JP4959223B2 - Tomography equipment - Google Patents

Description

  The present invention relates to a tomography apparatus that relatively rotates a radiation source and a subject, captures radiation transmission image data at each preset rotation angle, and creates tomographic image data from the transmission image data. The present invention relates to a tomographic apparatus capable of creating tomographic image data in which the influence of rotational shake is removed without depending on the shape of a subject.

  Conventionally, a tomography apparatus has been used to obtain a tomographic image of a subject. For example, a tomography apparatus such as a Laminograph (also referred to as a tomosynthesis apparatus) or a CT (Computer Tomograph) apparatus is used.

  A cone orbit type tomography apparatus irradiates a subject with radiation generated from a radiation source. Then, the radiation transmitted through the subject is detected by a radiation detector with a two-dimensional resolution. When irradiating radiation, the radiation source, the radiation detector, and the subject are rotated relative to each other about a rotation axis that is inclined with respect to the optical axis of the radiation. Then, transmission image data is obtained from the radiation detector each time the set angle is rotated. Then, the transmission image data is reconstructed to generate tomographic image data and three-dimensional image data of the subject. In order to relatively rotate the radiation and the subject, the subject may be rotated with respect to the radiation source and the radiation detector, or the radiation source and the radiation detector may be rotated with respect to the subject. Also good.

  However, in the above-described tomography apparatus, when the radiation and the subject are rotated around the rotation axis, the rotation axis may be shaken and the tomographic image data may be blurred.

  In view of this, a method for creating tomographic image data in which the influence of the rotational axis shake (hereinafter, also referred to as “rotational shake”) in the tomography apparatus has been studied.

For example, Patent Document 1 describes a tomography apparatus that obtains the magnitude of rotational shake from a transmission image obtained by an X-ray detector and moves the rotation mechanism so as to cancel the shake. In addition, a method for obtaining the magnitude of rotational shake by detecting the position of a specific portion instead of obtaining the magnitude of rotational shake from an image is also described. Specifically, the outer peripheral surface of the rotary table is finished into a perfect circle, and the position of one portion of the outer peripheral surface is detected using a contact type or non-contact type sensor to determine the magnitude of the rotational shake. .
JP 2005-106515 A

  However, the tomography apparatus described in Patent Document 1 as described above has the following problems.

  (1) There is a problem that a feature point clearly appears in a transmission image of a subject. That is, in order to obtain the magnitude of the shake of the rotation axis from the transmission image data of the subject obtained by the X-ray detector, a reference feature point is required on the transmission image. Further, even when the subject is rotated and the transmission direction is changed, this feature point must always be fixed to one point on the subject. Therefore, if the feature point of the subject is not clearly displayed on the transmission image and is not fixed to the subject, the magnitude of the rotational shake may not be calculated.

  (2) There is a problem that it is not easy to accurately process the outer peripheral surface of the rotary table into a perfect circle. Moreover, it is difficult to make the outer peripheral surface into a perfect circle due to the influence of scratches on the outer peripheral surface, distortion of the table when loaded, external thermal environment, and the like. Therefore, when the deviation of the outer periphery of the rotary table with respect to the perfect circle becomes larger than the magnitude of the shake of the rotating shaft, the magnitude of the runout cannot be calculated. That is, there is a case where the rotational shake cannot be corrected accurately.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a tomographic apparatus capable of generating tomographic image data from which the influence of rotational shake is removed without depending on the shape of the subject.

  The present invention takes the following means in order to solve the above problems.

The invention corresponding to claim 1 is mounted on the table member including a front surface portion on which the subject is placed, a back surface portion on which a mark is formed on the opposite side of the front surface portion, and the table member. A radiation source for irradiating the subject with radiation, a radiation detection means for detecting radiation transmitted through the subject, the radiation source, the radiation detection means, and the table member perpendicular to the surface portion of the table member A rotation mechanism that relatively rotates along a rotation axis, and when the subject is placed on the table member, the subject is detected from the radiation amount detected by the radiation detection means at a plurality of rotational positions of the rotation. and data collection means for collecting the transmitted image data of the specimen, and the TV camera for capturing images of the mark from the back side, corresponding to the collection of the transmission image data in the plurality of rotational positions It was based on the mark image obtained by the TV camera correction, and axis stabilization means for correcting the free transmission image data of rotational deflection of the collected transmitted image data by said data acquisition unit, by the shaft stabilization means The tomography apparatus includes reconstruction means for reconstructing a plurality of transmitted image data and creating tomogram data.

  The invention corresponding to claim 2 is a table member having a surface portion on which the subject is placed, a radiation source for irradiating the subject placed on the table member with radiation, and transmitted through the subject. Radiation detection means for detecting radiation, a rotation mechanism for relatively rotating the radiation source, the radiation detection means, and the table member along a rotation axis perpendicular to the surface portion of the table member, and the table member A parallel movement mechanism that translates the table member along the surface portion, and is fixed to the parallel movement mechanism so as to be parallel to the surface portion on the opposite side of the surface portion of the table member, If the subject is placed on the surface of the mark plate and the surface of the table member, the amount of radiation detected by the radiation detection means Based on mark position data obtained by the data collection means for collecting the transmission image data of the subject, the mark position detection means for detecting the position of the mark, and the mark position detection means, the data An axial shake correction unit that corrects the transmission image data collected by the collection unit to transmission image data without rotational shake, and a plurality of transmission image data corrected by the axial shake correction unit are reconstructed to obtain tomographic image data. A tomography apparatus comprising reconstruction means for creating.

Corresponding to claim 3 invention is a tomography apparatus that corresponds to 請 Motomeko 2, wherein the axis stabilization means is not transmitting the rotational run by matching the mark position data, the preset reference position A tomography apparatus for obtaining image data.

Corresponding to claim 4 invention is a tomography apparatus corresponding to claim 1, wherein the axis stabilization means includes shifting said mark image at a reference rotational position of the rotation between the mark images at each rotational position This is a tomographic apparatus that obtains a shift amount that achieves the best matching by taking the matching and corrects transmission image data at each rotational position based on the shift amount .

