Dependence of light scattering profile in tissue on blood vessel diameter and distribution: a computer simulation study

Abstract

Most methods for measuring light-tissue interactions focus on the volume reflectance while very few measure the transmission. We investigate both diffusion reflection and diffuse transmission at all exit angles to receive the full scattering profile. We also investigate the influence of blood vessel diameter on the scattering profile of a circular tissue. The photon propagation path at a wavelength of 850 nm is calculated from the absorption and scattering constants via Monte Carlo simulation. Several simulations are performed where a different vessel diameter and location were chosen but the blood volume was kept constant. The fraction of photons exiting the tissue at several central angles is presented for each vessel diameter. The main result is that there is a central angle that below which the photon transmission decreased for lower vessel diameters while above this angle the opposite occurred. We find this central angle to be 135 deg for a two-dimensional 10-mm diameter circular tissue cross-section containing blood vessels. These findings can be useful for monitoring blood perfusion and oxygen delivery in the ear lobe and pinched tissues.

Linear dependency of full scattering profile isobaric point on tissue diameter

“…As expected, as tissue diameter increases, so does the value of the isobaric point. In order to facilitate the presentation and to compare it to known results from the literature, 9,18 Figures 4(a), 4(b), and 4(c) present the average fraction of the reflected (squares) and forward transmitted photons (diamonds), respectively, versus scattering coefficients, for several tissue diameters.…”

“…The propagation path of each photon is calculated from the scattering constant, assuming the absorption is negligible. An MC simulation of photon migration within irradiated tissues was built 18 in order to calculate the full scattering profile at all possible exit angles. This simulation is based on the assumption that all photons reaching the tissue begin as ballistic photons.…”

“…7,[12][13][14][15][16] Very few methods test the transmitted light [2][3][4]17 or ballistic photons. 8 It has been previously suggested 18 looking for the first time at the full profile of light that is scattered (transmitted and reflected) at all possible exit angles from a circle of tissue, such as a fingertip joint, ear lobe, or pinched tissue. In this work, we found that the full scattering profile is affected by blood vessel diameter.…”

“…Since absorption due to blood vessels does not change the shape of the full scattering profile, it can influence the total scattered intensity and is neglected in the current simulations. We calculate the full scattering profile via MC simulation of a circular cross-section of tissue 13,18 in the nearinfrared (NIR) wavelength of 850 nm since it is common in photoplethysmography (PPG) measurements due to its high penetration depth and minimal scattering. 19,20 We investigate the dependency of the isobaric point in case of different tissue diameters and show that this phenomenon is independent of the value of the anisotropy factor.…”

Experimental system for measuring the full scattering profile of circular phantoms

“…We previously presented a full scattering profile simulation of a homogeneous cylindrical tissue [9][10][11], meaning reflection as well as transmission. In this work we present our unique set-up for noninvasive encircled measurements, and the cylindrical tissue-like phantoms that we prepared with different reduced scattering coefficients to mimic different physiological states.…”