A computer simulation of the temperature and damage distribution during a bipolar RFITT (radio-frequency current induced interstitial thermotherapy) application has been developed. The electric field and the heat transfer is calculated by the Finite Difference Method. The program calculates the distribution of electrical power density (heat generating term), temperature and tissue damage using standard and cooled bipolar needle applicators and displays the results graphically in real time. Whereby the changes of the tissue parameters due to the heating process are also taken into account. The computer program can not only be a means for therapy planning but as well for on-line therapy control. For this the program has the option to measure the output power of the RF-surgery generator and the tissue impedance via an A/D-converter. This gives more accurate simulation results. Furthermore the power output of the RF- generator can be controlled by the program via a D/A- converter. The option of measuring and steering the generator power allows the possible implementation of various control algorithms with the aim of performing an interstitial coagulation with high efficiency.

For prediction of the effectiveness of laser-induced thermotherapy (LITT) of liver metastases and for the planning of laser treatment it is indispensable to achieve knowledge about the intrahepatic light and temperature distribution in order to obtain data for an optimally adapted dosimetry. We evaluated the optical properties of normal and tumorous rabbit-liver ex-vivo using a double integrating sphere technique as well as a Monte-Carlo- simulation. These data were correlated with the measurement of the intrahepatic temperature distribution in-vivo during LITT. In our study we were able to show a positive correlation between ex-vivo results of optical properties and in-vivo results in temperature distribution. The absorption coefficient and scattering coefficients were significantly smaller in tumor tissue than in normal liver. This resulted in a higher optical penetration depth of the laser light into the tumor tissue (p < 0.01). Temperature measurement near the applicator was lower in tumor tissue, than that distant from the applicator (p < 0.01) corresponding to a higher temperature penetration depth. Both, higher optical and thermal penetration depth in the tumorous tissue was correlated with a significant increase in coagulation volume after LITT.

The objective was to investigate if diffusing laser fibers can be modeled as conductive heat sources without miscalculating coagulated volumes, and if finite element analysis, disregarding light transport, may be used for 3D treatment planning in interstitial laser thermotherapy (ILT). Temperature distributions and coagulated volumes with a diffusing laser fiber, as compared to a conductive heat source, were numerically calculated at equal output power and with optical tissue properties corresponding to coagulated human liver. Blood flow was absent in the model. The maximum temperature with the diffusing fiber was limited to 100 degree(s)C and 5, 10, 20 and 30 minutes heating time was studied. A 3D finite element model was used to calculate temperatures during heating with four cylindrical heat sources (no light emission) and results were compared to measured temperatures during laser irradiation in gel with known optical properties. Coagulated volumes with a single diffusing or conductive applicator ranged from 3.5 to 12.6 cm³ and differed less than 1% at all studied irradiation times. Calculated and measured temperatures with four applicators agreed excellently. The present study should be relevant to ILT of the human liver, when inflow is occluded.

Balloon thermal endometrial destruction (TED) is a recently developed method to treat heavy menstrual bleeding (menorrhagia). Numerical simulations of this treatment by use of the finite element method were performed. The mechanical deformation and the resulting stress distribution when a balloon catheter is expanded within the uterine cavity was estimated from structural analysis. Thermal analysis was then performed to estimate the depth of tissue coagulation (temperature > 55 degree(s)C) in the uterus during TED. The estimated depth of coagulation, after 30 min heating with an intracavity temperature of 75 degree(s)C, was approximately 9 mm when blood flow was disregarded. With uniform normal blood flow, the depth of coagulation decreased to 3 - 4 mm. Simulations with varying intracavity temperatures and blood flow rates showed that both parameters should be of major importance to the depth of coagulation. The influence of blood flow was less when the pressure due to the balloon was also considered (5 - 6 mm coagulation depth with normal blood flow).

LITT has been used for the treatment of benign and malignant tumors since 1983. In all cases the laser fiber/s have been arranged at or near the center of the lesion and the duration of treatment, or fiber tip type, modified in an attempt to destroy the whole tumor. During the last 8 years the author has treated 344 symptomatic patients with more than 1,400 benign uterine leiomyomas by LITT. The first 50 cases were treated traditionally with the fibers directed towards the center of the tumor. Six cases subsequently required second stage LITT and four failed and required hysterectomy. The remaining patients were either treated by directing the laser fibers towards the periphery, where feasible, or throughout the tumor in parallel 3 cm apart. The latter achieved columns of coagulated tissue 5 mm in diameter an strips of healthy tissue between, which subsequently died from tissue anoxia because blood vessels had been coagulated. Research showed that any remaining tissue was deprived of enzymes, hormone receptors and epidermal growth factor and, therefore, did not grow. It is concluded that with malignant tumors cure rather than palliation might be achieved if the laser fibers were directed towards the periphery where the blood vessels enter, and that the surrounding healthy tissue be sacrificed for about 1 cm to destroy micro-invaded tissue and tumor cells within lymphatics.

