Relation between speckle decorrelation and optical phase conjugation (OPC)-based turbidity suppression through dynamic scattering media: a study on in vivo mouse skin

Abstract

Light scattering in biological tissue significantly limits the accessible depth for localized optical interrogation and deep-tissue optical imaging. This challenge can be overcome by exploiting the time-reversal property of optical phase conjugation (OPC) to reverse multiple scattering events or suppress turbidity. However, in living tissue, scatterers are highly movable and the movement can disrupt time-reversal symmetry when there is a latency in the OPC playback. In this paper, we show that the motion-induced degradation of the OPC turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation - a popular conventional measure of scatterer movement. We investigated this decorrelation characteristic time through a 1.5-mm-thick dorsal skin flap of a living mouse and found that it ranges from 50 ms to 2.5 s depending on the level of immobilization. This study provides information on relevant time scales for applying OPC to living tissues.

Feedback-based wavefront shaping

“…Once a matching wavefront is found, the enhancement will decay in time; exactly following the trend of the temporal speckle autocorrelation function [73,74]. For long, it was believed that the relevant time scale for focusing light through the living skin was less than a millisecond (a typical time scale observed in dynamic speckle measurements).…”

Perspective: Wavefront shaping techniques for controlling multiple light scattering in biological tissues: Toward in vivo applications

“…However, since SHWSs do not work, we must return to holographic measurements. The most notable approach in this direction takes advantage of digital phase conjugation, 22,27,69,128 where the phase-conjugated beam can have arbitrarily larger power than the measured signal. This is critical for imaging or light delivery inside deep tissues.…”

Wavefront Shaping and Its Application to Enhance Photoacoustic Imaging

“…Therefore, traditionally scattering events have been regarded as an obstacle, and the speckle patterns generated by the coherent light propagation in tissue has been seen as one of the major noise sources in biomedical optical imaging [77,78]. However, recently, pioneering scientists have begun to explore the feasibility of exploiting scattering and the corresponding speckle patterns based on their deterministic feature within the medium's temporal correlation window [40,[63][64][65].…”

“…However, recently, researchers began to notice that the seemingly random scattering events and the resultant speckles are actually deterministic within a certain temporal window [37,38], and it is possible to reverse [39][40][41] or compensate for [42] the scattering-induced phase scrambling. To do so, researchers have developed several wavefront shaping (sometimes also referred to wavefront engineering) techniques, such as iterative wavefront optimization [23][24][25][26]28,[42][43][44][45][46][47][48][49][50][51], measuring the transmission matrix of the scattering medium [21,22,[52][53][54][55][56], and optical time reversal via phase conjugation [39,40,[57][58][59][60][61][62][63][64][65]. Nevertheless, the goals of these implementations are identical, i.e., to make light wavelets traveling along different optical paths interfere coherently at a region of interest (ROI) and form a bright optical spot (focus) out of the much darker background.…”