JP5522345B2 - CT apparatus and CT apparatus calibration method - Google Patents

Description

  The present invention relates to a computed tomography apparatus (hereinafter referred to as a CT (Computed Tomography) apparatus) that captures a cross-sectional image of a subject.

  A CT apparatus called a so-called RR (Rotate Rotate) method (third generation method) in a conventional CT apparatus irradiates a subject with radiation (X-rays) generated from a radiation source, and irradiates the subject with radiation light. Radiation having a plurality of one-dimensional or two-dimensional detection channels that are rotated relative to the radiation at a rotation axis that intersects the direction of the axis, and that transmits radiation from the subject at each predetermined rotational position during one rotation. This is detected by a detector, and a cross-sectional image or three-dimensional data of the subject is obtained (tomographic imaging) from the detector output.

  FIG. 8 shows a configuration of a CT apparatus described in Patent Document 1 as a conventional example (front view). An X-ray tube 101 and an X-ray detector 103 that detects a pyramid-shaped X-ray beam 102 generated from the X-ray tube 101 with a two-dimensional resolution are arranged to face each other, and are placed on a table 104 so as to enter the X-ray beam 102. A transmission image (transmission data) of the placed subject 105 is obtained.

  The table 104 is disposed on the rotation / elevation mechanism 106, and when taking a cross-sectional image of the subject 105, the transmission image is obtained at a plurality of rotation positions while the table 104 is rotated once by the rotation / elevation mechanism 106 with respect to the rotation axis RA. Get (referred to as scanning). A large number of transmission images obtained by this scan are processed by the control processing unit 107 to obtain cross-sectional images (one or many) of the subject 105.

  Further, the shift mechanism 108 can move the rotational axis RA and the X-ray detector 103 closer to or away from (shift from) the X-ray focal point F of the X-ray tube 101, and the distance between the X-ray focal point F and the rotational axis RA. The imaging distance FCD (Focus to Rotation Center Distance) and the detection distance FDD (Focus to Detector Distance) between the X-ray focal point F and the detection surface 103a of the X-ray detector 103 are changed, and the imaging magnification ( = FDD / FCD) can be changed.

  By the way, the control processing unit 107 sets the size of one pixel using the set values of FCD and FDD and reconstructs the cross-sectional image, so that the size of the subject can be measured on the obtained cross-sectional image. . Here, if the imaging magnification (= FDD / FCD) is accurate, the size of one pixel can be set accurately, and the size of the subject can also be measured accurately.

  However, since the X-ray focal point F is in the X-ray tube 101 and its exact position cannot be visually observed and it is difficult to set the FCD and FDD values accurately mechanically, it is conventionally known. A subject having a size of 2 is photographed and the dimensions are adjusted (the dimensions of one pixel are adjusted).

  In Patent Document 1, a tomographic image of a rotary table is obtained, and an imaging distance FCD ′ corrected by multiplying a currently used imaging distance FCD value by a ratio dt / dg between a diameter dg obtained on a cross-sectional image and an actually measured diameter dt. Find the value. Then, FCD calibration (dimension adjustment) is performed by calibrating (correcting the starting point) an FCD value reading encoder (not shown) of the shift mechanism 108.

  As a result, correct dimension alignment can be performed at the shift position after FCD calibration.

JP 2002-62268 A

  In the prior art, FCD calibration is performed by imaging a subject of a known size. To be precise, this is calibration for correctly matching the imaging magnification (= FDD / FCD), and each of FCD and FDD is adjusted. It is not calibrated correctly by itself. That is, if there is an error in the FDD value, the FCD value is not correctly calibrated. Therefore, the alignment can be accurately performed at the shift position where the FCD calibration is performed. However, when the FCD or the FDD is changed from that position, an error occurs in the alignment as the change amount is larger. For this reason, there is a problem that it is troublesome to use since it is necessary to perform FCD calibration every time the FCD or FDD is changed.

  An object of the present invention is to obtain a cross-sectional image with high dimensional accuracy without performing calibration each time the photographing magnification is changed.

In order to achieve the above object, a CT apparatus according to claim 1 of the present invention detects a radiation source that emits radiation toward a subject placed on a table, and radiation that has passed through the subject. A plurality of radiation detecting means for outputting as a transmitted image; a rotating means for rotating the table and the radiation relative to a rotation axis intersecting with the radiation; and a plurality of rotating means and the radiation detecting means. In a CT apparatus having scan control means for performing a scan for obtaining a transmission image of the subject at the rotation position, and reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan, An imaging distance setting unit that sets an imaging distance that is a distance between the radiation source and the rotation axis, and a detection distance setting unit that sets a detection distance that is a distance between the radiation source and the radiation detection unit. The first reference distance of the first reference body with a known size obtained by scanning with the first shooting distance set and the second shooting distance are set and scanned. Calibration calculation means for calibrating the shooting distance and the detection distance from the size on the second cross-sectional image of the second reference body having a known size different from that of the first reference body. The gist.

With this configuration, the first reference object having a known size (D0) obtained by the first FCD setting (FCD = g1, FDD = h1) is obtained by the calibration calculation means, where the shooting distance is FCD and the detection distance is FDD. (D1) on the cross-sectional image and the size on the second cross-sectional image of the other reference body of the known size (E0) obtained by the second FCD setting (FCD = g2, FDD = h1) From (E2) , the FCD and FDD errors (εg, εh) can be obtained by solving the simultaneous equations to calibrate both FCD and FDD.

  A CT apparatus according to a second aspect of the present invention is the CT apparatus according to the first aspect, further comprising photographing distance measuring means for measuring the photographing distance, and the photographing distance calibration is performed by offsetting the photographing distance measuring means. The gist is that the value is calibrated.

  With this configuration, since the offset value of the FCD measuring means can be calibrated from the error (εg) of the FCD, the correct FCD can be obtained even if the FCD is changed after the calibration of the FCD and FDD. By using and reconfiguring, even if the FCD is changed, a cross-sectional image with high dimensional accuracy can be obtained without performing calibration each time.

  A CT apparatus according to a third aspect of the present invention is the CT apparatus according to the first or second aspect, further comprising detection distance measuring means for measuring the detection distance, and the calibration of the detection distance is performed by the detection distance. The gist is that the offset value of the measuring means is calibrated.

  With this configuration, it is possible to calibrate the offset value of the FDD measuring means from the error (εh) of the FDD. Therefore, after calibrating the FCD and FDD, the correct FDD can be obtained even if the FDD is changed. Even if the FDD is changed by reconstructing it, a cross-sectional image with good dimensional accuracy can be obtained without performing calibration each time.

