JP2015150220A - X-ray CT apparatus and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus and an imaging method capable of reducing the exposure dose by accurately positioning an imaging site and limiting the range irradiated with X rays to a minimally required range.SOLUTION: A system control device 124 of the X-ray CT apparatus 1 captures scanogram images in two directions, i.e., LAT direction (Y-Z plane) and a PA direction (X-Z plane), and extracts shapes of the imaging sites from each of the captured scanogram images in the two directions. The system control device 124 then determines the approximate curve f(z) and f(z) representing the whole shape of the extracted shapes of the imaging sites. The system control device 124 calculates table correction values in vertical and horizontal directions to match points on the approximate curves f(z) and f(z) of respective imaging sites with the isocenter, then moves a table 105 by the table correction values and executes imaging of the subject.

Description

  The present invention relates to an X-ray CT apparatus and an imaging method, and more particularly to an imaging method for minimizing an X-ray irradiation amount and reducing an exposure dose in the X-ray CT apparatus.

  Conventionally, in an X-ray CT (Computed Tomography) apparatus, the imaging time can be shortened by increasing the number of X-ray detectors and increasing the rotational speed. Since this type of X-ray CT apparatus uses cone-beam X-rays that spread in the slice direction, volume data can be collected by irradiating a wide range of X-rays at once. However, there is a problem that the amount of X-ray irradiation increases because X-rays are irradiated over a wide range. In the first place, in radiography using an X-ray CT apparatus, there are many cases where an imaging target region is determined by prior inquiry and examination. However, with conventional imaging methods, data is also obtained for a range that is not originally necessary as volume data. A general method is to acquire an image and reconstruct an image by partially using necessary data after shooting. For this reason, particularly when a small part such as a vertebral body is to be imaged, an X-ray is irradiated on a region that is not originally necessary, which is useless.

  By the way, conventionally, a method for physically limiting X-ray irradiation outside the effective visual field by collimation or the like has been proposed. However, if the effective field of view is set small, it is necessary to correct the positional deviation between the center of the X-ray beam and the object to be imaged more accurately. In particular, when a curved portion such as a spine is formed and a portion that easily shifts is targeted, accurate alignment is required for each imaging position. For example, Patent Document 1 describes a method for setting the imaging position and imaging angle of a vertebral body. In the method described in Patent Document 1, an image from the side of the subject (LAT direction) is acquired by preliminary imaging, and a line smoothly connected from this image through the center point of each vertebra of the spine. A method is described in which a certain spinal column center line is detected, and the setting of the photographing position and the photographing angle (tilt angle) are calculated based on the spinal column center line.

JP-A-8-289888

  However, in the method described in Patent Document 1, the shooting position is calculated from an image in one direction (side). For this reason, it is impossible to accurately grasp the displacement of the spine when viewed from another direction (for example, the displacement in the left and right direction (X direction) with respect to the body axis (Z axis) when the subject is viewed from the front).

  The present invention has been made in view of the above-described problems, and an object of the present invention is to accurately align an imaging target region and thereby reduce an exposure dose, and It is to provide a photographing method.

  In order to achieve the above-described object, a first invention is an X-ray source that irradiates a subject with X-rays, and an X-ray detector that is disposed opposite to the X-ray source and detects X-rays transmitted through the subject. And a drive that mounts the X-ray source and the X-ray detector, and moves the position of the rotating table that rotates around the subject and the table on which the subject is placed in the vertical and horizontal directions, and the front-rear direction. The shape of the region to be imaged is determined from the bed apparatus provided with the apparatus, the scanogram acquisition unit that acquires the scanogram of the subject in the LAT direction and the PA direction, and the scanogram in each direction acquired by the scanano image acquisition unit. The shape extracting unit to be extracted, the approximate curve calculating unit for calculating the approximate curve representing the entire shape of the imaging target region extracted by the shape extracting unit, and the point on the approximate curve at each imaging position and the isocenter are matched. A table correction value calculation unit for calculating the vertical and horizontal table correction values for driving, and driving the table to move the table by the table correction values and perform imaging of the subject An X-ray comprising: a control unit; and a reconstruction calculation unit that collects transmission X-ray data detected by the X-ray detector and reconstructs an image based on the collected transmission X-ray data. CT device.

  According to a second aspect of the present invention, there is provided an X-ray source that irradiates a subject with X-rays, an X-ray detector that is disposed opposite to the X-ray source and detects X-rays transmitted through the subject, the X-ray source, and the X-ray source A bed apparatus equipped with an X-ray detector, a rotating disk that rotates around the subject, and a drive device that moves the position of the table on which the subject is placed in the vertical and horizontal directions; A scano image acquisition unit that acquires scanograms of the subject in the LAT direction and the PA direction, a shape extraction unit that extracts the shape of a part to be imaged from each scano image acquired by the scano image acquisition unit, and X-ray irradiation for setting a circumscribed rectangle for each region to be imaged in each direction extracted by the shape extraction unit and calculating a minimum X-ray irradiation range that can reconstruct the image of the region to be imaged using each circumscribed rectangle Range calculator An X-ray irradiation range limiting unit that adjusts a collimator aperture width or switches a bow tie filter so that the X-ray irradiation range is calculated by the X-ray irradiation range calculation unit, and an imaging that performs imaging of the subject An X-ray comprising: a control unit; and a reconstruction calculation unit that collects transmission X-ray data detected by the X-ray detector and reconstructs an image based on the collected transmission X-ray data. CT device.

  According to a third aspect of the present invention, there is provided a control device for an X-ray CT apparatus including a bed device capable of moving a table on which a subject is placed in a vertical direction, a horizontal direction, and a front-rear direction, and the subject in the LAT direction and the PA direction. A step of acquiring the scano image, a step of extracting the shape of the imaging target part from the acquired scano image in each direction, a step of calculating an approximate curve representing the overall shape of the extracted imaging target part, and each imaging position Calculating the vertical and horizontal table correction values for matching the point on the approximate curve and the isocenter in step, and moving the table by the table correction value and executing imaging of the subject And a process including the following.

  According to a fourth aspect of the invention, a control device of the X-ray CT apparatus acquires a scan image of the subject in the LAT direction and the PA direction, and extracts a shape of the imaging target region from each acquired scan image in each direction. Calculating a minimum X-ray irradiation range in which a circumscribed rectangle is set for each extracted region to be imaged in each direction, and an image of the region to be imaged can be reconstructed using each circumscribed rectangle. An imaging method characterized by executing a process including a step of adjusting a collimator aperture width or switching a bow tie filter so as to be an X-ray irradiation range and a step of executing imaging of a subject. .

  According to the present invention, it is possible to provide an X-ray CT apparatus and an imaging method capable of accurately aligning a region to be imaged and thereby reducing an exposure dose.

