Human Bone Loss Assessed by High-Resolution Peripheral Quantitative Computed Tomography and Ultrasonic Transmission Techniques

This study aims to investigate bone loss and recovery during simulated microgravity by high-resolution peripheral quantitative computed tomography (HR-pQCT) and ultrasonic transmission techniques, and to compare the efficacy of state-of-the-art ultrasonic transmission and backscatter techniques in assessing bone loss. Thirty-six male volunteers went through 90-day 6-degree head-down tilt bed rest and 180-day recovery. HR-pQCT was adopted to evaluate bone mineral density (BMD) and microstructure properties. Ultrasonic transmission measurements of calcaneal properties were performed, and were compared to previously reported backscatter measurements. The deterioration of the human skeleton was verified through significant bone loss (Total volumetric BMD (Tt.vBMD) reduced up to 2.16% until 30-day post-recovery) and microstructure deterioration (Cortical thickness reduced up to 6.88% after 90-day bed rest). Ultrasonic transmission measurements possessed comparable standardized long-term precision errors with HR-pQCT measurements. The ultrasonic transmission parameters exhibited significant correlations with bone densities (R up to 0.61, p < 0.001) and microstructure properties (R up to 0.60, p < 0.001) throughout bed rest and recovery periods. Multiple regression indicated that Tt.vBMD contributed significantly and independently in determining transmission parameters. The observed cortical thinning and changes in compartmental bone densities and areas provided evidence for the mechanism of endocortical bone transforming into the trabecular bone in response to bed rest. The results suggested the effectiveness of the transmission technique in monitoring immobilization-induced bone loss. The comparison between ultrasonic transmission, backscatter and HR-pQCT measurements promoted the application of the ultrasonic technique in assessing disuse-induced bone deterioration in long-term bed rest or spaceflights missions.