We study the effect of laser radiation on initially low scattering media such as egg white and crystalline substance. These media become highly scattering under laser irradiation. We perform and discuss three kinds of experiments, which elucidate the time dynamics of scattering of probe radiation. In the experiment of the first kind we investigate the pure photothermal denaturation of tissues under the effect of a Nd:YAG laser at a wavelength of 1440 nm (absorption coefficient in water is 26 cm^-1). The theoretical model is derived which enables us to estimate the temperature rise involved. It also allow us to estimate the corresponding kinetics parameters of photodenaturation and characteristics of probe light scattering. In the experiment of the second kind we perform multiple pulse irradiation of tissues by UV harmonics (the fourth and the fifth) of a Nd:YAP laser with the aim to determine the characteristics of pure photochemical modification of materials. In these experiments the fluences were small enough to prevent heating of the materials. The results of the above experiments both of the first and the second kind allow us to estimate the relative contributions of photochemical modification of a tissue and photothermal protein denaturation within the experiments of the third kind, in which we use the mentioned above UV solid state laser harmonics at fluences high enough to produce heating of the materials.

With a Q-switched Nd:YAG laser (the fundamental band and its harmonics), ablation characteristics have been investigated in vitro for porcine myocardium tissue. At a constant laser intensity of approximately 2.0 GW/cm², the laser pulses irradiated the tissue and the depth of the ablation hole formed was measured. After the laser irradiation, the tissue was histologically analyzed with an optical microscope and a polarization optical microscope to evaluate the laser-induced damage in the tissue. It was found that the ablation rate for a 1064-nm laser irradiation was comparably high to that for a 355-nm laser irradiation, and the ablation efficiency was lower for a 266-nm laser irradiation than for a 355-nm laser irradiation. During the ablation, strong plasma formation was observed for 266 nm and 1064 nm, while the laser-induced optical emission was dominated by fluorescence for 355 nm. The histology showed that the thermal damage thickness decreased with decreasing the wavelength for 266, 355, and 532 nm, but for 1064 nm thermal damage was very limited although a certain extent of mechanical damage was observed. Based on these experimental results, the ablation mechanism for each laser wavelength and the optimum laser wavelength for the TMLR (transmyocardial laser revascularization) are discussed.

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated using the egg white model. Dynamics of photothermal denaturation during CO₂ laser irradiation was observed by simultaneously controlling surface temperature and monitoring HeNe laser transmission of egg white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. A first order rate process was observed. Our experiments demonstrated that thermal feedback can effectively control/limit photothermal damage.

For hair removal commonly lasers are used with wavelengths being selectively absorbed by melanin .As a consequence, laser radiation leads to an increase of the temperature not only in melanin containing structures of the hair but also in the epidermis. Therefore, we simulated and studied the laser induced temperature development in tissue for various laser wavelengths and various pulse profiles. Modifying the beam parameters can improve the selectivity of the method. Monte- Carlo-Simulations were used to calculate light absorption in dermal structures, considering the tissue specific optical properties. The thermal diffusion in tissue was calculated by a finite difference method. The biological reaction due to the temperature rise was determined by an Arrhenius formalism and depends on temperature and time of laser-tissue interaction. The simulation program allows to calculate the temperature distribution and thermal damage for various temporal pulse profiles, fluence rates and irradiation geometries. Superficial cooling has an important influence and has been considered in the calculations. The results of our simulations for various laser types show differences in the thermal reaction which can be used to optimize the treatment modalities. The potential and limits of laser epilation can be estimated from these results. For example, a series of laser pulses has some advantages compared to a longer single pulse.

In this work, the localization of the ciliary body region of porcine eyes with laser optoacoustics was realized. The principle of laser optoacoustics combines the advantages of ultrasound and optical tomography. The absorption of short laser pulses in the near infrared generates thermoelastic stress waves in the ciliary muscle and the underlying pigmented epithelial layers. These stress transients were detected at the surface of the sclera with piezoelectric transducers in order to analyze the structure. The optoacoustical measurements of the ciliary body region at different positions from the corneoscleral limbus were composed to a grayscale image, which could be qualitatively compared to histological sections of this region. In these images the pigmented layers can be localized. The influence of the detectional wavelength on the optoacoustical signal in the NIR between 750 and 1052 nm was investigated. Furthermore, changes in the optoacoustic signal due to coagulation with a diode laser using typical therapeutical parameters could be observed.

