Tricorder-like technology “hears” tumors
Stemming from research into the remote detection of buried plastic explosives, the RF/ultrasound-imaging-based technology is being proposed more generally for detection of embedded objects in any media – such as water, soil, and even tissue – that is highly dispersive (i.e., where waves of different frequencies travel at different velocities). For medical applications, this could mean being able to use a "touchless ultrasound" approach that could detect tumors in early stage cancers.
The principle behind the technology is based on the fact that all materials expand and contract at different rates when heated, as would be the case – by a miniscule amount – when encountering microwave pulses produced by the technology. The resulting expansion and contraction produces ultrasound pressure waves that could then be detected and analyzed for anomalies.
Normally, medical ultrasound imaging requires skin contact in order to pick up a usable signal and avoid the drastic transmission loss that occurs when the signal travels from the skin to the air. To accommodate for this loss, the Stanford scientists used capacitive micromachined ultrasonic transducers (CMUTs), which are able to detect the much weaker signals traveling through the air.
"What makes the tricorder the Holy Grail of detection devices is that the instrument never touches the subject," says Assistant Professor Amin Arbabian. "All the measurements are made though the air, and that’s where we’ve made the biggest strides."
For their tests, the researchers used brief microwave pulses from their device – held about a foot away – to heat a flesh-like material implanted with a sample "target." The material was heated by about a thousandth of a degree – enough to cause it to produce expansion/contraction-induced ultrasound waves that the researchers were able to detect and use to reveal the location of the hidden target.
Medical research shows that tumors grow additional blood vessels – a process called angiogenesis – that enables them to grow bigger and more quickly. Blood vessels absorb heat differently than surrounding tissue, so it is expected that tumors would be detected as ultrasound hotspots using this technology.
"We think we could develop instrumentation sufficiently sensitive to disclose the presence of tumors, and perhaps other health anomalies, much earlier than current detection systems, non-intrusively and with a handheld portable device," says Arbabian.
The researchers expect that their detection system will be both more portable and less expensive than traditional medical imaging systems like magnetic resonance imaging (MRI) and computed tomography (CT), and safer than X-rays. They say they’re confident that this technology will become both "practical and widely available" in five to ten years.
For more, see the paper in the journal Applied Physics Letters, "Non-contact thermoacoustic detection of embedded targets using airborne-capacitive micromachined ultrasonic transducers."