Fixed gantry CT system having a non-uniform slit
A volumetric stationary CT system has at least one stationary array of x-ray detectors extending proximate at least a portion of an imaging volume, at least one stationary x-ray source proximate the stationary array or arrays of x-ray detectors, and a collimator having a slit with a non-uniform opening width. The collimator is intermediate the stationary x-ray source and the stationary array of x-ray detectors. The result is a uniform flux normal to the detector array across the entire length thereof.
1. A volumetric stationary CT system comprising:
a) at least one stationary array of x-ray detectors extending proximate at least a portion of an imaging volume;
b) at least one stationary x-ray source proximate said at least one stationary array of x-ray detectors; and
c) a collimator having a slit of a predetermined length with an adjustable opening width, said collimator disposed intermediate each of said at least one stationary x-ray source and said at least one stationary array of x-ray detectors; said slit for providing uniform irradiance at all points along said at least one stationary array of x-ray detectors.
2. The volumetric stationary CT system in accordance with claim 1 , wherein said at least one stationary array of x-ray detectors comprises at least one of the group: scintillators and direct conversion x-ray detectors.
3. The volumetric stationary CT system in accordance with claim 1 , wherein said irradiance varies by <10% over said at least one stationary array of x-ray detectors.
4. The volumetric stationary CT system in accordance with claim 1 , further comprising a target disposed in said imaging volume and wherein said stationary x-ray source produces a defocused spot on said target.
5. The volumetric stationary CT system in accordance with claim 1 , said at least one stationary x-ray source comprising an x-ray source tube having a focal spot, the dimensions of which focal spot being greater than said length of said collimator slit.
6. The volumetric stationary CT system in accordance with claim 4 , wherein said defocused spot has a diameter greater than 1 mm, allowing a uniform irradiance across said at least one stationary array of x-ray detectors.
7. A method of calculating the profile of a non-uniform collimator slit in a volumetric stationary CT system comprising a stationary array of x-ray detectors extending proximate at least a portion of an imaging volume, a stationary x-ray source proximate said stationary array of x-ray detectors, said non-uniform collimator slit disposed intermediate said stationary x-ray source and said stationary array of x-ray detectors, the steps comprising:
a) integrating the radiance of a source spot in one dimension;
b) determining integration limits from the slit width along the projection of the ray path from a point on the centerline of said stationary array of x-ray detectors to said source spot; and
c) adjusting the width of said slit to provide uniform irradiance at all points along said stationary array of x-ray detectors.
8. The method of calculating the profile of a non-uniform collimator slit in accordance with claim 7 , wherein said integrating step (a) is determined by at least one of the group: closed-form and numerically.
9. The method of calculating the profile of a non-uniform collimator slit in accordance with claim 7 , wherein said irradiance is calculated to be uniform to within ±10% over said stationary array of x-ray detectors.