Carnegie Mellon University
April 18, 2019

Sound steers light through the brain

By Olivia Olshevski

Krista Burns

Maysam Chamanzar, assistant professor of electrical and computer engineering, and his colleagues have introduced a groundbreaking technique to improve optical imaging technology by using non-invasive sound waves to shape light and control its trajectory deep into the tissue. This method can revolutionize optical imaging and manipulation in biology and many other applications. The results are published in two recent papers in the journals of Optics Express and Nature Communications.

The team has shown that high-frequency sound waves (i.e., ultrasound) can, in real time, shape and sculpt a beam of light into arbitrary patterns as it propagates through the tissue. In this method, ultrasound pressure waves slightly change the local density of the tissue, which translates into a local change of optical refractive index. The interaction of light with this ultrasonically-altered refractive index pattern defines the trajectory of light through the medium.

Shaping arbitrary patterns of light, or the so-called spatial light modulation, is already used in a variety of applications such as 3D displays, video projectors, holography, and biological imaging. The core of all of these technologies is a device called spatial light modulator (SLM), which modifies the beam of light to generate spatial patterns. In almost all existing implementations, light is first patterned externally and then launched onto the target medium. As a result, the trajectory of light cannot be modified after it is launched.

In contrast, Chamanzar’s idea allows researchers to pattern and reprogram light as it propagates inside the brain (or any other tissue) without the need to insert implantable devices into the tissue. As a result, scientists will be able to mitigate the effects of scattering and other environmental influences. This cutting-edge, first-of-its-kind method of patterning light using non-invasive ultrasonic waves benefits from the best of ultrasound and optical methods, and produces virtual, steerable optical beam patterns in situ, which can achieve higher resolution and better focusing of light beams deep inside most tissues.

Maysam Chamanzar, who invented this novel technique and led the project, describes the idea: “Light is an electromagnetic wave, and ultrasound is a pressure wave. The interesting part of our idea is that we use waves to control waves. Both types of waves can propagate through the target tissue, for examplethe brain, non-invasively, that is without causing any damage. The tantalizing notion of patterning light using ultrasound on the fly is mediated through interaction of light with the ultrasonically modulated medium.”  Read more