Out of This World
By Beth W. Orenstein  
Radiology Today  
Vol. 24 No. 8 P. 18    

When space travel was limited to astronauts, NASA would only consider candidates who were in pristine health. Carefully selecting astronauts based on health and fitness was one way of reducing the risk of serious medical emergencies while they were orbiting hundreds of miles above the Earth. In addition, at least one astronaut on each space flight is required to have the equivalent of paramedic-level training. Additionally, in the event of a medical emergency, a chief flight surgeon at Mission Control is stationed on the ground to talk the crew through emergency situations. 

In recent years, however, the number of astronauts and space tourists has risen. NASA is planning to build a long-term base on the moon by 2030 as well as launch the Gateway space station in lunar orbit to support its human deep space exploration plans, which include a future mission to Mars. Elon Musk’s SpaceX is advertising its Starship, a fully reusable transportation system designed to carry both crew and cargo to Earth’s orbit, the moon, Mars, and beyond. SpaceX says it will eventually carry up to 100 people on long-duration, interplanetary flights. Other private companies also are building commercial programs in outer space.

“It’s not just governments flying people into space anymore,” says Erik Antonsen, MD, PhD, MS, FAAEM, FACEP, an associate professor of space medicine at Baylor College of Medicine (BCM). The trend toward expanding space exploration requires a new look at how to keep travelers healthy, Antonsen says. “We are in a transition period for human spaceflight that really needs some updates on how we think about and do space medicine. Companies that are building space stations can’t just select the healthiest people. It really would hurt their business model if they tell people who are interested that they have to be very healthy to be considered.”

Next Generation Medicine
Antonsen says educators who have been involved in space medicine have already begun to respond. A number of new training programs have sprung up across the country that are different from previous training pathways for NASA flight surgeons, which were based on preventive medicine. “We now look to complement those programs with [more] of an acute care medical model,” he says.

One such program is the BCM and Massachusetts General Hospital (MGH) Space Medicine training program, a two year program for emergency medicine residency graduates that is designed to train them in clinical care, risk management, medical system design, research, and operational considerations supporting human activities in space. The program is administered by the department of emergency medicine at BCM and MGH, as well as the center for space medicine at BCM. It is sponsored by the Translational Research Institute for Space Health, the departments of emergency medicine at BCM and MGH, and commercial spaceflight partners. Antonsen is codirector of the fellowship.

Antonsen says the BCM-MGH program was started in 2021, around the same time as some other schools, with the goal of understanding “how we can enable everybody to fly in space. It’s to try to move away from a predominantly preventive model to a more multiaccess model that tries to balance preventive medicine with acute care response.”

Currently, the BCM-MGH program has three fellows in its two-year program. The fellows receive training and rotate through a variety of companies, operational experiences, and remote medicine experiences. The remote medicine experiences are important because they best mimic conditions related to space travelers.

“We also do lectures, didactics, and training for them that are specific to space flight,” Antonsen says. They learn about what happens to the body during spaceflight and what to include aboard the spacecraft for medical needs. Engineering medical equipment is challenging because space on spaceships is extremely limited, Antonsen notes.

Antonsen sees a large role for imaging and radiology in delivering this soon to-be newly needed health care in outer space. “There are a lot of forward-looking potential uses for radiology in this new space domain,” he says.

Ultrasound’s Key Role
Ultrasound has long been a part of medical care on space flights, Antonsen says. “It’s been on the space station for a long time.” Developments in ultrasound equipment have meshed well with the need for imaging in space. Ultrasound equipment is not only getting smaller and more compact but its capabilities are also improving. “Systems use less power and thus can more easily fit into the design of the spacecraft and needs of the crew’s health,” he says.

Incidental ultrasound findings in space have been critical. For example, in 2020, it was used to confirm a deep vein thrombosis in an astronaut on an International Space Station mission, Antonsen says. The ultrasound had been performed as part of a vascular research study and was guided in real-time and interpreted by two radiologists on Earth. The astronauts reviewed other ultrasound images and discovered more findings of interest in other crew members. In addition, astronauts can have urinary retention problems, and ultrasound can help identify what their postvoid residual is, Antonsen says.

Optical coherence tomography (OCT), effectively optical ultrasound, which images reflections from within tissue to provide cross-sectional images, is also in use in outer space. Many changes occur in the brain and eyes during space flight, Antonsen says. “We can do OCT in space to look at the back of the eyeball and use it to help us determine whether the changes we may see are nothing to worry about or something of concern that could potentially harm people down the road after a long spaceflight. There’s a lot of work going on in retinal imaging and space flights.” Spaceflight-Associated Neuro-Ocular Syndrome is a significant risk to human health in long duration spaceflight.

Ultrasound is also used to monitor, detect, and quantify venous gas emboli, contributing to studies on human prevalence of decompression sickness, which can be an issue for space travelers. Ultrasound is used postflight, as well. When astronauts return to Earth and land in the ocean in the middle of nowhere, the medical crew attending to them uses ultrasound to look for conditions such as dehydration and fluid responsiveness. Ultrasound is used to look for mineralized renal material to try to identify whether an astronaut/ space traveler is at risk of developing a kidney stone. “The imaging modality has enabled us to do an awful lot more than we otherwise would have been able to do pre, during, and postflight,” Antonsen says.

