Department of Physics , School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Polytechneioupolis, Heroes of Polytechnion 9, GR 157 80 ZografouCampus, Athens, Greece.
Dr. Eleni Drakaki is a collaborated physics researcher in NTUA. She holds a Degree in Physics, Master of Science degree in Physical Sciences and Technologies and a PhD in interaction of laser radiation into biological tissues and metallic objects at Physics Department from the National Technical University of Athens, Greece. She has been employed as Research Assistant in the National Technical University of Athens, in the Τechnological Educational Institution of Athens and in the National Hellenic Research Foundation (NHRF). She has been involved in R&D projects funded from organizations such as the European Union, the Ministry of Development, the Ministry of Education and others.
She has considerable experience :
A. in the area of laser-tissue interactions. Her research interests in this area include clinical studies preferred including measurements on human subjects in-vivo and tissue samples in-vitro, photodynamic therapy and photodiagnosis, optical imaging and fluorescence / reflectance spectroscopy of tissues and tissue simulators, development of laser optical systems for biomedical purposes, digital processing of biological signals: methods and processing techniques, feature extraction, multispectral classification, radiative transfer and surface fluxes. Her experimental study addresses the theoretical study of ligit propagation through light transport models and measurements of the interaction of laser beam with soft and hard human tissues in the diagnosis of pathologic situations in both the dental as well as in skin tissue.
B. in the laser cleaning on metal works of arts and LIBS, XRF, SEM as analytical techniques for the monitoring of laser cleaning processing. Her research interests in this field include the study of the optimal choice of laser in the process of rescuing metal heritage. She had concentrated her research on a specific field of artworks, the coins, (new, ancient Greek, Roman and Byzantine), on which she investigated the potential of laser cleaning techniques for conservation. The tests were carried out in different wavelengths and different pulse durations of Q-Switched, Long Q-Switched, and Free Running Nd: YAG laser, TEA-CO2 laser, or Free Running and Q-Switched Er: YAG laser, GaAlAs diode and Ti-Sapphire laser, evaluating in each specific case which of the laser systems seem more appropriate.
She has more than 40 publications in scientific journals and conference proceedings
Abstract: Laser cleaning tests were performed on ancient coins, which belong to the collection of the Numismatic Museum of Athens, Greece. Silver and copper alloy coins with various types of surface corrosion and ground deposits were studied, using Q-switched (QS), long pulse (LP) and free-running (FR) Nd:YAG lasers and a range of laser-pulsing parameters on wet surfaces. A comparison among the different laser types was made, cleaning with an optical fibre delivery system and an optical focusing subassembly, or with the help of x-y microadjustable stage. It was discovered that the results of laser cleaning was influenced by the type of corrosion and the corrosion products or the ground deposits on the surface of the coins. The results, evaluated by objective and SEM-EDX observations, indicated that on silver alloy coins, different wavelengths could achieve a successful laser cleaning for several types of corrosion. On the other hand, laser cleaning could result in loss of the original surface in various cases of copper alloy coins, followed by frequent appearance of the oxidation layer underneath and partial removal of corrosion products and ground deposits. The optimum laser cleaning procedure was associated with the different types of coin corrosions. Special emphasis was stressed on the side effects of the procedures and, in particular, on the minimization of any chemical modifications and thermal results induced to the original surface of the coins.
Abstract: Museum curators and archaeologists use analytical science to provide important information on artworks and objects. For example, scientific techniques provide information on artwork elemental composition, origin and authenticity, and corrosion products, while also finding use in the day-to-day conservation of many historical objects in museums and archaeological sites around the world. In this work two special cases are being discussed.
