Normal T₂ map profile of the entire femoral cartilage using an angle/layer-dependent approach

Purpose To create standard T₂ map profiles from the entire femoral cartilage of healthy volunteers in order to assess regional variations using an angular and layer-dependent approach. Materials and Methods Twenty healthy knees were evaluated using 3T sagittal images of a T₂ mapping sequence. Manual segmentation of the entire femoral cartilage was performed slice-by-slice by two raters using MatLab. Inter- and intrarater reliabilities were calculated using intraclass correlation coefficient (ICC) and Bland-Altman analysis. T₂ values were analyzed with respect to specific locations (medial condyle, trochlea, and lateral condyle), angles to B₀, and layers of cartilage (whole, deep, and superficial). Results Inter- and intrarater reliability obtained from the entire femoral cartilage was excellent (ICC = 0.84, 0.86, respectively). The ICCs around the trochlea were lower than those of the medial and lateral condyle. Both the inter- and intrarater Bland-Altman plots indicated larger differences in pixel count are seen as the size of the angular segment becomes larger. T₂ values were significantly higher in the superficial layer compared to the deep layer at each femoral compartment (P < 0.001). A magic angle effect was clearly observed, especially within the whole and deep layer over the medial and lateral femoral condyles, except for the superficial layer at the medial condyle. Conclusion The normal T₂ map profiles of the entire femoral cartilage showed variations in ICCs by location and in T₂ values by angles and layers. These profiles can be useful for diagnosis of early cartilage degeneration in a specific angle and layer of each condyle and trochlea.