An elliptical orbit backprojection filtering algorithm for SPECT

An orbit geometry where the central projection ray of the detector is not constrained to pass through the center-of-rotation for all projection angles can be useful to reduce uniformity artifacts and to avoid truncation when imaging noncentrally located organs. A backprojection filtering algorithm is presented for parallel geometry with an elliptical orbit acquisition. The algorithm is verified by computer simulations. It is shown that the point response function is shift invariant and has an analytical expression which is not the common 1/r but is a function of the orbit geometry