JPH1119079A - X-ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the detection output from decreasing at the ends in a slice thickness direction without expanding the X-ray strength distribution by a method wherein a two-dimensional X-ray detecting means wherein the widths in the slice thickness direction of respective detection elements, a large number of which are arranged, are made wider as being away from the slice center, is arranged in a manner to be confronted with an X-ray radiation means. SOLUTION: A collimator 12 is attached to an X-ray tube 11, and an X-ray detecting apparatus 13 is formed into an arc-shape, and by arranging a large number of X-ray detection elements under a twodimensional state, and the outputs from respective detection elements are input in a data collecting device 14, and the data regarding an X-ray absorption is collected. The X-ray detecting apparatus 13 comprises the large number of the detection elements which are twodimensionally arranged in the arc direction and a slice thickness direction, and the widths of respective detection elements are formed in such a manner that they are equal in the channel direction, but are narrower at the center, and wider at the end parts in the slice thickness direction. By this method, X-ray amounts which enter respective detection elements become approx. uniform, and the detection element outputs at the end parts become larger, and signals having a high S/N ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus, and more particularly to an improvement in an X-ray CT apparatus having a two-dimensional X-ray detector.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, an X-ray tube is normally radiated from an X-ray tube to a subject (human body) in a fan shape to transmit the subject, and the X-ray beam transmitted through the subject is transmitted. To
A large number of detection elements are detected by a multi-channel X-ray detector arranged in an arc shape, the output of each channel is sent to a data collection device to collect data, and an image reconstruction operation is performed using the collected data. Then, an image on the slice plane through which the fan-shaped X-rays are transmitted is obtained.

When the detection elements are arranged in an arc in one line, data can be collected only in one slice plane and an image can be reconstructed in only one slice plane. If a two-dimensional X-ray detector in which the detected elements are arranged in several rows in the slice thickness direction is used,
Data can be collected on several slice planes at the same time, and images of several slices can be obtained at one time. Further, when a two-dimensional X-ray detector is used, the data sampling density in the slice thickness direction is high, so that it is difficult to receive the partial volume effect even when the internal structure of the subject is finely changed. Benefits are obtained.

In a conventional two-dimensional X-ray detector, the width of a detection element in a slice thickness direction is constant (FIG. 5).

[0005]

However, the conventional two-dimensional X-ray detector having the same width in the slice thickness direction of the detection element as in the prior art has the following problems.
Since the X-ray beam emitted from the X-ray tube is narrowed in the slice thickness direction and spreads in a fan shape on a plane perpendicular to the slice thickness direction, the X-ray intensity distribution in the slice thickness direction is shown in FIG. As shown by the solid line 5 in FIG. 5, the intensity is strongest at the slice center, and becomes weaker as the distance from the center increases. Therefore, when the width W of the detection element is the same, the amount of X-rays incident on the element distant from the slice center becomes very small. Therefore, when the X-ray dose radiated from the X-ray tube is reduced, the output of the element deviated from the center of the slice is buried in noise and becomes substantially invalid, so that the radiated X-ray dose cannot be reduced. Also, it seems that the X-ray intensity distribution should be widened as shown by the dotted line B by loosening the aperture.
Then, the X-rays at the end that spread in the slice thickness direction will not be detected by any of the detection elements,
There is a problem that effective use of the radiation X-rays cannot be achieved and unnecessary X-ray exposure to the subject increases.

In view of the above, the present invention provides an X-ray CT apparatus having a two-dimensional X-ray detector improved so that the detection output at the end in the slice thickness direction does not decrease without expanding the X-ray intensity distribution. The purpose is to provide.

[0007]

In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises an X-ray radiating means for radiating an X-ray beam, and an X-ray radiating means for irradiating the X-ray beam. A two-dimensional arrangement in which a large number of detection elements are arranged in the slice plane direction and in the slice thickness direction, and the width of each detection element in the slice thickness direction is increased as the distance from the slice center increases; And X-ray detecting means.

