JP6930932B2 - Inclined CT imaging device - Google Patents

Description

An embodiment of the present invention relates to an inclined CT imaging apparatus that reconstructs a tomographic image of a subject from transmitted data obtained by detecting radiation transmitted through the subject.

A radiation inspection device that performs non-destructive inspection of a subject by irradiating the subject with radiation typified by X-rays, detecting the two-dimensional distribution of the radiation attenuated by passing through the subject, and imaging it. Are known. For example, a radiological examination device can detect voids existing inside a subject.

As a radiation inspection device, a tilted CT (Computed Tomography) imaging device that obtains a tomographic image of a subject while controlling a conical trajectory with respect to radiation is known. The tilted CT imaging device is also called a tomosynthesis device or a Laminograph device. The tilted CT imaging device collects radiation transmission data from a direction of 360 °, which is non-orthogonal to the rotation axis, while rotating the tilted CT imaging device with respect to the rotation axis perpendicular to the mounting surface. The tomographic image of the subject is reconstructed from the transmitted transmission data.

In this tilted CT imaging device, the positional relationship between the focal point of radiation, the rotation axis of the subject, and the radiation detector affects image blurring and the like. For example, assuming that the amount of positional deviation of the focal point of radiation is X mm and the imaging magnification is Y times, the amount of positional deviation Z on the detector is Z = XY. In recent years, high magnification and high resolution have been developed in tilted CT imaging devices, and the minute deviation of these positional relationships increases the amount of positional deviation Z. Therefore, the accuracy required for the positional relationship between the focus of radiation, the rotation axis of the subject, and the radiation detector is increasing.

Therefore, in the inclined CT imaging device, the table on which the subject is placed is moved so that the tomographic image approaches the area of the real image by utilizing the fact that the tomographic image becomes larger than the real image when these positional relationships are deviated. Therefore, a method for adjusting these positional relationships is known.

Japanese Unexamined Patent Publication No. 2001-153817

The positional relationship between the rotation axis of the subject and the detector is a specified angle and distance due to the follow-up complementary operation, and the positional relationship between the two does not collapse beyond the required accuracy unless there is disturbance such as vibration. The cause of the disruption of the positional relationship between the radiation focus, the subject's rotation axis, and the radiation detector is mainly the displacement of the radiation focus. The focus of radiation is displaced not only by exchanging the radiation source and filament, but also by changing the tube voltage and tube current, and the focus of radiation is also displaced by the outside air temperature and the temperature of the radiation source.

The translation mechanism on the rotary table is a mechanism for moving the point of interest of the subject on the rotation axis, and the cause of the positional deviation cannot be eliminated.

An object of the present embodiment is to provide an inclined CT imaging apparatus capable of correcting the positional relationship between the focal point of radiation, the rotation axis of a subject, and a radiation detector with high accuracy in order to solve the above-mentioned problems. And.

In order to achieve the above object, the tilted CT imaging apparatus of the present embodiment has a mounting surface for a subject, a rotating table that is rotatable around a rotation axis orthogonal to the mounting surface, and a radiation focus. A radiation source that irradiates the rotating table with radiation from the radiation focus, a detector that is located opposite the radiation source across the rotating table, detects radiation, and outputs transmitted data. With a tilting mechanism that changes the laminone angle formed by the center line of radiation detected by the detector and the rotation axis along the tilting surface within a range of 0 ° or more and 90 ° or less, and a plurality of rotation positions due to the rotation of the rotary table. A reconstruction unit that reconstructs a tomographic image of the subject based on the transmission data detected by the detector, a correction unit that corrects the position of the radiation focus according to the correction data, and correction data that generates the correction data. It includes a generation unit.

Then, the correction data generation unit is placed on the rotary table so as to be located at the center of the display unit that displays the perspective image and the perspective image displayed on the display unit based on the transmission data. An image that detects the displacement of the jig based on the jig, the rotation control unit that rotates the rotary table by 180 ° after the jig is placed, and the transmission data before and after the rotation by the rotation control unit. It has a processing unit and a calculation unit that calculates a positional deviation of the radiation focal point from the normal position based on the displacement of the jig detected by the image processing unit, and obtains the correction data for canceling the positional deviation. It is characterized by generating.

