Effects of 60 d ( -6°) Head-down Bed Rest on MR T_2 Relaxation Times of Articular Cartilage in Human Being

Abstract：Objective To study with MRI T_2 relaxation time whether 60 d head-down( -6°) bed rest affects the spatial dependency of articular cartilage T_2. Methods During seven young healthy men before and after 60 d head-down ( -6°) bed rest, quantitative magnetic resonance (MR) T_2 maps of knee articular cartilage were obtained with a multiecho, spin-echo sequence with a 1. 5-T MR imager. T_2 profiles of the patellar, distal femoral weight- and non-weight-bearing and proximal tibial weight-bearing were obtained. The T_2 values of cartilage between before and after bed rest were compared with paired-samples t test. Results There was no difference in pattern of spatial variation cartilage T_2 between before and after bed rest. There was a trend toward decrease of T_2 relaxation time values at deep of cartilage and increase at surface of cartilage after bed rest. After bed rest there was a statistically significant (P <0. 05) decrease in T_2 value of lateral and medial tibial cartilage, and non-weight-bearing distal femoral cartilage in the deep zoon at normalized distance of 0. 3 (lateral tibial) , 0.0 and 0. 1 ( medial tibial) , as well as 0.0 ( non-weight- bearing distal femoral cartilage) , respectively. But after bed rest there was a statistically significant (P < 0. 05) increase in T_2 of medial tibial cartilage at normalized distance of 0.4 and 0. 5. There was no statistically significant change in weight-bearing femoral cartilage and patella cartilage between before and after bed rest. Conclusion Sixty days head-down ( -6°) bed rest has a little bit effect on deep of tibial cartilage, but no effect on most part of the articular cartilage T_2.