'In-body GPS' system can track tumours, ingestible sensors

Boston: Scientists have developed a wireless 'in-body GPS' system that can pinpoint the location of ingestible implants and track tumors inside the body. 

In animal tests, the team demonstrated that the system dubbed ReMix can track the implants with centimeter-level accuracy. Similar implants could be used to deliver drugs to specific regions in the body.

To test ReMix, researchers from Massachusetts Institute of Technology (MIT) and Massachusetts General Hospital (MGH) in the US first implanted a small marker in animal tissues.

To track its movement, the researchers used a wireless device that reflects radio signals off the patient.

This was based on a wireless technology that the researchers previously demonstrated to detect heart rate, breathing, and movement. A special algorithm then uses that signal to pinpoint the exact location of the marker.

Interestingly, the marker inside the body does not need to transmit any wireless signal. It simply reflects the signal transmitted by the wireless device outside the body. Therefore, it does not need a battery or any other external source of energy.

A key challenge in using wireless signals in this way is the many competing reflections that bounce off a person's body. In fact, the signals that reflect off a person's skin are actually 100 million times more powerful than the signals of the metal marker itself.

To overcome this, the team designed an approach that essentially separates the interfering skin signals from the ones they're trying to measure.

They did this using a small semiconductor device, called a 'diode,' that mixes signals together so the team can then filter out the skin-related signals.

For example, if the skin reflects at frequencies of F1 and F2, the diode creates new combinations of those frequencies, such as F1-F2 and F1+F2.

When all of the signals reflected back to the system, the system only picks up the combined frequencies, filtering out the original frequencies that came from the patient's skin.

One potential application for ReMix is in proton therapy, a type of cancer treatment that involves bombarding tumors with beams of magnet-controlled protons.

The approach allows doctors to prescribe higher doses of radiation but requires a very high degree of precision, which means that it is usually limited to only certain cancers.

Its success hinges on something that's actually quite unreliable: a tumor staying exactly where it is during the radiation process. If a tumor moves, then healthy areas could be exposed to the radiation.

However, with a small marker like ReMix's, doctors could better determine the location of a tumor in real-time and either pause the treatment or steer the beam into the right position. 

Researchers clarify that ReMix is not yet accurate enough to be used in clinical settings. A margin of error closer to a couple of millimeters would be necessary for actual implementation.