JP3827555B2 - Gantry apparatus, X-ray CT system, operation console and control method therefor, computer program, and computer-readable storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gantry device for an X-ray CT system, a system using the gantry device, a control method, a computer program, and a storage medium.
[0002]
[Prior art]
In an X-ray CT (Computerized Tomography) system and apparatus, a device having a donut-shaped cavity (generally called a gantry device) and a top plate on which a subject is placed are directed toward the cavity of the gantry device. A transport device called a table to be transported, an operation console that gives various control signals to the gantry device and the transport device, and reconstructs and displays an X-ray tomogram based on signals (data) obtained from the gantry device Consists of.
[0003]
The gantry apparatus has an X-ray generation source (X-ray tube) provided with a subject interposed therebetween and an X-ray detector for detecting X-rays, and these are fixed to a rotating body. When scanning, a signal (data) corresponding to the X-ray dose transmitted (attenuated) through the subject at different rotation angles is obtained by driving the X-ray tube and rotating the rotating body. obtain. The operation console receives this signal, calculates the X-ray attenuation rate in a minute part on the tomographic plane of the subject, and displays the calculated value as a pixel value (referred to as CT value). Create a visual image. This image is generally called an X-ray tomographic image, and the process of creating the X-ray tomographic image is called an X-ray tomographic image reconstruction process or simply reconstruction.
[0004]
[Problems to be solved by the invention]
FIG. 7 shows the relationship between an X-ray tube and an X-ray detector of a normal gantry apparatus. The direction perpendicular to the drawing is the Z axis.
[0005]
In the figure, reference numeral 1000 denotes an X-ray tube serving as an X-ray generation source. Reference numeral 1001 denotes an X-ray detector that detects X-rays from the X-ray tube 1000, and approximately 1000 detection elements (for 1000 channels) are uniformly arranged as shown in the figure. Reference numeral 1002 denotes a collimator that determines an irradiation angle (fan angle θ and irradiation thickness in the Z-axis direction) of the X-ray tube.
[0006]
As described above, the X-ray tube 1000 and the X-ray detector 1002 are fixed to the rotating body of the gantry apparatus and rotate in the direction of arrow A around the imaging region center point O shown in the figure. Therefore, the range 1003 through which X-rays pass at all rotation angles is an area in which an X-ray tomographic image can be reconstructed, that is, an imaging field of view (FOV = Field Of View).
[0007]
In general, the diameter of this FOV (field of view) 1003 in the medical X-ray CT system is set to about 50 cm in accordance with the human abdomen where the cross section of the patient as the subject is maximized. In other words, the X-ray detector 1001 needs to have a length sufficient to ensure an FOV (imaging field of view) 1003.
[0008]
However, the X-ray detector 1001 is an expensive part for determining the image quality because of its mechanical and electrical accuracy and structure, and it is difficult to reduce the cost.
[0009]
The present invention provides a gantry device for an X-ray CT system, a system using the same, a control method, a computer program, and a computer program that can make an X-ray detector more inexpensive while ensuring a minimum imaging field of view. A storage medium is to be provided.
[0010]
[Means for Solving the Problems]
In order to solve this problem, for example, the gantry apparatus for an X-ray CT system of the present invention has the following configuration. That is,
An X-ray detector composed of an X-ray tube and a plurality of X-ray detection elements for detecting X-rays from the X-ray tube is provided across a cavity for placing or passing a subject. A gantry apparatus in an X-ray CT system for rotating around,
By making a position shifted by at least one X-ray detection element width with respect to an extension line connecting the X-ray tube and the center of rotation of the cavity portion as a center position in the arrangement direction of the X-ray detection elements. X-ray detectors arranged asymmetrically such that the number of X-ray detection elements on the left and right of the extension line is N, M (M> N),
A first irradiation mode in which X-rays irradiated from the X-ray tube are irradiated over the entire length of the X-ray detector with X-rays having an equal width with respect to the subject transport direction; and the M detections The second width of the X-ray irradiated from the X-ray tube is made thinner than the other regions from the end of the region having the elements to the region having MN X-ray detection elements. And switching means for switching between the irradiation modes.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.
[0012]
<Description of system configuration>
First, the overall configuration of the X-ray CT system of the embodiment will be described, and then the features of the embodiment will be described.
[0013]
FIG. 1 is a block diagram of an X-ray CT system in the embodiment. As shown in the figure, the system includes a gantry device 100 for detecting X-ray irradiation to the subject and X-rays transmitted through the subject, and placing the subject and placing the subject against the cavity of the gantry device 100. An operation console that performs various operation settings for the transport apparatus 300 that transports the gantry apparatus 100 and the transport apparatus 300 and reconstructs and displays an X-ray tomogram based on data output from the gantry apparatus 100 200.
