Methods

The conventional view posits that MR and PET are separate modalities, with MRI offering superior visualization of soft tissue anywhere in the body with some additional opportunities for physiological and biochemical measurement. PET, on the other hand, is recognized for its abilities to measure biochemical reactions (like glucose utilization) but it is seen as weak in its anatomic capability, due to limited spatial and temporal resolution. We see PET/MR as a paradigm-shifting new joint modality. Motion corrections derived from simultaneous MR are combined with Point Spread Function-corrections in the PET image reconstruction, allowing studies in human and animal subjects to achieve the full sensitivity and intrinsic resolution (~3mm) of the instrument, and enable novel explorations [1]. As we have demonstrated recently, and since PET and MR measurements are statistically independent, joint estimation of biochemical mechanisms that simultaneously affect both PET and MRI is guaranteed to improve SNR. Furthermore, we have already shown in the brain, that MR benefits from PET in the joint mapping of CBV and neurotransmission. Likewise, MRS benefits from PET in identifying areas to probe when differentiating between inflammation and tumoral processes, in the context of assessment of response to, and guidance of, radiotherapy [2]. In addition to physical improvement in image quality from simultaneous PET/MR imaging, we will explore the role of dual PET/MR radiopharmaceutical probes that can be used to probe simultaneously under the same conditions different physiological processes using a PET and an MR or an optical signal. Improvements in image quality and diagnostic accuracy will be illustrated in specific animal and patient studies and synergies between PET and MR will be discussed in the context of early diagnosis as well as guiding therapy. Beyond oncology, applications in cardiac (viability, perfusion and oxidative stress) and brain imaging (neurodegenerative disease, traumatic brain injury) will also be presented.

Acknowledgements

This work is supported by funding from the National Institutes of Health (R01HL110241, R01CA165221, R21EB021710, R01MH100350, R01HL118261) and the Gordon Foundation.