Simultaneous Whole-Body PET/MR Imaging in Comparison to PET/CT in Pediatric Oncology: Initial Results

Purpose: To compare positron emission tomography (PET)/magnetic resonance (MR) imaging and PET/computed tomography (CT) for lesion detection and interpretation, quantification of fluorine 18 (F-18) fluorodeoxyglucose (FDG) uptake, and accuracy of MR-based PET attenuation correction in pediatric patients with solid tumors. Materials and Methods: This prospective study had local ethics committee and German Federal Institute for Drugs and Medical Devices approval. Written informed consent was obtained from all patients and legal guardians. Twenty whole-body F-18-FDG PET/CT and F-18-FDG PET/MR examinations were performed in 18 pediatric patients (median age, 14 years; range, 11-17 years). F-18-FDG PET/CT and F-18-FDG PET/MR data were acquired sequentially on the same day for all patients. PET standardized uptake values (SUVs) were quantified with volume of interest measurements in lesions and healthy tissues. MR-based PET attenuation correction was compared with CT-derived attenuation maps (mu-maps). Lesion detection was assessed with separate reading of PET/CT and PET/MR data. Estimates of radiation dose were derived from the applied doses of F-18-FDG and CT protocol parameters. Descriptive statistical analyses were performed to report correlation coefficients and relative deviations for comparison of SUVs, rates of lesion detection, and percentage reductions in radiation dose. Results: PET SUVs showed strong correlations between PET of PET/CT (PETCT) and PET of PET/MR (PETMR) (r > 0.85 for most tissues). Apart from drawbacks of MR-based PET attenuation correction in osseous structures and lungs, similar SUVs were found on PET images corrected with CT-based mu-maps (13.1% deviation of SUVs for bone marrow and <5% deviation for other tissues). Lesion detection rate with PET/MR imaging was equivalent to that with PET/CT (61 areas of focal uptake on PETMR images vs 62 areas on PETCT images). Advantages of PET/MR were observed especially in soft-tissue regions. Furthermore, PET/MR offered significant dose reduction (73%) compared with PET/CT. Conclusion: Pediatric oncologic PET/MR is technically feasible, showing satisfactory performance for PET quantification with SUVs similar to those of PET/CT. Compared with PET/CT, PET/MR demonstrates equivalent lesion detection rates while offering markedly reduced radiation exposure. Thus, PET/MR is a promising modality for the clinical work-up of pediatric malignancies. (C) RSNA, 2014