New laser-based technique for anatomical-functional study of the medial prefrontal cortex (MPFC) of the brain of experimental animals (rats) is presented. The technique is based on making accurate well-controlled lesions to small MPFC and subsequent observing behavioral alterations in the lesioned animals relative to control ones. Laser produces smaller and more accurate lesions in comparison to those obtained by traditional methods, such as: mechanical action, chemical means, and electrical currents. For producing the brain lesions, a 10 W CO₂ CW laser is employed for reasons of its sufficiently high power, which is combined with relatively low cost-per-Watt ratio. In our experience, such power rating is sufficient for making MPFC lesions. The laser radiation is applied in a form of pulse series via hollow circular metallic waveguide made of stainless steel. The waveguide is of inner diameter 1.3 mm and 95 mm long. The anesthetized animals are placed in stereotaxic instrument. Via perforations made in the skull bone, the MPFC is exposed to the laser radiation. Several weeks later (after animal recuperation), standard behavioral tests are performed. They reveal behavioral changes, which point to a damage of some small regions of the MPFC. These results correlate with the histological data, which reveal the existence of small and accurate MPFC lesions. The present technique has good prospects for use in anatomical- functional studies of brain by areas. In addition, this technique appears to have considerable promise as a treatment method for some pathologies, e.g. the Parkinson's disease.

Feasibility of laser assisted micro-vascular anastomosis (LAMA) has already been proved for more than 15 years. But to our knowledge, equivalence between LAMA and conventional manual anastomosis (CMA) has never been demonstrated. With a Master Oscillator Power Amplifier diode laser (988 nm) and Fast Green FCF as chromophore, LAMA versus CMA were performed on the carotids of 92 Wistar rats. LAMA edge coaptation was achieved with three 10/0 stitches, irradiation with 3 shots of 500 mW in power and 800 nm in diameter. CMA was performed on the other side with six 10/0 stitches. At 2 months, 3 aneurysms were present on LAMA side and 3 on CMA side, the success rate was 96.7% on both sides. We established the equivalence of LAMA and CMA, in an interval of 5%, using a method of equivalence based on odds ratios and Chi-square test. Paired t-test comparing carotid flow, maximal Doppler frequencies, pulsatility and resistance index could not highlight any difference between the 2 methods. Histological analysis showed an earlier and better re-endothelialization on LAMA side. For the first time to our knowledge equivalent between LAMA and CMA has been demonstrated.

This study aimed to evaluate a 815 nm diode-laser system to assist wound closure. It was proposed to determine an optimal fluence being able to accelerate and improve heating process without thermal damage after laser irradiation. Male hairless rats with dorsal skin incisions were used for the study. Different fluences were screened (76 to 346 J/cm²) in a first phase with clinical examination at 3, 7, 15 and 21 days after surgery. Best results were obtained for a fluence of 145 J/cm² and 3 sec time of exposure. A second phase was conducted to valid these parameters with histological study and determination of tensile strength at 3, 7, 15 and 21 days after surgery. LASC was 4 times faster to process than conventional suture. In the laser group with an optimal fluence of 145 J/cm², healing was accelerated. The resulting scar was more indiscernible than in the control groups. Histological aspect was better with continuous epidermis and dermis at 3 days in most cases. Tensile strength was 30 to 58% greater than in control groups (1141 g/cm² at 7 days in the laser group versus 856 g/cm² and 724 g/cm² in the control groups, p < 0.001).

The compliance of microvascular anastomosis is an important predictive factor for long term patency of graft or vascular reconstruction. This experimental study compare the compliance of manual suture and laser assisted end to end microvascular anastomosis. In nine New-Zealand white rabbits we performed manual end-to-end suture anastomosis on the left femoral artery and laser assisted anastomosis on the right femoral artery, with a diode laser (wavelength 988 nm, power output 500 mW). Compliance was obtained by echotracking (CBI 8000 sonomicrometry system with 20 MHz implantable microprobe from Crystal-Biotech, USA) on the anastomosis site as well as upstream, and downstream from the anastomosis. Vessel compliance was lower on the manual suture side compared to the laser assisted anastomosis side, especially downstream from the anastomosis.

