Patent Number: 052241360
Section: claims

1. An apparatus for acquiring a tomographic projection set of an imaged object, the apparatus comprising: an x-ray generator for projecting a beam of x-rays through the imaged object at a plurality of angles about the imaged object gantry plane substantially perpendicular to a translation axis;  an x-ray detector opposing the x-ray generator through the imaged object for receiving the x-ray beam at the plurality of angles to create a projection set;  a table for supporting and translating the imaged object by a translation distance along a translation axis with the acquisition of the projection set during a first period, the translation being concurrent with the projections of the plurality of angles;  a means for alternately sweeping the beam by a predetermined compliance distance along the translation axis in a first direction during the first period, and in a second direction along the translation axis but counter to the translation of the imaged object during a second period, wherein the compliance distance is limited to less than the translation distance and wherein the beam of x-rays is received by the x-ray detector throughout the sweeping of the beam by the compliance distance. 2. The apparatus as recited in claim 1 including additionally an exposure controller for controlling the exposure of the imaged object by the x-ray beam during the first period so that the exposure during the first period is greater than the x-ray exposure of the imaged object by the x-ray beam during a second period. 3. The apparatus as recited in claim 2 wherein the exposure controller reduces the intensity of the x-ray beam during the second period. 4. The apparatus as recited in claim 1 wherein the means for alternatively sweeping sweeps the x-ray beam during a first portion of the first period so as to maintain the beam centered on a predetermined volume element on the translation axis in the imaged object within the predetermined compliance distance and stops the sweeping of the x-ray beam during a second portion of the first period at the limit of the predetermined compliance distance. 5. The apparatus as recited in claim 4 wherein the first portion is divided equally between the start and end of the first period. 6. The apparatus as recited in claim 1 wherein the means for alternatively sweeping, sweeps of the x-ray beam during the first period so as to maintain a constant angular motion of the beam during the first period. 7. The apparatus recited in claim 1 wherein the means for alternatively sweeping comprises a collimator positioned between the x-ray generator and the imaged object, the collimator having an aperture movable along the translation axis. 8. The apparatus recited in claim 1 wherein the means for alternatively sweeping comprises an x-ray source having a focal point movable along the translation axis and collimator having a aperture movable along the translation axis.