  A CT apparatus according to a fourth aspect of the present invention is the CT apparatus according to any one of the first to third aspects, wherein the first photographing distance or the first photographing distance is controlled by controlling the photographing distance setting means. The gist of the invention is to have calibration control means for setting the second photographing distance.

  With this configuration, the first FCD or the second FCD can be automatically set to a predetermined value by the calibration control means.

The CT apparatus according to claim 5 of the present invention is a radiation source that emits radiation toward a subject placed on a table, and radiation that detects radiation transmitted through the subject and outputs it as a transmission image. Detecting means, rotating means for rotating the table and the radiation relative to a rotation axis intersecting with the radiation, and controlling the rotating means and the radiation detecting means at a plurality of rotation positions; In the CT apparatus having scan control means for performing a scan for obtaining a transmission image of the subject, and reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan, the radiation source and the rotation axis An imaging distance setting means for setting an imaging distance that is a distance between the radiation source, a detection distance setting means for setting a detection distance that is a distance between the radiation source and the radiation detection means, and a first detection distance. The size of the known size first the first cross-sectional image of the reference body obtained by scanning with, and the second detection distance by setting the first reference body obtained by scanning The gist of the invention is to have calibration calculation means for calibrating the imaging distance and the detection distance from the size of the second reference body having a different known size on the second cross-sectional image.

With this configuration, the first reference object having a known size (D0) obtained by the first FDD setting (FCD = g1, FDD = h1) by the calibration calculation means, where the shooting distance is FCD and the detection distance is FDD. (D1) on the cross-sectional image and the size on the second cross-sectional image of the other reference body of the known size (E0) obtained with the second FDD setting (FCD = g1, FDD = h2) From (E2) , the FCD and FDD errors (εg, εh) can be obtained by solving the simultaneous equations to calibrate both FCD and FDD.

  A CT apparatus according to a sixth aspect of the present invention is the CT apparatus according to the fifth aspect, further comprising detection distance measuring means for measuring the detection distance, and the calibration of the detection distance is an offset value of the detection distance measuring means. The gist of this is calibration.

  With this configuration, it is possible to calibrate the offset value of the FDD measuring means from the error (εh) of the FDD. Therefore, after calibrating the FCD and FDD, the correct FDD can be obtained even if the FDD is changed. Even if the FDD is changed by reconstructing it, a cross-sectional image with good dimensional accuracy can be obtained without performing calibration each time.

  A CT apparatus according to a seventh aspect of the present invention is the CT apparatus according to the fifth or sixth aspect, further comprising photographing distance measuring means for measuring the photographing distance, the calibration of the photographing distance being the photographing distance. The gist is that the offset value of the measuring means is calibrated.

  With this configuration, since the offset value of the FCD measuring means can be calibrated from the error (εg) of the FCD, the correct FCD can be obtained even if the FCD is changed after the calibration of the FCD and FDD. By using and reconfiguring, even if the FCD is changed, a cross-sectional image with high dimensional accuracy can be obtained without performing calibration each time.

  An CT apparatus according to an eighth aspect of the present invention is the CT apparatus according to any one of the fifth to seventh aspects, wherein the first detection distance or the first detection distance is controlled by controlling the detection distance setting means. The gist is to have calibration control means for setting the second detection distance.

  With this configuration, the first FDD or the second FDD can be automatically set to a predetermined value by the calibration control means.

According to a ninth aspect of the present invention, there is provided a CT apparatus calibration method comprising: a radiation source that emits radiation toward a subject placed on a table; and a radiation that has passed through the subject to detect a transmission image. A plurality of rotations by controlling the radiation detection means for outputting, the rotation means for rotating the table and the radiation relative to a rotation axis intersecting the radiation, and the rotation means and the radiation detection means; A scan control means for performing a scan to obtain a transmission image of the subject at a position; a reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan; the radiation source; In a CT apparatus having an imaging distance setting means for setting an imaging distance that is a distance between the radiation source and a detection distance setting means for setting a detection distance that is a distance between the radiation source and the radiation detection means, Set the shadow distance, and obtaining a first sectional image by scanning the first reference body of known size, and set the second shooting distance different known from said first reference body obtaining a second sectional image by scanning the magnitude second reference body, said second magnitude and before Symbol second reference body on said first sectional image of the first reference body And a step of calibrating the shooting distance and the detection distance from the size on the second cross-sectional image.

By this method, the imaging distance is FCD, the detection distance is FDD, and the first reference body having a known size (D0) obtained by the calibration calculation means with the first FCD setting (FCD = g1, FDD = h1). (D1) on the cross-sectional image and the size on the second cross-sectional image of the other reference body of the known size (E0) obtained by the second FCD setting (FCD = g2, FDD = h1) From (E2) , the FCD and FDD errors (εg, εh) can be obtained by solving the simultaneous equations to calibrate both FCD and FDD.

According to a tenth aspect of the present invention, there is provided a CT apparatus calibration method comprising: a radiation source that radiates radiation toward a subject placed on a table; and a radiation that has passed through the subject is detected to form a transmission image. A plurality of rotations by controlling the radiation detection means for outputting, the rotation means for rotating the table and the radiation relative to a rotation axis intersecting the radiation, and the rotation means and the radiation detection means; A scan control means for performing a scan to obtain a transmission image of the subject at a position; a reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan; the radiation source; In a CT apparatus having an imaging distance setting means for setting an imaging distance that is a distance between the radiation source and a detection distance setting means for setting a detection distance that is a distance between the radiation source and the radiation detection means, Set the detection distance, and obtaining a first sectional image by scanning the first reference body of known size, and set the second detection distance, different known and the first reference body obtaining a second sectional image by scanning the magnitude second reference body, said second magnitude and before Symbol second reference body on said first sectional image of the first reference body And a step of calibrating the shooting distance and the detection distance from the size on the second cross-sectional image.

With this configuration, the first reference object having a known size (D0) obtained by the first FDD setting (FCD = g1, FDD = h1) by the calibration calculation means, where the shooting distance is FCD and the detection distance is FDD. (D1) on the cross-sectional image and the size on the second cross-sectional image of the other reference body of the known size (E0) obtained with the second FDD setting (FCD = g1, FDD = h2) From (E2) , the FCD and FDD errors (εg, εh) can be obtained by solving the simultaneous equations to calibrate both FCD and FDD.

  According to the present invention, it is possible to obtain a cross-sectional image with high dimensional accuracy without performing calibration each time the photographing magnification is changed.

