A Backprojection-Based Parameter Estimation Technique for Skew-Slit Collimation

To estimate geometric parameters in a skew-slit single photon emission computed tomography (SPECT) scan, a simple method is presented that uses a single point source and a backprojection process. The method employs one point source placed sufficiently far from the axis of rotation but in the field of view. A skew-slit geometry is considered where the estimated parameters include the focal lengths of both opaque planes and the location of multiple transaxial slits and a single axial slit. Computer simulations show that view-angle independent parameters can be uniquely estimated. Three experimental scans were performed, and the view-angle independent parameters were accurately estimated. Tilt, sagging, and mechanical shifts result in parameters that change depending on the view angle in the experimental scans. These view-angle dependent parameters were estimated using the single point-source technique, but reconstructed phantom images showed some error in the estimation of the view-angle dependent parameters.