New and Emerging Techniques: PET/MR

Following PET/CT and SPECT/CT, PET/MR hybrid imaging is the most recent addition to the palette of hybrid cardiac imaging modalities. PET/MR synergistically combines the excellent soft tissue contrast and detailed image resolution of MR with metabolic information provided by PET. Integrated PET/MR systems furthermore offer the ability to acquire hybrid imaging data simultaneously (1). Beyond exact co-registration of PET and MR data this can be applied for MR-based motion correction of PET data. These features open up several cardiac applications, e.g. evaluation of cardiac function and viability, diagnosis of cardiac inflammatory diseases and tumorous diseases. To fully assess the diagnostic potential of PET/MR, however, several technical challenges have to be considered: attenuation correction (AC) of the patient tissues in PET/MR has to be based on MR-images and is currently hampered by a limited number of tissue classes and undercorrection of bone tissue. Cardiac radiofrequency (RF) coils and ECG gating equipment are currently not considered in AC. Consequently quantification of PET data therefore might be biased. The clinical workflow is rather complex and needs to be tailored to cardiac examinations. Few research groups currently explore this new hybrid imaging modality in selected cardiac applications.