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 non centrally located organs. We present a backprojection filtering algorithm for parallel geometry with an elliptical orbit acquisition and verify the algorithm by computer simulations. We show that the point response function is shift invariant and has an analytical expression which is not the common l/rbut is a function of the orbit geometry.