The schematic diagram (front view) which showed the structure of CT apparatus which concerns on 1st embodiment of this invention. The schematic diagram (plan view) which showed the detailed structure of the shift mechanism 7 of CT apparatus which concerns on 1st embodiment of this invention. FIG. 5 is a flowchart of FCD and FDD calibration prior to tomography according to the first embodiment of the present invention. The schematic diagram (a) which shows the 1st cross-sectional image 13 of the reference | standard body 12, and the schematic diagram (b) which shows the 2nd cross-sectional image 14 of the reference | standard body 12. FIG. The geometrical view (plan view) explaining the size on a cross-sectional image. The flowchart of FCD and FDD calibration prior to tomography according to Modification 8 of the first embodiment of the present invention. The schematic diagram (front view) which showed the structure of CT apparatus concerning 2nd embodiment of this invention. The schematic diagram (front view) which showed the structure of the conventional CT apparatus.

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

(Configuration of the first embodiment of the present invention)
The configuration of the first embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a schematic view (front view) showing a configuration of a CT apparatus according to the first embodiment of the present invention.

  X-rays that detect a pyramidal X-ray beam (radiation) 2 that is a part of the X-rays emitted from the X-ray tube (radiation source) 1 and the X-ray focal point F of the X-ray tube 1 with two-dimensional resolution. The X-ray beam 2 transmitted through the subject 5 placed on the table 4 so as to enter the X-ray beam 2 is disposed by facing the detector (radiation detection means) 3 by the X-ray detector 3. Detected and output as a transmission image (transmission data).

  The table 4 is disposed on a rotation / elevation mechanism (rotation means) 6 and is rotated by a rotation / elevation mechanism 6 with respect to a rotation axis RA perpendicular to the X-ray beam 2 and is parallel to the rotation axis RA. Z-moved (lifted) in the direction. Here, the rotation axis RA is precisely set to intersect the X-ray beam 2 in a direction perpendicular to the X-ray optical axis L defined by the center line of the X-ray beam 2.

  Further, the shift mechanism (imaging distance setting means, detection distance setting means) 7 positions the rotation axis RA and the X-ray detector 3, and the imaging distance FCD (Focus to rotation Center Distance) and the detection distance FDD (Focus to Detector Distance). ) And the rotational axis RA and the X-ray detector 3 are moved closer to or away from the X-ray focal point F of the X-ray tube 1 to change the imaging distance FCD and the detection distance FDD.

  Here, the shift mechanism 7 is used to change the imaging magnification (= FDD / FCD) according to the purpose. The z movement of the rotation / lifting mechanism 6 moves the target portion of the subject 5 to the height of the X-ray beam 2. Used to match. The rotation of the rotation / elevating mechanism 6 is used to obtain a transmission image at a plurality of rotation positions by rotating the subject 5 with respect to the X-ray beam 2 when taking a cross-sectional image.

  FIG. 2 is a schematic diagram (plan view) showing a detailed configuration of the shift mechanism 7 of the CT apparatus according to the first embodiment of the present invention.

  The shift mechanism 7 arranges the rail 7b along the y direction which is the direction of the X-ray optical axis L on the base 7a, and moves the rotation / lifting mechanism 6 supported by the rail 7b in the y direction using the ball screw 7c. The ball screw 7c is fixed to the base 7a via the bearing 7d in accordance with the y direction, rotated by the motor 7e, and the engaged ball nut 7f is fed in the y direction, and the rotation / lifting mechanism 6 fixed to the ball nut 7f. Is moved in the y direction.

  Similarly, the shift mechanism 7 moves the column 8 of the X-ray detector 3 supported by the rail 7b in the y direction using the ball screw 7g. The ball screw 7g is fixed to the base 7a through the bearing 7h in accordance with the y direction, rotated by the motor 7i, and the engaged ball nut 7j is fed in the y direction, and the column 8 fixed to the ball nut 7j is moved in the y direction. Move to.

The shift mechanism 7 includes an FCD measuring unit (shooting distance measuring unit) 7k that measures FCD. The FCD measuring unit 7k includes an encoder 7k1 which is attached to the ball screw 7c and outputs a pulse signal at every fixed rotation angle, and a counter 7k2 which counts the pulse signal. The FCD measuring unit 7k outputs an FCD reading g. The FCD reading g is given by the equation:
g = Δg · ng + Og (1)
It is a value represented by Here, ng is the pulse count value from the starting point, Δg is the amount of movement in the y direction per pulse, Og is the offset value for adjusting g to FCD, and Og and Δg are mechanically obtained in advance and stored in the counter 7k2. is there.

The shift mechanism 7 has an FDD measurement unit (detection distance measurement means) 7m that measures FDD. The FDD measuring unit 7m includes an encoder 7m1 that is attached to the ball screw 7g and outputs a pulse signal at every fixed rotation angle, and a counter 7m2 that counts the pulse signal. The FDD measuring unit 7m outputs an FDD reading h. The FDD reading h is given by:
h = Δh · nh + Oh (2)
It is a value represented by Here, nh is the pulse count value from the start point, Δh is the amount of movement in the y direction per pulse, Oh is the offset value for adjusting h to FDD, and Oh and Δh are mechanically obtained in advance and stored in the counter 7m2. is there.

  The rotation / elevation mechanism 6 has a rotation angle measurement unit (not shown) and a lift position measurement unit (not shown) as well as the shift mechanism 7, and outputs the rotation angle φ and the lift position z.

  With reference to FIG. 1, as other components, a control processing unit 9 that controls each mechanism unit (rotation / lifting mechanism 6, shift mechanism 7) and processes transmission data from the X-ray detector 3. There are a display unit 9a for displaying processing results, an X-ray control unit (not shown) for controlling the X-ray tube 1, and the like.

  The control processing unit 9 is a normal computer and includes a CPU, a memory, a disk (nonvolatile memory), a display unit 9a, an input unit (keyboard, mouse, etc.) 9b, a mechanism control board, an interface, and the like.

  The control processing unit 9 receives the operation position signals (g, h, φ, z) output from the mechanism units 6 and 7 by the mechanism control board and controls the mechanism units 6 and 7 to control the position of the subject. In addition to performing alignment, scanning (tomographic scanning), etc., transmission data collection command pulses and the like are sent (controlled) to the X-ray detector 3.

  In addition, the control processing unit 9 collects transmission data from the X-ray detector 3 during tomography, stores it, reconstructs it, creates a cross-sectional image of the subject, and displays it on the display unit 9a.

  Further, the control processing unit 9 issues a command to an X-ray control unit (not shown), specifies tube voltage and tube current, and instructs X-ray emission and stop. The tube voltage and tube current can be changed according to the subject.