Using short 300 ns pulses of a Q-switch CO₂ laser at the wavelength of maximal hard tissue absorption (9.6 micrometer) we achieve charring-free ablation of bone tissue. An air-water spray prevents tissue parching and helps to avoid excessive rest-heat accumulation. The observed thermally altered layer at the cut surface in a cortical bone is of only 2 - 6 micrometer thickness. A long enough irradiation results in a progressively narrowing to the bottom wedge-shaped cut profile and in a drop of the ablation rate as compared to its initial value. The main reason for this is most likely an enhancement of a heat dispersion and growing light absorption by ablation products. An enlargement of the cut width helps to avoid these negative phenomena. Using this technique we overcome restriction on the cut depth and reduce noticeably the cut time. With 66 W of average power from the Q-switch CO₂ laser we need 1/2 min to produce a 6-mm deep and 10-mm long in vitro incision in a hard cortical bone (young bull femur). That time increases to 2 in for 10-mm depth.

In this work the dependence of the threshold energy and pulse duration for photodisruption was studied between 100 and 1500 femtoseconds using an erbium fiber laser system with subsequent chirped pulse amplification in a titanium-sapphire system. Cutting effects were analyzed in animal specimens like rabbit cornea and porcine eye globes. To perform intrastromal cuts, the laser beam was guided through a computer controlled delivery system. The treated tissue was analyzed by histological sections and by means of light and electron microscopy. Pressure transients were measured at the endothelium during the cutting procedure. Bubble formation and dynamics were studied using flash photography. The resulting gas bubbles were analyzed to their content, and photodissociation could be noticed. As a result of these studies a set of optimized parameters for pulse duration, scanning algorithm, pulse energy and the focusing and beam delivery system could be found. The thermal damage zone in the irradiated tissue was found to be smaller than 1 micrometer and maximum pressure transients at the endothelium could be determined to be in the range of some hundred millibars. Moreover, performing of intrastromal cuts and creation of a lenticule for achieving a refractive effect in the eye was demonstrated. The investigations show, that fs-pulses are a very precise tool for refractive surgery.

Under pulsed nanosecond laser irradiation of type I pure collagen over the 760 - 1070 nm spectral range, optical up- conversion of the incident radiation is observed. More specifically irradiation of collagen at 1064, 901, 892, 828, 785 and 766 nm produces monochromatic second harmonic signals at half the original wavelengths i.e. 532, 451, 446, 414, 393 and 383 nm respectively. The dependence of the second harmonic signal on the excitation intensity was found to be quadratic [log(I₅₃₂) equals 1.92*log(I₁₀₆₄]. A weaker third harmonic signal was also observed from collagen at 355 nm when irradiated by 1064 nm nanosecond pulses. This signal was found to bear a near cubic dependence upon the irradiation intensity ]log(I₃₅₆) equals 2.53*log(I₁₀₆₄)]. The polar distribution of the second harmonic radiation was recorded for both pure fibrous collagen as well a for collagen diluted in acetic acid and forming a semitransparent dry film. In the latter case, significant optical behavior was demonstrated, potentially important for further studies of these nonlinear phenomena and for novel applications.

Today most surgical treatment of spinal deformations is concentrated on invasive mechanical techniques with long operation times and major effects on the patient's mobility. The proposed minimally invasive technique using laser light for tissue ablation offers a possibility of gentle scoliosis treatment. It is thought that an early removal of the epiphysial growth zone on the convex side over several vertebrae results in a straightening of the spine. In a first evaluation, four different laser systems including argon ion, Nd:YAG (Q-switched), Nd:YAG (cw), and Ho:YAG laser were compared with respect to thermal damage to adjacent tissue, ablation rates, efficiency and laser handling. For in-vivo investigation, fresh lamb spine was used. Comparison showed that the Ho:YAG laser is the most appropriate laser for the given goal, providing efficient photoablation with moderate thermal effects on the adjacent tissue. In a second step the proposed minimally invasive operation technique was performed in in-vivo experiments on young foxhounds using 3D- thoracoscopic operation techniques. During these operations temperature mapping was done using fiber-optic fluorescent probes. After 12 months of normal growth the animals were sacrificed and x-ray as well as MRI was performed on the spine. First results show a positive effect of scoliotic growth in two cases. Being able to produce a scoliosis by hemiepiphysiodesis on the vertebra, It is thought that this technique is successful for a straightening of the spine on patients with scoliosis.

