Use of DXA-based software to identify astronauts at risk for persisting spaceflight-induced bone loss

Dual-energy X-ray absorptiometry (DXA) alone is not ideal for fracture risk assessment given its two-dimensional nature. We evaluated the 3D-Shaper software for its potential to detect an unappreciated hip trabecular bone loss in astronauts. DXA-based 3D-Shaper software showed promising results as a screening tool while minimizing radiation exposure.

Prolonged spaceflight results in bone loss, as assessed by DXA performed before and after long-duration missions. Hip trabecular loss, detected by QCT but not DXA, persists in some astronauts for up to 2 years after 6-month missions. Since QCT increases radiation exposure, we evaluated a DXA software (3D-Shaper) as a screening method to identify astronauts in whom inadequate recovery of hip trabecular bone would be likely confirmed with QCT.

Hip data from 23 ISS astronauts (19 M/4F) with pre- and postflight QCT and DXA were analyzed. These scans were obtained pre-flight (within 4 months of launch), immediately post-flight (within 22 days of return), and 1-year post-flight (within 11-14 months). Left total hip data by DXA, QCT, and 3D-Shaper were expressed as percent change from pre-flight and evaluated by repeated measures ANOVA. A regression analysis of 1-year post-flight data compared the abilities of DXA (total hip areal BMD [aBMD]) and 3D-Shaper (trabecular volumetric BMD [Trab vBMD]) to predict persisting trabecular bone deficits as determined by QCT.

Immediate postflight mean (SD) total hip aBMD was reduced by 3.9 (2.4)% with greater loss (p < 0.001) demonstrated by QCT and Shaper: 9.0 (7.2)% and 6.8 (4.5%), respectively. At 1-year post-flight, compared with QCT Trab vBMD change, R² for the regression analysis of 3D-Shaper Trab vBMD change was 0.40 vs. 0.14 for DXA total hip aBMD.

3D-Shaper software predicts QCT-detected trabecular bone loss better than DXA and has the potential to serve as a screening tool for QCT-detection of trabecular bone loss.