JPS639859B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a computer tomography device,
In particular, it relates to improvements in so-called second generation computerized tomography devices.

In the second generation computerized tomography apparatus, as shown in FIG. 1A, an X-ray tube 1 and a plurality of X-ray detectors 2 are arranged facing each other, and a plurality of X-ray tubes are spread out in a fan shape at a spread angle θ. The X-ray beam of
It should be detected by Then, a subject (patient) 4 is placed within the imaging area 3, and this subject 4
On the other hand, a linear scan is performed in which the X-ray tube 1 and the detector 2 are moved together in parallel as shown by the arrow. When this linear scan is completed once, as shown in FIG. 1B, the X-ray tube 1 and detector 2 are rotated together about the subject 4 by the fan-shaped spread angle Θ. From this rotated position, Figure 2B
As shown by the arrow in FIG. 1A, the linear scan is performed in a direction opposite to the direction of the linear scan in FIG. 1A by an angle Θ. In this way, the linear scanning is repeated by sequentially shifting the angle Θ, and the object 4 is linearly scanned by the X-ray beam pointing in all directions. Profile data from X-ray beams in all directions for the subject 4 is obtained from each detector 2.

By the way, when this second-generation computerized tomography system is used to image a pin-phantom, the image does not converge to one point, and artifacts such as star-shaped images are often observed as shown in Figure 2. be done. This may be caused by the fact that the actual position of the detector 2 (indicated by the solid line) is farther from the X-ray tube 1 than the calculated position (indicated by the dotted line), as shown in FIG. This occurs due to positional deviations between the X-ray tube 1 and the detector 2, such that the actual position of the X-ray tube 1 is farther or closer than the calculated position. In other words, when there is such a positional shift, the calculation processing of the profile data is performed according to the calculated value even though the calculated direction of the X-ray beam is different from the actual direction. This is because it will be put away. Since this artifact significantly degrades image quality, it is preferable to eliminate positional deviation to prevent it from occurring, but in actual mechanisms it is extremely difficult to prevent even the slightest positional deviation from occurring. be.

In view of the above, an object of the present invention is to provide a computerized tomography apparatus that is improved so that artifacts do not occur even if there is a mechanical displacement of the radiation source or the detector.

An embodiment of the present invention will be described below. Fourth
As shown in the figure, a case will be described in which the actual position (indicated by a solid line) of the detector 2 is far away from the calculated position (indicated by a dotted line). Let the spread angle (calculated) of the X-ray beam be θ, and the angle between each beam be Δθ (equal angle). Further, although the rotational movement of the detector 2 may be at an angle of 2Δθ, 4Δθ, etc., here, for example, the angle is assumed to be Δθ. In other words, in FIG. 4, the X-ray tube 1 and detector 2 first perform linear scanning at the position (direction) indicated by the solid line, and then rotated by an angle of 3ΔΘ and then perform linear scanning at the position (direction) indicated by the two-dot chain line. Let's do it. In the first linear scan, B ₁₁ , B ₁₂ ,
Five profile data corresponding to the five X-ray beam directions of B ₁₃ , B ₁₄ , and B ₁₅ were obtained, and in the second time, five X-ray beam directions of B ₂₁ , B ₂₂ , B ₂₃ , B ₂₄ , and B ₂₅ were obtained. Five pieces of profile data corresponding to the line beam direction are obtained. The profile data corresponding to the first B ₁₁ and B ₁₂ is the calculated X-ray beam direction R ₁ ,
It is supposed to be treated as _R2 . By the way, the second profile data corresponding to B ₂₄ and B ₂₅ has a rotation angle of 3ΔΘ, so originally (if there was no positional deviation) B ₂₄ would be in R ₁ ,
B ₂₅ should overlap R ₂ exactly, and therefore should be treated as corresponding to R ₁ and R ₂ in calculations. Among the profile data obtained in the first and second times, the data in the same calculated X-ray beam direction are averaged. Then, since the detector 2 is shifted in the same far direction with respect to the X-ray tube 1 in the first and second linear scans, the first actual X-ray beam B ₁₁ , B ₁₂ is shifted to the right side of the calculated X-ray beams R ₁ and R ₂ , and the second actual X-ray beam B ₂₄ ,
B ₂₅ is shifted to the left of the calculated X-ray beams R ₁ and R ₂ ,
The deviation between the two is always in the opposite direction. Therefore, by averaging, profile data can be obtained that can be considered to be from directions intermediate between B ₁₁ and B ₂₄ and B ₁₂ and B ₂₅ , that is, the calculated X-ray beam directions R ₁ and R ₂ .

