Comparison of Photosensitizer (AlPcS2) Quantification Techniques: In Situ Fluorescence Microsampling Versus Tissue Chemical Extraction¶

Abstract

A noninvasive in situ fluorescence-based method for the quantification of the photosensitizer chloroaluminum disulfonated phthalocyanine was compared to the highly accurate but nonreal time ex vivo spectrofluorometry method. Our in vivo fluorescence technique is designed to allow real-time assessment of photosensitizer in tumor and normal tissues and therefore temporally optimal light delivery. Laser-induced fluorescence was used to measure photosensitizer concentration from multiple microscopic regions of tissue. Ex vivo chemical extraction was used to quantify photosensitizer concentration in the same volume of tissue. The amount of photosensitizer in the vascular and/or parenchymal compartments of skeletal muscle and liver was determined by quantifying fluorescent signal in vivo, ex vivo and after blood removal. Confocal microscopy was used to spatially document photosensitizer localization 30 min and 24 h after delivery. While a linear correlation can exist between the fluorescence intensity measured by our fiber-optic bundle system and actual tissue concentration, temporal changes to this calibration line exist as the photosensitizer changes its partitioning fraction between the blood (vasculature) and the tissue parenchyma. In situ photosensitizer fluorescence microsampling (dosimetry) systems can be performed in real time and linearly correlated to actual tissue concentration with minimal intertissue variance. Tissue-specific differences may require temporal alterations in the calibration.

Photodynamic therapy of cerebral glioma – A review Part I – A biological basis

“…14,[150][151][152] In vivo methods have also been utilized to directly measure the concentration of PS present in the tumour tissue, even though PS aggregation, photobleaching and tissue optical properties can ultimately confuse the issue. [153][154][155][156][157][158] Light delivery and penetration to the target tissue containing the accumulated PS is the next important step in the process. The wavelength of light used, as well as the optical properties of the tissue, will have a bearing on the PDT process.…”

Measurement of fluorophore concentration in turbid media by a single optical fiber

“…Various concepts have been proposed for that purpose, ranging from tissue extraction [3] over fiber bundle probes [4,5] and ratioing techniques [6]. Recently, it has been suggested to use a single optical fiber for quantitative concentration measurements of fluor- [7].…”

Quantification of fluorophore concentration in vivo using two simple fluorescence-based measurement techniques

“…2,4,9 Rather than using tissue-specific calibration curves, we have examined the use of a single calibration curve from tissue-simulating phantoms to perform quantitative fluorescence measurements in vivo. We have also considered the possibility that the fluorescence quantum yield of our model fluorophore may be different in vivo than in the tissue-simulating phantoms.…”

“…Panjehpour et al 4 showed that sulphonated aluminum phthalocyanine fluorescence measured in rats depended linearly on concentration, which was determined by chemical extraction of tissue samples. A more recent study by Lee et al 9 compared measurements of AlPcS 2 concentration using a fiber bundle probe 10 to a chemical extraction technique. They used measurements of concentration in vivo to calibrate the probe, and used that calibration to quantify uptake in muscle and liver.…”

“…The fluorescence lifetime is an important component of this study because it is related to the fluorescence quantum yield, which may be different in tissues than in external calibration standards. 9,13 Differences in the fluorescence quantum yield could be erroneously interpreted as differences in fluorophore concentration. Changes in the fluorescence lifetime, however, do not necessarily reflect physical changes ͑e.g., interactions that cause the fluorophore to become nonfluorescent͒ that the fluorophore may undergo in vivo and which could also affect the fluorescence quantum yield.…”