Changes in optical properties ofex vivorat prostate due to heating

Abstract

This study examines the effectiveness of a single, first-order Arrhenius process in accurately modelling the thermally induced changes in the optical properties, particularly the reduced scattering coefficient, mu(s)', and the absorption coefficient, mu(a), of ex vivo rat prostate. Recent work has shown that mu(s)' can increase as much as five-fold due to thermal coagulation, and the observed change in mu(s)' has been modelled well according to a first-order rate process in albumen. Conversely, optical property measurements conducted using pig liver suggest that this change in mu(s)' cannot suitably be described using a single rate parameter. In canine prostate, measurements have indicated that while the absorption coefficient varies with temperature, it does not do so according to first-order kinetics. A double integrating sphere system was used to measure the reflectance and transmittance of light at 810 nm through a thin sample of prostate. Using prostate samples collected from Sprague Dawley rats, optical properties were measured at a constant elevated temperature. Tissue samples were measured over the range 54-83 degrees C. The optical properties of the sample were determined through comparison with reflectance and transmittance values predicted by a Monte Carlo simulation of light propagation in turbid media. A first order Arrhenius model was applied to the observed change in mu(s)' and mu(a) to determine the rate process parameters for thermal coagulation. The measured rate coefficients were Ea = (7.18 +/- 1.74) x 10(4) J mol(-1) and Afreq = 3.14 x 10(8) s(-1) for mu(s)'. It was determined that the change in mu(s)' is well described by a single first-order rate process. Similar analysis performed on the changes in mu(a) due to increased temperatures yielded Ea = (1.01 +/- 0.35) x 10(5) J mol(-1) and Afreq = 8.92 x 10(12) s(-1). The results for mu(a) suggest that the Arrhenius model may be applicable to the changes in absorption.

Colorectal tumors and hepatic metastases differ in their optical properties—relevance for dosimetry in laser-induced interstitial thermotherapy

“…High absorption corresponds to a penetration depth in the lower wavelength range, that is, 2.26 mm for healthy colon and 3.38 for colon carcinoma tissue, while the highest penetration depths coincide with low absorption at the upper end of the spectral range investigated. Other authors have also described this course of the optical penetration depth in relation to absorption [31,36,37].…”

Thermal modeling of lesion growth with radiofrequency ablation devices

“…Data from experimental studies, where tissues are exposed to uniform temperatures for controlled time intervals, are fit to the Arrhenius equation to determine the frequency factor A (s -1 ), and the activation energy Δ E (J mol -1 ). Arrhenius parameters have been determined in skin [31-35], artery [36,37], blood [38-40], pancreas [41,42], heart [43], cornea [44-46], muscle [47], prostate [48], ovary [49], kidney [50-52], and liver [30,52,53]. For a specified exposure temperature and time, the fit parameters A and Δ E determine the amount of cell damage incurred for a specific tissue type.…”

Diffuse optical tomography to monitor the photocoagulation front during interstitial photothermal therapy: Numerical simulations and measurements in tissue-simulating phantoms

“…This distance is denoted as "d" throughout this paper (note that: d+r = 8 mm). The optical properties assigned to the homogenous mesh as well as to the anomalies corresponded to the values used in the experimental phantoms for the different wavelengths employed (see Table 1) and were selected to be representative of typical soft tissues in this spectral range [29,34].…”