It is a block diagram which shows the structure of the inclined type CT imaging apparatus. It is a block diagram which shows the detailed structure of the photographing control part. It is a block diagram which shows the detailed structure of a radiation source. It is a schematic diagram which shows the correction principle of a focal point when a lamino angle is zero. It is a schematic diagram which shows the correction principle of a focal point when a lamino angle is not zero. It is a block diagram which shows the structure of the correction data generation part. It is a flowchart which shows the calculation operation of correction data. It is a schematic diagram which shows the fluoroscopic image for position confirmation. It is a schematic diagram which shows the state which the jig is placed in the center of an image. It is a schematic diagram which detects the center of gravity of the jig before and after rotation. It is a schematic diagram which generates correction data from a position shift. It is a block diagram which shows another example of the structure of the inclined type CT imaging apparatus. It is a schematic diagram which shows the database of correction data. It is a flowchart which shows the operation of the inclined type CT imaging apparatus using the database of correction data.

(First Embodiment)
Hereinafter, the inclined CT imaging apparatus according to the first embodiment will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an inclined CT imaging device. The inclined CT imaging device 1 irradiates the subject 100 with radiation from each direction, detects the radiation transmitted through the subject 100, and re-creates the tomographic image of the subject 100 from each transmitted data obtained by the detection. Constitute. The rotation axis RA of the subject 100, which is the axis for changing the irradiation direction, and the radiation center line RC, which is the center line of the detected radiation, intersect at a non-orthogonal lamino angle θ. The tilted CT imaging device 1 includes a radiation source 2, a detector 3, a rotary table 4, and a data processing unit 8.

The radiation source 2 irradiates a radiation beam toward the subject 100. Radiation is, for example, X-rays. The radiation beam is radiation emitted from the focal point Fa in a conical shape. The radiation source 2 is, for example, an X-ray tube, which is a transmissive microfocus X-ray tube having a small focal Fa or a nanofocus X-ray tube having a focal Fa of 1 μm or less. In the X-ray tube, the filament 22 and the target 21 such as tungsten are opposed to each other with a target angle of 0 ° or more (see FIG. 3), the filament 22 emits an electron beam, and the target 21 is directed from the filament 22. The emitted and accelerated electron beams collide, and the target 21 generates X-rays from the collision of the electron beams.

The rotary table 4 and the translation mechanism 41 are a mounting table for the subject 100. The rotary table 4 and the translation mechanism 41 are formed in a hollow inside using plastic or carbon as a material in order to reduce the absorption of radiation. The rotary table 4 is interposed between the radiation source 2 and the detector 3 so that the mounting surface faces the radiation source 2. The rotary table 4 includes a rotary mechanism 42 and an elevating mechanism 43. The translation mechanism 41 moves the subject 100 in the X-axis and Y-axis directions parallel to the mounting surface. The X-axis direction is a uniaxial direction parallel to the mounting surface. The Y-axis direction is parallel to the mounting surface and orthogonal to the X-axis.

The rotation mechanism 42 has a rotation axis RA parallel to the Z axis, and rotates the rotary table 4 around the Z axis. The Z-axis direction is a direction orthogonal to the mounting surface of the rotary table 4, in other words, is orthogonal to the X-axis direction and the Y-axis direction. The radiation source 2 and the rotary table 4 are aligned so that the focal point Fa is located on the extension line of the rotary axis RA. However, replacement of the radiation source 2, replacement of the filament 22, change of the tube voltage, change of the tube current, movement of the inclined CT imaging device 1, outside air temperature, temperature of the radiation source 2, total irradiation time of radiation, continuous radiation. The focus Fa may be displaced from the normal position Fc due to the irradiation time, the total usage time of the target 21, or a combination of two or more of these factors. The normal position Fc is a point located on the extension line of the rotation axis RA.

The elevating mechanism 43 moves the rotary table 4 along the Z-axis direction. The imaging magnification of the subject 100 changes as the rotary table 4 moves up and down by the elevating mechanism 43. The imaging magnification is represented by FDD / FOD, which is the ratio of the imaging distance FOD from the focal point Fa at the normal position Fc to the subject 100 and the detection distance FDD from the focal point Fa at the normal position Fc to the detector 3.

