Ultrasound waves are able to compress and rarefy, or thin, whatever medium they are flowing through. In compressed regions, light travels more slowly compared to rarefied regions. In this paper, the team shows that this compression and rarefication effect can be used to sculpt a virtual lens in the target medium for optical imaging. This virtual lens can be moved around without disturbing the medium simply by reconfiguring the ultrasound waves from outside. This enables imaging different target regions, all noninvasively.
The published method is a platform technology that can be applied in many different applications. In future, it can be implemented in the form of a handheld device or wearable surface patch, depending on the organ being imaged. By placing the device or patch on the skin, the clinician would be able to easily receive optical information from within the tissue to create images of what's inside without endoscopy's many discomforts and side effects.
The closest current applications for this technology would be endoscopic imaging of brain tissue or imaging under the skin, but this technique can also be used in other parts of the body for imaging. Beyond biomedical applications, this technique can be used for optical imaging in machine vision, metrology, and other industrial applications to enable non-destructive and steerable imaging of objects and structures at the micron scale.
The researchers showed that the properties of the virtual "lens" can be tuned by changing the parameters of the ultrasonic waves, allowing users to "focus" images taken using the method at different depths through the medium. While the LSA paper is focused on the method's efficacy for closer-to-the-surface applications, the team has yet to find the limit to how deep within the body's tissue this ultrasonically-assisted optical imaging method can reach.
"What distinguishes our work from conventional acousto-optic methods is that we are using the target medium itself, which can be biological tissue, to affect light as it propagates through the medium," explains Chamanzar. "This in situ interaction provides opportunities to counterbalance the non-idealities that disturb the trajectory of light."
This technique has many potential clinical applications, such as diagnosing skin disease, monitoring brain activity, and diagnosis and photodynamic therapy for identifying and targeting malignant tumors.
