Optical property measurements of turbid media in a small-volume cuvette with frequency-domain photon migration

Abstract

A frequency-domain photon migration ͑FDPM͒ technique is developed for quantitative measurement of the absorption and reduced scattering coefficients of highly turbid samples in a small-volume ͑0.45-ml͒ reflective cuvette. We present both an analytical model for the FDPM cuvette and its experimental verification, using calibrated phantoms and suspensions of living cells. FDPM model fits to experimental data demonstrate that the reduced scattering ͑ s Ј͒ and absorption ͑ a ͒ coefficients can be derived with accuracies of 5-10% and 10 -15%, respectively. Changing the cuvette wall reflectivity alters the frequency-dependent behavior of photon density waves ͑PDWs͒. For highly reflective wall boundaries ͑R eff Ն 90 -95%͒, PDW confinement leads to substantial enhancement in both amplitude and phase compared with identical samples in infinite media. Results from experiments on microsphere suspensions are compared with predictions from Mie theory to assess the potential of this method to interpret scattering properties in terms of scatterer size and density. Optical property measurements of biological cell suspensions are reported, and the possibility of optically monitoring cell physiology in a carefully controlled environment is demonstrated.

Characterizing liquid turbid media by frequency-domain photon-migration spectroscopy

“…36 A discrepancy between experimental and Mie theory values has also been reported for measurements in a microsphere suspension. 12 The Coquoz et al 12 experimental results overestimated the reduced scattering by 6.5 to 28% at 811 nm and 1 to 8% at 849 nm compared to Mie theory values.…”

“…Xu and Patterson 14 report scattering data at 750 nm by making measurements in diluted samples of Intralipid®-20% in water from 0.3 to 2% concentration. Coquos et al 12 report reduced scattering coefficients at 811 and 849 nm by making measurements in a solution of Intralipid® with an added absorber. The reduced scattering reported by Spinelli et al 33 and Martelli and Zaccanti 34 for Intralipid®-20% is scaled down to a 2% concentration for comparison.…”

“…Currently all the frequency-domain instruments report optical properties of Intralipid® at a few discrete wavelengths. These wavelengths are often constrained to the availability of semiconductor diode lasers: Coquoz et al 12 report at 674, 811, and 849 nm; Madsen et al 13 at 670 nm; Xu and Patterson 14 at 750 nm; and Bevilacqua et al 15 at 672, 800, 806, 852, 896, 913, and 978 nm.…”

Diffuse optical spectroscopic imaging of subcutaneous adipose tissue metabolic changes during weight loss

“…Based on the magnitude of weight loss observed in our study (11.7 ± 3.4 % of starting weight, T0 to T12) and the time course, we can postulate that the increases in NIR scattering amplitude (mean + 17.0% from T0 to T12) observed are related to a reduction in adipocyte size. In the NIR range (650–1000 nm), the light scattering parameters “ A ” and “ b ” correspond to the distributions of density and size of scattering particles ( 41 , 42 ), respectively, that are comparable in dimension to the optical wavelength ( 32 , 43 ). Therefore, reduction in adipocyte volume associated with CR likely leads to several effects: 1) an increase in the density of subcellular contributors to scattering per unit volume due to relatively reduced cytoplasm; 2) increased density of extracellular matrix (ECM, e.g.…”

Complete parameterization of temporally and spectrally resolved laser induced fluorescence data with applications in bio-photonics

“…Alternative approaches were based on temporally resolving the fluorescence decays, as the fluorescence lifetime should be insensitive to the elastic properties of the sample. The instruments used were based on the measurement of a transient fluorescence decay following pulsed laser excitation [27,33,34], on the demodulation and phase delay observed in frequency domain methods [35][36][37][38], or on single photon counting using mode-locked lasers [39,40]. Whereas steady-state measurements of fluorescence emission were discretized in a large number of spectral bands, fluorescence decays were usually collected over a broad emission band determined simply by the sensitivity of the detector (typically a photo multiplying tube (PMT), an avalanche photodiode (APD) [34] or an intensified camera (ICCD)) [33,41].…”