  As shown in FIG. 1, a control processing unit 9 reads a software and functions as a functional block for the CPU to function as a calibration control unit (calibration control means) 9c for performing scanning for calibration of FCD and FDD. A calibration calculation unit (calibration calculation unit) 9d that calibrates the offset values of FCD and FDD from the cross-sectional image obtained by the scanning in step S9, and a scan control unit (scan control unit) 9e that performs tomographic scanning are obtained by scanning. A reconstruction unit (reconstruction means) 9f for creating a cross-sectional image from the transmission data.

(Operation of the first embodiment)
The operation will be described with reference to FIGS.

  FIG. 3 is a flowchart of FCD and FDD calibration prior to tomography according to the first embodiment of the present invention.

  The readings g and h of the FCD and FDD measured by the FCD measuring unit 7k and the FDD measuring unit 7m are calculated by Expressions (1) and (2) and output. Here, the y-direction movement amounts Δg and Δh per pulse used for the calculation are accurately obtained, whereas the offset values Og and Oh are not accurate. This is because the X-ray focal point F is in the X-ray tube 1 and the detection surface 3a is not embedded on the surface of the X-ray detector 3 but on the inner surface. This is because it is difficult to obtain the offset values Og and Oh mechanically accurately.

Therefore, if Δg and Δh are accurate, the true values of FCD and FDD and the readings g and h have only offset errors εg and εh,
FCD true value = g + εg (3)
FDD true value = h + εh (4)
There is a relationship.

  Therefore, prior to tomography, FCD and FDD calibration is performed as described below according to the flow of FIG. Here, the calibration of the FCD is a calibration of the offset value Og of the FCD measuring unit 7k, and is a process of obtaining and storing the offset error εg. The FDD calibration is a calibration of the offset value Oh of the FDD measuring unit 7m, and is a process for obtaining and storing the offset error εh.

  In step S <b> 1, the operator places a reference body 12 having a known size on the table 4. For example, a cylindrical member is used as the reference body 12 and is placed so that the axis of the cylinder is parallel to the rotation axis RA. Further, a known diameter D0 measured accurately in advance is input to the control processing unit 9 and stored therein. However, if it is already stored, there is no need to input it.

  When the operator inputs a calibration start in step S2, the calibration control unit 9c controls the shift mechanism 7 to move the rotation axis RA and the X-ray detector 3 to perform the first FCD and FDD settings. For example, the reading values g and h of FCD and FDD are set to predetermined values g1 and h1, respectively.

  In step S3, the calibration control unit 9c issues (controls) a command to the scan control unit 9e, and the scan control unit 9e controls tomography, rotates the reference body 12 with respect to the X-ray beam 2, and performs a plurality of rotations. A transmission image is obtained for the position. The calibration control unit 9c further issues (controls) a command to the reconstruction unit 9f, and the reconstruction unit 9f processes the obtained transmission images for a plurality of rotation positions and is perpendicular to the rotation axis RA of the reference body 12. A first cross-sectional image 13 in the direction is obtained and stored in a memory in the control processing unit 9.

  FIG. 4A is a schematic diagram showing a first cross-sectional image 13 of the reference body 12. On the first cross-sectional image 13, the reference body 12 is circular.

  In step S4, the calibration control unit 9c controls the shift mechanism 7 to move the rotation axis RA, and performs second FCD and FDD settings. For example, the reading value g of the FCD is set to a predetermined value g2. Here, the setting of the FDD remains unchanged as the reading value h1.

  In step S5, as in step S3, the calibration control unit 9c issues (controls) commands to the scan control unit 9e and the reconstruction unit 9f, and a second cross-sectional image in the direction perpendicular to the rotation axis RA of the reference body 12 is obtained. 14 is obtained and stored in the memory in the control processing unit 9.

  FIG. 4B is a schematic diagram showing a second cross-sectional image 14 of the reference body 12. The reference body 12 is circular on the second cross-sectional image 14.

  In step S6, the calibration calculation unit 9d obtains the diameter D1 of the reference body 12 on the first cross-sectional image 13. This is required by known image processing techniques. For example, the diameter S of the pixel unit can be obtained by calculating the area S of the reference body 12 in units of the number of pixels and calculating 2 × SQRT (S / π). The actual dimension diameter D1 can be obtained by multiplying the pixel unit diameter by the actual dimension per pixel.

  Furthermore, the calibration calculation unit 9d similarly obtains the diameter D2 of the reference body 12 on the second cross-sectional image 14.

In step S7, the calibration calculation unit 9d performs two diameter measurements,
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1, h1. Measurement 2; Formula from the measurement of the diameter D2 on the image with respect to the true diameter D0 at g2, h1.
εg = g1 · g2 · (D1−D2) / (g1 · D2−g2 · D1) (5)
εh = h1 · {g1 · D2 · (D1−D0) −g2 · D1 · (D2−D0)}
/{D0.(g1, D2-g2, D1)} (6)
And the offset errors εg and εh of the FCD and FDD are obtained and stored in the memory in the control processing unit 9.

  The FCD and FDD calibration is completed by the above steps S1 to S7.

  Next, the operator places the subject 5 on the table 4 instead of the reference body 12, and sets the desired FCD and FDD positions (g, h) and the z position of the table by inputting to the input unit 9b. Furthermore, a tomographic command is input. The scan control unit 9e controls tomography, rotates the subject 5 with respect to the X-ray beam 2, and obtains transmission images at a plurality of rotational positions. The reconstruction unit 9f uses the offset errors εg and εh stored for the reading values g and h of the FCD and FDD to calculate the true values of the FCD and FDD using the equations (3) and (4). A transmission image at a plurality of rotational positions obtained using the true values of FCD and FDD is processed to obtain a cross-sectional image in the target portion of the subject 5.

  In this embodiment, it is not necessary to frequently perform FCD and FDD calibration. When the arrangement of the X-ray tube 1 or the X-ray detector 3 is changed, the shift mechanism is repaired, or during periodic inspections, etc. Just do it.

<Derivation of Formula (5) and Formula (6)>
The derivations of equations (5) and (6) are based on the premise that the error in g is only the offset error εg (equation (3)). In other words, this is an assumption that the difference (g2−g1) in the FCD reading between the first FCD and FDD settings and the second FCD and FDD settings is accurate.

  FIG. 5 is a geometric view (plan view) for explaining the size on the cross-sectional image. When the reconstruction unit 9f performs the reconstruction process, what is projected on the detection surface 3a with the actual dimension d using the values of FCD and FDD recognized by the reconstruction unit 9f is the actual dimension on the cross-sectional image. D is reconfigured so that D becomes a value calculated by D = d · FCD / FDD (the size of one pixel is set as such).