The root end cut, also called apicoectomy, consists on the surgical removal of the root's end, as one of the last alternatives for teeth preservation. This procedure may be done with conventional diamond burs, as well as Er:YAG laser only, or in association with Nd:YAG laser. In this paper, the quality of the root end cut for the different mentioned procedures, was compared for a better analysis of these techniques, regarding surface finishing. The Er:YAG laser dosimetry applied during the experiment was of 400 mJ/10 Hz, using a laser beam with a 0.8 mm diameter. The Nd:YAG laser was irradiated at 1.5 W/10 Hz, being the samples submitted to a scanning electron microscope. On the Er:YAG laser irradiated samples, there was absence of smear layer, as well as the presence of some open dentinal tubules, presenting the surface a smooth texture. On the roots cut with the Er:YAG laser, in association with the Nd:YAG laser, below the ablative regime, there was the presence of a melted dentin surface, with an appearance which suggests a non-crystalline structure, closing the tubules. Regarding the conventional apicoectomy, the samples presented a plain surface, with the dentinal tubules being closed by the smear layer.

Laser-induced thermotherapy (LITT) is a so called in-situ- ablation technique which is used for the treatment of liver tumors. Coagulation necrosis is induced by transmitting the laser irradiation via quartz fibers directly into the tumor tissue. LITT represents similarly to surgical liver resection a local treatment form for liver metastases. The Nd-YAG laser (1064 nm) was used. The application system was placed percutaneously under open MRI control. On-line monitoring was done with MRI for evaluation of the postoperative follow-up we performed MRI-controls every 3 months. A total of 20 patients were treated. Due to the irradiation plan performed preoperatively, the treated tumors could be completely ablated by hyperthermia in all procedures. Complications were pleural effusion in 7 patients and a bile fistula and subcapsulary liver hematoma in one patient each. Local control of tumor growth can be achieved in tumors having undergone complete hyperthermic ablation. An assessment of the method regarding a prognostic benefit is not yet possible due to the short follow-up period and the small patient population.

Purpose: The aim of this study was to determine the energy (J/mm³ tumor volume) and temperature required for a complete in-situ-ablation of experimental liver tumors. Methods: LITT was performed in VX-2 tumor-bearing rabbits using Nd-YAG-Laser (1064 nm) with a diffuser-tip applicator and a temperature feedback-system. The animals were randomized into 4 groups (n equals 20) that differed in the target temperature at the tumor border [45 degrees Celsius, 50 degrees Celsius, 55 degrees Celsius and 60 degrees Celsius]. Histological examination was done at 0 h, 24 h, 96 h and 14 days after LITT. Results: The pretreatment tumor volume of 2191 +/- 61 mm³ was the same for all groups (p > 0.05). Energy and temperature required and the rate of incomplete tumor-ablation (recurrences) are listed below (* equals p < 0.05, Kruskal-Wallis test. Conclusions: (1) To achieve complete in-situ-ablation under the given conditions, it is necessary to apply laser-energy of 3 J/mm³ tumor volume. (2) A minimum temperature of 60 degrees Celsius on the tumor border presumed an application of 10 minutes.

Previously we have developed a free boundary model for local thermal coagulation induced by laser light absorption when the tissue region affected directly by laser light is sufficiently small and heat diffusion into the surrounding tissue governs the necrosis growth. In the present paper keeping in mind the obtained results we state the point of view on the necrosis formation under these conditions as the basis of an individual laser therapy mode exhibiting specific properties. In particular, roughly speaking, the size of the resulting necrosis domain is determined by the physical characteristics of the tissue and its response to local heating, and by the applicator form rather than the treatment duration and the irradiation power.

