X-ray or gamma ray systems or devices – Accessory – Alignment
Reexamination Certificate
2000-01-03
2001-11-27
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Alignment
C378S004000, C378S011000, C378S019000, C378S020000, C378S205000
Reexamination Certificate
active
06322248
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray impinging position alignment method and an X-ray tomographic imaging method and apparatus, and more particularly to an X-ray impinging position alignment method for an X-ray emitting/detecting apparatus that emits an X-ray generated from an X-ray tube onto an X-ray detector through a collimator, and an X-ray tomographic imaging method and apparatus for performing imaging with the X-ray impinging position alignment.
In X-ray CT (computed tomography), an X-ray emitting/detecting apparatus for emitting an X-ray generated from an X-ray tube onto an X-ray detector through a collimator is rotated around (i.e., scans) a subject to be examined, and projection data for the subject is measured using the X-ray in a plurality of view directions around the subject to produce (i.e., reconstruct) a tomographic image based on the projection data.
The X-ray emitting apparatus emits an X-ray beam having a width in which an imaging range is contained and a certain thickness in the direction perpendicular to the width. The thickness of the X-ray beam is determined by the degree of opening of an X-ray passing aperture of the collimator.
The X-ray detecting apparatus detects the X-ray by a multi-channel X-ray detector comprising multiple X-ray detector elements arranged in an array in the direction of the X-ray beam width. The multi-channel X-ray detector has a length (i.e., width) corresponding to the X-ray beam width in the direction of the X-ray beam width, and a length (i.e., thickness) greater than the X-ray beam thickness in the direction of the X-ray beam thickness.
Some X-ray detectors comprise the X-ray detector element array having two rows to simultaneously obtain projection data for two slices. In such X-ray detectors, the two rows of the array are disposed adjacent to each other in parallel, and the X-ray beam impinges upon the detector equally apportioned in the thickness direction. Each thickness of the X-ray beam impinging upon each of the two rows of the array at the subjects isocenter determines the slice thickness of the tomographic image.
In the X-ray tube, an X-ray focus shifts due to thermal expansion caused by a temperature rise during use or the like, resulting in displacement of the X-ray beam in the thickness direction after passing through the collimator aperture. If the X-ray beam is displaced in the thickness direction, the distribution proportion of the X-ray beam thickness between the two rows of the array varies and the respective slice thicknesses for the subject projected on the two series of the array become unequal.
Thus, a technique is employed involving providing the two rows of the array with respective reference channels, monitoring the ratio between X-ray counts at the reference channels, detecting a shift in the X-ray impinging position if the ratio is not equal to one, and adjusting the collimator position, thereby controlling the X-ray impinging position to remain at a fixed position.
However, since the above technique for controlling the impinging position should be started only after the X-ray is emitted and a scan is started, the X-ray impinging position does not always coincide with a fixed position immediately after the beginning of the scan, or rather it may be shifted from the fixed position more often than not. Accordingly, there is a problem that an image initially obtained is subject to quality degradation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an X-ray impinging position alignment method to make an X-ray impinging position coincide with a fixed position from the beginning of a scan, and an X-ray tomographic imaging method and apparatus that performs imaging with such X-ray impinging position alignment.
In accordance with a first aspect of the present invention, there is provided an X-ray impinging position alignment method, in performing tomographic imaging by scanning a subject using an X-ray emitting/detecting apparatus for emitting an X-ray generated from an X-ray tube onto an X-ray detector through a collimator, comprising the steps of: predicting an X-ray focus position at the X-ray tube based on the temperature of the X-ray tube prior to beginning the scan and scan conditions intended to be currently used; and adjusting a position of the collimator and/or a position of the X-ray detector according to the predicted position so that the X-ray generated from the X-ray tube impinges upon a fixed position on the X-ray detector.
In accordance with a second aspect of the present invention, there is provided an X-ray tomographic imaging method, in performing tomographic imaging by scanning a subject using an X-ray emitting/detecting apparatus for emitting an X-ray generated from an X-ray tube onto an X-ray detector through a collimator, comprising the steps of: predicting an X-ray focus position at the X-ray tube based on the temperature of the X-ray tube prior to beginning the scan and scan conditions intended to be currently used; adjusting a position of the collimator and/or a position of the X-ray detector according to the predicted position so that the X-ray generated from the X-ray tube impinges upon a fixed position on the X-ray detector; and performing tomographic imaging by scanning the subject using the X-ray emitting/detecting apparatus after being position-adjusted by the adjusting step.
In accordance with a third aspect of the present invention, there is provided an X-ray tomographic imaging apparatus for performing tomographic imaging by scanning a subject using an X-ray emitting/detecting apparatus for emitting an X-ray generated from an X-ray tube onto an X-ray detector through a collimator, comprising: focus position predicting means for predicting an X-ray focus position at the X-ray tube based on the temperature of the X-ray tube prior to beginning the scan and scan conditions intended to be currently used; and position adjusting means for adjusting a position of the collimator and/or a position of the X-ray detector according to the predicted X-ray focus position so that the X-ray generated from the X-ray tube impinges upon a fixed position on the X-ray detector.
In any one of the first through third aspects of the invention, it is preferred that the scan conditions include at least a tilt angle of the X-ray emitting/detecting apparatus and a scan time in that the X-ray focus position can be predicted properly in an axial scan.
In any one of the first through third aspects of the invention, it is preferred that the scan conditions include at least a tilt angle and an azimuth angle of the X-ray emitting/detecting apparatus in that the X-ray focus position can be predicted properly in a stationary scan.
In the above cases, it is preferred that the scan conditions further include an X-ray focus size in that the X-ray focus position can be predicted properly when the X-ray focus size is changed.
The X-ray impinging position alignment method and the X-ray tomographic imaging method and apparatus of the first through third aspects of the present invention can adjust the position(s) of the collimator and/or the X-ray detector according to the X-ray focus position predicted prior to beginning a scan, causing the X-ray to impinge upon a fixed position on the X-ray detector from the very beginning of the scan.
Thus, the present invention can implement an X-ray impinging position alignment method to make an X-ray impinging position coincide with a fixed position from the beginning of a scan, and an X-ray tomographic imaging method and apparatus that performs imaging with such X-ray impinging position alignment.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 5550886 (1996-08-01), Dobbs et al.
patent: 6185275 (2001-02-01), Toth et al.
patent: 6169914 (1994-06-01), None
patent: 7116157 (1995-05-01), None
patent: 10-118058 (1998-05-01), None
patent: 10-2111
Nukui Masatake
Yanagita Hirofumi
GE Yokogawa Medical Systems Limited
Kim Robert H.
Kojima Moonray
Thomas Courtney
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