Fast transmission CT reconstruction for SPECT using a block-iterative algorithm

We present an iterative transmission reconstruction algorithm based on prin ciples used for block-iterative emission reconstruction. Filtered backproje ction (FBP) is adequate for transmission CT image reconstruction under idea l conditions. In cases where insufficient count rates are obtained, FBP suf fers from significant biases. Our block-iterative transmission algorithm is developed by analogy to ordered-subset emission CT algorithms. We, show si milarities between our algorithm and a previously-proposed Ordered-Subset C onvex (OSC) algorithm. Under ideal conditions, our block-iterative transmis sion algorithm generates estimates of attenuation line integrals that are n ot significantly different from those from FBP or OSC. In the case of very low count-rate data, our block-iterative algorithm produces line integral e stimates that are less biased than those from FBP and nearly identical to t hose from OSC. We show that our algorithm is more computationally efficient than OSC. We conclude that our block-iterative method is a viable alternat ive to FBP and other iterative algorithms, especially under poor imaging co nditions.