JP4610795B2 - Slice thickness determination method, slice thickness determination apparatus, program, and X-ray CT apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a slice thickness determination method, a slice thickness determination apparatus, a program, and an X-ray computed tomography (CT) apparatus, and more particularly to an X-ray CT apparatus that performs a helical scan. The present invention relates to a slice thickness determination method, a slice thickness determination apparatus, a program, and an X-ray CT apparatus that performs a helical scan.
[0002]
[Prior art]
In the X-ray CT apparatus, transmission X-ray data (data) of a plurality of views (view) is acquired for an object to be imaged by an X-ray irradiation / detection apparatus, and a tomographic image of the object is acquired by an image generation apparatus based on the transmission X-ray data. Generate (reconfigure).
[0003]
The X-ray irradiation apparatus shapes a cone-shaped X-ray beam emitted from the focal point of an X-ray tube into a fan-shaped X-ray beam using a collimator and irradiates the imaging space.
[0004]
The X-ray detection apparatus is a multi-channel X-ray detection system in which a large number of detection elements are arranged in an array along the fan-shaped spread of the X-ray beam. Detect with instrument. By rotating (scanning) such an X-ray irradiation / detection device around an object, transmission X-ray data of a plurality of views is acquired.
[0005]
A so-called helical scan is performed by turning the X-ray irradiation / detection device along a spiral trajectory. In the helical scan, the object is continuously scanned over a predetermined length in the body axis direction. Therefore, a plurality of tomographic images having different slice positions on the body axis are obtained based on the acquired transmission X-ray data. Can be reconfigured.
[0006]
As a kind of X-ray detector, multi-row X-ray detection in which a plurality of detection element arrays are arranged in the direction of the thickness of a fan-shaped X-ray beam and the X-ray beams are simultaneously received by a plurality of detection element arrays There is a vessel.
[0007]
In a multi-row X-ray detector, X-ray detection signals for a plurality of slices can be obtained at a time in one scan, so that it is used as an X-ray detector for efficiently performing a multi-slice scan. . When a multi-row X-ray detector is used, helical scanning with a large pitch can be performed, so that the imaging efficiency is improved.
[0008]
When high-speed imaging is required, high-speed helical scan is performed with a frame rate as the number of frames for image reconstruction during one rotation of the X-ray irradiation / detection device, for example, about six. Image reconstruction with a frame rate of 6 is also referred to as real time reconstruction.
[0009]
[Problems to be solved by the invention]
The X-ray CT apparatus is equipped with the largest scale image reconstruction device so that real-time recon can be performed whenever necessary, but the largest scale image is not necessarily seen from the use of the user's X-ray CT apparatus. In many cases, a reconfiguration device is not necessary.
[0010]
In such a case, it is conceivable to reduce the scale of the image reconstruction device and implement it. However, since the frame rate of the image reconstruction decreases as the size is reduced, the slice of the reconstructed image with respect to the helical scan pitch. Thickness consistency can be compromised.
[0011]
Therefore, an object of the present invention is to provide a method and apparatus for determining a slice thickness that matches a helical pitch regardless of the frame rate of image reconstruction, a program for causing a computer to realize such a slice thickness determination function, and An X-ray CT apparatus provided with such a slice thickness determining apparatus is realized. Another object is to display a real-time tomographic image on it.
[0012]
[Apparatus for solving the problems]
(1) In one aspect of the invention for solving the above-described problem, a tomographic image of the object is generated using transmission X-ray data on a predetermined slice thickness of the object to be imaged acquired by the helical scan. A slice thickness determination method for an X-ray CT apparatus, wherein a slice thickness is determined based on a moving distance D of a slice position per revolution of a helical scan and a number of frames F of tomographic image generation per revolution time of the helical scan. The slice thickness determination method is characterized in that T is determined by the following equation.
[0013]
Record
T ≧ D / F
(2) According to another aspect of the invention for solving the above-described problem, a tomographic image of the object is generated using transmission X-ray data of a predetermined slice thickness of the object to be imaged acquired by the helical scan. A slice thickness determination apparatus for an X-ray CT apparatus, wherein a slice thickness is determined based on a moving distance D of a slice position per revolution of a helical scan and a number of frames F of tomographic image generation per revolution time of the helical scan. A slice thickness determining device comprising slice thickness determining means for determining T by the following equation.
