JP2011019801A - Tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tomographic apparatus, enlarging the size of a visual field almost without alteration of hardware. <P>SOLUTION: This tomographic apparatus includes a motor 16 for rotating an FPD (flat panel type X-ray detector) 3 around the axis of a radiation shaft connecting an X-ray tube 2 and the center of a flat panel type X-ray detector (FPD) 3; and a function of controlling to perform rotary scanning in the state of rotating the FPD 3 around the axis of the irradiation shaft using a motor 16, thereby generating an area where the size of a visual field is enlarged by rotation of the irradiation shaft around the axis so that the size of a visual field can be enlarged almost without alteration of hardware. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a tomographic apparatus used in the medical field, industrial field, and the like.

  An X-ray tomography apparatus will be described as an example of the tomography apparatus. In the X-ray tomography apparatus, the attenuation of X-rays irradiated from an X-ray tube as an irradiation source through a subject is abbreviated as a rectangular flat panel X-ray detector (hereinafter appropriately referred to as “FPD”). ) Is detected. In order to collect projection data (projected images) obtained by the FPD at various angles with respect to the subject, the X-ray tube and the FPD are rotated around the body axis of the subject, or the subject. Rotation scanning is performed while scanning the lens around the axis of the body axis. Reconstruction is performed based on projection data (projected image) obtained by such rotational scanning, and a tomographic image is acquired. At this time, it is a necessary condition that the tomographic image can be reconstructed at any angle by the irradiation X-rays irradiated from the X-ray tube covering the entire subject.

  However, since the size of the FPD is finite, when a large subject is imaged, the shadow projected on the FPD may “out” the FPD field of view. The protrusion to the side of the detector parallel to the rotation axis (in this case, the body axis of the subject) seriously affects the flatness of the tomographic image.

  In contrast to this out-of-view truncation, a problem to be solved mathematically by devising a reconstruction algorithm is called “ROI (Region Of Interest) reconstruction”. In addition, various correction methods have been proposed in which the protruding portion is estimated and restored on projection data (projection image) to reduce the influence (see, for example, Patent Documents 1 and 2).

  On the other hand, as hardware (H / W) countermeasures, an offset scan (see, for example, Patent Document 3), a detector size (for example, see Patent Document 4), and a plurality of X-ray tubes are provided. It has been proposed to enlarge the irradiation range (for example, see Patent Document 5), scan the detector in the rotation direction, and enlarge the field of view (for example, see Patent Document 6).

US Pat. No. 6,810,102 JP 2004-0665706 A Japanese Patent No. 3540916 JP 2002-233522 A JP 09-234192 A JP-A-11-253435

  However, the above-described ROI reconstruction method is still under study, and there are still problems in practical use such as stability against noise and reconstruction processing time. Further, the correction processing for the projected image has a problem that the estimation accuracy is lowered when the amount of protrusion is large.

  With regard to hardware measures, the above-described offset method scanning (scanning) requires collection at 360 ° rotation, and scanning at 180 ° rotation (scanning) (also called “half scan” or “short scan”). There is a restriction that it cannot be applied. Further, the expansion of the above-described detector size, the expansion of the irradiation range by a plurality of X-ray tubes, and the expansion of the field of view by scanning the rotation plane of the detector require a large hardware change.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a tomographic apparatus capable of enlarging the visual field size with almost no hardware change.

In order to achieve such an object, the present invention has the following configuration.
That is, the tomography apparatus according to the present invention is a tomography apparatus that performs tomography, a radiation irradiating unit that irradiates radiation, a rectangular radiation detecting unit that detects radiation transmitted through a subject, and the radiation irradiation. Reconfiguration based on the data obtained by the rotational scanning in the rotational scanning means, the rotational scanning means for performing the rotational scanning while scanning the relative rotation of the subject and the radiation detection means, and the subject. Reconstructing means for acquiring a tomographic image, and detecting rotation means for rotating the radiation detecting means around an axis of an irradiation axis that is an axis connecting the radiation irradiating means and the center of the radiation detecting means. And a control means for controlling to perform the rotational scanning in a state where the radiation detecting means is rotated by the detection rotating means around the axis of the irradiation axis. It is intended.