Overall configuration diagram of X-ray CT apparatus 1 (A) Scanogram 31 in the LAT direction (YZ plane), (b) Vertebral bodies 4a, 4b, 4c, 4d and reference points Sa, Sb extracted from the scan image 32 in the PA direction (XZ plane), respectively. , Sc, Sd The figure explaining the approximate curve (f _LAT (z)) of a vertebral body region The figure explaining calculation of the table correction value q by the approximated curve ( _fLAT (z)) of a vertebral body area | region The figure explaining calculation of tilt angle (theta) ₁ by the approximate curve _fLAT (z) of a vertebral body area | region The figure explaining the calculation method of the width | variety of the X direction or the Y direction of each vertebral body 4 The flowchart which shows the procedure of the imaging | photography process of the 1st Embodiment of this invention. Flow chart showing the procedure of beam width calculation processing Overall configuration diagram of an X-ray CT apparatus 1A of the second embodiment Example of imaging target region (heart) 81 extracted from scan image 71 in PA direction (XZ plane) The figure explaining the circumscribed rectangle and reference line lO _(PA) of the imaging target region 81 extracted from the scan image 71 in the PA direction The figure explaining the circumscribed rectangle of the imaging | photography object site | part 82 extracted from the scan image 72 of a LAT direction, reference line lO _(LAT), etc. The flowchart which shows the procedure of the imaging | photography process of the 2nd Embodiment of this invention.

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

[First Embodiment]
First, the overall configuration of the X-ray CT apparatus 1 will be described with reference to FIG.
As shown in FIG. 1, the X-ray CT apparatus 1 includes a scan gantry unit 100, a bed 150, and a console 120. The scan gantry unit 100 is an apparatus that irradiates a subject with X-rays and detects X-rays transmitted through the subject. The console 120 is a device that controls each part of the scan gantry unit 100 and acquires transmission X-ray data measured by the scan gantry unit 100 to generate an image. The bed 150 is a device that places a subject on the bed and carries the subject into and out of the X-ray irradiation range of the scan gantry unit 100.

  The scan gantry unit 100 includes an X-ray source 101, a turntable 102, a collimator 103, a bow tie filter 103a, an X-ray detector 106, a data acquisition device 107, a gantry control device 108, a collimator control device 109, an X-ray control device 110, a tilt. A control device 112 and a bow tie filter switching device 113 are provided.

The console 120 includes an input device 121, a display device 122, an image processing device 123, a system control device 124, and a storage device 125.
The bed 150 includes a driving device 152 that moves the position of the table 105 back and forth and right and left, a vertical movement device 153 that adjusts the height of the table, and a bed control device 151 that controls operations of the driving device 152 and the vertical movement device 153. Is provided.

  An opening 104 is provided in the turntable 102 of the scan gantry unit 100, and the X-ray source 101 and the X-ray detector 106 are arranged to face each other through the opening 104. The subject placed on the bed 150 is inserted into the opening 104. The turntable 102 rotates around the subject by a driving force transmitted from the turntable drive device through a drive transmission system. The turntable driving device is controlled by a gantry control device 108.

  Further, the rotating disk 102 not only rotates at right angles to the subject body axis, but also performs a so-called tilt operation that is tilted so as to be non-perpendicular to the subject body axis. The tilt control device 112 tilts the turntable 102 to a predetermined tilt angle θ in accordance with a control signal from the system control device 124. The center of rotation of the turntable 102 is the center of photographing and the center of gantry tilt. Hereinafter, these centers are called isocenters.

  During the tilt operation, the tilt control device 112 tilts the turntable 102 to a predetermined tilt angle θ with respect to the subject body axis. The tilt angle θ is defined as a reference (0 degree) when the scan gantry unit 100 is positioned at right angles to the subject body axis, the direction inclined from the reference toward the bed 150 is minus, and the reference is inclined from the reference in the opposite direction to the bed 150. With the direction being positive, it can be tilted up to about 30 degrees in the positive and negative directions, for example. Note that the plus direction and the minus direction of the tilt angle θ may be defined in reverse to the above-described directions.

  The X-ray source 101 is controlled by the X-ray control device 110 to irradiate X-rays having a predetermined intensity continuously or intermittently. The X-ray controller 110 controls the X-ray tube voltage and the X-ray tube current applied or supplied to the X-ray source 101 according to the X-ray tube voltage and the X-ray tube current determined by the system controller 124 of the console 120. To do.

  A collimator 103 is provided at the X-ray irradiation port of the X-ray source 101. The collimator 103 limits the irradiation range of X-rays emitted from the X-ray source 101. For example, it is formed into a cone beam (conical or pyramidal beam). The opening width of the collimator 103 is determined by the system controller 124, and the opening operation is controlled by the collimator controller 109.

  A bow tie filter 103a for adjusting the intensity of X-rays is provided at the X-ray irradiation port of the X-ray source 101. The bow tie filter 103a is for making the intensity of X-rays incident on the X-ray detector 106 have a predetermined distribution, and is made of an X-ray absorber such as aluminum. The shape of the bow tie filter 103a is, for example, a cross-sectional shape in which the attenuation rate of irradiated X-rays increases as it goes from the center to the end in the rotation direction (channel direction) of the X-ray source 101. In this embodiment, the bow tie filter 103a having a plurality of shapes is provided, and the bow tie filter switching device 113 switches the bow tie filter 103a to be used according to the X-ray irradiation range determined by the system control device 124.

  X-rays irradiated from the X-ray source 101, passing through the collimator 103, and passing through the subject enter the X-ray detector 106.

  The X-ray detector 106 includes, for example, about 1000 X-ray detection element groups configured by a combination of a scintillator and a photodiode in the channel direction (circumferential direction), for example, about 1-320 in the column direction (body axis direction). It is an arrangement. The X-ray detector 106 is disposed so as to face the X-ray source 101 through the subject. The X-ray detector 106 detects the X-ray dose irradiated from the X-ray source 101 and transmitted through the subject, and outputs it to the data acquisition device 107.

  The data collection device 107 collects X-ray doses detected by the individual X-ray detection elements of the X-ray detector 106, converts them into digital data, and sequentially outputs them to the image processing device 123 of the console 120 as transmitted X-ray data. To do.

  The image processing device 123 acquires the transmission X-ray data input from the data collection device 107 and performs preprocessing such as logarithmic conversion and sensitivity correction to create projection data necessary for reconstruction. The image processing device 123 reconstructs an image such as a tomographic image using the generated projection data. The system control device 124 stores the image data reconstructed by the image processing device 123 in the storage device 125 and displays it on the display device 122.

  The display device 122 includes a display device such as a liquid crystal panel and a CRT monitor, and a logic circuit for executing display processing in cooperation with the display device, and is connected to the system control device 124. The display device 122 displays an image output from the image processing device 123 and various information handled by the system control device 124.

  The system control device 124 is a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The system control device 124 performs photographing processing according to the processing procedure shown in FIG. Details of the photographing process will be described later.

  The storage device 125 is a data recording device such as a hard disk, and stores in advance programs, data, and the like for realizing the functions of the X-ray CT apparatus 1.

  The input device 121 includes, for example, a keyboard, a pointing device such as a mouse, a numeric keypad, various switch buttons, and the like, and outputs various instructions and information input by an operator to the system control device 124. The operator operates the X-ray CT apparatus 1 interactively using the display device 122 and the input device 121. The input device 121 may be a touch panel type input device configured integrally with the display screen of the display device 122.

  The bed 150 includes a table 105 on which a subject is placed, a vertical movement device 153, a table driving device 152, and a bed control device 151. The table 105 is moved up and down by the control of the bed control device 151, and the body axis direction. Move back and forth, or move in a direction perpendicular to the body axis and parallel to the floor (left-right direction). The bed control device 151 moves the table 105 according to the table correction value determined by the system control device 124 before the start of the main imaging, and performs the object positioning operation. Further, during the actual shooting, the bed control device 151 moves the table 105 at the bed moving speed and moving direction determined by the system control device 124 based on the shooting conditions.