According to a fifth aspect of the present invention, in the tomography apparatus according to the second aspect, the axial shake correcting means includes the mark position data obtained by the mark position detecting means and a preset reference without rotational shake. A tomography apparatus that calculates a rotational shake amount based on mark position data and controls the parallel movement mechanism to move a distance corresponding to the calculated rotational shake amount.

<Action>
Therefore, the present invention has the following effects by taking the above-described means.

The invention corresponding to claim 1 captures an image of the mark from the back surface side , a table member having a front surface portion on which the subject is placed, and a back surface portion having a mark formed on the opposite side of the front surface portion. and the TV camera for, on the basis of the mark image obtained by the TV camera, the configuration of an axial stabilization means for correcting the free transmission image data of rotational deflection of the transmitted image data, the position of the mark Mc the shake amount rotary can determined Mel be detected and.

  The invention corresponding to claim 2 supports the table member, translates the table member along the surface portion, and is parallel to the surface portion on the opposite side of the surface portion of the table member. A mark plate fixed to the translation mechanism and having a mark-formed surface portion, mark position detection means for detecting the position of the mark, and transmission based on the mark position data obtained by the mark position detection means With a configuration including an axial shake correction unit that corrects image data to transmission image data without rotational shake, the position of the mark Mc can be detected three-dimensionally to obtain the rotational shake amount three-dimensionally.

In the invention corresponding to claim 3, in addition to the operation corresponding to claim 2 , the shaft shake correcting means, when the rotational shake occurs based on the mark position data and the preset reference position, The magnitude of the rotational runout can be obtained. Therefore, it is possible to obtain transmission image data having no rotational shake.

In the invention corresponding to claim 4, in addition to the operation corresponding to claim 1 , the matching is best achieved by taking matching by rotating and shifting the mark image at the reference rotation position and the mark image at each rotation position. The shift amount can be obtained, and the magnitude of the rotational shake at each rotational position can be obtained. Therefore, the shake of the rotating shaft can be corrected.

In the invention corresponding to claim 5 , in addition to the operation corresponding to claim 2, the shaft shake correcting means includes mark position data obtained by the mark position detecting means and reference mark position data having no preset rotational shake. Therefore, when the rotational shake occurs, the magnitude of the rotational shake can be obtained and the translation mechanism can be controlled to cancel the rotational shake. Therefore, it is possible to obtain transmission image data having no rotational shake.

  According to the present invention, it is possible to create tomographic image data from which the influence of rotational shake is removed without depending on the shape of the subject.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
(1-1. Configuration)
FIG. 1 is a schematic diagram showing a configuration of a tomography apparatus 10 according to the first embodiment of the present invention.

  The tomography apparatus 10 creates tomographic image data of the subject 5 and includes a subject placement unit 20, an X-ray irradiation unit 30, a mark position detection unit 40, and a data processing unit 50.

  The subject placement unit 20 includes a table member 21 on which the subject 5 is placed, an XY mechanism (parallel movement mechanism) 22, a rotation mechanism 23, an elevating mechanism 24, and a mechanism control unit 25. In the subject placement unit 20, an elevating mechanism 24 is fixed to a floor by a support member or the like (not shown), and a rotating mechanism 23, an XY mechanism 22, and a table member 21 are installed thereon in that order.

  The table member 21 is placed on the placement surface (front surface portion) 21A on which the subject 5 is placed, and on the opposite side of the placement surface 21A, and the mark surface (back surface portion) on which a large number of dot-like marks M are formed. ) 21B. The table member 21 is supported by the XY mechanism 22. When the table member 21 is translated, moved up and down, and rotated, an X-ray can be irradiated to an arbitrary part of the subject 5 placed on the placement surface 21A. The table member 21 is made of a material that easily transmits X-rays. Thereby, useless attenuation of the X-ray beam B is eliminated. The marks M may be regularly formed in a lattice shape, or may be irregularly formed as shown in FIG.

  The XY mechanism 22 moves the table member 21 along the placement surface 21 </ b> A according to a control signal from the mechanism control unit 25. The XY mechanism 22 is supported by the rotation mechanism 23. For convenience, in FIG. 1, the direction from left to right is the X direction, the direction from the front to the back is the Y direction, and the placement surface 21A is parallel to the XY plane.

  The rotation mechanism 23 rotates the XY mechanism 22 in response to a control signal from the mechanism control unit 25. Specifically, the rotation mechanism 23 supports the XY mechanism 22 by a large-diameter bearing having a hollow shaft member, and rotates the XY mechanism 22 in the Z direction orthogonal to the XY plane. Further, the X-ray beam B1 can pass through the hollow portion of the bearing. Thereby, the X-ray tube 31 and the X-ray detector 32 and the table member 21 are rotated relative to the rotation axis R of the rotation mechanism 23. The rotation mechanism 23 is supported by the lifting mechanism 24. The rotating mechanism 23 itself does not rotate. In the following description, a generic term for such a non-rotating configuration may be referred to as “non-rotating side”.

  The elevating mechanism 24 elevates the rotating mechanism 23 in the Z direction that is the direction of the rotation axis R. The lifting mechanism 24 is supported from the floor by a support member (not shown). The elevating mechanism 24 is arranged so as not to block the X-ray beam B1.

  When the mechanism control unit 25 receives the control signal from the data processing unit 50, the mechanism control unit 25 executes control for driving the XY mechanism 22, the rotation mechanism 23, and the lifting mechanism 24. That is, the mechanism control unit 25 can adjust the position of the table member 21 by sending a control signal to the XY mechanism 22, the rotation mechanism 23, and the lifting mechanism 24.

  The X-ray irradiation unit 30 includes an X-ray tube 31 and an X-ray detector 32. In the X-ray irradiation unit 30, the X-ray tube 31 and the X-ray detector 32 are arranged so as to face the imaging region center point C on the rotation axis R of the table member 21 with the table member 21 interposed therebetween. The The X-ray tube 31 and the X-ray detector 32 are supported from the floor by a support member (not shown). Although not shown in the drawings, the X-ray irradiation unit 30 includes a high voltage generator that supplies a high voltage to the X-ray tube 31 and an X-ray tube control unit that controls the tube voltage and tube current.