Since the width of a large number of detection elements in the slice thickness direction is increased as the distance from the slice center increases, even if the X-ray intensity distribution is narrow, the amount of X-rays incident on the detection elements decreases. And the ends are not very different. For this reason, the output of the detection element at the end is not so small, and the radiation X-ray dose from the X-ray radiation means can be reduced.
Further, since the end portion of the X-ray intensity distribution is also detected, the emitted X-ray can be effectively used, and the exposure dose to the subject is not increased.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, an X-ray tube 11 and an X-ray detector 13 are arranged to face each other. The X-ray tube 11 is provided with a collimator 12 for narrowing the X-ray beam. The X-ray detector 13 is formed in an arc shape, and a large number of X-ray detection elements are two-dimensionally arranged. The output from each detection element is input to the data collection device 14 to collect data on X-ray absorption.

An X-ray tube 11 (and a collimator 12);
A subject (not shown) is inserted into the space between the X-ray detector 13 (and the data acquisition device 14), and these are integrally rotated around the subject as indicated by arrows. This rotation plane is called a slice plane,
Data about this plane is collected from each direction, and data from each direction is sent to an image reconstruction device (not shown) to perform image reconstruction processing, and an X-ray absorption distribution image on the slice plane is obtained as a tomographic image.

The X-ray detector 13 includes a large number of detection elements two-dimensionally arranged in an arc direction (channel direction, slice plane direction) and slice thickness direction (direction perpendicular to the rotation plane). For example, 5 in the channel direction
About 100 to 1000 pieces, 4 to 8 in the slice thickness direction
It is arranged in about pieces. As shown in FIG. 2, the width of each detection element is equal in the channel direction, but is narrower (W1) at the center and wider (W2) at the end in the slice thickness direction.

The X-ray beam emitted from the X-ray tube 11 is
As shown in FIG. 3, the collimator 12 narrows down the slice in the slice thickness direction so as to correspond to the slice plane thickness for obtaining a tomographic image of the subject. Therefore, the X-ray intensity distribution in the slice thickness direction is as shown by the curve A in FIG. 4, and is highest at the center of the slice, and rapidly falls off the center according to the distance from the center. However, in the X-ray detector 13, as described above, the width of the detection element in the slice thickness direction is narrow as W1 at the center portion and wide as W2 at the end portion. It will not change much. Therefore, the output of the detection element at the end becomes large, and a signal having a high S / N ratio can be obtained.

Further, as can be seen from FIG. 4, all the X-ray beams corresponding to the ends (hemes) of the X-ray intensity distribution are also incident on the detection elements at the ends. The X-ray beam emitted from the light source is not wasted (in contrast, when the width is equal to W as shown in FIG. 5, the incident X-ray dose differs greatly between the center and the end, and the end element Is reduced, and if the X-ray intensity distribution is widened to avoid this, the amount of X-ray beams deviating from the X-ray detector increases and the useless X-ray dose increases, as described above.) In the vicinity of the center in the slice thickness direction, since data can be collected for a slice plane having a very small thickness (W1), a good image not affected by the partial volume effect can be obtained.

The above description is for one embodiment, and it goes without saying that the present invention is not intended to be limited to this description. For example, in the above description, four detection elements are arranged in the slice thickness direction, but this number can be other numbers, and various other specific configurations can be employed.

[0015]

As described above, the X-ray C of the present invention
According to the T device, the amount of X-rays incident on the detection element distant from the center in the slice thickness direction is secured, and the S / N
A signal with a good ratio can be obtained, and an image with good image quality can be reconstructed. Further, the X-ray intensity distribution can be broadened to avoid increasing unnecessary X-ray exposure. Since a sufficient signal can be obtained from the detection element at the end, the radiation X-ray dose can be reduced and the exposure dose to the subject can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention.

FIG. 2 is a development view of an X-ray detector.

FIG. 3 is a schematic side sectional view for explaining an X-ray emission state in a slice thickness direction.

FIG. 4 is a graph showing a relationship between an X-ray intensity distribution in a slice thickness direction and a detection width in the embodiment.

FIG. 5 is a graph showing a relationship between an X-ray intensity distribution in a slice thickness direction and a detection width in a conventional example.

[Explanation of symbols]

 Reference Signs List 11 X-ray tube 12 Collimator 13 X-ray detector 14 Data collection device

Claims (1)

[Claims] 1. An X-ray emitting means for emitting an X-ray beam;
A large number of detection elements are arranged in a slice plane direction and a slice thickness direction so that the X-ray beam is incident thereon, and the width of each detection element in the slice thickness direction is set. An X-ray CT apparatus comprising: a two-dimensional X-ray detection unit that is wider as being away from a slice center.