Ultimate Telemedicine
Antonsen says it’s important to have crew members who are trained in some of the basics of performing, reading, and interpreting scans because of the time lag involved with sending images to physicians at Mission Control. Often, someone at Mission Control guides them to obtain the appropriate images for both clinical and research purposes. “It’s the ultimate telemedicine,” Antonsen says. However, “when you start going further away from Earth, you eventually start losing the ability to have real-time guidance. For people doing radiological imaging of crews, it becomes a different challenge.” This is especially true for missions planned to Mars. It can take 45 minutes for a message to reach Mission Control and then return to the spacecraft, he says.

Antonsen says he’d like to see the space fellowship residents trained in IR procedures that could play a role in delivering health care in an emergency. What if someone were to get appendicitis? Obviously, there isn’t going to be a surgeon available to operate, nor an operating room in which to perform the surgery. “But if the traveler’s appendix were to perforate, you could use an IR technique to drain the abscess and try to temporize them that way,” he says. Similarly, if a traveler were to develop kidney stones, which could be the result of the microgravity environment signaling the body to reabsorb calcium into the blood, an IR technique could be used to insert a nephrostomy tube through the skin and into the kidney to help drain urine.

The first BCM-MGH space fellow has completed an ultrasound fellowship for emergency medicine, “and it’s a massive strength he brings to the program,” Antonsen says. The fellows are not being trained as radiologists, but they are taught certain radiological procedures that they may need to do while providing medical care during a space mission. Ideally, Antonsen says, the fellows will receive multispecialty training. “What we eventually would like to do is build the program out so that other specialties come and participate in these training programs. It’s not just preventive or emergency medicine pathways that are available but a shared pathway like critical care where folks from radiology could come in and teach the fundamentals as part of the core curriculum.”

To date, less than 700 people worldwide have gone up in space. “So, we don’t have a huge amount of data, and we’re still learning about the effects of space travel on the human body,” Antonsen says. “But as we see those numbers increase, we want to be prepared, and that’s the goal of our fellowship program.”

Harnessing X-rays
John Choi, MD, PhD, resident physician in IR at the Keck School of Medicine of the University of Southern California in Los Angeles, agrees that increased commercial activity in space will lead to more humans in space. More humans in space, such as on trips to Mars, “will be the driver for inflight space medicine and inflight space radiology,” he says.

Choi says the significant mass and electricity requirements of modern X-ray equipment, compared with ultrasound, have prevented its use in space. However, he says, “To do true clinical medicine in space during a mission, the full spectrum of radiology, including X-ray imaging, is needed.” While ultrasound is essential in space because it is portable and does not require much power, it can’t diagnose disease deep within the body, including life-threatening medical issues such as blood clots in major arteries of the heart, lungs, or brain, Choi says. X-ray imaging would also be useful in the management of chronic conditions such as nephrolithiasis and osteopenia, he adds.

“In addition to diagnostic applications, X-ray imaging could also enable interventional radiology procedures as well as new insights into the effects of space/microgravity on the human body,” Choi says.

Choi and his team believe that it may be possible to do X-ray imaging in space and are exploring a demonstration harnessing the natural radiation that is always present in space to collect X-ray images with minimal equipment. For the purpose of the demonstration, the team is using a form of X-ray equipment that is simpler than today’s digital technology and film. Their idea is to passively convert radiation into visible light that can then be captured with a digital camera, bypassing the need for sending powered X-ray equipment into space.

“The technology components to generate a radiograph in space already exist,” Choi says. “For example, we already have portable X-ray machines in the hospital. However, adapting those pieces for safe launch and safe operation aboard a manned spaceflight is a difficult and resource-intensive process.”

The team is working with SpaceX’s Falcon 9 rocket which will launch the Polaris Dawn mission from the historic Launch Complex 39A at Kennedy Space Center in Florida no later than next year. They are assembling the materials they need for the Polaris Dawn crew to use when conducting the experiment onboard. Choi believes “there is likely enough ambient radiation to cast an X-ray shadow.” Although this is not sufficient for clinical applications, if successful, it would be the first demonstration of a radiograph in space, he says. “These experiments would also be useful for characterizing the ambient noise background, which is critical for designing future X-ray imaging experiments.”

As more advanced in-flight imaging capabilities, including X-ray-based cross-sectional imaging, become possible, some form of formal radiology training will become increasingly important for medical personnel aboard spacecraft. “While reliance on an Earth-based radiologist may be possible in the near future, increasing distances of interplanetary travel will likely necessitate some form of radiology expertise among the crew, due to the roundtrip time delay for Earth communications, and thus radiology must be considered an important part of in-flight space medicine,” Choi says.

“There is no fundamental reason we cannot implement X-ray imaging in a spacecraft for clinical applications; it is a matter of cost vs benefit,” Choi says. “X-ray-based imaging is absolutely necessary for the full practice of modern medicine, and it is only a matter of time before it becomes a necessary part of in-flight space medicine.”

— Beth W. Orenstein of Northampton, Pennsylvania, is a freelance medical writer and a regular contributor to Radiology Today.