JP2002017715A - X-ray ct system, its control method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT system capable of reducing the useless exposure of a subject while ensuring required S/N and positive X-ray irradiation to a required X-ray detector, and to provide a control method and a storage medium. SOLUTION: An initial aperture width Wo for positively irradiating a detection array in use with the complete shadow of X-ray beams is determined on the basis of a set slice thickness, and an aperture width W is adjusted to Wo (step S102). Scanning is then started (step S104), and the X-ray detected dose Rn of an observed reference channel in a present slice position n is measured (step S105). In the case the X-ray detected dose of the observed reference channel is larger than the specified rate of the reference X-ray dose determined by a scanning condition (step S106), the present aperture width W is narrowed by a prescribed micro width ΔW (step S107).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray CT (Computerized Tomography) for obtaining an X-ray tomographic image of a subject by X-ray irradiation.
ograpy) system, and more particularly to an X-ray CT system capable of suppressing unnecessary exposure to a patient, a control method thereof, and a storage medium.

[0002]

2. Description of the Related Art Conventionally, a multi-slice X-ray CT system for performing imaging using a plurality of detector arrays has been known. The multi-slice X-ray CT system has an advantage that a plurality of X-ray tomographic images and / or an X-ray tomographic image having a desired slice thickness can be obtained by one scan.

In general, an X-ray CT apparatus is provided with an aperture between an X-ray tube, which is an X-ray source, and an object for defining an X-ray irradiation range on the object. The aperture forms a slit through which X-rays pass using a member made of an X-ray shielding material (such as lead or tungsten). In a multi-slice X-ray CT system, the width of this slit is adjusted according to a desired slice thickness.

The adjustment of the width of the slit has a great effect on the exposure dose of the patient (subject) and the image quality of the reconstructed X-ray tomographic image. If the width of the slit is increased more than necessary, useless exposure to the subject increases, although it does not contribute to improvement of the image quality of the reconstructed X-ray tomographic image. On the other hand, if the width of the slit is too narrow and the required X-ray detector is not irradiated with the X-ray beam, it causes degradation such as image blur and artifacts. Therefore, the width of the slit is adjusted based on the desired slice thickness so as to reliably irradiate the required X-ray detector with the main shadow of the X-ray beam.

[0005]

However, at present, when the width of the slit is adjusted based on the desired slice thickness so that all the X-ray detectors are reliably irradiated with the true shadow of the X-ray beam. However, there is a problem that unnecessary exposure to the subject is inevitable. Such unnecessary exposure to the subject must be avoided as much as possible. On the other hand, when the X-ray irradiation range is reduced as much as possible to avoid unnecessary exposure to the subject, the X-ray dose detected in the detection channel at the end of the X-ray detector is reduced, and the S / N is reduced. There is a risk of lowering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it has been found that unnecessary X-ray irradiation to an X-ray detector and necessary S / N are ensured while unnecessary exposure to a subject is ensured. It is an object of the present invention to provide an X-ray CT system, a control method thereof, and a storage medium capable of reducing the amount of noise.

[0007]

To achieve the above object, for example, an X-ray CT system according to the present invention has the following arrangement. That is, an X-ray CT system that performs imaging at a predetermined slice thickness using an X-ray source that generates X-rays and a plurality of rows of detector arrays arranged in a direction in which a subject is transported. An aperture having a slit for determining a slice thickness at the time of imaging, which defines an X-ray irradiation range in the transport direction to the detector array, and adjusting means for adjusting the width of the slit, comprising: A first adjusting means for adjusting the width of the slit to a first width based on a predetermined slice thickness, and an X-ray detection amount in a predetermined detection channel constituting the detector array, A second step of finely adjusting the width of the slit so as to have a predetermined ratio with respect to an X-ray detection amount for realizing imaging;
And adjusting means.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram of an X-ray CT system according to an embodiment. As shown in the figure, the system includes a gantry device 100 for irradiating a subject with X-rays and detecting X-rays transmitted through the subject, and various operation settings for the gantry device 100. An operation console 200 reconstructs and displays an X-ray tomographic image based on the output data.

The gantry apparatus 100 has the following configuration, including the main controller 1 that controls the entire system.

Reference numeral 2 denotes an interface for communicating with the operation console 200. Reference numeral 3 denotes a gantry having a hollow portion for transporting a subject lying on the table 12 (in a direction perpendicular to the drawing). Is an X-ray tube 4 (controlled by an X-ray tube controller 5) as an X-ray source, an aperture 6 for forming a slit for defining an X-ray irradiation range, and an opening width of the formed slit. A motor 7a for adjustment is provided. This motor 7
The driving of a is controlled by the aperture controller 7.