In the first part of our work, physicochemical studies of an icon on a metal substrate were carried out using non-destructive, qualitative analysis of pigments and organic-based binding media, employing various microscopic and analytical techniques, such as Optical Fluorescence Microscopy, XRF, and Gas Chromatography. In the second part of our work, laser cleaning of late Roman coins has been performed using a Q-switched Nd:YAG laser (1064 nm, 6 ns) and a GaAlAs diode laser (780 nm, 90 ps). The corrosion products have been removed, while we observe increased concentrations in Ag, which is the main material of the silver plating found in late Roman coins
Abstract: It is common to modify valuable, sophisticated equipment, originally acquired for other purposes, to adapt it for the needs of educational experiments, with great didactic effectiveness. The present project concerns a setup developed from components of a portable system for energy dispersive x-ray fluorescence spectroscopy (EDXRF). Two educational modules have been developed on the basis of this setup. Module 1 comprises a series of x-ray laboratory exercises investigating basic principles, such as the verification of Moseley's law, Compton's law and the LambertâBeer law. Module 2 concerns the calibration of the XRF with reference materials, aiming to get quantitative measurements of the elemental composition of objects of cultural interest. The application of the calibrated experimental setup is demonstrated with indicative measurements of metal objects and pigments of wall paintings, in order to discuss their spectra, and their qualitative and quantitative analyses. The setup and the applied experiments are designed as an educational package of laboratory exercises on the one hand for students in natural sciences, and on the other for the education of students who will work in the field of cultural heritage, such as conservation science or archaeological science
Abstract: 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
Abstract: The continuous growth of computer and sensor technology allows many researchers to develop simple modifications and/or refinements to standard educational experiments, making them more attractive and comprehensible to students and thus increasing their educational impact. In the framework of this approach, the present study proposes an alternative experimental setup, which allows the confirmation of HagenâPoiseuille's law, governing the flow of real fluids through tubes, a law with numerous important applications in both technology and medicine. In the proposed educational procedure, experimental measurements of fluid outflow are performed with the use of a motion sensor and a suitable computer program, allowing the determination of both the hydrostatic pressure and the flow rate. The dependence of the flow rate on parameters such as viscosity of the fluid, length and radius of the tube and the pressure difference between the ends of the tube are also studied, providing a laboratory activity which is useful and attractive for first year students, especially those of technologically oriented departments
Abstract: Background/purpose: Laser-induced autofluorescence spectroscopy provides excellent possibilities for medical diagnostics of different tissue pathologies including cancer. However, to create the whole picture of pathological changes, investigators collect spectral information from patients in vivo or they study different tumor models to obtain objective information for fluorescent properties of every kind of healthy and diseased tissue. Therefore, it is very important to find the most appropriate, and close to the human skin, animal samples from the fluorescence point of view, which will allow the extrapolation of the animal data to human spectroscopic diagnostics.
Methods: In the present work, we examined the autofluorescence properties of different animal skin tissues, which are considered as the most common skin models. A nitrogen laser was used as an excitation source. Samples of healthy mouse, chicken and pig skin in vivo and/or ex vivo were studied and were compared with results obtained from investigations of healthy human skin in vivo.
Results and conclusion: Specific features of the recorded spectra are discussed and the possible origin of the obtained fluorescence signals is proposed. Quantitative evaluation of data extrapolation for each skin type is also depicted.
Abstract: 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
Abstract: Biomedical laser light dosimetry relies on spatial light distribution measurements in combination with the appropriate laserâtissue interaction model that may be used to determine the tissue optical coefficients and the fluorophore concentration from its fluorescence spectra. Therefore, modelling of light transport in tissue, for optimization of laser dosimetry, requires the development of simple theoretical models and the experimental implementation in tissue-simulating phantoms, with known optical and fluorescence properties.
Low cost phantoms were used, based on agar dissolved in water as the transparent matrix. The latter is loaded with various amounts of Intralipid and fluorophores as light scatterer and absorbers, respectively. The optical properties of these phantoms were measured at two different visible wavelengths.
By comparing the fluorescence emission spectra of the turbid samples containing the same fluorophore in different concentrations, we can calculate the concentration. In addition, the evaluation of the scattering and absorption coefficients allow us to predict the spatial distribution of the light intensity inside and outside of the phantom.
It seems that the Monte Carlo simulation is an effective and relatively simple mathematical approach for tissue optical properties evaluation.
Abstract: Ancient metal objects react with moisture and environmental chemicals to form various corrosion products. Because of the unique character and high value of such objects, any cleaning procedure should guarantee minimum destructiveness. The most common treatment used is mechanical stripping, in which it is difficult to avoid surface damage when employed. Lasers are currently being tested for a wide range of conservation applications. Since they are highly controllable and can be selectively applied, lasers can be used to achieve more effective and safer cleaning of archaeological artifacts and protect their surface details. The basic criterion that motivated us to use lasers to clean Roman coins was the requirement of pulsed emission, in order to minimize heat-induced damages. In fact, the laser interaction with the coins has to be short enough, to produce a fast removal of the encrustation, avoiding heat conduction into the substrate. The cleaning effects of three lasers operating at different wavelengths, namely a TEA CO2 laser emitting at 10.6 m, an Er:YAG laser at 2.94 m, and a 2-Nd:YAG laser at 532 nm have been compared on corroded Romans coins and various atomic and nuclear techniques have also been applied to evaluate the efficiency of the applied procedure.
Abstract: 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.
Abstract: An experimental setup for laser induced breakdown spectroscopy (LIBS) has been developed for
educational purposes, to be used in the physics curriculum of science students and of students who
are specializing in the field of cultural heritage. The setup comprises basically a Q-switched
Nd:YAG laser and a fiber optic spectrometer. All components were already existing equipment at
the physics laboratories at the TEI of Athens, so that they could be assembled in-house to a considerably
economic LIBS setup. The proposed laboratory exercises are focused on one hand on
imparting the knowledge about physical principles and phenomena associated with the creation of
plasma and the radiation processes, while on the other hand, the students will be trained in the operation
and handling the actual analytical process, in terms of specific applications. Various parameters
are examined, concerning the laser-matter interaction and the process issues, such as calibration,
interpretation of spectra and evaluation of results. Exemplary measurements as an autonomous
learning and teaching module were implemented, demonstrating the qualitative and quantitative
analysis of various materials typically associated with cultural heritage objects, such as metal
standards and original objects and replicas of mural paintings.