We suggest to use laser osteoperforation as a new approach to surgical treatment of acute haemotogenic osteomyelitis. In the present work this approach is studied in experiment on 30 rabbits with an emphasis on a role of hypertermia. The osteomyelitis was produced with the help of an original technique by percutaneous introduction of microorganisms `Staph. Aureus' in medullar channel. The animals were divided into 2 group, experimental (17 rabbits) and control (13). On the 7th day of the illness all animals were subjected to the osteoperforation, with Nd:YAG laser (1064 nm) in the first group and with mechanic drill in the second. During the laser osteoperforation the dynamic control of temperature was performed simultaneously in 5 - 7 points in medullar channel. The original measuring- computational system designed for temperature measurements in the presence of intense laser radiation was used. Significant increase of temperature in medulla was fixed near laser channels, in the range up to 2 mm. In the experimental group the perforation results rapid positive clinical changes and convalescence of all animals confirmed by clinical, roentgenological, and histological tests. In the control group there was no positive dynamics, there were intermuscular phlegmon and plo-inflammatory changes in medulla, sequestra were formed. The reason of such an advantage of laser perforation consists in new factors of action in addition to decompression of medullar channel (available in both methods). The laser produces hypertermia of the medulla which kills a significant part of microorganisms, and it creates intensive radiation field which, possible, stimulates reparative processes.

The problems of contact measurement of temperature in the presence of intensive radiation are discussed. A new measuring-calculative method for thermometry in such conditions is presented. The method has been realized in a setup including: miniature thermodetectors, amplifiers, analog-to-digital converter and a computer with software to record thermodetector temperatures, to recalculate them to medium temperatures and to display the results. The setup and the method have passed testing in model experiments and are successfully applied to thermometry in various biological tissues irradiated by near infrared lasers.

Cranial rat bone was irradiated by 2.1 micrometers Holmium YAG laser radiation. Quantitative edge rates were calculated. Histologic sections were investigated by light and electron microscopy. 18 cases of hard fibrous or calcified spinal and cranial meningiomas and neurinomas were operated upon using pulsed laser beam. In rat cranial bone ablation rate ranged between 3 - 5/10 mm per pulse. Perifocal thermal damage was observed in a zone of 20 - 90 micrometers around the lesion. In all human cases tumors could be removed totally without additional neurological deficit. In vivo heat development was measured by an IR-camera.

Bone ablation with 400 ns pulses of a mechanically Q- switched CO₂ laser is reported. A miniature water spray was used, which alleviates tissue carbonization, even at high laser pulse repetition rates, and increases ablation efficiency. An ablation threshold of less than 2 J/cm², an optimal energy density of 10 J/cm², and a corresponding specific ablation energy of 25 - 30 J/mm³ was found for pig thighbone compacta at (lambda) equals 9.57 micrometers , and a beam waist diameter of 0.5 mm.

As ultrafast laser technology advances, it is of importance to evaluate the potential of sub-100-fs laser pulses for laser surgery. We have extended the investigation of laser- induced optical breakdown on hard and soft tissues down to laser pulse widths of 20 fs. Powerful 20-fs to 100-ps pulses from a single Ti:sapphire oscillator/amplifier laser source at 800 nm were focused in vitro onto the surface of fresh human corneas and human enamel to a spot of 60 - 70 micron in diameter. The threshold for ablation was determined by increasing the pulse energy while monitoring scattered probe light at ejected ablation particles. Our experiments show a slower decrease of the threshold fluence in dependence of the pulse width in the femtosecond regime than in the picosecond regime. Unlike previously suggested, no saturation behavior could be observed at the shortest available pulse widths. For the shortest pulses with 20 fs width, we measured a threshold of 0.38 J/cm² and 0.42 J/cm² for cornea and enamel, respectively. For the longest pulses at 100 ps, the threshold fluence was 4.3 J/cm² and 2.06 J/cm², respectively. Comparison to theoretical models and to previous data determines the contribution of multi-photon and avalanche processes. Our results suggest an optimum laser pulse width of several hundred femtoseconds for most applications in ultrashort pulse laser surgery.

Slab gel electrophoresis is a major tool for size-separation of DNA fragments and proteins. However, conventional slab gel electrophoresis uses a large gel to obtain sufficient separation and it takes several hours to separate, because conventional detectors using radio isotopes and fluorescence are affected by the strongly light-scattering gel and do not have enough spatial resolution to be applied to a miniaturized gel. Thermal lens microscope (TLM), which we have developed, has spatial resolution of micrometer level, and is not easily affected by the scattered light and can maintain high spatial resolution. We demonstrate here high- speed separation using a miniaturized gel and successive high spatial resolution detection using TLM. Using a miniaturized gel one-tenth of conventional gel in size, DNA fragments (100 base pair ladder sample) were separated in 5 to 15 minutes, which was about one order of magnitude faster than using a conventional gel, and successfully detected by TLM.