The gantry 3 also includes an X-ray detector 8 for detecting X-rays transmitted through the subject, and a data collector 9 for collecting data obtained from the X-ray detector 8. X
The X-ray tube 4, the aperture 6, and the X-ray detector 8 are provided at positions opposing each other with a hollow portion therebetween, that is, with the subject interposed therebetween, and rotate around the gantry 3 in a state where the relationship is maintained. It works. This rotation is performed by a rotation motor 10 driven by a drive signal from a motor controller 11. The table 12 on which the subject is placed is transported in the Z-axis direction, and is driven by a table motor 13.

The main controller 1 analyzes various commands received via the interface 2 and, based on the analyzed commands, the X-ray tube controller 5, aperture controller 7, motor controller 11, table motor controller 14, and data collection unit. Various control signals are output to the unit 9. The main controller 1 also performs a process of transmitting the data collected by the data collection unit 9 to the operation console 200 via the interface 2.

The operation console 200 is a so-called workstation, and as shown, a CPU 51 for controlling the entire apparatus, a ROM 52 for storing a boot program and a BIOS, and an R functioning as a main storage.
The following configuration is provided, including the AM53.

The HDD 54 is a hard disk drive, which provides an OS, various instructions to the gantry device 100, a diagnostic program for reconstructing an X-ray tomographic image based on data received from the gantry device 100, and a scan program. Control programs and the like are stored. VRA
M55 is a memory for expanding the image data to be displayed, and can be displayed on the CRT 56 by expanding the image data and the like here. 57 and 58
Are a keyboard and a mouse for performing various settings. An interface 59 communicates with the gantry device 100.

The configuration of the X-ray CT system in the embodiment is generally as described above. Next, the structure and operation of the X-ray tube 4, aperture 6, and X-ray detector 8 will be described with reference to FIGS. This will be described in more detail.

FIG. 2 is a diagram showing the main components of the X-ray tube 4, aperture 6, and X-ray detector 8. Although not shown, these components are supported on a predetermined base of the gantry device 3.

Referring to FIG. 1, an X-ray tube 4 includes a housing 41.
In addition, the structure has a built-in cathode sleeve 42 containing a focusing electrode and a filament, and a rotating target 43, and emits X-rays from a focal point f.

The X-ray detector 8 in the embodiment is
As shown in the figure, it is assumed that the detection arrays 81 to 88 are composed of eight columns. Of course, the invention is not limited by the size of the particular detection array. The cells 8r at one end or both ends of each detection array are configured such that an X-ray beam is directly incident without transmitting through the subject even when the subject is imaged, and is used as a reference channel.

The aperture 6 is made of a member made of an X-ray shielding material such as lead, and as shown in the figure, the X-ray radiated from the X-ray tube 4 in the Z-axis direction (in the direction D1 shown in the figure, the body axis of the subject). An aperture 6a (which will be described in detail later) that defines an X-ray irradiation range (corresponding to the direction) and an irradiation range (fan angle) between the aperture 6a and the X-ray tube 4 in the longitudinal direction of the X-ray detector 8 are defined. It comprises an aperture 6b which consists of two fixed shielding plates. With this arrangement, the slit 15 for defining the X-ray irradiation range is formed.

In the above configuration, the apertures 6a, 6b
The Z-axis of the slit 15 defined by
The width in the 1) direction (hereinafter simply referred to as an opening width) can be changed by causing the aperture 6a to perform a mechanical operation.
This operation is realized by the motor 7a, and its specific structure will be described with reference to FIG.

FIG. 3A is a top view of the aperture 6a (as viewed from the X-ray tube 4).

The aperture 6a includes two shielding plates 60, 6
1 and a parallel crank member 62 for connecting the ends thereof. The ends of the parallel crank member 62 and the ends of the shield plates 60 and 61 are respectively connected to a rotating shaft 63a,
63b is rotatably supported by the shaft to form a parallel link mechanism. This allows the shielding plates 60, 61 to remain parallel to each other. A rotation shaft 64 is provided at a central position of each crank of the parallel crank member 62, and the rotation shaft 64 is rotated by driving the motor 7a around this rotation shaft.

With this configuration, when the motor 7a is driven and the rotating shaft 64 is rotated clockwise, the shielding plates 60 and 61 are gradually spaced apart from each other while keeping their parallel as shown in FIG. Can be expanded. In this manner, the gap between the shielding plates 60 and 61 defines the opening width of the slit 15, and the width can be adjusted.