[0014]
The gantry apparatus 100 includes the following configuration including the gantry controller 1 that controls the entire system.
[0015]
2 is an interface for communicating with the operation console 200, 3 is a rotating body having a cavity for passing a subject (subject), and an X-ray tube which is an X-ray generation source inside 4 (driven and controlled by the X-ray tube controller 5), a collimator 6 having a slit for determining the X-ray irradiation width is provided. The collimator 6 operates in accordance with the motor 7 (driven by the motor controller 8), and details thereof will be described later.
[0016]
Further, the rotating body 3 includes an X-ray detection unit 9 including a plurality of detection elements that detect X-rays transmitted through the subject, and a data collection unit 10 that collects data obtained from the X-ray detection unit 9. Also equipped. The X-ray tube 4 and the X-ray detection unit 9 are provided at positions facing each other across the hollow portion, and are held by the rotating body 3 in a state where the relationship is maintained, and rotate along the arrow A shown in the figure. ing. This rotation operation is performed by the rotary motor 11 driven by a drive signal from the motor controller 12.
[0017]
Reference numeral 13 denotes a tilt motor for changing the tilt angle (tilt angle) of the gantry apparatus 100, and reference numeral 14 denotes a motor controller that supplies a drive signal to the tilt motor 12 under the control of the gantry controller 1. An operation panel 15 is provided with various switches such as a gantry tilt angle change switch and ON / OFF of a positioning light. Reference numeral 16 denotes a positioning light that irradiates the subject with an optical mark for positioning the subject.
[0018]
The X-ray detection unit 9 may have either one row or multiple rows of detection elements. In this connection, a system composed of one row of detection element groups is called a single slice X-ray CT system, and a multi-row case is called a multi-slice X-ray CT system. In the embodiment, in order to simplify the description, a single-slice X-ray CT system having one row of detection elements will be described.
[0019]
The gantry controller 1 of the gantry apparatus 100 analyzes various commands received via the I / F 2 and outputs various control signals to the X-ray tube controller 5 and the motor controller 12 based on the analysis. . The gantry controller 1 also performs processing for sending the data collected by the data collection unit 10 to the operation console 200 via the I / F 2.
[0020]
On the other hand, the transport apparatus 300 includes the following configuration including the table controller 21.
[0021]
Reference numeral 22 denotes an operation panel including an instruction switch for instructing raising and lowering of the transfer device 300, a switch for instructing movement of the top plate, and the like. 23 denotes a height of the top plate and a cavity portion of the gantry device 100 of the top plate. It consists of a sensor group that detects the amount of extension. Reference numeral 24 denotes a motor for changing the height of the apparatus including the top plate, and reference numeral 25 denotes a motor controller that applies a drive signal under the control of the table controller 21. Reference numeral 26 denotes a top plate on which the subject is placed. The material is easy to transmit X-rays and has a strength to maintain the state on which the subject is placed. Therefore, a foam material such as acrylic is used as CFRP (Carbon Fiber Reinforced). Reinforced with plastics). Reference numeral 27 denotes a motor that carries the top plate 26 in the Z-axis direction, and 28 denotes a motor controller that applies a drive signal to the motor 27. Reference numeral 29 denotes an interface for connecting to the operation console.
[0022]
In the above configuration, the table controller 21 of the transport apparatus 300 controls the transport of the top plate 26 in the Z-axis direction in accordance with an instruction from the operation panel 22 or an instruction from the operation console 200. Further, in accordance with an instruction from the operation panel 22, the apparatus itself is moved up and down, that is, the table 26 is moved up and down.
[0023]
Next, the operation console 200 will be described. The operation console 200 is a so-called workstation. As shown in the figure, the operation console 200 includes a CPU 51 that controls the entire apparatus, a ROM 52 that stores a boot program and a BIOS, and a RAM 53 that functions as a main storage device. .
[0024]
The HDD 54 is a hard disk device, in which a control program for giving various instructions to the OS and the gantry apparatus 100 and for reconstructing an X-ray tomogram based on data received from the gantry apparatus 100 is stored. .
[0025]
The VRAM 55 is a memory for developing image data to be displayed, and can be displayed on the CRT 56 by developing the image data or the like here. Reference numerals 57 and 58 denote a keyboard and a mouse for performing various settings. Reference numeral 59 denotes an interface for communicating with the gantry apparatus 100.
[0026]
<Description of collimator structure>
The structure and operation of the collimator 6 in the embodiment will be described with reference to FIG.