Here, the function of the X-ray CT apparatus 1 of the present invention will be described.
As shown in FIG. 1, the X-ray CT apparatus 1 of the present invention includes a scanogram acquisition unit 21, a shape extraction unit 22, an approximate curve calculation unit 23, a table correction value calculation unit 24, a tilt angle calculation unit 25, and an X-ray irradiation. A range calculation unit 26, an imaging control unit 27, and a reconstruction calculation unit 28 are included.

  The scanogram acquisition unit 21 acquires scanograms 31 and 32 obtained by imaging a subject from a LAT (Lateral) direction and a PA (Postero-Anterior) direction, respectively (see FIG. 2). When the body axis of the subject is the Z axis, the left-right direction (width direction) orthogonal to the body axis is the X direction, and the front-rear direction (body thickness direction) orthogonal to the body axis is the Y direction, what is a scan image in the LAT direction? 3 is a scano image obtained by irradiating X-rays from a direction perpendicular to the YZ plane. The scan image in the PA direction is a scan image obtained by irradiating X-rays from a direction perpendicular to the XZ plane. Scano images in each direction are taken and acquired before the main shooting.

  The shape extraction unit 22 extracts the shape of the part to be imaged from the scano image in each direction acquired by the scano image acquisition unit 21. In particular, the outline shape of the part to be imaged is extracted. In the present embodiment, as shown in FIG. 2, the shape extraction unit 22 extracts vertebral body regions (vertebral bodies 4a, 4b, 4c, 4d,...) From the two scan images 31 and 32 of LAT and PA. An example of extraction will be described. In the following description, when the entire vertebral body is described without distinguishing individual vertebral bodies, reference numeral 4 is used for the vertebral bodies, and reference numerals such as 4a, 4b,... Are used for the individual vertebral bodies. And Since the vertebral body 4 has a higher CT value than other parts, it can be extracted relatively easily. However, in order to improve the extraction accuracy, the shape may be extracted after performing edge enhancement processing. In the edge enhancement process, for example, a filter process such as a high-pass filter is performed on the acquired scano images 31 and 32. This facilitates extraction of feature points. The extraction of the vertebral body 4 is not limited to this method, and the shape extraction may be performed by any method.

  FIG. 2A shows an example of the scan image 31 in the LAT direction, and FIG. 2B shows an example of the scan image 32 in the PA direction. The shape extraction unit 22 extracts the shapes of the vertebral bodies 4a to 4d of the imaging target regions (the lumbar vertebra in the example of FIG. 2) from the scanograms 31 and 32 as shown in FIG. In FIG. 2, the body axis direction is the Z direction, the body front-rear direction is the Y direction, and the body width direction is the X direction. That is, the scan image 31 in the LAT direction is a projection image on the YZ plane, and the scano image 32 in the PA direction is a projection image on the XZ plane.

The approximate curve calculation unit 23 calculates an approximate curve representing the overall shape of the imaging target region extracted by the shape extraction unit 22. When the imaging target site is the vertebral body 4, the approximate curve calculation unit 23 determines the reference points Sa _LAT , Sb _LAT , Sc _LAT in the LAT direction for the vertebral bodies 4 a to 4 d in the LAT direction and the PA direction extracted by the shape extraction unit 22. , Sd _LAT, and reference points Sa _PA , Sb _PA , Sc _PA , Sd _PA in the PA direction are calculated.

The reference points Sa _LAT , Sb _LAT , Sc _LAT , Sd _LAT and Sa _PA , Sb _PA , Sc _PA , Sd _PA are generally projected images of the vertebral body 4 in a shape close to a rectangle. And the intersection of the diagonal lines of the rectangle is used as the reference point. It is desirable to set the reference point at the center of each vertebral body 4.

It is known that the vertebral body 4 is not a perfect rectangle, and the lumbar vertebrae and the like are particularly deformed and displaced due to the large load applied throughout the body. However, the alignment processing performed in the present embodiment is not so problematic with respect to the deviation in the Z-axis direction (body axis direction), and it is important to accurately detect the deviation in the Y-axis direction and the X-axis direction. Become. Therefore, in the scan image 31 in the LAT direction, for example, a straight line that is perpendicular to the Z axis (parallel to the Y axis) and bisects the area of the vertebral body 4 is calculated. It is desirable that the midpoint of the segment to be separated is the reference point _SLAT . Similarly, for the PA direction, for example, a straight line that is perpendicular to the Z axis (parallel to the X axis) and bisects the area of the vertebral body 4 is calculated, and the straight line is divided by the left and right extracted sides. it is desirable that the reference point S _PA midpoint.

For the scan image 31 in the LAT direction, the reference point S _LAT is calculated for each vertebral body 4 included in the scan image 31. 24 reference points S _LAT are obtained for the entire spine. The approximate curve calculation unit 23 obtains an approximate curve f _LAT (z) from these reference points S _LAT . The method of _{obtaining the} approximate curve f _LAT (z) can be obtained using a known interpolation method. It should be noted that a partial approximate curve f _LAT (z) may be calculated by selecting some continuous arbitrary reference points S _LAT among the calculated reference points. For example, in the example of FIG. 3, the approximate curve f _LAT (z) is calculated from the vertebral bodies 4 of two blocks of the thoracic vertebra and the lumbar vertebra.

The approximate curve calculation unit 23 obtains an approximate curve f _LAT (z) from the scan image 31 in the LAT direction. The approximate curve f _LAT (z) is a function representing the relationship between the body axis direction Z and the body thickness direction Y.
The approximate curve calculation unit 23 also obtains the approximate curve f _PA (z) from the scan image 32 in the PA direction as in the LAT direction. The approximate curve f _PA (z) is a function representing the relationship between the body axis direction Z and the body width direction X.

The table correction value calculation unit 24 calculates table correction values in the vertical direction and the horizontal direction for matching the points on the approximate curves f _LAT (z) and f _PA (z) at the respective photographing positions with the isocenter. From the approximate curve f _LAT (z), a correction value (correction value in the Y direction) in the height (elevation) direction of the table 105 is obtained. From the approximate curve f _PA (z), the correction value in the horizontal direction of the table 105 (correction value in the X direction) is obtained.

FIG. 4 is a diagram for explaining an example in which the table correction value is calculated using the scan image 31 in the LAT direction. f _LAT (z) is the approximate curve calculated by the approximate curve calculation unit 23, and the dotted line is the isocenter line 5 indicating the isocenter position. In FIG. 4, the Z axis indicates the body axis direction of the subject, and the Y axis indicates the body thickness (back to abdomen) direction of the subject facing up.
In order to match the position of each vertebral body 4 extracted from the scan image 31 in the LAT direction with the isocenter, the approximate curve f _LAT (z) only needs to be on the isocenter line 5 at each imaging position. 4 (a), the point p ₁ represents a single imaging position. The difference q from the isocenter in the direction perpendicular to the Z axis at the point p ₁ becomes the height correction value of the table 105.

  When the isocenter line 5 is expressed as a reference (y = 0), the relationship of the following formula (1) is established.

  Therefore, the correction value q in the vertical direction (Y direction) of the table 105 is obtained by the following equation (2).

As shown in FIG. 4 (b), if the imaging position is moved to the position of the point p ₂ and point p _3, each of the photographing positions p _2, the vertical direction similarly table also p ₃ (Y-direction) Correction values q ₂ and q ₃ are obtained.

