{"id":17184,"date":"2019-12-24T05:27:26","date_gmt":"2019-12-24T05:27:26","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=17184"},"modified":"2020-06-09T12:13:08","modified_gmt":"2020-06-09T12:13:08","slug":"researchers-produce-first-laser-ultrasound-images-of-humans","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/researchers-produce-first-laser-ultrasound-images-of-humans\/","title":{"rendered":"Researchers produce first laser ultrasound images of humans"},"content":{"rendered":"\n

MIT News Office <\/strong><\/p>\n\n\n\n

\"\"
MIT<\/figcaption><\/figure>\n\n\n\n

Technique may help remotely image and assess health of infants, burn victims, and accident survivors in hard-to-reach places.<\/strong> <\/p>\n\n\n\n

For most people, getting an ultrasound is a relatively easy procedure: As a technician gently presses a probe against a patient\u2019s skin, sound waves generated by the probe travel through the skin, bouncing off muscle, fat, and other soft tissues before reflecting back to the probe, which detects and translates the waves into an image of what lies beneath.<\/p>\n\n\n\n

Conventional ultrasound doesn\u2019t expose patients to harmful radiation as X-ray and CT scanners do, and it\u2019s generally noninvasive. But it does require contact with a patient\u2019s body, and as such, may be limiting in situations where clinicians might want to image patients who don\u2019t tolerate the probe well, such as babies, burn victims, or other patients with sensitive skin. Furthermore, ultrasound probe contact induces significant image variability, which is a major challenge in modern ultrasound imaging.<\/p>\n\n\n\n

Now, MIT engineers have come up with an alternative to conventional ultrasound that doesn\u2019t 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. When trained on a patient\u2019s skin, one laser remotely generates sound waves that bounce through the body. A second laser remotely detects the reflected waves, which researchers then translate into an image similar to conventional ultrasound.<\/p>\n\n\n\n

In a\u00a0paper<\/a>\u00a0published today by\u00a0Nature<\/em>\u00a0in the journal\u00a0Light: Science and Applications<\/em>, 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 6 centimeters below the skin. These images, comparable to conventional ultrasound, were produced using remote lasers focused on a volunteer from half a meter away.<\/p>\n\n\n\n

\u201cWe\u2019re at the beginning of what we could do with laser ultrasound,\u201d says Brian W. Anthony, a principal research scientist in MIT\u2019s Department of Mechanical Engineering and Institute for Medical Engineering and Science (IMES), a senior author on the paper. \u201cImagine 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.\u201d<\/p>\n\n\n\n

Anthony\u2019s co-authors on the paper are lead author and MIT postdoc Xiang (Shawn) Zhang, recent doctoral graduate Jonathan Fincke, along with Charles Wynn, Matthew Johnson, and Robert Haupt of MIT\u2019s Lincoln Laboratory.<\/p>\n\n\n\n

Yelling into a canyon \u2014 with a flashlight<\/strong><\/p>\n\n\n\n

In recent years, researchers have explored laser-based methods in ultrasound excitation in a field known as photoacoustics. Instead of directly sending sound waves into the body, the idea is to send in light, in the form of a pulsed laser tuned at a particular wavelength, that penetrates the skin and is absorbed by blood vessels.<\/p>\n\n\n\n

The blood vessels rapidly expand and relax \u2014 instantly heated by a laser pulse then rapidly cooled by the body back to their original size \u2014 only to be struck again by another light pulse. The resulting mechanical vibrations generate sound waves that travel back up, where they can be detected by transducers placed on the skin and translated into a photoacoustic image.<\/p>\n\n\n\n

While photoacoustics uses lasers to remotely probe internal structures, the technique still requires a detector in direct contact with the body in order to pick up the sound waves. What\u2019s more, light can only travel a short distance into the skin before fading away. As a result, other researchers have used photoacoustics to image blood vessels just beneath the skin, but not much deeper.<\/p>\n\n\n\n

Since sound waves travel further into the body than light, Zhang, Anthony, and their colleagues looked for a way to convert a laser beam\u2019s light into sound waves at the surface of the skin, in order to image deeper in the body.\u00a0<\/p>\n\n\n\n

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). \u00a0As 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.<\/p>\n\n\n\n

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. \u00a0This 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\u2019s 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.<\/p>\n\n\n\n

\u201cIt\u2019s like we\u2019re constantly yelling into the Grand Canyon while walking along the wall and listening at different locations,\u201d Anthony says. \u201cThat then gives you enough data to figure out the geometry of all the things inside that the waves bounced against \u2014 and the yelling is done with a flashlight.\u201d<\/p>\n\n\n\n

In-home imaging<\/strong><\/p>\n\n\n\n

The researchers first used the new setup to image metal objects embedded in a gelatin mold roughly resembling skin\u2019s water content. They imaged the same gelatin using a commercial ultrasound probe and found both images were encouragingly similar. They moved on to image excised animal tissue \u2014 in this case, pig skin \u2014 where they found laser ultrasound could distinguish subtler features, such as the boundary between muscle, fat, and bone.<\/p>\n\n\n\n

Finally, the team carried out the first laser ultrasound experiments in humans, using a protocol that was approved by the MIT Committee on the Use of Humans as Experimental Subjects. After scanning the forearms of several healthy volunteers, the researchers produced the first fully noncontact laser ultrasound images of a human. The fat, muscle, and tissue boundaries are clearly visible and comparable to images generated using commercial, contact-based ultrasound probes.<\/p>\n\n\n\n

The researchers plan to improve their technique, and they are looking for ways to boost the system\u2019s performance to resolve fine features in the tissue. They are also looking to hone the detection laser\u2019s capabilities. Further down the road, they hope to miniaturize the laser setup, so that laser ultrasound might one day be deployed as a portable device.<\/p>\n\n\n\n

\u201cI can imagine a scenario where you\u2019re able to do this in the home,\u201d Anthony says. \u201cWhen I get up in the morning, I can get an image of my thyroid or arteries, and can have in-home physiological imaging inside of my body. You could imagine deploying this in the ambient environment to get an understanding of your internal state.\u201d\u00a0<\/p>\n\n\n\n

This research was supported in part by the MIT Lincoln Laboratory Biomedical Line Program for the United States Air Force and by the U.S. Army Medical Research and Material Command’s Military Operational Medicine Research Program.<\/p>\n
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