  The X-ray tube 31 irradiates the subject 5 placed on the table member 21 with the X-ray beam B. Specifically, the X-ray beam B radiated from the X-ray focal point F of the X-ray tube 31 passes through the subject 5 and the table member 21. A part B <b> 1 of the X-ray beam B is detected by the X-ray detector 32. The X-ray center line (hereinafter also referred to as the optical axis) Bc and the rotation axis R of the rotation mechanism 23 intersect at any angle α within the range of 20 ° to 70 °. As the X-ray tube 31, a microfocus X-ray tube having a focal size of about 1 μm can be used. The “X-ray focal point” refers to a convergence point when the irradiated X-ray beam is traced in reverse.

  The X-ray detector 32 detects X-rays transmitted through the subject 5 with two-dimensional resolution, and has a function of sending the detected signal to the data collection unit 51 as “transmission image data”. For such an X-ray detector 32, an FPD (Flat Panel Detector) can be used. The FPD is an array of X-ray detection elements arranged in a matrix. In addition, X-ray I.D. I. (X-ray image intensifier) and a TV camera (television camera) can also be used. As the X-ray detector 32 according to the present embodiment, a digital output is used, but an analog output can be used if an AD converter is provided.

  The mark position detection unit 40 is for detecting the position of the mark M, and sends the image of the mark surface 21B to the shaft shake correction unit 52 as “mark image data”. In the present embodiment, the mark position detection unit 40 is configured by a combination of a TV camera 41 and a distance meter 42. In the mark position detection unit 40, the TV camera 41 and the distance meter 42 are shielded from X-rays so as not to be deteriorated by irradiation with the X-ray beam B, but are omitted in FIG. . X-ray shielding is performed, for example, by installing lead glass on the front surfaces of the TV camera 41 and the distance meter 42 or covering the periphery of the main body with lead. When a shield is installed, the measurement light is bent and detected by a mirror or the like.

  The TV camera 41 is supported by a rotating mechanism 23 (non-rotating side: a structure that does not rotate) via a support frame 43. The TV camera 41 is adjusted so that its optical axis coincides with the rotation axis R. That is, the center point O which is the center of the visual field of the TV camera 41 coincides with the rotation axis R (within the installation error). The TV camera 41 captures the mark Mc closest to the point Rc on the rotation axis R on the mark surface 21B. Therefore, the range of the visual field can be narrowed and photographing can be performed at a high magnification. The mark image data of the mark surface 21 </ b> B detected by the TV power mela 41 is sent to the shaft shake correction unit 52. Note that the mark image data includes the values of the X component and the Y component of “mark position data” indicating the position of the mark Mc.

  The TV camera 41 is a combination of an optical system of a microscope and an image sensor such as a CCD that can capture a moving image. Here, a digital output is used, but an analog output can be provided with an AD converter. If an optical system having a deep depth of field is used, the image can be prevented from blurring when the height of the mark surface 21B fluctuates.

  The distance meter 42 is supported in the vicinity of the TV camera 41 by a rotating mechanism 23 (non-rotating side: non-rotating configuration) via a support frame 43. The distance meter 42 measures the distance to the mark surface 21B. That is, the position in the normal direction (Z direction) of the mark surface 21B is detected, and the height h to the mark Mc is detected without contact. As such a distance meter 42, for example, a non-contact distance meter using light such as a laser displacement meter can be used. Data indicating the height to the mark Mc detected by the distance meter 42 is sent to the shaft shake correction unit 52 as “mark distance data”. Note that the mark distance data is the value of the Z component of the mark position data.

  The data processing unit 50 includes a data collection unit 51, an axial shake correction unit 52, and a reconstruction unit 53. Specifically, the data processing unit 50 includes a general computer including a CPU, a main memory, a hard disk, a keyboard, a mouse, a printer, a display unit, various interfaces, and the like. The data processing unit 50 stores the transparent image data, or displays the sequentially transmitted transparent image data as a moving image on the display unit. Further, tomographic image data and three-dimensional image data created by reconstructing transmission image data are stored or displayed. Further, a control signal is sent to the mechanism control unit 25 based on an input from each interface, and a tomographic scanning operation is performed.

  The data processing unit 50 stores functional blocks of software such as the data collection unit 51, the shaft shake correction unit 52, and the reconstruction unit 53 in the hard disk, and loads these software from the hard disk into the main memory to function. Is demonstrated.

  The data collection unit 51 is for collecting transmission image data of the subject 5 detected by the X-ray detection unit 32 when the subject 5 is placed on the table member 21. Further, the data collection unit 51 sends the collected transmission image data to the axial shake correction unit 52.

  The shaft shake correction unit 52 acquires the mark image data of the mark surface 21B from the TV camera 41, and acquires the mark distance data from the distance meter 42 to the mark Mc. Based on these data, the shaft shake correction unit 52 corrects the transmission image data sent from the data collection unit 51 to transmission image data having no rotational shake. Specifically, the shaft shake correction unit 52 calculates the X component and the Y component of the mark position data indicating the position of the mark Mc from the mark image data on the mark surface 21B. Each time the rotation mechanism 23 rotates the table member 21, the rotational shake amount is calculated based on the position of the mark Mc and a preset reference position. Here, the reference position is a center point when the data collection unit 51 collects transmission image data. In this way, each time the table member 21 is rotated by the rotation mechanism 23 and the transmission image data of the subject 5 is captured, the center point O of the mark image captured by the TV camera 41 and the position of the selected mark Mc The amount of rotational shake is calculated based on Specifically, in the mark image shown in FIG. 3, the distance (ΔX, ΔY) from the center point O of the mark image to the mark position Mc is obtained as the rotational shake amount. The rotational shake amounts (ΔX, ΔY) obtained here are, to be precise, values obtained by adding the actual shake amount of the rotation axis R and the movement amount of the mark Mc when there is no shake. Using this rotational shake amount, transmission image data free from rotational shake can be obtained by the processing in steps S7 to S11 described later. Further, the corrected transmission image data without rotational shake is sent to the reconstruction unit 53.

  The reconstruction unit 53 is for reconstructing a plurality of transmission image data, and has a function of creating tomographic image data. Here, the reconstruction unit 53 receives the transmission image data from the axial shake correction unit 52 and creates tomographic image data of the subject 5.

