T(1ρ)-mapping for assessing knee joint cartilage in children with juvenile idiopathic arthritis — feasibility and repeatability

BACKGROUND: Ongoing arthritis in children with juvenile idiopathic arthritis (JIA) can result in cartilage damage. OBJECTIVE: To study the feasibility and repeatability of T(1ρ) for assessing knee cartilage in JIA and also to describe T(1ρ) values and study correlation between T(1ρ) and conventional MRI scores for disease activity. MATERIALS AND METHODS: Thirteen children with JIA or suspected JIA underwent 3-tesla (T) knee MRI that included conventional sequences and a T(1ρ) sequence. Segmentation of knee cartilage was carried out on T(1ρ) images. We used intraclass correlation coefficient to study the repeatability of segmentation in a subset of five children. We used the juvenile arthritis MRI scoring system to discriminate inflamed from non-inflamed knees. The Mann-Whitney U and Spearman correlation compared T(1ρ) between children with and without arthritis on MRI and correlated T(1ρ) with the juvenile arthritis MRI score. RESULTS: All children successfully completed the MRI examination. No images were excluded because of poor quality. Repeatability of T(1ρ) measurement had an intraclass correlation coefficient (ICC) of 0.99 (P<0.001). We observed no structural cartilage damage and found no differences in T(1ρ) between children with (n=7) and without (n=6) inflamed knees (37.8 ms vs. 31.7 ms, P=0.20). However, we observed a moderate correlation between T(1ρ) values and the juvenile arthritis MRI synovitis score (r=0.59, P=0.04). CONCLUSION: This pilot study suggests that T(1ρ) is a feasible and repeatable quantitative imaging technique in children. T(1ρ) values were associated with the juvenile arthritis MRI synovitis score.