JPH03103241A - X-ray tomography apparatus - Google Patents

Abstract

PURPOSE:To shorten the time required for feeding a body to be examined at the time of collecting the data, to shorten the time for restricting the body and also, to shorten the collection time of plural slice faces by executing a spiral scan with the combination of the movement of an X-ray source and the movement of the body. CONSTITUTION:From an X-ray tube 3, fan beam-like X rays are generated, and an X-ray detector 4 detects the fan beam as one unit. Also, the fan beam can execute not only a 360 deg. rotation but also a ten times continuous or infinite times continuous rotation. Also, while a fan beam is rotating continuously and collecting the data, the body M is moved continuously by a bed driving controller 8. Accordingly to such a constitution, for instance, it becomes equivalent to a fact that the fan beam executes a translation motion in the body axis direction, while rotating against a still body M and the fan beam moves spirally around the body M and collects the data, and the collection time is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention belongs to the technical field of X-ray tomography devices (hereinafter referred to as X-ray CT devices).

(Conventional technology and issues to be solved) Conventional, X-ray CT
The device is configured to measure X for a desired slice plane of a subject, e.
When obtaining a tomographic image (hereinafter referred to as a tomographic image), while the patient's position is fixed, the X-ray tube is rotated around the patient in a vertical plane having the slice plane, and X-rays are emitted from the X-ray tube. , all projection data from all directions on the slice plane are collected, image reconstruction is performed based on this total projection data, and a tomographic image of the desired slice plane is displayed on the display device. It was configured to display images.

Then, when trying to obtain a plurality of tomographic images for a plurality of different slice planes of the patient using the X-ray CT apparatus,
1800 or 36 x-ray tubes per first slice plane
After collecting all projection data for the first slice plane through 00 rotations, the X-ray tube is stopped;
Taking the time to horizontally move the patient so that the x-ray tube is in a vertical plane with the second slice plane, and then rotating the x-ray tube and exposing the x-ray to the second slice plane. Must be.

Therefore, the conventional X-ray CT apparatus has a problem in that when a plurality of tomographic images are obtained for different slice planes, the patient is restrained for a long time, resulting in a decrease in the operating efficiency of the X-ray CT apparatus. Furthermore, conventional X-ray CT equipment has
When obtaining multiple tomographic images for different slice planes of a patient injected with contrast agent, the projection data is collected for the first slice plane and the projection data for the last slice plane. Another problem is that it is not possible to obtain multiple tomographic images under the same physiological state because the patient's physiological state changes.

The present invention has been made in view of the above circumstances, and aims to shorten the time required to transport the subject during data collection, reduce the time required to restrain the subject, and shorten the time required to collect multiple slice planes. The purpose of this invention is to provide an X-ray CT apparatus that can perform

[Structure of the Invention (Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an X-ray source that irradiates X-rays while rotating around a subject; an X-ray detector for detecting X-rays, a scanning means for performing spiral scanning by relatively moving the X-ray source and the subject, and data for collecting data obtained from the detector. The present invention is characterized by comprising a collection means and an image reconstruction means for reconstructing an image based on data supplied from the data collection means.

(Function) A spiral scan can be performed by combining the movement of the X-ray source and the movement of the subject.

(Example) The present invention will be specifically explained below using Examples.

FIG. 1 is a system block diagram of an X-ray CT apparatus showing an embodiment of the present invention. Reference numeral 1 denotes a pedestal, which is equipped with an insertion hole 6 into which the subject M placed on the bed top plate 2 is inserted, and which holds the inserted subject M between the two and connects to an X-ray tube 3 as an X-ray source. An X-ray detector 4 is placed opposite to it. here,
The X-ray tube 3 is controlled to generate X-rays by a high-pressure generator 7, and the insertion hole 6 is controlled by an X-ray tube drive controller 5.
It is configured to rotate around the X
The ray detector 4 is composed of a plurality of individual detectors arranged in an array along the circumferential surface of a cylindrical holding member arranged diagonally, and detects the X-rays transmitted through the subject from the X-ray tube 3. is always received by a part of the detector 4. Further, the bed top 2 can be continuously moved along the body axis direction of the subject M by a bed drive control device 8 (sometimes referred to as subject moving means). 9 is a data acquisition device that collects data obtained by the X-ray detector 4; 10 is a correction calculation device for converting the data in the data collection device into appropriate reconstruction data; l1 is a correction calculation device An image reconstruction device 10 performs image reconstruction based on data sent from the image reconstruction device 11, and a display device 12 performs display based on image data sent from the image reconstruction device 11. Reference numeral 13 denotes a system control device that controls each of the above-mentioned devices.

Next, the operation will be explained.

In the above apparatus, it is assumed that the X-ray tube 3 generates fan-beam X-rays (hereinafter simply referred to as fan beams), and the X-ray detector 4 detects this fan beam as a unit. Furthermore, this fan beam does not stop at 3600 rotations, but in this example, it rotates at 10 rotations.
It is assumed that continuous rotation or infinite continuous rotation is possible.