The table correction value calculation unit 24 uses the same method as in the LAT direction, from the approximate curve f _PA (z) in the PA direction, in the left-right direction (X direction) of the table 105 at each shooting position p ₁ , p ₂ , p ₃ ,. ) Is calculated. The table correction value calculation unit 24 notifies the imaging control unit 27 of the calculated table correction value.

The imaging control unit 27 controls the table 105 to move the table 105 in the vertical direction and the horizontal direction by the table correction value obtained by the table correction value calculation unit 24. As a result, the center of the vertebral body (the reference points S _LAT and S _{PA in} the LAT direction and the PA direction of each vertebral body 4a, 4b,...) Is always in the isocenter at each imaging position p ₁ , p ₂ , p ₃ ,. Aligned.

The tilt angle calculation unit 25 calculates the tilt angle θ of the turntable 102 based on the approximate curve f _LAT (z) calculated from the scan image 31 in the LAT direction. The tilt angle θ is an angle at which a cross section perpendicular to each vertebral body 4 can be photographed at all times.

In FIG. 5, a straight line g (z) is a tangent line at an arbitrary reference point S _tilt on the approximate curve f _LAT (z), and a straight line h (z) is a reference point S _tilt on the approximate curve f _LAT (z). The normal at. The tilt angle calculation unit 25 obtains an angle θ ₁ formed by a perpendicular to the Z axis when the normal h (z) intersects the Z axis. The angle θ ₁ is the tilt angle at the reference point S _tilt . The tilt angle calculation unit 25 notifies the imaging control unit 27 of the calculated tilt angle.

The imaging control unit 27 notifies the tilt control device 112 of the tilt angle calculated by the tilt angle calculation unit 25. The tilt control device 112 drives a tilt drive device (not shown) so that the relative angle between the rotating disk 102 of the scan gantry unit 100 and the table 105 becomes the tilt angle obtained by the tilt angle calculation unit 25. As a result, the turntable 102 is tilted to the calculated tilt angle θ ₁ . Tilt angle theta ₁ is calculated respectively for each imaging position determined, for example, every vertebral body.

Here, a method for calculating the imaging position of each vertebral body 4 will be described.
In order to capture a plurality of cross-sections for one vertebral body 4, the tilt angle calculation unit 25 calculates the length of each vertebral body 4a, 4b, 4c, 4d,... Along the approximate curve f _LAT (z). , And the respective imaging positions (imaging ranges) of the vertebral bodies 4a, 4b, 4c, 4d,. There is an intervertebral part (gap) between the vertebral bodies. For this reason, as shown in FIG. 6, when the perpendicular of the Z-axis is moved in the Z-axis direction, there is no intersection at the intervertebral portion, but the vertebral body extracted at a certain position is touched. If it is further moved, it has two or more intersections (a1, b1, etc.) and touches again at one point. That is, the position of the contact point where the Z-axis perpendicular line and the vertebral body first contact each other is set as the imaging start position, and the position where the contact point becomes one point is set as the imaging end position. In this way, the imaging range in the Z-axis direction of each vertebral body 4a, 4b, 4c, 4d,. The tilt angle calculation unit 25 sets a reference point S _tilt for calculating the tilt angle within the determined shooting range. Then, a normal line h (z) of the approximate curve f _LAT (z) at the set reference point S _tilt is obtained, and an angle θ ₁ formed by the normal line h (z) and the Z-axis perpendicular is defined as a tilt angle.

  The X-ray irradiation range calculation unit 26 calculates a minimum X-ray irradiation range in which an image of the imaging target part can be reconstructed based on the shape of the imaging target part extracted by the shape extraction unit 22. The X-ray irradiation range calculated here is each X-ray beam width in the body axis direction (slice direction) and body width direction (channel direction) near the isocenter.

First, a method for calculating the X-ray irradiation range in the body width direction will be described.
The X-ray irradiation range calculation unit 26 calculates the width of the vertebral body 4. In general, the vertebral body 4 has a cylindrical shape. Therefore, the vertebral bodies are extracted from the scan images 31 and 32 in two directions (LAT direction and PA direction), and the approximate diameter of the vertebral bodies is obtained.
Since the width of the vertebral body obtained here is a width for determining the beam width of the isocenter portion, the minimum beam width capable of imaging the entire vertebral body can be determined by determining the maximum width.

A beam width calculation method will be described with reference to FIG.
A dotted line 5 in FIG. 6 is a straight line (isocenter line 5) indicating an isocenter. As an example, FIG. 6 shows a third lumbar vertebra (vertebral body 4) extracted from a scan image in the LAT direction. Although the adjacent vertebral bodies are actually extracted by the shape extraction unit 22, they are not shown. There is an intervertebral part (gap) between the vertebral bodies. Compared to a vertebral body having a high CT value, the intervertebral portion, which is a soft tissue, has a low CT value. Therefore, the intervertebral portion is not often erroneously extracted. Therefore, the extracted vertebral body has a gap (portion where nothing is extracted) between adjacent vertebral bodies.

First, a method for calculating the width of the vertebral body in the Z direction will be described.
A perpendicular line is drawn from the isocenter line 5 toward the figure (vertebral body 4) shown in FIG. As a premise, the table 105 is installed so as to move parallel to the isocenter line 5. Therefore, the perpendicular drawn from the isocenter line 5 intersects perpendicularly to the Z axis. When this perpendicular is moved in the Z-axis direction, it intersects with the extracted vertebral body contour at one point, and then intersects at two or more points. When intersecting at two or more points, the movement continues, and the width in the Z direction of one vertebral body 4 is from the position where it first contacts at one point to the position where it contacts at one point next. The X-ray irradiation range calculation unit 26 notifies the collimator controller 109 of the calculated vertebral body width in the Z direction as the beam width in the body axis direction (slice direction).

  Next, a method for calculating the vertebral body width in the direction orthogonal to the Z direction (the Y direction in the scan image 31 in the LAT direction and the X direction in the scan image 32 in the PA direction) will be described.

As shown in FIG. 6, a point where a perpendicular drawn from the isocenter line 5 intersects with the isocenter line 5 is o (o ₁ , o ₂ ,..., O _n ), and a point _where the extracted vertebral body 4 intersects with the ventral side. a (a ₁ , a ₂ ,... a _n ), and b (b ₁ , b ₂ ,... b _n ) are points intersecting one side of the back side. It is assumed that the subject is imaged on the back during scanogram imaging. Although it is ideal to make the step width of the perpendicular movement as small as possible, it may be a step width having a certain width in order to reduce the calculation burden.

X-ray irradiation range calculation unit 26, the direction of the vertebral body width perpendicular to the Z-direction _{| o n a n -o n b} n | a determined (n = 1,2, ···, n ). The maximum value of the vertebral body widths at each step position is defined as the width of the vertebral body in the Y-axis direction.

  The X-ray irradiation range calculation unit 26 obtains the vertebral body width by a similar method also from the scan image in the PA direction. The maximum value of the vertebral body width obtained from the scan image in the LAT direction and the vertebral body width obtained from the scan image in the PA direction is set as the beam width at the isocenter portion. The X-ray irradiation range calculation unit 26 notifies the calculated beam width to the collimator control device 109 or the bow tie filter switching device 113.

  The collimator control device 109 and the bow tie filter switching device 113 limit the X-ray irradiation range in the body axis direction and the body width direction so that the beam width calculated by the X-ray irradiation range calculation unit 26 is obtained.