An apical filling material should establish, as perfect as possible, the hermetic sealing of an apical cavity. However, a gap is formed between the filling material (gutta-percha) and the root canal wall. The egress of irritants into the root canal system to the periapical tissues is considered the principal cause of fails in apicoectomy and retro-filling, being assumed that irritants penetrate mainly through the gap located between the gutta-percha and the dentin. In this paper, we report the observation of an enlargement of the apical gap, after laser apicoectomy, comparing to conventional apicoectomy. The samples were divided into groups, and the conventional apicoectomy group, together with the Er:YAG laser group (400 mJ/10 Hz) produced both similar results, being the gap unaltered. On the other hand, the samples that were irradiated with the Er:YAG laser, followed by Nd:YAG laser irradiation (1.5 W/10 Hz) presented a larger gap, conclusions that were drawn from Scanning Electronic Microscope analysis. The enlargement of the gap was due to the fusion of the dentin on the border, close to the gutta-percha. This pronounced behavior might have been caused by the surface discontinuity, imposing a non-homogeneous condition, in relation to heat propagation, existing many clinical applications of these observations.

The biological-tissue response to laser irradiation has been a subject of intense research recently, because of the potential applications to non-invasive disease diagnosis. In this work, bovine liver was irradiated with 1060 nm laser light, both in the ablative and non-ablative regime. The light emitted by the tissue was detected in the visible spectra. The ablative regime was characterized by the strong signal generated due to photo-induced disruption of the biological tissue, resulting in strongly luminescent plasma. Under the non-ablative regime, it was possible to detect visible light, which may be attributed to non-linear, multi-photon absorption, upconversion or other cooperative optical effect in the tissue molecules. The optical processes involved are discussed.

Barrett's oesophagus is a metaplstic condition resulting from acid reflux that affects a small but significant percentage of the population. Detection of pre-malignant changes within this tissue may allow for preemptive treatment against oesophageal cancer. Optical biopsies using elastic scattering spectroscopy are being investigated as a possible in-situ diagnostic technique.

The incidence of oesophageal and laryngeal cancer has risen over past decades. The early detection of disease is vital for improved prognosis. The current gold standard method of tissue diagnosis is histopathology, which is invasive, costly and somewhat subjective. Raman spectroscopy however has potential for the non-invasive, early, in-vivo diagnosis of the biochemical changes associated with malignancy. Good quality Raman spectra have been measured in vitro using oesophageal and laryngeal tissue. Multivariate analysis has been implemented using principal component and linear discriminant analysis techniques. Sensitivity and specificity of more than 80% has been achieved for the discrimination of dysplasia and cancer, for both oesophageal and laryngeal tissue. On comparison with histopathology these results are seen to be an improvement, since pathology lacks sensitivity and specificity due to the subjective nature of the diagnosis. Thus illustrating that excellent discrimination between normal, dyspalstic and cancerous tissue can be achieved using Raman Spectroscopy.

Patients with hypermobility syndrome (HS) and Ehlers-Danlos syndrome (EDS) were investigated by means of in vivo near- infrared Fourier-transform Raman spectroscopy. HS is a benign and common condition (up to 5 percent of the population of the Western World). EDS is a rare, inherited connective tissue disease characterized by joint hypermobility, skin hyperextensibility, and other, occasionally serious, organ changes. EDS and HS may be related disorders. We investigated 13 patients with HS, 8 patients with EDS, and 24 healthy volunteers by means of in vivo Raman spectroscopy. The patients were classified according to Beighton and Holzberg et al. No difference in age between the three groups was found (HS 41 (33-49), EDS 36 (25-47), controls 37 (31-42); mean, 95% confidence intervals, respectively). Spectral differences were found in the intensity of the amide-III bands around 1245 and 1270 cm^-1 in HS and EDS compared with healthy skin (Kruskal-Wallis, p equals 0,02 for intensity ratios (I₁₂₄₅/I₁₂₇₀) between the investigated groups). To elucidate the character of the alterations in the amide-III bands a curve fitting procedure was applied. In conclusion, Raman spectroscopy may aid in the diagnosis of HS and EDS. Moreover the technique may be useful for analyzing the molecular changes occurring in these syndromes.