  [Operation / Effect] According to the tomography apparatus according to the present invention, the radiation detecting means and the radiation detecting means perform scanning in which the rectangular radiation detecting means detects the radiation irradiated from the radiation irradiating means and transmitted through the subject. The rotation scanning means rotates relative to the subject while rotating (rotational scanning). The reconstruction means performs tomography by performing reconstruction and acquiring a tomographic image based on the data obtained by the rotational scanning by the rotational scanning means. The tomography apparatus includes detection rotation means for rotating the radiation detection means around the axis of the irradiation axis, which is an axis connecting the radiation irradiation means and the center of the radiation detection means. Further, the tomography apparatus includes a control unit that performs control so that rotation scanning is performed in a state where the radiation detection unit is rotated by the detection rotation unit around the axis of the irradiation axis, thereby rotating the axis around the axis of the irradiation axis. This creates an area where the visual field size is enlarged. Depending on the tomographic apparatus, there may be a detection rotation means that rotates the radiation detection means around the axis of the irradiation axis in order to align the imaging direction with the body axis of the subject. By providing only the control means in addition to the conventional detection rotation means, the visual field size can be enlarged. Further, even when the detection rotation means for rotating the radiation detection means around the axis of the irradiation axis is not provided, the visual field size can be enlarged by providing only the detection rotation means and the control means. As described above, the visual field size can be expanded without changing hardware.

  In the above-described invention, the out-of-field protrusion correcting means for correcting the out-of-field that protrudes from the irradiation field of radiation from the radiation irradiating means to the radiation detecting means based on the data obtained by the rotational scanning by the above-described rotating scanning means. It is preferable to provide. As described above, a region in which the visual field size is enlarged is formed by rotation around the axis of the irradiation axis. However, the visual field becomes narrower as the distance from the region (for example, the central slice surface) increases. Therefore, it is possible to estimate a protruding portion with higher accuracy by correcting the out-of-field protrusion correction unit that is out of the irradiation field based on the data obtained by the rotational scanning by the above-described rotating scanning unit. It becomes possible.

  Further, in a preferred example of these inventions described above, scanning is performed while relatively moving the radiation irradiating means, the radiation detecting means, and the subject in parallel along the rotational axis of the rotational scanning by the rotational scanning means. A linear scanning means for performing linear scanning is provided. By performing linear scanning in addition to rotational scanning, a tomographic image in a direction parallel to the rotational axis can be obtained.

  Further, in the invention provided with the linear scanning means, the field of view that corrects the outside of the visual field that protrudes from the irradiation field of radiation from the radiation irradiating means to the radiation detecting means based on the data obtained by the linear scanning by the linear scanning means. It is preferable to provide an outside protrusion correcting means. Obtaining data (projected image, so-called scout image) of a subject from a specific angle or a plurality of angles (irradiated radiation) by linear scanning while the radiation detection means is rotated around the axis of the irradiation axis Thus, it is possible to obtain information related to the size of the subject such as the subject's existing range (that is, the contour position of the subject), and this information can be used for overshoot correction as conventional estimation information. It is possible to estimate a protruding portion having a high height.

  According to the tomographic apparatus of the present invention, the detection rotation means for rotating the radiation detection means around the axis of the irradiation axis, which is the axis connecting the radiation irradiation means and the center of the radiation detection means, and the axis of the irradiation axis And a control means for controlling to perform rotational scanning in a state in which the radiation detection means is rotated around the detection rotation means, thereby creating a region in which the visual field size is enlarged by rotation around the axis of the irradiation axis. The field of view size can be expanded with almost no change in clothing.

