The goals of this research are to develop novel quantitative methods for simultaneous whole- body (WB) PET-MR imaging, validate these methods in a woodchuck model of spontaneous hepatocellular carcinoma and evaluate their clinical value, compared to PET-CT, in monitoring response to therapy in liver metastases. Simultaneous PET-MR is a novel and promising imaging modality that is generating substantial interest in the medical community and offers the scientific community many challenges and opportunities. Unlike sequentially- acquired WB PET-CT scans, the simultaneous acquisition of MR and PET data can be used to incorporate MR motion and anatomical MR priors within the PET reconstruction model. We hypothesize that the additional MR information will yield substantial improvement of PET in terms of lesion detection and activity estimation. We have formed a multi-disciplinary team that consists of scientists and clinicians to develop quantitative methods for PET-MR and evaluate clinically the improvement that can be achieved over conventional sequential PET-CT.