JPH03103242A - X-ray tomographic apparatus - Google Patents

Abstract

PURPOSE:To shorten the time required for feeding a body to be examined at the time of collecting the data and to shorten the time for restricting the body and also, to shorten the collection time of plural slice faces by executing a scan so as to move a thickness corresponding the portion of one slice tomography surface in a short time. CONSTITUTION:In the case of considering the data obtained by one rotation of an X-ray tube extending from a slice point S1 to S2, when data obtained by two rotations extending from S1 to S3 are bundled as the data of a one- rotation portion by an expression 2P(theta, phi)P12(theta, phi)+P23(theta, phi), (in this regard, theta, P12(theta, phi), and P23(theta, phi) denote the turning angle of an X-ray tube 3 and an X-ray fan beam FB, projection data obtained while the phase position of the X-ray tube 3 to the body M reaches S2 from S1, and projection data obtained while the phase position reaches S3 from S2 in the same way, respectively), it can be reconstituted as the scan data for representing a slice position X2. the method can be deduced to the case the image of a one-slice portion is obtained by three rotations or above. Accordingly, the time for restricting the body is shortened, and the collection time of plural slice faces can be shortened.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention belongs to the technical field of X-ray tomography apparatuses (hereinafter referred to as X-ray CT apparatuses).

(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 a display device. configured to display.

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,
After collecting all projection data for the first slice plane by rotating the x-ray tube 180' or 3600 rotations per slice plane, the x-ray tube is stopped and the second slice plane is rotated. The patient must be moved horizontally over time so that the tube is positioned in a vertical plane with a second plane of slices, and then the tube must be rotated and exposed for the second slice plane.

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 object to be covered with a predetermined thickness in a direction perpendicular to the rotating surface while rotating around the subject. an X-ray source that emits X-rays that pass through the sample; an X-ray detector that detects the X-rays that pass through the sample; and an X-ray source that moves by a distance shorter than the predetermined thickness in one rotation time. a subject moving means for moving the subject in the body axis direction during rotational movement of the X-ray source at a speed; a data collecting means for collecting data obtained from the detector; and a data collecting means supplied from the data collecting means. The apparatus is characterized in that it has an image reconstruction means for reconstructing an image based on the data.

(Function) It is possible to scan by moving an amount equivalent to the thickness of one slice tomographic plane in a short time.

(Example) The present invention will be specifically explained below with reference to an example. Fig. 2 is a system block diagram of an X-ray CT apparatus showing an example of the present invention. Reference numeral 1 denotes a pedestal, which is provided with an insertion hole 6 into which a subject M placed on the bed top plate 2 is inserted;
An X-ray tube 3 serving as an X-ray source and an X-ray detector 4 are arranged opposite to each other with the inserted subject M between them. Here, the X-ray tube 3 is configured to have its X-ray generation controlled by a high-pressure generator 7 and to rotate around the insertion hole 6 by an X-ray tube drive control device 5. The X-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 the line always detector 4
It is now accepted in some parts of the country. Further, the bed top 2 can be continuously moved along the body axis direction of the subject M by the bed drive control device 8 (
(Sometimes referred to as a means for moving the subject). 9 is a data acquisition device that collects data obtained by the X-ray detector 4; 10 is a correction calculation device for appropriately reconstructing the data in the data collection device; and 11 is a correction calculation device. It is an image reconstruction device that performs image reconstruction based on data sent from the device 10, and 12 is a display device that performs display based on image data from the image reconstruction device 1l. 13 is 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 360° rotation, and in this example, it rotates at 10°.
It is assumed that continuous rotation or infinite continuous rotation is possible.

Such continuous rotation can be achieved by using known slip rings or by employing electron beam scanning as disclosed in US Pat. No. 4,158↓42. While such a fan beam is continuously rotating and collecting data, the bed drive control device 8
Accordingly, the subject M moves continuously.

Assume that this amount of movement is, for example, an advance of Pmm per one 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. Data will be collected (spiral scan). That is, a spiral scan is performed by a combination of movements of 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 A CT device that rotates the instrument relatively (
The above-mentioned spiral data can also be obtained using a third generation CT device. 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,
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. A known method (USP No. 4,149,247) can be considered. Furthermore, if the data obtained in two rotations from the point S1 to 83 are bundled (overlaid) as data for one rotation using the following equation (1), it can be reconstructed as a scan data representing 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 from 0 to 360°.

P1 (θ, ψ) is the projection data obtained while the relative position of the X-ray tube 3 with respect to the subject M is from 81 to S2 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 32 to 33.

The above method can be used up to the point where an image for one 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 for each angle θ, which often results in clipping effects. This will result in artifacts called. 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 (i.e., X'''X+) in Fig. 2. As the X-ray tube rotates, the slice plane moves in the direction of the subject's body axis, and for example, at θ=180°, the X-ray tube position is at the initial position X1.
, but a position advanced by P/2 from there (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 180° but also for the entire range 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, when 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/2a+m using a collimator, etc. 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 similarly. 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. Start collecting projection data at θ = 0°, and move to a position θma almost close to θ = 360'.
If you complete the collection of projection data for one image at 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. child? The principle of the correction calculation device is that one part of the data used for image reconstruction of one tomographic plane (slice plane), which is obtained at the beginning or the final part, is used for one tomographic plane obtained before or after that. This is to correct the surface data using data obtained at the same rotation angle.

The projection data obtained from θ=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).

p' (θ, φ)・W(θ)・P1■(θ.φ) +
(IW (θ))・P 23 (360°+θ,φ)・
...(2) Here, W(θ) is θ=0 as shown in Figure 7.
0 and O, and θ=θX is 1, and it is a function that connects them with, for example, a straight line without any steep changes.

Instead of such correction, conversely, data P' has been subjected to the calculation process of the following equation (3), which corrects the data obtained from θ=θY to θmax with the data obtained from the previous rotation.
(θ.ψ) is substituted (has the same meaning as θY?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, θmaw is 0, 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 is created by one rotation from S1 to S2 and a slight extension from that, but one image is created by two or three rotations and a slight extension from that. Needless to say, it is possible to do so.

In the embodiments described above, if the relationship between the table movement amount P per fan beam rotation and the slice width t is selected such that p<t, the deviation of the scan plane per spiral rotation is small, and therefore artifacts are reduced. occurrence is reduced.

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 days. 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. X-ray CT that can be shortened and reduce artifacts due to clipping effects
equipment can be provided.

[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, 11
...Image reconstruction device, 12...Display device, 13.
...System control device. Figure 5 W(11})

Claims (1)

[Scope of Claims] An X-ray source that emits X-rays that pass through the subject at a predetermined thickness in a direction perpendicular to the rotating plane while rotating around the subject; an X-ray detector that detects the X-rays;
subject moving means for moving the subject in the body axis direction during rotational movement of the X-ray source at a speed at which the radiation source moves by a distance shorter than the predetermined thickness per rotation; and 1. An X-ray tomography apparatus comprising: a data collection means for collecting data; and an image reconstruction means for reconstructing an image based on the data supplied from the data collection means.