Photobleaching measurements of pigmented and vascular skin lesions:
results of a clinical trial
Kristine Rozniecea, Janis Lesinsb, Alexey Lihachevb, Janis Spigulisb
a
Skin Diseases and Sexually Transmitted Disease Clinic, Briana str.2, Riga, Latvia, LV-1001;
b
Institute of Atomic Physics and Spectroscopy, University of Latvia, Raina blvd.19, Riga, Latvia,
LV-1586
ABSTRACT
The autofluorescence photobleaching intensity dynamics of in vivo skin and skin pathologies under continuous 532 nm
laser irradiation have been studied. Overall the 47 human skin malformations were investigated by laser induced skin
autofluorescence photobleaching analysis. Details of equipment are described along with some measurement results
illustrating potentiality of the technology.
Keywords: in vivo skin, photobleaching, autofluorescence, pigmented skin
1. INTRODUCTION
Timely detection and evaluation of skin pathologies is a topical problem of modern clinical diagnostics, because number
of occurrence of such pathologies (incl., deadly melanomas) in Europe and throughout the world keeps on growing. The
most precise method at present to identify the skin diseases is the biopsy – a sample removal from the damaged skin area
with consequent histological analysis. It is a painful, destructive, time-consuming and rather expensive method. Modern
bio-photonics researches are developing new non-invasive “optical biopsy” methods, which are faster and more patientfriendly. Possible applications of laser excited skin autofluorescence photobleaching parameters in diagnostics cause
special interest at present.
Fluorescence intensity decrease during a lasting optical excitation is well known as photo-bleaching effect. Laser-excited
tissue autofluorescence photo-bleaching (AFPB) have been studied extensively over recent decades. Most of the authors
observed that the bleaching fluorescence intensity can be well described by double exponential equation in two phases.
The intensity usually tends to a constant fluorescence background level after a while. Some researchers have dealt with
AFPB studies by laser excitation at ultra-violet (337 nm), violet (405 nm), blue (442 nm), green (532 nm) and red (632
nm) wavelengths, both under continuous and pulsed excitations in a wide range of power densities (1 to 500 mW/cm 2)
[1-3].
Mechanism of the skin AFPB effect has not been explained in details so far, but several hypotheses are examined
experimentally. Summarizing the available literature data it was stated that the skin AF photobleaching effect application
opportunities for skin diagnostics were not considered in the researches done during the time period from 1993 to 2005.
Our research as a continuation of previous studies [4-6] is aimed to develop the AFPB analysis in order to find a
potential method for diagnostics of skin pathologies. Safety and well being of human subjects involved in a clinical trial
have been provided according to permission of the local ethics committee.
2. MATERIALS AND EQUIPMENT
The measurement setup comprises a cw laser (532 nm) with focusing output SMA-connector, Y-shaped optical fiber
bundle for delivery of the laser radiation to the skin probe and the fluorescent light to spectrometer AvaSpec-2048-2 (via
a laser-blocking filter) which was connected to PC. The emitting and detecting fibers were placed 3 mm from the skin.
The typical excitation time was 1-2 minutes, the spectrometer integration time 0.5 sec, laser power density on the skin
~65mW/cm2, area of the excited skin surface ~ 0.3cm2 [4]. Intensity-time dependent array is normalized by maximum
AF intensity; the data is fitted to the double-exponential bleaching expression [1] with subsequent extraction of
bleaching rates τ1 and τ2. This results in curves of AFPB dynamics and corresponding bleaching rates.
3. RESULTS AND DISCUSSION
Fig.1. presents healthy skin and melanoma autofluorescence intensity dynamics. The figure shows distinguishable
differences of photo-bleaching, where AF intensity of healthy skin bleaches exponentially while AF intensity of
melanoma varies around the initial value. Fig.2 demonstrates dynamics of AF intensity of healthy skin and pigmented
and vascular lesions. Each of skin pathologies has a specific AFPB characteristic, especially differ the dynamic features
of pigmented cellular nevus and cherry angioma. In case of pigmented cellular nevus the initial intensity of AF is
remarkably low and it tends to hold constant whereas the intensity of cherry angioma (vascular formation) rapidly falls.
Results include three skin photo-types of patients (confirmed by dermatologist), i.e., Fig.2 represents cherry angioma of
skin phototype II and pigmented cellular nevus of III phototype.
1.05
Pigmented cellular nevus
Healthy skin
Fluorescence intensity (norm.u.)
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0
10
20
30
40
50
60
Time (sec)
Fig.1. Dynamics of the autofluorescence intensity for healthy skin and pigmented cellular nevus, 532 nm laser excitation,
registration at 600 nm, power density 65 mW/cm2.
Pigmented cellular nevus
Cherry angioma
Healthy skin
1.05
Fluorescence intetsity (norm.u.)
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
-10
0
10
20
30
40
50
60
Time (sec)
Fig.2. Dynamics of the autofluorescences intensity for some skin pathologies and healthy skin, 532 nm laser excitation,
registration at 600 nm, power density 65 mW/cm2.
4. CONCLUSSIONS
Results of the present study show considerable sensitivity of skin pathologies of the AF photbleaching analysis method.
This methodology has a great potential for fast and patient-friendly diagnostics in dermatology. Dynamics of AFPB
intensity are mainly dependent on a variety of skin chromophore distribution of various pathologies. The more
homogeneous is a certain pathology structure, the more regular is its bleaching (following the double-exponential
model). The smallest intensity bleaching has been observed in cases of highly pigmented cellular nevus, though the most
rapid bleaching refers to vascular formations as to cherry angioma and hemangioma. Since the AFPB mechanism is still
under discussion, additional studies by use of this methodology would promote a better understanding of the AFPB
mechanisms that take place in the human skin.
ACKNOWLEDGMENTS
The financial support of European Social Fund (grant #2009/0211/1DP/1.1.1.2.0/09/APIA/VIAA/077) is highly
appreciated.
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