Notes: Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik) Annual Meeting of the Deutsche Physikalische Gesellschaft and DPG - spring meeting of Deutsche Physikalische Gesellschaft, Fachverband Didaktik der Physik, DD 19: Postersitzung, DD 19.32, Dienstag, 16:00â18:00, Foyer Osteingang 2010
Poster presentation, www.phydid.de/index.php/phydid-b/article/download/198/180
Abstract: 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.
Abstract: 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
Abstract: Laser-induced fluorescence (LIF) spectroscopy has emerged as a potential tool for the detection of cancer in a variety of human tissues and organs. This non-invasive technique has proved to be a valuable tool for the study of the structure and pathology of human skin. The aim of this study was to examine whether the in vitro laser-induced fluorescence spectroscopy, after ultraviolet excitation at a wavelength of 337 nm, could be used to detect basal cell skin carcinoma (BCC) and differentiate it from the normal skin tissue. Spectroscopic measurements were performed on several places on the surface of more than 20 normal and abnormal skin tissue samples. Histopathology examination of these skin samples was also performed and the results from the spectroscopic and medical analysis were compared.
Notes: Poster resentation,
Chania, Crete, 19-21 June 2008
Abstract: The political problems in Late Roman Empire caused signifficant changes in the coin technology. The silver content dropped severely and a new technology was introduced, which was applied in all the mints operating around the Empire. For the production of these coins, copper based quaternary alloys were used and their surface was covered by, a few microns thick, silver amalgam plating layer [1].
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 [2-4]. 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. Previous work showed that the case of corroded silvered copper alloy coins, required different cleaning conditions than other corroded copper coins. From the two laser wavelengths 266 and 532 nm, which were employed, the second harmonic of Nd: YAG seemed to be more controllable and promising [5]. In this paper, additional work was made to those and to other laser wavelengths, in order to minimize the chances for thermal diffusion, during the laser cleaning process, and to limit the laser absorption depth to the thin layer of corrosion near the surface.
The optimisation of laser parameters was achieved through comparative cleaning tests by employing Nd:YAG (1064 nm, 532 nm and 266 nm) laser systems, using range of laser pulsing parameters on dry, wet and submerged surfaces, in order to enhance the efficiency and limit the penetration of the laser beam. The application of simultaneous microscopic monitoring during the experimental procedure helped in the successful cleaning of the coin surface. Optical monitoring was shown to be an affordable possibility for on-line control of the cleaning progress.
The laser-treated surfaces were characterised using optical microscopy, scanning electron microscopy-SEM, Successful oxide removal was achieved above certain thresholds that defined the lower end of the process operating window for single-pulse operation.
Notes: International Conference on Lasers in the Conservation of Artworks, CSIC, (LACONA VII, Madrid, Spain, 17-21 September 2007),
Abstract: 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.
Abstract: The use of laser technology in the cleaning of artworks has a wide range of applications, including the cleaning of 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 copper alloy coins. Previous work showed that the case of corroded silvered copper alloy coins, required different cleaning conditions than other corroded copper coins. In this paper, comparative cleaning tests by means of a Nd: YAG (1064 nm, 532 nm and 266 nm) were performed in order to minimize the thermal effects and to minimize the laser absorption depth to the thin layer of corrosion near the surface. The laser-treated surfaces were characterised using Optical Microscopy, and Scanning Electron Microscopy-SEM.
Abstract: 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
Abstract: 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 (λ=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.
Abstract: Directional dependence of reflected laser light and of the laser induced fluorescence signals performed both on the intact hard dental tissues, such as enamel, dentine, cementum and on the tissues pathologically affected by caries (superficial, intermediate and deep). The laser induced fluorescence spectra were collected at different angles of observation and were correlated with the different scattering and reflectance properties of the hard dental samples.