[0027]
FIG. 2A is a top view of the collimator 6 viewed from the X-ray tube 4 side. The collimator 6 includes X-ray shielding plates (mainly composed of lead, tungsten, etc.) 6a, 6b that define the fan angle, and slit plates 6e, 6f (mainly lead, tungsten, etc.) that define the irradiation width in the Z-axis direction. Composed of). The slits of the slit plates 6e and 6f have a width H ₀ And H ₁ (<H ₀ ) And their boundaries are slanted as shown.
[0028]
In addition, a linear gear 6d that is fed with a gear 7a that is pivotally supported on the rotating shaft of the motor 7 is provided on one side of the end portion of the slit plate 6e, and the motor 7 is driven to rotate the gear 7a. The plates 6e and 6f are moved along the arrow B shown in the figure.
[0029]
Therefore, the state shown in FIG. 2A can be shifted to the state shown in FIG.
[0030]
In the embodiment, in order to adjust the slice thickness, the thickness can be adjusted by the link mechanism of the slit plates 6e and 6f and the connecting rods 6h and 6g. Further, in multi-slice X-ray CT of a plurality of rows of X-ray detectors, the X-ray can be irradiated to the detector with an appropriate X-ray width.
[0031]
Although details will be described later, in the embodiment, when the axial scan is performed, the collimator 6 is controlled to the states of FIGS. 2A and 2B, and when the helical scan is performed, the state of FIG. Will be controlled.
[0032]
The collimator 6 according to the present embodiment includes two X-ray shielding plates 6e and 6f that define an X-ray irradiation range in the Z-axis direction, and connecting rods 6g and 6h (the same length) for connecting the end portions thereof. ). Connection portions between the connecting rods 6g and 6h and the shielding plates 6e and 6f are pivotally supported so as to be rotatable with respect to each other. Only the illustrated shaft 6i is a rotating shaft of a further motor 70 (shown by a broken line because it is behind the X-ray shielding plate 6e) and is fixed to the connecting rod 6g. With this configuration, the shielding plates 6e and 6f can be kept parallel to each other. Further, since the shaft 6i of the connecting rod 6g serves as the rotating shaft of the motor 70, when the motor 70 is driven, the X-ray shielding plate 6f becomes an X-ray shielding plate as shown in FIG. 6e can be gradually approached while maintaining a parallel state.
[0033]
Further, as shown in the figure, the shielding plate 6e is provided with a substantially trapezoidal shielding piece 6e '. The drive shaft of the motor 8a is engaged with the end side 8 of the shielding plate 6e, and the direction of the arrow D in the figure (also the Z axis). Can be moved to. In other words, this 8, 8a ₁ The slice thickness is H ₀ Can change independently.
[0034]
Further, as shown in FIG. 2 (c), a further shielding piece 6e '' is fixed to the tip of the shielding piece 6e 'so as to be rotatable at the position a shown in the figure, and is attached to the gear 9 equidistant from the position a. By providing the mechanism of the meshing motor 9a (drive shaft thereof), the shielding piece 6e '' rotates around the point a or the virtual center. The slit width H of the collimator 6 is obtained by rotating the shielding piece 6e ″. ₁ To H ₀ Angle of inclination θ ₀ Can be controlled.
[0035]
Further, in FIG. 2, driving the motor 7 moves the X-ray shielding plates 6e and 6f to the left side in the drawing, and can cope with the helical scan as shown in FIG.
[0036]
According to the above configuration, it is necessary to add the motor 70 and the motors 8a and 9a in addition to FIG. 1 described in the embodiment. Further, the gantry controller 1 of the gantry apparatus 100 causes the motor 70 to drive the gantry controller 100 so that the irradiation range in the Z-axis direction can be defined in accordance with a set pitch at the time of helical scanning described later. become.
[0037]
As can be understood from the above description, when an X-ray tomographic image of an FOV (imaging field of view) 35 in FIG. 4 to be described later at the time of helical scanning is to be obtained, the internal FOV (imaging field of view) 34 is a half scan. In the region Q between the FOV (field of view) 34, an X-ray tomographic image is reconstructed with data by a full scan. Since the latter data requires a scan time slightly less than twice that of the former data, in order to make the slice thicknesses of the X-ray tomographic images of these two regions equal, H ₁ Is H ₀ About half the width of H ₁ H for each slice defined by ₀ Needs to be adjusted. Although the structure becomes complicated, as shown in FIG. ₀ , H ₁ Can be set independently.
[0038]
In the axial scan, while the rotating body 3 of the gantry apparatus 100 is rotated and X-rays are being exposed, the movement of the top plate 26 of the transport apparatus 300 (transport of the subject in the Z-axis direction) is stopped. In this scanning method, after the exposure is completed, the top plate 26 is moved to a predetermined position and stopped, and the exposure is performed again. In the helical scan, the movement of the top plate 26 of the transport apparatus 300 (transport of the subject) and the exposure by the rotation of the rotating body 3 of the gantry apparatus 100 are performed simultaneously, and the subject is spirally formed. Scanning method to scan.
