Dartmouth Engineering Study Presents Simple, Affordable Tool to Measure Tissue Oxygen and Health

(l to r) Co-author Jason Gunn, lab manager, and first author Protik Chandra Biswas, research associate, with co-author Brian Pogue, Dartmouth's Robert A. Pritzker Professor of Biomedical Engineering. (Photo by Katie Lenhart)

"The pulse oximeters used in emergency rooms, ambulances, and home care effectively measure blood oxygen, but that actually doesn't change much until you're basically near death," said Brian Pogue, Dartmouth's Robert A. Pritzker Professor of Biomedical Engineering and co-author of the study. "What we really want is not the blood oxygen, but the tissue oxygen. That's a much more subtle indicator of tissue function and a better dynamic indicator of health." 

Conventional ways of measuring tissue oxygen require expensive camera systems and attaching or injecting extra sensors in an inpatient setting. This new tool, part of a study published in Biosensors and Bioelectronics, uses a regular cell phone camera paired with a pulsed LED light and a topical activation cream. 

The cream stimulates production of a molecule called Protoporphyrin IX that occurs naturally inside all living cells and is a known oxygen reporter. "It has a useful quirk that when activated, it's quenched by oxygen," explained Pogue, "and when it's not quenched by oxygen, it emits a tiny light signal. That's what our measurement tool is picking up."

The idea of using cell phones as a time-sequenced measurement system isn't new, "but nobody has used them for tissue oxygen before," said Pogue. The team—including first author Protik Chandra Biswas, Dartmouth research associate, and co-author Jason Gunn, manager of Pogue's lab—figured out how to bring that idea together with an oxygen reporter that they know already exists naturally in tissue.

Many common peripheral vascular diseases are detected and diagnosed through tissue oxygen sensing. Doctors use that information to help determine when to perform vascular surgery or when to amputate a limb. These types of procedures come with high costs and high morbidity rates. "So for somebody who has limb atrophy, the ability to use a cell phone for day-to-day monitoring of tissue oxygen has a lot of value for making major health decisions," Pogue said.

When it comes to monitoring tissue health in cases of wound healing or infection, the system is even simpler because there's no need for the activation cream. "Any inflammatory response in tissue already increases production of Protoporphyrin IX," said Pogue. "It's the trend over time that matters." If the inflammation is working, the tissue stays oxygenated while it repairs itself, followed by a decrease in Protoporphyrin IX as the inflammation subsides. 

The group is expanding testing to explore even more use cases such as classifying infection severity and making other tissue function decisions. "We started another study with a surgeon in Wisconsin who does burn care," added Pogue. "She's monitoring her patients right now to look at Protoporphyrin IX levels and oxygen in burned tissue to see if it's diagnostic for when to do a skin graft."

That sort of regular monitoring over many days is where the tool's simplicity becomes especially valuable. "That's when expensive camera systems don't make a lot of sense," said Pogue. The researchers have asked Charlie Sober '29 and Yigithan Akkus '29, both Dartmouth undergraduate students in the First-Year Research in Engineering Experience (FYREE) program, to help design a user-friendly app for their tool. Pogue added, "Something easy and intuitive for daily monitoring that can open up this area of medicine to being cost-effective and doable."