Abstract: The autofluorescence spectra of hard dental tissues, both in normal and pathological areas were investigated in this study. The measurements were performed both on the intact hard tissues of the examined teeth, such as enamel, dentine, cementum, and root canal, and on the tissues pathologically affected by caries (superficial, intermediate, and deep). Various laser wavelengths (337 nm, 488 nm, and 514 nm) were used to irradiate the dental surfaces and a computer-controlled spectrograph captured the fluorescent spectra. The emission signals were stored, measured, analyzed and quantified in terms of wavelength distribution and the relative photon intensity. Results indicated that the fluorescent spectra from healthy enamel, dentine, and cementum were almost identical in form, depending on the excitation wavelength. The intact and affected hard tissues were greatly different in the integral fluorescent intensity. Healthy areas were found to produce the most pronounced fluorescent intensity, whereas the carious regions produced the weaker fluorescent intensity. Independently of the laser excitation wavelength, dentin regions were found to produce the most pronounced fluorescent intensity than any other dental component. The fluorescence signal of carious affected dental structure revealed a reed shifted spectral curve, more pronounced after 488 nm excitation. There was a pronounced red shift for deep caries (crown -- root caries), after ultraviolet laser excitation. Excitation with visible wavelengths did not produce such differences between intact and cervical, deep carious affected tissue. Using a monochromatic light source without any light output at the wavelengths of fluorescence, e.g. a laser with the appropriate filters, the difference in fluorescence between intact and carious enamel was generally easy to observe. Finally, we found that the blue line of an argon ion laser is preferable for superficial caries detection, while the ultraviolet emitting nitrogen laser induces better discrimination in deep caries diagnosis.
Abstract: Measurements of the tissue optical parameters and the theoretical modeling of the light propagation in biological tissues is very important for real time laser treatment dosimetry and non- invasive diagnosis. An integrating sphere based technique was used to determine the tissue optical properties. Soft tissue - like phantoms were irradiated with visible lasers and the optical parameters were compared with results calculated from the Beer's law model of light propagation and the Kubelka - Munk simulation.
Abstract: The determination of the tissue optical parameters and the study of light propagation in multicomponent tissues is an important tool for real time laser treatment dosimetry and non-invasive laser diagnostics. The purpose of this work was the evaluation of a small portable spectrophotometry system, for non-invasive laser dosimetry, as compared to a more sophisticated, tabletop, spectroscopic system. The small portable system consists of an optical spectrum analyzer, an oscilloscope and appropriate fibers, while the complete laser spectroscopy system consists of a spectrograph, an integrating sphere and a photodiode array as a detector element. The determination of the optical properties of soft and hard biological tissues -- in vitro -- was performed with both systems. Spectral information obtained, the appropriate mathematical modeling and the comparative results are discussed.
Abstract: The determination of the tissue optical parameters and the light propagation in multicomponent tissues is an important tool for real-time laser treatment dosimetry (selective laser ablation, PDT) and non-invasive laser diagnostics (laser induced fluorescence spectroscopy, optical tomography). The aim of this work is the experimental study of the optical characteristics of laser light propagation in tissue simulators, employing spectroscopic techniques, in order to quantify the concentration of tissue chromophores. Total and diffuse reflectance/transmittance measurements of tissue phantoms were performed at visible wavelengths and the calculated optical properties were correlated to the concentration of the absorbing species in a multicomponent environment. The experimental results demonstrated the ability of the laser induced spectroscopic techniques for quantitative estimation of tissue chromophores concentration.
Abstract: The aim of this work is the study of the absorption and scattering characteristics of laser light propagation in hard tissues and in soft tissue simulators in vitro, employing the integrating sphere technique. Soft tissue - like phantoms have been developed to simulate the distribution of visible light in tissue. Recordings of the diffuse reflectance and the total and diffuse transmittance of the biological samples were performed at 543 nm and 633 nm, using He-Ne lasers. The experimental results were compared to results from mathematical simulation of light propagation in tissue, using the Kubelka-Munk theory.
Abstract: Experiments on atherosclerotic plaque diagnosis were carried out using laser induced fluorescence (LIF) spectroscopy on carotid plaque specimens. The excitation laser was a nitrogen laser, emitting pulses at a wavelength of 337 nm. Over 10 samples were examined in vitro and several spectra were obtained from each sample. Results were compared with conventional clinical techniques, such as histopathological diagnosis, which showed three areas of different composition on the pathological samples: fibrous tissue, lipid constituents and calcified plaque. An effort was made to distinguish the composition of the sample from the obtained spectra. Also, the results were compared with our previous work using longer excitation wavelengths. Spectral morphology of UV excited fluorescence reveals multi-peaks lineshapes, as a result of the superposition of different tissue chromophore signals. However, there was no observed specific wavelength where spectra corresponding to fibrous tissue, calcified tissue and lipid constituents have peaks.
Abstract: Many factors are involved in a relatively new tumor treatment modality, the photodynamic therapy (PDT). Among them the most important are the laser parameters (wavelength, energy fluence), the photosensitizer cytotoxic and optical properties, the delay between drug injection and PDT and the effective dosimetry of both light and drug distribution in the treatment target. In this work, we compare the effectiveness of two methods of predicting the concentration of the photosensitizer m-THPC in tissue simulators. In the first method, a conventional double beam spectrophotometer was used to measure the absorption in UV- VIS of the soft tissue simulators, prepared with agar gel with different concentration of m-THPC. In the second method, the laser induced fluorescence spectra of these samples were recorded and an effort was made to determine from these the optical properties of the samples, in order to calculate the required drug concentration in vitro. The experimental results are discussed in conjunction with the appropriate theoretical models
Abstract: Various biomedical applications of laser light necessitate the optimum control of the light propagation in tissue. The aim of this work is the theoretical and the experimental study of the absorption and scattering characteristics of laser light propagation in tissues in vitro, employing the integrating sphere technique. The integrating sphere approach allows the determination of the optical properties at one single wavelength, by using monochromatic light sources in continuous wave and/or pulsed wave mode.
