Patent Number: 
Section: claims

1. A method for determining tracking control parameters for positioning an x-ray beam of a computed tomography imaging system, the imaging system including a movable collimator positionable in steps and a detector array including a plurality of rows of detector elements, said method comprising: obtaining detector samples at a plurality of collimator step positions while determining a position of a focal spot of the x-ray beam;  determining a beam position for each detector element at each collimator step utilizing the determined focal spot positions, a nominal focal spot length, and geometric parameters of the x-ray beam, collimator, and detector array; and  determining a detector element differential error according to ratios of successive collimator step positions. 2. A method in accordance with  claim 1  wherein the plurality of detector rows are z-axis detector rows, and the detector array has a centerline perpendicular to the z-axis, an outer detector row, and an inner detector row; said method further comprising determining a collimator z-axis position offset from the detector array centerline at a point at which outer detector row signals are reduced to a full width at a half maximum. claim 1 3. A method in accordance with  claim 1  further comprising offset-correcting and view-averaging the obtained detector samples at a plurality of collimator step positions to obtain a set of detector samples for each collimator step position used in determining a beam position transfer function and determining a differential error for selection of the target beam position. claim 1 4. A computed tomography imaging system comprising an x-ray source, a detector array including a plurality of rows of detector elements, and a movable collimator positionable in steps and configured to collimate and position an x-ray beam produced by said x-ray source on said detector array, said system configured to: obtain detector samples at a plurality of collimator step positions while determining a position of a focal spot of the x-ray beam;  determine a beam position for each detector element at each collimator step utilizing the determined focal spot positions, a nominal focal spot length, and geometric parameters of the x-ray beam, collimator, and detector array; and  determine a detector element differential error according to ratios of successive collimator step positions. 5. A system in accordance with  claim 4  wherein the plurality of detector rows are z-axis detector rows, and the detector array has a centerline perpendicular to the z-axis, an outer detector row, and an inner detector row; and said system further configured to determine a collimator z-axis position offset from the detector array centerline at a point at which outer detector row signals are reduced to a full width at a half maximum. claim 4 6. A system in accordance with  claim 4  further configured to offset-correct and view-average the obtained detector samples at a plurality of collimator step positions to obtain a set of detector samples for each collimator step position used in determining a target beam position transfer function and in determining said differential-error for selection of said target beam position. claim 4