The detector 3 is located on the opposite side of the rotary table 4 from the radiation source 2, and faces the focal point Fa of the radiation source 2 in an angle range of 0 ° or more and 90 ° or less. The detector 3 has a two-dimensionally expanding surface for detecting radiation, and detects transmission data according to the transmission path of radiation. The transmission data is a two-dimensional distribution of radiation intensity attenuated according to the transmission path of radiation.

The detector 3 is composed of, for example, an image intensifier (I.I.) and a camera. I. I. Expands the scintillator surface made of cesium iodide or the like that emits light when excited by radiation in a two-dimensional manner, converts the two-dimensional distribution of the incident radiation into a fluorescence image, and increases the luminosity of the fluorescence image. In the camera, image pickup elements such as CCD and CMOS are arranged side by side to capture a fluorescence image. The detector 3 may be a flat panel detector (FPD). The FPD has a photodiode and a TFT switch along the scintillator surface. The photodiode converts a fluorescent image into an electric charge and stores it, and when an ON signal is given, the TFT switch outputs the electric charge stored in the photodiode.

The detector 3 includes a tilting mechanism 31. The tilting mechanism 31 moves the detector 3 along the tilting surface while maintaining the posture in which the detector 3 faces the focal point Fa. For example, the tilt plane is set orthogonal to the X-axis and parallel to the YZ plane defined by the Y-axis and the Z-axis. That is, the tilting mechanism 31 sets the lamino angle θ formed by the radiation center line RC and the rotation axis RA of the rotation table 4 in the range of 0 ° or more and 90 ° or less. The radiation center line RC is a line connecting the center point Dc of the radiation detected by the detector 3 and the focal point Fa.

The data processing unit 8 is a so-called computer and various control circuits, and is composed of a processor, a memory, a storage, a driver circuit, a display unit, and an operation unit. The processor, also called a CPU or MPU, executes an instruction in the program and outputs an execution result. The memory temporarily stores the execution result of the processor when the program is expanded and the processor instructs it. The storage stores programs and various data. When the execution result of the processor is a control signal, the driver circuit supplies a power signal according to the control signal to each part. The display unit is an image display means such as a liquid crystal display or an organic EL display. The operation unit is an input interface such as a mouse or a keyboard.

The data processing unit 8 includes a shooting control unit 5, a reconstruction unit 6, and a correction data generation unit 7 by executing a program by the processor. The imaging control unit 5, the reconstruction unit 6, and the correction data generation unit 7 may be realized by hardware logic regardless of software.

The imaging control unit 5 sets the imaging conditions, generates a control signal according to the data by the imaging conditions and the correction generated by the correction data generation unit 7, and translates the radiation source 2, the detector 3, the tilting mechanism 31, and the rotary table 4. It controls the mechanism 41, the rotation mechanism 42, and the elevating mechanism 43. The imaging conditions include tube voltage, tube current, irradiation time, lamino angle θ, rotation angle and speed, projection angle pitch, imaging magnification, binning size, etc., which are stored in advance or input by the user. When imaging a tomographic image, a lamino angle control signal that tilts the detector 3 until the lamino angle θ is non-orthogonal is given to the tilt mechanism 31, and a radiation irradiation control signal such as a tube voltage and a tube current is sent to the radiation source 2. Then, a rotation control signal for rotating the rotary table 4 is given to the rotary mechanism 42 during irradiation of the radiation beam, and each transmission data is captured from the detector 3.

As shown in FIG. 2, the photographing control unit 5 includes a focus correction unit 51 and a correction data storage unit 52. Here, as shown in FIG. 3, a deflection coil 23 is provided between the filament 22 and the target 21 in the radiation source 2. When an electric current is passed through the deflection coil 23, magnetic force lines are generated in the path of the electron beam. The electron beam emitted from the filament 22 is deflected by the magnetic force lines, and the focal point Fa moves. The focus correction unit 51 is composed of the deflection coil 23 and a driver circuit that allows a current to flow through the deflection coil 23. A current is passed through the deflection coil 23 to position the focus Fa at a reference position Fc when irradiating a radiation beam. ..

