Head movement is a major issue in dynamic brain PET imaging. The introduction of a simultaneous MR-PET scanner enabled new opportunities to use MR information for PET motion correction. Here we present a novel method based on routinely acquired MRI sequences. Multi-contrast MR images are co-registered to extract motion parameters. These motion parameters are then used to guide PET image reconstruction. Results on both phantom and human data provide evidences that this method can significantly enhance image contrast and reduce motion artefact in brain PET images, without affecting MR protocol.