PET/MR clinical applications growing

Once limited to research novelty, PET/MR has expanded significantly, and in particular in neuroimaging applications and oncologic use—especially for imaging head and neck tumors, according to a review in the September issue of Current Radiology Reports.

The report estimates PET/MR’s time of arrival into clinical use at 2007 for brain imaging, but several other clinical indications have opened up for the hybrid, including cardiac PET/MR and pediatric imaging. Karin Anna Herrmann, MD, PhD, from the department of radiology at University Hospitals Case Medical Center and Case Western Reserve University in Cleveland, Ohio, and colleagues reported on a number of PET-related modalities, including PET/CT and PET/MR, and related several opportunities for the modality’s growth and its potential dose-reduction power.

“[PET/MR] is a new hybrid imaging modality combining two powerful diagnostic imaging tools,” wrote Herrmann et al. “The individual strengths and weaknesses of these two imaging modalities are believed to be synergistic and complementary in that the advantages of either component compensates for the limitations of the other. Thus, PET/MRI combines the highest anatomical detail as well as biochemical and functional information provided by MRI with the metabolic, molecular, and physiologic information from PET.”

An unpublished independent multireader study noted in the review compared FDG PET/CT and PET/MR of 14 subjects with head and neck neoplasms and indicated that the latter correctly identified 80 percent of the FDG-avid lesions caught by PET/CT. Complete inter-reader agreement in staging was documented for 11 out of the 14 subjects in the study and additional lymph node involvement was detected by PET/MR in the remaining cases. 

“Current evidence shows overall good correlation between PET/CT and PET/MRI in lesion detection across most publications and oncologic diseases,” wrote the authors. “However, there is lack of clearly defined prospective studies with a sufficient number of patients to validate these findings.”

PET/MR may be more useful for a new generation of biomarkers, but optimization and clearly defined protocols are needed to open the door to standard use. Still, it is uncertain whether PET/MR will ever gain the level of acceptance that its predecessor, PET/CT, has now reached.