Therefore, from the measurement 1, the diameter D1 obtained by reconstructing the projection of the diameter d1 on the detection surface by using g1 and h1 is expressed by the following equation:
D1 = d1 · g1 / h1 (7)
It is represented by Also, in equation (7), if g1 and h1 are true values of FCD and FDD, D1 should be a true value D0. Therefore, referring to equations (3) and (4),
D0 = d1 · (g1 + εg) / (h1 + εh) (8)
The relationship can be guided. When d1 is eliminated from the equations (7) and (8), the equation:
D1 / D0 = g1 · (h1 + εh) / {h1 · (g1 + εg)} (9)
Is obtained.

Considering measurement 2 in the same manner,
D2 / D0 = g2 · (h1 + εh) / {h1 · (g2 + εg)} (10)
(In the formula (9), D1 is replaced with D2 and g1 is replaced with g2).

  Next, equations (9) and (10), which are simultaneous equations for unknowns εg and εh, can be solved to derive equations (5) and (6). <> End

(Effects of the first embodiment)
The main point of the first embodiment is to simultaneously calibrate the offset values of the FCD and the FDD by measuring the size of the reference body on the cross-sectional image of the reference body in two FCD and FDD settings.

  According to the first embodiment, the first cross section of the reference body 12 having a known size (D0) obtained by the calibration calculation unit 9d with the first FCD and FDD settings (FCD = g1, FDD = h1). The size on the second cross-sectional image of the reference body 12 having the known size (D0) obtained by the size (D1) on the image and the second FCD and FDD settings (FCD = g2, FDD = h1) ( From D2), it is possible to calibrate both FCD and FDD by finding the errors (εg, εh) of FCD and FDD by solving simultaneous equations.

  Further, since the offset value Og of the FCD measuring unit 7k can be calibrated from the FCD error (εg), the correct FCD can always be obtained even if the FCD is changed after the calibration of the FCD and FDD. The cross-sectional image with good dimensional accuracy can be obtained without performing calibration each time the FCD is changed by reconstructing using the.

  Further, since the offset value Oh of the FDD measuring unit 7m can be calibrated from the FDD error (εh), the correct FDD can always be obtained even if the FDD is changed after the FCD and FDD calibration. The cross-sectional image with good dimensional accuracy can be obtained without performing calibration each time even if the FDD is changed by reconstructing using.

  Therefore, according to the first embodiment, a cross-sectional image with high dimensional accuracy can be obtained without performing calibration each time the imaging magnification is changed.

(Modification of the first embodiment)
In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

(Modification 1)
In the first embodiment, the same reference body 12 is used for measurement 1 (first FCD, FDD setting) and measurement 2 (second FCD, FDD setting), and only FCD is changed. If different reference bodies may be used in step 2, both FCD and FDD may be changed even if FDD is changed.

(Case 1) For example, when a reference body having a diameter E0 is used in measurement 2 and both FCD and FDD are changed, the calibration calculation unit 9d has two diameter measurements,
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1 and h1. Measurement 2; After measuring the diameter E2 on the image with respect to the true diameter E0 at g2 and h2, the equation:
[epsilon] g = g1, g2, {h1, E0, (D1-D0) -h2, D0, (E2-E0)}
/ {G1, h2, D0, E2-g2, h1, D1, E0} (11)
[epsilon] h = h1, h2, {g1, E2, (D1-D0) -g2, D1, (E2-E0)}
/ {G1, h2, D0, E2-g2, h1, D1, E0} (12)
And the offset errors εg and εh of the FCD and FDD are obtained and stored in the memory in the control processing unit 9.

(Case 2) For example, when only FCD is changed in measurement 1 and measurement 2 using different reference bodies, two diameter measurements are performed.
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1, h1 Measurement 2; After measuring the diameter E2 on the image with respect to the true diameter E0 at g2, h1, the equation (11 ) And εg and εh are obtained using an equation in which h2 is replaced by h1 in equation (12).

(Case 3) For example, when only FDD is changed in measurement 1 and measurement 2 using different reference bodies, two diameter measurements,
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1 and h1. Measurement 2; After measuring the diameter E2 on the image with respect to the true diameter E0 at g1 and h2, the equation (11 ), Εg and εh are obtained using an equation in which g2 is replaced with g1 in equation (12).

(Case 4) For example, when both FCD and FDD are changed in measurement 1 and measurement 2 using the same reference body, two diameter measurements,
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1 and h1. Measurement 2; After measuring the diameter D2 on the image with respect to the true diameter D0 at g2 and h2, the equation (11 ), And εg and εh are obtained by using equations in which E0 and E2 are replaced by D0 and D2 respectively in equation (12).

(Case 5) For example, when only the FDD is changed using the same reference body in measurement 1 and measurement 2, two diameter measurements
Measurement 1; Measure the diameter D1 on the image with respect to the true diameter D0 at g1 and h1 Measurement 2; After measuring the diameter D2 on the image with respect to the true diameter D0 at g1 and h2, the equation (11 ), And εg and εh are obtained using equations in which g2, E0, and E2 are replaced with g1, D0, and D2, respectively, in equation (12).

  When different reference bodies are used for measurement 1 and measurement 2 in Modification 1, a large imaging magnification is set for a small reference body, and a small imaging magnification is set for a large reference body, so that a reference is made on a transmission image. If the body does not stick out and does not become too small, εg and εh can be accurately obtained. Alternatively, it is the same even if a small reference body is selected when the photographing magnification is large and a large reference body is selected when the photographing magnification is small.

<Derivation of Formula (11) and Formula (12)>
The derivations of equations (11) and (12) are based on the premise that the errors of g and h are only offset errors εg and εh (equation (3) and equation (4)). In other words, this is a premise that the difference in the FCD reading g (g2−g1) and the difference in the FDD reading h (h2−h1) between the first setting and the second setting are accurate.

Considering in the same way as the derivation of Equation (5) and Equation (6),
D1 / D0 = g1 · (h1 + εh) / {h1 · (g1 + εg)} (13)
Is obtained.

Similarly, for measurement 2, the formula:
E2 / E0 = g2 · (h2 + εh) / {h2 · (g2 + εg)} (14)
(Equation in which g1, h1, D0, and D1 are replaced with g2, h2, E0, and E2 in Equation (13)) is obtained.