[0039]
<Description of scan>
First, an axial scan in the structure of an X-ray detector in a normal X-ray CT system will be described.
[0040]
FIG. 3 shows the positional relationship between the rotating X-ray tube and the X-ray detector in the axial scan. In the figure, now the point P ₀ Assume that the X-ray tube is positioned (hereinafter referred to as an initial position). At this time, the range of the fan angle θ irradiated by the X-ray tube, that is, the point P ₁ ~ Point P ₂ Is irradiated with X-rays (which is also the length of the X-ray detector). From this position, it rotates around the origin O in the direction of the arrow A in the figure, and the point P ₁ When the X-ray tube is positioned (exactly on the extension line of the center O and point P), the initial position (point P ₀ P which is X-rays irradiated at the position of ₀ → P ₁ X-ray P in the opposite direction to ₁ → P ₀ Is obtained. And the X-ray tube is P ₂ X-ray P irradiated at the initial position ₀ → P ₂ X-ray P with opposite direction ₂ → P ₀ Is obtained.
[0041]
In other words, the X-ray tube is point P ₁ ~ Point P ₂ The initial position P of the X-ray tube ₀ This means that X-rays facing in all directions irradiated from can be detected. Therefore, the X-ray tube rotates at 180 ° + fan angle θ and the point P ₂ , X-ray transmission in all directions for the FOV (field of view) can be detected. ₂ X-ray tomographic image can be reconstructed at the stage located at (5). This reconstruction method is called half scan, and the method of reconstructing by rotating 360 ° is called full scan.
[0042]
The above is the axial scan by the structure of the normal X-ray CT system, but the structure of the X-ray detector 9 in this embodiment and the positional relationship with respect to the X-ray tube 4 are as shown in FIG.
[0043]
3 is different from FIG. 3 in that the X-ray detector 9 in the embodiment eliminates the X-ray detection element corresponding to the illustrated broken line portion 31 and is configured with a smaller number of detection elements. A point where the detection element is present at the opposite end of the reference numeral 33 (that is, the center of the X-ray detector 9 is shifted from the line connecting the X-ray tube 4 and the rotation center of the rotating body). . The amount of deviation needs to be equal to or greater than the length in the arrangement direction of at least one X-ray detection element, but actually, the amount of deviation is further shifted by a plurality of elements (details will be described later).
[0044]
According to this configuration, the X-ray tomographic image can be reconstructed in the central portion 32 (symmetrical portion) with respect to the FOV (imaging field of view) indicated by reference numeral 34 in the procedure described above. In other words, when the X-ray tube 4 is at the position shown in the drawing, is rotated in the A direction, and is positioned on the extended line of the line segment 36, the X of the subject existing in the FOV (imaging field of view) 34 is detected. The tomographic image can be reconstructed (however, as will be described later, it may be reconstructed using transmission X-ray data in the same direction (360-degree transmission X-ray data)).
[0045]
In the present embodiment, the FOV (imaging field of view) 34, that is, the diameter of the small imaging region is generally set to about 25 cm suitable for the head scan of the subject. That is, the detection element of the broken line portion 31 at one end exceeding the 25 cm photographing field is eliminated.
[0046]
On the other hand, the FOV (imaging field of view) 35 is larger than the FOV (imaging field of view) 34 (corresponding to the FOV (imaging field of view) in FIG. 3), but the end of the X-ray irradiated at the position of the X-ray tube 4 shown in FIG. Even if the X-ray tube 4 is located at the point P, it cannot be detected. That is, it cannot be reconstructed by half scan.
[0047]
Therefore, in order to obtain two pieces of data of the line segment 37, it is necessary to wait for the X-ray tube 4 to rotate once and return to the initial position again. That is, two coaxial X-ray transmission data (360-degree X-ray data) necessary for helical scan correction are obtained for the region Q outside the FOV (imaging field of view) 34 and inside the FOV (imaging field of view) 35. In order to obtain, it is necessary to scan twice in the region 33 of the X-ray detector 9 in FIG. When the rotation is 360 °, there is also facing data in the FOV (field of view) 34, and there is no facing data outside, but reconstruction is possible.
[0048]
Therefore, in the case of a scan for obtaining a tomographic image of the FOV 35 (mainly the abdomen of the subject), a set of identical paths is compared with the case of a scan for obtaining a tomographic image of the FOV 34 (mainly the head of the subject). However, as shown in FIG. 4, the same axial scan as before can be realized with the X-ray detector 9 composed of fewer detection elements. In other words, it can be said that a larger FOV can be secured when an X-ray detector configured with the same number of detection elements as in the prior art is used.