The correction data storage unit 52 is mainly configured to include storage, and stores correction data 5a of the focal point Fa. The focus correction unit 51 reads out the correction data 5a and causes the current value indicated by the correction data 5a to flow through the deflection coil 23. That is, the correction data 5a is a current value that moves the focal point Fa to the reference position Fc.

The reconstruction unit 6 reconstructs the tomographic image from the transmission data captured at each projection angle pitch. In the reconstruction process, for example, FeldKamp's filter-corrected back-projection method or ART (Algebraic Reconstruction Technique) successive approximation method is used.

The correction data generation unit 7 replaces the radiation source 2, replaces the filament, changes the tube voltage, changes the tube current, moves the inclined CT imaging device 1, outside air temperature, the temperature of the radiation source 2, and the total irradiation time of radiation. , The continuous irradiation time of radiation, the total usage time of the target, etc., or the correction data 5a for returning the focal point Fa displaced due to a combination of these two or more factors to the normal position Fc is generated, and the correction data storage unit 52 To memorize.

FIG. 4 is a schematic diagram showing the correction principle of the focal point Fa. First, for simplicity, it is assumed that the detector 3 has been moved to a position where the lamino angle is 0 °, as shown in FIG.

It is assumed that the focal point Fa is displaced by the vector C from the normal position Fc. On the rotary table 4, the jig 71 is placed on the line La connecting the center point Dc of the detector 3 and the focal point Fa. The center point Dc is a point on an extension of the rotation axis RA passing through the normal position Fc. At this time, the positional deviation between the orthogonal point Tx between the rotation axis RA and the rotation table 4 and the center of gravity Wa of the jig 71 is defined as the vector B. Further, the point where the line Lb passing through the focal point Fa and the orthogonal point Tx intersects the detector 3 is defined as the point Da, and the deviation between this point Da and the center point Dc is defined as the vector A.

At this time, the following equation (1) holds for the component in the X-axis direction and the component in the Y-axis direction, and the equation (2) is derived from the equation (1).
A: B = FDD: FOD ... (1)
B × FDD = C × (FDD-FOD) ・ ・ ・ (2)

Further, the following equation (3) holds for the component in the X-axis direction and the component in the Y-axis direction, and the equation (4) is derived from the equation (3).
C: B = FDD: (FDD-FOD) ... (3)
B × FDD = C × (FDD-FOD) ・ ・ ・ (4)

Then, the equation (5) is derived from the equations (2) and (4).
C = A × FOD / (FDD-FOD) ・ ・ ・ (5)

Here, the rotary table 4 is rotated 180 degrees with the jig 71 placed on the wire La. At this time, the jig 71 moves to the position P on the opposite side of the rotation shaft RA. Assuming that the point where the line Lc connecting the focal point Fa and the center of gravity Wb of the jig 71 after rotation intersects the detector 3 is the point Db, the point Da is the midpoint between the center point Dc and the point Db. Assuming that the deviation between the center line Dc and the point Db is the vector D, 1 / 2D is substituted for the vector A in the equation (5), and the following equation (6) is obtained.
C = 1/2 x D x FOD / (FDD-FOD) ... (6)

When the formula (6) is rearranged, the formula (7) becomes the following formula.

Therefore, the vector D is obtained by image processing of the perspective image obtained by mounting the jig 71 and rotating it by 180 ° and converting the transmission data or the transmission data into a matrix of luminance values. Then, the equation (7) is calculated using the FDD and FOD included in the shooting conditions, the reciprocal of the imaging magnification M, and the vector D as parameters. As a result, the vector C, which is the positional deviation of the focal point Fa from the normal position Fc, can be calculated. By converting the inverse vector of the vector C into the current value of the deflection coil 23 and passing it through the deflection coil 23, the positional deviation of the focal point Fa of the radiation is corrected, and the focal point Fa is positioned at the normal position Fc.

The above is the case where the laminone angle θ is zero. When the lamino angle θ is taken into consideration, as shown in FIG. 5, a line parallel to the Y axis is drawn from the point Db toward the line Lb, and the intersection with the line Lb is defined as the point Dd. When the lamin angle θ is not zero, the positional deviation Cy in the Y-axis direction is expressed by substituting the distance Dy between the point Db and the point Dd for the Y-axis component of the vector A in the equation (5). The distance Dy is Dy = D / cosθ as shown in FIG. That is, the positional deviation Cy can be expressed by the following equation (8), where θ is the Lamino angle. Since there is no tilt for the distance Cx of the positional deviation in the X-axis direction, it can be expressed by the same equation (9) as the equation (7).

