MRI Studies Find Source of Vision Impairment in Astronauts, Changes in Brain Matter of Football Players with Head Impact

Volume changes in cerebrospinal fluid (CSF), the clear fluid that helps cushion the brain and spinal cord while circulating nutrients and removing waste materials, is the primary reason for visual impairment in long-duration astronauts, according to a study presented at RSNA 2016.

Flight surgeons and scientists at NASA began seeing a pattern of visual impairment in astronauts who flew long-duration space missions. The astronauts had blurry vision, and further testing revealed, among several other structural changes, flattening at the back of their eyeballs and inflammation of the head of their optic nerves. The syndrome, known as visual impairment intracranial pressure (VIIP), was reported in nearly two-thirds of astronauts after long-duration missions aboard the International Space Station (ISS).

To learn more about the role of CSF in spaceflight-induced visual impairment and eye changes, study lead author Noam Alperin, PhD, professor of radiology and biomedical engineering at the University of Miami Miller School of Medicine in Miami, FL, and colleagues performed high-resolution orbit and brain MRI scans before and shortly after spaceflights for seven long-duration mission ISS astronauts.

They compared results with those from nine short-duration mission space shuttle astronauts. Using advanced quantitative imaging algorithms, the researchers looked for any correlation between changes in CSF volumes and the structures of the visual system.

The results showed that, compared to short-duration astronauts, long-duration astronauts had significantly increased post-flight flattening of their eyeballs and increased optic nerve protrusion. Long- duration astronauts also had significantly greater post-flight increases in orbital CSF volume, or the CSF around the optic nerves within the bony cavity of the skull that holds the eye, and ventricular CSF volume—volume in the cavities of the brain where CSF is produced. The large post-spaceflight ocular changes observed in ISS crew members were associated with greater increases in intraorbital and intracranial CSF volume.

“The research provides, for the first time, quantitative evidence obtained from short- and long-duration astronauts pointing to the primary and direct role of the CSF in the globe deformations seen in astronauts with visual impairment syndrome,” Dr. Alperin said.

Another study utilizing MRI and presented at RSNA found changes in both the gray and white matter that correlated with exposure to head impacts in high school football players after just one season.

The study included 24 players from a high school football team in North Carolina, each of whom wore a helmet outfitted with the Head Impact Telemetry System (HITS) during all practices and games. The helmets are lined with six accelerometers, or sensors, that measure the magnitude, location and direction of a hit. Data from the helmets can be uploaded to a computer for analysis.

In the study, each player underwent pre- and post-season imaging: a specialized MRI scan, from which diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) data were extracted to measure the brain’s white matter integrity, and a magnetoencephalography (MEG) scan, which records and analyzes the magnetic fields produced by brain waves. Diffusion imaging can measure the structural white matter changes in the brain, and MEG assesses changes in function.

The research team calculated the change in imaging metrics between the pre- and post-season imaging exams. They measured abnormalities observed on diffusion imaging and abnormally increased delta wave activity on MEG. The imaging results were then combined with player-specific impact data from the HITS. None of the 24 players were diagnosed with a concussion during the study.

“Change in diffusion imaging metrics correlated most to linear acceleration, similar to the impact of a car crash,” said Elizabeth Moody Davenport, PhD, a postdoctoral researcher at UT Southwestern Medical Center in Dallas, Texas, who led the analysis. “MEG changes correlated most to rotational impact, similar to a boxer’s punch. These results demonstrate that you need both imaging metrics to assess impact exposure because they correlate with very different biomechanical processes.”

Dr. Davenport said similar studies are being conducted this fall, and a consortium has been formed to continue the brain imaging research in youth contact sports across the country. “Without a larger population that is closely followed in a longitudinal study, it is difficult to know the long-term effects of these changes,” she said. “We don’t know if the brain’s developmental trajectory is altered, or if the off-season time allows for the brain to return to normal.”