JPH03103238A - X-ray tomography apparatus - Google Patents

Abstract

PURPOSE:To decrease the restriction time of a body to be examined, and also, to shorten the collection time of plural slice faces by reconstituting an image by using continuous data in an arbitrary position in the data obtained by a spiral scan. CONSTITUTION:By operating an X-ray driving controller 5 and a bed driving controller 8, spiral data is obtained by the rotational movement of an X-ray source 3 and the continuous movement of a body M to be examined, and collected in a data collecting device 9. Subsequently, with respect to the spiral data, by a correction arithmetic unit 10, adjacent data is evaluated continuously as a shift and the generation of an artifact is reduced, and thereafter, by an image reconstituting device 11, the data of a continuous plural rotation portion in an arbitrary position are bundled and one piece of image is formed, and reconstituted by decreasing the artifact. Accordingly, the time required for feeding the body at the time of collecting the data is shortened, the time for restricting the body examined can be decreased, and also, 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 the display device. It was designed 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,
Rotate the X-ray tube 180° or 36° for the first slice plane.
After 00 rotations and collecting all projection data for the first slice plane, stop the operation of the X-ray tube;
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 object, the present invention includes an X-ray source that irradiates X-rays while rotating around a subject, and an an X-ray detector for detecting the X-rays; a subject moving means for continuously moving the subject in the body axis direction during rotational movement of the X-ray source; and collecting data obtained from the detector. An X-ray tomography apparatus having a data acquisition means and capable of performing a spiral scan on a subject, which captures data obtained by this spiral scan, and selects any of the captured data The present invention is characterized by having an image reconstruction means for reconstructing an image using continuous data of positions.

(Function) Spiral data can be obtained by rotating the X-ray source and continuously moving the subject, and a tomographic image at an arbitrary position can be obtained from this spiral data.

(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 it 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. The line 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; and 11 is a correction calculation device. An image reconstruction device performs image reconstruction based on data sent from the image reconstruction device 10, 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 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 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
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 in one rotation of the wire tube, image reconstruction can be 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. In addition, 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 representative of the slice position X2. You can also.

P=(Lφ)P・・(“・φ)゛2・・(e・φ)・・
・(1) 2 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 3600.

P■2 (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 81 to 82 in Fig. 2, and P23 (θ, ψ) is also the projection data relative to the X-ray tube. This is projection data obtained between positions 82 and 83.

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

If the number of data to be bundled is small, a tomographic image of a thin slice can be obtained, and if the number of data to be bundled is large, a tomographic image of a thick slice can be obtained. By arbitrarily selecting the number of pieces of data to be bundled in this manner, a tomographic image of a slice of any thickness can be obtained.

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 two images 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 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 = 180', the X-ray tube position is not at the initial position X1, but by P/2 from there. Advanced position (X=X
l +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=0° 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 1 revolution of the X-ray fan beam, and the X-ray fan beam FB is focused to t/2mm by a collimator. 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=
The intensity profile and position in the slice thickness direction of the X-ray fan beam obtained at X, and X''X2,
C and D were obtained in the same way. 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=0° and 180
In the slice thickness direction of the projection data obtained at .degree., waveforms E and F are obtained, respectively.

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=00, and reached a position θma almost close to θ=360°.
If you complete the collection of projection data for one image with w, will the scan plane to be measured be out of sync between P(0, ψ) and P(θmaI, ψ)? Therefore, the content of the data will be quite different. 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 of the data used for image reconstruction of one tomographic plane (slice plane), the l part obtained at the beginning or the This correction is performed using data obtained at the same rotation angle in the tomographic data.

The projection data obtained from θ=0 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°+θ1φ)
...(2) Here, W(θ) is θ= as shown in FIG.
To 0°? , 0, and θ=θX, and 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 θmaI with the data obtained from the previous rotation.
(θ.ψ) (θY has the same meaning as θX).

p' (θ1φ)・W(θ)・P1■(θ,φ) +
(IW (θ))・P23(θ-360”,φ) ・・
-(3) Here, W(θ) is a function where θ=θY and l1θmaX are 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 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. It goes without saying that this is also possible.

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 the projection data obtained from 0 to 3600
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).
This must be done at such a high speed that the return speed (on return) can be ignored, but this is fully possible by employing the 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 above 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.

In the present invention, since data is continuously collected within a certain range in the body axis direction of the subject, the starting point of the data range used for reconstruction is S in FIG. , S1, etc., which are located directly above the subject, but also any spiral position can be taken.

Here, it goes without saying that the data range used for reconstruction requires data for at least half a revolution.

As described above, the present invention can obtain an arbitrary tomographic image in the body axis direction of the subject by arbitrarily determining the position of the data range used for reconstruction in a spiral shape.

[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 and furthermore can obtain a tomographic image at an arbitrary position of a subject.

[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, 1o...Correction calculation device, 11
...Image reconstruction device, 12...Display device, 13.
...System control device.

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;
The object moving means continuously moves the object in the body axis direction during the rotational movement of the radiation source, and the data collecting means collects the data obtained from the detector, An X-ray tomography device that can perform spiral scanning, which captures data obtained through this spiral scanning and reconstructs the image using continuous data at arbitrary positions among the captured data. An X-ray tomography apparatus characterized by having a reconstruction means.