Low-power wireless in-body “GPS” keeps track of implants
Called ReMix, the system promises a way to allow medical practitioners a way to “see” inside the human body in a less expensive, invasive, and time-consuming manner than traditional methods. According to the researchers, their method opens future possibilities where doctors could implant sensors to track tumors or dispense drugs.
In animal tests, the researchers showed that they can track the implants with centimeter-level accuracy. In the test, the researchers implanted a small marker in animal tissues and then used a wireless device that reflects radio signals off the “patient” to track its movement.
They used a low-power Wi-Fi wireless technology similar to radar and sonar imaging that they had previously demonstrated to detect heart rate, breathing, and movement. A special algorithm uses the reflected signal to pinpoint the exact location of the marker.
The implanted marker itself does not need to transmit any wireless signal – it simply reflects the signal transmitted by the wireless device outside the body. Therefore, it doesn’t need a battery or other external source of energy.
A key challenge in this approach is making sense of the many competing reflections that bounce off a body – the signals that reflect off a person’s skin are 100 million times more powerful than the signals of the metal marker itself, say the researchers. To overcome this, the researchers designed an approach that essentially separates the interfering skin signals from those of the marker.
They did this using a semiconductor device called a diode, or RF mixer circuit, that mixes signals together allowing the researchers to then filter out the skin-related signals. For example, if the skin reflects at frequencies 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. The original frequencies that came from the patient’s skin are filtered out.
One potential application for ReMix, say the researchers, is in proton therapy – a cancer treatment that involves bombarding tumors with beams of magnet-controlled protons. Proton therapy allows doctors to prescribe higher doses of radiation, but requires a very high degree of precision, which means that it’s usually limited to only certain cancers.
It requires that a tumor stay exactly in place during the radiation process – if a tumor moves, which is not uncommon, then healthy areas could be exposed to the radiation. However, using a small marker like that used in ReMix, doctors could potentially better determine the location of a tumor in real time and either pause the treatment or steer the beam into the right position.
Currently ReMix is not yet accurate enough to be used in clinical settings, say the researchers, as a margin of error closer to a couple of millimeters would be necessary for actual implementation. However, looking ahead, they hope to combine the wireless data with medical data – such as that from magnetic resonance imaging (MRI) scans – to further improve the system’s accuracy.
In addition, the researchers plan to continue to reassess the algorithm and the various trade-offs needed to account for the complexity of different bodies.
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