Ultrashort echo-time enhanced T2∗ (UTE-T2∗) mapping of articular cartilage is a novel quantitative MRI technique with the potential to visualize deep cartilage characteristics better than standard T2 mapping. The feasibility and intersession repeatability of UTE-T2∗ mapping of cartilage in vivo has not previously been evaluated.
Eleven asymptomatic subjects underwent repeat UTE-T2∗ imaging on a whole-body 3T MRI scanner on three consecutive days. Full-thickness, superficial and deep regions of interest (ROIs) were evaluated in the central weight-bearing zones of the medial femoral condyle (cMFC) and tibial plateau (cMTP). Intersession precision error across subjects was evaluated by the root-mean-square average coefficients of variation (RMSA-CV) and by the median of intra-subject standard deviations (SDs) of UTE-T2∗ values in each ROI.
UTE-T2∗ values in vivo were found to be repeatable with relative (RMSA-CV) intersession precision errors of 8%, 6%, 16% for full-thickness, superficial and deep cMFC ROIs, corresponding to absolute errors (SD) of 1.2, 1.5, 1.5 ms, respectively. In cMTP tissue, UTE-T2∗ relative repeatability was 8%, 8%, 13%, corresponding to absolute repeatability of 1.0, 1.5, 2.1 ms (full-thickness, superficial, deep). UTE-T2∗ values were higher in superficial cartilage compared to deep in both cMFC (P≪0.001) and cMTP (P=0.0004) regions.
In vivo 3D UTE-T2∗ mapping at 3T is feasible and can be implemented using a standard clinical MRI scanner and knee coil. Intersession precision error of UTE-T2∗ values in full-thickness ROIs in the weight-bearing regions of asymptomatic subjects is under 1.2 ms or 8% (RMSA-CV). Significant zonal and regional variations of UTE-T2∗ were seen.