Because the new technique does not rely on the use of an ultrasound probe, the read-out technique is not subject to image variability (upon probe pressure and orientation), a major challenge in modern ultrasound imaging.
Here the ultrasound waves are generated remotely by a pulsed laser light tuned at a particular wavelength to penetrates the skin and to be absorbed by blood vessels. The blood vessels rapidly expand and relax, instantly heated by a laser pulse then rapidly cooled by the body back to their original size, only to be struck again by another light pulse. The resulting mechanical vibrations generate sound waves that travel through the skin, bouncing off muscle, fat, and other soft tissues before reflecting back to the skin.
The researchers used a second laser to remotely detect the reflected waves (through the Doppler effect) and translate them into an image similar to conventional ultrasound. This contactless ultrasound imaging technique may help remotely image and assess health of infants, burn victims, and accident survivors in hard-to-reach places. Scanning the forearms of several volunteers, the authors of the paper report the observation of common tissue features such as muscle, fat, and bone, down to about 6 centimetres below the skin, all done from half a meter away.
Although at this point, the laser ultrasound (LUS) images are only comparable to images achieved at the early stages of medical ultrasound imaging decades ago, the researchers are confident those could be drastically improved by leveraging known beam forming and image processing techniques already used for ultrasound imaging.