  Next, equations (13) and (14), which are simultaneous equations for the unknowns εg and εh, can be solved to derive equations (11) and (12). <> End

(Modification 2)
In the first embodiment and the first modification, a plurality of cylindrical reference bodies having different sizes may be prepared in advance, and the operator may use any one or two of them. In this case, the true diameter (known diameter) of all the reference bodies is measured in advance and stored in the memory of the control processing unit 9. The calibration calculator 9d compares the obtained diameter D1 on the cross-sectional image with the stored true value diameter, and then selects the closest true value diameter D0. Thereby, the reference body is automatically specified, and D0 is obtained. Further, the true diameter E0 (or D0) closest to the diameter E2 (or D2) on the obtained cross-sectional image is selected. Thereby, the reference body is automatically specified, and E0 (or D0) is obtained.

  This eliminates the need for the operator to input the true diameter of the reference body or input the identification of the reference body.

(Modification 3)
In the first embodiment, the shift mechanism 7 changes both the shooting distance FCD and the detection distance FDD. However, the shift mechanism 7 may be a shift mechanism 7 that changes only the shooting distance FCD and does not change the detection distance FDD. In this case, the shift mechanism (detection distance setting means) 7 is detection distance setting means for setting the detection distance FDD to one fixed value. In this case, the error εh of the FDD fixed value is obtained by calibration of the FDD.

  In the first embodiment, the shift mechanism 7 may be configured such that only the detection distance FDD is changed and the shooting distance FCD is not changed. In this case, calibration is performed when only the FDD described in the first modification is changed and the second cross-sectional image is taken (case 3 and case 5). In this case, the shift mechanism (shooting distance setting means) 7 is a shooting distance setting means for setting the shooting distance FCD to one fixed value. In this case, the error εg of the FCD fixed value is obtained by the calibration of the FCD.

(Modification 4)
In the first embodiment, the control processing unit 9 uses the FCD and FDD offset errors εg and εh obtained and stored by FCD and FDD calibration to perform correction calculation on the reading values g and h of the FCD and FDD. Although the true values of FCD and FDD are calculated, εg and εh are transmitted to the FCD measuring unit 7k and the FDD measuring unit 7m, respectively, and the offset values Og and Oh of the FCD and FDD are corrected and stored. Good.

  According to this modification, the reading values g and h of the FCD and FDD output from the FCD measuring unit 7k and the FDD measuring unit 7m become the true values of the FCD and FDD, respectively, so that the control processing unit 9 needs to perform correction calculation. Disappears.

(Modification 5)
In the first embodiment, the cylindrical member is used as the reference body, but it may not be cylindrical. For example, a square or rectangular prism or an irregular shape may be used. For example, when a prism is used, an area is obtained on a cross-sectional image, and if the square root of this area can be used as an amount instead of the diameter of the first embodiment, the length of both sides is obtained and the length of both sides is obtained. The average length can also be used as an alternative to diameter. Further, for example, when an irregular reference body is used, the square root of the area can be used as an amount instead of the diameter of the first embodiment.

  In the first embodiment, the radius may be obtained instead of the diameter. In short, what is necessary is just to obtain | require the quantity showing a magnitude | size.

(Modification 6)
In the first embodiment, each of the first cross-sectional image and the second cross-sectional image may be a plurality of cross-sectional images at a plurality of positions in the z direction instead of one. In this case, the statistical accuracy can be improved by obtaining the diameter by averaging the diameters of the reference bodies obtained on the respective cross-sectional images.

(Modification 7)
In the first embodiment, when the diameter of the reference body is obtained on the cross-sectional image, the diameter is obtained using area measurement, but this is not a limitation. For example, a general method for measuring dimensions on an image can be used. For example, a method may be used in which the center (center of gravity) of the reference body is obtained, the diameters are obtained from profiles on a plurality of line segments passing through the center, and averaged.

(Modification 8)
In the first embodiment, referring to FIG. 3, the first FCD and FDD setting (step S2) and the second FCD and FDD setting (step S4) are automatically performed by the calibration control unit 9c. In this setting, the operator may freely set FCD and FDD.

  Further, only the first FCD and FDD settings are set by the operator, and the second FCD and FDD settings (step S4) are set by the calibration controller 9c automatically changing the FCD by a predetermined amount. Also good. An example of the action of FCD / FDD calibration in this case will be described below.

  FIG. 6 is a flowchart of FCD and FDD calibration prior to tomography according to Modification 8 of the first embodiment of the present invention.

  In step S11, the operator performs first FCD and FDD settings. Thereby, g1 and h1 are set as reading values of FCD and FDD desired by the operator.

  In step S12, the operator, among a plurality of cylindrical reference bodies of different sizes prepared in advance, has a reference body 12 having a size such that the reference body does not protrude or become too small on the transmission image. Is selected and placed on the table 4. The diameters of the plurality of reference bodies are measured in advance and stored in the control processing unit 9.

  When the operator inputs a calibration start in step S13, the calibration control unit 9c performs tomography in the same manner as in step S3 of the first embodiment, obtains a first cross-sectional image of the reference body 12, and within the control processing unit 9 Store in the memory.

In step S14, the calibration control unit 9c controls the shift mechanism 7 to move the rotation axis RA, and performs second FCD and FDD setting. Here, a predetermined formula, for example, a formula,
The smaller of g2 = (3 · g1) and (0.8 · h1) is used .... (15)
Then, g2 is calculated and the FCD reading g is set to g2. Here, the setting of the FDD remains unchanged as the reading value h1.

  In step S15, the calibration control unit 9c performs tomography similarly to step S5 of the first embodiment, obtains a second cross-sectional image of the reference body 12, and stores it in the memory in the control processing unit 9.

  In step S16, the calibration calculation unit 9d obtains the diameter D1 of the reference body 12 on the first cross-sectional image as in step S6 of the first embodiment, and also the diameter D2 of the reference body 12 on the second cross-sectional image. Ask for.

  In step S17, the calibration calculation unit 9d first compares the obtained diameter D1 or D2 with the diameters (known diameters) of the plurality of reference bodies that have been measured and stored in advance, and is the closest known Select diameter D0. Thereby, the reference body is automatically specified, and D0 is obtained. Next, the calibration calculation unit 9d obtains the offset errors εg and εh of the FCD and FDD and stores them in the memory in the control processing unit 9 as in step S7 of the first embodiment.

(Modification 9)
In the first embodiment, the FCD and FDD are changed by moving the rotation axis RA and the X-ray detector 3, but may be changed by moving the X-ray tube 1 or the X-ray focal point F.