Total and diffuse reflectance spectra of hard and soft opaque tissues were measured at 543 nm and 633 nm (continuous wave mode). Additionally, laser induced fluorescence spectra were obtained at 337 nm (pulsed wave mode), as an alternative of the reflectance/transmittance measurements. Excitation fluorescence spectra of biological tissues reflect the electronic ground-state configurations of the absorbing molecule and thus can be related to the distribution of the absorbing species in a multicomponent molecular environment. The scattered light from the samples was measured and recorded with a spectrograph, equipped with a photodiode array. The experimental results were compared with results from mathematical simulation of light propagation in dense tissue.
Abstract: It is common to use valuable, sophisticated equipment, that has been acquired for other use, to be modified, adapted and developed for the needs of additional educational experiments, with greater didactic effectuality. We have developed a system, composed of parts from a portable system for XRF spectroscopy, aiming at: i) the formation of familiar and conventional laboratory exercises, like the verification of Moseley's law, Compton's law and Lambert-Beer's law; ii) the calibration with reference materials of the XRF experimental system, to be applied for accurate measurements of the elemental composition of objects of cultural interest. After the calibration of the experimental setup, indicative measurements of metal objects are shown, in order to discuss their spectra and their qualitative and quantitative analysis. The system and the applied experiments are designed as an educational package of laboratory exercises for students in physical sciences and especially adapted for the education of students who will work with Cultural Heritage, such as conservation scientists and archaeometrists.
Abstract: The continuous growth of computer and sensor technology allows many researchers to develop simple modifications and/or refinements to standard educational experiments, making them more attractive and comprehensible to students and thus increasing their educational impact. In the framework of this approach, the present study proposes an alternative experimental setup, which allows the confirmation of HagenâPoiseuille's law, governing the flow of real fluids through tubes, a law with numerous important applications in both technology and medicine. In the proposed educational procedure, experimental measurements of fluid outflow are performed with the use of a motion sensor and a suitable computer program, allowing the determination of both the hydrostatic pressure and the flow rate. The dependence of the flow rate on parameters such as viscosity of the fluid, length and radius of the tube and the pressure difference between the ends of the tube are also studied, providing a laboratory activity which is useful and attractive for first year students, especially those of technologically oriented departments
Notes: 71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik) Annual Meeting of the Deutsche Physikalische Gesellschaft and DPG - spring meeting of the Division Condensed Matter-Didaktik der Physik-Poster, Frühjahrstagung Regensburg 2007 (March 27 â 29, 2007) ΤÏμο ÏÏακÏικÏν ÏλÏν ÏÏν εÏγαÏιÏν Ïε CD,
Abstract: This poster presents the scientific research carried out on two outdoor bronze monuments, which were cast from the same model and foundry, but for the past 100 years are exposed in two very different environments in Greece. One of them is located in Athens, erected in 1904 in one of the busiest and polluted streets in the city. In the other case, it was erected in 1900 in Nafplio, a small city (150 km from Athens) only 100 m from the seaside. The aim of the study was to compare between the corrosion types found on the two monuments and correlate the observed differences to the specific exposure environments
Notes: poster ÏÏο 7th EC conference Safeguarded Cultural Heritage - Understanding & Viability for the Enlarged Europe. Prague May 31st - June 3rd, 2006.
Notes: 6th international conference of Lasers in the conservation of Artworksâ LACONA VI 21/9/2005-25/9/2005, Academy of Fine Arts, Vienna, Austria. Book of Abstracts
Abstract: In this work we study the autofluorescence spectra of hard dental tissues, both in normal and pathology areas. The measurements were performed both on the intact hard tissues of a tooth, such as enamel, dentine, cementum, and root canal, and on the tissues pathologically affected by caries (superficial, intermediate, and deep).
