Purpose or Case Report: Diffusion weighted (DW) imaging is a standard component of many MRI exams. For musculoskeletal examinations, DW is used as a tool for assessing malignant and infectious/inflammatory processes. A recently developed novel silent and distortionless DWI sequence (DW-SD) has been previously shown to have less distortion and noise as well as having equivalent diffusion contrast and ADC values in normal tissues to standard echo-planar DW imaging (DW-EPI). We aim in this study to validate and assess this novel DW-SD method in pediatric extremity pathology cases.
Methods & Materials: DW-SD was implemented from a multi-segmented Rotating Ultra-Fast Imaging Sequence (RUFIS), modified with sinusoidal diffusion preparation gradients. The images were reconstructed with a total variation constraint. Phase cycling was used to reduce eddy current effects. With IRB approval and informed consent/assent, 33 pediatric patients (mean age 11.2 years, range 6 months–18 years) referred for extremity scans at 3T (MR750, GE Healthcare) and found to have osseous and/or soft tissue pathology were recruited (September 2018-October 2019). All examinations had both DW-SD and DW-EPI performed. DW-SD/EPI parameters: FOV: 160x160 mm, matrix: 128x128, slice thickness: 4mm, NEX: 2.5, b-values: 50 and 600. ADC values of both sequences were compared in lesions, normal bone marrow and normal muscle (two sided Wilcoxon sign-rank test). Comparative visualization of pathology was also assessed on b600 images and ADC maps (from -2=DW-EPI more delineated to +2=DW-SD more delineated, 0=same).
Results: Pathologies were malignant/benign/unknown osseous lesions (n=4/10/4), osseous/soft tissue infections (n=7/3), malignant soft tissue lesion (n=3) and other (n=2). DW-SD and DW-EPI ADC values for pathology, bone marrow and muscle had no significant difference (p=0.14, p=0.24 and p=0.16 respectively). Comparative visualization on b600/ADC was assessed as -2/EPI best delineation in 0/3%, -1/EPI preferred in 3/6%, 0/same in 61/45%, +1/SD preferred in 33/39%, +2/SD best delineation in 3/6%. DW-SD was at least preferred in all soft tissue pathologies due to greater geometric distortion seen on DW-EPI.
Conclusions: Silent distortionless diffusion has comparable ADC quantification with conventional DW-EPI in pediatric soft tissue and osseous pathologic lesions. DW-SD is likely to yield improved delineation of pathology due to reduced geometric distortion compared with conventional DW-EPI.