Effect of hydration on signal intensity of gelatin phantoms using low-field magnetic resonance imaging: Possible application in osteoarthritis

Five gelatin phantoms were constructed to study the effect of matrical hydr ation on magnetic resonance imaging (MRI) signal intensity using a low-fiel d strength imager, Water content of the phantoms ranged from 75 to 95% weig ht/weight. Signal intensity values of each phantom were measured using five imaging sequences: proton density, T1-weighted, T2-weighted, inversion rec overy with short inversion time, and inversion recovery with long inversion time. There was significant positive correlation (p < .05) of signal inten sity with differences in hydration using the T2-weighted sequence and the i nversion recovery sequence with short inversion time. Significant negative correlations (p < .05) were found with T1-weighted imaging and the inversio n recovery sequence with long inversion time. In a second part of the study , in vivo focal variations in MRI signal intensity were evaluated in a cani ne cranial cruciate ligament deficient model of osteoarthritis. Signal inte nsity measurements were obtained from multiple areas of articular cartilage to identify an initial stage in osteoarthritis that is characterized in pa rt by increased hydration of articular cartilage. At 6 weeks post-transecti on of the cranial cruciate ligament, an increase in signal intensity was de tected in the articular cartilage of the weight-bearing portion of the late ral femoral condyle and the caudal portion of the medial tibial condyle wit h T1-weighted imaging. The increase in signal intensity may reflect increas ed proteoglycan synthesis by chondrocytes that also occurs early in the pat hogenesis of osteoarthritis.