Camera-based, Touch-free Technology to Measure Vital Signs
- 01 July 2015
Tracking vital signs non-invasively could save preemies’ skin.
Rice University Houston, TX
A team of engineers at Rice University are developing a highly accurate, touch-free system that uses a video camera to monitor patients’ vital signs simply by looking at their faces. While the technique isn’t new, they say that their version allows the software to work under conditions that have so far stumped earlier systems.
Called DistancePPG, the researchers claim that their system can measure a patient’s pulse and breathing just by analyzing the changes in one’s skin color over time. While 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. They say that this system will be particularly helpful to monitor premature infants for whom blood pressure cuffs or wired probes can pose a threat to their sensitive and delicate skin. In fact, they were his inspiration.
In 2013, the researchers visited Texas Children’s Hospital to talk to doctors and get ideas. Observing newborn babies in the neonatal ICU, they saw multiple wires attached to the infants, posing risks to skin that could easily tear. The wires monitored the babies’ pulses and heart rate, and while the wires weren’t a problem in and of themselves, when the babies would roll or need to be attended to, the wires would be taken off and put back on. That removal and replacement, they say, is what could potentially damage the infants’ delicate skin.
They 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, which worked well for monitoring Caucasians in bright rooms, they say.
But, the technique had difficulty in detecting color change in darker skin tones. In addition, the light was not always bright enough. And, third, 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. (See Figure 1)
Their key finding, they explain, was that the strength of the skin-color change signal is different in different regions of the face, so they developed a weighted-averaging algorithm, which 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 DistancePPG can perceive a pulse rate to within one beat per minute, even for diverse skin tones under varied lighting conditions.
For more information, visit http://sh.rice.edu/camera_vitals.html