It is a block diagram of the tomography apparatus which concerns on an Example. It is a schematic diagram of the detection surface of a flat panel X-ray detector (FPD). (A) is a plan view before rotating the flat panel X-ray detector (FPD) around the axis of the irradiation axis, and (b) is the axis of the irradiation axis of the flat panel X-ray detector (FPD). It is a top view when rotating around the center. (A) is a top view for demonstrating the relationship between a visual field width and a visual field height typically, (b) is a top view when the restriction | limiting of a visual field height is eased using protrusion correction | amendment together. It is the correspondence table which calculated the visual field height on condition that the maximum visual field width in case of the side length of a flat panel type X-ray detector (FPD), and the visual field width exceeds the side length which is the original visual field width. It is the correspondence table which showed the relationship between visual field height, visual field width, and visual field expansion rate. (A) And (b) is a top view for demonstrating performing protrusion correction | amendment by interpolating the protrusion area | region in a slice surface with the center slice surface of a visual field area | region. (A) And (b) is a top view for demonstrating performing protrusion correction | amendment by interpolating the protrusion area | region in a slice surface by the edge part of a visual field area | region. It is the schematic diagram which showed the absorptivity when it sees from the axis | shaft orthogonal to the body axis of a subject. It is a top view for demonstrating acquisition of the scout image by linear scanning. (A) is a top view before rotating the rectangular flat panel type | mold X-ray detector (FPD) which concerns on a modification around the axial center of an irradiation axis | shaft, (b) is the rectangular flat panel type | mold which concerns on a modification. It is a top view when rotating an X-ray detector (FPD) around the axis center of an irradiation axis.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of a tomography apparatus according to an embodiment. In this embodiment, X-rays will be described as an example of radiation.

  As shown in FIG. 1, the tomography apparatus includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that emits X-rays toward the subject M, and X-rays that have passed through the subject M. And an C-type arm 4 that supports the X-ray tube 2 and the FPD 3. The X-ray tube 2 corresponds to the radiation irradiation means in this invention, and the FPD 3 corresponds to the rectangular radiation detection means in this invention.

  In addition, the tomography apparatus includes a top plate control unit 5 that controls the elevation and horizontal movement of the top plate 1, an FPD control unit 6 that controls the FPD 3, and a high voltage that generates the tube voltage and tube current of the X-ray tube 2. X-ray tube controller 8 having a voltage generator 7, A / D converter 9 that digitizes an X-ray detection signal as a charge signal from the FPD 3, and X-ray detection output from the A / D converter 9 An image processing unit 10 that performs various processes based on signals, a controller 11 that controls each of these components, a memory unit 12 that stores processed images, an input unit 13 in which an operator performs input settings, A monitor 14 for displaying the processed image, a C-arm control unit 15 for controlling the rotational movement and linear movement of the C-arm, and the like.

  The top board control unit 5 performs control such that the top board 1 is horizontally moved in the body axis z direction perpendicular to the paper surface of FIG. 1, and is moved up and down in the vertical direction (x axis in FIG. 1). These controls are performed by controlling a top plate drive mechanism (not shown) including a motor and an encoder (not shown).

  The FPD controller 6 gives a signal to a gate line (not shown) for driving a detection element d (see FIG. 2) of the FPD 3 to be described later, and selects a data line (not shown) for reading a charge signal from the detection element d. The FPD 3 is controlled by giving a signal to perform.

  The high voltage generator 7 generates a tube voltage and a tube current for irradiating X-rays, and gives them to the X-ray tube 2. The X-ray tube controller 8 controls a collimator (not shown) of the X-ray tube 2 to set an X-ray irradiation field.

  The controller 11 is configured by a central processing unit (CPU) and the like, and the memory unit 12 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 13 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like.

  The image processing unit 10 performs various processes as projection data (projection image) obtained by projecting the X-ray detection signal onto the detection surface of the FPD 3 and out of the field of view that protrudes from the X-ray irradiation field from the X-ray tube 2 to the FPD 3 And a reconstruction unit 10b that reconstructs the projection data corrected by the projection correction unit 10a and acquires a tomographic image. The protrusion correction will be described later with reference to FIGS. The protrusion correction unit 10a corresponds to the out-of-field protrusion correction unit in the present invention, and the reconstruction unit 10b corresponds to the reconstruction unit in the present invention.

  The memory unit 12 is configured to write and store each image processed by the image processing unit 10. The top panel control unit 5, FPD control unit 6, X-ray tube control unit 8, and C-type arm control unit 15 are also configured with a CPU or the like, like the controller 11.

