JPH0622949A - X-ray tomograph - Google Patents

Abstract

PURPOSE:To provide an X-ray tomograph which prevents the generation of artifact due to the difference of the sensitivity variation of each detector due to the variation of the focus point of an X-ray tube, when the focus point of the X-ray tube is shifted by the heating and expansion of the X-ray tube. CONSTITUTION:An X-ray tomograph is equipped with an X-ray tube 1, a plurality of detectors 2 which are arranged in array form on the arc of a circle having a prescribed point as the center so that a object to be diagnos is inserted between the X-ray tube 1 and an X-ray tube 1 installed oppositely to the X-ray tube 1, and a plurality of collimators 3 installed in correspondence with the detectors 2, and the X-ray tube 1 is arranged so that each collimator 3 forms a prescribed angle for the incidence direction of the X-ray generated in the X-ray tube 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an X-ray tomographic imaging apparatus,
In particular, it relates to the configuration of the collimator of the detector used in the X-ray tomography apparatus and the arrangement of the X-ray tube and the detector.

[0002]

2. Description of the Related Art An X-ray tomographic imaging apparatus (hereinafter referred to as an X-ray CT apparatus) has a rotation driving unit, and the rotation driving unit rotates to perform X-ray tomography imaging. Is configured. An X-ray tube and a position where X-rays generated from the X-ray tube are generated in the rotation drive unit (hereinafter referred to as a focus).
A plurality of detectors arranged on a circular arc of a circle centered on and a collimator provided corresponding to the detectors are mounted.
An object to be diagnosed is inserted between the X-ray tube and the detector, X-rays are generated from the X-ray tube, and the X-rays pass through the object to be diagnosed and are detected by the detector. Diagnosis of the diagnostic object is performed.

In the above structure, the collimator is provided for removing scattered rays, but the angular dependence (Polar Response) with respect to the sensitivity of an arbitrary detector is as shown in FIG. The conventional X-ray CT apparatus is designed to detect X-rays at the position where the detector has the highest sensitivity, that is, the sensitivity peak position. That is, in FIG. 8, it is designed so that the angle θ = 0 °.

However, in a multi-channel type detector using a plurality of detectors, the sensitivity peak positions of all the detectors cannot be perfectly matched due to manufacturing errors and the like. For example, a case where the vicinity of the sensitivity peak position is used for X-ray detection will be described with reference to FIG. By repeating the X-ray irradiation on the object to be diagnosed, the X-ray tube heats up,
It is assumed that the X-ray tube has expanded and the focus position of the X-ray tube has moved from A to A '. When the focus position of the X-ray tube is A, the first detector detects the X-ray at the sensitivity peak position as shown by D1, and the second detector except the sensitivity peak position as shown by D2. It is assumed that the X-ray is detected at the position of. At this time, when the focus position of the X-ray tube moves to A ', the sensitivity of the first detector changes from a to a'and the sensitivity of the second detector changes from b to b'. Therefore, the sensitivity of the first detector is ΔI
It will decrease by a and the sensitivity of the second detector will increase by ΔIb.

Therefore, in the conventional X-ray CT apparatus, the sensitivity peak positions of the respective detectors cannot be perfectly matched to each other due to a manufacturing error or the like. Therefore, when the focal position of the X-ray tube is moved, each detection is performed. The rate of change in the sensitivity of the vessel is different. as a result,
Ring-shaped artifacts appear in the image due to variations in the sensitivity change rate of each detector.

[0006]

As described above, in the conventional X-ray CT apparatus, since X-ray detection is used at the sensitivity peak position of the detector, the X-ray tube is heated and expanded to cause X-ray detection. When the focus position of the X-ray tube moves, the sensitivity change rate of each detector due to the movement of the focus position is different,
There was a problem that artifacts appeared.

The present invention has been made based on the above-mentioned circumstances. Even when the focal position of the X-ray tube moves due to heating and expansion of the X-ray tube, the focal position of the X-ray tube changes. It is an object of the present invention to provide an X-ray CT apparatus that prevents the occurrence of artifacts due to the difference in sensitivity change of each detector.

[0008]

The present invention has taken the following means in order to solve the above problems.

