Dartmouth researchers have developed a cell phone-based tool that monitors tissue health by using a naturally occurring molecule to measure cellular oxygen levels. The tool could provide a simple and affordable at-home method for detecting disease and making treatment decisions that is superior to current methods, according to a new study in Biosensors and Bioelectronics.
"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," says 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."
Current methods for measuring tissue oxygen involve expensive camera systems or require extra sensors injected into the body or attached in an inpatient setting. The reasearch team based in Dartmouth's Thayer School of Engineeing 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 indicator. "It has a useful quirk that when activated, it's quenched by oxygen," Pogue explains. "When Protoporphyrin IX is 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," Pogue says. The team—which includes first author Protik Chandra Biswas, a research associate in Pogue's lab, and co-author Jason Gunn, manager of Pogue's lab—figured out how to pair that idea 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 says.
For monitoring tissue health in cases of healing wounds or infection, the system is even simpler because there's no need for the cream to activate Protoporphyrin IX, Pogue says. Inflamed tissue stays oxygenated while it repairs itself, followed by a decrease in Protoporphyrin IX as the inflammation subsides. "Any inflammatory response in tissue already increases production of Protoporphyrin IX," Pogue says. "It's the trend over time that matters."
The group is expanding testing of their method to explore even more uses, such as classifying infection severity and making other tissue-function decisions. "We started another study with a surgeon in Wisconsin who does burn care," Pogue says. "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, Pogue says: "That's when expensive camera systems don't make a lot of sense."
In the meantime, the researchers have turned to undergraduate students in Dartmouth's First-Year Research in Engineering Experience program for help with designing a user-friendly app. "Something easy and intuitive for daily monitoring that can open up this area of medicine to being cost-effective and doable," Pogue says.
