ASTIGMATIC SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY IMAGING WITH A DISPLACED CENTER OF ROTATION

A filtered backprojection algorithm is developed for single photon emi ssion computed tomography (SPECT) imaging with an astigmatic collimato r having a displaced center of rotation. The astigmatic collimator has two perpendicular focal lines, one that is parallel to the axis of ro tation of the gamma camera and one that is perpendicular to this axis. Using SPECT simulations of projection data from a hot rod phantom and point source arrays, it is found that a lack of incorporation of the mechanical shift in the reconstruction algorithm causes errors and art ifacts in reconstructed SPECT images. The collimator and acquisition p arameters in the astigmatic reconstruction formula, which include foca l lengths, radius of rotation, and mechanical shifts, are often partly unknown and can be determined using the projections of a point source at various projection angles. The accurate determination of these par ameters by a least squares fitting technique using projection data fro m numerically simulated SPECT acquisitions is studied. These studies s how that the accuracy of parameter determination is improved as the di stance between the point source and the axis of rotation of the gamma camera is increased. The focal length to the focal line perpendicular to the axis of rotation is determined more accurately than the focal l ength to the focal line parallel to this axis. (C) 1998 American Assoc iation of Physicists in Medicine.