FIG. 6 is a block diagram showing a configuration of a correction data generation unit 7 that generates correction data 5a based on this principle. As shown in FIG. 6, the correction data generation unit 7 includes a jig 71, a perspective image display unit 72, a rotation control unit 73, an image processing unit 74, and a position deviation calculation unit 75.

The jig 71 is separate from the inclined CT imaging device 1, can be placed on the rotary table 4, has a shape that makes it easy to detect the point of interest such as the center of gravity, and has, for example, an acute angle and four from the center. An arm is an equal-length cross, a cone with an acute-angled center, or a pyramid with an acute-angled center.

The fluoroscopic image display unit 72 mainly includes a processor and a display unit, converts transparent data into an image of a fluoroscopic image, and displays the transparent image so that the user can visually grasp it. Typically, the transparent data is subjected to a process such as logarithmic conversion and then converted into a luminance value to generate a grayscale image of the perspective image and drawn in a video memory. The fluoroscopic image display unit 72 enables the position of the jig 71 to be adjusted so as to be placed on the line La connecting the radiation detection center point Dc of the detector 3 and the focal point Fa. That is, the user mounts the jig 71 so that the image of the jig 71 is positioned at the center of the image displayed on the fluoroscopic image display unit 72.

The rotation control unit 73 is mainly configured to include a driver circuit, and controls the rotation mechanism 42 to rotate the rotary table 4 by 180 °. The image processing unit 74 mainly includes a processor, detects the center of gravity Wa and the center of gravity Wb of the jig 71 reflected in the perspective image before and after rotation, and calculates the vector from the center of gravity Wa to the center of gravity Wb. That is, the image processing unit 74 differs between the image coordinates of the center of gravity Wa and the image coordinates of the center of gravity Wb. When detecting the center of gravity Wa and the center of gravity Wb, contour enhancement processing such as binarization may be performed. Further, the same mask as the jig 71 may be stored, the jig 71 may be detected by pattern matching, and the center of gravity may be calculated.

The position shift calculation unit 75 mainly includes a processor, and uses the vector from the center of gravity Wa to the center of gravity Wb acquired by the image processing unit 74, and the FDD and FOD included in the shooting conditions or the inverse of the shooting magnification M. From the above equations (8) and (9), the distance Cx in the X-axis direction and the distance Cy in the Y-axis direction, which are the positional deviations between the focal point Fa and the normal position Fc, are calculated. Then, the inverse vector (−Cx, −Cy) of the calculation result is converted into the current value of the deflection coil 23. When converting to the current value, the inverse vector and the current value conversion table or conversion formula may be stored in advance.

The calculation operation of such correction data 5a is shown in the flowchart of FIG. In this calculation operation, the radiation source 2 is replaced, the filament is replaced, the tube voltage is changed, the tube current is changed, the inclined CT imaging device 1 is moved, the outside air temperature changes, and the temperature of the radiation source 2 changes. Is changed, the total irradiation time of radiation reaches a certain value, the continuous irradiation time of radiation reaches a certain value, and the total usage time of the target reaches a certain time.

First, the user places the jig 71 on the mounting surface of the rotary table 4 (step S01). After the jig 71 is placed, when the user inputs an instruction to shoot using the operation unit (step S02), the imaging control unit 5 images the jig 71 (step S03), and the fluoroscopic image display unit 72 displays the image. A fluoroscopic image Px (see FIG. 8) for confirming the position of the jig 71 is displayed (step S04). That is, by transmitting the control signal by the imaging control unit 5, the radiation source 2 irradiates the radiation beam, the detector 3 generates transmission data from the incident radiation, and the fluoroscopic image display unit 72 brightens the transmission data. Convert it to a value and display it on the display.