[0049]
In the projection data of FIG. 5, the horizontal axis represents the arrangement (channel) of the detection elements of the X-ray detector, and the vertical axis represents the relationship between data collection points (called views) for each rotation angle of the rotating body 3 of the gantry apparatus 100. Is shown. In the figure, the hatched portion 1 indicates the missing portion 31 in FIG. 4, and the X-ray tomogram in the FOV (imaging field of view) 34 indicates that half-scan reconstruction can be performed with data up to view i, and FOV (imaging field of view). For 35 (FOV34 (shooting field of view) and area Q), it is shown that the data of the rotated view is further utilized.
[0050]
The explanation of the axial scanning is as described above. However, as shown in FIG. ₀ P when in position ₀ → P ₁ X-rays heading to the X-ray tube 4 are detected. ₁ P when located in ₁ → P ₀ When the X-rays facing each other (180-degree opposed X-rays) are detected, the amount of rotation of the rotator 3 for obtaining one X-ray tomographic image can be reduced. Further, in the case where 180-degree opposed X-rays cannot be obtained, in order to obtain X-ray data after 360 degrees, a rotation amount twice that amount is required. The former scan is called a half scan, and the latter scan is called a full scan. The expression is also used in the following helical scan.
[0051]
Next, the helical scan will be described.
[0052]
In the helical scan, exposure by the X-ray tube 4 while the rotating body 3 of the gantry apparatus 100 is rotating and conveyance of the subject by the conveyance device 300 are performed simultaneously.
[0053]
First, in the helical scan, the FOV (imaging field of view) 34 in FIG. 4 can be realized by either a half scan or a full scan, as will be easily understood by those skilled in the art from the above description. Therefore, hereinafter, a helical scan for obtaining an X-ray tomographic image of the FOV (imaging field of view) 35 in FIG. 4 will be described.
[0054]
As described with reference to FIGS. 4 and 5, when an X-ray tomographic image of the FOV 35 is obtained, the rotator 3 needs to rotate more than when an X-ray tomographic image of the FOV 34 is obtained. That is, in order to obtain an X-ray tomographic image in the region B of the FOV 35, half scanning is not possible, but full scanning is only possible (in the case of FOV 34, either half scanning or full scanning is possible).
[0055]
On the other hand, in the case of the helical scan, the greater the elapsed time, the greater the amount of conveyance of the subject in the Z-axis direction, so that the slice thickness of the obtained X-ray tomographic image becomes thicker and is obtained as a result. The resolution of the tomographic image in the body axis direction (Z-axis direction) is low.
[0056]
Now, the half scan time for obtaining the X-ray tomographic image of FOV 34 is T ₀ (The time required from view 1 to view i in FIG. 5), the full scan time required to obtain the X-ray tomographic image of the FOV 35 is T ₁ (Time required from view 1 to view j) T ₀ <T ₁ It can be easily understood from the above explanation that this relationship exists. Therefore, when trying to obtain a helical scan of the abdomen of the subject and obtaining an X-ray tomographic image in the FOV 35, the resolution in the body axis direction is high in the FOV 34 inside thereof (data from view 1 to view i is obtained). On the contrary, the data necessary to reconstruct the X-ray tomographic image of the region Q outside the FOV 34 must be obtained over a long time, so the slice thickness is thick. As a result, there arises a problem that the resolution in the body axis direction is lowered.
[0057]
Therefore, in the present embodiment, the region Q between the FOV 35 and the FOV 34 is dealt with by scanning from the beginning so that the slice thickness becomes thin.
[0058]
FIG. 2C shows exactly the state of the collimator 6 in this helical scan. The width H at the slit of the collimator 6 in FIG. ₀ This part determines the width of the region 32 of the X-ray detector 9 shown in FIG. ₁ (= 1/2 · H ₀ The portion) is for determining the width of the region 33 in FIG.
[0059]
Further, the boundary between 32 and 33 of the X-ray detector 9 and the C position (the center position where the width gradually changes) in FIG. There is a reason why the change in width is not two steps but changes gradually (substantially linearly). In the X-ray CT system, an X-ray tomographic image is reconstructed arithmetically using transmitted X-ray data. Therefore, if the X-ray exposure dose differs discontinuously from a certain position, a false called an artifact is generated near the boundary. An image tends to occur on the reconstructed image. Further, in the helical scan, since the time difference in scanning is also the difference in Z-axis position, the resolution in the Z-axis direction is deteriorated by setting the slit shape of the collimator 6 to the state shown in FIG. 4 can be suppressed, and the slice thickness of the region Q in FIG.
