Enhancement of SPECT reconstructions by means of coregistered MR data

The diagnostic potential of brain SPECT imaging is limited by its low spatial resolution. We propose an iterative reconstruction technique that is based on the conjugate gradient (CG) algorithm and offers the possibility of improving the spatial resolution of the SPECT activity map of a patient, provided that an MR scan of the same patient is available. The SPECT data are reconstructed twice. The first reconstruction is to permit an accurate coregistration of the MR image to the SPECT one. Then, this coregistered MR image is used as the starting point for the CG algorithm, which solves a "shifted problem." While the iterations are carried out, the MR signal of low spatial frequency is replaced by the SPECT activity. However, the high spatial frequency anatomical features contained in the MR image are weakly affected by the SPECT projector-backprojector operator. They remain in the iterates and increase their diagnostic potential. If an appropriate number of iterations is performed, quantitation is not significantly affected.