Such continuous rotation can be achieved using known slip rings or by employing electron beam scanning as disclosed in US Pat. No. 4,158,142. While such a fan beam is continuously rotating and collecting data, the bed drive control device 8
Sample M is designed to move continuously.

Assume that the amount of movement is, for example, an advance of Pmm per rotation of the fan beam. With this configuration, for example, it is equivalent to the fan beam rotating and translating in the body axis direction with respect to the stationary subject M, and the fan beam moves spirally around the subject M. (spiral scan). That is, a spiral scan is performed by relatively moving the X-ray source and the subject. Data obtained in this manner can be defined as spiral data. Therefore, in addition to a CT device (fourth generation CT device) that rotates only the X-ray tube 3 with the X-ray detector 4 fixed as in this embodiment, it is also possible to detect The above-mentioned spiral data can also be obtained by a CT device (third generation CT device) that rotates the device relatively. If the positions of the X-ray source and fan beam of the spiral scan are observed from the direction perpendicular to the body axis direction, a sinusoidal waveform XL with a period Pmm as shown in FIG. 2 will be drawn.

Next, a method of reconstructing an image from the data obtained as described above will be explained. First, in general, there is a method in which the entire scan range is divided into small elements and reconstructed at once.For example, from slice point S to 82 in Figure 2
When considering data obtained from one rotation of the wire tube, image reconstruction is performed for each plane by approximating that the fan beam position is fixed at the center of positions X1 and X2 in the X direction in Figure 2. Known method (USP No. 4 1 4 9 2
4 7) is possible. In addition, if the data obtained in two rotations from the point SE to 83 are bundled (overlaid) as data for one rotation using the following formula (1), it can be reconstructed as scan data representing the slice position X2. You can also.

? Here, θ is the rotation angle of the X-ray tube 3 and the X-ray fan beam FB, as shown in FIG. 3, and takes a value of 0 to 3600.

P1 (θ, ψ) is the projection data obtained while the relative position of the X-ray tube 3 with respect to the subject M ranges from 31 to 32 in Fig. 2, and P23 (θ, ψ) is the same X-ray projection data. This is the projection data obtained while the relative position of the tube was from 82 to 83.

The above method can be used up to the point where an image corresponding to the S slice is obtained by three or more rotations.

Furthermore, the same effect as the above case can be obtained by independently reconstructing the projection data obtained in each rotation and averaging the obtained plural images.

As mentioned above, creating a single image by bundling data for a plurality of consecutive rotations is useful in reducing artifacts. That is, in general, in an X-ray CT apparatus,
The thickness of the X-ray fan beam when viewed from the side is approximately proportional to the X-ray tube since the X-rays are not parallel. When inspecting a subject with an X-ray beam in this way, if the subject has large changes in the slice thickness direction, the projection data will contain slightly inconsistent parts at each angle θ, which often causes an artifact called the clipping effect. It will give rise to A phenomenon similar to this occurs also in the case of the present invention, which will be explained with reference to FIG. In FIG. 4, A is the intensity profile of the X-ray fan beam in the slice thickness direction obtained when the X-ray tube is at position 81 in FIG. 2 (ie, X=X1). The slice thickness at this time is tmm. As the X-ray tube rotates, the slice plane moves in the direction of the subject's body axis. For example, at θ=↓80°, the X-ray tube position is not at the initial position X1, but advances by P/2 from there. position (x=x.+p
/2).

Here, if P=t, the intensity profile and position of the X-ray fan beam in the slice thickness direction at θ=180' will be as shown in FIG. 4B. Here, in the waveforms A and B, the hatched portions mean that different subjects are being measured.

Image reconstruction calculations are performed on the premise that all projection data are the results of measuring the exact same subject, so the hatched portions in the waveforms A and B cause some distortion to the image. I think that the. This is true not only for the relationship between θ=00 and 1800 but also for all ranges of θ. Particularly, in the data collection method of this embodiment, development similar to the clipping effect described above is likely to occur.

The present invention solves these problems using the following principle. For example, if you want to obtain an effective slice width of tmm, the subject M is sent at a rate of t/2mm per rotation of the X-ray fan beam, and the X-ray fan beam FB is narrowed down to t/2mm by a collimator or the like. I have to. As a result, an intensity profile and position as shown in FIG. 5 is obtained.

In the same figure, A and B each have a relative X-ray tube position of X=
X. and the intensity profile and position in the slice thickness direction of the X-ray fan beam obtained at X=X2, C,
D was obtained in the same manner. As a result, by bundling the projection data as shown in equation (1) above, a profile and position as shown in FIG. 6 can be obtained. That is, θ=00 and 180
Waveforms E and F are obtained in the slice thickness direction of the projection data obtained at .degree.

The hatched portion is relatively small compared to the case of FIG. 4 described above. In other words, image distortion is reduced.

