Light distribution modulated diffuse reflectance spectroscopy

Abstract

Typically, a diffuse reflectance spectroscopy (DRS) system employing a continuous wave light source would need to acquire diffuse reflectances measured at multiple source-detector separations for determining the absorption and reduced scattering coefficients of turbid samples. This results in a multi-fiber probe structure and an indefinite probing depth. Here we present a novel DRS method that can utilize a few diffuse reflectances measured at one source-detector separation for recovering the optical properties of samples. The core of innovation is a liquid crystal (LC) cell whose scattering property can be modulated by the bias voltage. By placing the LC cell between the light source and the sample, the spatial distribution of light in the sample can be varied as the scattering property of the LC cell modulated by the bias voltage, and this would induce intensity variation of the collected diffuse reflectance. From a series of Monte Carlo simulations and phantom measurements, we found that this new light distribution modulated DRS (LDM DRS) system was capable of accurately recover the absorption and scattering coefficients of turbid samples and its probing depth only varied by less than 3% over the full bias voltage variation range. Our results suggest that this LDM DRS platform could be developed to various low-cost, efficient, and compact systems for in-vivo superficial tissue investigation.

Physicochemical understanding of biomineralization by molecular vibrational spectroscopy: From mechanism to nature

“…The depolarization rate of the microscope objective used is ≈0.005, which is much smaller than the difference between the depolarization rates of normal enamel and caries, allowing the marking of caries. [ 56 ] Polarized Raman spectroscopy revealed that healthy enamel exhibited strong Raman polarization anisotropy, while all early caries showed low Raman polarization anisotropy. [ 214 ] The Raman spectroscopy generated by ν 1 PO 4 3− vibrations was strongly polarized, while the polarization dependence was weaker in the caries region.…”

“…The simplest example is the occurrence of calculus, which is caused by bacteria on the enamel surface forming a biofilm that further induces the onset of mineralization. [ 55 , 56 , 57 , 58 , 59 ] The end‐stage of atherosclerosis is pathological mineralization, which generally begins with lipid and complex sugar accumulation, hemorrhage, and thrombosis, followed by fibrous tissue proliferation and mineral crystallization. [ 7 , 60 , 61 , 62 ] Urinary stones are a complex of calcium oxalate and carbonate apatite, which is also due to pathological mineralization.…”

Advances in Monte Carlo Simulation for Light Propagation in Tissue

“…Recovering the absorption and scattering coefficient of the medium is essential to categorize it as normal tissue or as tumor. ( 5) Inverse MC was used in diffuse reflectance spectroscopy to compute the optical properties of the medium [108]. (6) Photoacoustic imaging was used for early detection of prostate cancer for which MC was used to design light delivery [38].…”