  The C-type arm control unit 15 performs control for rotating the C-type arm 4 around the body axis z of the subject M, control for moving the C-type arm 4 along the body axis z, and the like. By rotating the C-arm 4 in this way, the X-ray tube 2 and the FPD 3 supported by the C-type arm 4 are rotated around the body axis z of the subject M, and linearly moved in parallel along the body axis z. Let These controls are performed by controlling a C-arm drive mechanism (not shown) including a motor, an encoder (not shown), and the like.

  Further, a motor 16 is built in a place where the C-type arm 4 supports the FPD 3, and the C-type arm control unit 15 controls the motor 16 to connect the X-ray tube 2 and the center of the FPD 3. The FPD 3 is controlled to rotate around the axis of the irradiation axis. Further, the C-type arm controller 15 controls the C-type arm 4 so that the X-ray tube 2 and the FPD 3 are rotated in a state where the FPD 3 is rotated around the axis of the irradiation axis. The C-type arm control unit 15 corresponds to the rotation scanning unit, the linear scanning unit, and the control unit in the present invention, and the motor 16 corresponds to the detection rotation unit in the present invention.

  Next, the FPD 3 will be described with reference to FIG. FIG. 2 is a schematic diagram of the detection surface of the FPD 3. The FPD 3 has a rectangular and flat detection surface. In this embodiment, the detection surface is a square. As shown in FIG. 2, the FPD 3 has a plurality of detection elements d sensitive to X-rays arranged in a matrix on the detection surface. For example, 1536 vertical × 1536 horizontal detection elements d are arranged on a detection surface having a size of about 20 cm long × 20 cm wide.

  Next, rotation around the axis of the irradiation axis of the protrusion correction unit 10a and the FPD 3 will be described with reference to FIGS. 3A is a plan view before the FPD is rotated around the axis of the irradiation axis, and FIG. 3B is a plan view when the FPD is rotated around the axis of the irradiation axis. FIG. 4A is a plan view for schematically explaining the relationship between the field width and the field height, and FIG. 4B relaxes the restriction on the field height by using the protrusion correction together. FIG. 5 is a correspondence table in which the maximum field width when the side length of the FPD and the field height under the condition that the field width exceeds the side length that is the original field width are calculated. 6 is a correspondence table showing the relationship between the visual field height, the visual field width, and the visual field enlargement ratio, and FIGS. 7A and 7B show the protrusion area on the slice plane and the center of the visual field area. FIG. 9 is a plan view for explaining that the protrusion correction is performed by interpolation on the slice plane, and FIG. 8A and FIG. ) Is a plan view for explaining that the protrusion correction is performed by interpolating the protrusion area on the slice plane at the edge portion of the visual field area, and FIG. 9 is an axis orthogonal to the body axis of the subject. FIG. 10 is a schematic diagram showing the absorptance when viewed from above, and FIG. 10 is a plan view for explaining acquisition of a scout image by linear scanning. 3 to 10, an example in which the FPD 3 is a square FPD 3 having a side length A and is rotated by 45 ° around the axis of the irradiation axis as shown in FIG. 3B will be described.

  At the time of normal tomography, the FPD 3 is installed in a posture as shown in FIG. 3A in both rotation scanning and linear scanning. That is, it is installed so that one side of the FPD 3 is parallel to the body axis z (see FIG. 1) of the subject M. When one side of the FPD 3 is not parallel to the body axis z, in normal tomography, the FPD 3 is rotated around the axis of the irradiation axis by the rotational drive of the motor 16 (see FIG. 1) so as to be parallel. Fine adjustment is made to the posture shown in FIG. When the FPD 3 is rotated by 45 ° around the axis of the irradiation axis from the posture shown in FIG. 3A, the posture shown in FIG. 3B is obtained.

