Comparing Whole-Body Diffusion-weighted MRI to Conventional Imaging: Staging Pediatric Bone and Soft-Tissue Sarcomas

Purpose To determine agreement between conventional staging and whole-body (WB) diffusion-weighted imaging (DWI) MRI in newly diagnosed pediatric sarcomas and to compare the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of each approach for lesion detection. Materials and Methods In this prospective single-center study (January 2014-February 2019), 47 participants (25 male participants; median age, 11.7 years [IQR, 7.49-15.63 years]) with Ewing sarcoma (n = 19), osteosarcoma (n = 7), rhabdomyosarcoma (n = 20), or non-rhabdomyosarcoma soft-tissue sarcoma (n = 1) underwent conventional staging and research-only WB MRI (T1-weighted, short tau inversion recovery, DWI). Using biopsy or clinical follow-up as the reference standard, authors determined staging agreement between conventional imaging, including PET/CT, and WB DWI instead of PET/CT. Two radiologists, aware of primary diagnoses but blinded to other information, recorded and scored lesions on a five-point Likert scale. A blinded nuclear medicine radiologist reviewed WB PET/CT images, recorded lesion locations, and scored them using the same method. One radiologist reconciled lesions with anatomic imaging. Primary outcomes were per-participant staging agreement and lesion-level sensitivity, specificity, PPV, and NPV. Statistical analysis used the Wilcoxon rank sum test for continuous variables and the McNemar test for paired proportions; P ≤ .05 indicated significance. Results There was 91.5% agreement among participants when comparing WB DWI and conventional staging (95% CI: 79.6, 97.6). Among 631 unique lesions, WB DWI sensitivity was 65.5% versus 30.2% for PET/CT (P < .001), while PET/CT specificity was 86.7% versus 66.4% for WB DWI (P < .001). WB DWI depicted more than twice as many malignant bone or bone marrow (151 vs 60) and lymph node sites (59 vs 28) as PET/CT. Conclusion WB DWI offered high agreement with conventional staging and higher sensitivity but lower specificity than PET/CT for metastatic lesion detection in pediatric sarcomas. Keywords: Diffusion-weighted MRI, Pediatric, Sarcoma, Staging, Whole-Body Imaging Supplemental material is available for this article. © RSNA, 2025.