RT Journal Article ID 46a7c27267b3ab34 A1 Zhao, Lu A1 Nielsen, Kristian Pagh A1 Juzeniene, Asta A1 Juzenas, Petras A1 Lani, Vladimir A1 Ma, Li-Wei A1 Stamnes, Knut A1 Stamnes, Jakob J. A1 Moan, Johan T1 Spectroscopic Measurements of Photoinduced Processes in Human Skin after Topical Application of the Hexyl Ester of 5-Aminolevulinic Acid JF Journal of Environmental Pathology, Toxicology and Oncology JO JEP(T) YR 2006 FD 2006-02-13 VO 25 IS 1-2 SP 307 OP 320 AB Although 5-aminolevulinic acid, ALA, and its derivatives, have been widely studied and applied in clinical photodynamic therapy (PDT), there is still a lack of reliable and non-invasive methods and technologies to evaluate physiological parameters of relevance for the therapy, such as erythema, melanogenesis, and oxygen level. We have investigated the kinetics of these parameters in human skin in vivo during and after PDT with the hexyl ester of ALA, ALA-Hex. Furthermore, the depth of photosensitizer (protoporphyrin IX, PpIX) production after different application times was investigated. It was found that the depth increased with increasing application time of ALA-Hex. We also investigated the depth of PpIX before and after light exposure causing 50% photobleaching at 407 nm. The PpIX localized in superficial layers of the normal tissue was removed during the bleaching. Thus, after bleaching, the remaining PpIX was localized mainly in the deeper layers of normal tissue. We have applied fluorescence emission spectroscopy, fluorescence excitation spectroscopy, and reflectance spectroscopy in the study of the above-mentioned parameters. In conclusion, fluorescence excitation spectroscopy and reflectance spectroscopy are simple, useful, reliable, and noninvasive techniques in the evaluation of the processes taking place in human skin in vivo during and after PDT. Using these methods we were able to quantify melanogenesis, O2 level, erythema, vasoconstriction, and vasodilatation. PB Begell House LK https://www.dl.begellhouse.com/journals/0ff459a57a4c08d0,5d84548f012e18bf,46a7c27267b3ab34.html