A non-contact approach to ultrasound imaging, which could be of value in remote patient monitoring and other applications, has been advanced by MIT researchers. The all optical laser ultrasound system produced images comparable to those from conventional systems when used to scan human volunteers from a distance of half a 
Schematic of the laser ultrasound system. Source: X. Zhang et al.meter.
Two eye- and skin-safe 1,550 nm lasers are deployed, with one pulsed laser focused on a patient’s skin to generate sound waves that travel through the body. Skin surface motion induced by reflected sound waves alters the laser’s frequency, which can be measured. A second continuous laser remotely detects these changes which are translated into an image. When applied to scan the arms of volunteers, the method proved capable of distinguishing common tissue features such as muscle, fat and bone, down to about 6 cm below the skin.
In addition to the potential to produce inexpensive, detailed images without physical contact, the laser ultrasound technique described in Light: Science and Applications eliminates inconsistencies that can arise from independent operator variabilities. The researchers plan to improve the method’s image resolution and to miniaturize the equipment to support portability.
