X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-03-10
2001-06-05
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S008000, C378S162000, C378S205000, C378S207000
Reexamination Certificate
active
06243439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CT scanning apparatus, and more particularly to a partial CT scanning apparatus suitable for partially radiographing tooth, jaw and face areas, for example.
2. Description of the Prior Art
A CT scanning apparatus generally comprises an X-ray source moving along a circular orbit around an object and an X-ray image pickup portion moving along a circular orbit on the opposite side of the X-ray source with respect to the object. In the image pickup portion, a line sensor arranged in a line or in a circular orbit detects X-rays passing through the object, and an X-ray image is built. In addition to this type of apparatus, an apparatus for carrying out radiographing by using a spiral orbit while an object placed on a bed is moved, and an apparatus for radiographing three-dimensional areas by using a two-dimensional image sensor, such as a TV camera, in its image pickup portion are also known.
In the case of these apparatuses, a blurred image is generated because of displacements of the X-ray source and the X-ray image pickup portion from their original orbits and movement of the object, even if the resolution of the image pickup system is raised. If the displacements from the orbits occur in the same pattern, the displacements can be corrected on the basis of the pattern when the image is built. However, if the displacements do not occur in the same pattern, correction is difficult. Furthermore, regarding the movement of the object, when the object is a living body in particular, the object itself may move during radiographing, and the so-called “moving artifact” occurs. To prevent this problem, the patient under test is required to be secured to a bed, for example. This further causes a problem of making the apparatuses larger in overall size.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide a partial CT scanning apparatus for carrying out partial CT scanning to radiograph teeth, jaws and the like in particular, being capable of stably obtaining high-resolution images by improving image quality so that, in spite of displacements of the X-ray source and the X-ray image pickup portion from their original orbits, movement of the object and the like, the effects of these displacements can be eliminated by image processing. A second object of the present invention is to provide a partial CT scanning apparatus having the above-mentioned functions, and being compact in size and low in cost.
In order to attain the above-mentioned objects, the CT scanning apparatus of the present invention comprises an image pickup system having an X-ray source being rotated along a circular orbit around an object and a two-dimensional X-ray image pickup portion disposed opposite to the X-ray source with the object therebetween and being rotated along a circular orbit, and is configured to rotate the image pickup system so as to radiograph three-dimensional areas inside the object, wherein a substance capable of being detected as an X-ray image is used as a position marker, the position marker is disposed so as to be positioned in the image pickup view of the image pickup system during the rotation of the image pickup system and radiographed together with the object, a correction amount for each X-ray image is calculated from the position of the image of the position marker in an obtained two-dimensional X-ray image, the two-dimensional X-ray image is corrected by using the correction amount, and a CT image is built.
In an ideal case, the image of the position marker in the X-ray image obtained by radiographing moves in a sine curve. Therefore, the difference between the actual position in the X-ray image and the ideal position changing in the sine curve corresponds to displacements due to displacements from the orbits or movement of the object. Accordingly, the image of the position marker taken in the X-ray image is traced to obtain a correction amount in accordance with the position of the image, and the X-ray image is moved in parallel to carry out back projection. As a result, errors in the mechanical, electrical and other systems due to displacements of the image pickup system from original orbits and errors due to displacements caused by movement of the object during radiographing are all corrected in all the horizontal and vertical directions. The effects of “moving artifact” and the like can thus be eliminated, and a clear image can be built, whereby accurate diagnosis can be attained. Furthermore, the accuracy of the mechanical system of the apparatus may be lowered to some extent. Consequently, the apparatus can be made compact in size and low in cost, and can be calibrated easily.
Moreover, instead of radiographing the position marker together with the object as described above, only the position marker is radiographed before regular radiographing. From the position of the image of the position marker in the obtained two-dimensional X-ray image, it is possible to calculate error data regarding the image pickup system in each X-ray image. As a result, a two-dimensional X-ray image during regular radiographing can be corrected by using the data, whereby errors in the image pickup system can be eliminated. In addition, the data can also be used to find and remedy improper portions in the mechanical, electrical and other systems, which may cause errors.
Concrete configurations of the CT scanning apparatus in accordance with the present invention will be clarified by explanations regarding an embodiment described below.
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Arai Yoshinori
Suzuki Masakazu
Ho Allen C
Kabushiki Kaisha Morita Seisakusho
Kim Robert H.
Koda & Androlia
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