A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo

Abstract

A model based upon steady-state diffusion theory which describes the radial dependence of diffuse reflectance of light from tissues is developed. This model incorporates a photon dipole source in order to satisfy the tissue boundary conditions and is suitable for either refractive index matched or mismatched surfaces. The predictions of the model were compared with Monte Carlo simulations as well as experimental measurements made with tissue simulating phantoms. The model describes the reflectance data accurately to radial distances as small as 0.5 mm when compared to Monte Carlo simulations and agrees with experimental measurements to distances as small as 1 mm. A nonlinear least-squares fitting procedure has been used to determine the tissue optical properties from the radial reflectance data in both phantoms and tissues in vivo. The optical properties derived for the phantoms are within 5%-10% of those determined by other established techniques. The in vivo values are also consistent with those reported by other investigators.

The sensitivity of normal brain and intracranially implanted VX2 tumour to interstitial photodynamic therapy

“…The extent of neuron damage beyond coagulative Appendix The fluence at the boundary of necrosis can be calculated indirectly by applying a mathematical model of the light distribution in optically turbid media (Driver et al, 1991;Arnfield et al, 1992;Farrell and Patterson, 1992) based on average optical properties of the target tissue. In the present study, in addition to direct determination of the fluence at the radius of necrosis, the local fluence-rate measurements, ¢(r), at the three different radial distances, r, were used to derive the optical interaction coefficients of the target tissues, using a modified solution of the diffusion necrosis becomes smaller for longer time delays between photosensitiser and light administration, favouring longer time delays (Muller and Wilson, 1993).…”

“…The multifibre detector technique demonstrated might be well suited for deep-seated malignancies when non-invasive monitoring (Farrell et al, 1992b;Farrell and Patterson, 1992) is not applicable.…”

Light scattering spectroscopy identifies the malignant potential of pancreatic cysts during endoscopy

“…Use of this probe requires an invertible theory that accurately describes reflectance signals from fibers separated by distances smaller than the inverse of the reduced scattering coefficient. The classical diffusion approximation 26 will not work since it fails to take into account the contribution of photons which have undergone several low-angle scattering events plus a single large-angle scattering event. It is precisely these photons which are sensitive to the structure of the epithelial layer.…”

“…$$R_i^d\left[{\mu }_s^{\prime }(\lambda )\right]=\frac{1}{{\pi }^2{r}_s^2{r}_i^2}\underset{A_s}{\int }{dA}_s\underset{A_i}{\int }{dA}_i{R}^d\left[{\mu }_s^{\prime }(\lambda )\left|{\mathrm{boldr}}_s-{\mathrm{boldr}}_i\right|\right]$$ where R d is the well-known diffuse reflectance density 26,50 . The integrals here are numerically calculated over the area of the source fiber A s with radius r s and collection fibers A i with radii r i ( i =1, 2).…”

Automated Systems Based on Machine Vision for Inspecting Citrus Fruits from the Field to Postharvest—a Review

“…The radial intensity of the backscattering profiles was calculated by obtaining the average value of all pixels within each circular ring with one pixel size. This work used the Gaussian-Lorentzian (GL) cross product distribution function to describe backscattering profiles from backscattering images and was later enhanced in Lorente et al (2015) to include a physical approach consisting in extracting optical properties of fruits by Farrell's diffusion theory (Farrell et al 1992). Despite the fact that these works have some interest because they try to develop new approaches to detect decay lesions avoiding the problems related with UV illumination, the practical implementation of LBI still needs research because the laser has to point exactly to the damage in order to be able to detect it.…”