  As a configuration other than those described above, the tomography apparatus 10 includes illumination that illuminates the mark surface 21B, a shielding box (not shown) that shields X-rays, and the like. The shielding box stores the subject 5, the subject placement unit 20, the X-ray irradiation unit 30, and the mark position detection unit 40 so as not to emit X-rays to the outside and supports the members. It fulfills the role of

(1-2. Operation)
Next, the operation of the tomography apparatus 10 according to the present embodiment will be described using the flowchart of FIG.

(Tomographic scan)
First, the subject 5 is placed on the table member 21 by the operator (step S1). At this time, transmission image data of a moving image having a frame rate corresponding to real time or the like is displayed on a display unit such as a display. Therefore, the operator manually operates the XY mechanism 22, the rotation mechanism 23, and the lifting mechanism 24 while observing a transmission image displayed on the display. Then, the desired part of the subject 5 is matched with the imaging region center C (step S2).

  Next, X-ray irradiation conditions, imaging conditions such as the number of collection points per rotation, and reconstruction conditions such as slice width, slice pitch, and number of slices are input to the data processing unit 50 by the operator. Based on these conditions, a tomographic scan for collecting data at a number of points is started during one rotation scan (step S3).

  When a tomographic scan is started, a control signal for rotating the rotation mechanism 23 according to the input imaging conditions is sent from the data processing unit 50 to the mechanism control unit 25. Then, the mechanism control unit 25 rotates the rotation mechanism 23, and transmission image data is sent from the X-ray detector 32 to the data collection unit 51 at every rotation pitch determined by the number of collection points per rotation (step S4). Further, the mark image data and the mark distance data are respectively sent from the TV camera 41 and the distance meter 42 to the shaft shake correction unit 52 corresponding to the rotation pitch at which the transmission image data is collected (step S5).

  The tomographic scan can be performed by continuous rotation or stopped at each rotation pitch. Further, the transmission image data, mark image data, and mark distance data collected by the data processing unit 50 have a large data capacity and cannot be stored only by the main memory. Therefore, it is temporarily stored in the hard disk and read into the main memory when processing is performed. In other words, data in the middle of processing or data after processing is stored in the main memory, but is stored in the hard disk in a timely manner when there is a large amount of data or when nonvolatile storage is desired. Hereinafter, the description of the memory is omitted.

  After execution of data collection as described above, if the position of the mark Mc exists at the center point O of the mark image and the mark height h is the same as the mark height h0 at the first data collection point, the table Assuming that the rotation axis R of the member 21 is not shaken, the next data collection is executed without executing the rotation shake correction (step S6-Yes, step S12).

  On the other hand, if the position of the mark Mc deviates from the center point O of the mark image after execution of data collection, or if the mark height h is not the same as the first mark height h0, it is assumed that rotational shake has occurred. Then, rotational shake correction processing is executed (step S6-No).

(Correction of rotational shake)
The rotational shake is corrected by the following procedure.

  First, the “first shake vector S” is calculated by the shaft shake correction unit 52 based on the mark position data (step S7).

  Specifically, the distance (ΔX, ΔY) between the position of the mark Mc and the center point O of the mark image is obtained. That is, mark image data as shown in FIG. 3 is sent from the mark position detection unit 40 to the shaft shake correction unit 52. In actuality, many marks appear in the mark image, but FIG. 3 schematically shows only the mark Mc to be measured. The axial shake correction unit 52 selects a mark Mc that is closest to the center O of the mark image from among a large number of marks, and tracks this mark as a measurement target. Therefore, the shaft shake correction unit 52 calculates the actual length (mm) of the deviation in the X direction and the Y direction measured from the center of the mark image at the center of gravity of the mark Mc as ΔX and ΔY. At this time, ΔX and ΔY can be obtained by calibrating in advance how many mm of the mark surface 21B corresponds to one pixel of the mark image.

Further, the shaft shake correction unit 52 calculates the difference ΔZ between the height h up to the mark Mc and the mark height h0 measured at the time of the first data collection by the equation:
ΔZ = h−h0 (1)
Ask for.

  The first shake vector S (ΔX, ΔY, ΔZ) on the mark surface 21B is calculated by the shaft shake correction unit 52 by the procedure described above.

  Subsequently, the “second shake vector Sd” is calculated by the shaft shake correction unit 52 based on the first shake vector (step S8).

  As a premise, orthogonal coordinates ξ, η, ζ obtained by inclining the orthogonal coordinates XYZ by an angle α are defined as shown in FIG. ζ is the optical axis Bc direction, and η is the Y direction. Further, the orthogonal coordinates ξd, ηd on the detection surface 32A are as shown in FIG. ξd and ηd are pixel directions, which coincide with the ξ and η directions, respectively.

The conversion of the first shake vector S (ΔX, ΔY, ΔZ) into such ξ, η, ζ coordinates is expressed by the following equation:
Δξ = △ X ・ cos (α) + △ Z ・ sin (α) (2)
Δη = △ Y (3)
Δζ = − △ X ・ sin (α) + △ Z ・ cos (α) (4)
Can be calculated.

Using these values, the second vector Sd (Δξd, Δηd), which is the projection of the first shake vector onto the detection surface 32A, is expressed by the following equation:
mag '= FDD / (FCD− △ ζ) (5)
Δξd = mag '・ △ ξ (6)
Δηd = mag '・ △ η (7)
Can be calculated.

  FDD represents the distance between F and D, and FCD represents the distance between F and C. Further, mag ′ represents the geometric enlargement ratio when shake occurs.

  With the procedure described above, the second shake vector Sd (Δξd, Δηd) on the detection surface 32A is calculated by the shaft shake correction unit 52.

  Subsequently, the “third shake vector Sg” is calculated by the shaft shake correction unit 52 based on the second shake vector (step S9).

Specifically, since one pixel size on the detection surface 32A is a known value, from the second shake vector Sd (Δξd, Δηd) on the detection surface 32A,
△ i = △ ξd / one pixel size on the detection surface (8)
△ j = △ ηd / one pixel size on the detection surface ...... (9)
The third shake vector Sg (Δi, Δj) on the transmission image created by the transmission data can be obtained based on the above.

