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20 February 2008Optical imaging of structures within highly scattering material using a lens and aperture to form a spatiofrequency filter
Angular Domain Imaging (ADI) is a high resolution, ballistic imaging method that utilizes the angular spectrum of
photons to filter multiply-scattered photons which have a wide distribution of angles from ballistic and quasi-ballistic
photons which exit a scattering medium with a small distribution of angles around their original trajectory. Such spatial
gating has been previously accomplished using a scanning array of collimating holes micromachined into a silicon wafer
section. We now extend that work to include using a wide-beam, full-field, converging lens and pinhole aperture system
to capture images in a single exposure. We have developed an analysis of resolution and sensitivity trade-offs of such a
system using Fourier optics theory to show that the system resolution is primarily governed by collimation ability at
larger aperture sizes and by spatiofrequency (Fourier space-gated) filtering at smaller aperture sizes. It is found that
maximum sensitivity is achieved when spatiofrequency resolution and collimation resolution are equal. Planar, high
contrast, phantom test objects are observed in 5 cm thick media with effective scattered to ballistic photon ratios
>1.25×107:1 using a wide-beam, full-field lens and aperture system. Comparisons are made between ballistic imaging
with the lens and aperture system and with the scanning silicon micromachined collimating array. Monte-Carlo
simulations with angular tracking validate the experimental results.
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Nick Pfeiffer, Paulman Chan, Glenn H. Chapman, Fartash Vasefi, Bozena Kaminska, "Optical imaging of structures within highly scattering material using a lens and aperture to form a spatiofrequency filter," Proc. SPIE 6854, Optical Interactions with Tissue and Cells XIX, 68541D (20 February 2008); https://doi.org/10.1117/12.764341