The first X-ray tomography apparatus of the present invention is an X-ray tomography apparatus.
X-ray tube for generating X-rays and an array on a circular arc of a circle centered on a predetermined point so that the object to be diagnosed is inserted between the X-ray tube and the X-ray tube. And a plurality of collimators provided corresponding to the detectors, and X generated from the X-ray tube.
The X-ray tube is arranged such that each collimator has a predetermined angle with respect to the incident direction of a ray.

The second X-ray tomographic imaging apparatus of the present invention is an X-ray tomography apparatus.
The X-ray tube that generates X-rays and the X-ray tube that is provided so as to face the X-ray tube and that is inserted between the X-ray tube and the object to be diagnosed
A plurality of detectors arranged on an arc of a circle centered on the generation position of X-rays generated from the X-ray tube; and a plurality of collimators provided corresponding to the detectors.
Each of the collimators is arranged at a predetermined angle with respect to the incident direction of the X-ray generated from the X-ray tube.

[0011]

As a result of taking the above-mentioned means, the following effects occur.

According to the first and second X-ray tomographic imaging apparatus of the present invention, the X-rays are configured to enter the collimator obliquely. Therefore, even if the focal position of the X-ray tube moves due to heating and expansion of the X-ray tube, the sensitivity change rate of each detector does not change. It is possible to prevent the occurrence of artifacts due to the difference in sensitivity change.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, an X according to an embodiment of the present invention
A line CT device will be described.

FIG. 1 is an X-ray CT according to the first embodiment of the present invention.
FIG. 3 is a schematic diagram showing a positional relationship between a detector and a collimator of the apparatus and a focal position of an X-ray tube.

The X-ray CT apparatus has a rotation drive unit, and is configured to perform X-ray tomographic image photography when the rotation drive unit (not shown) rotates. An X-ray tube 1, a detector 2, and a collimator 3 are mounted on this rotation drive unit. According to FIG. 1, the plurality of detectors 2 are X
It is provided so as to face the wire tube 1 and is arranged in an array on a circular arc of a circle centered at point A, and collimators 3 are arranged corresponding to the detectors 2. Further, the object to be diagnosed is inserted between the X-ray tube 1 and the detector 2, and the object to be diagnosed is diagnosed by irradiating the object to be diagnosed with X-rays. The collimator 3 is used to prevent scattered ray components and the like from entering the detector.

In the conventional X-ray CT apparatus, the X-ray tube 1 and the detector 2 are arranged so that the focal position of the X-ray tube 1 is at the point A. According to the present invention, point A is the detector center axis X-
The focal point of the X-ray tube 1 is set at a point that has moved a predetermined distance in the vertical direction from X '.

With the above construction, since X-rays are incident on the detector at a portion of the sensitivity other than the sensitivity peak (obliquely with respect to the collimator) from the beginning, as shown in FIG. In the part, it changes almost linearly, and
The sensitivity change rate changes in proportion to the focal length. Therefore, as shown in FIG. 2, even when the focal position of the X-ray tube moves from A to A ′ due to expansion and heating of the X-ray tube,
The sensitivities of the detectors D1 and D2 are from a to a ', b, respectively.
From b to b ′, the rate of change in sensitivity of the detectors D1 and D2 changes in proportion to the moving distance of the focus.
ΔIa = ΔIb, and the rate of change in sensitivity is detected by the detectors D1 and D.
Since 2 is the same, the measurement can be performed with sufficient accuracy without the appearance of artifacts.

FIG. 3 is a diagram showing a modification of the first embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. Unlike FIG. 1, FIG. 3 does not move the focal position of the X-ray tube 1 in the direction perpendicular to the detector central axis XX ′, but moves the focal position of the X-ray tube relative to the detector central axis. It is configured to be rotated around the point B.

Also according to this modification, since X-rays are incident on the detector from the beginning on a portion of the sensitivity other than the sensitivity peak (obliquely with respect to the collimator), the same effect as in FIG. 1 can be obtained.

Next, the fact that the rate of change in sensitivity becomes constant by shifting the focus position will be specifically described with reference to FIGS. 4 and 5.

FIG. 4 is a diagram showing the angle dependence of the detection sensitivity. In FIG. 4, the vertical axis represents the sensitivity, and the horizontal axis represents the focal position of the X-ray tube when the central axis of the detector is 0 °. Figure 5
FIG. 4 is a diagram showing the positional relationship between the focal point of the X-ray tube and one detector and collimator.

