E. Drakaki

Laser-Induced Fluorescence and Reflectance Spectroscopy for the Discrimination of Basal Cell Carcinoma from the Surrounding Normal Skin Tissue

The object of this study was to investigate whether laser-induced skin autofluorescence (LIF) and/or light reflectance spectra could provide a useful contrast between basal cell carcinoma (BCC) tissues and the surrounding healthy skin. Unstained human skin samples, excised from humans undergoing biopsy examination, were irradiated with a nitrogen laser (λ = 337 nm) for excitation of autofluorescence and a tungsten halogen lamp for the reflectance measurements. The ex vivo spectroscopic results were correlated with the histopathology images to distinguish the areas of BCC from those of the surrounding health skin. A simple spectral analysis technique was also applied for better skin diagnosis. In conclusion, it seems that LIF and reflectance spectra could be used to differentiate neoplastic from normal skin tissue using an appropriate classification model analysis.

In vitro fluorescence measurements and Monte Carlo simulation of laser irradiation propagation in porcine skin tissue.

In dermatology, the in vivo spectral fluorescence measurements of human skin can serve as a valuable supplement to standard non-invasive techniques for diagnosing various skin diseases. However, quantitative analysis of the fluorescence spectra is complicated by the fact that skin is a complex multi-layered and inhomogeneous organ, with varied optical properties and biophysical characteristics. In this work, we recorded, in vitro, the laser-induced fluorescence emission signals of healthy porcine skin, one of the animals, which is considered as one of the most common models for investigations related to medical diagnostics of human cutaneous tissues. Differences were observed in the form and intensity of the fluorescence signal of the porcine skin, which can be attributed to the different concentrations of the native fluorophores and the variable physical and biological conditions of the skin tissue. As the light transport in the tissue target is directly influencing the absorption and the fluorescence emission signals, we performed Monte Carlo simulation of the light distribution in a five-layer model of human skin tissue, with a pulsed ultraviolet laser beam.

Dynamic model of thermal reaction of biological tissues to laser-induced fluorescence and photodynamic therapy

Abstract. The aim of this work was to evaluate the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed ultraviolet (UV) laser (λ=337  nm) and a continuous-wave (cw) visible laser beam (λ=632.8  nm) using Monte Carlo modeling. Finite-element methodology was used for heat transfer simulation. The analysis of the results showed that heat is not localized on the surface, but is collected inside the tissue in lower skin layers. The simulation was made with the pulsed UV laser beam (used as excitation source in laser-induced fluorescence) and the cw visible laser (used in photodynamic therapy treatments), in order to study the possible thermal effects.

Thermal distribution in biological tissue at laser induced fluorescence and photodynamic therapy

Laser induced fluorescence spectroscopy and photodynamic therapy (PDT) are techniques currently introduced in clinical applications for visualization and local destruction of malignant tumours as well as premalignant lesions. During the laser irradiation of tissues for the diagnostic and therapeutic purposes, the absorbed optical energy generates heat, although the power density of the treatment light for surface illumination is normally low enough not to cause any significantly increased tissue temperature. In this work we tried to evaluate the utility of Monte Carlo modeling for simulating the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed UV laser and a continuous wave visible laser beam. The analysis of the results showed that heat is not localized on the surface, but it is collected inside the tissue. By varying the boundary conditions on the surface and the type of the laser radiation (continuous or pulsed) we can reach higher than normal temperature inside the tissue without simultaneous formation of thermally damaged tissue (e.g. coagulation or necrosis zone).

Comparative evaluation of ultrafast laser beam interaction with the silvering in late Roman coins

This work investigates the influence of the pulse duration and the wavelength on the laser cleaning of thin silver plating layers found in late Roman coins. Comparative cleaning tests were performed using Nd:YAG (1064 nm and 532 nm - 6 ns), GaAlAs diode (780 nm - 90 ps) and Ti-Sapphire regenerative amplifier (800 nm - 100 fs) laser systems. The cleaning results on the plated areas were characterised by high resolution optical microscopy, SEM-EDX, XRF and micro-profilometry.

A diffusion approximation model of light transport in multilayered skin tissue

In dermatology, biophotonic methods offer high sensitivity and non-invasive measurements of skin tissue optical properties, in various physiological and pathological conditions. There are numerous skin processes, which can be examined and characterized using diagnostic optical spectroscopy, as the monitoring of skin aging, diagnosis of benign and malignant cutaneous lesions, dosimetry in photodynamic therapy (PDT), etc. Several mathematical models have been used to calculate the tissue optical properties from experimental measurements and to predict the light propagation in soft tissues, like skin, based on transport theory or Monte Carlo modeling. This work analyses the phenomena which are observed experimentally during the irradiation of skin, such as the absorption, reflectance, scattering, fluorescence and transmission of laser light. The study was carried out on animal skin samples, extracted post-mortem. In this work we also tried to evaluate the utility of diffusion approximation modeling for measuring the light intensity distribution in the skin samples with cw visible laser beam (&lgr;=632.8 nm). The diffusion theory model was tested for the simulation results of the spatial light distribution within a five-layer model of animal skin tissue. We have studied the dependence towards the depth and the radial distance of the photon density of the incident radiation.