Hereinafter, the operation of controlling the opening width will be described in detail.

FIG. 4 is a flowchart showing a procedure for controlling the opening width in the embodiment. The operator starts the scan planning program on the operation console 200,
The scan plan is advanced according to the scan condition input screen displayed on the CRT 56 (step S101). In this operation, the operator sets various scanning conditions such as a slice position, a slice thickness, an X-ray tube current value, and the like. The set scan conditions are stored in the RAM 53.

When the scan conditions are set, step S
Proceeds to 102 to determine the initial opening width W ₀ for umbra of the X-ray beam to the detector array (determined by the slice thickness is set) to be used is surely irradiated, the opening width by driving the motor 7a It is adjusted to W ₀ (first control).

Here, an example is shown. FIG. 5A is a sectional view taken along line AA of FIG. In the drawing, reference numerals 81a to 88a denote cells of a certain channel of each of the detection arrays 81 to 88. The state shown in the figure is a case in which four hatched detection arrays 83 to 86 are used in accordance with the slice thickness set in step S101, and the detection arrays 83 to 86 are reliably irradiated with the true shadow of the X-ray beam. as it is, in step S102, and shows a state in which the opening width W is adjusted to W _0. However, in this state, the detection arrays other than the four-row detection arrays 83 to 86 to be used are irradiated with useless X-rays. Therefore, in the embodiment of the present invention, the irradiation range is minimized by the following control without affecting the X-ray irradiation to the detection array to be used.

At this time, the detection arrays 83 to 8 to be used
The reference channels (82r and / or 87r shown in the top view of the X-ray detector 8 in FIG. 3B) in the outer arrays 82 and / or 87 adjacent to the arrays 83 and 86 at both ends of FIG. It is used as a “reference channel of interest” in subsequent processing.

After the adjustment of the aperture width W in step S102, the reference X-ray dose of the target reference channel is set (step S103). This, for example, be possible to predict the amount of X-rays incident on the target reference based on the set scanning conditions, the X-ray detected amount predicted here, a reference X-ray dose R _p. Thereafter, the scan is started in response to a scan start command from the operator (step S104).

Then, the X-ray detection amount Rn of the target reference channel at the current slice position _n is measured (step S105). Next, whether the value of R _n / R _p is larger than a predetermined value T ₁ (for example, 0.9), that is, whether the X-ray detection amount of the reference channel of interest is larger than 90% of the reference X-ray dose, Is determined (step S106). Here, if yes, the process proceeds to step S107, and the current opening width W is reduced to a predetermined minute width Δw (for example, 0.2 mm).
And then proceed to step S110. If the decision result in the step S106 is no, a step S10
Proceed to 8. In step _S108, R n / value of _{R p} is a predetermined value _{T 2} (e.g., 0.6) or not greater than, that is, whether the X-ray detected amount of interest the reference channel is less than 60% of the reference X-ray dose Is determined. here,
If yes, the process proceeds to step S109, where the current opening width W is increased by a predetermined minute width Δw (for example, 0.2 mm), and then the process proceeds to step S110. In a normal state, the process does not proceed to step S109, but is for preventing overcontrol due to a rise in the X-ray tube temperature or the like. If the decision result in the step S108 is no, the process proceeds to a step S110.

Then, in step S110, it is determined whether or not to continue the scan. If the scan is to be continued, the process returns to step S105 to repeat the processing (of course, the z-axis position is updated to move the slice position). If not, the process ends.

By the above processing, the reference channel of interest
The X-ray detection amount of the channel is the standard X-ray dose R _pLess than 90% of
The aperture width is reduced until the
To secure the necessary X-ray beam irradiation range
The range can be reduced.

Further, in consideration of the movement of the focal point f due to the temperature change of the X-ray tube 4, in addition to the above processing, for example, every time the opening width of the slit is adjusted, the reference channels 82r, 87r at both ends are adjusted. It is preferable that the position of the aperture 6 can be controlled so that the X-ray detection amounts are equal.
By controlling the aperture position, it is possible to irradiate an X-ray beam with the center of the focal point f always at the center of the X-ray detector 8.