[0014]
Record
T ≧ D / F
(3) According to another aspect of the invention for solving the above-described problem, a tomographic image of the object is generated using transmission X-ray data of a predetermined slice thickness of the object to be imaged acquired by the helical scan. A program for causing a computer to realize a slice thickness determination function for an X-ray CT apparatus, which is a moving distance D of a slice position per one revolution of a helical scan and the number of frames F for generating a tomographic image per one revolution time of a helical scan. Is a program that causes a computer to realize the function of determining the slice thickness T by the following equation.
[0015]
Record
T ≧ D / F
(4) According to another aspect of the invention for solving the above problem, a tomographic image of the object is generated using transmission X-ray data of a predetermined slice thickness of the object to be imaged acquired by the helical scan. In the X-ray CT apparatus, the slice thickness T is determined by the following formula based on the moving distance D of the slice position per revolution of the helical scan and the number of frames F of tomographic image generation per revolution time of the helical scan. An X-ray CT apparatus comprising: a slice thickness determining means.
[0016]
Record
T ≧ D / F
(5) In another aspect of the invention for solving the above-described problem, an X-ray irradiation apparatus that irradiates a fan-shaped X-ray beam, and a plurality of X-ray detection elements are arranged to spread the fan-shaped X-ray beam. An X-ray irradiation / detection device having an X-ray detection device arranged in a direction and facing the X-ray irradiation device across the object to be imaged is rotated around the object to be imaged along a spiral trajectory. Transmission X-ray data acquisition means for acquiring transmission X-ray data for a predetermined slice thickness of the object; Tomographic image generation means for generating a tomographic image of the object using the transmission X-ray data; and X-ray irradiation The slice thickness T is determined by the following equation based on the moving distance D of the slice position per revolution of the detection device and the number of frames F of the tomographic image generation per revolution time of the X-ray irradiation / detection device. Slice thickness determination means An X-ray CT apparatus characterized by comprising a.
[0017]
Record
T ≧ D / F
An X-ray CT apparatus characterized by comprising:
[0018]
(6) In another aspect of the invention for solving the above-described problems, an X-ray irradiation apparatus that irradiates a fan-shaped X-ray beam, and a plurality of X-ray detection elements are arranged to spread the fan-shaped X-ray beam. An X-ray detection device having a plurality of detection element arrays arranged in the direction in the direction of the thickness of the fan-shaped X-ray beam and facing the X-ray irradiation device across the object to be imaged A transmission X-ray data acquisition means for acquiring transmission X-ray data for the object by rotating the X-ray irradiation / detection device around the object to be imaged along a spiral trajectory; and the object using the transmission X-ray data A tomographic image generating means for generating a tomographic image, a moving distance D of a slice position per rotation of the X-ray irradiation / detection device, and a frame for generating the tomographic image per rotation time of the X-ray irradiation / detection device Based on the number F, the slice thickness T is It is an X-ray CT apparatus characterized by comprising a slice thickness determining means for determining the serial equation.
[0019]
Record
T ≧ D / F
In the invention according to each aspect described in (1) to (6), based on the moving distance D of the slice position per revolution of the helical scan and the number of frames F of tomographic image generation per revolution time of the helical scan, Since the slice thickness T is determined by the equation T ≧ D / F, the slice thickness that matches the helical pitch can be determined regardless of the frame rate of the image reconstruction.
[0020]
It is preferable that the tomogram generation means includes a plurality of tomogram generation units that can operate in parallel in terms of speeding up tomogram generation.
It is preferable that the number of tomogram generation units is variable in terms of making the scale of the tomogram generation apparatus variable.
[0021]
It is preferable that the tomographic image generating means includes means for displaying a tomographic image in real time in that a scan site is diagnosed in real time.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiment. FIG. 1 shows a block diagram of an X-ray CT apparatus. This apparatus is an example of an embodiment of the present invention. An example of an embodiment relating to the apparatus of the present invention is shown by the configuration of the apparatus. An example of an embodiment related to the method of the present invention is shown by the operation of the apparatus.
[0023]
As shown in FIG. 1, the apparatus includes a scanning gantry 2, an imaging table 4, and an operation console 6. The scanning gantry 2 has an X-ray tube 20. X-rays (not shown) radiated from the X-ray tube 20 are shaped by the collimator 22 into, for example, a fan-shaped X-ray beam, that is, a fan beam, and irradiated to the X-ray detector 24. The portion composed of the X-ray tube 20 and the collimator 22 is an example of an embodiment of the X-ray irradiation apparatus in the present invention.