  Regarding the beam width in the body axis direction, the X-ray beam outside the calculated X-ray irradiation range may be physically blocked by collimation. Alternatively, the dose other than the beam width may be attenuated by the bow tie filter 103a.

  On the other hand, if the beam width in the body width or body thickness direction completely shuts off X-rays in the peripheral part other than the calculated X-ray irradiation range, the image cannot be reconstructed. For this reason, when limiting the X-ray irradiation range in the body width or body thickness direction, the bow tie filter 103a is used so that the calculated X-ray irradiation range has a predetermined X-ray intensity, and the peripheral portion is subjected to image reconstruction. Attenuate to achieve minimum x-ray intensity required for configuration.

  The imaging control unit 27 drives the table driving device 152 or the vertical movement device 153 based on various imaging conditions and the table correction value calculated by the table correction value calculation unit 24 to correct the position of the table 105. Perform imaging of the subject. In imaging of the subject, the imaging control unit 27 controls the X-ray control device 110, the gantry control device 108, the collimator control device 109, the bow tie filter switching device 113, the tilt control device 112, and the bed control device 151 based on the imaging conditions. Send a control signal.

  The X-ray control device 110 controls electric power input to the X-ray source 101 based on a control signal input from the system control device 124. The gantry control device 108 controls the drive system of the turntable 102 according to the photographing conditions such as the rotation speed, and rotates the turntable 102. The bed control device 151 aligns the bed 150 to a predetermined shooting start position based on the shooting range set as the shooting condition. During imaging, the table 105 is moved in the Z-axis direction at a predetermined speed based on imaging conditions such as a bed speed (spiral pitch), and the table is calculated based on the table correction value calculated by the table correction value calculation unit 24. The height position and the horizontal position of 105 are adjusted.

The tilt control device 112 tilts the turntable 102 to the tilt angle θ ₁ based on the tilt angle control signal input from the system control device 124. The collimator control device 109 adjusts the opening width of the collimator 103 based on the control signal input from the system control device 124. The bow tie filter switching device 113 switches the bow tie filter 103a based on a control signal input from the system control device 124.

  X-rays are irradiated to the imaging region with the table position, tilt angle, and beam width adjusted. The transmitted X-ray data that has passed through the imaging region is detected by the X-ray detector 106, collected by the data collection device 107, converted into digital data, and sent to the reconstruction calculation unit 28.

  The reconstruction calculation unit 28 reconstructs a tomographic image of the imaging region based on the transmission X-ray data detected by the X-ray detector 106 and collected by the data collection device 107. The reconstructed tomographic image is stored in the storage device 125 and sent to the system control device 124 and displayed on the display device 122.

Next, with reference to FIG. 7 and FIG. 8, the procedure of the imaging process of the first embodiment will be described.
The system control device 124 of the X-ray CT apparatus 1 executes imaging processing according to the procedure shown in the flowchart of FIG. That is, the system control device 124 reads a program and data related to the photographing process from the storage device 125 and executes processing based on the program and data.

  In the X-ray CT apparatus 1, the operator acquires scanograms 31 and 32 of the patient to be imaged (step S101). Scan images 31 and 32 to be acquired are a scan image 31 in the LAT direction (projected image on the YZ plane) and a scan image 32 in the PA direction (projected image on the XZ plane).

Next, the system control device 124 extracts the vertebral body region 4 from each of the acquired scano images 31 and 32 (step S102), and an approximate curve f _LAT (z) representing the overall shape of the extracted vertebral body region 4. , F _PA (z) is calculated (step S103). f _LAT (z) is an approximate curve calculated from the scan image 31 in the LAT direction, and f _PA (z) is an approximate curve calculated from the scan image 32 in the PA direction. In the vertebral body region 4, a plurality of vertebral bodies are continuously arranged. The system controller 124 calculates approximate curves f _LAT (z) and f _PA (z) for all or part of a vertebral body region including a plurality of continuous vertebral bodies.

The system controller 124 calculates the correction value in the vertical direction and the correction value in the horizontal direction of the table 105 so that the approximate curves f _LAT (z) and f _PA (z) calculated in step S102 pass through the isocenter. (Step S104). A table correction value in the vertical direction is calculated from the approximate curve f _LAT (z). A table correction value in the left-right direction is calculated from the approximate curve f _PA (z).

Further, the system control device 124 calculates a tilt angle θ ₁ for capturing a tomographic image having a cross section perpendicular to the vertebral body 4 to be imaged from the approximate curve f _LAT (z) (step S105).

Further, the system control device 124 calculates a minimum beam width that can reconstruct a tomographic image to be imaged (step S106). In the beam width calculation process in step S106, as shown in FIG. 8, the system controller 124 extracts the vertebral body 4 to be imaged from the scan image 31 in the LAT direction and the scan image 32 in the PA direction (step S201). The width of the extracted vertebral body is calculated (step S202). As described above, if the width of the vertebral body is, for example, the width in the Y direction, the intersection points a ₁ and b ₁ between the contours of the ventral and dorsal sides of the extracted vertebral body 4 and the perpendicular of the isocenter line 5 are obtained. Obtained by calculating the distance between the intersection points a ₁ and b ₁ . Similarly, the width in the X direction is also obtained by calculating each intersection point between the extracted contour line of the vertebral body 4 in the body width direction and the perpendicular line of the isocenter line 5 and calculating the distance between each intersection point. The system control device 124 sets the larger one of the calculated vertebral body width in the Y direction and vertebral body width in the X direction as the minimum vertebral body width.

  Note that the vertebral body width in the body axis direction (Z direction) is obtained by obtaining a point where the perpendicular of the isocenter line 5 and the vertebral body 4 are in contact with each other at one point, and calculating the distance between the contact points. The system controller 124 sets the calculated vertebral body width in the Z direction to the minimum vertebral body width (Z direction).

  The system control device 124 obtains an adjustment value of the beam width (selection of the opening width of the collimator 103 and the bow tie filter 103a) so as to be the vertebral body width calculated in step S202 (step S203). The beam width in the slicing direction (Z direction) may completely block X-rays applied to the region other than the vertebral body to be imaged, so that the collimator aperture width corresponding to the Z vertebral body width calculated in step S202 Can be determined. As for the vertebral body widths in the Y direction and the X direction, in order to reconstruct an image, it is necessary to acquire information by irradiating the area around the imaging target area with X-rays. Therefore, the bow tie filter 103a formed so that the X-ray intensity is “high” in the region of the vertebral body width and the X-ray intensity is “low” in the region other than the vertebral body width is selected.

Returning to the description of FIG.
The system control device 124 sets an imaging range for imaging with the table position, tilt angle, and beam width calculated in steps S104 to S106 (step S107). This imaging range can be obtained from the width of the corresponding vertebral body 4 in the body axis direction.

  The system control device 124 notifies the table correction value calculated in step S104 to the bed control device 151 and notifies the tilt control device 112 of the tilt angle calculated in step S105 to move the table 105 and adjust the tilt angle. Is executed. As a result, the vertebral body 4 to be imaged coincides with the isocenter (step S108).

  Further, the system control device 124 notifies the collimator control device 109 and the bow tie filter switching device 113 so that the beam width calculated in step S106 is obtained. The collimator controller 109 adjusts the collimator aperture width so as to be the notified beam width. The bow tie filter switching device 113 switches to a bow tie filter having a shape suitable for the notified beam width (step S109).

