Star Trek realness: "Tricorder" tech tracks cancer

Experiments leading towards the development of such a device were published in Applied Physics Letters and presented at the International Ultrasonics Symposium in Taipei, Taiwan.

The research, led by Assistant Professor Amin Arbabian and Research Professor Pierre Khuri-Yakub, was meant to help the detection of buried plastic explosives, but the researchers claimed that the technology could also provide a new way to detect early stage cancers.

Two scientific principles are involved in the making of the device: first, that all materials expand and contract when stimulated with electromagnetic energy, such as light or microwaves. Second, that this expansion and contraction produces ultrasound waves that travel to the surface and can be detected remotely. The basic principle of this interaction was first revealed in 1880 when Alexander Graham Bell was experimenting with wireless transmission of sound via light beams. Bell used light to make sound emanate from a receiver made of carbon black, which replicated a musical tone. Stanford engineers built on the principles demonstrated in Bell's experiment to develop a device to "hear" hidden objects.

Proof of principle

The new work was spurred by a challenge posed by the Defense Advanced Research Projects Agency (DARPA), best known for sponsoring the studies that led to the Internet. DARPA sought to develop a system to detect plastic explosives buried underground – improvised explosive devices (IEDs) – that are currently invisible to metal detectors. The task included one important limitation: the detection device could not touch the surface in question, so as not to trigger an explosion.

All materials expand and contract when heated, but not at identical rates. Ground, especially muddy ground soaked with water, absorbs more heat than plastic. In a potential battlefield application, the microwaves would heat the suspect area, causing the muddy ground to expand and thus squeeze the plastic. Pulsing the microwaves would generate a series of ultrasound pressure waves that could be detected and interpreted to disclose the presence of buried plastic explosives. Stanford engineers built capacitive micromachined ultrasonic transducers, or CMUTs, that can specifically discern the weaker ultrasound signals that jumped from the solid, through the air, to the detector.

"What makes the tricorder the Holy Grail of detection devices is that the instrument never touches the subject," Arbabian said. "All the measurements are made though the air, and that's where we've made the biggest strides."

After solving the technical challenges of detecting ultrasound which is not touching the ground, the Stanford researchers aimed at their ultimate goal, that is, to use the device in medical applications without touching the skin.

Touchless ultrasound

Arbabian's team used brief microwave pulses to heat a flesh-like material that had been implanted with a sample "target." Holding the device from about a foot away, the material was heated by a mere thousandth of a degree. Yet even that slight heating caused the material to expand and contract – which, in turn, created ultrasound waves that the Stanford team was able to detect to disclose the location of the target, all without touching the "flesh," just like the Star Trek tricorder.

"We've been working on this for a little over two years," Khuri-Yakub said. "We're still at an early stage but we're confident that in five to ten to fifteen years, this will become practical and widely available."

Prior medical research has shown that tumors grow additional blood vessels to nourish their cancerous growth. Blood vessels absorb heat differently than the surrounding tissue, so tumors should show up as ultrasound hotspots. "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," Arbabian stated.

Moreover, the researchers believe that their microwave and ultrasound detection system will be more portable and less expensive than other medical imaging devices such as MRI or CT, and safer than X-rays.