Reproducibility of Quantitative Double-Echo Steady-State T Mapping of Knee Cartilage.

Background: Cartilage T can detect joints at risk of developing osteoarthritis. The quantitative double-echo steady state (qDESS) sequence is attractive for knee cartilage T mapping because of its acquisition time of under 5 minutes. Understanding the reproducibility errors associated with qDESS T is essential to profiling the technical performance of this biomarker.

Purpose: To examine the combined acquisition and segmentation reproducibility of knee cartilage qDESS T using two different regional analysis schemes: 1) manual segmentation of subregions loaded during common activities and 2) automatic subregional segmentation.

Study Type: Prospective.

Subjects: 11 uninjured participants (age: 28 ± 3 years; 8 (73%) female).

Field Strength/sequence: 3-T, qDESS.

Assessment: Test-retest T maps were acquired twice on the same day and with a 1-week interval between scans. For each acquisition, average cartilage T was calculated in four manually segmented regions encompassing tibiofemoral contact areas during common activities and 12 automatically segmented regions from the deep-learning open-source framework for musculoskeletal MRI analysis (DOSMA) encompassing medial and lateral anterior, central, and posterior tibiofemoral regions. Test-retest T values from matching regions were used to evaluate reproducibility.

Statistical Tests: Coefficients of variation (%CV), root-mean-square-average-CV (%RMSA-CV), and intraclass correlation coefficients (ICCs) assessed test-retest T reproducibility. The median of test-retest standard deviations was used for T precision. Bland-Altman (BA) analyses examined test-retest biases. The smallest detectable difference (SDD) was defined as the BA limit of agreement of largest magnitude. Significance was accepted for P < 0.05.

Results: All cartilage regions across both segmentation schemes demonstrated intraday and interday qDESS T CVs and RMSA-CVs of ≤5%. T ICC values >0.75 were observed in the majority of regions but were more variable in interday tibial comparisons. Test-retest T precision was <1.3 msec. The T SDD was 3.8 msec.

Data Conclusion: Excellent CV and RMSA-CV reproducibility may suggest that qDESS T increases or decreases >5% (3.8 msec) could represent changes to cartilage composition.

Technical Efficacy: Stage 2.