UCSF

Magnetic Resonance Imaging (MRI) of cartilage offers unique insights into biochemical and microstructural processes of degeneration that might be useful in characterizing the early stages of Osteoarthritis. Quantitative MR imaging sequences enable us to map magnetic relaxation parameters of the tissue, including T_1ρ and T₂, which are highly sensitive to microscopic changes in cartilage. Different imaging strategies and mathematical models have been used to quantify T_1ρ. In this study we compare two strategies for T_1ρ imaging: the SPGR-based MAPSS sequence, and the FSE-based CUBE sequence. The sequences were evaluated using simulation, phantom scans, and in vivo human scans. The CUBE sequence appears to outperform the MAPSS sequence in terms of SNR efficiency and repeatability on the basis of phantom and human studies. The CUBE sequence was then used to evaluate the feasibility of performing multi-exponential T_1ρ quantification in a 63 TSL scan of a porcine knee specimen. The multi-exponential T_1ρ procedure was able to identify two spin populations, even when the number of TSLs used to fit the model was reduced to 16. This data suggests the feasibility of performing multi-component T_1ρ imaging in vivo, especially if combined with advanced accelerating techniques in the future. The results from this study need to be confirmed by larger scale studies.