Monte Carlo simulation of light fluence in tissue in a cylindrical diffusing fibre geometry

Abstract

The propagation of light emitted by a linear light diffuser in a cylindrical hollow organ was investigated by means of the Monte Carlo (MC) method. The height and radius of the cavity, scattering (mu(s)) (or reduced scattering, mu'(s)) and absorption (mu(a)) coefficients, anisotropy (g), and refractive indices of the media involved (n1, n2) are required as input data by the MC code, as are characteristics of the light diffuser (length, delivered power and emission profile). Results of our MC model were tested by measuring the light fluence rate in a tissue-simulating phantom (mu(a) = 0.5 cm(-1), mu(s) = 23 cm(-1) and g = 0.75) irradiated at 633 nm with a cylindrical diffuser. Since geometric and optical parameters determine the behaviour of light propagation in tissue, MC simulations with different sets of input parameters were carried out to provide qualitative as well as quantitative data useful in planning photodynamic therapy. Data are reported on light penetration and fluence rate build-up at mu(a) and mu'(s) values ranging between 0.1 and 5 cm(-1) and 2.5 and 50 cm(-1), respectively. Furthermore, results suggest that a shift and spread could occur in the isofluence curves along the symmetry axis, which depend on the diameter of the treated lumen as well as on the emission profile of the light diffuser. Using our data it is possible to estimate how inaccuracy in knowledge of the optical coefficients can affect (i.e. usually by increasing) the light dose scheduled at a certain depth into tissue.

White Monte Carlo for time-resolved photon migration

“…Since WMC does not rely on the high albedo assumption, this method should be more reliable in the regime when scattering and absorption coefficients are of comparable magnitude. ͑For an example of nonwhite MC without being based on the high albedo assumption, we refer to the work of Farina et al 32 ͒. In most types of biological tissue, the difference between traditional MC and WMC can, however, be disregarded.…”

Laser-enhanced cavitation during high intensity focused ultrasound: An in vivo study

“…The laser fluence was first measured at the surface of the tissue sample, and the mean of the Monte Carlo (MC) method was used to estimate the laser fluence inside the tissue. 28 In order to test the capability of generating cavitation at different depths, we used ex vivo chicken breast tissues with different thicknesses to cover the region of interest on the small animal ( Fig. 1 dotted line circled area).…”

Photodynamic therapy for the treatment of atherosclerotic plaque: Lost in translation?

“…Thus, at a given distance from the diffuser, the exact light dose delivered as primary incidence can be computed as long as d << L (with d =the distance between the diffuser surface and the vessel wall, and L =the irradiation length of the diffuser; see Figure ). This distance “ d ” is an important parameter not only because it affects the irradiance as the illuminated surface is equal to 2π dL , but also because it has an influence on the shape of the illumination spot . It is important to note that additional features of good light distributors are that they do not compress the organ, which would result in a reduction in the perfusion and suboptimal PDT results.…”