[0024]
The X-ray detector 24 has a plurality of detection elements arranged in an array in the direction of expansion of the fan-shaped X-ray beam. The X-ray detector 24 is an example of an embodiment of an X-ray detection apparatus according to the present invention. The configuration of the X-ray detector 24 will be described later.
[0025]
The X-ray tube 20, the collimator 22, and the X-ray detector 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device is an example of an embodiment of the X-ray irradiation / detection device according to the present invention. The X-ray irradiation / detection apparatus will be described later.
[0026]
A data collection unit 26 is connected to the X-ray detector 24. The data collection unit 26 collects detection signals of individual detection elements of the X-ray detector 24 as digital data.
[0027]
X-ray irradiation from the X-ray tube 20 is controlled by an X-ray controller 28. The connection relationship between the X-ray tube 20 and the X-ray controller 28 is not shown. The collimator 22 is controlled by a collimator controller 30. The connection relationship between the collimator 22 and the collimator controller 30 is not shown.
[0028]
The components from the X-ray tube 20 to the collimator controller 30 described above are mounted on the rotating unit 34 of the scanning gantry 2. The rotation of the rotating unit 34 is controlled by the rotation controller 36. The connection relationship between the rotating unit 34 and the rotation controller 36 is not shown.
[0029]
The imaging table 4 carries an imaging target (not shown) in and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the object and the X-ray irradiation space will be described later.
[0030]
The operation console 6 has a data processing device 60. The data processing device 60 is configured using, for example, a computer. A control interface (interface) 62 is connected to the data processing device 60. The control gantry 2 and the imaging table 4 are connected to the control interface 62. The data processing device 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62.
[0031]
The data acquisition unit 26, the X-ray controller 28, the collimator controller 30 and the rotation controller 36 in the scanning gantry 2 are controlled through the control interface 62. Note that illustration of individual connections between these units and the control interface 62 is omitted.
[0032]
A data collection buffer 64 is also connected to the data processing device 60. A data collection unit 26 of the scanning gantry 2 is connected to the data collection buffer 64. Data collected by the data collection unit 26 is input to the data processing device 60 through the data collection buffer 64.
[0033]
The data processing device 60 performs image reconstruction using transmission X-ray data of a plurality of views collected through the data collection buffer 64. For the image reconstruction, for example, a filtered back projection method or the like is used.
[0034]
The data processing device 60 includes a dedicated arithmetic unit (unit) that performs arithmetic operations for image reconstruction. That is, for example, as shown in FIG. 2, it has reconstitution units (reconstruction units) 612, 614, 616 that execute image reconstruction operations under the control of a computer 602. The recon unit 612 is always mounted, and the recon units 614 and 616 are mounted according to user options. The recon units 612, 614, and 616 are an example of an embodiment of a tomogram generation unit in the present invention.
[0035]
As the number of mounted recon units is increased as an option, the ability of image reconstruction is improved and the frame rate of the reconstructed image is increased by their parallel operation. Real-time recon is possible in the maximum mounting state.
[0036]
A storage device 66 is also connected to the data processing device 60. The storage device 66 stores various data, programs, and the like. When the data processing device 60 executes the program stored in the storage device 66, slice thickness determination and a reconstructed image, which will be described later, are performed.
[0037]
A display device 68 and an operation device 70 are also connected to the data processing device 60. The display device 68 displays the reconstructed image and other information output from the data processing device 60. The operation device 70 is operated by a user and inputs various instructions and information to the data processing device 60. The user operates the present apparatus interactively using the display device 68 and the operation device 70.
[0038]
FIG. 3 shows a schematic configuration of the X-ray detector 24. As shown in the figure, the X-ray detector 24 is a multi-channel X-ray detector in which a plurality of detection elements 24 (ik) are arranged in an array.
[0039]
The plurality of detection elements 24 (ik) as a whole form an X-ray incident surface curved in a cylindrical concave shape. i is a channel number, for example, i = 1 to 1000. k is a column number, for example, k = 1,2. The detection elements 24 (ik) each have the same column number k and constitute a detection element array. Note that the number of detection element rows of the X-ray detector 24 is not limited to two rows, but may be, for example, four rows or more as shown in FIG. 4, or one row as shown in FIG. It may be a thing.
