Abstract
PURPOSE: Magnetic resonance imaging of ex vivo cartilage measures parameters such as T(2) and magnetization transfer ratio (MTR), which reflect structural changes associated with osteoarthritis. Samples are often immersed in aqueous solutions to prevent dehydration and to to improve susceptibility matching. This study sought to determine the extent to which T(2) and MTR changes are attributable to immersion alone and to identify immersion conditions to minimize this confounding factor. METHODS: T(2) and MTR were measured before and after immersion for up to 24 hours at 4°C. Bovine nasal and articular cartilage and human articular cartilage were studied. Experimental groups included undisturbed immersion in Fluorinert FC-770, a susceptibility-matched, hydrophobic liquid with minimal tissue penetration, and immersion in Fluorinert, Dulbecco's phosphate-buffered saline (DPBS), or saline, with removal from the magnet between scans. (19) F and (1) H-MRI were used to detect cartilage penetration by Fluorinert and swelling, respectively. RESULTS: Saline and DPBS immersion rapidly increased T(2) , wet weight and cartilage volume and decreased MTR, suggesting increased water content for all cartilage types. Fluorinert-immersed samples exhibited minimal changes in T(2) or MTR. No ingress of Fluorinert was detected after 2 weeks of continuous immersion at 4°C. CONCLUSION: Ex vivo quantitative MR studies of cartilage may be confounded by the effects of immersion in aqueous solution, which may be comparable to or larger than effects attributed to pathology. These effects may be mitigated by immersion in perfluorocarbon liquids such as Fluorinert FC-770.