Routine clinical microbiological identification of pathogenic micro-organisms is largely based on nutritional and biochemical tests. Laboratory results can be presented to a clinician after 2 - 3 days for most clinically relevant micro- organisms. Most of this time is required to obtain pure cultures and enough biomass for the tests to be performed. In the case of severely ill patients, this unavoidable time delay associated with such identification procedures can be fatal. A novel identification method based on confocal Raman microspectroscopy will be presented. With this method it is possible to obtain Raman spectra directly from microbial microcolonies on the solid culture medium, which have developed after only 6 hours of culturing for most commonly encountered organisms. Not only does this technique enable rapid (same day) identifications, but also preserves the sample allowing it to be double-checked with traditional tests. This, combined with the speed and minimal sample handling indicate that confocal Raman microspectroscopy has much potential as a powerful new tool in clinical diagnostic microbiology.

A recently developed multiple fiber system for treating malignant tumors with interstitial photodynamic therapy was used in studies on rats with colon adenocarcinoma inoculated into the muscles of the hind legs. The animals were intraperitonially administrated (delta) -aminolevulinic acid (ALA), which is metabolized to protoporphyrin IX (PpIX) in the tissue. The treatment system consists of a laser light source, a beam-splitting system dividing the light into three or six output fibers and a dosimetry program calculating the optimal fiber position within the tumor as well as the treatment time needed to obtain a given threshold value of the light dose. One aim of the study was to compare the treatment outcome with the modelled dosimetry predictions. Tumor reduction was examined three days post treatment. A volume decrease was found in 85% of the treated tumors. The mean volume reduction was 44%, with one tumor completely disappearing. Histopathological examination three days post treatment showed substantial necrotic parts which, however, to a smaller extent were present also for non-treated tumors. These results indicated that the tumors have been under treated and the light dose has to be increased. Measurements of the build-up and photo-induced bleaching of PpIX using laser-induced fluorescence were also performed during the experiments.

Light-induced Fluorescence (LIF) technique is based on fluorescence emitted from intracellular chromophores upon illumination of cells by monochromatic light. We compared LIF emitted from a pair of normal and malignant murine cell lines, differing in H-ras expression. The malignant cells fluoresced significantly less than the normal cells, upon excitation at 290 +/- 10 nm. For both cell types, fluorescence decreased with decreasing cell concentration, but at each concentration, the normal cells fluoresced more than the malignant cells. The effect of viability and metabolic stage of the cells on this pattern was compared. The difference among the cells was not due to a difference in protein or DNA content. Thus, this model system demonstrates the specific contribution of H-ras to sub-cellular chromophores, resulting in a significant difference in their autofluorescence intensity, while measuring both emission and excitation scans. This study suggests a potential use of the LIF technique to distinguish between normal and malignant cells and tissues.

A method for simultaneous fluorescence spectroscopic measurement of surface membrane fluidity, platelet aggregation, and intracellular calcium concentration was developed. The capacity of the system to assess platelet activation associated with coronary artery angioplasty and anti-platelet treatment was confirmed. This approach offers a new analytical technique for circulating platelet activation.

Fluorescence spectra of scattering and non scattering solutions of rhodamine 6G and IR125 have been measured. The experimental data have been analyzed with a Gaussian parametric model to give some parameters that are related to the changes of scattering properties of fluorescent solutions. In addition, complementary measurements of diffuse reflectance have allowed us to test an analytical model generally used in order to recover intrinsic fluorescence spectra.

Many approaches to imaging of unstable plaque have been applied to detect vascular thrombosis and occlusion with only moderate success. LFS detected significant and specific changes in thrombogenic plaque in a rabbit model. Fluorescence emission intensity analysis of structural characteristics may provide an optical diagnostic technique for early recognition of unstable coronary syndromes.

