Abstract
Light may traverse a turbid material, such as blood, without encountering any of its pigment containing structures, a phenomenon known as sieve effect. This phenomenon may result in a decrease in the amount of light absorbed by the material. Accordingly, the corresponding sieve factor needs to be accounted for in optical investigations aimed at the derivation of blood biophysical properties from light transmittance measurements. The existing procedures used for its estimation either lack the flexibility required for practical applications or are based on general formulas that incorporate other light and matter interaction phenomena such as detour (scattering) effects. In this paper, a ray optics framework is proposed to estimate the sieve factor for blood samples. It employs a first principles approach to account for the distribution, orientation and shape of the cells that contain hemoglobin, the essential (oxygen-carrying) pigment found in human blood. Within this framework, ray-casting techniques are used to determine the probability that light can traverse a blood sample without encountering any of these cells. The predictive capabilities of the proposed framework are demonstrated through a series of in silico experiments. Its effectiveness is further illustrated by visualizations depicting the different blood parameterizations considered in the simulations.
Highlights
The study of the optical properties of blood is essential for a wide scope of biomedical applications
An increase in the number of erythrocytes decreases the amount of unoccupied space within the volume of blood sample, which, in turn, increases the probability of light intersecting these cells
The sieve factor is expected to decrease as hematocrit increases [21]
Summary
The study of the optical properties of blood is essential for a wide scope of biomedical applications. The pigments’ absorption spectra used in this task are usually obtained under in vitro conditions, i.e., their extinction coefficients are computed using light transmission measurements performed in homogeneous solutions in which these pigments (or chromophores) are uniformly distributed [9]. In their native (in situ) state, natural pigments (e.g., hemoglobin and chlorophyll) are found in cells or organelles. To account for changes in the lengthening of the optical pathlength under in situ conditions when using in vitro absorption (or extinction) curves, several researchers choose to employ a parameter, known as the differential pathlength factor [12, 13], to scale these curves
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