[0040]
The detection element 24 (ik) is configured by a combination of, for example, a scintillator and a photodiode. However, the present invention is not limited to this. For example, a semiconductor detection element using cadmium tellurium (CdTe) or an ionization chamber type detection element using Xe gas (gas) may be used.
[0041]
FIG. 6 shows the interrelationship among the X-ray tube 20, the collimator 22, and the X-ray detector 24 in the X-ray irradiation / detection apparatus. 6A is a diagram showing a state seen from the front of the scanning gantry 2, and FIG. 6B is a diagram showing a state seen from the side. As shown in the figure, the X-rays radiated from the X-ray tube 20 are shaped by the collimator 22 into a fan-shaped X-ray beam 400 and irradiated to the X-ray detector 24.
[0042]
FIG. 6A shows the spread of the fan-shaped X-ray beam 400. The spreading direction of the X-ray beam 400 coincides with the channel arrangement direction in the X-ray detector 24. In (b), the thickness of the X-ray beam 400 is shown. The thickness direction of the X-ray beam 400 coincides with the direction in which a plurality of detection element rows are arranged in the X-ray detector 24.
[0043]
With the body axis intersecting the fan surface of the X-ray beam 400, the object 100 placed on the imaging table 4 is carried into the X-ray irradiation space, for example, as shown in FIG. The scanning gantry 2 has a cylindrical structure including an X-ray irradiation / detection device inside.
[0044]
The X-ray irradiation space is formed in the inner space of the cylindrical structure of the scanning gantry 2. An image of the object 100 sliced by the X-ray beam 400 is projected onto the X-ray detector 24. X-rays transmitted through the object 100 are detected by the X-ray detector 24. The thickness th of the X-ray beam 400 applied to the object 100 is adjusted by the aperture of the collimator 22.
[0045]
The X-ray irradiation / detection device including the X-ray tube 20, the collimator 22, and the X-ray detector 24 continuously rotates (scans) around the body axis of the object 100 while maintaining their mutual relationship. In parallel with the rotation of the X-ray irradiation / detection device, the imaging table 4 is continuously moved in the body axis direction of the object 100 as indicated by an arrow 42. As a result, the X-ray irradiation / detection apparatus turns relative to the target 100 along a spiral trajectory surrounding the target 100, and so-called helical scanning is performed.
[0046]
Projection data of a plurality of views (for example, about 1000) per rotation of the helical scan is collected. Projection data is collected by the system of X-ray detector 24 -data collection unit 26 -data collection buffer 64. Hereinafter, the projection data is also referred to as view data.
[0047]
When the detection element rows of the X-ray detector 24 are two rows, data for two slices are collected all at once as shown in FIG. As shown in the figure, when the distance between the centers of the two slices is d and the movement distance in the body axis direction of the X-ray irradiation / detection device per revolution of the helical scan is L, L / d is This is called helical scan pitch.
[0048]
When the pitch is 1, the movement distance L per turn is equal to the slice center distance d. The distance d between the slice centers is equal to the slice thickness. When a helical scan of pitch 1 is performed, the detection element array on the rear side in the traveling direction follows the spiral trajectory followed by the detection element array on the front side one delay behind.
[0049]
The situation is shown in FIG. 9 by a diagram. In the diagram of the figure, the horizontal axis is the distance in the body axis direction, and the vertical axis is the number of turns. The view angle is also shown on the vertical axis. The origin of the coordinates of each axis is the initial position of the rear detection element array. The initial position of the front detection element array is at a distance d from the origin in the body axis direction. In addition, the position of each detection element row | line | column is represented by each slice center position.
[0050]
As shown in Diagram A of the figure, the detection element array on the front side moves from d to 2d in the first turn, that is, from the view angle 0 ° to 360 °, and from the second turn, that is, from the view angle 360 °. It moves from 2d to 3d by turning up to 720 °, and then moves by distance d for each turn.
[0051]
On the other hand, as shown in Diagram B, the rear detection element array moves from the origin to d in the first turn (0 ° to 360 °) and in the second turn (360 ° to 720 °). Move from d to 2d, and then move by distance d for each turn.
