Hans-Georg Eberle

An Initial Assessment of the Optical Properties of Human Laryngeal Tissue

The optical properties of human laryngeal tissue have been examined over the whole wavelength range from 400 to 2,200 nm to facilitate the development of new laser applications. Tissue samples were taken from healthy vocal fold and from vocal fold of patients with papillomatosis and with chronic, nonspecific laryngitis. The transmission and scattering properties of the tissue samples were recorded with a computer-guided integrating-sphere system. From the measured data the optical properties were calculated by means of the inverse Monte Carlo simulation. In the 500- to 600-nm range papilloma tissues had a considerably higher absorption than healthy vocal fold. When applying the optical tissue properties as a possible influencing factor of the effectiveness of laser systems, laser applications at this wavelength range may be useful in the ablation of papilloma tissue.

Effects of different IR laser systems on the tympanic membrane

Lasers suitable for myringotomy are the erbium:YAG laser (2940 nm) and the carbon-dioxide laser (10600 nm). The study examines the laser-tissue interaction with tympanic membranes of guinea-pigs, horses and formalin-fixed human tympanic membranes and the effects demonstrated by light-microscopy and scanning-electron-microscopy. The minimum energy densities for a perforation with the erbium:YAG laser in guinea-pig ear drums and formalin-fixed human tympanic membranes are 8 J/cm2 and 16 J/cm2 respectively. There are no thermic side effects. With the carbon-dioxide laser thermic side effects only occur with energy transmission via silver halide polycrystalline fiber. The minimum power density for perforation is 400 W/cm2 (pulse duration 50 ms). With the microslad 719 micromanipulator (Sharplan, Israel, Tel Aviv), the minimum power densities for perforation of guinea-pig and horse eardrums and for formalin-fixed human tympanic membranes are 150 W/cm2, 300 W/cm2 and 600 W/cm2 (pulse duration: 50 ms) respectively. The minimum power density to achieve a perforation with the SwiftLaseTM 757 scanner (Sharplan, Israel, Tel Aviv), is 250 W/cm2 in guinea-pig eardrums (pulse duration: 100 ms). A prototype of a hand-held carbon-dioxide laser otoscope is suitable for performing laser myringotomies in formalin-fixed human tympanic membranes.

Application of a laser radar photogoniometer in the diagnosis of osteoporosis

First results on angle dependent light scattering performed on normal and osteoporotic human bone tissue in vitro are presented. The scattering distributions are measured in cw mode as well as in time-resolved (time-gated) mode. Significant differences in the angular distribution of 675 nm laser radiation transmitted through normal or osteoporotic bones are found in cw-scattering measurements. For aspiring in situ results the transition in time-resolved measurements is needed to suppress the disturbing soft tissue signals. In this way, a characterization of the bone part is aimed by selectively recording the scattered signal in a suitable chosen time window. The measurements principle is based on time-correlated single photon counting using a 10 ps laser diode (830 nm) and a micro channel plate- photomultiplier tube. First in vitro results on human lumbar vertebrae (L1) obtained with this equipment show a correlation between the thermal peak position and the FWHM of the scattered light pulses and the bone mineral densities determined by Dual X-ray absorptiometry. The angle dependent scattering curves give distinct indications on the bone status in transmission mode.

IR Lasers and Application Systems for Myringotomy

Abstract.The study examines an Er:YAG laser (2940 nm) and different application systems of the CO2 laser (10 600 nm) with regard to their suitability for a one-shot laser myringotomy of an adequate perforation size (∼2 mm). The laser–tissue interaction of the Er:YAG laser and the CO2 laser in fresh tympanic membranes of horses (thickness: 80–100 µm) as well as in formalin-fixed human tympanic membranes (thickness: 100 µm) is studied correlating perforation diameters to the applied power/energy density and the effects demonstrated by light and scanning electron microscopy are analysed. Using the Er:YAG laser with a focused laser beam (spot diameter: 400 µm) or with a maximally defocused laser beam (spot diameter: 1600 µm) perforations of an adequte size (2 mm) can only be achieved with multiple laser pulses. Histological studies disclose only minimal thermic side effects in the adjacent tissue in both specimens. If the CO2 laser radiation is transmitted via a silver halide polycrystalline fibre (diameter: 900 µm) a maximal perforation diameter of 1300 µm is achieved with significant thermic side effects such as coagulation. Using an Acuspot™ 710 micromanipulator (focused beam diameter: 180 µm) combined with a SilkTouch™ scanner a maximal perforation diameters of 1700 µm can be achieved in horse tympanic membrane with one laser pulse. A prototype of a hand-held CO2 laser otoscope in combination with the SilkTouch™ scanner is suitable for performing laser myringotomies with a diameter of 2 mm with a single laser pulse in fresh horse tympanic membrane.

Laser Myringotomy with Different IR Laser Systems

Summary Lasers suitable for myringotomy are the erbium:YAG laser (2 940 nm) and the CO2laser (10 600 nm). The study examines the laser-tissue interaction with tympanic membranes of guineapigs, horses and formalin-fixed human tympanic membranes and the effects demonstrated by light-microscopy and scanning-electron-microscopy. The minimum energy densities for a perforation with the erbium:YAG laser in guinea-pig eardrums and formalin-fixed human tympanic membranes are 8 J/cm2 and 16 J/cm2 respectively. There are no thermic side effects. With the CO2laser thermic side effects only occur with energy transmission via silver halide polycrystalline fiber. The minimum power density for perforation is 400 W/cm2 (pulse duration 50 ms). With the microslad 719 micromanipulator (Sharplan, Israel, Tel Aviv), the minimum power densities for perforation of guineapig and horse eardrums and for formalin-fixed human tympanic membranes are 150 W/cm2, 300 W/cm2 and 600 W/cm2 (pulse duration: 50 ms) respectively. The minimum power density to achieve a perforation with the SwiftLase™ 757 scanner (Sharplan, Israel, Tel Aviv), is 250 W/cm2 in guinea-pig eardrums (pulse duration: 100 ms). A prototype of a hand-held CO2laser otoscope is suitable for performing laser myringotomies in formalin-fixed human tympanic membranes.

Laser-induced breakdown in silver halide crystals and polycrystalline fibers

The maximal laser power transmitted through polycrystalline silver halide fibers is limited by their IR absorption and optical strength. The mechanisms of the IR absorption and laser-induced breakdown (LIB) thresholds Pc in AgClxBr1-x crystals and polycrystalline fibers were studied. Investigations, including mechanical treatments, heat treatments, and luminescence properties were performed to clarify the reason for the IR absorption and LIB in silver halide crystals and fibers. From these experiments we concluded that one of the reasons for LIB may be the avalanche of electrons in the conduction band of the crystal. These seed electrons are produced by the IR absorption of the cation vacancies in these crystals. A simple annealing procedure for reduction of the IR absorption of fibers is proposed.

Optical catheters based on silver halide infrared fibers

Laser power transmission, luminescence, mechanical behavior and effects of various thermal treatments have been investigated on mixed sliver halide crystals. This knowledge may suggest ways of optimizing the fabrication of optical fibers from such crystals. Anti-reflection coating for high-power 10.6 micrometer light transmission was studied both on crystals and fibers. Laser power transmission and mechanical properties of the fibers also have been investigated. On the basis of these experiments the prototype of the medical catheter was produced and surgery experiments with this catheter have been performed.