Patent Number: 056087764
Section: claims

1. A twin beam computed tomography scanner for performing a helical scan, comprising: an x-ray source for generating an x-ray to be projected generally towards, and at least partially through, an object;  a detector array comprising a plurality of detector cells, said cells arranged to form at least two cell rows;  a beam splitter positioned so that the x-ray projected from said x-ray source is substantially split to form at least two beams prior to being projected at least partially through the object;  a data acquisition system coupled to said detector array; and  a controller coupled to said data acquisition system and to said beam splitter for controlling said beam splitter so that the x-ray beams from said beam splitter do not substantially impinge on edge regions of said detector cells.  projecting an x-ray beam from the source towards the object and through the beam splitter as the source rotates around the object and as the object moves axially relative to the source along a z-axis;  detecting whether any beam impinges upon an edge region of a detector cell; and  if a beam impinges upon the edge region of a detector cell, then adjusting the beam splitter so that the beams do not substantially impinge upon the detector cell edge region. 2. A scanner in accordance with claim 1 wherein said detector cells are arranged so that a first edge of a first cell in a first cell row is adjacent a first edge of a first cell in a second cell row. 3. A scanner in accordance with claim 2 wherein each of said detector cells comprises at least a first edge region in which the sensitivity response of said detector cell is lower than the sensitivity response with respect to at least one other cell location. 4. A scanner in accordance with claim 3 wherein a collimator is positioned so as to substantially block x-rays from impinging on said first edges of said first and second cells. 5. A scanner in accordance with claim 1 wherein said beam splitter comprises a beam splitting member configured to cause a first input beam to be split into at least two output beams. 6. A scanner in accordance with claim 5 wherein said beam splitting member is constructed of x-ray absorbing material. 7. A scanner in accordance with claim 5 wherein said beam splitter further comprises first and second collimating members, said beam splitting member at least partially positioned in a beam path which extends between said first and second collimating members. 8. A scanner in accordance with claim 7 wherein said beam splitting member is movable relative to at least one of said collimating members. 9. A scanner in accordance with claim 5 wherein said beam splitting member has an elongate elliptical shape and is rotatable relative to at least one of said collimating members. 10. A scanner in accordance with claim 5 wherein said beam splitting member has a triangular shape. 11. A scanner in accordance with claim 5 further comprising first and second spaced collimating members, the relative orientations of said first and second collimating members and said beam splitting member being selectively adjustable based on a helical pitch. 12. A method of generating projection data for an object using a scanner having a beam splitter, an x-ray source and an x-ray detector array having at least two rows of detector cells, each detector cell having at least one edge region, said method comprising the steps of: 13. A method in accordance with claim 12 wherein the beam splitter includes first and second collimating members and a beam splitting member, and the relative orientation of the first and second collimating members and the beam splitting member is selected substantially based on helical pitch. 14. A method in accordance with claim 12 further comprising the step of collimating the x-ray beam prior to the beam being at least partially projected through the object. 15. A computed tomography system for performing a helical scan and for generating an image of an object, said system comprising an x-ray source, an x-ray detector array having adjacent rows of detector cells positioned to receive x-rays emitted from said x-ray source, and a pre-patient collimator positioned so that the x-ray projected from said x-ray source is substantially split to form at least two beams prior to being projected at least partially through the object to be imaged, said system further comprising an offset detector data acquisition system, a reference detector data acquisition system, a motor controller and a motor, said data acquisition systems coupled to said detector array, outputs from said data acquisition systems coupled to said motor controller, said motor being coupled to said pre-patient collimator and configured to control said pre-patient collimator so that the x-ray beams from said pre-patient collimator do not substantially impinge on edge regions of said detector cells. 16. A computed tomography system in accordance with claim 15 wherein said pre-patient collimator comprises a housing, a beam splitting member, and first and second collimating members. 17. A computed tomography system in accordance with claim 16 wherein said beam splitting member is movable relative to said collimating members.