Measurements of the optical properties of tissue in conjunction with photodynamic therapy

Abstract

A simple optical dosimeter was used to measure the light intensity in rat liver and muscle in vivo with fibers positioned at different depths to investigate whether the light penetration changed during photodynamic therapy 1PDT2. The results were then correlated with measurements of the three optical-interaction coefficients µ s , µ a , and g for wavelengths in the range 500-800 nm for PDT-treated and nontreated rat liver and muscle tissue in vitro. A distinct increase in the absorption coefficient was seen immediately after treatment, in agreement with the decreasing light intensity observed during the treatment, as measured with the optical dosimeter. The collimated transmittance was measured with a narrow-beam setup, and an optical integrating sphere was used to measure the diffuse reflectance and total transmittance of the samples. The corresponding optical properties were obtained by spline interpolation of Monte Carlo-simulated data. To ensure that the measured values were correct, we performed calibration measurements with suspensions of polystyrene microspheres and ink.

MRI thermometry in phantoms by use of the proton resonance frequency shift method: application to interstitial laser thermotherapy

“…The equipment, as well as the calibration and measurement procedure, has been described previously by Nilsson et al (1995Nilsson et al ( , 1998. Briefly, three parameters, the reflectance, the transmittance and the total attenuation coefficient (µ t ) were determined.…”

“…The optical properties may be altered by addition of scattering and absorbing agents, such as polystyrene microspheres and India ink or molecular dyes (Marijnissen and Star 1984, Madsen et al 1992, Nilsson et al 1995. Solid phantoms based on an epoxy resin and silica spheres have been developed by Firbank et al (1995) and Sukowski et al (1996).…”

Multiple polynomial regression method for determination of biomedical optical properties from integrating sphere measurements

“…5,6 The optical properties, 7 i.e., the absorption coefficient a , the scattering coefficient s , and the anisotropy parameter g, are often determined by measurement of the total diffuse reflectance R and the diffuse transmittance T of a thin sample in an integrating sphere setup. However, it is only possible to determine a and the reduced scattering coefficient Ј s ϭ ͑1 Ϫ g͒ s from pure R and T measurements.…”

“…Furthermore, the analytical solutions of R͑ a , Ј s ͒ and T͑ a , Ј s ͒ are not accurate; thus most contemporary approaches are based on numerical methods, which provide more accurate calculations of R͑ a , Ј s ͒ and T͑ a , Ј s ͒, e.g., the inverse addingdoubling ͑IAD͒ method 14 or methods involving Monte Carlo simulations. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] For all the above methods it is common that a ͑R, T͒ and Ј s ͑R, T͒ have to be determined by iterative numerical calculations. This may prove to be to slow in some cases, e.g., applications involving real-time multiwavelength analysis.…”

“…Finally, we compare the performance of the MPR method with that of the IAD method and another Monte Carlo-based method, the so-called Monte Carlo spline interpolation ͑MCSI͒ method. 5 …”