  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.
