Researchers develop ‘in-body GPS’ system to track tumours

Researchers from the Massachusetts Institute of Technology (MIT) and Massachusetts General Hospital in the United States have developed a wireless 'in-body GPS' system that can track tumours and pinpoint the location of ingestible implants inside the body.

In tests conducted on animals, the system called ‘ReMix’ was found to be able to easily track the implants with centimetre-level accuracy. Similar implants could be used to deliver drugs to specific regions in the body.

The Test: Key Highlights

To test ReMix, the researchers 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.

The marker inside the body does not need to transmit any wireless signal, as it 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.

Key Challenge

The scientists found that a key challenge in using wireless signals in this way was 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 were trying to measure.

The researchers did this using a small semiconductor device called a 'diode,' which mixes signals together so the team can then filter out the skin-related signals. Hence, 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 reflect back to the system, the system only picks up the combined frequencies, filtering out the original frequencies that came from the patient's skin.


According to the researchers, ReMicx can be potentially used in proton therapy, a type of cancer treatment that involves attacking tumours 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.

The Drawback

One of the major drawbacks of the ReMix system is that it is not yet accurate enough to be used in clinical settings.

According to researchers, a margin of error closer to a couple of millimetres would be necessary for actual implementation.

However, the system’s success is based on something that's actually quite unreliable- a tumour staying exactly where it is during the radiation process. If the tumour moves, then healthy areas could be exposed to the radiation.


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