Fast reconstruction of truncated transmission SPECT data

A least squares technique for reconstructing truncated data is presented when no a priori information is considered. It is applied to transmission SPECT data. The method consists in including the ramp filter into the conjugate gradient to speed convergence. The sinogram is extrapolated with zeros for filtering but extrapolated values are not considered during backward and forward projections. The first iteration presents artefacts that are corrected as soon as the second iteration. Tikhonov method is used to guarantee a unique solution and stabilize the reconstruction process. The resulting images are biased but this bias is recovered inside the field of view by a simple scaling process. The algorithm is fast and easy to regularize.