[0060]
As described above, in the helical scan for obtaining the X-ray tomographic image of the FOV 35, the area Q in FIG. 4 is thin from the beginning with respect to the Z axis of the X-ray irradiated to the area 33 of the X-ray detector 9. Has been. When the X-ray tomographic image of the FOV 35 is reconstructed, the slice thickness of the region Q and the slice thickness of the FOV 34 inside the region Q are substantially equal to each other, and it becomes possible to prevent deterioration in resolution in the Z-axis direction. In addition, in the vicinity of the boundary between the regions 32 and 33 of the X-ray detector 9, the width of the irradiated X-ray in the Z-axis direction gradually changes, so that the occurrence of artifacts can be suppressed.
[0061]
<Description of control>
The processing procedure in the operation console 200 for performing the operation described above is as follows.
[0062]
Hereinafter, a description will be given with reference to the flowchart of FIG.
[0063]
First, in step S1, whether the scan is an axial scan or a helical scan is selected using the keyboard 57, the mouse 58, and the like.
[0064]
When the axial scan is selected, the process proceeds to step S2, and a command is issued to the gantry apparatus 100 so that the collimator 6 is in the axial scanning position (the state shown in FIG. 2A). When receiving this command, the gantry controller 1 of the gantry apparatus 100 outputs a control signal to the motor controller 8 to drive the motor 7 and move the slit plates 6e and 6f to the axial scanning position of FIG. It will be.
[0065]
Next, the process proceeds to step S3, and it is selected whether or not the site to be scanned is the head, that is, whether the FOV is the FOV 34 or FOV 35 in FIG.
[0066]
When the FOV 35 (mainly the abdomen, etc.) that is the size photographing field of view is selected, the process proceeds to step S4, and full scan (scan using the 360-degree view) is set. On the other hand, when a small imaging region such as the head, that is, FOV 34 is selected, the user is allowed to select either half or full scan.
[0067]
Thus, when the FOV is determined, an axial scan is performed in accordance with the determined content (step S6), reconstruction (step S7), display and print output (step S8) are performed.
[0068]
On the other hand, if the helical scan is selected in step S1, the process proceeds to step S9, and a command is sent to the gantry apparatus 100 so that the collimator 6 is in the helical scan position (the state shown in FIG. 2C). To emit. When receiving this command, the gantry controller 1 of the gantry apparatus 100 outputs a control signal to the motor controller 8 to drive the motor 7 and move the slit plates 6e and 6f to the helical scanning position of FIG. .
[0069]
Next, the process proceeds to step S10, and it is selected whether the part to be scanned is a small imaging area (head or the like) (whether it is FOV 34 or FOV 35).
[0070]
When the FOV 35, which is a large imaging region of the size imaging field of view (mainly the abdomen, etc.) is selected, the process proceeds to step S11, and setting is performed so as to be a fusion process of full scan and half scan. That is, since the FOV 35 is divided into the region Q and the FOV 34 as shown in FIG. 4, the region Q is set to be full scan and the FOV 34 is half scan. If it is determined that the scan target is the head, it is selected whether to perform full scan or half scan.
[0071]
In subsequent steps S13 to S15, the same processing as in steps S6 to S8 is performed.
[0072]
As described above, according to the present invention, while reducing the number of X-ray detection elements constituting the X-ray detector, the center position is connected to the center line connecting the X-ray tube and the rotation center of the gantry rotating body. By shifting from the FOV, it is possible to secure an FOV of the same size as before. Therefore, with respect to the X-ray CT system, in particular, the gantry apparatus, more specifically, the X-ray detector, the cost can be reduced with a smaller configuration.
[0073]
Also, the shape of the gantry collimator and its slice thickness H ₁ , H ₀ By controlling the above, it is possible to perform scanning suitable for each of the helical scan and the axial scan, and to reconstruct an X-ray tomographic image with excellent image quality for each.
[0074]
In the embodiment, as shown in FIG. ₀ , H ₁ However, if these two widths are stepped at right angles, the transmission X-ray data may be smoothed by calculation by weighted interpolation between them. The weighting process by calculation and the structure of FIG. 2 may be used in combination.
[0075]
In the embodiment, the slit shape for the axial scan and the slit shape for the helical scan are switched by moving one collimator 6, but two slits may be prepared and switched appropriately. Absent. Therefore, the present invention is not limited by the structure and operation related to switching shown in the above embodiment.