[0052]
The projection data obtained by such a turn has different slice positions on the body axis for each view. That is, as shown in Diagram A, in the front detection element array, projection data from a view angle of 0 ° to 360 °, that is, projection data for one scan becomes projection data at each slice position from a distance d to 2d. . In the rear detection element array, as shown in diagram B, projection data for one scan is projection data at each slice position from distance 0 to d. All the projection data are projection data for slices having a thickness d.
[0053]
FIG. 10 shows a diagram when there are four detection element rows. In the figure, diagrams A, B, C, and D are diagrams of the first, second, third, and fourth detection element arrays from the front, respectively. These diagrams also represent the respective view data. The view data is view data for a slice having a thickness d.
[0054]
When there are five or more detection element rows, there are five or more similar diagrams. When there are two detection element rows, for example, only diagrams C and D are used, and when there are only one detection device row, for example, only diagram D is provided.
[0055]
The pitch of the helical scan is 3. As a result, as shown in Diagram A, the first detection element array moves from 3d to 6d in the first scan, and thereafter moves by a distance of 3d for each scan. As shown in Diagram B, the second detector element array moves from 2d to 5d in the first scan, and thereafter moves by a distance of 3d for each scan. As shown in Diagram C, the third detection element array moves from d to 4d in the first scan, and thereafter moves by a distance of 3d for each scan. As shown in Diagram D, the fourth detection element array moves from the origin to 3d in the first scan, and thereafter moves by a distance of 3d for each scan.
[0056]
In the present embodiment example, a half reconstruction technique is used for image reconstruction. The half-recon technique is a technique in which image reconstruction is performed using view data in an angle range of 180 ° by a parallel X-ray beam, and is well known in the technical field of X-ray CT apparatuses.
[0057]
When fan beam X-rays are used for view data collection, image reconstruction is performed using view data in an angle range obtained by adding a fan angle to 180 °. Therefore, if the fan angle is 60 °, for example, view data in an angle range of 240 ° is used.
[0058]
As view data having an angle range of 240 °, for example, view data having an angle range of 0 ° to 240 ° can be extracted. By reconstructing an image using the view data in the angle range in the view data indicated by the diagram D, a tomographic image at the slice position d is obtained. The slice thickness of this tomographic image is d.
[0059]
As view data having an angle range of 240 °, view data having an angle range of 120 ° to 360 ° can also be extracted. By reconstructing an image using the view data in the angle range in the view data indicated by the diagram D, a tomographic image at the slice position 2d is obtained. The slice thickness of this tomogram is also d.
This tomographic image is a tomographic image adjacent to the tomographic image at the slice position d.
[0060]
As view data having an angle range of 240 °, view data having an angle range of 240 ° to 480 ° can also be extracted. By reconstructing an image using the view data in this angle range in the view data indicated by the diagram D, a tomographic image at the slice position 3d is obtained. The slice thickness of this tomogram is also d.
This tomographic image becomes a tomographic image adjacent to the tomographic image at the slice position 2d.
[0061]
In the same manner, tomographic images at slice positions 4d, 5d, 6d,... Can be sequentially obtained by performing image reconstruction using view data in an angle range of 240 ° that is sequentially shifted by 120 °. it can. All are tomographic images having a slice thickness d, whereby a plurality of continuous tomographic images can be obtained without gaps between slices, that is, gapless. The same applies to the view data of diagrams C, B, and A. However, the slice position of the tomographic image sequentially differs by the distance d.
[0062]
The number of frames of the tomographic image obtained in this way is 3 frames per traveling distance 3d of the helical scan, as shown in FIG. Since the traveling distance 3d is the moving distance of the slice position per revolution of the helical scan, a tomographic image of 3 frames is obtained per revolution time of the helical scan. That is, the frame rate of the tomographic image is 3 frames / rotation.
[0063]
In other words, when the maximum image reconstruction capability of the data processing device 60 is 3 frames / rotation, the slice thickness of the tomographic image is set to d corresponding to the travel distance 3d per revolution of the helical scan. Thus, tomographic images of a plurality of slices continuous in a gapless manner can be obtained.
[0064]
The frame rate of image reconstruction by the data processing device 60 can be changed as appropriate within the range of the maximum capacity of 3 frames / rotation. That is, for example, 1.5, 1.0, 0.75, and the like can be set. Corresponding to such a frame rate, the slice thicknesses for obtaining a plurality of gapless continuous tomographic images are 2d, 3d and 4d, respectively.