By rotating 45 ° in this way, the field width W can be expanded to the maximum field width W _max which is the length of the diagonal line of the FPD 3 while the field width is the side length A in the past. . Here, the FPD 3 is a square having a side length A and is rotated by 45 ° around the axis of the irradiation axis, whereby the maximum visual field width W _max is expressed by W _max = (√2) × A, and the maximum (√2 ) The visual field width W can be expanded up to double. Here, in a direction orthogonal to the direction along the visual field width W, as shown in FIG. 4A, the height when a rectangular visual field region (illustrated by stippling) is secured with the visual field width W in the rotated FPD 3. In this specification, the height is defined as “field height”, and the height is defined as H.

However, as shown in FIG. 3, the visual field width W increases in the vicinity of the central slice plane that is parallel to the rotation plane and includes the irradiation axis, but the visual field narrows as the distance from the central slice plane increases. The field width W is wider than the side length A (original field width) up to the stipple region shown in FIG. 3B, but the field width W becomes narrower than the side length A when moving away from the region. Go. However, if the visual field height under the condition that the visual field width W exceeds the side length A (original visual field width) is H _{W ≧ A} , the visual field height H _{W ≧ A} is H _{W ≧ A} = {( √2) -1} × A. Therefore, even when a square FPD 3 with a side of 20 cm to 40 cm is rotated by 45 ° around the axis of the irradiation axis, as shown in FIG. 5, about 10 cm can be secured, so the field height H _{W ≧ A} is limited. However, there are many cases where there is no problem in practical use.

  As described above, an example in which the visual field height H is limited and a rectangular visual field region is secured is shown in FIG. FIG. 6 shows the relationship between the field height H, field width W, and field magnification factor. FIG. 6 is a trial calculation of the visual field enlargement ratio in the case of the square FPD 3 when the side length A is A = 20 cm. Here, the visual field expansion ratio is represented by the difference between the visual field width W and the side length A with respect to the side length A (original visual field width), and is represented by (W−A) / A as shown in FIG. 6. It should be noted that the visual field enlargement ratio means that only the visual field is enlarged, and does not mean that an area in the visual field or the entire pixel is enlarged.

As is clear from FIG. 6, the higher the visual field height H, the narrower the visual field width W and the smaller the visual field magnification rate. Although not shown in FIG. 6, as shown in FIG. 5, when the side length A is 20 cm, the field height H _{W ≧ A} under the condition that the field width W exceeds the side length A (original field width). Is 8.3 cm, so when the field height H is H _{W ≧ A} , the field width W is 20 cm, which is the same as the side length A, and the field magnification ratio is clearly 0%.

  Taking FIG. 6 as an example, in the case of a tomographic image having a slice width of 2 cm, for example, if the field height H is limited to the width of 2 cm, the field of view can be expanded to 31%. Therefore, for example, in the conventional configuration, the FPD 3 is not rotated about the axis of the irradiation axis as shown in FIG. Then, after specifying the slice position that needs to be inspected, the FPD 3 is rotated around the axis of the irradiation axis as shown in FIG. Operation is also conceivable.

  When the FPD 3 is rotated by 45 ° around the axis of the irradiation axis, when the restriction on the visual field height H is relaxed at a height as shown in FIG. 4B, along the edge of the FPD 3 A visual field area can be secured up to the area illustrated by the pointillism. On the other hand, the area illustrated by the upper right diagonal line is outside the visual field that protrudes from the irradiation visual field. Therefore, by correcting the out-of-field by the protrusion correction unit 10a (see FIG. 1), it is possible to estimate the protrusion part with higher accuracy.

Specifically, when the subject M is a human body, the structure of the subject M hardly changes in the direction of the body axis z. Therefore, the simplest method is to set the protrusion area on each slice plane to the maximum field of view. It can be considered that the central slice plane of the visual field area having the width W _max is used as it is. More specifically, as shown in FIG. 7A, the pixel value of the central slice surface of the visual field area indicated by a thick frame is illustrated in the protruding area indicated by the upper right diagonal line in the visual field height H direction. By sticking each of them as indicated by the arrows in the middle, it is possible to interpolate the protruding area as shown in the stippled area as shown in FIG. 7B.