Furthermore, when performing a spiral scan as described above, there are the following problems. We started collecting projection data at θ=09 and reached a position θma almost close to θ=360°.
If you complete the collection of projection data for one image with I, the content of the data will be quite different because the scan planes to be measured are different between P (0, ψ) and P (θmaX, ψ). become. It is well known that when there is a discontinuous difference between adjacent data, artifacts are more likely to occur than when there is a continuous shift. In order to solve such problems, the present invention includes a correction calculation device 10 that performs the following processing. The principle of this correction calculation device is that one part of the data used for image reconstruction of one tomographic plane (slice plane), obtained at the beginning or at the end, is used for the data obtained before or after that. This correction is performed using data obtained at the same rotation angle in the tomographic data.

? The projection data obtained from =O to θX is data P' (θ
, ψ) (θX is arbitrarily set depending on the width of the required image reconstruction area and the degree of artifact reduction).

? '(θ,φ)・W(θ)・P1■(θ,φ)+(1
-W(θ))・P 23(360'+θ,φ)...
(2) Here, W(θ) is a function that takes 0 at θ=00 and 1 at θ=θX, as shown in FIG. 7, and connects them with, for example, a straight line without any steep changes.

Instead of such correction, conversely, data P' is subjected to the calculation process of the following equation (3), which corrects the data obtained from θ=θY to θmat with the data obtained from the previous rotation.
(θ, ψ) (θY has the same meaning as θX).

P' (θ,φ)・W(θ)・P1■(θ,φ)+(1
-W(θ))・P23(θ-360°, φ)...(
3) Here, W(θ) is a function where θ=θY is 1, θmax is O, and there is no steep change between them, for example, by a straight line.

By providing such a correction calculation device 10, adjacent data can be evaluated as continuous deviations, so that the occurrence of artifacts can be reduced. The above correction was for the case where an image was created by one rotation from S1 to 32 and a slight extension from that, but one image was created by making two or three rotations and a slight extension from that. Needless to say, it is possible to do so.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the above embodiment, one image is created from projection data obtained from 0 to 360 degrees.
Although the present invention has been described with respect to T, it can also be applied to an X-ray CT apparatus as shown in FIG. 8, which performs image reconstruction from less than 3,600 scan data. That is, the X-ray source moves reciprocatingly or one-way at high speed on the trajectory XL, and the detector group 4' is arranged along a range of about 2/3 of the circumference, and the object M is repeatedly scanned. should be sent continuously. In this case as well, it is possible to obtain projection data for one image by moving the X-ray source 3' from a to b. According to such a device, a trajectory that looks like a series of U-shaped scans can be obtained as shown in FIG. The data obtained by this can be defined as deformed spiral data. in this case,
In FIG. 8, the movement of the X-ray source 3' is faster than the movement speed from position a to position b (during data collection).
Although the return speed must be negligible, this is fully possible by employing the well-known electron beam scan. According to the apparatus of this embodiment, since the moving time of the X-ray source 3' can be shortened, the slice interval Pmm can also be minimized, and therefore the equation (1)
If an image for one slice is created by overlapping a large number of projection data by extension, it becomes easy to reduce artifacts.

[Effects of the Invention] According to the present invention described in detail above, it is possible to shorten the time required to transport the subject during data collection, reduce the time to restrain the subject, and reduce the time required to collect multiple slice planes. It is possible to provide an X-ray CT apparatus that can be shortened.

[Brief explanation of drawings]

FIG. 1 is a system block diagram showing an embodiment of the present invention;
Fig. 2 is a schematic explanatory diagram showing the relative trajectory of the X-ray source according to the above embodiment, Fig. 3 is a schematic explanatory diagram showing the state of the fan beam according to the above embodiment, and Fig. 4 is the reason why distortion occurs in the image. , FIG. 5 and FIG. 6 are respectively explanatory diagrams of the reason why distortion occurring in an image can be reduced by employing the embodiment apparatus of the present invention, and FIG. 7 is an explanatory diagram of the function used in the correction calculation. FIG. 8 is a schematic explanatory diagram showing another embodiment of the present invention, and FIG. 9 is an explanatory diagram of the relative trajectory of the X-ray source according to the other embodiment. 1... Frame, 2... Bed top plate, 3, 3'... X-ray source, 4... X-ray detector, 5...
・X-ray drive control device, 6...detector drive device, 7.
...High pressure generator, 8...Bed drive control device, 9
...data collection device, 10...correction calculation device,
■1... Image reconstruction device, 12... Display device,
13... System control device. Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] An X-ray source that emits X-rays while rotating around a subject; an X-ray detector that detects X-rays that have passed through the subject;
a scanning means that performs a spiral scan by relatively moving a radiation source and the subject; a data collection means that collects data obtained from the detector; and a data collection means based on the data supplied from the data collection means. An X-ray tomography apparatus comprising an image reconstruction means for reconstructing an image.