Rice University researchers are developing a highly accurate, touch-free system that uses a video camera to monitor patients' vital signs just by looking at their faces. The technique isn't new, but researchers in Rice's Scalable Health Initiative are making it work under conditions that have so far stumped earlier systems.
Their version, DistancePPG, can measure a patient's pulse and breathing just by analyzing the changes in one's skin color over time. Where other camera-based systems have been challenged by low-light conditions, dark skin tones, and movement, DistancePPG relies on algorithms that correct for those variables.
Graduate student Mayank Kumar, the project's lead graduate researcher, and his colleagues were aware of an emerging technique that used a video camera to detect nearly imperceptible changes in a person's skin color due to changes in blood volume underneath the skin. Pulse and breathing rates can be determined from these minute changes.
That worked just fine for monitoring Caucasians in bright rooms, he says. But there were three challenges. One was the technique's difficulty in detecting color change in darker skin tones. And the light was not always bright enough. The last, and perhaps hardest problem, was that patients sometimes move. The Rice team solved these challenges by adding a method to average skin-color change signals from different areas of the face and an algorithm to track a subject's nose, eyes, mouth, and whole face.
"Our key finding was that the strength of the skin-color change signal is different in different regions of the face, so we developed a weighted-averaging algorithm," Kumar says. "It improved the accuracy of derived vital signs, rapidly expanding the scope, viability, reach and utility of camera-based vital-sign monitoring."
By incorporating tracking to compensate for movement-even a smile-DistancePPG perceived a pulse rate to within one beat per minute, even for diverse skin tones under varied lighting conditions.
Kumar says he expects the software to find its way to mobile phones, tablets, and computers so people can reliably measure their own vital signs whenever and wherever they choose.
[Source: Rice University]