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    By Kristi Luther

    DOT Levels Up: High-Speed Optical Imaging Shows Promise

    High-density diffuse optical tomography

    Above: A paper co-authored by Adam T. Eggebrecht, PhD, (left) showed that flashing light at a faster speed results in a more precise brain image.

    High-density diffuse optical tomography (HD-DOT) — a brain-mapping tool developed at Washington University School of Medicine for imaging research — is already revolutionary for several reasons: the technology is portable, silent and less invasive and cheaper than methods like functional MRI (fMRI) and PET. HD-DOT is especially attractive for young study participants who have trouble sitting still and for whom radiation or sedation are not ideal. HD-DOT requires only that the patient to wear a cap connected to fiber optics, which is portable enough to be used at the bedside or even in an operating room.

    Now a recent modeling paper co-authored by Adam T. Eggebrecht, PhD, assistant professor of radiology, shows how using a particular type of light, known as frequency-domain near-infrared spectroscopy (FD NIRS), improves image quality beyond what has previously been possible. Frequency-domain (FD) produces twice as many measurements as the continuous wave (CW) measurements that are the current standard for HD-DOT in Eggebrecht’s lab. With CW, light flashes in the kilohertz range, “which sounds like it’s quick, but it’s not,” says Eggebrecht. With FD, light flashes in the megahertz range, 1,000 times faster. The result is a more precise brain image.

    “Basically, we image brain function by turning each light on like a flashlight — one by one by one — over a small amount of time, and we cycle through the field of view to see what the brain is doing.”

    While scientists have studied FD NIRS since the mid-1990s, cost has largely been prohibitive. Eggebrecht says it’s much cheaper to build a large channel count system using CW measurements, which is why his lab focuses its efforts on CW. The lab boasts the largest high-density CW system in the world, combining 96 sources and 92 detectors for over 1,200 measurements per wavelength of light.

    When Eggebrecht’s colleague Hamid Dehghani, PhD, of the University of Birmingham in the United Kingdom, procured an FD system in 2016, the two discussed collaborating and eventually decided that a high-density configuration made sense for both of their purposes. Eggebrecht then booked a flight to the UK to collect data. It’s this data that led them to produce the modeling paper “High-density functional diffuse optical tomography based on frequency-domain measurements improves image quality and spatial resolution,” published in Neurophotonics in August.

    Fortunately Eggebrecht will no longer need a trip to the UK to investigate FD data, as his team has procured its own FD system. The system, which arrived in December 2019, establishes the lab as the largest combined CW-FD team in the world.

    Although more expensive than the CW setup the lab has been using for years, FD is still cheaper than MRI — not to mention more portable and less invasive. Both CW and FD are also absolutely silent, which proves helpful when imaging children with an autism diagnosis, a major focus of Eggebrecht’s research.

    “Kids could wear these caps while they’re directly interacting with their mom or caregiver or a member of the lab, and we can image their brain function during these natural interactions,” he says. “The idea is that FD can provide higher image quality so that potentially down the road we can image their brain function more precisely while in more naturalistic settings.”