Differentiation of human cartilage degeneration by functional MRI mapping-an ex vivo study.

OBJECTIVE: To evaluate whether the response to loading of cartilage samples as assessed ex vivo by quantitative MRI (qMRI) mapping techniques can differentiate intact and early degenerative cartilage. METHODS: Upon IRB approval and written informed consent, 59 macroscopically intact osteochondral samples were obtained from the central lateral femoral condyles of patients undergoing total knee replacement. Spatially resolved T1, T2, T2*, and T1ρ maps were generated prior to and during displacement-controlled quasi-static indentation loading to 405 µm (Δ1/2) and 810 µm (Δ1). Upon manual segmentation, absolute qMRI parameters and loading-induced relative changes (δ1/2, δ1) were determined for the entire cartilage sample and distinct zones and regions. Based on their histologically determined degeneration as quantified according to Mankin (Mankin sum scores [MSS], range 0-14), samples were dichotomised into intact (int; MSS 0-4, n = 35) and early degenerative (ed, MSS 5-8, n = 24). RESULTS: For T1ρ, consistent loading-induced increases were found for δ1/2 and δ1. Throughout the entire sample, increases in T1ρ were significantly higher in early degenerative than in intact samples (Δ1/2(ed) = 23.8 [q25 = 18.1, q75 = 29.0] %; Δ1/2(int) = 12.7 [q25 = 5.9, q75 = 19.5] %; p < 0.0005), according to Wilcoxon's signed-rank test). Zonal and regional analysis revealed these changes to be most pronounced in the sub-pistonal area. No significant degeneration-dependent loading-induced changes were found for T1, T2, or T2*. CONCLUSION: Aberrant load-bearing of early degenerative cartilage may be detected using T1ρ mapping as a function of loading. Hence, the diagnostic differentiation of intact versus early degenerative cartilage may allow the reliable identification of early and potentially reversible cartilage degeneration, thereby opening new opportunities for diagnosis and treatment of cartilage pathologies. KEY POINTS: • T1ρ mapping of the cartilage response to loading allows the reliable identification of early degenerative changes ex vivo. • Distinct response-to-loading patterns of cartilage tissue as assessed by functional MRI techniques are associated with biomechanical and histological tissue properties. • Non-invasive functional MR imaging techniques may facilitate the more sensitive monitoring of therapeutic outcomes and treatment strategies.

Functional MR Imaging Mapping of Human Articular Cartilage Response to Loading.

Purpose To determine if multiparametric magnetic resonance (MR) imaging mapping can be used to quantify the response to loading of histologically intact human knee cartilage. Materials and Methods Institutional review board approval and written informed consent were obtained. Twenty macroscopically intact cartilage-bone samples were obtained from the central lateral femoral condyles in 11 patients undergoing total knee replacement. A clinical 3.0-T MR imaging system was used to generate T1, T1ρ, T2, and T2* maps with inversion recovery, spin-lock multiple gradient-echo, multiple spin-echo, and multiple gradient-echo sequences. Serial mapping was performed at three defined strain levels (strain 0 [δ0], 0%; strain 1 [δ1/2], 19.8% ± 4.6 [standard deviation]; strain 2 [δ1], 39.5% ± 9.3) by using displacement-controlled static indentation loading. The entire sample and specific cartilage zones (superficial zone [SZ], transitional zone [TZ], and deep zone [DZ]) and regions (subpistonal area [SPA] and peripistonal area [PPA]) were defined as regions of interest. Upon log transformation, repeated measures analysis of variance was used to detect groupwise regional and zonal differences. Load-induced relative changes were determined and analyzed by using paired Student t test and Spearman correlation. Biomechanical testing (unconfined compression) and histologic assessment (Mankin score) served as the reference standard. Results All samples were histologically intact. Strain-related decreases were found at the SZ and TZ for T1 and T2*; for T1ρ, increases were seen in all zones; and for T2, increases were seen at the SZ and PPA only. Significant parameter changes in the entire sample depth of SPA versus PPA were found for δ1/2 (T1ρ, 14% ± 12 vs 6% ± 9) and δ1 (T1, -4% ± 5 vs -1% ± 3; T1ρ, 13% ± 12 vs 7% ± 7; T2*, -9% ± 12 vs -2% ± 8). SPA versus PPA changes were significant at the SZ and TZ (T1), TZ and DZ (T1ρ), and SZ (T2*). No significant correlations were found between relative changes and biomechanical or histologic parameters. Conclusion Serial multiparametric MR imaging mapping can be used to evaluate cartilage beyond mere static analysis and may provide the basis for more refined graduation strategies of cartilage degeneration. © RSNA, 2016 Online supplemental material is available for this article.