X-ray or gamma ray systems or devices – Beam control – Scanner
Reexamination Certificate
2000-03-20
2002-01-15
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Scanner
C378S149000
Reexamination Certificate
active
06339636
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image recording method and apparatus. This invention particularly relates to a radiation image recording method and apparatus for use in a cone-beam computed tomography system (a cone-beam CT system).
2. Description of the Prior Art
Techniques for recording and reproducing radiation images have widely been used in practice, wherein a radiation image having been obtained by irradiating radiation to an object and causing the radiation carrying image information of the object to impinge upon a radiation detector is converted into an image signal, the image signal is subjected to appropriate image processing, and a visible image is reproduced from the processed image signal.
FIG. 6
is a perspective view showing a conventional X-ray tomographic image recording apparatus
100
, in which X-rays
108
are irradiated in a cone beam-like form to an object
102
. The X-ray tomographic image recording apparatus
100
is disclosed in, for example, Japanese Unexamined Patent Publication No. 9(1997)-253079. The X-ray tomographic image recording apparatus
100
comprises an X-ray source
104
and a two-dimensional detector
106
, which are located so as to stand facing each other with the object
102
intervening therebetween. The X-ray source
104
and the two-dimensional detector
106
are rotated in a pair around the object
102
. During the rotation, at a plurality of positions of rotation, the X-rays
108
carrying image information of the object
102
are detected as X-ray images by the two-dimensional detector
106
. X-ray image signals representing the X-ray images having thus been obtained are fed into an image processing section
110
and utilized for reconstructing a three-dimensional image. In this manner, a tomographic image of a desired cross-section of the object can be obtained.
However, with the cone beam-like X-rays
108
, the range irradiated simultaneously to the X-rays
108
is wide. Therefore, when the cone beam-like X-rays
108
passes through the object
102
, much scattered X-rays occur. The problems thus occur in that the scattered X-rays impinge upon the two-dimensional detector
106
, and much noise occurs in the detected image. In order to solve the problems with regard to noise due to the scattered X-rays, a technique has heretofore been utilized, wherein a scattered radiation removing grid is located between the object
102
and the two-dimensional detector
106
in order to remove the scattered X-rays occurring when the X-rays
108
pass through the object
102
.
However, in cases where the scattered radiation removing grid is located between the object
102
and the two-dimensional detector
106
, even if the scattered X-rays are removed by the grid, the problems occur in that the grid causes moire to occur in the image during the image processing. Further, part of the X-rays
108
carrying the image information of the object
102
is absorbed by the grid, and a signal-to-noise ratio of the detected image signal becomes low.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a radiation image recording method, wherein scattered radiation is capable of being removed efficiently such that no loss of an image signal due to a grid occurs.
Another object of the present invention is to provide an apparatus for carrying out the radiation image recording method.
The present invention provides a radiation image recording method, comprising the steps of:
i) locating a radiation source and a radiation detector with an object intervening therebetween,
ii) locating a set of radiation blocking plates, each of which has at least one slit, between the radiation source and the radiation detector such that the object intervenes between the radiation blocking plates, and such that the slits of the radiation blocking plates are aligned in a straight line with the radiation source,
iii) shifting the set of the radiation blocking plates stepwise in a direction along which radiation having been produced by the radiation source scans the object, such that the state in which the slits of the radiation blocking plates and the radiation source are aligned with one another in the straight line is kept,
iv) after each step of the shifting, rotating the radiation source, the set of the radiation blocking plates, and the radiation detector around the object, and
v) recording radiation image patterns of the object during the rotation.
The term “radiation scanning an object” as used herein means that the radiation, which has passed through the slit of the radiation blocking plate close to the radiation source and has been shaped by the slit into a fan beam, moves with respect to the object and in the direction which intersects with the plane of the fan beam.
The present invention also provides a radiation image recording apparatus, comprising:
i) a radiation source,
ii) a radiation detector, which is located so as to stand facing the radiation source with an object intervening between the radiation detector and the radiation source,
iii) a set of radiation blocking plates, each of which has at least one slit and which are located between the radiation source and the radiation detector such that the object intervenes between the radiation blocking plates, and such that the slits of the radiation blocking plates are aligned in a straight line with the radiation source,
iv) means for shifting the set of the radiation blocking plates stepwise in a direction along which radiation having been produced by the radiation source and having been shaped by the slit of the radiation blocking plate close to the radiation source into a fan beam scans the object, such that the state in which the slits of the radiation blocking plates and the radiation source are aligned with one another in the straight line is kept,
v) means for rotating the radiation source, the set of the radiation blocking plates, and the radiation detector around the object after each step of the shifting, and
vi) image recording means for recording radiation image patterns of the object at a plurality of positions of rotation during the rotation.
With the radiation image recording method and apparatus in accordance with the present invention, the set of the radiation blocking plates, each of which has at least one slit, are located with the object intervening therebetween. The set of the radiation blocking plates are shifted stepwise in the direction along which the radiation having been produced by the radiation source scans the object, such that the state in which the slits of the radiation blocking plates and the radiation source are aligned with one another in the straight line is kept. Also, after each step of the shifting, the radiation source, the set of the radiation blocking plates, and the radiation detector are rotated around the object. During the rotation, radiation image patterns of the object are recorded. Therefore, the radiation image recording method and apparatus in accordance with the present invention have the effects described below. Specifically, the radiation having been produced by the radiation source is restricted by the slit of the radiation blocking plate, which is close to the radiation source, into a fan beam-like shape. The fan beam impinges upon the object. Therefore, little scattered radiation occurs when the fan beam passes through the object. Also, the scattered radiation coming from the object is removed by the slit of the radiation blocking plate, which is close to the radiation detector. As a result, image patterns containing little noise can be obtained. Further, the set of the radiation blocking plates are shifted stepwise, the entire image recording system is rotated around the object after each step of the shifting, and the radiation image patterns of the object are recorded during the rotation. In this manner, the image patterns of the entire area of the object are obtained. From the thus obtained image patterns, a three-dimensional image having good image quality can
Dunn Drew A.
Kim Robert H.
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