[0065]
A tomogram of slice thickness 2d is reconstructed using data obtained by adding the view data of diagrams D and C, or data obtained by adding the view data of diagrams B and A. A tomographic image having a slice thickness of 3d is reconstructed using data obtained by adding view data of diagrams D, C and B, or data obtained by adding view data of diagrams C, B and A. A tomogram having a slice thickness of 4d is reconstructed using data obtained by fully adding the view data of diagrams D to A.
[0066]
The pitch of the helical scan can be 6. In this case, as shown in FIG. 11, the first detection element array moves from 3d to 9d in the first scan as shown by diagram A, and thereafter moves by a distance of 6d for each scan. As shown in Diagram B, the second detection element array moves from 2d to 8d in the first scan, and thereafter moves by a distance of 6d for each scan. As shown in Diagram C, the third detection element array moves from d to 7d in the first scan, and then moves by a distance 6d for each scan. As shown in Diagram D, the fourth detection element array moves from the origin to 6d in the first scan, and then moves by a distance 6d for each scan.
[0067]
When there are five or more detection element rows, there are five or more similar diagrams. When there are two detection element rows, for example, only diagrams C and D are used, and when there are only one detection device row, for example, only diagram D is provided.
[0068]
A tomographic image at the slice position 2d is obtained by reconstructing an image by half reconversion using view data in an angle range of 0 ° to 240 ° in the view data indicated by the diagram D. The slice thickness of this tomographic image is d.
[0069]
A tomographic image at the slice position 3d is obtained by reconstructing an image by half reconstitution using view data in an angle range of 60 ° to 300 ° in the view data indicated by the diagram D. The slice thickness of this tomogram is also d. This tomographic image becomes a tomographic image adjacent to the tomographic image at the slice position 2d.
[0070]
A tomographic image at the slice position 4d is obtained by reconstructing an image by half reconstitution using view data having an angle range of 120 ° to 360 ° in the view data indicated by the diagram D. The slice thickness of this tomogram is also d. This tomographic image is a tomographic image adjacent to the tomographic image at the slice position 3d.
[0071]
In the same manner, by performing image reconstruction using view data in an angle range of 240 ° that is sequentially shifted by 60 °, tomographic images at slice positions 5d, 6d, 7d,. it can. All are tomographic images having a slice thickness d, whereby a plurality of tomographic images that are continuous without gaps can be obtained. The same applies to the view data of diagrams C, B, and A. However, the slice position of the tomographic image sequentially differs by the distance d.
[0072]
The number of frames of the tomographic image obtained in this way is 6 frames per traveling distance 6d of the helical scan, as shown in FIG. Since the traveling distance 6d is the moving distance of the slice position per revolution of the helical scan, a tomographic image of 6 frames is obtained per revolution time of the helical scan. That is, the frame rate of the tomographic image is 6 frames / rotation.
[0073]
Conversely, when the maximum image reconstruction capability of the data processing device 60 is 6 frames / rotation, the slice thickness of the tomographic image is set to d corresponding to the travel distance 6d per revolution of the helical scan. Thus, tomographic images of a plurality of slices continuous in a gapless manner can be obtained.
[0074]
The frame rate of image reconstruction by the data processing device 60 can be changed as appropriate within the range of the maximum capacity of 6 frames / rotation. That is, for example, 3.0, 2.0 and 1.5 can be set. Corresponding to such a frame rate, the slice thicknesses for obtaining a plurality of gapless continuous tomographic images are 2d, 3d and 4d, respectively.
[0075]
A tomogram of slice thickness 2d is reconstructed using data obtained by adding the view data of diagrams D and C, or data obtained by adding the view data of diagrams B and A. A tomographic image having a slice thickness of 3d is reconstructed using data obtained by adding view data of diagrams D, C and B, or data obtained by adding view data of diagrams C, B and A. A tomogram having a slice thickness of 4d is reconstructed using data obtained by fully adding the view data of diagrams D to A.
[0076]
To generalize the above, when the maximum capability of image reconstruction is F frame / rotation, the slice thickness T of the tomographic image is determined by the following equation corresponding to the moving distance D of the slice position per revolution of the helical scan. By doing so, a plurality of continuous tomographic images can be obtained without gaps.
[0077]
T = D / F (1)
Since the gapless state can be maintained if the slice thickness is equal to or greater than (1) a given value, the equation for determining the slice thickness may be the following equation.
