Fast 3D image reconstruction for rotating slat collimated gamma cameras

As an alternative to the use of traditional parallel hole collimators, SPECT imaging can be performed using rotating slat collimators. A gain in image quality could be expected from the higher photon collection efficiency, however, the plane integral data measured by this type of collimator require a reconstruction to invert the three-dimensional (3D) Radon transform. The use of iterative methods to do fully 3D reconstruction is computationally much more expensive compared to a classical SPECT reconstruction. A computationally attractive alternative to direct 3D reconstruction could be to use two subsequent inversion steps, where the first step would consist of reconstructing the plane integral data to conventional SPECT sinograms and the second step would be a classical SPECT reconstruction. In this work, an algorithm of the Maximum Likelihood Expectation Maximization (MLEM) type which integrates these two steps into one algorithm is proposed as an alternative to two subsequent MLEM reconstructions. A simulation study validates the new approach with respect to a two step MLEM reconstruction. Results indicate that the integration of two MLEM iteration loops into one can provide improved image quality regarding contrast recovery and noise. Moreover it avoids determining a stopping rule for the first step in the 2-step approach.