  Thereafter, the system control device 124 performs imaging for the imaging range obtained in step S107 (step S110). Transmitted X-ray data obtained by imaging is sent to the image processing device 123. The reconstruction calculation unit 28 of the image processing device 123 reconstructs a tomographic image of the vertebral body 4 based on the acquired transmission X-ray data (step S111). The reconstructed tomographic image is stored in the storage device 125 and sent to the system control device 124 and displayed on the display device 122 (step S112).

As described above, the X-ray CT apparatus 1 according to the first embodiment of the present invention acquires the scan images 31 and 32 in the LAT direction and the PA direction, and respectively acquires the scan images 31 and 32 in the two directions. The shape of the imaging target part is extracted, and approximate curves f _LAT (z) and f _PA (z) representing the entire shape of the extracted imaging target part are calculated. Then, the table correction values in the vertical and horizontal directions for matching the points on the approximate curves f _LAT (z) and f _PA (z) and the isocenter at each photographing position are calculated, and the table is moved by the table correction value. And subject imaging.

  In this way, table correction values are obtained from the two-direction scanograms. Therefore, the table position can be accurately corrected vertically and horizontally with respect to the deviation in the X direction and the Y direction. In particular, since the table correction value is obtained in accordance with the shape of the approximate curve, it is suitable when, for example, a curved portion such as a vertebral body region in which a plurality of vertebral bodies are continuous is taken as an imaging target. In addition, since an approximate curve is obtained using scanograms of individual patients, it is suitable for radiographing a region that is likely to be displaced, such as a vertebral body, and has a large individual difference.

The vertebral body region is curved in an S shape as a whole, and each vertebral body is inclined with respect to the body axis (Z axis). The inclination of each vertebral body can be obtained from the approximate curve f _LAT (z) in the LAT direction, and the tilt angle can be adjusted in accordance with the inclination of the vertebral body. Thereby, a tomographic image of a cross section orthogonal to each individual vertebral body can be acquired. Furthermore, since the beam width is adjusted in accordance with the width of the vertebral body 4 in a state where the center of the vertebral body to be imaged coincides with the isocenter, the exposure dose can be minimized.

  In the flowchart of FIG. 7, the flow in the case of executing all of the vertical and horizontal table position correcting functions, the tilt angle adjusting function, and the beam width limiting function has been described. It is not limited to. For example, one or two of these functions may be selected and performed.

  In the first embodiment, the case where the imaging target region is a vertebral body has been described as a preferred example, but the present invention can also be applied to a region other than the vertebral body. In the second embodiment, an imaging method in the case where a part other than the vertebral body is an imaging target part will be described.

[Second Embodiment]
The second embodiment of the present invention will be described with reference to FIGS.

  FIG. 9 is a diagram illustrating a configuration of an X-ray CT apparatus 1A according to the second embodiment. In FIG. 9, the same components as those in the X-ray CT apparatus 1 (see FIG. 1) of the first embodiment are denoted by the same reference numerals, and redundant description is omitted. Hereinafter, differences from the first embodiment will be described.

  The system control device 124A of the X-ray CT apparatus 1A according to the second embodiment includes a scano image acquisition unit 21, a shape extraction unit 22, a reference range calculation unit 61, a reference line calculation unit 62, an X-ray irradiation range calculation unit 63, A table correction value calculation unit 64 and an imaging control unit 65 are included.

  The scano image acquisition unit 21 acquires scan images in the LAT direction and the PA direction, as in the first embodiment.

  As in the first embodiment, the shape extraction unit 22 extracts the shape of the part to be imaged from the scano image in each direction acquired by the scano image acquisition unit 21. In the second embodiment, a single object is used instead of a portion where a plurality of the same shape like the vertebral body region is continuously arranged. Hereinafter, the heart will be described as an example.

FIG. 10 is a diagram in which an imaging target region (heart) 81 is extracted from a scan image 71 in the PA direction (XZ plane) acquired by the scanano image acquisition unit 21.
As shown in FIG. 10, the shape extraction unit 22 extracts the shape of the imaging target region 81 from the scanogram 71. At this time, the shape extraction processing may be performed after performing edge enhancement processing or the like on the scanogram 71 in order to increase the extraction accuracy.

  Depending on the part, the difference in CT value from the peripheral part is small, and extraction may be difficult. However, since the shape extraction process in the present embodiment is intended to identify the position and range of the imaging target region, the detailed shape is not a problem. The assumed position of the region to be imaged may be specified using a region model that takes into account individual differences such as body type. Further, the operator may manually extract the shape of the imaging target part.

  The reference range calculation unit 61 obtains the reference range of the imaging target part 81 extracted by the shape extraction unit 22. The reference range is determined based on a rectangle that circumscribes the imaging target region 81. The reference range calculation unit 61 calculates a reference range by using a circumscribed rectangle for each part to be imaged extracted from the scan images 71 and 72 in the LAT direction and the PA direction.

Here, a reference range calculation method will be described with reference to FIG. FIG. 11 shows the contour shape of the imaging target region 81 extracted from the scan image 71 in the PA direction (XZ plane).
The reference range calculation unit 61 sets a straight line orthogonal to the Z axis (body axis), and scans the imaging target region 81 in the Z direction using this straight line. Then, the points z ₁ and z _{2 at} which the straight line perpendicular to the Z axis (body axis) is in contact with the imaging target region 81 are obtained. The straight lines l _z1 and l _z2 shown in FIG.

Next, the reference range calculation unit 61 scans the periphery of the imaging target region 81 in the X direction using a straight line orthogonal to the X axis. Then, the points x ₁ and x _{2 at} which the straight line orthogonal to the X axis contacts the imaging target part 81 are obtained. The straight lines l _x1 and l _x2 shown in FIG. A rectangle formed by these straight lines l _x1 , l _x2 , l _z1 , l _z2 is a circumscribed rectangle of the imaging target region 81. This circumscribed rectangle is set as a reference range in the PA direction.

The reference range calculation unit 61 similarly determines reference points z ₁ , z ₂ , y ₁ , and y ₂ for the imaging target region 82 extracted from the scan image 72 in the LAT direction. FIG. 12 shows the contour shape of the imaging target region 82 extracted from the scan image 72 in the LAT direction (YZ plane).

The reference range calculation unit 61 scans the periphery of the imaging target region 82 in the Z-axis direction using a straight line orthogonal to the Z-axis (body axis). Then, the points z ₁ and z _{2 at} which the straight line orthogonal to the Z axis (body axis) is in contact with the imaging target region 82 are obtained. The straight lines l _z1 and l _z2 shown in FIG.

Next, the reference range calculation unit 61 scans the periphery of the imaging target region 82 in the Y direction using a straight line orthogonal to the Y axis. Then, the points y ₁ and y _{2 at} which the straight line perpendicular to the Y axis contacts the imaging target part 82 are obtained. The straight lines l _y1 and l _y2 shown in FIG. A rectangle formed by these straight lines l _y1 , l _y2 , l _z1 , and l _z2 is a circumscribed rectangle of the imaging target region 82, and this circumscribed rectangle is set as a reference range in the LAT direction.

Based on the respective reference ranges in the LAT direction and the PA direction calculated by the reference range calculation unit 61, the reference line calculation unit 62 uses the reference lines l _{O (LAT)} 1, L 0 _{( PA)} .
The reference lines l _{O (LAT)} and l _{O (PA)} are parallel to the Z axis and are straight lines located at the center of the extracted imaging target portions 81 and 82. For example, it is desirable that the straight lines that bisect the areas of the extracted imaging target portions 81 and 82 be the reference lines l _{O (LAT)} and l _{O (PA)} (see FIGS. 11 and 12).

