Andrew Dunn has spent the last 25 years chasing a seemingly simple question: How can surgeons actually see what's happening to blood flow inside the brain while they're operating? Now, after nearly three decades of work, his team at the University of Texas at Austin has delivered an answer that could reshape the way neurosurgeons work.
The stakes could not be higher. During brain surgery, even a brief interruption in blood flow can mean the difference between a patient walking out fully recovered and living with permanent, life-altering damage. Yet tracking that flow across the entire surgical field has remained one of the most fundamental and challenging problems in the operating room. Surgeons have lacked a practical way to see quantitative, moment-by-moment measurements of how blood is moving through the tissue they're operating on.
The technology Dunn's lab developed, called sinusoidal intensity modulation speckle imaging (SIMSI), builds on decades of research into laser speckle contrast imaging—a technique already used in biomedical research. When laser light hits tissue, the moving red blood cells create a distinctive granular, shimmering pattern. By analyzing how that pattern blurs, researchers can map blood flow across an entire field of view at once, without touching the tissue or injecting dyes. The problem was that conventional speckle imaging could only tell surgeons whether flow was increasing or decreasing, not by how much or what the absolute measurements were.
SIMSI changes that equation with an elegant solution. By adding precise modulation to the laser illumination—varying the light intensity in a sinusoidal pattern at controlled frequencies during each camera exposure—the team encoded information about fast blood flow dynamics directly into the speckle images themselves. Hengfa Lu, a postdoctoral fellow in Dunn's Functional Optical Imaging Laboratory who led the development of the SIMSI framework, explains the significance: "By intentionally modulating the illumination during the exposure and using a newly derived imaging model, we can recover fast blood flow dynamics that would otherwise be averaged out."
What makes this breakthrough practical is what it doesn't require. SIMSI works with standard camera hardware—no high-speed cameras needed, no tissue contact, no complex injectable tracers. The result is a quantitative, real-time map of blood flow dynamics across a wide surgical field, made with equipment already familiar to hospital operating rooms.
Dunn's journey to this moment began in 2001 when he documented the first use of laser speckle to image brain blood flow. In 2010, he translated the technology into the operating room for the first time. This latest advancement, published in the Proceedings of the National Academy of Sciences, represents a maturation of that vision into something clinically practical.
The applications extend well beyond neurosurgery. SIMSI could improve monitoring during cardiac surgery, help assess tissue viability in reconstructive procedures, guide treatment decisions in stroke care, and support research into conditions ranging from dementia to traumatic brain injury. In 2024, Dunn worked with UT's Discovery to Impact commercialization hub to license his SpeckleView surgical imaging platform to Austin-based medical device startup Dynamic Light—a sign that the technology is ready to leave the laboratory and enter hospitals.
For neurosurgeons and their patients, that transition from research to the operating room represents something profound: a way to see more clearly, make better decisions, and ultimately, prevent the kind of damage that can alter a life in an instant.