In this way, positional deviation can be corrected by obtaining calculated profile data in one X-ray beam direction by averaging two profile data obtained by two linear scans. That is, for example, as shown in FIG. 5, the profile data from each detector 2 is sent to the averaging circuit 6 through the preamplifier 5, and the above-mentioned calculation is performed for all linear scans, and then the profile data is sent to the convolution circuit 7 and back. If the image is processed by the projection circuit 8 and displayed by the CRT 9, an image free of artifacts can be obtained.

According to the above-mentioned averaging operation, no matter what the positional deviation, the two actual X-ray beams that are treated as one X-ray beam direction in the calculation will be on both sides of the calculated X-ray beam. Since the deviation always occurs at the same deviation angle, the positional deviation can always be corrected.

Note that when the fan-shaped spread angle Θ of the X-ray beam is large, the deviation angle of the X-ray beam becomes larger at the peripheral detectors and becomes smaller at the center. Therefore, if the angle of rotational movement is set to around Θ/2, the error in the direction of the X-ray beam near the center will become larger due to the averaging operation. In such a case, as shown in FIG. 6, an averaging operation may be performed for several (m) X-ray beams around the large deviation angle. To do this, the angle of rotational movement is (n-m)ΔΘ (n is the number of X-ray beams in one linear scan, (n-1)Δθ
= Θ), the angle of the rotational movement is adjusted to be larger than Θ/2 so that only two adjacent linear scans overlap with respect to m peripheral lines. This is preferable because the overall scanning time is also shortened.

As described above with respect to the embodiments, according to the present invention, even if there is a mechanical positional shift in a radiation source or a radiation detector, the computer tomography system corrects this and prevents artifacts from occurring. A device is obtained. Therefore, it becomes easy to adjust the focus of the radiation source and the alignment of the radiation detector.

[Brief explanation of the drawing]

Figures 1A and B are schematic diagrams for explaining scanning of a radiation beam in a second-generation computer tomography system, Figure 2 is a diagram showing artifacts, and Figure 3 is a diagram for explaining positional deviation states. 4 is a schematic diagram showing the direction of the radiation beam in one embodiment of the present invention, FIG. 5 is a block diagram showing the data processing system of one embodiment, and FIG. 6 is another embodiment. FIG. 2 is a schematic diagram showing the direction of a radiation beam in FIG. 1...X-ray tube, 2...X-ray detector, 3...imaging area, 4...subject, 5...preamplifier, 6...
Averaging circuit, 7... Convolution circuit,
8... Back projection circuit, 9...
CRT.

Claims (1)

[Claims] 1. A radiation source and a plurality of radiation detectors are disposed facing each other so that each of the detectors detects a plurality of radiation beams spreading in a fan shape at a predetermined spread angle, and the radiation source and the radiation detector At the same time, the radiation source and the radiation detector are rotated by a predetermined angle with respect to the object, and the linear scan is performed in a direction that differs by this predetermined angle. In a computer tomography apparatus that performs the linear scanning in the direction, the rotation angle for each linear scanning direction is smaller than the spread angle of the fan shape, and profile data in a predetermined calculated radiation beam direction is scanned in one linear scan. The data obtained as the profile data in the radiation beam direction in the step and the data obtained as the profile data in the same radiation beam direction in another adjacent linear scan are averaged to obtain the data. Computerized tomography equipment.