Breast tissues can be investigated by means of the frequency- resolved spectroscopy, using the transmittance data. A model based on the Fourier transform of the time-resolved transmittance is firstly established, by considering the slightly compressed breast tissues as a finite homogeneous slab of different thicknesses. Two methods of determining the optical properties of this arrangement are presented. The former allows to use moderate modulation frequency of about 100 MHz, while the second requires a limited frequency range of 10 - 20 MHz, in accordance with the low frequency approximation. Under these conditions, computations reveal the potential of extracting the main optical tissue properties from the recorded phase angle shift and modulation linked to transmittance data, at fixed operating modulation frequency. In each case, graphical or numerical solutions can provide good estimates of both reduced scattering and absorption coefficients.

A diagnostic method to detect differences between diseased and normal tissue from bladder carcinoma by FTIR-microspectroscopy is described. Regions of interest on 10 micrometer thin tissue sections where mapped in transmission mode. After IR-Mapping, the samples have been analyzed with common pathological techniques. Quadratic discriminant as well as correlation analysis was applied to the obtained IR-maps allowing differentiation between cancerous and normal tissue. In the case of the correlation analyses it is further possible to distinguish between different types of tissue.

Infrared (IR) absorption spectra are well known for their selectivity and minutiae fingerprint of molecular structure. The biochemical changes in the sub-cellular levels developing in abnormal cells, including a majority of cancer forms, manifest themselves in different optical signatures, which can be detected in infrared spectroscopy. The molecular vibrational modes which are responsible for IR absorption spectra, are characteristic of the biochemistry of the cells and their sub-cellular components. We measured the infrared absorption spectra of monolayers of cultured normal and ras gene transformed mouse fibroblasts, using microscopic infrared system (micro-FTIR) technique. The absorption for normal cells was higher than the malignant ones in the spectral range 1000 - 1500 and 2800 - 3000 cm^-1. The effect on phospholipid metabolism due to ras gene incorporation is also discussed.

Several fiber optic probes attached single- or multi-fiber light delivery systems have been competitively examined for purposes of in vivo tissue fluorescence spectroscopy with endoscopic technique use. The effects of the probes' designs and excitation/receiving fiber geometry on fluorescence spectra are analyzed with the sensor optical efficiency (SOE) coefficient and the tip coupling efficiency (TCE) one calculated by means of ray tracing. The profiles of the excitation beam as well as fluorescence profiles were simulated with uniform and Gaussian cross power distributions, whereas the diameter of the tissue surface area from which fluorescence light was collected was taken as five diameter of the tissue surface area directly illuminated by the excitation beam. The plots of the SOE-coefficients versus changeable probe-tissue gap simulated possible peristaltic tissue movement during clinical in situ spectroscopic optical biopsy would be a helpful tool for specialists to design novel endoscopic fiber optic catheters to differentiate normal and pathologic tissues.

A novel spectral image-analysis system was used for tumor fluorescence and reflectance imaging in an animal model and in patients. Transcutaneous fluorescence imaging was carried out on Balb/c mice bearing subcutaneous C26 colon carcinoma after intraperitoneal (i.p.) administration of 5-aminolevulinic acid (ALA), a metabolic precursor of protoporphyrin-IX (PP), and of a novel photosensitizer tetrahydroporphyrin (THP). Tumors were clearly observable by fluorescence detection using green light excitation. Tumor versus normal tissue uptake of the photosensitizing agents was determined by monitoring fluorescence intensity. Maximal PP accumulation in tumor was observed 3 h after i.p. injection of ALA, whereas THP showed selective accumulation in tumor 24 h after administration. Reflectance spectroscopy was employed to study pigmented human skin lesions (nevus, pigmented BCC and pigmented melanoma). In the near-infrared region (800-880 nm) pigmented BCC and melanoma exhibited a differently shaped reflectance spectrum compared to normal skin and nevus. Spatially and spectrally resolved imaging, in combination with mathematical algorithms (such as normalization, spectral similarity mapping and division) allowed unambiguous detection of malignancies. Optical biopsy results from a total of 51 patients showed 45 benign nevi, 3 pigmented BCC and 3 malignant melanomas, as confirmed by histology.