A team of scientists at MIT has developed a new sensor that, they say, can enable long-term monitoring of oxygen levels in cancerous tumors, which may advance diagnosis and treatment.

Since cancer cells thrive when deprived of oxygen, tumors in low-oxygen environments tend to be more resistant to therapy and spread more aggressively. Measuring the oxygen levels of tumors could help doctors make decisions about treatments, but, until now, there has been no reliable, noninvasive way to take these measurements. The team has invented an injectable device that reveals oxygen levels over several weeks and can be read with magnetic resonance imaging (MRI).

Using this kind of sensor, doctors may be able to better determine radiation doses and to monitor whether treatments are having the desired effect, according to the researchers. The injectable device is made of two types of silicone—one that provides the MRI signal, and one that offers structural support. This is the first MRI sensor of any kind that can be left in the body for extended periods of time. So far, the team has tested it in rats for up to four weeks.

MRI is often used to diagnose tumors, but currently the technology can only reveal the size and location of a tumor. With the new MIT sensor, doctors could track the state of the tumor and predict how it might respond to radiation treatment, according to the researchers.

To test the sensors, the researchers implanted them in the hind legs of rats and then measured how the signal changed as the rats breathed pure oxygen, regular air, and pure oxygen again. The sensors detected changes in oxygen pressure as small as 15 millimeters of mercury, and it took less than 10 minutes to see the effects of a change in inhaled gas.

This type of sensor could also be useful for monitoring blood flow in diabetic patients, who often experience restricted circulation in their extremities, or people who have suffered traumatic injuries.