(Modification 10)
In the first embodiment, the offset errors εg and εh are obtained from the first cross-sectional image and the second cross-sectional image obtained by the two FCD and FDD settings, respectively, but each of the three or more FCD and FDD settings. The offset errors εg and εh may be obtained using the obtained three or more cross-sectional images. In this case, although there is redundancy as data, they are averaged, and offset errors εg and εh with improved statistical accuracy can be obtained. As a specific calculation of εg and εh in this case, for example, two are selected from three or more cross-sectional images, εg and εh are obtained in the same manner as in the first embodiment, and the two combinations are changed. It is calculated by averaging the obtained εg and εh.

(Modification 11)
In the first embodiment, as the FCD measuring unit 7k and the FDD measuring unit 7m, an encoder attached to a ball screw and a counter that counts the pulse signal of the encoder are used, but the invention is not limited thereto. For example, instead of an encoder that measures the rotation angle, a straight-ahead encoder that measures a straight movement and outputs a pulse signal may be used.

  Moreover, you may use a laser distance meter etc. as the FCD measurement part 7k and the FDD measurement part 7m, for example.

(Modification 12)
As radiation, not only X-rays but also radiation that is transparent to the subject, such as γ rays and microwaves, can be used depending on the subject.

(Configuration of the second embodiment of the present invention)
The configuration of the second embodiment of the present invention will be described below with reference to FIG.

  FIG. 7 is a schematic view (front view) showing a configuration of a CT apparatus according to the second embodiment of the present invention.

  X-rays that detect a pyramidal X-ray beam (radiation) 32 that is a part of the X-rays emitted from the X-ray tube (radiation source) 31 and the X-ray focal point F of the X-ray tube 31 with two-dimensional resolution. The X-ray beam 32 transmitted through the subject 36 placed on the table 35 so as to enter the X-ray beam 32 is disposed on the shift mechanism 34 so as to face the detector (radiation detection means) 33. It is detected by the line detector 33 and output as a transmission image (transmission data).

  The X-ray tube 31 and the X-ray detector 33 are rotated together with the shift mechanism 34 by a rotation mechanism 37 (rotation means) about a rotation axis RA perpendicular to the X-ray beam 32. Is supported by Here, the rotation axis RA is accurately set so as to intersect the X-ray beam 32 in a direction perpendicular to the X-ray optical axis L defined by the center line of the X-ray beam 32.

  Further, the shift mechanism (imaging distance setting means, detection distance setting means) 34 positions the X-ray tube 31 and the X-ray detector 33, and the imaging distance FCD (Focus to rotation Center Distance) and the detection distance FDD (Focus to Detector Distance). ) And the X-ray tube 31 and the X-ray detector 33 are moved closer to or away from the rotation axis RA to change the imaging distance FCD and the detection distance FDD.

  The table 35 is disposed on the lifting mechanism 40 and is moved (lifted) in the z direction parallel to the rotation axis RA.

  Here, the shift mechanism 34 is used to change the imaging magnification (= FDD / FCD) according to the purpose, and the elevating mechanism 40 is used to adjust the target portion of the subject 36 to the height of the X-ray beam 32. It is done. The rotation mechanism 37 is used to obtain a transmission image at a plurality of rotation positions by rotating the X-ray beam 32 with respect to the subject 36 when taking a cross-sectional image.

  The shift mechanism 34 includes an FCD measurement unit (shooting distance measurement unit) (not shown) that measures FCD and an FDD measurement unit (detection distance measurement unit) (not shown) that measures FDD. The FCD measurement unit and the FDD measurement unit measure FCD and FDD, respectively, as in the first embodiment, and output an FCD reading g and an FDD reading h.

  Similarly to the shift mechanism 34, the rotation mechanism 37 and the lifting mechanism 40 each have a rotation angle measurement unit (not shown) and a lift position measurement unit (not shown), and output the rotation angle φ and the lift position z.

  As other components, the control unit 9 that controls each mechanism unit (shift mechanism 34, rotation mechanism 37, elevating mechanism 40) and processes transmission data from the X-ray detector 33, processing results, etc. There are a display unit 9a for displaying, an X-ray control unit (not shown) for controlling the X-ray tube 31, and the like.

  The control processing unit 9 is a normal computer and has the same configuration as the first embodiment, and includes a CPU, memory, disk (nonvolatile memory), display unit 9a, input unit (keyboard, mouse, etc.) 9b, mechanism control board, interface, Etc.

  The control processing unit 9 receives the operation position signals (g, h, φ, z) output from the mechanism units 34, 37, and 40 by the mechanism control board and controls the mechanism units 34, 37, and 40. In addition to performing alignment and scanning (tomographic scanning) of the subject, transmission data collection command pulses and the like are sent (controlled) to the X-ray detector 33.

  The control processing unit 9 collects transmission data from the X-ray detector 33 during tomography, stores it, reconstructs it, creates a cross-sectional image of the subject, and displays it on the display unit 9a.

  Further, the control processing unit 9 issues a command to an X-ray control unit (not shown), specifies tube voltage and tube current, and instructs X-ray emission and stop. The tube voltage and tube current can be changed according to the subject.

  As shown in FIG. 7, the control processing unit 9 reads a software and functions as a functional block for the CPU to function as a calibration control unit (calibration control means) 9c that performs scanning for calibration of FCD and FDD. A calibration calculation unit (calibration calculation unit) 9d that calibrates the offset values of FCD and FDD from the cross-sectional image obtained by the scanning in step S9, and a scan control unit (scan control unit) 9e that performs tomographic scanning are obtained by scanning. A reconstruction unit (reconstruction means) 9f for creating a cross-sectional image from the transmission data.

(Operation of the second embodiment)
In the operation of the second embodiment, the FCD and FDD setting by the shift mechanism 7 and the change of the rotation angle φ by the rotation / lifting mechanism 6 and the z movement according to the first embodiment are respectively performed in the second embodiment. Only the FCD and FDD setting by the shift mechanism 34, the change of the rotation angle φ by the rotation mechanism 37, and the z movement by the elevating mechanism 40 are replaced. The relative movement between the subject 36 and the X-ray beam 32 due to these movements is exactly the same in the first embodiment and the second embodiment.

  Therefore, since the operation of the second embodiment is the same as that of the first embodiment, the description is omitted.

(Effect of the second embodiment)
According to the second embodiment, the same effects as in the first embodiment can be obtained, but in addition, since the tomography can be performed without rotating the subject, the tomography can be performed even with a weak subject. There is.

(Modification of the second embodiment)
In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the same modifications as in the first embodiment are possible. is there. The following modifications are also possible.