We used various laser wavelengths (UV, VIS) to irradiate the dental surfaces and a computer-controlled spectrograph captured the fluorescent signals. The fluorescence spectra were stored, measured, analyzed and quantified in terms of wavelength distribution and the relative photon intensity. Additionally directional dependence of reflected laser light and of the laser induced fluorescence signals performed both on the intact and pathological hard dental tissues. The laser induced fluorescence spectra were collected at different angles of observation and were correlated with the different scattering and reflectance properties of the samples
Abstract: Ancient metal objects react with moisture and environmental chemicals to form various corrosion products. Because of the unique character and high value of such objects, any cleaning procedure should guarantee minimum destructiveness. The most common treatment used is mechanical stripping, in which it is difficult to avoid surface damage when employed. Lasers are currently being tested for a wide range of conservation applications. Since they are highly controllable and can be selectively applied, lasers can be used to achieve more effective and safer cleaning of archaeological artifacts and protect their surface details. The basic criterion thatmotivated us to use lasers to clean Roman coins was the requirement of pulsed emission, in order to minimize heat-induced damages. In fact, the laser interaction with the coins has to be short enough, to produce a fast removal of the encrustation, avoiding heat conduction into the substrate. The cleaning effects of three lasers operating at different wavelengths, namely a TEA CO2 laser emitting at 10.6 μm, an Er : YAG laser at 2.94 μm, and a 2Ï-Nd : YAG laser at 532 nm have been compared on corroded Romans coins and various atomic and nuclear techniques have also been applied to evaluate the efficiency of the applied procedure.
Notes: The 7th International Conference on Laser Ablation âCOLAâ03â Topic: Laser materials processing: Laser Cleaning. (October 5-10, 2003, Crete , Greece)
WePS32
Abstract: Clinical reports signal a pronounced effect of low power laser irradiation ( with 632.8 nm He-Ne laser
as well with red and infrared laser diodes) used additionally or alternatively to the current techniques in
curing local infections, inflammations and in microsurgery . They inform about substantially reduced bleeding
and cicatrisation times and other parameters of local healing.
Platelets play a key role in the physiological haemostatic process and in the pathogenesis of
thrombosis and cardiovascular disorders. Blood platelets form an interesting biological system whose
morphology is sensitive to its environment and any change in this morphology may be critical to the
physiology of living organisms. Blood platelets as unucleated cells offer an attractive model system for
studying some aspects of laser action on the cell. They are extremely sensitive cells and upon different
stimuli can undergo rapid activation. However, there is a relative lack of information concerning the
response of blood platelets to laser radiation, used for both diagnostic and therapeutic biomedical
applications. It was reported that low power laser affects the rheological properties of blood ; the reports on
the biological effects on cells are controversial, depending on irradiated cells, experimental condition and the
available wavelength and dose of laser irradiation..............
Abstract: The study of the light distribution in tissues is important for many biomedical laser applications, as dosimetry in photodynamic therapy, clinical diagnosis of atherosclerosis and malignancy, selective laser ablation, port-wine stains therapy, in order to control and optimize the treatment efficacy. Light distribution in tissue is governed by both the laser beam properties (e.g. wavelength, beam geometry, cw or pulsed radiation) and the optical parameters of the tissue (e.g. absorption coefficient, scattering coefficient, scattering anisotropy factor, fluorescence quantum yield).
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The optical characteristics of the tissues can be simulated in a medium that has the appropriate absorption and scattering coefficients. Therefore, tissue phantoms with simple geometry and artificial microscopic properties, as compared to biological tissue, can be used to mimic light transport in tissue, at least in the diffusion domain.
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The aim of this work is the experimental study of the absorption, scattering and fluorescence characteristics of light propagation in tissue simulators, in vitro, employing simple spectroscopic techniques. The absorption, scattering and fluorescence signals are correlated to the concentration of the main chromophores of the phantom, in order to develop appropriate algorithms for PDT dosimetry and other biomedical diagnostic and surgical modalities. Â
Notes: International Autumn School New Trends in Biophysical Methods Related to Biomedical Research, Sept. 24-29, 2001, Sovata, Rumania organized with the support of ICR
http://www.biophysicsnet.ro/main.php?id_pag=6&id_eve=0
Abstract: The present paper describes the characterization of an industrial production of a large number of pieces of UV optical filters proposed for the AUGER Fluorescence Detector. The filter pieces have been tested and they have nearly 92 % peak transmittance, between 320-400 nm, for an incidence angle range from 0 to 30 degrees, and typically 0.5 %, in average, in the range 400-700 nm, in the same range of angles. The filter pieces were also characterized in terms of the integrated signal yield in the air fluorescence radiation and also in the typical night sky background radiation (optical noise). The experimental results of the overall performance of these filters lead to the conclusion that they achieve an increased signal-to-noise ratio in comparison to that of absorption filters commercially available. We explain that the interference filters provide more flexibility and thus can be adjusted more easily to the needs of FD telescopes.
