Backward sensing FUS modulated light from a brain phantom through human adult skull specimen.

Near-infrared (NIR) diffusive reflection spectroscopy is widely useful in medical applications. However, its spatial resolution is low, especially when studying deep tissue. Focused ultrasound (FUS) modulated light, also known as acousto-optic (AO) can be used to improve the spatial resolution of optical sensing of deep tissue based on detection of the modulated photons from focal area of the FUS. In this study, we investigated FUS-modulated light in deep bio-tissue phantoms in reflection mode through a human adult skull specimen. The experiment setup used an optical fiber (source fiber) to guide coherent light illuminating the sample surface, and another optical fiber (detection fiber) to receive optical signal to be sent to a photoreceiver. First, we investigated AO signal coming from deep tissue, accepted by the detection fiber located 3 cm away from the source fiber. Then we studied the effects of ultrasonic modulation frequency and detection fiber diameter on the AO signal intensity. Finally, we studied the effect of adult human skull specimen on AO signal from brain phantom which was in the skull. The results show that it is possible to detect AO signals from a brain phantom through a human skull, although the skull specimen reduced the AO signal intensity by approximately 50% at the applied FUS pressure level. This study provides useful insights toward future AO sensing of the human brain when using FUS-modulated light.