Time-reversed photoacoustic guided time-reversed ultrasonically encoded optical focusing

TL;DR

This paper introduces TRPA-TRUE, a novel method combining photoacoustic guidance and optical phase conjugation to improve deep-tissue optical focusing, overcoming limitations of traditional TRUE in scattering and heterogeneous media.

Contribution

The paper presents a new approach integrating photoacoustic signals and optical phase conjugation for enhanced deep-tissue optical focusing, addressing ultrasound focusing and pressure tagging limitations.

Findings

Significantly improved focusing accuracy over conventional TRUE

Effective in acoustically heterogeneous media like transcranial focusing

Simulation results demonstrate potential for practical deep-tissue imaging

Abstract

Deep-tissue optical imaging is a longstanding challenge limited by scattering. Both optical imaging and treatment can benefit from focusing light in deep tissue beyond one transport mean free path. Wavefront shaping based on time-reversed ultrasonically encoded (TRUE) optical focusing utilizes ultrasound focus, which is much less scattered than light in biological tissues as the 'guide star'. However, the traditional TRUE is limited by the ultrasound focusing area and pressure tagging efficiency, especially in acoustically heterogeneous medium. Even the improved version of iterative TRUE comes at a large time consumption, which limits the application of TRUE. To address this problem, we proposed a method called time-reversed photoacoustic wave guided time-reversed ultrasonically encoded (TRPA-TRUE) optical focusing by integrating ultrasonic focus guided by time-reversing PA signals, and the ultrasound modulation of diffused coherent light with optical phase conjugation (OPC), achieving dynamic focusing of light into scattering medium. Simulation results show that the focusing accuracy of the proposed method has been significantly improved compared with conventional TRUE, which is more suitable for practical applications that suffers severe acoustic distortion, e.g. transcranial optical focusing.