The user confirms the position confirmation fluoroscopic image Px, and if the jig 71 is not located at the center of the position confirmation fluoroscopic image Px (steps S05, No), the user operates the translation mechanism 41 to position the jig 71. While changing (step S06), an imaging instruction using the operation unit is given (step S02), the imaging of the jig 71 (step S03) and the display of the fluoroscopic image Px for position confirmation (step S04) are repeated. As shown in FIG. 8, the fluoroscopic image display unit 72 may display a marker M such as a cross display indicating the center of the image on the fluoroscopic image Px for position confirmation. Further, it is preferable to embed a material having a low radiation transmittance in the position W of the center of gravity of the jig 72. The user can easily position the jig 71 at the center of the position confirmation fluoroscopic image Px by aligning the marker M such as the cross display with the position W of the center of gravity reflected in the image of the jig 72.

When the jig 71 is located at the center of the fluoroscopic image Px for position confirmation (step S05, Yes), the jig 71 is on the line La connecting the center point Dc of the detector 3 and the focal point Fa, as shown in FIG. Located in. The user inputs a shift instruction to the position deviation calculation step using the operation unit (step S07). At this time, the image processing unit 74 temporarily stores the fluoroscopic image immediately before the transition instruction input in the RAM (step S08).

When the shift instruction is input, the rotation control unit 72 rotates the rotary table 4 on which the jig 71 is placed by 180 ° (step S09). The jig 71 moves to the side opposite to the position that existed before the rotation, with the rotation axis RA as the midpoint. In other words, it moves in the opposite direction with the rotation axis RA passing through the normal position Fc and the radiation detection center point Dc of the detector 3 as the axis of symmetry. When the rotation of 180 ° is completed, the image pickup control unit 5 again images the jig 71 (step S10), and the image processing unit 74 temporarily stores the fluoroscopic image after the rotation in the RAM (step S11). ..

Here, the position confirmation fluoroscopic image Px stored before rotation is referred to as a pre-rotation image Pb, and the fluoroscopic image stored after rotation is referred to as a post-rotation image Pa. As shown in FIG. 10, the image processing unit 74 detects the coordinates (Xa, Ya) of the center of gravity Wa and the coordinates (Xb, Yb) of the center of gravity Wb of the jig 71 from both the pre-rotation image Pb and the post-rotation image Pa. (Step S12). Then, the image processing unit 74 calculates the coordinate difference (Xd, Yd) by differentiating the coordinates of the center of gravity Wa and the center of gravity Wb (step S13).

When the coordinate difference (Xd, Yd) is calculated, the position shift calculation unit 75 determines the lamino angle θ, the shooting distance FOD and the detection distance FDD, or the imaging magnification based on the imaging conditions when the pre-rotation image and the post-rotation coordinates are imaged. M is acquired (step S14), and the positional deviation Cx in the X-axis direction and the positional deviation Cy in the Y-axis direction are calculated (step S15). That is, the positional deviation Cx of the X-axis component is calculated using the equation (9) with the X-axis component Xd of the coordinate difference (Xd, Yd), the shooting distance FOD and the detection distance FDD, or the reciprocal of the imaging magnification M as parameters. Further, using the equation (8) with the Y-axis component Yd of the coordinate difference (Xd, Yd), the laminone angle θ, the shooting distance FOD and the detection distance FDD or the reciprocal of the imaging magnification M as parameters, the position shift Cy of the Y-axis component To calculate.

When the position shift (Cx, Cy) is calculated, the position shift calculation unit 75 sets the inverse vector (-Cx, -Cy) of this position shift (Cx, Cy) of the deflection coil 23 as shown in FIG. It is converted into a current value (step S16) and stored in the correction data storage unit 52 as correction data 5a. If the focus correction unit 51 reads the correction data 5a from the correction data storage unit 52 and positions the focus Fa at the normal position Fc when irradiating the subject 100 with a radiation beam, the subject 100 with less misalignment The tomographic image of is obtained.

As described above, the inclined CT imaging device 1 corrects the position of the focal point Fa by the correction data generation unit 7 that generates the correction data 5a for positioning the focal point Fa of the radiation at the normal position Fc, and the correction data 5a. The focus correction unit 51 is provided. The correction data generation unit 7 includes a fluoroscopic image display unit 72, a jig 71, a rotation control unit 73, an image processing unit 74, and a position deviation calculation unit 75.

