Engineers at Massachusetts Institute of Technology have come up with an alternative to conventional ultrasound that does not require contact with the body to see inside a patient.
The new laser ultrasound technique leverages an eye- and skin-safe laser system to remotely image the inside of a person, which may one day allow doctors to assess the health of infants, burn victims, and accident survivors in hard-to-reach places from the comfort of their chambers.
"We're at the beginning of what we could do with laser ultrasound," said study senior author Brian Anthony from MIT.
"Imagine we get to a point where we can do everything ultrasound can do now, but at a distance. This gives you a whole new way of seeing organs inside the body and determining properties of deep tissue, without making contact with the patient," Anthony said.
In a paper published by Nature in the journal Light: Science and Applications, the team reported generating the first laser ultrasound images in humans.
The researchers scanned the forearms of several volunteers and observed common tissue features such as muscle, fat, and bone, down to about 6 centimetres below the skin.
These images, comparable to conventional ultrasound, were produced using remote lasers focused on a volunteer from half a metre away.
In this unconventional ultrasound method, when trained on a patient's skin, one laser remotely generates sound waves that bounce through the body, said the study.
A second laser remotely detects the reflected waves, which researchers then translate into an image similar to conventional ultrasound, it added.
Based on their research, the team selected 1,550-nanometer lasers, a wavelength which is highly absorbed by water (and is eye- and skin-safe with a large safety margin).
As skin is essentially composed of water, the team reasoned that it should efficiently absorb this light, and heat up and expand in response. As it oscillates back to its normal state, the skin itself should produce sound waves that propagate through the body.
The researchers tested this idea with a laser setup, using one pulsed laser set at 1,550 nanometers to generate sound waves, and a second continuous laser, tuned to the same wavelength, to remotely detect reflected sound waves.
This second laser is a sensitive motion detector that measures vibrations on the skin surface caused by the sound waves bouncing off muscle, fat and other tissues. Skin surface motion, generated by the reflected sound waves, causes a change in the laser's frequency, which can be measured.
By mechanically scanning the lasers over the body, scientists can acquire data at different locations and generate an image of the region.
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