  Alternatively, as shown in FIG. 8A, the pixel value of the edge portion of the visual field area shown by a thick frame is shown in the protruding area shown by the upper right diagonal line in the visual field height H direction as indicated by an arrow in the figure. By sticking to each, it is possible to interpolate the protruding region as shown in the stippling as shown in FIG. In the case of FIG. 8, compared to FIG. 7, the protrusion correction is performed using the pixel value of the edge portion of the visual field area closer to the central slice surface of the visual field area as viewed from the protruding area. A protruding portion with high accuracy can be estimated.

  In addition, when the subject M is a human body, as shown in FIG. 9, the structure of the subject M is closer to the edge along the y-axis (see FIG. 1) orthogonal to the body axis z. Since the X-ray absorption rate increases as the line absorption rate decreases and the closer to the center, it can be considered to interpolate the protruding area on each slice plane by dividing the pixel value of the visual field area by the absorption rate. It is done. More specifically, according to the location of the protruding region, the location can be interpolated by dividing the pixel value of the visual field region by the absorption rate corresponding to the location. Therefore, when interpolating the edge of the protruding area, divide the pixel value of the viewing area by a small absorption rate corresponding to the edge, and when interpolating the center of the protruding area, Divide the pixel value of the field of view by the larger absorption rate.

  The method described above performs out-of-field correction by the protrusion correction unit 10a by using the same data, that is, performs out-of-field correction by the protrusion correction unit 10a based on data obtained by rotational scanning. However, it is not limited to these methods. As in the method described below, the out-of-field correction by the protrusion correction unit 10a may be performed by using data obtained in advance before tomography. Here, a method for performing out-of-field correction by the protrusion correction unit 10a based on data obtained by linear scanning will be described below.

Specifically, in addition to tomography by rotational scanning, an X-ray CT scout image (also called “slot scanning” in an X-ray fluoroscopic apparatus) with the FPD 3 rotated by 45 ° around the axis of the irradiation axis. ). That is, with the FPD 3 rotated by 45 ° around the axis of the irradiation axis, X-rays are irradiated from directly above the x-axis (see FIG. 1) (an angle of 0 ° with respect to the x-axis). On the other hand, linear scanning is performed in which the X-ray tube 2 and the FPD 3 are linearly moved in parallel along the body axis z. Then, a plurality of projected images are acquired by linear scanning. As shown in FIG. 10, these projected images P ₁ , P ₂ ,..., P _i−1 , P _i , P _{i + 1} ,..., P _n−1 , P _n are connected in the body axis z direction. As a result, a scout image S is obtained. At this time, the projection image _{P 1, P 2, ...,} P i-1, P i, P i + 1, ..., field width W is expanded to the maximum field width _{W max} as _{P n-1, P n} By using only the vicinity of the central slice surface, it is possible to obtain a scout image in which the visual field width W is enlarged.

  This scout image can be used for out-of-field correction by the protrusion correction unit 10a as look-ahead information indicating the change in the outer shape of the subject M in the direction along the body axis z that is the rotation axis. In addition to the 0 ° angle described above, a similar scout image is acquired while irradiating X-rays from the direction rotated about 90 ° around the body axis z (the y-axis direction), and each slice is obtained. By approximating the outer shape of the subject M at the position with an ellipse or the like, it can be used to improve the accuracy of the overhang correction.

  In this way, the reconstruction unit 10b (see FIG. 1) performs reconstruction on the projection image (projection data) corrected by the protrusion correction unit 10a to obtain a tomographic image. For the reconstruction processing, a Feldkamp method using a well-known filtered back projection (FBP) (also called “filtered back projection method”) may be performed. Note that the reconstruction processing of the present embodiment is performed on the data after out-of-field correction by the protrusion correction unit 10a, and therefore is not different from the conventional reconstruction processing. Therefore, in this specification, the description of a specific reconstruction process is omitted.

  According to the tomography apparatus according to the present embodiment, X-ray scanning is performed by the rectangular flat panel X-ray detector (FPD) 3 that detects X-rays irradiated from the X-ray tube 2 and transmitted through the subject M. The C-type arm control unit 15 relatively moves the tube 2 and the FPD 3 and the subject M while rotating the C-type arm 4 (rotational scanning). In this embodiment, the subject M is fixed, and the X-ray tube 2 and the FPD 3 are rotated around the body axis z of the subject M, so that the X-ray tube 2 and the FPD 3 and the subject M are rotated. And rotate relative to each other. The reconstruction unit 10b performs tomography by performing reconstruction and acquiring a tomographic image based on data obtained by rotational scanning in the C-type arm control unit 15.