[0076]
Further, as in the above-described embodiment, in order to make both axial / helical functions, not only the structure of the gantry apparatus 100 but also the processing procedure in the operation console 200 needs to be adapted accordingly. The operation console 200 is based on the processing procedure of the CPU 51, and its function substantially depends on the program. Therefore, the present invention also includes a computer program, and a storage medium (floppy, CDROM, etc.) storing the program is naturally included in the category of the present invention in order to install the program in the computer. It is what
[0077]
In general, X-rays are irradiated to the center of the X-ray detection element of the X-ray detector on an extension line connecting the X-ray tube and the rotation center of the gantry apparatus rotating body. There is a technique in which the extension line passes through the position of w / 4 (or 3w / 4), where w is the width in the rolling direction of the detection element. This utilizes the fact that the position is 3w / 4 (or w / 4) when rotated 180 degrees, and substantially doubles the resolution of the X-ray detection element. When the present invention is applied to such a technique, the number of X-ray detection elements can be further halved, and the cost can be further reduced.
[0078]
【The invention's effect】
As described above, according to the present invention, it is possible to secure the same X-ray tomographic image calculation region as before, while reducing the number of X-ray detection elements of the X-ray detector included in the X-ray CT system. Become.
[Brief description of the drawings]
FIG. 1 is a block diagram of an X-ray CT system.
FIG. 2 is a diagram for explaining the structure and operation of a collimator in the embodiment.
FIG. 3 is a diagram illustrating a relationship between a scanning operation and FOV in a normal configuration.
FIG. 4 is a diagram illustrating a relationship between a scanning operation and FOV in the configuration of the embodiment.
FIG. 5 is a diagram illustrating a relationship between transmitted X-ray data (ch) and a view (angle) in the embodiment.
FIG. 6 is a flowchart showing an operation processing procedure of the operation console in the embodiment.
FIG. 7 is a diagram showing the relationship between an X-ray tube and an X-ray detector and FOV.

Claims (11)

An X-ray detector composed of an X-ray tube and a plurality of X-ray detection elements for detecting X-rays from the X-ray tube is provided across a cavity for placing or passing a subject. A gantry apparatus in an X-ray CT system for rotating around,
By making a position shifted by at least one X-ray detection element width with respect to an extension line connecting the X-ray tube and the center of rotation of the cavity portion as a center position in the arrangement direction of the X-ray detection elements. X-ray detectors arranged asymmetrically such that the number of X-ray detection elements on the left and right of the extension line is N, M (M> N),
A first irradiation mode in which X-rays irradiated from the X-ray tube are irradiated over the entire length of the X-ray detector with X-rays having an equal width with respect to the subject transport direction; and the M detections The second width of the X-ray irradiated from the X-ray tube is made thinner than the other regions from the end of the region having the elements to the region having MN X-ray detection elements. Switching means for switching between irradiation modes;
A gantry apparatus for use in an X-ray CT system. N is the number of detection elements that can reconstruct an X-ray tomogram of the subject's head, and M is the number of detection elements that can reconstruct an X-ray tomogram of the abdomen of the subject. The gantry apparatus in the X-ray CT system according to claim 1. In addition, an input means for inputting an instruction of axial scan or helical scan is provided,
The switching means switches to the first irradiation mode when an axial scan is instructed by the input means, and switches to the second irradiation mode when a helical scan is instructed. The gantry apparatus in the X-ray CT system according to Item 1. The switching means is means for controlling a collimator provided in the vicinity of the X-ray tube,
The collimator forms a slit for defining an X-ray irradiation range in the Z-axis direction, and the slit is composed of first and second regions, and the first region has a constant interval of H _0. And the second region is a region that becomes H ₁ smaller than H ₀ ,
The control means includes
In the case of the first irradiation mode, the irradiation range of the X-ray tube is defined by the first region,
In the case of the second irradiation mode, the boundary between the first region and the second region is located at the position corresponding to the MNth end from the end of the region having the M detection elements. The gantry apparatus in the X-ray CT system according to claim 1, wherein the gantry is controlled as follows. 5. The gantry apparatus for an X-ray CT system according to claim 4, wherein a boundary portion between the first region and the second region has a shape in which the interval gradually changes. 6. The gantry in the X-ray CT system according to claim 4, further comprising changing means for changing a slit interval between the first and second regions of the collimator. apparatus. An X-ray CT system comprising the gantry apparatus according to any one of claims 1 to 6. An X connected to the gantry apparatus according to claim 1 for controlling the gantry apparatus and reconstructing an X-ray tomographic image based on transmission X-ray data obtained by the X-ray detector of the gantry apparatus. An operation console in a line CT system,
A first selection means for selecting whether to perform an axial scan or a helical scan;
Second selection means for selecting whether or not to scan a small imaging region of the subject;
When an axial scan is selected by the first selection unit, an instruction to switch to the first irradiation mode is output to the switching unit of the gantry apparatus, and when a helical scan is selected Instruction information output means for outputting an instruction to switch to the second irradiation mode;
