Zero echo time pediatric musculoskeletal magnetic resonance imaging: initial experience

Background Projection radiography (XR) is often supplemented by both CT (to evaluate osseous structures with ionizing radiation) and MRI (for marrow and soft-tissue assessment). Zero echo time (ZTE) MR imaging produces a “CT-like” osseous contrast that might obviate CT. Objective This study investigated our institution’s initial experience in implementing an isotropic ZTE MR imaging sequence for pediatric musculoskeletal examinations. Materials and methods Pediatric patients referred for extremity MRI at 3 tesla (T) underwent ZTE MR imaging to yield images with contrast similar to that of CT. A radiograph-like image was also created with ray-sum image processing. We assessed ZTE–CT/XR anatomical image quality (S anat ) from 0 (nondiagnostic) to 5 (outstanding). Further, we made image comparisons on a 5-point scale (S comp ) (range of −2 = conventional CT/XR greater anatomical delineation to +2 = ZTE–CT/XR greater anatomical delineation; 0=same) for three cohorts: (1) ZTE–XR to conventional radiography, (2) ZTE–CT to conventional CT and (3) pathological lesion assessment on ZTE–XR to conventional radiography. We measured cortical thickness of ZTE–XR and ZTE–CT and compared these with conventional imaging. We calculated confidence interval of proportions, Wilcoxon rank sum test and intraclass correlation coefficients for inter-reader agreement. Results Cohorts 1, 2 and 3 consisted of 40, 20 and 35 cases, respectively (age range 0.6−23.0 years). ZTE–CT versus CT and ZTE–XR versus radiography of cortical thicknesses were not significantly different ( P =0.55 and P =0.31, respectively). Cortical delineation was rated diagnostic or better (score of 3, 4 or 5) in all cases (confidence interval of proportions = 100%) for ZTE–CT/XR. Similarly, intramedullary cavity delineation was rated diagnostic or better in all cases for ZTE–CT, and ZTE–XR was at least diagnostic in 58–63% of cases. For cohort 2, cortex and intramedullary cavity S comp for ZTE–CT was comparable to those of conventional CT, with confidence interval of proportion (sum of score of −1 to +2) of 93−100% and 95%, respectively. Pathology visualized on ZTE–CT/XR was comparable; S comp confidence interval of proportions was 95%/97–100%, with improved delineation of non-displaced fractures on ZTE–XR. Readers had moderate to near-perfect intraclass correlation coefficient (range=0.60–0.93). Conclusion Implementation of a diagnostic-quality ZTE MRI sequence in the pediatric population is feasible and can be