According to FIG. 4, the portion where the rate of change of the detection sensitivity (detector output) does not change linearly but shows a gentle change is ± with respect to the center axis (angle θ = 0 °) of the detector.
It is about 0.2 °, and the sensitivity changes almost linearly in other portions. The reason for this is that the focus of the X-ray tube and the detector have a certain area.

The peak variation due to manufacturing error is
In FIG. 5, although it depends on the thickness t and the length L of the collimator plate of the collimator, this variation is ± 0.1 °.
It is considered to be the degree.

Therefore, if the collimator is tilted by about 0.3 ° in FIG. 3, the variation in the sensitivity change becomes small.

Further, when R + L = 1000 mm, it is 1000 × tan 0.3 ° to 4.7 (mm), so it is sufficient to shift the focus by about 5 mm in FIG.

Therefore, in FIG. 1, the focus may be shifted by about 5 mm, and in FIG. 3, the focus of the X-ray tube 1 may be moved by rotational movement about the point B of about 0.3 °.
Also, this value is a value that changes depending on the focus size, manufacturing error, and the like.

FIG. 6 shows an X-ray CT according to the second embodiment of the present invention.
It is the schematic which shows the detector of an apparatus, a collimator, and the relationship of a X-ray focal point position. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

1 and 3, the focal position of the X-ray tube 1 is shifted so that the X-rays obliquely enter the detector and the collimator, but in FIG. 6, the focal position of the X-ray tube 1 is not displaced. The collimators are arranged so as to be oblique with respect to the X-ray incident direction, and the X-rays are obliquely incident on each collimator.

Also in this embodiment, since X-rays are incident on the detector from the beginning on a portion of the sensitivity other than the sensitivity peak (obliquely with respect to the collimator), the same reason as in the first embodiment is applied. The effect of is obtained.

The present invention is not limited to the above embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0031]

According to the present invention, the following effects can be obtained.

According to the X-ray tomographic imaging apparatus as described in the first and second embodiments of the present invention, the X-rays are obliquely incident on the collimator. Therefore,
Even if the focus position of the X-ray tube moves due to heating and expansion of the X-ray tube, the sensitivity change rate of each detector does not change. Therefore, the sensitivity change of each detector due to the change of the focus position of the X-ray tube. It is possible to prevent the occurrence of artifacts due to the difference between

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration according to a first embodiment of an X-ray CT apparatus of the present invention.

FIG. 2 is a diagram for explaining that the sensitivity change rate of each detector is the same when the focus of the X-ray tube moves in the present invention.

FIG. 3 is a diagram showing a modification of the first embodiment of the X-ray CT apparatus of the present invention.

FIG. 4 is a diagram showing a specific example of angle dependence of detector sensitivity.

FIG. 5 is a diagram showing the focal position of the X-ray tube and the arrangement of one detector and collimator.

FIG. 6 is a diagram showing a configuration according to a second embodiment of the X-ray CT apparatus of the present invention.

FIG. 7 is a diagram for explaining a conventional example.

FIG. 8 is a diagram showing a focus movement of an X-ray tube and a sensitivity change rate.

FIG. 9 is a diagram showing the movement of the focal point of the X-ray tube and the rate of change in sensitivity.

[Explanation of symbols]

 1 ... X-ray tube, 2 ... Detector, 3 ... Collimator.

Claims (2)

[Claims] 1. An X-ray tube for generating X-rays and a circle having a predetermined point as a center so that an object to be diagnosed is inserted between the X-ray tube and the X-ray tube. In an X-ray tomographic imaging apparatus including a plurality of detectors arranged in an array on a circular arc and a plurality of collimators provided corresponding to the detectors, an X-ray generated from the X-ray tube An X-ray tomographic imaging apparatus, wherein the X-ray tube is arranged such that each collimator has a predetermined angle with respect to the incident direction of a ray. 2. An X-ray tube for generating an X-ray, and an X-ray tube which is provided so as to face the X-ray tube so that a diagnostic object is inserted between the X-ray tube and the X-ray tube. An X-ray tomographic imaging apparatus comprising: a plurality of detectors arranged on an arc of a circle having a position where an X-ray is generated as a center; and a plurality of collimators provided corresponding to the detectors. An X-ray tomographic imaging apparatus, wherein the collimators are arranged at a predetermined angle with respect to the incident direction of X-rays generated from a X-ray tube.