Preliminary Exploration of T_1ρ and T₂ Mapping in Porcine Articular Cartilage Using Very-Low-Field Magnetic Resonance Imaging.

Abstract

The high prevalence of osteoarthritis emphasizes the need for a cost-effective and accessible method for its early diagnosis. Recently, the portability and affordability of very-low-field (VLF) magnetic resonance imaging (MRI, 10-100 mT) have caused it to gain popularity. Nevertheless, there is insufficient evidence to quantify early degenerative changes in cartilage using VLF MRI. This study assessed the potential of T_1ρ and T₂ mapping for detecting degenerative changes in porcine cartilage specimens using a 50 mT MRI scanner. T₂- and T_1ρ-weighted images were acquired using a 50 mT MRI scanner with 2D spin-echo and triple-refocused T_1ρ preparation sequences. MRI scans of porcine cartilage were also acquired using a 3 T MRI scanner for comparison. A mono-exponential algorithm was applied to fit a series of T₂- and T_1ρ-weighted images. T₂ values for CuSO₄·5H₂O solutions measured via Carr-Purcell-Meiboom-Gill (CPMG) and spin-echo sequences were compared to verify the algorithm's reliability. The nonparametric Kruskal-Wallis statistical test was used to compare T₂ and T_1ρ values. Experimental repeatability was assessed using the root-mean-square of the coefficient of variation (rmsCV). T₂ values of the CuSO₄·5H₂O solutions obtained using the spin-echo sequence showed differences within 2.3% of those obtained using the CPMG sequence, indicating the algorithm's reliability. The T_1ρ values for varying concentrations of agarose gel solutions were higher than the T₂ values. Furthermore, 50 mT and 3 T MRI results showed that both the T_1ρ and T₂ values were significantly higher for porcine cartilage degraded for 6 h vs intact cartilage, with p-values of 0.006 and 0.01, respectively. Our experimental results showed good reproducibility (rmsCV < 8%). We demonstrated the feasibility of quantitative cartilage imaging via T₂ and T_1ρ mapping at 50 mT MRI for the first time.