Enhancement of SPECT reconstructions by means of coregistered MR data

The diagnostic potential of brain SPECT imaging is limited by its low spati al resolution. We propose an iterative reconstruction technique that is bas ed on the conjugate gradient (CG) algorithm and offers the possibility of i mproving the spatial resolution of the SPECT activity map of a patient, pro vided that an MR scan of the same patient is available. The SPECT data are reconstructed twice. The first reconstruction is to perm it 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, w hich solves a "shifted problem." While the iterations are carried out, the MR signal of low spatial frequency is replaced by the SPECT activity. Howev er, the high spatial frequency anatomical features contained in the MR imag e are weakly affected by the SPECT projector-back-projector operator. They remain in the iterates and increase their diagnostic potential. If an appro priate number of iterations is performed, quantitation is not significantly affected.