Space microgravity has a serious impact on the health of the astronaut's musculoskeletal system and the success of space missions. For example, space microgravity will induce severe bone loss and a high risk of bone fracture. Besides, different bone loss rates will occur in different parts and regions of bone. The X-ray-based equipment for diagnosing bone disease can evaluate bone health, but it has ionizing radiation and is too large to monitor real-time bone quality in space. Therefore, it is of great importance and urgency to develop a portable instrument that is easy to operate without ionizing radiation to evaluate bone density in space microgravity environment.

Recently, we have investigated the feasibility of quantitative ultrasonic backscatter in evaluating human cortical and trabecular bone densities in vivo based on a head-down-tilt bed rest study, with 36 subjects being tested through 90 days of bed rest and 180 days of recovery. Backscatter measurements were performed using a novel ultrasonic backscatter bone diagnostic (UBBD) instrument. Backscatter parameters were calculated with a dynamic signal-of-interest method, which was proposed to ensure the same ultrasonic interrogated volume in cortical and trabecular bones. The backscatter parameters exhibited significant correlations with site-matched bone densities provided by high-resolution peripheral quantitative computed tomography (0.33<|R|<0.72, p<0.05). Some bone densities and backscatter parameters exhibited significant changes after the 90-day bed rest. The proposed method can be used in characterizing bone densities, and the portable UBBD device might be used in non-invasively revealing mean bone loss after long-term bed rest and microgravity conditions of spaceflight missions. The research results provide important theoretical basis and experimental data for the diagnosis of bone loss for astronauts in space station, and exert significance for the quantitative ultrasound non-invasively monitoring bone health in space missions.

The relevant research was published inUltrasound in Medicine and Biology, on April 2, 2021, with the title of "Ultrasonic backscatter measurements of human cortical and trabecular bone densities in a head-down bed rest study". The doctoral student Dongsheng Bi is the first author, and Professor Dean Ta is the corresponding author. This work was supported by the National Natural Science Foundation of China, Space Medical Experiment Project of China Manned Space Program, Program of Shanghai Academic Research Leader, etc.（Dongsheng Bi, Zhongquan Dai, Duwei Liu, Feng Wu, Chengcheng Liu, Ying Li, Boyi Li, Zhili Li, Yinghui Li and Dean Ta*, Ultrasound in Medicine and Biology, 47, 8, 2404-2415, 2021）