In addition, the image when shake occurs is shifted by the third shake vector Sg and the enlargement ratio is changed by the factor fm, compared to the image when shake does not occur. This enlargement factor fm is given by the equation:
fm = mag ′ / (mag ′ of Δζ = 0) = FCD / (FCD−Δζ) (10)
It is expressed as

  By the procedure described above, the third shake vector Sg (Δi, Δj) and the enlargement factor change factor fm are obtained each time data is collected by the shaft shake correction unit 52.

  Subsequently, the shake correction of the rotation axis R is performed on the transmission image data collected by the data collection unit 51 based on the third shake vector Sg.

  Specifically, a process of moving the transmission image data collected by the data collection unit 51 in the reverse direction by the third shake vector Sg (that is, shifting by −Sg) is performed (step S10). Then, 1 / fm enlargement processing is performed with the screen center of the transmission image as a fixed point (step S11). Thereby, the shift of the image due to the rotational shake and the change of the enlargement ratio are corrected, and the transmission image data when there is no shake of the rotation axis R is obtained.

  In this correction, correction is performed so that the mark Mc is always at the center point O on the mark image. Thereby, the transmission image is corrected to a transmission image when an ideal rotation is performed around the mark Mc.

(Reconfiguration process)
When the tomographic scan ends (S12-Yes), the corrected transmission image data is reconstructed by the reconstruction unit 53, and tomographic image data is created (step S13). On the other hand, if the scan has not ended (S12-No), the rotation mechanism 23 rotates by a preset angle, and the next data collection is executed.

  To reconstruct tomographic image data from transmission image data, Feldkamp's cone beam CT reconstruction algorithm (LAFeldkamp, LCDavis and JWKress, Practical cone-beam algorithm, J.Opt.Soc.Am.A / Vo1.1, No.6 / June1984) etc. can be used. When supplemented with a conceptual diagram shown in FIG. 6, first, a number of collected transmission image data D1 is logarithmically converted to obtain a plurality of projection image data D2. Then, a spatial filter process is performed on each of these projection image data D2. In the spatial filter processing, high-cut processing is performed in the GX direction along the detector tilt plane G, and high-frequency enhancement processing (corresponding to Ramachandran & Lakshminarayanan filter processing in CT or the like) is performed in the GY direction orthogonal to the GX direction. Next, the projection image data D2 subjected to the spatial filter processing is three-dimensionally projected back toward the X-ray focal point F onto a virtual cross-sectional matrix CSM fixed to the subject 5. Then, by integrating the backprojected data, tomographic image data is obtained. When the back projection is performed, the cutoff frequency in the high cut processing in the GX direction is increased as the inclination angle α is increased.

  The tomographic image data can be created by the procedure described above. Moreover, not only one piece of tomographic image data but also a number of pieces of tomographic image data arranged at equal intervals can be created. As a result, three-dimensional image data can be obtained. In general, the tomographic image data is reconstructed on a surface along the mounting surface 21A, but it can be reconstructed even on other surfaces.

(1-3. Effect)
As described above, according to the tomography apparatus 10 according to the present embodiment, the table member 21 including the mark surface 21B on which the mark Mc is formed, the TV camera 41 and the distance meter for detecting the position of the mark Mc. 42 and an axial shake correction unit 52 that corrects the transmission image data to transmission image data having no rotational shake based on the position data of the mark Mc obtained by the TV camera 41 and the distance meter 42. The rotational shake amount can be obtained three-dimensionally by detecting the position of the mark Mc in a three-dimensional manner. From this rotational shake amount, the third shake vector Sg and the enlargement factor change factor fm can be obtained for each collection point of the transmission image data. Therefore, accurate rotational shake correction can be performed on the transmission image data.

  Supplementally, since the mark Mc on or near the rotation axis R is detected by visible light by the TV camera 41, the field of view of the TV camera 41 to be photographed can be narrowed and the magnification can be increased. Therefore, the position of the mark Mc can be detected with high accuracy. As a result, it is possible to correct the rotational shake accurately for the transmission image data.

  Further, since the rotational shake amount of the table member 21 on which the subject 5 is placed is obtained, the shake of the table member 21 due to the play of the XY mechanism 22 and the shake due to the change of the warp during the rotation of the table member 21 are also included. Can be corrected.

  In addition, since the amount of rotational shake is obtained by photographing the mark Mc, machining that finishes the outer peripheral surface of the table member 21 into a perfect circle becomes unnecessary. Supplementally, it is extremely difficult to detect a runout of the rotation axis R of several μm with high accuracy by machining the table member 21 having a diameter of about 1 m into a perfect circle. On the other hand, if the tomography apparatus 10 according to the present embodiment is used, the position of the mark M can be detected with a high magnification ratio, so that the shake of the rotation axis R can be detected with high accuracy.

  Further, since the tomography apparatus 10 according to this embodiment is a conical orbit type tomography apparatus, even a flat subject can perform tomography with a short X-ray transmission path. Further, even in the case of a flat subject, the tomographic imaging with a high magnification can be performed by bringing the imaging region center point C close to the X-ray focal point. In particular, it is possible to suitably inspect a substrate or the like on which components are mounted.

  In the present embodiment, a number of marks are formed on the table member 21, and the position of the mark Mc closest to the center point O of the mark image is tracked and measured. Here, “tracking” is to make the mark closest to the position of the mark Mc in the image of the mark surface 21B obtained in the previous scan as a new mark Mc, and the movement distance of the mark for each data collection is If the distance between adjacent marks is ½ or less, one mark can be continuously tracked.

<Second Embodiment>
FIG. 7 is a conceptual diagram of a tomography apparatus 10S according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part same as the already demonstrated part, and the overlapping description is abbreviate | omitted. In addition, the following description is also omitted in the following embodiments.

  The tomography apparatus 10S according to the present embodiment does not form the mark M on the back surface side of the table member 21, but is fixed to the XY mechanism 22 (XY non-moving side) in parallel with the front surface portion of the table member 21. A plate 26 is provided. A dot-like mark M is formed on the surface portion of the mark plate 26. The mark M is aligned with the rotation axis R, but may not be perfectly aligned. Also, it may be a plurality instead of one. When only one mark M is formed, selection of the mark M closest to the center of the visual field (center point O) of the mark image and tracking of the selected mark M become unnecessary. The mark plate 26 is formed of a member that easily transmits X-rays.

