Infectious Disease

Widespread utilization of FDG-PET has revealed that infection and immune-mediated inflammatory disorders are readily detected by this technique. Simultaneous PET/MRI may improve our understanding of the interaction between neurochemistry/neurotransmitter-mediated processes and their functional, metabolic, and hemodynamic consequences in healthy brains and various diseases. The most clinically relevant advantages of PET/MRI compared to PET/CT include reduction in radiation exposure, higher soft tissue resolution, and co-acquisition. The superior soft tissue contrast of MRI compared to CT allows a better anatomic layout that provides for a more detailed assessment of soft tissues. In addition, for equivalent injected activity, PET/MRI allows a 20% reduction in radiation exposure compared to PET/CT if attenuation correction only is used or up to 60–73% when both attenuation correction and diagnostic quality CT studies are acquired with PET/CT (Atkinson et al., Abdom Radiol 41:13338–48, 2016; Schafer et al., Radiology 273:220–31, 2014). Moreover, the potential to extend PET data counting over the entire MR acquisition time improves the quality of the PET images and allows the injected activity to be reduced in an inversely proportional manner. This advantage of reduced dose is particularly beneficial in the pediatric population. Acquiring both PET and MR in a single session on a hybrid system minimizes patient discomfort while maximizing clinical information and optimizing registration of both modalities. It incorporates simultaneous assessment of noninvasive biomarkers based on multiparametric imaging comprising morphologic, functional, and metabolic features. The combination of reduced ionizing radiation exposure, superior soft tissue resolution, and multiple quantitative biomarkers leverages PET/MRI to a highly promising modality for imaging of inflammatory and infectious diseases. In this chapter, we review the use of PET/MRI in inflammatory and infectious CNS disorders. We hope that education on the potential for this very important application will lead to future more widespread utilization in the clinical setting.