  The tomography apparatus according to the present embodiment includes a motor 16 that rotates the FPD 3 around the axis of an irradiation axis that is an axis connecting the X-ray tube 2 and the center of the FPD 3. Furthermore, in the tomography apparatus according to the present embodiment, the C-type arm control unit 15 includes a function of performing control so that rotational scanning is performed in a state where the FPD 3 is rotated by the motor 16 around the axis of the irradiation axis. An area in which the visual field size is enlarged is formed by rotation around the axis of the irradiation axis.

  Depending on the tomography apparatus, as described in FIG. 3A, the imaging direction should be aligned with the body axis z of the subject M (that is, one side of the FPD 3 should be parallel to the body axis z of the subject M). In some cases, a motor 16 that rotates the FPD 3 around the axis of the irradiation axis is conventionally provided. In that case, in addition to the conventional motor 16, only the above-described functions are provided to increase the size of the field of view. Can do. Even if the motor 16 for rotating the FPD 3 around the axis of the irradiation axis is not provided, the visual field size can be enlarged by providing only the motor 16 and the function. As described above, the visual field size can be expanded without changing hardware.

  In the present embodiment, preferably, the outside of the visual field that protrudes from the X-ray irradiation field from the X-ray tube 2 to the FPD 3 is corrected based on the data obtained by the rotational scanning in the C-type arm control unit 15 described above. An overhang correction unit 10a is provided. As described above, a region in which the visual field size is enlarged is formed by rotation around the axis of the irradiation axis. However, the visual field becomes narrower as the distance from the region (for example, the central slice surface) increases. Therefore, based on the data obtained by the rotational scanning in the C-type arm control unit 15 described above, the protrusion correction unit 10a corrects the out-of-view area that protrudes from the irradiation field, thereby estimating a protruding part with higher accuracy. It becomes possible.

  In the present embodiment, preferably, the X-ray tube 2 and the FPD 3 and the subject M are moved relative to each other in parallel along the rotational axis of rotation scanning (body axis z in the present embodiment) in the C-type arm control unit 15. In addition, the C-type arm control unit 15 has a function of performing linear scanning that performs scanning while linearly moving. In the present embodiment, the subject M is fixed, and the X-ray tube 2 and the FPD 3 are linearly moved in parallel along the body axis z, so that the X-ray tube 2 and the FPD 3 and the subject M are linearly moved. Move. By performing linear scanning in addition to rotational scanning, a tomographic image in a direction parallel to the rotational axis can be obtained.

  Further, even in the case where the function of linear scanning is provided as in the present embodiment, preferably, the data obtained by linear scanning is outside the field of view that protrudes from the irradiation field of X-rays from the X-ray tube 2 to the FPD 3. An overhang correction unit 10a for correcting based on the above is provided. Data of the subject M (irradiated X-rays) from a specific angle or a plurality of angles (angles of 0 ° and 90 ° in this embodiment) with the FPD 3 rotated around the axis of the irradiation axis ( By obtaining a projected image, so-called scout image, by linear scanning, information on the size of the subject M such as the existence range of the subject M (that is, the contour position of the subject M) can be obtained. Is used for the overhang correction as conventional estimation information, so that it is possible to estimate the overhang portion with higher accuracy.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, X-rays are taken as an example of radiation, but the present invention can also be applied to tomography using radiation other than X-rays (for example, γ-rays).

  (2) In the above-described embodiment, the X-ray tube 2 and the FPD 3 are rotated around the body axis z of the subject M by the C-arm 4 as shown in FIG. And a gantry that accommodates the FPD 3, and the tomography can be performed by causing the subject to enter the opening of the gantry and rotating the X-ray tube 2 and the FPD 3 around the body axis z of the subject M in the gantry. Good.

