Abstract
A probe is described that when immersed into a highly scattering fluid provides a measurement of its scattering and absorbing properties at a single optical wavelength. It uses recently available low-cost proximity sensor modules to estimate the mean flight times of photons diffusely transmitted between near-infrared sources and detectors at two different separations. The probe has been designed with a specific application for enabling the rapid and efficient production of fluids, which mimic the optical properties of biological tissues. The potential of the device is demonstrated using precalibrated solutions of intralipid, an intravenous nutrient, and absorbing dye. It is shown that a combination of time-of-flight measurements at two source–detector separations can uniquely specify the absorption coefficient and the transport scattering coefficient.
Highlights
The development and evaluation of instruments for biomedical optics applications frequently require the use of objects that mimic the optical properties of biological tissues, known as phantoms.[1]
Phantoms are most often used for applications in optical spectroscopy, imaging, and dosimetry where sources and detectors are placed on the surface of tissue with separations between a few millimeters and several centimeters
We describe a low-cost tool for producing fluids with tissue-like optical properties without the need for prior characterization of the scattering and absorbing agents
Summary
The development and evaluation of instruments for biomedical optics applications frequently require the use of objects that mimic the optical properties of biological tissues, known as phantoms.[1]. The tool can be produced in the form of a “dipstick” that provides an instantaneous measure of μa and μs[0] during the mixing of the components Such a concept has been proposed and explored before, most recently by Zhou et al.,[9] previous investigations have focused either on measurements of intensity (i.e., diffuse reflectance or transmittance) or have required complex and expensive bench-top systems based on time-domain[10] or frequency-domain measurements.[11] Measurements of intensity are notoriously influenced by the coupling between the optical sources/detectors and the medium; for example, a small stain, scratch, or air bubble on the surface of the probe would be likely to corrupt the measurement. A measurement of flight times of photons traveling through a highly scattering medium yields a broad distribution sometimes known as a temporal point spread function,[12] of which hti is the weighted average flight time Combining these equations, it can be shown that. While statistical uncertainties in measurements of hti will inevitably compromise the accuracy and uniqueness of the solutions, both may be improved by combining data acquired at additional separations
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