An elliptical orbit backprojection filtering algorithm for SPECT

An orbit geometry where the central projection ray of the detector does not pass through the center of rotation for all projection angles can be useful for reducing uniformity artifacts, and, more importantly, for avoiding truncation when imaging the heart with converging collimators. A backprojection filtering algorithm for an elliptical orbit geometry is presented. It is shown that the point response function for parallel geometry is shift-invariant and is equal to l/r modulated by the orbit geometry. The algorithm is verified by computer simulations