X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-12-27
2003-01-21
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000
Reexamination Certificate
active
06510194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for acquiring transmitted-radiation image data, and more particularly to a transmitted-radiation image data acquiring method and apparatus that is applied to a cone-beam computed tomograph (CT) which emits conical radiation to a subject in different directions of projection, acquires transmitted-radiation image data for each direction of projection, and generates volume data of the subject, based on the transmitted-radiation image data.
2. Description of the Related Art
In the field of medical imaging, research for detecting three-dimensional radiation image information has been undertaken. For example, a helical CT and a cone-beam CT have been proposed (see “Cone-Beam CT—Present Status and Future Prospects,” Image Information (M), pp. 122-127, January 1988 and Japanese Unexamined Patent Publication No. 9(1997)-253079).
In the cone-beam CT, a radiation source and an area sensor (two-dimensional solid radiation detector) are disposed with a subject therebetween. While the radiation source and the area sensor are being rotated relatively with respect to the subject, conical radiation is emitted from the radiation source to the subject. The radiation transmitted through the subject is detected by the area sensor, whereby the transmitted-radiation image data of the subject is obtained at a different rotational position, i.e., for each direction of projection. Based on the obtained transmitted-radiation image data of the subject, the volume data of the subject is acquired. Based on the volume data of the subject, a three-dimensional image or a fault image is displayed on an image display such into as a CRT display, or the three-dimensional image or the like is temporarily stored in a storage device. Here, the solid radiation detector means a detector with a semiconductor device, which detects radiation and converts it to an electrical signal, as an essential part.
In the above-mentioned conventional cone-beam CT, incidentally, the area of a three-dimensional image or a fault image that can be displayed is an area which is formed by the overlapping portions in all directions of projection which the area sensor detects, specifically an inscribed circle of a total-radiation emitted area which is formed by conical radiation in each direction of projection that the area sensor can detect. That is, an image area that can be displayed is determined by the emission angle of radiation and the detection area of the area sensor. If the image area is enlarged, it will become necessary to emit conical radiation to the subject at a wider angle and to detect more of the wide-angle radiation transmitted through the subject with the area sensor. In other words, there is a need to employ a large-area sensor and to emit enough wide-angle radiation to cover the entire surface of the wide-area sensor to the subject.
However, it is difficult to fabricate a large-area sensor having a large detection area. Even if the sensor could be fabricated, it will be expensive, resulting in an increase in the cost of the cone-beam CT. For this reason, in the conventional cone-beam CT, it is difficult to display the image of a large area.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned circumstances. Accordingly, it is an object of the present invention to provide a data acquiring method and apparatus which is capable of obtaining a large area quantity of transmitted-radiation image data without using a large-area sensor. Another object of the present invention is to provide a data acquiring method and apparatus that is capable of improving picture quality degradation due to scattered lines.
The first method according to the present invention is a method of acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the method comprising the steps of
employing a line sensor as the solid radiation detector; and
obtaining an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area for each direction of projection.
In the first method according to the present invention, an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area for each direction of projection. Therefore, the detection area can be enlarged and it becomes possible to acquire a larger area quantity of transmitted-radiation image data without using a large-area sensor. If the present invention is applied to the cone-beam CT, it will become possible to display a three-dimensional image or a fault image of a larger area.
Here, the “entire detection area” means the entire range of a desired area to be obtained. For example, when it is assumed that an area sensor is used as the solid radiation detector, the “entire detection area” is equivalent to the entire detection area of the area sensor.
Detecting the radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area means that any method may be employed if detection is performed by moving the line sensor so that the sensor covers the entire detection area. For example, a single line sensor may be moved so that it covers the entire detection area. Alternatively, a plurality of line sensors may be moved so that each line sensor covers a predetermined range and movement of each line sensor may be added up in order to cover the entire detection area.
Note that in moving the line sensor, it is preferable to move the line sensor along a circular arc with respect to the radiation source. The same applies to the following description.
The second method according to the present invention is a method of acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the cone radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the method comprising the steps of
employing a plurality of line sensors as the solid radiation detector;
dividing an entire detection area for each direction of projection into a plurality of division areas;
disposing each line sensor in each division area so that each line sensor is movable within the division area; and
obtaining an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with each line sensor, while each line sensor is being moved within each division area.
In the second method according to the present invention, the entire detection area for each direction of projection is divided into a plurality of division areas. Each line sensor is disposed in each division area so that each line sensor is movable within the division area, and an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with each line sensor, while each line sensor is being moved within each division area. Therefore, as with the aforementioned first method and apparatus, it becomes possible to acquire a larger area quantity of transmitted-radiation image data, while the movable range of each line sensor is being reduced. In addition, it becomes possible to display a three-dimensional image or a f
Dunn Drew A.
Fuji Photo Film Co. , Ltd.
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