Experimental study on the effect of wavelength and fluence in the laser cleaning of silvering in late Roman coins (Mid 3rd/4th century AD)

The political problems in Late Roman Empire caused significant changes in the coin technology. The silver content dropped severely and a new technology, in all the mints operating around the Empire, was introduced. For the production of these coins, copper based quaternary alloys were used and their surface was covered by a silver amalgam plating layer. Hoards of these coins have been recovered in thousands from across the Empire, however, their treatment has been problematic. Both mechanical and chemical cleaning results in the damage or the complete destruction of the thin silver layer. The use of laser technology in the cleaning of works of art has a wide range of applications which includes metallic objects. The main aim of this work was to investigate the use of lasers in the cleaning of the thin silver plating layers found in late Roman coins. The optimisation of laser parameters was achieved through comparative cleaning tests by employing Nd:YAG (532 nm and 266 nm) laser systems. The cleaning results on the plated areas were characterised by optical microscopy, and SEM-EDX analysis. Following a systematic investigation and many cleaning trials on two different wavelengths and fluence values, optimum irradiation parameters were thoroughly demonstrated. Microscopic observations of the cleaned areas evidenced complete removal of the encrustation and high selectivity of the laser cleaning. Neither thermal or mechanical injuries, nor cuprite blackening were observed on the cleaned surfaces at the optimum laser cleaning technique, using 532 nm of the Nd: YAG laser.

Laser cleaning experimental investigations on ancient coins

Laser cleaning tests were performed on ancient (Roman and Byzantine) coins, which belong to the collection of the Numismatic Museum of Athens, Greece. Coins with various types of surface corrosion were studied, using Q-switched Nd:YAG, CO2 and Er:YAG lasers and a range of laser pulsing parameters on dry and wet surfaces. A section of each object was cleaned mechanically, by the conservators of the museum in order to show the results of this method. It was discovered that the results of laser cleaning was influenced by the type of corrosion of the surface of the coins. X-ray fluorescence was applied as analytical technique. The results show that XRF could provide detail information about the surface chemical nature of the treated objects, as well as about their past and present state and it leaded to recommendations for restoration with the appropriate laser cleaning conditions.

Biophotonics in diagnosis and modeling of tissue pathologies

Biophotonics techniques are applied to several fields in medicine and biology. The laser based techniques, such as the laser induced fluorescence (LIF) spectroscopy and the optical coherence tomography (OCT), are of particular importance in dermatology, where the laser radiation could be directly applied to the tissue target (e.g. skin). In addition, OCT resolves architectural tissue properties that might be useful as tumour discrimination parameters for skin as well as for ocular non-invasive visualization. Skin and ocular tissues are complex multilayered and inhomogeneous organs with spatially varying optical properties. This fact complicates the quantitative analysis of the fluorescence and/or light scattering spectra, even from the same tissue sample. To overcome this problem, mathematical simulation is applied for the investigation of the human tissue optical properties, in the visible/infrared range of the spectrum, resulting in a better discrimination of several tissue pathologies. In this work, we present i) a general view on biophotonics applications in diagnosis of human diseases, ii) some specific results on laser spectroscopy techniques, as LIF measurements, applied in arterial and skin pathologies and iii) some experimental and theoretical results on ocular OCT measurements. Regarding the LIF spectroscopy, we examined the autofluorescence properties of several human skin samples, excised from humans undergoing biopsy examination. A nitrogen laser was used as an excitation source, emitting at 337 nm (ultraviolet excitation). Histopathology examination of the samples was also performed, after the laser spectroscopy measurements and the results from the spectroscopic and medical analysis were compared, to differentiate malignancies, e.g. basal cell carcinoma tissue (BCC), from normal skin tissue. Regarding the OCT technique, we correlated human data, obtained from patients undergoing OCT examination, with Monte Carlo simulated cornea and retina tissues for diagnosis of ocular diseases.

Optical spectroscopic studies of animal skin used in modeling of human cutaneous tissue

Optical spectroscopy and in particular laser-induced autofluorescence spectroscopy (LIAFS) and diffuse reflectance spectroscopy (DRS), provide excellent possibilities for real-time, noninvasive diagnosis of different skin tissue pathologies. However, the introduction of optical spectroscopy in routine medical practice demands a statistically important data collection, independent from the laser sources and detectors used. The scientists collect databases either from patients, in vivo, or they study different animal models to obtain objective information for the optical properties of various types of normal and diseased tissue. In the present work, the optical properties (fluorescence and reflectance) of two animal skin models are investigated. The aim of using animal models in optical spectroscopy investigations is to examine the statistics of the light induced effects firstly on animals, before any extrapolation effort to humans. A nitrogen laser (&lgr;=337.1 nm) was used as an excitation source for the autofluorescence measurements, while a tungsten-halogen lamp was used for the reflectance measurements. Samples of chicken and pig skin were measured in vitro and were compared with results obtained from measurements of normal human skin in vivo. The specific features of the measured reflectance and fluorescence spectra are discussed, while the limits of data extrapolation for each skin type are also depicted.