(Modification 1)
In the second embodiment, the table 35 is moved by the elevating mechanism 40 by z, but the X-ray tube 31 and the X-ray detector 33 may be integrally moved by z. In short, the table 35 and the X-ray beam 32 may be relatively moved by z.

  DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray beam, 3 ... X-ray detector, 3a ... Detection surface, 4 ... Table, 5 ... Subject, 6 ... Rotation / lifting mechanism, 7 ... Shift mechanism, 7a ... Base, 7b ... Rail, 7c ... Ball screw, 7d ... Bearing, 7e ... Motor, 7f ... Ball nut, 7g ... Ball screw, 7h ... Bearing, 7i ... Motor, 7j ... Ball nut, 7k ... FCD measuring unit, 7k1 ... Encoder, 7k2 ... Counter 7m ... FDD measurement unit, 7m1 ... encoder, 7m2 ... counter, 8 ... support, 9 ... control processing unit, 9a ... display unit, 9b ... input unit, 9c ... calibration control unit, 9d ... calibration calculation unit, 9e ... scan Control unit, 9f ... reconstruction unit, 12 ... reference body, 13 ... first sectional image, 14 ... second sectional image, 31 ... X-ray tube, 32 ... X-ray beam, 33 ... X-ray detector, 33a ... detection surface, 34 ... shift mechanism, 35 Table, 36 ... Subject, 37 ... Rotating mechanism, 38 ... Base, 39 ... Support, 40 ... Elevating mechanism, 101 ... X-ray tube, 102 ... X-ray beam, 103 ... X-ray detector, 103a ... Detection surface, 104 ... Table 105 ... Subject 106 ... Rotation / lifting mechanism 107 ... Control processing unit 108 ... Shift mechanism

Claims (10)

A radiation source that emits radiation toward a subject placed on a table, radiation detection means that detects radiation transmitted through the subject and outputs it as a transmission image, and a rotation axis that intersects the radiation Scan control for performing a scan for obtaining a transmission image of the subject at a plurality of rotation positions by controlling the rotation means for relatively rotating the table and the radiation, and the rotation means and the radiation detection means. And a CT apparatus having reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan,
An imaging distance setting means for setting an imaging distance which is a distance between the radiation source and the rotation axis;
Detection distance setting means for setting a detection distance that is a distance between the radiation source and the radiation detection means;
The size obtained on the first cross-sectional image of the first reference body of a known size obtained by scanning with the first photographing distance set and the second photographing distance set on the scan Calibration calculation means for calibrating the shooting distance and the detection distance based on a size on the second cross-sectional image of the second reference body having a known size different from that of the first reference body. CT device. The CT apparatus according to claim 1,
A photographing distance measuring means for measuring the photographing distance;
The CT apparatus, wherein the photographing distance calibration is a calibration of an offset value of the photographing distance measuring means. The CT apparatus according to claim 1 or 2,
Having a detection distance measuring means for measuring the detection distance;
The CT apparatus, wherein the detection distance calibration is calibration of an offset value of the detection distance measuring means. The CT apparatus according to any one of claims 1 to 3,
A CT apparatus comprising calibration control means for controlling the photographing distance setting means to set the first photographing distance or the second photographing distance. A radiation source that emits radiation toward a subject placed on a table, radiation detection means that detects radiation transmitted through the subject and outputs it as a transmission image, and a rotation axis that intersects the radiation Scan control for performing a scan for obtaining a transmission image of the subject at a plurality of rotation positions by controlling the rotation means for relatively rotating the table and the radiation, and the rotation means and the radiation detection means. And a CT apparatus having reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan,
An imaging distance setting means for setting an imaging distance which is a distance between the radiation source and the rotation axis;
Detection distance setting means for setting a detection distance that is a distance between the radiation source and the radiation detection means;
The size obtained on the first cross-sectional image of the first reference body of a known size obtained by scanning with the first detection distance set and the second detection distance obtained by scanning Calibration calculation means for calibrating the shooting distance and the detection distance based on a size on the second cross-sectional image of the second reference body having a known size different from that of the first reference body. CT device. The CT apparatus according to claim 5, wherein
Having a detection distance measuring means for measuring the detection distance;
The CT apparatus, wherein the detection distance calibration is calibration of an offset value of the detection distance measuring means. The CT apparatus according to claim 5 or 6,
A photographing distance measuring means for measuring the photographing distance;
The CT apparatus, wherein the photographing distance calibration is a calibration of an offset value of the photographing distance measuring means. The CT apparatus according to any one of claims 5 to 7,
A CT apparatus comprising calibration control means for controlling the detection distance setting means to set the first detection distance or the second detection distance. A radiation source that emits radiation toward a subject placed on a table, radiation detection means that detects radiation transmitted through the subject and outputs it as a transmission image, and a rotation axis that intersects the radiation Scan control for performing a scan for obtaining a transmission image of the subject at a plurality of rotation positions by controlling the rotation means for relatively rotating the table and the radiation, and the rotation means and the radiation detection means. Means, reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan, imaging distance setting means for setting an imaging distance that is a distance between the radiation source and the rotation axis, In a CT apparatus having a detection distance setting means for setting a detection distance that is a distance between a radiation source and the radiation detection means,
Setting a first imaging distance and scanning a first reference body of a known size to obtain a first cross-sectional image;
Setting a second imaging distance and scanning a second reference body of a known size different from the first reference body to obtain a second cross-sectional image;
From the size on the second sectional image size before Symbol second reference body on said first sectional image of the first reference body, comprising the steps of: calibrating the imaging distance and the detected distance A method for calibrating a CT apparatus, comprising: A radiation source that emits radiation toward a subject placed on a table, radiation detection means that detects radiation transmitted through the subject and outputs it as a transmission image, and a rotation axis that intersects the radiation Scan control for performing a scan for obtaining a transmission image of the subject at a plurality of rotation positions by controlling the rotation means for relatively rotating the table and the radiation, and the rotation means and the radiation detection means. Means, reconstruction means for reconstructing a cross-sectional image of the subject from the transmission image obtained by the scan, imaging distance setting means for setting an imaging distance that is a distance between the radiation source and the rotation axis, In a CT apparatus having a detection distance setting means for setting a detection distance that is a distance between a radiation source and the radiation detection means,
Setting a first detection distance and scanning a first reference body of a known size to obtain a first cross-sectional image;
Setting a second detection distance and scanning a second reference body of a known size different from the first reference body to obtain a second cross-sectional image;
From the size on the second sectional image size before Symbol second reference body on said first sectional image of the first reference body, comprising the steps of: calibrating the imaging distance and the detected distance A method for calibrating a CT apparatus, comprising:

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