MIT Scientists Develops 1st Laser Ultrasound, Not Requiring Body Contact

MIT scientists have developed a new ultrasound technique that does not require contact with the body to see inside a patient, an advance that may help remotely image and assess health of infants, burn victims, and accident survivors in hard-to-reach places.

Conventional ultrasound does not expose patients to harmful radiation as X-ray and CT scanners do, and it is generally noninvasive.

However, it does require contact with a patient's body, and as such, may be limiting in situations where clinicians might want to image patients who don't tolerate the probe well.

Ultrasound probe contact induces significant image variability, which is a major challenge in modern ultrasound imaging, according to the researchers from the Massachusetts Institute of Technology (MIT) in the US.

The new laser ultrasound technique leverages an eye and skin safe laser system to remotely image the inside of a person.

When trained on a patient's skin, one laser remotely generates sound waves that bounce through the body, the researchers said.

A second laser remotely detects the reflected waves, which researchers then translate into an image similar to conventional ultrasound.

In the journal Light: Science and Applications, the team reports 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 six centimeters below the skin.

These images, comparable to conventional ultrasound, were produced using remote lasers focused on a volunteer from half a metre away.

"We're at the beginning of what we could do with laser ultrasound," said Brian W. Anthony, a principal research scientist at 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.

The team selected 1,550-nanometre lasers, a wavelength which is highly absorbed by water, and is eye- and skin-safe.

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 said.

They 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, the researchers said.

Skin surface motion, generated by the reflected sound waves, causes a change in the laser's frequency, which can be measured, they said.

By mechanically scanning the lasers over the body, scientists can acquire data at different locations and generate an image of the region.