Photothermal (PT) and Photoacoustic (PA) Step-Scan FT-IR measurements are successful tools for thickness determination of layered samples. Aiming to separate optically between different layered tissues, we have been able to distinguish skin, liver and muscle tissues by means of PT and PA measurement techniques. Performing Step-Scan FT-IR measurements, the PT and PA phase and amplitude signals follow the tissue's absorption peaks which corresponds to the transmission spectra. These results are supported and confirmed by a simulation using the Finite- Difference-Method whereat the basic spectral data from transmission measurements and some assumed thermal properties of investigated tissues have been inserted.

In this paper, we present a study of pure arachidonic acid, arachidic acid, other fatty acids (FA) and mixtures with cholesterol (Ch) in different ratio of compounds, having smectic C liquid crystal (LC) properties. Very thin systems (`membranes') of FA and mixtures, manufactured by us, were subjected to some electrical measurements, that show a new distribution, induced by Ch, of the space charge in the system. The FA and mixtures' samples were also sandwiched between two glass plates of transparent SnO₂ electrodes and studied under dc and ac electric fields. The hysteresis curves of the current versus the applied voltage exhibited a nonlinear dielectric feature and a negative resistance. We studied the change of the fundamental IR and second harmonic pulsed beam of a Nd³⁺ glass laser, in the time domain, after passing through our samples; the optical output power of a He-Ne laser beam ((lambda) equals 6328 angstroms, P_max equals 20 mW), from the LC cells situated between parallel and crossed polarizers was registered. A nonlinear optical behavior of the samples and some memory effects were emphasized. Also a correlation between the electric and optical nonlinearity of the samples seems to be possible.

CW transillumination of tissue phantoms at 1064 and 820 nm has been performed, by measuring the profile of transmitted light transverse to the direction of the incident beam for various values of the scattering and absorption coefficients and for different viewing angles of the photodetector and sample thicknesses. The set of measurements, compared with the results of Monte Carlo simulations, allows to derive a CW optical characterization of tissue-like samples and to assess the possible resolution improvement of collimated detection with narrow viewing angles.

Photothermal (PT) and Photoacoustic (PA) Step-Scan FT-IR measurements are successful tools for thickness determination of layered samples. Aiming to separate optically between different layered tissues, we have been able to distinguish skin, liver and muscle tissues by means of PT and PA measurement techniques. Performing Step-Scan FT-IR measurements, the PT and PA phase and amplitude signals follow the tissue's absorption peaks which corresponds to the transmission spectra. These results are supported and confirmed by a simulation using the Finite- Difference-Method whereat the basic spectral data from transmission measurements and some assumed thermal properties of investigated tissues have been inserted.

We determined and compared to the optical properties of five samples obtained from xenotransplanted chick embryos chorio- allantoic membrane tumors, five samples obtained from xenotransplanted chick embryos yolk sac membrane tumors, and five samples of concentrated tumor cells suspension (small cell lung carcinoma OAT 75). The absorption coefficient (mu) _a, the scattering coefficient (mu) _s, the anisotropy factor g, and the reduced scattering coefficient (mu) _s' were evaluated in the spectral range from 600 nm to 900 nm with a step width of 10 nm from double integrating sphere measurements using an inverse Monte Carlo technique. The results have shown that the optical properties of the concentrated tumor cell suspension are similar to those of the chorio-allantoic membrane tumor, but are essentially different from the optical properties of the yolk sac membrane tumor. Cell vitality tests have shown that the cells were alive during and after the experiments. Therefore, the tumor cell suspension can serve as an optical model of the chorio-allantoic membrane tumor in situ for testing and developing novel diagnostic and therapeutic techniques.

The photoinduced effects of hypericin, a polycyclic quinone, on collagen has been investigated. It was found that after laser irradiation at both 532 nm and 337 nm, the spectral form of triple helix structure collagen fluorescence, changed to a spectral profile bearing resemblance to that of its polypeptide single chain counterpart, gelatin, or heated collagen. The effect of Chlorin e₆ on collagen was also investigated and proved to be dissimilar to that of hypericin and not indicative of profound structural alterations. Second Harmonic Generation (SHG) of 1064 nm- nanosecond laser radiation in collagen was studied. While it was very efficient for pure collagen, the signal intensity was found to diminish by at least an order of magnitude after hypericin photosensitization or heating. The above noted fluorescence spectra form alteration was also observed in a smaller scale in collagen rich chicken tissue (tendon). Non sensitized chicken tendon tissue exhibited very efficient SHG, unlike skin and artery samples.