Note that the length h shown in FIGS. 11 and 12 is the distance between the straight lines l _z1 and l _z2 . This indicates the length of the imaging target portions 81 and 82 in the Z-axis direction. That is, the shooting start position or the shooting end position is the point z ₁ and the point z ₂ , respectively.

The X-ray irradiation range calculation unit 63 determines the X-ray beam width based on the reference lines l _{O (LAT)} and l _{O (PA)} calculated by the reference line calculation unit 62.
The X-ray beam widths are the distances between the perpendicular lines 85 and 86 drawn from the contact point x ₁ and the point x ₂ to the reference line 10 _(PA) from the circumscribed rectangle of the imaging target region 81 in the PA direction shown in FIG. The largest one of the distances of the vertical lines 87 and 88 drawn from the contact point y ₁ and the point y ₂ to the reference line 10 _(LAT) from the circumscribed rectangle calculated from the imaging target region 82 in the LAT direction shown in FIG. Is obtained, and the obtained value is taken as the X-ray beam width at the isocenter portion.

The table correction value calculation unit 64 calculates the vertical correction value and the horizontal correction value of the table 105 from the reference lines l _{O (LAT)} and l _{O (PA) of the} region to be imaged. The table correction value calculation unit 64 calculates the table correction values in the vertical direction and the horizontal direction in the same manner as the table correction value calculation unit 24 of the first embodiment. In the second embodiment, the table correction values are calculated by replacing the approximate curves f _LAT (z) and f _PA (z) with the reference lines l _{O (LAT)} and l _{O (PA)} . In the second embodiment, since the approximate curve f (z) in the first embodiment is a reference line (straight line), the table correction value may be obtained once for each of the PA direction and the LAT direction. It is not necessary to obtain for each shooting position.

  The imaging control unit 65 narrows the X-ray beam width to the X-ray irradiation range calculated by the X-ray irradiation range calculation unit 63 and executes imaging of the imaging target region. Further, the table 105 is moved in accordance with the vertical and horizontal table correction values calculated by the table correction value calculation unit 64, and imaging of the imaging target region is executed.

The operation of the X-ray CT apparatus 1A in the second embodiment will be described with reference to FIG.
In the second embodiment, the system control device 124A of the X-ray CT apparatus 1A executes imaging processing according to the procedure shown in the flowchart of FIG. That is, the system control device 124A reads a program and data related to the photographing process from the storage device 125, and executes processing based on the program and data.

  In the X-ray CT apparatus 1A, the operator acquires scanograms 71 and 72 of the patient to be imaged (step S301). Scan images 71 and 72 to be acquired are a scan image 71 in the LAT direction (YZ plane) and a scan image 72 in the PA direction (XZ plane).

Next, the system control device 124A extracts the shapes of the imaging target parts 81 and 82 from the acquired scanograms 71 and 72, respectively (step S302), obtains a circumscribed rectangle of the extracted imaging target parts 81 and 82, and circumscribes them. A reference range is determined based on the rectangle (step S303). Further, the system control device 124A calculates reference lines l _{O (LAT)} and l _{O (PA)} that _{bisect the} imaging target region from the reference range determined in step S303 (step S304). The reference lines l _{O (LAT)} and l _{O (PA)} are obtained for both the PA direction and the LAT direction, respectively. Further, it is desirable that the reference lines l _{O (LAT)} and l _{O (PA)} are straight lines that divide the areas of the imaging target portions 81 and 82 into two equal parts.

  The system control device 124A calculates an imaging range, an X-ray beam width, and a table correction value from the reference line and the reference range calculated in steps S303 to S304 (step S305).

In the imaging range, the contact points z ₁ and z ₂ between the imaging target parts 81 and 82 and the circumscribed rectangle shown in FIGS. 11 and 12 are set as the imaging start position and the imaging end position.

With respect to the beam width in the rotation direction (channel direction) of the turntable 102, the X-ray beam width is the reference line l 0 _(PA) from the contact point x ₁ and the point x ₂ with the circumscribed rectangle of the imaging target region 81 in the PA direction. And the lengths of the perpendiculars 87 and 88 drawn from the respective contacts y ₁ and y ₂ to the reference line 10 _(LAT) from the contact points y ₁ and y ₂ with the circumscribed rectangle of the imaging target region 82 in the LAT direction. The maximum value is doubled.
Further, if the length of the Z direction of the imaging target site 81 (body axis direction) is smaller than the length of the slice direction of the X-ray detector 106 includes a contact point z ₁ and the contact point z ₂ obtained by the circumscribing rectangle of the above Is the beam width in the slice direction (body axis direction).

The table correction value in the vertical direction is obtained so that the reference line l _{O (LAT) of} the imaging target region 82 extracted from the scan image 72 in the LAT direction matches the isocenter line 5. That is, the distance in the Y-axis direction between the isocenter line 5 and the reference line 10 _(LAT) is used as a table correction value in the vertical direction (Y direction).

The table correction value in the left-right direction is obtained so that the reference line l _{O (PA) of} the imaging target region 81 extracted from the scan image 71 in the PA direction matches the isocenter line 5. That is, the distance in the X-axis direction between the isocenter line 5 and the reference line lO _(PA) is used as a table correction value in the left-right direction (X direction).

  The system control device 124A sends a control signal to the bed control device 151, and moves the table 105 to the shooting range (shooting start position) calculated in step S305. Further, based on the table correction value calculated in step S305, the table 105 is moved vertically and horizontally (step S306).

  Further, the system control device 124A limits the beam width (step S307). The beam width is limited, for example, by adjusting the collimator opening width or switching the bow tie filter 113a. In particular, limiting the beam width in the rotation direction (channel direction) of the turntable 102 is performed by switching the bow tie filter 113a. The system control device 124A sends a control signal to the bow tie filter switching device 113, switches to the bow tie filter 103a suitable for the X-ray beam width calculated in step S305, and limits the X-ray beam width (X-ray irradiation range). .

  The beam width in the body axis direction is limited by adjusting the collimator aperture width or switching the bow tie filter 113a. The system controller 124A sends a control signal to the collimator controller 109, and adjusts the collimator aperture width to be suitable for the X-ray beam width calculated in step S305.

  Thereafter, the system control device 124 performs shooting in the shooting range obtained in step S305 (step S308). Transmitted X-ray data obtained by imaging is sent to the image processing device 123. The reconstruction calculation unit 28 of the image processing device 123 reconstructs a tomographic image of the vertebral body based on the acquired transmission X-ray data. (Step S309). The reconstructed tomographic image is stored in the storage device 125 and sent to the system control device 124A and displayed on the display device 122 (step S310).

As described above, the X-ray CT value 1A of the second embodiment acquires the scanograms 71 and 72 taken from the LAT direction and the PA direction, and is taken from the acquired scanograms 71 and 72 in the respective directions. A target line 81, 82 is extracted, a range in each of the X, Y, and Z directions of the imaging target part is determined from each rectangle circumscribing the extracted imaging target parts 81, 82, and a reference line l that bisects the imaging target part _{O (PA)} and lO _(LAT) are obtained, and based on the reference lines lO _(PA) and lO _(LAT) , the minimum X-ray beam width including the entire region to be imaged is calculated. The X-ray irradiation range is narrowed down to the beam width and imaging of the imaging target region is executed.
Therefore, it is possible to perform imaging while limiting the X-ray beam width to the minimum necessary range. Thereby, the exposure amount can be reduced.