  (3) In the above-described embodiment, by rotating the X-ray tube and the FPD in a state where the subject is fixed, the X-ray tube and the FPD and the subject are rotated and rotated relatively. Similarly, the X-ray tube and the FPD are linearly moved in a state where the subject is fixed, so that the X-ray tube and the FPD and the subject are linearly moved relatively linearly. It is not limited to. For example, by rotating the subject together with the couchtop 1 (see FIG. 1) on which the subject is placed, rotational scanning may be performed in which the X-ray tube and the FPD are rotated relative to the subject. The X-ray tube and the FPD may be linearly moved relative to the subject by linearly moving the subject together with the top plate. In each scan in which the subject is rotated or linearly moved, the X-ray tube and the FPD may be fixed, or the X-ray tube and the FPD may be rotated or linearly moved (for example, the direction in which the subject is moved). Reverse direction).

  (4) In the above-described embodiment, the protrusion correction unit 10a is provided. However, even if the height of the field of view is limited, if there is no practical problem when performing tomography, the protrusion correction unit 10a is not necessarily required.

  (5) In the above-described embodiment, linear scanning is performed, but linear scanning is not always necessary, and tomographic imaging using only rotational scanning may be used.

(6) In the embodiment described above, the rectangular radiation detection means (FPD 3 in the embodiment) is a square, but any rectangle other than a square can be applied as long as it is a rectangle. Even in this case, it is only necessary to rotate from the posture shown in FIG. 11A to the maximum visual field width W _max which is the length of the diagonal line of the FPD 3 as in the posture shown in FIG. .

(7) In the above-described embodiment, the rectangular radiation detection means (FPD 3 in the embodiment) is expanded around the axis of the irradiation axis in order to expand the maximum visual field width W _max that is the length of the diagonal line (see FIG. 3). Although rotated by 45 °, the rotation is not necessarily limited to 45 °. If the visual field width is wider than the conventional one, it may be rotated at an angle of less than 45 ° (for example, 15 °, 30 °, etc.). Even in the case of the rectangular FPD 3, it is not always necessary to rotate it so as to expand to the maximum visual field width W _max which is the length of the diagonal line.

2 ... X-ray tube 3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 10a ... Overflow correction | amendment part 10b ... Reconstruction part 15 ... C-type arm control part 16 ... Motor A ... Side length W ... Field-of-view width _Wmax ... Maximum field-of-view width S ... Scout image M ... Subject

Claims (4)

  A tomography apparatus that performs tomography, a radiation irradiating unit that irradiates radiation, a rectangular radiation detecting unit that detects radiation transmitted through a subject, the radiation irradiating unit and the radiation detecting unit, and the subject A rotational scanning unit that performs rotational scanning that scans while rotating relative to each other, and a reconstruction unit that performs reconstruction on the basis of data obtained by rotational scanning by the rotational scanning unit and acquires a tomographic image And a detection rotation means for rotating the radiation detection means around the axis of the irradiation axis, which is an axis connecting the radiation irradiation means and the center of the radiation detection means, and the detection around the axis of the irradiation axis A tomography apparatus comprising: a control unit configured to perform control so that the rotation scanning is performed in a state where the radiation detection unit is rotated by a rotation unit.   The tomography apparatus according to claim 1, wherein the out-of-field that protrudes from the irradiation field of radiation from the radiation irradiation unit to the radiation detection unit is corrected based on data obtained by rotational scanning by the rotational scanning unit. A tomography apparatus comprising an out-of-view protrusion correcting means.   3. The tomography apparatus according to claim 1, wherein the radiation irradiating unit, the radiation detecting unit, and the subject are relatively parallel to each other along a rotational axis of rotational scanning performed by the rotational scanning unit. A tomography apparatus comprising: linear scanning means for performing linear scanning that performs scanning while linearly moving in a straight line.   4. The tomography apparatus according to claim 3, wherein the outside of the visual field that protrudes from the irradiation field of radiation from the radiation irradiation means to the radiation detection means is corrected based on data obtained by linear scanning by the linear scanning means. A tomography apparatus comprising an out-of-view protrusion correcting means.

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