Purpose or Case Report: To determine if diffusion weighted imaging (DWI) adds value to PET/MRI in pediatric solid tumors.
Methods & Materials: After obtaining IRB approval, all pediatric simultaneous PET/MR studies with DWI performed between April 2015 and August 2017 were concurrently interpreted by 2 blinded readers (board certified pediatric and nuclear medicine radiologists) in 2 sessions. In session 1, the 2 readers had access to whole body PET, Dixon, and HASTE images. Images were assessed for quality, number and location of lesions, designation as malignant or not. After 6 weeks, in session 2 the above images were re-reviewed by same readers with DWI added, for the above assessment with the added value of DWI. The results of the two sessions were compared by an independent reviewer.
Results: PET/MR with DWI was available in 20 cases (10 boys), age range: 5 months-18 years (median 10.7 years). Tumors included: rhabdomyosarcoma (6), Ewing sarcoma (4), neurofibromatosis-1 (5), post-transplant lymphoproliferative disease (2), clear cell renal carcinoma (1), squamous cell carcinoma (1), and neuroblastoma (1). A total of 44 lesions were identified in session 1; 23 designated malignant and 21 benign. DWI did not detect any additional distant foci of disease in session 2. No change in final diagnosis or local extent of disease was noted in 19/20 cases. In one patient with Ewing sarcoma the local extent of osseous tumor was greater with DWI than with PET.
Conclusions: Diffusion weighted imaging had no impact on distant staging in our pediatric cohort, but may add value in local staging. Routine performance of whole body DWI can be eliminated and limited to the region of interest in pediatric patients undergoing PET/MRI to improve patient throughput.