The fluoroscopic image display unit 72 displays the perspective image Px for position confirmation based on the transmission data. The jig 71 is placed on the rotary table 4 so as to be located at the center of the position confirmation fluoroscopic image Px. The rotation control unit 73 rotates the rotary table 4 by 180 ° after the jig 71 is placed. The image processing unit 74 detects the displacement of the jig 71 based on the pre-rotation image Pb and the post-rotation image Pa. The position deviation calculation unit 75 calculates the position deviation of the radiation focus Fa from the normal position Fc based on the displacement of the jig 71. Then, the focus correction unit 51 moves the focus Fa so as to make this positional deviation zero.

That is, the focus Fa is detected so as to detect the deviation of the radiation focus Fa, which is the cause of the positional relationship between the radiation focus Fa, the rotation axis RA of the subject 100, and the detector 3, and to eliminate the deviation of the focus Fa. I tried to move itself. As a result, the positional relationship between the focal point Fa of the radiation, the rotation axis RA of the subject 100, and the detector 3 can be corrected with high accuracy, and the blurring of the tomographic image is reduced even at high imaging magnification and high resolution. High quality images can be captured.

(Second Embodiment)
Next, the inclined CT imaging apparatus 1 according to the second embodiment will be described in detail with reference to the drawings. The same configurations and the same functions as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 12, the radiation source 2 is attached to the translation mechanism 24. The translation mechanism 24 moves the radiation source 2 in the X-axis direction and the Y-axis direction. The translation mechanism 24 is, for example, a ball screw mechanism that moves the radiation source 2 in the X-axis direction and the Y-axis direction. When power such as a pulse signal is supplied to the rotary motor in the X-axis direction, the translation mechanism 24 moves the radiation source 2 in the X-axis direction and supplies power such as a pulse signal to the rotary motor in the Y-axis direction. Then, the radiation source 2 is moved in the Y-axis direction.

That is, in the inclined CT imaging device 1, even if the focus correction unit 51 includes a deflection coil 23 that deflects the electron beam in the radiation source 2, the radiation source 2 itself is moved in the X-axis and Y-axis directions. The translation mechanism 24 may be provided. When the correction data 51 for making the position shift of the focus Fa zero is calculated, the focus correction unit 51 including the translation mechanism 24 outputs a signal of the number of pulses corresponding to the position shift amount Cx in the X-axis direction to the X of the translation mechanism 24. It supplies to the rotary motor of the axis, moves the radiation source 2 in the X-axis direction, supplies a signal of the number of pulses corresponding to the amount of positional deviation Cy in the Y-axis direction to the rotary motor of the Y-axis, and supplies the radiation source 2 to the Y-axis rotary motor. Move in the direction. In this case, the correction data 5a is the number of pulses for rotating the rotary motor.

(Third Embodiment)
Next, the tilted CT imaging device 1 according to the third embodiment will be described in detail with reference to the drawings. The same configurations and the same functions as those of the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 13 is a database of correction data 5a stored in the correction data storage unit 52. As shown in FIG. 13, the correction data 5a includes tube voltage, tube current, total irradiation time of radiation, continuous irradiation time of radiation, outside air temperature, heat carried by the radiation source, and total use of the target of the radiation source. It is stored in association with the focal position information 5b including at least one of the times.

FIG. 14 is a flowchart showing the operation of the inclined CT imaging device 1. First, the user sets imaging conditions for imaging the subject 100 (step S21). When the shooting conditions are set, the correction data generation unit 7 searches the database of the correction data storage unit 52 for the focus change information 5b included in the shooting conditions (step S22). If there is no matching focus change information 5b as a result of the search (steps S23, No), the correction data generation unit 7 displays a message recommending the generation of the correction data 5a on the display unit (step S24).

When the user instructs the generation of the correction data 5a using the operation unit (step S25, Yes), the correction data generation unit 7 generates the correction data 5a (step S26). In step S26, steps S01 to 16 are executed. Then, the generated correction data 5a and the focus change information 5b included in the shooting conditions are associated and stored in the correction data storage unit 52.

