26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Selective Photon Collection Enhances Depth-Resolved Contrast

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Speaker

Prof. Alexandre Douplik (Toronto Metropolitan University)

Description

High-resolution optical imaging in biological tissues is fundamentally limited by photon scattering, which reduces interrogation depth and degrades spatial resolution and absorption-based contrast. Existing scatter-rejection techniques often require complex instrumentation or compromise imaging performance. This study investigates numerical aperture (NA) gating, based on spatial-angular restriction, as a simple and cost-effective approach for enhancing optical interrogation in highly scattering media.
NA gating restricts the collection angle, suppressing photons exiting at larger scattering angles while preferentially detecting ballistic and weakly scattered (“snake”) photons that retain directional and spatial information. Related scatter-rejection methods include angular filtering using Angular Filter Arrays, Angular Domain Imaging, aperture restriction, and 2f/4f optical configurations [1,2]; temporal gating of early-arriving photons [3]; and polarization and confocal filtering approaches [4,5].
Here, NA gating was investigated in multilayered scattering tissues employing low-NA fiberoptic plates and aperture/iris restrictions [6]. Photon trajectory tracking enabled quantitative assessment of the relationship between angular acceptance and interrogation depth.
The results demonstrate that restricted-angle detection can increase interrogation depth by up to an order of magnitude in highly scattering environments. However, suppression of the diffuse photon background may require illumination intensities one to two orders of magnitude higher, potentially increasing thermal loading. Temperature monitoring and cooling strategies should therefore be considered for biomedical applications.
The approach is being translated toward real-time in vivo imaging of skin microcirculation and may be combined with optical clearing, fluorescence imaging, photoacoustic imaging, and optical coherence tomography to further improve imaging depth and contrast.
REFERENCES
[1] F. Vasefi et al., Opt. Express, 16, 21492–21504, 2008.
[2] Y.-M. Wang et al., Opt. Express, 12, 1157–1168, 2004.
[3] E. M. Hillman et al., Phys. Med. Biol., 46, 1117–1130, 2001.
[4] M. Sormaz et al., Opt. Express, 18, 23746–23755, 2010.
[5] S. P. Schilders et al., Appl. Opt., 37, 5320–5326, 1998.