Diagnostic Imaging Online
June 3, 2002

Diffuse optical tomography takes baby steps on Earth before launching into space

A portable lightweight brain imaging cap using diffuse optical tomography (DOT) may give fMRI a run for its money. It could eventually be used on Earth to diagnose stroke and in space to measure health risks related to long-duration flights.

Study participants complete motor performance tasks while wearing the brain imaging cap and undergoing fMRI. Results will be compared to validate the imaging cap's accuracy in accessing brain activity. (Photos courtesy of L. Barry Hetherington, NSBRI)
Functional brain activation during the performance of a simple motor task (colors) as measured by DOT coregistered with and overlaid on an anatomical MR image of the person performing the task. Color indicates the magnitude of blood oxygenation change during the task relative to baseline. Bright dots "floating" above the head are actually vitamin E capsules used to localize the optical probe with respect to the MRI. (Provided by G. Strangman)

The brain cap is being developed by the smart medical systems team at the National Space Biomedical Research Institute in Houston. Led by NSBRI director Dr. Jeffrey Sutton, the team will investigate how the cap can detect brain function during the performance of important tasks in real-world scenarios. The team hopes to use the cap in space to measure neurobehavioral problems, head trauma, and changes in intracranial pressure, all possible side effects to extended stays.

Near-infrared spectroscopy is the technology that underlies DOT, according to Gary Strangman, Ph.D., director of the neural systems group at Massachusetts General Hospital. DOT uses a sensing probe that collects multiple overlapping near-infrared spectroscopy measurements. This information enables the generation of images from the detected diffuse light.

The medical systems team at the NSBRI and the MGH Photon Migration Lab are conducting validation studies on the new technology. Researchers expect to enroll 40 subjects in the 12 to 18-month study, according to Strangman. The study will look into how well the cap's performance stacks up against fMRI, now the gold standard for noninvasive measurement of brain activity.

Alhough fMRI exhibits better spatial resolution, DOT and the brain cap have several advantages, including portability and lower costs.

"The cost of DOT imaging is much lower than with MRI," Strangman said. "At MGH, a typical MR scan will cost on the order of $1000/hour. This covers instrument upkeep, upgrades, technical personnel. DOT equipment requires virtually no upkeep and no auxiliary technical personnel."

While the researchers look forward to using the brain imaging cap in space, most DOT research is focused on such Earth-based applications as mammography and detection of hemorrhagic or ischemic stroke. Strangman admits the space work, while promising, is probably three to five years away from regular clinical use.

"Any novel technology must first be validated and characterized on the ground before considering either KC135 flights (an airplane that flies parabolic trajectories to provide short periods of weightlessness) or shuttle- or space station-based studies," he said.

-- By Merlina Trevino