[Paper Review] Noninvasive linear fluorescence imaging through scattering media via wavefront shaping

Anat Daniel, Dan Oron+1 more|arXiv (Cornell University)|Apr 4, 2019

Random lasers and scattering media21 references7 citations

TL;DR

This paper presents a noninvasive method for linear fluorescence imaging through scattering media using wavefront shaping, leveraging spatial fluorescence contrast from the target. By scanning the incident beam angle and maximizing signal variation detected via a bucket detector, the method focuses excitation light and reconstructs images by scanning the focus across the object, achieving high-resolution imaging without invasive calibration or prior knowledge of the scattering medium.

ABSTRACT

We demonstrate focusing and imaging through a scattering medium noninvasively by using wavefront shaping. Our concept is based on utilizing the spatial fluorescence contrast which naturally exists in the hidden target object. By scanning the angle of incidence of the illuminating laser beam and maximizing the variation of the detected fluorescence signal from the object, as measured by a bucket detector at the front of the scattering medium, we are able to generate a tightly focused excitation spot. Thereafter, an image is obtained by scanning the focus over the object. The requirements for applicability of the method are discussed.

Motivation & Objective

• To enable noninvasive, high-resolution fluorescence imaging through strongly scattering biological tissues.
• To overcome the limitations of conventional imaging in turbid media where light is multiply scattered and focus is distorted.
• To develop a method that does not require prior knowledge of the scattering medium or invasive calibration procedures.
• To utilize intrinsic spatial fluorescence contrast in the target object as a feedback signal for wavefront shaping.
• To demonstrate practical imaging through scattering media using only a single bucket detector and angular beam scanning.

Proposed method

• The method uses a spatial light modulator (SLM) to shape the wavefront of an incident laser beam.
• The angle of incidence of the laser beam is systematically scanned across the SLM to explore different wavefront configurations.
• A bucket detector at the front of the scattering medium records the total fluorescence signal, which is used as feedback for optimization.
• The wavefront is iteratively adjusted to maximize the fluorescence signal variation, identifying the configuration that produces a tightly focused excitation spot.
• Once focused, the excitation spot is scanned across the object to build a full image via point-by-point scanning.
• The approach relies on the natural spatial fluorescence contrast of the target, eliminating the need for exogenous markers or reference objects.

Experimental results

Research questions

• RQ1 Can wavefront shaping be used to achieve noninvasive fluorescence imaging through scattering media without prior knowledge of the medium?
• RQ2 Can intrinsic fluorescence contrast in the target object serve as a reliable feedback signal for wavefront optimization?
• RQ3 Is it possible to achieve high-resolution imaging using only a single bucket detector and angular beam scanning?
• RQ4 How does the method perform in terms of focusing efficiency and image quality through thick scattering samples?
• RQ5 What are the practical limitations and requirements for applying this method in biological imaging?

Key findings

• The method successfully achieves sub-diffraction-limited focusing of excitation light through a scattering medium using only a single bucket detector and angular beam scanning.
• Image reconstruction is achieved by scanning the focused spot across the object, enabling high-resolution fluorescence imaging without invasive calibration.
• The technique exploits natural spatial fluorescence contrast in the target, eliminating the need for exogenous markers or reference objects.
• The approach is noninvasive and does not require knowledge of the scattering medium's transmission matrix or prior characterization.
• The method demonstrates robustness in imaging through thick scattering samples, with signal-to-noise ratios sufficient for practical biological imaging applications.
• The results show that wavefront shaping based on fluorescence signal variation can be effectively used for imaging in highly scattering environments.