Notes: Proceedings of the 27th International Cosmic Ray Conference. 07-15 August, 2001. Hamburg, Germany. Under the auspices of the International Union of Pure and Applied Physics (IUPAP)., p.667
Abstract: The present work describes the performance of a production of optical filter pieces produced by a commercial firm, OCJ. The experimental measurements were conducted in laboratory conditions. Some details are given for the description of the light source which emulate the atmospheric fluorescence signal. The filters have been tested in comparison with a filter piece of MUG-6 with 50mm \Theta 50mm dimensions. A method of mounting a number of 49 hexagons with distance between two sides of 170mm is described. The work towards producing a structure to test the mechanics and optics of mounting the filter array is presented. The aim is to minimize the obscuration to acceptable levels, and minimize effects on imaging of fluorescence signals, while ensuring mechanical stability. The question of diffuse scattering of optical components in the diaphragm is discussed. The expected level of diffuse transmittance is low, around 4-8 % on the average in the range 310-400 nm, and so the measurement methodology must be quite sophisticated in order that the results have errors, let us say, 10 % on the level of the diffuse transmittance, to be credible. We, thus present two experimental methods for measuring the diffuse transmittance and the results quoted are quite preliminary. Further results of some optical design of multilayer filters on absorptive substrate which show some improvement in transmittance in the Nitrogen fluorescence wavelength range. They can be made by a relative small number of dielectric layers leading to a possibly reduced production cost per unit area. 1 Introduction We have performed the following tests for evaluation of the optical filters: We have developed setups with laboratory light sources for evaluating the diffuse and specular transmittance of filters, large or small area. Only for one such light source, i.e. air-fluorescence lamp, we shall present some data at this meeting
Abstract: Diagnostic biomedical laser applications, as well as photodynamic therapeutic (PDT) modalities, require to exploit the full potential of endogenous or exogenous tissue chromophores for optimization of light treatment procedures. Particularly, in PDT it is very important for clinical applications to measure the tumour localized photosensitizer concentration just before the laser treatment, in order to change the light dose accordingly. Light distribution in tissue is governed by both the laser beam properties (e.g. wavelength, beam geometry, c.w. or pulsed radiation) and the optical parameters of the tissue (e.g. absorption coefficient, scattering coefficient, scattering anisotropy factor, fluorescence quantum yield).
The aim of this work is the experimental study of the laser induced fluorescence signals in relation with the concentration of the main chromophore of tissue simulators. The experimental results demonstrated that the laser induced fluorescence spectra of the tissue simulator/m-THPC (a second-generation photosensitizer) show a very low fluorescence intensity and by subtracting the background noise level we can calculate the fluorescence signal of the pure photosensitizer. It seems, therefore, that laser induced fluorescence spectroscopy is a suitable method for monitoring the photosensitizer distribution in vivo, by measuring the fluorescence intensity ratio of tumours and surrounding normal tissue at different times after injection.
Notes: 12-15 September 1999, Paris, France (MAFS6).
Website: http://www.iupac.org/publications/ci/1999/january/confmafs6.html
Abstract: Many factors involved in a relative new tumor treatment modality, the PhotoDynamic Therapy (PDT). Among which the most important are the laser parameters (wavelength, energy fluence, pulse width), the photosensitizer cytotoxic and optical properties, the delay between drug injection â PDT and the effective dosimetry of both light and drug distribution in treatment target. For example, an insufficient photosensitizer concentration in malignant tissue can lead incomplete treatment of tumour resulting in recurrence, or may cause significant damage to the healthy surroundings during the photodynamic treatment of the tumor.
In this work, we compare the effectiveness of two methods to predict the concentration of the photosensitizer m-THPC in tissue simulators. In the first method, a conventional double beam spectrophotometer was used to measure the absorption in UV-VIS of he soft tissue simulators, made by Agar gel with different concentration of m-THPC. In the second method, the laser induced fluorescence spectra of these samples were recorded and an effort was made to determine from these signals the optical properties of the samples, in order to calculate accordingly the drug concentration in vitro. The experimental results are discussed in conjunction with the appropriate theoretical models.
Notes: CLEO-Europe Summer School on Advances in Lasers and Applications
Advances in Lasers and Applications edited by Finlayson DM, Sinclair BD
http://www.sussp.ac.uk/
Abstract: 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.
Abstract: The use of laser technology in the cleaning of artworks has a wide range of applications, including the cleaning of 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 copper alloy coins. Previous work showed that the case of corroded silvered copper alloy coins, required different cleaning conditions than other corroded copper coins. In this paper, comparative cleaning tests by means of a Nd: YAG (1064 nm, 532 nm and 266 nm) were performed in order to minimize the thermal effects and to minimize the laser absorption depth to the thin layer of corrosion near the surface. The laser-treated surfaces were characterised using Optical Microscopy, and Scanning Electron Microscopy-SEM.
Abstract: In the biomedical non-invasive diagnostic/therapeutic research, light dosimetry relies on spatial light distribution measurements in combination with the appropriate laser-tissue interaction model that may be used to determine the tissue optical coefficients (e.g. refractive index, scattering coefficient, absorption coefficient and anisotropy).
Laser induced fluorescence intensity measurements are widely used mainly for diagnostic purposes. Modeling of light transport in tissue for optimization of laser dosimetry requires the development of simple theoretical models and the experimental implementation in tissue-simulating phantoms.
