Purpose or Case Report: Cartilage imaging in adults has been a rich area of research in which MR T2 and T1rho mapping provide complementary information regarding the extracellular matrix, including collagen fibers and glycosaminoglycans, respectively. However, in the pediatric population, there remains a need to obtain normative data for these variables during skeletal maturation.

The purpose of this study is to provide complementary information regarding cartilage during skeletal maturation with T2 and T1rho maps.
Methods & Materials: Twenty two asymptomatic subjects (5 to 23 yrs, mean 14.6 +/- 5.3 yrs, 10 female,12 male) underwent knee MRI including axial and sagittal T2 and T1 rho mapping with 3T scanner. Mean T2 and T1rho of the patella and distal femur (anterior, central, and posterior) were measured. Physeal patency (open, closing/closed) was recorded. Mean values were correlated with age (Pearson correlation) and compared based on physeal patency (t-test) and location (1-way ANOVA). In addition, spatial variation (mean values as a function of normalized distance from the osteochondral to articular surface) was evaluated for patellar and distal femoral cartilage.
Results: There was a statistically significant decrease in mean T2 and T1rho as a function of age (r= -0.60 and -0.59 respectively, p<0.05). The open physis group had longer T2 (anterior: 52.4 vs. 46.5, posterior: 50.6 vs. 41.9 msec) and T1rho (anterior: 51.9 vs. 42.6, posterior: 53.0 vs. 46.7) than the closing/closed physis group at the anterior and posterior femur (p<0.05). The open physis group had longer values than the closing/closed group at the patella on T2 (45.1 vs. 38.6, p<0.05), but no difference on T1rho. The central femur showed longer T2 (53.7 msec) and T1 rho values (49.2 msec) than anterior and posterior with statistical significance on T2 (p<0.05). Spatial variation of T2 and T1rho showed similar patterns in the patellar and femoral cartilage, initially decreasing just beyond the osteochondral junction and then gradually increasing toward the articular surface.
Conclusions: Contrary to adult senescent changes, which result in increased T2 and T1rho due to degeneration, skeletal maturation results in a sequential decrease in both T2 and T1rho in cartilage. There is regional variation in cartilage with the longest value in the weight bearing portion. Despite T2 and T1 rho reflecting different properties of the microstructure of cartilage, spatial variation follows similar patterns for both maps.