Further, it is desirable that the above-described reference lines l _{O (PA)} and l _{O (LAT)} are straight lines that divide the circumscribed rectangle area into two equal parts. A value obtained by doubling the larger one of the X-direction distance and the Y-direction distance from these reference lines l _{O (PA)} and l _{O (LAT)} to the end of the imaging target region (contact point with the circumscribed rectangle), whichever is greater X-ray beam width. By obtaining the X-ray beam width in this way, the minimum X-ray beam width including the entire imaging target region can be calculated with a simple calculation process for any part of the shape.

Further, the reference lines l _{O (PA)} and l _{O (LAT)} calculated by the above method are set at the center of the imaging target region. For this reason, the X-ray beam width is narrowed down after obtaining and aligning table correction values in the X and Y directions so that the reference lines l _{O (PA)} and l _{O (LAT)} coincide with the isocenter. The line irradiation range can be minimized.

  The preferred embodiment of the X-ray CT apparatus according to the present invention has been described above, but the present invention is not limited to the above-described embodiment. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1,1A ... X-ray CT apparatus 100 ......... Scan gantry part 101 ......... X-ray source 102 ......... Rotary disk 103 ......... Collimator 103a ... Bow-tie filter 106 ......... X-ray detector 109 ... ... Collimator control device 112 ......... Tilt control device 113 ......... Bow tie filter switching device 120 ... ... Console 121 ... ... Input device 122 ... ... Image processing device 123 ... ... Storage device 124 ... ... System control Device 125 ......... Display device 105 ......... Table 150 ......... Bed device 151 ...... Bed control device 21 ......... Scano image acquisition unit 22 ......... Shape extraction unit 23 ......... Approximate curve calculation Unit 24 ………… Table correction value calculation unit 25 ………… Tilt angle calculation unit 26 ………… X-ray irradiation range calculation unit 27 ………… Shooting control unit 28 ………… Configuration calculating unit 61 ............ reference range calculation unit 62 ............ reference line calculation unit 63 ............ X-ray irradiation range calculation section 64 ............ table correction value calculation unit 65 ............ photographing control unit

Claims (9)

An X-ray source for irradiating the subject with X-rays;
An X-ray detector arranged to face the X-ray source and detecting X-rays transmitted through the subject;
A rotary disk that is mounted with the X-ray source and the X-ray detector and rotates around the subject;
A bed apparatus provided with a driving device for moving the position of the table on which the subject is placed in the up-down, left-right, and front-back directions;
A scanogram acquisition unit that acquires scanograms of the subject in the LAT direction and the PA direction;
A shape extraction unit that extracts the shape of each imaging target part from the scano image in each direction acquired by the scano image acquisition unit;
An approximate curve calculation unit for calculating an approximate curve representing the overall shape of the imaging target region extracted by the shape extraction unit;
A table correction value calculation unit for calculating vertical and horizontal table correction values for matching a point on the approximate curve and an isocenter at each photographing position;
An imaging control unit that drives the table driving device to move the table by the table correction value and executes imaging of the subject;
A reconstruction calculation unit that collects transmission X-ray data detected by the X-ray detector and reconstructs an image based on the collected transmission X-ray data;
An X-ray CT apparatus comprising: A tilt angle calculator for calculating a tilt angle of the rotating disk for irradiating X-rays from a direction orthogonal to each position on the approximate curve calculated from the scan image in the LAT direction;
A tilt control device for tilting the turntable to the tilt angle calculated by the tilt angle calculation unit;
The X-ray CT apparatus according to claim 1, further comprising: An X-ray irradiation range calculation unit that calculates a minimum X-ray irradiation range that can reconstruct the image of the imaging target region based on the shape of the imaging target region extracted by the shape extraction unit;
An X-ray irradiation range limiting unit that performs adjustment of a collimator aperture width or switching of a bow tie filter so as to be the X-ray irradiation range calculated by the X-ray irradiation range calculation unit;
The X-ray CT apparatus according to claim 2, further comprising:   The X-ray CT apparatus according to claim 1, wherein the imaging target region is a vertebral body, and the approximate curve is an approximate curve indicating an overall shape of a vertebral body region including a plurality of continuous vertebral bodies. An X-ray source for irradiating the subject with X-rays;
An X-ray detector arranged to face the X-ray source and detecting X-rays transmitted through the subject;
A rotary disk that is mounted with the X-ray source and the X-ray detector and rotates around the subject;
A bed apparatus provided with a driving device for moving the position of the table on which the subject is placed in the up-down, left-right, and front-back directions;
A scanogram acquisition unit that acquires scanograms of the subject in the LAT direction and the PA direction;
A shape extraction unit that extracts the shape of each imaging target part from the scano image in each direction acquired by the scano image acquisition unit;
X-rays that set a circumscribed rectangle for each region to be imaged in each direction extracted by the shape extraction unit, and calculate a minimum X-ray irradiation range that can reconstruct the image of the region to be imaged using each circumscribed rectangle An irradiation range calculation unit;
An X-ray irradiation range limiting unit that performs adjustment of a collimator aperture width or switching of a bow tie filter so as to be the X-ray irradiation range calculated by the X-ray irradiation range calculation unit;
An imaging control unit that performs imaging of the subject;
A reconstruction calculation unit that collects transmission X-ray data detected by the X-ray detector and reconstructs an image based on the collected transmission X-ray data;
An X-ray CT apparatus comprising: A reference line calculation unit using a line that bisects the area of the imaging target region extracted by the shape extraction unit as a reference line;
A table correction value calculation unit for calculating vertical and horizontal table correction values for matching the reference line and the isocenter;
The X-ray CT apparatus according to claim 5, wherein the imaging control unit drives the table driving device to move the table by the table correction value and performs imaging of the subject. X-ray irradiation range calculation unit
A line that bisects the area of the region to be imaged extracted by the shape extraction unit is used as a reference line, and the distance in the X direction or Y direction between the reference line and the circumscribed rectangle in both the LAT direction and the PA direction, respectively. The X-ray CT apparatus according to claim 5, wherein the X-ray irradiation range is a value that is twice as large as the obtained distance. A control device for an X-ray CT apparatus provided with a bed apparatus that can move the position of a table on which a subject is placed vertically, horizontally, and back and forth,
Acquiring a scanogram of the subject in the LAT direction and the PA direction;
Extracting the shape of the imaging target part from each acquired scano image in each direction;
Calculating an approximate curve representing the overall shape of the extracted imaging target region;
Calculating vertical and horizontal table correction values for matching a point on the approximate curve and an isocenter at each photographing position;
Moving the table by the table correction value and performing imaging of the subject;
The imaging method characterized by performing the process containing these. The control device of the X-ray CT apparatus is
Acquiring scan images of the subject in the LAT direction and the PA direction;
Extracting the shape of the imaging target part from each acquired scano image in each direction;
Setting a circumscribed rectangle for each of the extracted imaging target parts in each direction, and calculating a minimum X-ray irradiation range that can reconstruct the image of the imaging target part using each circumscribed rectangle;
Adjusting the collimator aperture width or switching the bow tie filter so as to be the calculated X-ray irradiation range;
Performing imaging of the subject;
The imaging method characterized by performing the process containing these.

Images