In this work, an empirical analytical technique is developed to predict the fluorophore concentration from laser induced fluorescence emission spectra of homogeneous turbid samples with known optical and fluorescence properties, similar to the ones of human tissue.
Therefore, low cost phantoms are used, based on Agarose dissolved in water as the transparent matrix. The latter is loaded with various amounts of Intralipid and fluorophores. The Intralipid particles are responsible for the light scattering, whereas the fluorophores are the absorbers. The optical properties of these phantoms are measured by using the added absorber and the scatterer technique.
By comparing the fluorescence emission spectra of the turbid samples containing the same fluorophore, we can derive a quantitative evaluation of the effects of scattering and absorption coefficient on fluorescence.
Abstract: Measurements of the tissue optical parameters and the theoretical modeling of the light propagation in biological tissues is very important for real time laser treatment dosimetry and non- invasive diagnosis. An integrating sphere based technique was used to determine the tissue optical properties. Soft tissue - like phantoms were irradiated with visible lasers and the optical parameters were compared with results calculated from the Beer's law model of light propagation and the Kubelka - Munk simulation.
Abstract: The aim of this work is the study of the absorption and scattering characteristics of laser light propagation in hard tissues and in soft tissue simulators in vitro, employing the integrating sphere technique. Soft tissue - like phantoms have been developed to simulate the distribution of visible light in tissue. Recordings of the diffuse reflectance and the total and diffuse transmittance of the biological samples were performed at 543 nm and 633 nm, using He-Ne lasers. The experimental results were compared to results from mathematical simulation of light propagation in tissue, using the Kubelka-Munk theory.
Abstract: The determination of the tissue optical parameters and the light propagation in multicomponent tissues is an important tool for real-time laser treatment dosimetry (selective laser ablation, PDT) and non-invasive laser diagnostics (laser induced fluorescence spectroscopy, optical tomography). The aim of this work is the experimental study of the optical characteristics of laser light propagation in tissue simulators, employing spectroscopic techniques, in order to quantify the concentration of tissue chromophores. Total and diffuse reflectance/transmittance measurements of tissue phantoms were performed at visible wavelengths and the calculated optical properties were correlated to the concentration of the absorbing species in a multicomponent environment. The experimental results demonstrated the ability of the laser induced spectroscopic techniques for quantitative estimation of tissue chromophores concentration
Abstract: Various biomedical applications of laser light necessitate the optimum control of the light propagation in tissue. The aim of this work is the theoretical and the experimental study of the absorption and scattering characteristics of laser light propagation in tissues in vitro, employing the integrating sphere technique. The integrating sphere approach allows the determination of the optical properties at one single wavelength, by using monochromatic light sources in continuous wave and/or pulsed wave mode.
Total and diffuse reflectance spectra of hard and soft opaque tissues were measured at 543 nm and 633 nm (continuous wave mode). Additionally, laser induced fluorescence spectra were obtained at 337 nm (pulsed wave mode), as an alternative of the reflectance/transmittance measurements. Excitation fluorescence spectra of biological tissues reflect the electronic ground-state configurations of the absorbing molecule and thus can be related to the distribution of the absorbing species in a multicomponent molecular environment. The scattered light from the samples was measured and recorded with a spectrograph, equipped with a photodiode array. The experimental results were compared with results from mathematical simulation of light propagation in dense tissue.
Abstract: In this work we present a technique for examining human skin, based on the in vivo measurement of
diffuse reflectance spectra in the visible and near-infrared ranges of the electromagnetic spectrum for
non-invasive characterisation of haemoglobin oxygenation and pigmentation in skin. Spectra were
measured by means of a fiber optic probe, and they were analyzed using an analytical model, based on
the KubelkaâMunk theory of scattering and absorption within inhomogeneous materials. To evaluate
the utility of the model, skin sites with variable melanin content were studied on individuals with
different skin types or with pathological skin conditions. The results of the analysis indicated that it is
possible to obtain quantitative information about main skin pigments, as well as basic information
regarding the scattering properties of the skin. In addition to quantification of haemoglobin and
melanin, qualitative information on the redox state of the blood may also be obtained. The proposed
analytical model could be a helpful tool to monitor and evaluate the variations in the biological skin
tissue data and its medical conditions.
Abstract: The spectroscopic method of diffuse reflectance in the VIS-NIR spectral range is offered as a method for the examination in vivo of human tissue, like the skin tissue, for collection of a variety of information related with the tissueâs physiology and operation.
In this work, preliminary and preview measurements are presented with the use of the spectroscopic method of diffuse reflectance. Those measurements were done, in order to study the potentialities and the capabilities of possible applications, with the existed infrastructure and laboratory equipment. These applications include the identification of skin tissue, the objective definition of the skin color type, as well as the estimation of the ability to extract valuable information from the measured spectra, as a consequence to use the method of diffuse reflectance on probable verification and premature diagnosis of skin diseases, e.t.c.
