How to Provide Gadolinium-Free PET/MR Cancer Staging of Children and Young Adults in Less than 1 h: the Stanford Approach

PURPOSE: To provide clinically useful gadolinium-free whole-body cancer staging of children and young adults with integrated positron emission tomography / magnetic resonance (PET/MR) imaging in less than 1 h. PROCEDURES: In this prospective clinical trial, 20 children and young adults (11–30 years old, 6 male, 14 female) with solid tumors underwent 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) PET/MR on a 3T PET/MR scanner after intravenous injection of ferumoxytol (5mg Fe/kg) and [(18)F]FDG (2–3 MBq/kg). Time needed for patient preparation, PET/MR image acquisition and data processing was compared before (n = 5) and after (n = 15) time-saving interventions, using a Wilcoxon test. The ferumoxytol-enhanced PET/MR images were compared with clinical standard staging tests regarding radiation exposure and tumor staging results, using Fisher's exact tests. RESULTS: Tailored workflows significantly reduced scan times from 36 to 24 min for head to mid thigh scans (p < 0.001). These streamlined PET/MR scans were obtained with significantly reduced radiation exposure (mean 3.4 mSv) compared to PET/CT with diagnostic CT (mean 13.1 mSv; p = 0.003). Using the iron supplement ferumoxytol “off label” as an MR contrast agent avoided gadolinium chelate administration. The ferumoxytol-enhanced PET/MR scans provided equal or superior tumor staging results compared to clinical standard tests in 17 out of 20 patients. PET/MR had comparable detection rates for pulmonary nodules equal or greater 5 mm (94% vs. 100%), yet detected significantly fewer lung nodules compared to PET/CT for smaller nodules (20% vs 100%) (p = 0.03). [(18)F]FDG-avid nodules were detected with slightly higher sensitivity on the PET of the PET/MR compared to the PET of the PET/CT (59% vs 49%). CONCLUSION: Our streamlined ferumoxytol-enhanced PET/MR protocol provided cancer staging of children and young adults in less than 1 h with equivalent or superior clinical information compared to clinical standard staging tests. The detection of small pulmonary nodules with PET/MR needs to be improved.