector moving mechanism (variable means)
14 ... XY mechanism (correction means)
15 ... Rotating mechanism (rotating means)
16 ... xz mechanism 17 ... mechanism control unit 18 ... reconstruction unit (reconstruction means)
19: Calculation unit (calculation means)
20: Correction unit (correction means)
30 ... X-ray beam 31 ... X-ray beam (radiation)
32 ... Subject 33 ... Reference subject 33a ... Plate 33b ... Metal ball

Claims (4)

A tomography apparatus for reconstructing a tomographic image of a subject from transmission data obtained by detecting radiation emitted from a radiation source and transmitted through the subject placed on a table by a radiation detector,
Rotating means for rotating at least one of the subject, the radiation source, and the radiation detector so that the subject and the radiation have a relative rotational relationship with respect to a predetermined rotation axis;
Variable to move at least one of the radiation source or the radiation detector or tilt the rotation axis so as to change a lamino angle formed by an optical axis connecting the radiation source and the radiation detector and the rotation axis. Means,
When the rotation means performs control over one rotation in a state where the lamino angle is set to 0 ° and a reference object used for measurement of the amount of shake of rotation is placed on the table, every predetermined rotation angle Calculating means for obtaining a rotational shake amount from transmission data detected by the radiation detector;
When the lamino angle is set to a value other than 0 ° and the transmission data of the subject is detected by the radiation detector, when the rotation means controls the rotation, the table or the light is controlled according to the rotation angle of the rotation. A correcting means for correcting the rotational shake by giving a movement to cancel the rotational shake amount to the shaft;
A tomography apparatus characterized by comprising: A tomography apparatus for reconstructing a tomographic image of a subject from transmission data obtained by detecting radiation emitted from a radiation source and transmitted through the subject placed on a table by a radiation detector,
Rotating means for rotating at least one of the subject, the radiation source, and the radiation detector so that the subject and the radiation have a relative rotational relationship with respect to a predetermined rotation axis;
Variable to move at least one of the radiation source or the radiation detector or tilt the rotation axis so as to change a lamino angle formed by an optical axis connecting the radiation source and the radiation detector and the rotation axis. Means,
When the rotation means performs control over one rotation in a state where the lamino angle is set to 0 ° and a reference object used for measurement of the amount of shake of rotation is placed on the table, every predetermined rotation angle Calculating means for obtaining a rotational shake amount from transmission data detected by the radiation detector;
When the laminating angle is set to a value other than 0 ° and the radiation detector detects the transmission data of the subject, the rotation detection is controlled by the rotation means to detect the radiation according to the rotation angle for detecting the transmission data. Correction means for performing correction for canceling the amount of shake of the rotation with respect to transmission data detected by the instrument;
A tomography apparatus characterized by comprising:   The tomography apparatus according to claim 1, wherein the calculation unit obtains a vector from the center to the reference object as the amount of shake of the rotation on the transmission data.   The calculation means uses the vector from the point on the circular orbit drawn so as to minimize the difference from the orbit drawn by the subject on the transmission data to the reference subject as the amount of rotation shake. The tomography apparatus according to claim 1, wherein the tomography apparatus is obtained.

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