Accuracy of Noninvasive in vivo Measurements of Photosensitizer Uptake Based on a Diffusion Model of Reflectance Spectroscopy

Abstract

This study compares the photosensitizer concentration measured noninvasively in vivo by diffuse reflectance spectroscopy with the results of postmortem tissue solubilization and fluorometric assay. The reflectance spectrometer consists of a fiber optic surface probe, spectrometer and charge-coupled device (CCD) array detector. The surface probe has eight detection fibers separated from the light source fiber by distances ranging from 0.85 to 10 mm. The imaging spectrometer disperses the light from each detector fiber onto the two-dimensional CCD array, while maintaining spatial separation of each individual spectrum. A single exposure of the CCD therefore captures the reflectance spectrum ar eight distances and over a range of 300 nm. From the spectra, the tissue's optical scattering and absorption coefficients are determined using a diffusion model of light propagation. Changes in the tissue absorption are used to estimate the photosensitizer concentration. Normal New Zealand White rabbits were injected with aluminum phthalocyanine tetrasulfonate (AlPcS4) and probe measurements made 24 h after injection on the dorsal skin, on muscle after surgically turning the skin back and on liver. For skin, the noninvasive estimate to proportional to the true concentration but low by a factor of 3. Based on Monte Carlo modeling of multilayered systems, this underestimate is attributed to the layered structure of the skin and nonuniform AlPcS4 distribution. A comparison of the noninvasive concentration estimates to the postmortem assay results finds good agreement for liver tissue even though application of the diffusion model is not strictly justified.

Spatial Laser Induced Fluorescence Imaging (SLIFIMG) Analysis to Assess Tissue Photosensitizer Uptake

“…The uptake and retention of i.v. administered photosensitizer by tumor tissue is one of several fundamental determinants of the clinical effectiveness of PDT as mentioned by Weersink, R. A., et al, 1997, Chen, Q., et al., 1996, Love, W. G., et al, 1996 and Windahl, T., et al, 1993 which comply with our obtained results that study of PS tissue uptake reflects many aspects that facilitate the understanding and how we can optimally benefit from this useful treatment modality [17][18][19][20]. Using Matlab to study and analyze tissue auto fluorescence was applied by Kamath SD and Mahato KK 2007 the demonstrated that Matlab is a good tool for the spectral analysis and classification for discrimination of autofluorescence spectra of pathologically certified normal, premalignant, and malignant oral tissues [21].…”

In vivo absorption spectroscopy of tumor sensitizers with femtosecond white light

“…22 Similar results have also been reported by Cubeddu et al 21 for AlS 2 Pc, where the in vivo absorption spectrum peaked at 685 nm compared with 672 nm for absorption in aqueous solution 23 and cell cultures. 24 Furthermore, Weersink et al 19 found a redshift to ϳ680 nm of the absorption peak of tetrasulphonated aluminum phthalocyanine ͑AlS 4 Pc͒ in rabbit skin, which is in agreement with the findings for AlS 2 Pc. Stratonnikov et al, 18 however, found a redshift of the absorption peak of Photosence (NIOPIC, Russia) in human lip in vivo of only 4 nm, as compared with the aqueous solution.…”

Evaluation of Diffuse Reflectance in Multi-layered Tissue for High Intensity Laser Therapy

“…Because melanin and water have a wavelength-dependent absorption coefficient, the distribution of these components (melanin, water) influences the optical properties of skin [34]. The light absorption by water in tissue is higher at λ =1064 nm than at visible wavelengths [35]. Thereby, the high diffuse reflectance, which was also found at λ=1064 nm with short radius, may arise from high absorption by water in the skin tissue.…”