The state shown in FIG. 7A is a case where a relatively thick slice thickness is set in step S101 and all the hatched detection arrays 81 to 88 are used, and the detection arrays 81 to 88 are used. umbra of the X-ray beam shows a state in which the opening width W is adjusted to W ₀ to be reliably irradiated to 88. In this case, the endmost detection array 8
The reference channel (81r or 88r shown in the top view of the X-ray detector 8 in FIG. 2B) in one of the arrays 1 and 88 is used as a normal data acquisition channel and a reference channel of interest. It will also be used as a channel. Then, this target reference channel, as shown in FIG. 8, that it will not reference X-ray dose following X-ray dose by controlling the opening width as described above (e.g., 90% of the reference X-ray dose R _p) only incident In consideration of this, when the reference channel is used as normal data, it can be used after performing a correction for compensating for the reduced X-ray dose. According to another embodiment in which the reference channel can be shifted to the outside, for example, even if the X-ray dose in this portion is controlled to be 90%, the X-rays are actually 100% in the active channel actually used. % Can be geometrically arranged. When it is necessary to inspect the fluctuation of the X-ray intensity, another reference channel may be used.

As a result, as shown in FIG. 8, the required exposure range of the X-ray beam can be ensured while the exposure range can be reduced.

Next, means for further improving the accuracy of the above control operation will be described.

FIG. 9A is a sectional view taken along line BB of FIG. As shown in the drawing, each detection array of the X-ray detection unit 8 is formed in an arc shape centered on the focal point f so that the distance from the focal point f to the detection channel is equal in each detection array. Therefore, the center of the X-ray detector 8 is B,
Assuming that the end of the X-ray detector 8 is B ', fB = fB'.

On the other hand, since the aperture 6a has a linear shape as shown, the intersection of fB and the aperture 6a is represented by A, f.
Assuming that an intersection A ′ between B ′ and the aperture 6a is fA <f
A ′, AB> A′B ′. That is, the slit 15
X-rays that have passed through the X-ray detector 8
Reach different distances. Since the X-ray beam that has passed through the slit 15 naturally spreads radially, the longer the distance between the slit 15 and the detection surface on the detection surface of the X-ray detection unit 8, the larger the X-ray irradiation area. This is illustrated in FIG. FIG.
Is a top view of the slit 15 and the X-ray detection unit 8,
An area S is an X-ray irradiation area on the detection surface of the conventional X-ray detector 8. An area S ′ is an X-ray irradiation area on the detection surface after control by the above-described control operation.

As described above, although the X-ray irradiation area can be reduced by the above control operation, a useless X-ray irradiation area still remains. In addition, the amount of X-ray detection at the end of the X-ray detection unit 8 is reduced by this control operation.
It can also be said that the S / N has decreased.

Therefore, in the embodiment, as shown in FIG. 10, the shape of the aperture 6a is also formed in an arc shape centered on the focal point f. As a result, the arrival distance of the X-rays passing through the slit 15 to the X-ray detection unit 8 becomes equal irrespective of the passing position of the slit 15, and the detection surface of the X-ray detection unit 8 is uniformly irradiated with the X-rays. Will be. As a result, FIG.
The shape of the X-ray irradiation area S ′ shown in FIG.
, It is possible to substantially eliminate a useless irradiation area for the X-ray detection unit 8.

It is impossible to perform the parallel movement operation between the shield plates by the parallel link mechanism as shown in FIG. 3 with respect to the arc-shaped aperture 6a. Therefore, such parallel movement of the arc-shaped aperture 6a is as follows.
For example, this is realized by a linear motion mechanism using a linear slide as shown in FIG. FIG. 3A is a top view of the aperture 6a, and FIG. 3B is a cross-sectional view taken along line CC. Each of the shielding plates 60 and 61 is movably supported by a linear guide 71 along a linear motion rail 70. Thereby, the parallel movement operation of the shielding plates 60 and 61 is possible. In addition,
Although the illustration of the opposite end is omitted in this figure, the opposite side may be similarly provided with a linear motion rail so as to be driven (the same applies to FIGS. 12 and 13 described later).

As a control mechanism for the parallel movement operation, for example, a mechanism in which a ball screw is attached to a linear guide and the ball screw is driven by a motor 7a can be considered.
Specifically, as shown in FIG. 12, ball screws 72 are attached to the respective linear guides 71 in opposite directions, and are connected by couplings 73. With such a configuration, it is possible to perform the parallel movement operation with one motor.

As shown in FIG. 13, a link mechanism is constituted by a fixed link 74 attached to each linear guide 71 so as to be parallel to each other, and a crank 75 rotatably supported by a rotating shaft 76. And the drive may be controlled by the motor 7a with the rotation shaft 76 as a fulcrum.

Alternatively, although not shown, it is possible to directly control the position of the linear guide 71 using a linear motor.