[0078]
T ≧ D / F (2)
In this manner, since an appropriate slice thickness is determined in accordance with the frame rate of image reconstruction and the travel distance per revolution of the helical scan, the number of recon units mounted in the data processing device 60 is reduced to reduce the frame of image reconstruction. Even when the rate is lowered, tomographic images of a plurality of slices continuous in a gapless manner can be obtained.
[0079]
Conversely, for users who do not require real-time recon, it is possible to provide an X-ray CT apparatus with a reduced price by reducing the number of recon units mounted. Although such an X-ray CT apparatus has a low frame rate for image reconstruction, gapless multi-slice imaging is possible, and there is no inconvenience in use.
[0080]
The operation of this apparatus will be described. FIG. 12 shows a flow chart of the operation of this apparatus. As shown in the figure, in step 902, the user sets scan conditions. Thereby, the tube voltage / tube current, scan time, scan pitch, scan range, etc. of the X-ray tube are set.
[0081]
The scan time is the time required for one turn of the helical scan. The scan speed is determined by setting the scan time. The scan pitch is a helical scan pitch. Thus, the slice position moving distance per turn is determined.
[0082]
If the frame rate of image reconstruction is adjustable within the range of the maximum capacity of the data processing device 60, the frame rate may be set here. When the frame rate is not particularly set, the frame rate at the maximum capability of image reconstruction is automatically set as a default value.
[0083]
Next, in step 904, the slice thickness is determined by the data processing device 60. The slice thickness is determined using the above-described equation (1) or (2) based on the scan pitch and frame rate set as described above. The data processing device 60 is an example of an embodiment of slice thickness determining means in the present invention.
[0084]
Next, in step 906, a helical scan is performed. Thereby, the object 100 is continuously scanned over a predetermined range in the body axis direction, and, for example, four systems of projection data corresponding to four detection element arrays are acquired. The part consisting of the scanning gantry 2 and the imaging table 4 related to the data acquisition by the helical scan is an example of the embodiment of the transmission X-ray data acquisition means in the present invention.
[0085]
Next, in step 908, image reconstruction is performed by the data processing device 60. Image reconstruction is performed by half recon. In this case, the slice thickness of the tomographic image is the slice thickness determined in step 904. Thereby, tomographic images of a plurality of slices continuous in a gapless manner can be obtained in real time.
[0086]
Next, in step 910, the tomographic image is displayed on the display device 68 in real time almost simultaneously with the scan and used for diagnosis and the like, and stored in the storage device 66. The portion composed of the data processing device 60 and the display device 68 is an example of an embodiment of tomographic image generation means in the present invention.
[0087]
A program that causes a computer to realize the function of determining the slice thickness as described above is recorded on a recording medium so as to be readable by the computer. As the recording medium, for example, a magnetic recording medium, an optical recording medium, a magneto-optical recording medium, and other appropriate recording media are used. The recording medium may be a semiconductor storage medium. In this document, a storage medium is synonymous with a recording medium.
[0088]
【The invention's effect】
As described above in detail, according to the present invention, a method and apparatus for determining a slice thickness that matches a helical pitch regardless of the frame rate of image reconstruction, and such a slice thickness determination function is realized in a computer. And an X-ray CT apparatus equipped with such a slice thickness determination apparatus can be realized. Furthermore, a tomographic image can be displayed in real time.
[Brief description of the drawings]
FIG. 1 is a block diagram of an exemplary apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram of a data processing apparatus.
FIG. 3 is a schematic diagram of an X-ray detector.
FIG. 4 is a schematic diagram of an X-ray detector.
FIG. 5 is a schematic diagram of an X-ray detector.
FIG. 6 is a schematic diagram of an X-ray irradiation / detection apparatus.
FIG. 7 is a schematic diagram of an X-ray irradiation / detection apparatus.
FIG. 8 is a schematic diagram of an X-ray irradiation / detection apparatus.
FIG. 9 is a diagram showing a trajectory diagram of a plurality of detection element arrays in a helical scan.
FIG. 10 is a diagram showing a trajectory diagram of a plurality of detection element arrays in a helical scan.
FIG. 11 is a diagram illustrating a trajectory diagram of a plurality of detection element arrays in a helical scan.
FIG. 12 is a flowchart of the operation of the apparatus according to the example of the embodiment of the present invention.