  As described above, the tomography apparatus 10S according to the present embodiment includes the mark plate 26 without forming the mark M on the table member 21, and therefore, compared with the tomography apparatus 10 according to the first embodiment. This eliminates the need for a large number of marks on a large area.

<Modification of Embodiment of the Present Invention>
Hereinafter, modifications of the embodiment of the present invention will be described.

(Modification 1)
In the first and second embodiments, the first shake vector S is measured with reference to the center of the visual field of the mark image. Then, every time data is collected, the shake of the rotation axis R is corrected by returning the mark Mc to the center point O of the mark image. That is, with the mark Mc as a reference point, the transmitted image is corrected as if the mark Mc is the center of rotation. On the other hand, the reference point can be set other than the mark Mc.

  For example, the shake of the rotation axis R can be corrected using the visual field center at the first data collection point as a reference point. FIG. 8 is an explanatory diagram of how to determine the shake vector S in the first modification. Here, the position of the mark M in the first data collection is represented by a point M0. Then, when there is no shake on the rotation axis R, the position of the mark M when rotated by the angle φ is represented by a point Mφ0 on the circumference having the radius of the point M0 and the center point O of the mark image. This means the position of the mark M when the rotation axis R is not shaken when the angle φ is rotated. Therefore, the difference between the point Mφ indicating the position of the mark M actually measured and the point Mφ0 can be obtained as the shake vector S. As a result, transmission image data can be corrected using the center of the field of view of the mark image at the time of the first data collection as a reference point.

(Modification 2)
In the first and second embodiments, the mark position detection unit 40 uses the TV camera 41 and the distance meter 42, but may be the TV camera 41 alone. In this case, the TV camera 41 is an autofocus type. That is, since the mark image is automatically photographed while focusing on the mark surface 21B, the mark height h can be obtained from the amount of operation of autofocus. An example of the principle of autofocus is shown in FIG. The TV camera 41 includes an optical system 91, an imaging unit 92, a control unit 93, and a mechanism unit 94. The imaging unit 92 outputs an image to the control unit 93, the control unit 93 obtains the magnitude of the high frequency component of the image, controls the mechanism unit 94 in a direction in which the magnitude increases, and the mechanism unit 94 has the optical axis 95. The optical system 91 or the optical system 91 and the imaging unit 92 are moved along Thereby, focusing is automatically performed, and the height h from the movement amount of the mechanism portion 94 to the mark M can be calculated. There are various other autofocus methods, and any of them can be used.

  Further, the autofocus TV camera 41 and the distance meter 42 may be used in combination. When used together, the distance h to the mark M is obtained by the distance meter 42, and the autofocus function of the TV camera 41 is used only for focusing.

  Further, the distance meter 42 may be a distance measuring device using a laser displacement meter, a distance measuring device using a triangulation method using ordinary light, or a distance measuring device that operates by auto-focusing.

(Modification 3)
In the first and second embodiments, the rotating mechanism 23 and the XY mechanism 22 are provided on the lifting mechanism 24, but the lifting mechanism 24 may be provided between the table member 21 and the XY mechanism 22. The XY mechanism 22 and the rotating mechanism 23 may be provided. However, when it is provided between the XY mechanism 22 and the rotating mechanism 23, when the distance between the TV camera 41 and the mark surface changes greatly due to elevation, refocusing (autofocus) is required. Further, when the change in the distance is large, the enlargement ratio of the mark image changes, and this needs to be corrected. That is, it is necessary to change the value of how many mm on the mark surface one pixel of the mark image corresponds to the distance.

(Modification 4)
In the first and second embodiments, the TV camera 41 and the distance meter 42 may be supported from the non-rotating side (configuration that does not rotate), or may be supported from the floor side. However, if the distance between the TV camera 41 and the mark surface changes greatly due to elevation, refocusing (autofocus) is necessary. Further, when the change in the distance is large, the enlargement ratio of the mark image changes, so that it is necessary to correct this.

(Modification 5)
In the first embodiment, the subject 5 is rotated. However, the X-ray irradiation unit 30 including the X-ray tube 31 and the X-ray detector 32 may be rotated. In this case, the mark position detection unit 40 (TV camera 41 and distance meter 42) is fixed to the X-ray irradiation unit 30 and rotated together.

  FIGS. 10A to 10C are schematic diagrams of tomography apparatuses 10A to 10C according to the fifth modification. The same number is attached | subjected to the component same as 1st and 2nd embodiment, and the description is abbreviate | omitted. The tomography apparatus 10 according to Modification 5 includes a rotating frame 44. The rotating frame 44 is a member that fixes the X-ray irradiation unit 30 (the X-ray tube 31 and the X-ray detector 32) and the mark position detection unit 40 (the TV camera 41 and the distance meter 42) to rotate together. It is. 10A to 10C, “FL.” Means that it is supported from the floor side.

  A tomography apparatus 10A shown in FIG. 10A is a modification of the first embodiment, and the X-ray tube 31, the X-ray detector 32, the mark position detection unit 40, and the rotating frame 44 rotate integrally. Is. Further, the XY mechanism 22 moves the table member 21 to change the imaging region.

  A tomography apparatus 10B shown in FIG. 10B is obtained by rearranging the XY mechanism 22 between the rotation mechanism 23 and the floor in the tomography apparatus 10A. In the tomography apparatus 10 </ b> B, the imaging region is changed by moving the X-ray irradiation unit 30.

  A tomography apparatus 10C shown in FIG. 10C is a modification of the second embodiment, and the X-ray tube 31, the X-ray detector 32, the mark position detection unit 40, and the rotating frame 44 rotate integrally. Is.

  In FIGS. 10A to 10C, the lifting mechanism 24 is not shown. The elevating mechanism 24 can be arranged at various positions. For example, in the tomography apparatuses 10A and 10C shown in FIGS. 10A and 10C, between the table member 21 and the XY mechanism 22, between the XY mechanism 22 and the floor, and between the rotating frame 44 and the rotating mechanism 23. Or between the rotation mechanism 23 and the floor. In FIG. 10B, the table member 21 is disposed between the floor, the rotating frame 44 and the rotating mechanism 23, the rotating mechanism 23 and the XY mechanism 22, and the XY mechanism 22 and the floor. it can.

