I was at the NASA Johnson Space Center in Houston earlier this month for my annual medical exam. This exam is part of the Longitudinal Study on Astronaut Health, an occupational surveillance program for former astronauts (see my earlier blog about this proactive medical surveillance program.) In addition to the usual physical exam and laboratory tests, this year I also had a DXA (dual-energy x-ray absorptiometry) scan to assess my bone health.
When astronauts live in weightlessness for long periods (as I did in 2009), our bones lose some of their density. If we did nothing to prevent this, then we would lose about 8 – 12 % of our bone calcium during a six-month expedition. Worrisome. To minimize this loss, astronauts aboard the International Space Station optimize our nutritional intake, take Vitamin D supplementation and partake in an intensive resistance exercise program.
As a former astronaut, I submit to a series of whole body and regional DXA scans every three years. Bone demineralization is such a concern that we like to stay on top of the issue. The good news is that these scans indicate that astronauts regain most of our bone mineral density postflight. What’s less certain is that we have regained our original bone strength.
I’m sure you’re wondering “how is it possible that bone could recover its mineral content after flight but still lose strength?”. Well, the rebuilt bone structure of an astronaut after flight might be inferior to what it was before flight. (Recall that bone is a dynamic tissue that is continually remodeling itself). If the internal bone architecture is sub-optimal, then we could be at risk for fractures.
Dr. Steven Boyd, a University of Calgary biomedical engineer and professor at the Schulich School of Engineering, the Faculty of Kinesiology and the Cumming School of Medicine, is in the midst of a research study to answer this bone strength question. He seeks to understand whether bone microarchitecture is affected by life in weightlessness and how it recovers as astronauts adapt back to life on earth. The study is funded by the Canadian Space Agency.
A DXA scanner does not produce images with high enough resolution to reveal bone microarchitecture. Dr. Boyd has a special CT scanner that does. Boyd’s team has installed imaging technology called micro-computed tomography (µCT) at the NASA Johnson Space Center. Members of his research team travel periodically to Houston to scan the ankle and arm bones of astronauts with the µCT before and after their six-month expeditions to the International Space Station. Associated engineering tools back at the McCaig Institute for Bone and Joint Research produce a three-dimensional virtual model that can distinguish micro-level changes in bone tissue and better assess bone strength.
I love the name for Dr. Boyd’s research project. It’s called TBone, probably to reflect the novel ‘three-dimensional bone’ imaging techniques he uses. However, the next time I eat a t-bone steak, I’ll closely examine the internal structure of the bone on my dinner plate and think about the truss-like trabeculae that give strength to our bones.
I’m proud that the University of Calgary is addressing such a key question for the space program. As a former astronaut, I have a personal investment in the answer. The research results will also be relevant to osteoporosis patients on Earth and to future astronauts who will fly on long duration voyages to Mars.