[Explanation of symbols]
2 Scanning gantry
20 X-ray tube
22 Collimator
24 X-ray detector
26 Data collection unit
28 X-ray controller
30 Collimator controller
34 Rotating part
36 rotation controller
4 Shooting table
6 Operation console
60 Data processing device
602 computer
612-616 Recon unit
62 Control interface
64 Data collection buffer
66 Storage device
68 display devices
70 Operating device
100 target
400 X-ray beam

Claims (9)

A slice thickness determination method for an X-ray CT apparatus for generating a tomographic image of an object using transmission X-ray data about a predetermined slice thickness of an object to be imaged acquired by a helical scan,
Based on the moving distance D of the slice position per revolution of the helical scan and the number of frames F of the tomographic image generation per revolution time of the helical scan, the slice thickness T is determined by the following equation:
A method for determining a slice thickness.
T ≧ D / F A slice thickness determination apparatus for an X-ray CT apparatus that generates a tomographic image of an object using transmission X-ray data on a predetermined slice thickness of an imaging target acquired by a helical scan,
Slice thickness determining means for determining the slice thickness T by the following formula based on the moving distance D of the slice position per revolution of the helical scan and the number F of frames of tomographic image generation per revolution time of the helical scan,
A slice thickness determining apparatus comprising:
T ≧ D / F A program that causes a computer to realize a slice thickness determination function for an X-ray CT apparatus that generates a tomographic image of the object using transmission X-ray data of a predetermined slice thickness of an object to be imaged acquired by a helical scan. And
A function of determining the slice thickness T by the following equation based on the moving distance D of the slice position per revolution of the helical scan and the number of frames F of tomographic image generation per revolution time of the helical scan;
A program characterized by causing a computer to realize.
T ≧ D / F An X-ray CT apparatus that generates a tomographic image of an object using transmission X-ray data on a predetermined slice thickness of an object to be imaged acquired by a helical scan,
Slice thickness determining means for determining the slice thickness T by the following formula based on the moving distance D of the slice position per revolution of the helical scan and the number F of frames of tomographic image generation per revolution time of the helical scan,
An X-ray CT apparatus comprising:
T ≧ D / F An X-ray irradiation apparatus that irradiates a fan-shaped X-ray beam, and a plurality of X-ray detection elements arranged in a direction in which the fan-shaped X-ray beam spreads, facing the X-ray irradiation apparatus with an object to be imaged interposed therebetween X-ray irradiation / detection device having an X-ray detection device for rotating transmission X-ray data about a predetermined slice thickness of the object by rotating the X-ray irradiation / detection device around the object to be imaged along a spiral trajectory Data acquisition means;
A tomographic image generation means for generating a tomographic image of the object using the transmitted X-ray data;
Based on the moving distance D of the slice position per turn of the X-ray irradiation / detection device and the number of frames F of the tomographic image generation per turn time of the X-ray irradiation / detection device, the slice thickness T is Slice thickness determining means determined by the equation;
An X-ray CT apparatus comprising:
T ≧ D / F
An X-ray CT apparatus comprising: An X-ray irradiation apparatus that irradiates a fan-shaped X-ray beam, and a detection element array in which a plurality of X-ray detection elements are arranged in a direction in which the fan-shaped X-ray beam spreads, An X-ray irradiation / detection device having a plurality of X-ray irradiation devices arranged in a direction and facing the X-ray irradiation device across the object to be imaged is arranged along a spiral trajectory around the object to be imaged. A transmission X-ray data acquisition means for rotating and acquiring transmission X-ray data for the object;
A tomographic image generation means for generating a tomographic image of the object using the transmitted X-ray data;
Based on the moving distance D of the slice position per turn of the X-ray irradiation / detection device and the number of frames F of the tomographic image generation per turn time of the X-ray irradiation / detection device, the slice thickness T is Slice thickness determining means determined by the equation;
An X-ray CT apparatus comprising:
T ≧ D / F The tomogram generation means includes a plurality of tomogram generation units operable in parallel.
The X-ray CT apparatus according to claim 5 or 6, characterized by the above. The number of tomographic image generation units is variable.
The X-ray CT apparatus according to claim 7. The tomographic image generating means includes means for displaying a tomographic image in real time,
The X-ray CT apparatus according to any one of claims 5 to 8, wherein the X-ray CT apparatus is characterized by that.

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