(Modification 6)
In the first and second embodiments, the distance FDD between the X-ray focal point F and the center D of the detection surface 32A, the distance FCD between the X-ray focal point F and the imaging region center C, the imaging region center C and the center of the detection surface 32A. The distance CDD from D can be adjusted by making it variable continuously or stepwise. Thereby, the geometric enlargement ratio becomes variable. This can be achieved by providing a mechanism for changing the position of any two or all of the rotation mechanism 23, the X-ray tube 31 and the X-ray detector 32, including translation and / or tilting.

  In addition, the crossing angle α between the rotation axis R and the optical axis Bc can be made variable continuously or stepwise by this position changing mechanism. As the crossing angle α approaches 90 °, the resolution of the cross-sectional image data in the Z direction increases. On the other hand, when the crossing angle α is 0 °, the resolution in the Z direction is lost. When the crossing angle α approaches 90 °, the X-ray absorption of the subject 5 (a plate-like object such as a substrate) increases and the image quality of the tomographic image decreases. Therefore, when the crossing angle α is variable in the range of 0 ° to 90 °, the apparatus can be used for various subjects 5.

(Modification 7)
The first and second embodiments relate to a tomographic apparatus that creates tomographic image data, but can also be used as a fluoroscopic apparatus. As explained in the sixth modification, if the function of making the distances FDD, FCD, and CDD variable is added, the geometric magnification can be changed, and if the function of changing the crossing angle α is added, the perspective angle can be changed. Can do. When the crossing angle α is variable and the angle α is around 0 °, the mark position detector 40 (the TV camera 41 and the distance meter 42) and the X-ray beam B1 interfere with each other. Therefore, when used as a fluoroscopic device, a mechanism for retracting the mark position detection unit 40 is provided.

(Modification 8)
In the first and second embodiment bears and other modified examples, when the crossing angle α between the rotation axis R and the optical axis Bc is 90 °, it can be used as a general cone beam CT apparatus. FIG. 11 is a schematic diagram of a tomography apparatus 10D in Modification 8. In FIG. 11, the same components as those in the tomography apparatus 10 according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The mark position detection unit 40 is a combination of the TV camera 41 and the distance meter 42 according to the first embodiment. FL. Indicates that it is supported from the floor side. The tomography apparatus 10D is a modification of the tomography apparatus 10 according to the first embodiment, but the same modification can be made to the tomography apparatus 10S according to the second embodiment.

  The same modification can be made to the tomography apparatus according to the modified example 5. In this case, the cone beam CT apparatus in which the X-ray irradiation unit 30 rotates is obtained.

  Further, when the X-ray detector 32 is replaced with a one-dimensional detector, a single-slice CT apparatus that detects only the X-ray beam B irradiated on a plane perpendicular to the rotation axis R is obtained.

  As described above, the present invention can also be applied to a cone beam CT apparatus and a sicilling slice CT apparatus.

(Modification 9)
In the first and second embodiments, the dot-like mark M is formed on the mark surface, but various methods can be used for forming the mark. For example, printing, a laser marker, or etching can be used. It is also possible to randomly form point marks by spray painting. A pattern of the material of the table member 21 or the mark plate 26 may be used as a mark. Further, the shape of the mark itself may not be circular.

  Further, the position of the mark M in the mark image does not necessarily need to be obtained by measuring the center of gravity, and a method such as pattern matching may be used. For example, the mark image (φ = 0 °) at the time of the first scan is stored, and the first mark image is rotated by an angle φ (with respect to a predetermined point, for example, the center point O). The deviation after the second time may be measured by shifting and matching the mark image at the rotation angle φ. Here, the shift amount that provides the best matching is the shake vector. Furthermore, when this matching method is used, it is not necessary to identify individual marks, and the entire mark image may be treated as one pattern. As a result, the marks do not have to be separated one by one, but may be connected marks (such as arabesque patterns).

(Modification 10)
In the first and second embodiments, the axial shake correction unit 52 obtains the rotational shake amount from the mark position data output from the mark position detection unit 40, and corrects the transmission image data from the rotational shake amount. On the other hand, instead of correcting the transmission image data, the shake of the rotating shaft may be corrected by relatively moving the table member 21 and the X-ray irradiation unit 30. Specifically, the shaft shake correction unit 52 can correct the shake of the rotation axis R by relatively moving the table member 21 and the X-ray irradiation unit 30 by a distance corresponding to the rotation shake amount. In this case, as a moving mechanism that relatively moves the table member 21 and the X-ray irradiation unit 30, an existing mechanism can be used, or a new mechanism can be added. The shaft shake correction unit 52 controls the moving mechanism via the mechanism control unit 25.

  Further, the movement in the X and Y directions can be controlled by using the XY mechanism 22 according to the first and second embodiments, and the movement in the Z direction can be controlled by using the lifting mechanism 24. During tomography (during rotation), the XY mechanism 22 and the lifting mechanism 24 are stationary, so there is no problem even if they are used. Further, these may be added without diverting them. Moreover, since the relative movement is sufficient, the X-ray irradiation unit 30 may be moved in the reverse direction.

  Also in the modified example 5, the movement in the X and Y directions can be controlled by using the existing XY mechanism 22, and the movement in the Z direction can be controlled by using the lifting mechanism 24. Similarly, during tomography (during rotation), the XY mechanism 22 and the lifting mechanism 24 are stationary, so there is no problem even if they are used. Further, these may be added without diverting them. Moreover, since the relative movement is sufficient, the X-ray irradiation unit 30 may be moved in the reverse direction.

(Modification 11)
In the first and second embodiments, when obtaining tomographic image data, the so-called “horizontal division method” or “vertical division method” may be used. Here, the “horizontal division method” refers to tomographic image data obtained by obtaining rotational shake amounts for all transmission image data, correcting each of the transmission image data, and then executing reconstruction processing. It is a method to create. In addition, the “vertical division method” is a method in which the amount of rotational shake is obtained for each data collection point, and the correction and reconstruction processing of the transmission image data is executed. In this vertical division method, the tomogram data reconstructed at the next data collection point is added to the tomogram data created by the reconstruction process. Further, the tomographic image data may be created by a method combining the horizontal division method and the vertical division method.

