title: Anti-Stokes fluorescence from endogenously formed protoporphyrin IX--implications for clinical multiphoton diagnostics.
abstract: Multiphoton imaging based on two-photon excitation is making its way into the clinics, particularly for skin cancer diagnostics. It has been suggested that endogenously formed protoporphyrin IX (PpIX) induced by aminolevulinic acid or methylaminolevulinate can be applied to improve tumor contrast, in connection to imaging of tissue autofluorescence. However, previous reports are limited to cell studies and data from tissue are scarce. No report shows conclusive evidence that endogenously formed PpIX increases tumor contrast when performing multiphoton imaging in the clinical situation. We here demonstrate by spectral analysis that two-photon excitation of endogenously formed PpIX does not provide additional contrast in superficial basal cell carcinomas. In fact, the PpIX signal is overshadowed by the autofluorescent background. The results show that PpIX should be excited at a wavelength giving rise to one-photon anti-Stokes fluorescence, to overcome the autofluorescent background. Thus, this study reports on a plausible method, which can be implemented for clinical investigations on endogenously formed PpIX using multiphoton microscopy.
authors.affiliation: Department of Dermatology, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Despina
authors.initials: D
authors.lastname: Kantere
authors.forename: Stina
authors.initials: S
authors.lastname: Guldbrand
authors.forename: John
authors.initials: J
authors.lastname: Paoli
authors.forename: Mattias
authors.initials: M
authors.lastname: Goksör
authors.forename: Dag
authors.initials: D
authors.lastname: Hanstorp
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Wennberg
authors.forename: Maria
authors.initials: M
authors.lastname: Smedh
authors.forename: Marica B
authors.initials: MB
authors.lastname: Ericson
mesh_terms: D006801:Humans; D007259:Infrared Rays; D007834:Lasers; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D057054:Molecular Imaging; D011524:Protoporphyrins / Q000378:metabolism*; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology; D013050:Spectrometry, Fluorescence
chemical_list: D011524:Protoporphyrins; C028025:protoporphyrin IX