X-ray or gamma ray systems or devices – Beam control – Collimator
Reexamination Certificate
2001-09-12
2003-01-14
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Collimator
C378S150000, C378S019000
Reexamination Certificate
active
06507642
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a collimator control method and apparatus and an X-ray CT (computed tomography) apparatus, and more particularly to a method and apparatus for controlling a collimator for defining an impingement position of an X-ray beam on an X-ray detector, and an X-ray CT apparatus comprising such a collimator control apparatus.
An X-ray CT apparatus acquires signals of transmitted X-rays for a plurality of views with respect to an imaging object by an X-ray emitting/detecting apparatus, and produces a tomographic image of the object by an image producing apparatus based on the signals of transmitted X-rays.
The X-ray emitting apparatus forms a cone-shaped X-ray beam emitted from a focus of an X-ray tube into a fan-shaped X-ray beam by a collimator, and projects the fan-shaped X-ray beam toward an imaging space.
The X-ray detecting apparatus detects the X-rays passing through the imaging space by a multi-channel X-ray detector that comprises a multiplicity of X-ray detector elements arranged in an array along the extent of the fan of the X-ray beam. Such an X-ray emitting/detecting apparatus is rotated (or scans) around the object to acquire the signals of transmitted X-rays for the plurality of views.
One of several types of the multi-channel X-ray detector is a detector element array comprising a plurality of detector element rows arranged side by side in the thickness direction of the fan-shaped X-ray beam to simultaneously receive an X-ray beam by the plurality of rows of the detector element array. Since such an X-ray detector can obtain X-ray detected signals for a plurality of slices together in one scan, it is used as an X-ray detector for efficiently performing a multi-slice scan.
Such X-ray detectors include an X-ray detector element array that comprises two rows and obtains projection data for two slices together. In such an X-ray detector, two rows of the array are disposed adjacent to each other in parallel, and illuminated by an X-ray beam equally divided in the thickness direction of the X-ray beam. The thicknesses of the X-ray beam impinging upon the two rows of the array at an isocenter of the object determines the slice thicknesses of tomographic images.
The X-ray tube undergoes an X-ray focus shift caused by thermal expansion or the like due to a temperature rise during use, which shift appears as displacement in the thickness direction of the X-ray beam after passing through an aperture of the collimator. When the X-ray beam shifts in the thickness direction, the division of the thickness of the X-ray beam becomes unequal between the two rows of the array. Equality between the slice thicknesses of two tomographic images is therefore lost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a collimator control method and apparatus for keeping a constant X-ray impingement position on an X-ray detector, and an X-ray CT apparatus comprising such a collimator control apparatus.
(1) In one aspect for solving the aforementioned problem, the present invention is a collimator control method, comprising the steps of: forming X-rays emanating from a focus of an X-ray tube into a fan-shaped beam by a collimator, and projecting the fan-shaped beam onto a detector element array comprising a plurality of detector element rows arranged side by side in the thickness direction of the fan-shaped beam, each of which detector element rows comprises a plurality of X-ray detector elements disposed in line in the extent direction of the fan-shaped beam; detecting an error between an impingement position of the fan-shaped beam and a predetermined impingement position in the direction of the side-by-side arrangement of the detector element rows on the detector element array; and controlling the collimator based on the detected error so that the impingement position of the fan-shaped beam coincides with the predetermined impingement position.
(2) In another aspect for solving the aforementioned problem, the present invention is a collimator control apparatus, comprising: an X-ray tube for generating X-rays emanating from a focus; a collimator for forming the X-rays into a fan-shaped beam; a detector element array comprising a plurality of detector element rows arranged side by side in the thickness direction of the fan-shaped beam, each of which detector element rows comprises a plurality of X-ray detector elements disposed in line in the extent direction of the fan-shaped beam; error detecting means for detecting an error between an impingement position of the fan-shaped beam and a predetermined impingement position in the direction of the side-by-side arrangement of the detector element rows on the detector element array; and control means for controlling the collimator based on the detected error so that the impingement position of the fan-shaped beam coincides with the predetermined impingement position.
(3) In still another aspect for solving the aforementioned problem, the present invention is an X-ray CT apparatus, comprising: an X-ray tube for generating X-rays emanating from a focus; a collimator for forming the X-rays into a fan-shaped beam; a detector element array comprising a plurality of detector element rows arranged side by side in the thickness direction of the fan-shaped beam, each of which detector element rows comprises a plurality of X-ray detector elements disposed in line in the extent direction of the fan-shaped beam; an error detecting apparatus for detecting an error between an impingement position of the fan-shaped beam and a predetermined impingement position in the direction of the side-by-side arrangement of the detector element rows on the detector element array; a control apparatus for controlling the collimator based on the detected error so that the impingement position of the fan-shaped beam coincides with the predetermined impingement position; a signal acquiring apparatus for acquiring X-ray detected signals for a plurality of views with an X-ray emitting/detecting system including the X-ray tube, the collimator and the detector element array rotated around an axis that is in parallel with the thickness direction of the fan-shaped beam; and a tomographic image producing apparatus for producing tomographic images for slices crossed by the fan-shaped beam based on the X-ray detected signals.
In the invention of the aspects described in (1)-(3), since an error in an impingement position of an X-ray beam is detected in the direction of the side-by-side arrangement of the detector element rows on the detector element array, and the collimator is controlled based on the detected error so that the impingement position of the X-ray beam coincides with a predetermined impingement position, the X-ray impingement position can be kept constant on the detector element array.
In the invention of these aspects, it is preferred to detect the error based on a ratio of a difference between X-ray detected signals to a sum of those X-ray detected signals, which X-ray detected signals are detected by X-ray detector elements that are adjacent in the direction of the side-by-side arrangement of the detector element rows, because an error measurement can be obtained independent of the magnitude of the X-ray detected signals.
(4) In still another aspect for solving the aforementioned problem, the present invention is a collimator control method, comprising the steps of: forming X-rays emanating from a focus of an X-ray tube into a fan-shaped beam by a collimator, and projecting the fan-shaped beam onto a detector element array comprising a plurality of detector element rows arranged side by side in the thickness direction of the fan-shaped beam, each of which detector element rows comprises a plurality of X-ray detector elements disposed in line in the extent direction of the fan-shaped beam; detecting an error between an impingement position of the fan-shaped beam and a predetermined impingement position in the direction of the side-by-side arrangement of the detector element rows on the
Fujishige Takashi
Gohno Makoto
Nukui Masatake
Dunn Drew A.
GE Medical Systems Global Technology Company LLC
Gemmell Elizabeth
Kojima Moonray
LandOfFree
Collimator control method and apparatus, and X-ray CT apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Collimator control method and apparatus, and X-ray CT apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Collimator control method and apparatus, and X-ray CT apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3056934