  In the first and second embodiments, a known algorithm such as ART (Algebraic Reconstruction Technique) may be used as a method for creating tomographic image data.

(Modification 12)
In the first and second embodiments, transmission image data detected by the X-ray detector 32, tomographic image data and three-dimensional image data obtained by processing the same, and mark image data photographed by the TV camera 41 are displayed. Displayed in the section. At this time, the data displayed on the display unit can be printed by a printer, recorded as digital data, or transmitted through a line.

(Modification 13)
In the first and second embodiments, the X-ray tube 31 is disposed above the table member 21, but the X-ray tube 31 may be disposed below. In this case, the X-ray detector 32 is arranged on the upper side so that it is turned upside down. The device may be installed in any direction. For example, the mounting surface 21B may be a horizontal surface, a vertical surface, or an inclined surface.

(Modification 14)
In the first and second embodiments, X-rays are used as radiation, but other radiation can be used as long as it is transmissive radiation. For example, gamma rays, neutron rays, microwaves, visible light for transparent objects, and the like can be used.

(Modification 15)
The first and second embodiments may be used in combination with the configurations and processing methods of Modifications 1 to 14.

<Others>
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, you may combine a component suitably in different embodiment.

1 is a schematic diagram showing a configuration of a tomography apparatus 10 according to a first embodiment of the present invention. It is a figure which shows the concept of the mark surface 21B which concerns on the same embodiment. It is a figure which shows the concept of the mark image which concerns on the same embodiment. It is a flowchart for demonstrating operation | movement of the tomography apparatus 10 concerning the embodiment. It is a figure for demonstrating the correction process of rotational shake in the embodiment. It is a figure for demonstrating the reconstruction process of the tomogram data in the embodiment. It is a conceptual diagram of the tomography apparatus 10S which concerns on the 2nd Embodiment of this invention. 10 is an explanatory diagram of how to determine a shake vector S in Modification 1. FIG. It is a figure which shows an example of the principle of general autofocus. 10 is a schematic diagram of tomography apparatuses 10A to 10C in Modification 5. FIG. It is a schematic diagram of tomography apparatus 10D in Modification 8.

Explanation of symbols

5 ... Subject 10, 10S, 10A, 10B, 10C, 10D ... Tomography apparatus,
20 ... Subject placement unit, 21 ... Table member, 21A ... Placement surface, 21B ... Mark surface,
22 ... XY mechanism, 23 ... Rotation mechanism, 24 ... Elevating mechanism, 25 ... Mechanism control unit,
26 ... Mark plate, 30 ... X-ray irradiation part, 31 ... X-ray tube, 32 ... X-ray detector,
40: Mark position detection unit, 41 ... TV camera, 42 ... Distance meter, 43 ... Support frame,
44 ... Rotating frame, 50 ... Data processing unit, 51 ... Data collection unit, 52 ... Axial shake correction unit,
53 ... Reconstruction unit, 91 ... Optical system, 92 ... Imaging unit, 93 ... Control unit, 94 ... Mechanism unit,
B ... X-ray beam, C ... imaging area center point, O ... mark image center point,
M ... mark, R ... rotation axis.

Claims (5)

A table member comprising a front surface portion on which the subject is placed and a back surface portion on which a mark is formed on the opposite side of the front surface portion;
A radiation source for irradiating the subject placed on the table member with radiation;
Radiation detecting means for detecting radiation transmitted through the subject;
A rotation mechanism that relatively rotates the radiation source, the radiation detection means, and the table member along a rotation axis perpendicular to the surface portion of the table member;
When the subject is placed on the table member, data collection means for collecting transmission image data of the subject from the radiation dose detected by the radiation detection means at a plurality of rotational positions of the rotation ;
A TV camera for taking an image of the mark from the back side ;
Based on the mark image obtained by the TV camera in correspondence with the collection of transmission image data at the plurality of rotation positions, the transmission image data collected by the data collection means is corrected to transmission image data without rotational shake. Shaft shake correction means;
A tomography apparatus comprising: reconstruction means for reconstructing a plurality of transmission image data corrected by the axial shake correction means to generate tomogram data. A table member having a surface portion on which the subject is placed;
A radiation source for irradiating the subject placed on the table member with radiation;
Radiation detecting means for detecting radiation transmitted through the subject;
A rotation mechanism that relatively rotates the radiation source, the radiation detection means, and the table member along a rotation axis perpendicular to the surface portion of the table member;
A translation mechanism that supports the table member and translates the table member along the surface portion;
A mark plate having a surface portion on which a mark is formed, fixed to the parallel movement mechanism so as to be parallel to the surface portion on the opposite side of the surface portion of the table member;
A data collecting means for collecting transmission image data of the subject from the radiation dose detected by the radiation detecting means when the subject is placed on the surface portion of the table member;
Mark position detection means for detecting the position of the mark;
Based on the mark position data obtained by the mark position detection means, an axial shake correction means for correcting the transmission image data collected by the data collection means to transmission image data without rotational shake,
A tomography apparatus comprising: reconstruction means for reconstructing a plurality of transmission image data corrected by the axial shake correction means to generate tomogram data. A radiographic apparatus according to 請 Motomeko 2,
The shaft shake correcting means calculates a rotational shake amount based on the mark position data and a preset reference position, and corrects the transmitted image data without rotational shake according to the calculated rotational shake amount. A tomography apparatus characterized by this.   The tomography apparatus according to claim 1,
  The shaft shake correcting means obtains a shift amount that provides the best matching by taking a matching by rotation and shift between the mark image at a reference rotation position and the mark image at each rotation position, and based on the shift amount Correct transmission image data at each rotation position
A tomographic apparatus characterized by that. The tomography apparatus according to claim 2,
The shaft shake correcting means calculates a rotational shake amount based on the mark position data obtained by the mark position detecting means and preset reference mark position data having no rotational shake, and calculates the calculated rotational shake amount. A tomography apparatus that controls the translation mechanism to move a corresponding distance.

Images