When a small imaging region is selected as a scan target by the second selection unit, an X-ray tomographic image is obtained by using transmitted X-ray data that are 180 degrees opposite to each other and the N X-ray detection elements sandwiching the extension line. First setting means for setting either to reconstruct or to reconstruct an X-ray tomogram using 360-degree X-ray data in the same direction;
When an area other than the small imaging region is selected as a scan target by the second selection means and an axial scan is selected by the first selection means, the same X-ray detection element of the X-ray detector is set at 360 degrees. Second setting means for setting to reconstruct an X-ray tomographic image using X-ray data in a direction;
When an area other than the small imaging region is selected as a scan target by the second selection unit and a helical scan is selected by the first selection unit, an X-ray tomography by both N X-ray detection elements sandwiching the extension line An X-ray tomographic image is reconstructed using transmitted X-ray data facing 180 degrees for a small imaging area where the image can be reconstructed, and 360-degree X-ray data in the same direction is used for an area outside the small imaging area. And third setting means for setting so as to reconstruct the X-ray tomographic image,
An operation console in an X-ray CT system, wherein an X-ray tomographic image is reconstructed according to the setting content of any one of the first to third setting means. An X connected to the gantry apparatus according to claim 1 for controlling the gantry apparatus and reconstructing an X-ray tomographic image based on transmission X-ray data obtained by the X-ray detector of the gantry apparatus. A control method of an operation console in a line CT system,
A first selection step for selecting whether to perform an axial scan or a helical scan;
A second selection step for selecting whether or not to scan a small imaging region of the subject;
When an axial scan is selected in the first selection step, an instruction to switch to the first irradiation mode is output to the switching unit of the gantry apparatus, and when a helical scan is selected An instruction information output step for outputting an instruction to switch to the second irradiation mode;
When a small imaging region is selected as a scan target in the second selection step, an X-ray tomographic image is obtained by using transmitted X-ray data opposed to each other by 180 degrees by both N X-ray detection elements sandwiching the extension line. A first setting step for setting either to reconstruct or to reconstruct an X-ray tomographic image using 360-degree X-ray data in the same direction;
When an area other than the small imaging region is selected as a scan target in the second selection step and an axial scan is selected in the first selection step, the same X-ray detection element of the X-ray detector has 360 ° A second setting step for setting to reconstruct an X-ray tomographic image using X-ray data in a direction;
When an area other than the small imaging region is selected as a scan target in the second selection step and a helical scan is selected in the first selection step, an X-ray tomogram by both N X-ray detection elements sandwiching the extension line An X-ray tomographic image is reconstructed using transmitted X-ray data facing 180 degrees for a small imaging area where the image can be reconstructed, and 360-degree X-ray data in the same direction is used for an area outside the small imaging area. And a third setting step for setting to reconstruct an X-ray tomographic image,
A method for controlling an operation console in an X-ray CT system, wherein an X-ray tomographic image is reconstructed according to the setting contents of any one of the first to third setting steps. An X connected to the gantry apparatus according to claim 1 for controlling the gantry apparatus and reconstructing an X-ray tomographic image based on transmission X-ray data obtained by the X-ray detector of the gantry apparatus. A computer program for an operation console in a line CT system,
A program code of a first selection step for selecting whether to perform an axial scan or a helical scan;
A program code of a second selection step for selecting whether or not to scan a small imaging region of the subject;
When an axial scan is selected in the first selection step, an instruction to switch to the first irradiation mode is output to the switching unit of the gantry apparatus, and when a helical scan is selected , A program code of an instruction information output step for outputting an instruction to switch to the second irradiation mode,
When a small imaging region is selected as a scan target in the second selection step, an X-ray tomographic image is obtained by using transmitted X-ray data opposed to each other by 180 degrees by both N X-ray detection elements sandwiching the extension line. A program code of a first setting step for setting either to reconstruct or to reconstruct an X-ray tomogram using 360-degree X-ray data in the same direction;
When an area other than the small imaging region is selected as a scan target in the second selection step and an axial scan is selected in the first selection step, the same X-ray detection element of the X-ray detector has 360 ° A program code of a second setting step for setting to reconstruct an X-ray tomographic image using X-ray data in a direction;
When an area other than the small imaging region is selected as a scan target in the second selection step and a helical scan is selected in the first selection step, an X-ray tomogram by both N X-ray detection elements sandwiching the extension line An X-ray tomographic image is reconstructed using transmitted X-ray data facing 180 degrees for a small imaging area where the image can be reconstructed, and 360-degree X-ray data in the same direction is used for an area outside the small imaging area. And a program code for a third setting step for setting so as to reconstruct an X-ray tomogram. A computer-readable storage medium storing the computer program according to claim 10.

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