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MRI sensor to change oxygen monitoring

May 7, 2014

News

Life Sciences

Biological Sciences

A new MRI sensor could change the way oxygen is monitored in the body and aid cancer diagnosis and treatment. Low oxygen environments allow cancer cells to thrive with tumours tending to be more resistant to therapy and metastasising more aggressively. Lack of a reliable and non-invasive way to make measurements led MIT researchers to develop an injectable device that can be left in the body for extended periods of time. The sensor is made of two types of silicone, one to provide the MRI signal, and another to offer structural support. It combines PDMS and DDMPS, which has an oily consistency and can be dissolved in PDMS to give a swollen polymer. Researchers shaped this into a 1.5mm sensor that could be implanted during a biopsy. They also developed smaller particles that could be injected through a needle and clump together to form a solid sensor. DDMPS absorbs molecular oxygen which alters the spin of protons in silicon and can be detected by MRI. Measuring the shift in the MRI signal reveals how much oxygen is present and could enable doctors to track the state of a tumour and predict how it might respond to radiation treatment.

The device can also be created as a suspension of microparticles that are injected into the body, where they clump together. In this image, the particles are suspended in saline before injection. Credit Vincent Liu and Jay Sy.

Researchers implanted the sensors in the hind legs of rats and measured how the signal changed as the rats breathed pure oxygen, regular air, then pure oxygen again. The sensor detected a change in oxygen pressure as small as 15mm of mercury, and it took less than 10 minutes for the changes to be observed. The experiment was repeated four weeks later and yielded the same results. The sensor could help doctors track the state of a tumour and predict how it might respond to radiation treatment. An accurate reading of oxygen present could help doctors calculate how much radiation might be necessary. Researchers anticipate the sensor could help scientists lean more about tumour biology. “A opposed to just studying the genetic profile of tumour cells, this could also reveal how they’r interacting with the stroma that surrounds the tumour,” said Professor Michael Cima, who led the study. “Oxygen tension, as simple as it sounds, is a good measure of what’s happening in a tumour.” The research has been published in Proceedings of the National Academy of Sciences. Solid MRI contrast agents for long-term, quantitative in vivo oxygen sensing