Correction for tissue optical properties enables quantitative skin fluorescence measurements using multi-diameter single fiber reflectance spectroscopy.
OBJECTIVE
Fluorescence measurements in the skin are very much affected by absorption and scattering but existing methods to correct for this are not applicable to superficial skin measurements.


METHODS
The first use of multiple-diameter single fiber reflectance (MDSFR) and single fiber fluorescence (SFF) spectroscopy in human skin was investigated. MDSFR spectroscopy allows a quantification of the full optical properties in superficial skin (μa, μs' and γ), which can next be used to retrieve the corrected - intrinsic - fluorescence of a fluorophore Qμa,x(f). Our goal was to investigate the importance of such correction for individual patients. We studied this in 22 patients undergoing photodynamic therapy (PDT) for actinic keratosis.


RESULTS
The magnitude of correction of fluorescence was around 4 (for both autofluorescence and protoporphyrin IX). Moreover, it was variable between patients, but also within patients over the course of fractionated aminolevulinic acid PDT (range 2.7-7.5). Patients also varied in the amount of protoporphyrin IX synthesis, photobleaching percentages and resynthesis (>100× difference between the lowest and highest PpIX synthesis). The autofluorescence was lower in actinic keratosis than contralateral normal skin (0.0032 versus 0.0052; P<0.0005).


CONCLUSIONS
Our results clearly demonstrate the importance of correcting the measured fluorescence for optical properties, because these vary considerably between individual patients and also during PDT. Protoporphyrin IX synthesis and photobleaching kinetics allow monitoring clinical PDT which facilitates individual-based PDT dosing and improvement of clinical treatment protocols. Furthermore, the skin autofluorescence can be relevant for diagnostic use in the skin, but it may also be interesting because of its association with several internal diseases.
Department of Dermatology, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
T A
TA
Middelburg
Department of Radiation Oncology, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
C L
CL
Hoy
Department of Dermatology, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
H A M
HA
Neumann
Department of Radiation Oncology, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
A
A
Amelink
Department of Dermatology, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands; The Centre for Optical Diagnostics and Therapy, Department of Otorhinolaryngology-Head and Neck Surgery, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands. Electronic address: d.robinson@erasmusmc.nl.
D J
DJ
Robinson
D000368:Aged; D005260:Female; D005336:Fiber Optic Technology; D005453:Fluorescence; D006801:Humans; D055623:Keratosis, Actinic / Q000188:drug therapy / Q000473:pathology*; D008297:Male; D061848:Optical Imaging / Q000379:methods; D055620:Optical Phenomena; D038761:Photobleaching; D010778:Photochemotherapy; D011524:Protoporphyrins / Q000096:biosynthesis; D012867:Skin; D013050:Spectrometry, Fluorescence / Q000295:instrumentation / Q000379:methods; D013057:Spectrum Analysis
D011524:Protoporphyrins; C028025:protoporphyrin IX
Absorption; Fluorescence spectroscopy; Photodynamic therapy; Reflectance spectroscopy; Scattering; Skin