When the correction data 5a is stored, the focus correction unit 51 positions the focus Fa according to the correction data 5a (step S27). Alternatively, if the focus change information 5b included in the shooting information exists in the database (steps S23, Yes), the focus correction unit 51 reads out the correction data 5a combined with the corresponding focus change information 5b (step S23, Yes). S28), the focus Fa is positioned according to the correction data 5a (step S27). Then, after the subject 100 is placed, imaging including irradiation of the radiation beam by the radiation source 2 and generation of a tomographic image of the reconstruction unit 6 is started (step S29). Alternatively, if there is no generation instruction (step S25, No), the operation of correcting the focal point Fa to the normal position Fc is omitted and shooting is started (step S29).

By registering the correction data 5a in advance according to each focus change information 5b in this way, it is possible to omit the work of generating the correction data 5a every time the shooting conditions and the like change, resulting in labor reduction and efficiency. It can be improved.

(Other embodiments)
Although embodiments according to the present invention have been described herein, these embodiments are presented as examples and are not intended to limit the scope of the invention. The above-described embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The embodiments and modifications thereof are included in the scope and the gist of the invention as well as the invention described in the claims and the equivalent scope thereof.

1 Tilt type CT imaging device 2 Radiation source 21 Target 22 Filament 23 Deflection coil 24 Translation mechanism 3 Detector 31 Tilt mechanism 4 Rotation table 41 Translation mechanism 42 Rotation mechanism 43 Elevating mechanism 5 Imaging control unit 51 Focus correction unit 52 Correction data storage unit 5a Correction data 5b Focus change information 6 Reconstruction unit 7 Correction data generation unit 71 Jigger 72 Perspective image display unit 73 Rotation control unit 74 Image processing unit 75 Positional deviation calculation unit 8 Data processing unit

Claims (5)

A rotary table that has a mounting surface for the subject and can rotate around a rotation axis that is orthogonal to the mounting surface.
A radiation source having a radiation focus and irradiating the rotary table with radiation from the radiation focus,
A detector that is located opposite the radiation source across the rotary table, detects radiation, and outputs transmitted data.
A tilting mechanism that changes the lamino angle formed by the center line of radiation detected by the detector and the rotation axis along the tilting surface within a range of 0 ° or more and 90 ° or less.
A reconstruction unit that reconstructs a tomographic image of the subject based on the transmission data detected by the detector at a plurality of rotation positions due to the rotation of the rotary table.
A correction unit that corrects the position of the radiation focus according to the correction data,
A correction data generation unit that generates the correction data,
With
The correction data generation unit
A display unit that displays a fluoroscopic image based on the transparent data,
A jig placed on the rotary table so as to be located at the center of the fluoroscopic image displayed on the display unit, and
After the jig is placed, a rotation control unit that rotates the rotary table by 180 ° and
An image processing unit that detects the displacement of the jig based on the transmission data before and after rotation by the rotation control unit.
A calculation unit that calculates the positional deviation of the radiation focal point from the normal position based on the displacement of the jig detected by the image processing unit.
Have,
Generating the correction data that offsets the misalignment,
An inclined CT imaging device characterized by. According to the following equations (1) and (2), the calculation unit determines the positional deviation Cx of the radiation focal point in the direction orthogonal to the tilting surface and the positional deviation of the radiation focal point in the direction along the tilting surface. Calculating Cy,
The inclined CT imaging apparatus according to claim 1.

[Dx is the displacement of the jig in the direction orthogonal to the tilting surface, Dy is the displacement of the jig in the direction along the tilting surface, FOD is the imaging distance from the focal point to the subject, and FDD is the detector from the focal point. Detection distance to, θ is the Lamino angle] The radiation source has filaments and targets that are opposed to each other.
The correction unit has a deflection coil between the filament and the target, and a current that cancels the positional deviation of the radiation focal point calculated by the calculation unit is passed through the deflection coil.
The inclined CT apparatus according to claim 1 or 2. The correction unit includes a moving mechanism for moving the radiation source.
The inclined CT apparatus according to claim 1 or 2. A storage unit for storing the correction data is provided.
The correction unit determines at least one of tube voltage, tube current, total irradiation time of radiation, continuous irradiation time of radiation, outside air temperature, heat carried by the radiation source, total usage time of the target of the radiation source, and the like. The included focus change information and the correction data are stored in association with each other.
The correction unit changes the radiation focus to the normal position by the correction data corresponding to the focus change information.
The inclined CT imaging apparatus according to any one of claims 1 to 4.

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