[0046]

As described above, according to the present invention,
Reliable X-ray irradiation to required X-ray detector and required S
It is possible to provide an X-ray CT system, a control method thereof, and a storage medium capable of reducing unnecessary exposure to a subject while securing / N.

[Brief description of the drawings]

FIG. 1 is a block configuration diagram of an X-ray CT system according to an embodiment.

FIG. 2 is a main part configuration diagram of an X-ray tube 4, an aperture 6, and a detection unit 8.

FIG. 3 is a diagram for explaining the structure and operation of an aperture 6a according to the embodiment.

FIG. 4 is a flowchart illustrating a control procedure of an opening width of a slit in the embodiment.

FIG. 5 is a diagram for explaining an operation of controlling an opening width of a slit according to the embodiment.

FIG. 6 is a diagram for explaining an operation of controlling the opening width of the slit according to the embodiment.

FIG. 7 is a diagram for explaining a control operation of an opening width of a slit according to the embodiment.

FIG. 8 is a diagram for describing an operation of controlling the opening width of the slit according to the embodiment.

FIG. 9 is a diagram for explaining the state of X-ray irradiation according to the embodiment.

FIG. 10 is a diagram for explaining a structure of an aperture 6a according to the embodiment.

FIG. 11 is a diagram for explaining the operation of the aperture 6a.

FIG. 12 is a diagram for explaining the operation of the aperture 6a.

FIG. 13 is a diagram for explaining the operation of the aperture 6a.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Inoyama 4-7, Asahigaoka, Hino-shi, Tokyo 127 GE Yokogawa Medical Systems Co., Ltd. F-term (reference) 4C093 AA22 BA08 CA34 EA02 EA14 EB18 FA16 FA43 FA60

Claims (6)

[Claims] 1. An X-ray CT system for performing imaging at a predetermined slice thickness using an X-ray source for generating X-rays and a plurality of detector arrays arranged in a transport direction of a subject. An aperture having a slit for defining an X-ray irradiation range in the transport direction to the plurality of detector arrays and determining a slice thickness at the time of imaging, and an adjustment unit for adjusting a width of the slit, comprising: Adjusting means for adjusting the width of the slit to a first width based on a predetermined slice thickness; and detecting the amount of X-rays in a predetermined detection channel constituting the detector array by a predetermined slice. An X-ray CT system, comprising: a second adjusting means for finely adjusting the width of the slit so as to have a predetermined ratio with respect to an X-ray detection amount for realizing imaging at a thickness. 2. The X-ray CT according to claim 1, wherein the predetermined detection channel is a detection channel at a position where X-rays are directly incident on the subject without transmitting through the subject during imaging. system. 3. The X-ray CT system according to claim 1, wherein the aperture and the detector array are shaped along an arc centered on the X-ray source. 4. An X-ray source for generating X-rays, an aperture having a slit having a width corresponding to an irradiation range of the generated X-rays in the transport direction of the subject, and arranged in the transport direction of the subject. A method of controlling an X-ray CT system including a plurality of rows of detector arrays and performing imaging with a predetermined slice thickness, wherein a first width of the slit is adjusted to a first width based on a predetermined slice thickness. Adjusting step, the slit of the slit such that the X-ray detection amount in a predetermined detection channel constituting the detector array has a predetermined ratio to the X-ray detection amount for realizing imaging at a predetermined slice thickness. A second adjusting step of finely adjusting the width; and a control method of the X-ray CT system. 5. An X-ray source for generating X-rays, an aperture having a slit having a width corresponding to an irradiation range of the generated X-rays in a transport direction of the subject, and an X-ray source arranged in the transport direction of the subject. A storage medium comprising a plurality of rows of detector arrays and storing a program code for an X-ray CT system for performing imaging with a predetermined slice thickness, wherein the width of the slit is set to a first width based on a predetermined slice thickness. A program code of a first adjustment step for adjusting the amount of X-rays detected in a predetermined detection channel constituting the detector array is a predetermined amount with respect to an X-ray detection amount for realizing imaging at a predetermined slice thickness. And a program code for a second adjustment step of finely adjusting the width of the slit so as to be a ratio. 6. An X-ray source for generating X-rays, an X-ray detector for detecting X-rays generated from the X-ray source, interposed between the X-ray source and the X-ray detector, And a slit that regulates an irradiation range of the X-rays from the X-ray source to the X-ray detector. The slit and the X-ray detector have a shape along an arc centered on the X-ray source. X-ray CT characterized by the following:
system.