Dr. Zach J. Simmons Profile

Dr. Zach J. Simmons

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Proceedings Article | 4 March 2019 Presentation

Spatially resolved spectral 4pi optical scattering goniometry and experimental refractive index autocorrelations (Conference Presentation)

Zach Simmons, Jeremy Rogers

Proceedings Volume 10876, 108760G (2019) https://doi.org/10.1117/12.2510672

KEYWORDS: Scattering, Tissue optics, Light scattering, Refractive index, Scatter measurement, Laser scattering, Tissues, Diagnostics, Optogenetics, Optical imaging

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Optical scattering properties are important diagnostic indicators with sensitivity to sub-resolution tissue structure as well as being necessary parameters for modeling light transport. Improved understanding of scattering in tissue is essential for optimizing and interpreting image contrast, modeling optogenetics, and developing next-generation optical imaging approaches. Despite the importance of optical scattering properties, most measurement methods rely on approximations or assumptions about the shape of the angular distribution of scattered light (phase function) or lack the spatial resolution to characterize heterogeneous tissue. There is a need for a spatially resolved method to quantify the optical scattering properties including the shape of the phase function. This work presents a lens-based spectral goniometry system and spatially resolved measurement of 4pi optical scattering phase functions. Angle-space measurement of scattering is performed by imaging the Fourier plane of a high-NA microscope objective. By combining forward and backward images and varying the illumination beam angle, the entire 4pi phase function can be acquired. This method enables several capabilities: a) Spatially resolved measurement of properties combined with stage scanning provides mapping of layered or heterogeneous tissues with <100 micron sampling. b) By inverting the angular scattering measurements, this approach allows characterization of refractive index autocorrelation. c) As a camera and lens based measurement technique that collects large solid-angles of scattering in a single image, the non-axially symmetric scattering signature of fibrous or oriented tissue can be characterized. These applications as well as instrument design and analysis methodology will be presented.

Proceedings Article | 14 March 2018 Presentation

Spatial and spectral mapping of optical scattering phase function, p(θ,φ; x,y,λ), from layered tissues (Conference Presentation)

Jeremy Rogers, Zach Simmons

Proceedings Volume 10499, 1049912 (2018) https://doi.org/10.1117/12.2290865

KEYWORDS: Scattering, Tissues, Light scattering, Tissue optics, Scatter measurement, Retina, Microscopy, Spectroscopy, Diagnostics, Optical imaging

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Optical scattering properties in tissue are diagnostic markers, ingredients to increasingly sophisticated models, and undergird many optical imaging modalities. Advances in all these areas hinge on obtaining high fidelity scattering measurements. A new optical scattering goniometry method is discussed which measures scattering into 4π sr from small (~100um) tissue regions in flat-mounted samples. This novel tissue scattering gonoimeter images the back focal plane of two opposing microscope objectives to collect light in the forward and backward direction and has several key advantages: (1) scanning the incident angle allows measurement of scattering over 4π steradians to determine the complete scattering phase function of tissue, (2) specificity of measuring scattering from small ~50um regions combined with obliquely sectioned tissue allows mapping of layered tissue, (3) spectral characterization through tuning illumination wavelength, (4) concurrent measurement of scattering coefficient. This opens up the prospect of a new level of detail in the characterization of optical scattering from tissue, including distinguishing properties of thin layers. A tissue system of particular interest and an excellent candidate on which to apply this new goniometry method is the retina. Existing measurements are limited to bulk retina properties or inferred from methodologies that do not have access to transmitted scattering. Scattering coefficient and anisotropy measurements are presented for the various retinal layers. These novel measurements may be used to model light transport and scattering in the retina. Examples of modeling imaging modalities based on scattered light are discussed.

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