Johannes Tschepe

Flexible waveguides for Er-YAG laser radiation delivery

Flexible plastic waveguides (FPW) were devised for the delivery of Er-YAG laser radiation. The FPW characteristics were studied under various conditions. In vitro studies were carried out to explore the drilling procedure on extracted teeth and the FPW-tissue mutual effects. The results which were obtained proved that the FPW as a delivery device might be a substitute hand applicator for the pneumatic turbine for drilling in teeth.<<ETX>>

Acoustical waves via optical fibers for biomedical applications

This paper presents recent results on a combined optical and acoustical system for a new endoscopic controlled laser and ultrasound surgical therapy (LUST). The goal is the combined employment of the cavitation ultrasonic surgical aspiration (CUSA) and the laser in endoscopic surgery. With such a system the CUSA technique can be used for selective tissue cutting and the laser for blood coagulation, vaporization, general tissue cutting (all this with cw lasers) and photoablation (with pulsed lasers). The transmission of acoustical energy via optical fibers is theoretically calculated. First experimental results on the transmission of high power ultrasound (US) via a silica fiber are shown. Furthermore future biomedical applications including angioplasty and endoscopic surgery are discussed.

Transmission of laser radiation and acoustical waves via optical fibers for surgical therapy

This paper looks back on the transmission of acoustical shock waves via optical fibers. After that it presents recent results on an optical and acoustical system of a new combined endoscopical laser and ultrasound surgical therapy (LUST) for coagulation and tissue disintegration. Theoretical calculations concerning the transmission of acoustic energy via optical fibers are shown. In first experiments on the transmission of high power ultrasound via a silica fiber of 800 mm length a longitudinal elongation of up to 30 micrometers at the distal end with a simultaneous laser transmission was achieved. A magnetostrictive ultrasound transducer with a frequency of 26 kHz and a Nd:YAG laser (25 W cw) was used.

Thermal effects due to interaction of infrared radiation with guiding films of flexible waveguides

The effect of external energy source on waveguides transmitted blackbody radiation is examined. It is shown that the radiometric signal is increased because of external heat sources. This effect can be avoided by a proper external protecting layer. The transmitted laser energy is another cause of heating the waveguides walls. To analyze these effects, the wall temperature was recorded by thermocouples and thermal camera. It is shown that the most-affected regions in the waveguide are the curved regions and the distal end. Gas cooling and external metal layers reduce this undesired heating of the walls.

Flexible plastic waveguides suitable for large interval of the infrared radiation spectrum

Flexible plastic waveguides (FPW) were first developed for CO2 laser radiation. Further investigation of the factors which influence the quality of the reflecting and refracting layers, have led to the development of a method of smoothing of the substrate and the layers. A mechanism of controlling the dielectric layer thickness was also devised. Based on this knowledge we produced waveguides which can transmit several wavelengths of laser radiation. Measurements of the transmission characteristics of FPW coupled to Er-YAG (2.94 micrometers ), and Ho-YAG (2.1 micrometers ), CO (5.5 micrometers ), CO2 (10.6 and 9.6 micrometers ), and TEA laser (9.6 micrometers ), under various conditions (power, bending) were made and show good results. The use of the FPW in transmitting these types of laser radiation may broaden the spectrum of uses of the waveguides in medical application, i.e., hard tissues (bone, teeth) and in the eyes.

Flexible waveguides for the delivery of high-power Er-YAG laser radiation

In a previous research project a flexible plastic hollow waveguide has been developed in our laboratory. The waveguide was prepared by depositing silver (Ag) layer and silver iodine (AgI) overlayer on the inner surface of a plastic tube. The said waveguide proved to be a very suitable means for delivering high power CO2 laser energy ((lambda) equals 10.6 micrometers ) in any desired tortuous path, having small attenuation. Through the same waveguide it is possible to transmit non-coherent infrared energy from a thermal energy source to a detector. In this paper we present a new type of waveguide which is suitable for the transmission of Er- YAG laser radiation ((lambda) equals 2.94 micrometers ). Such energy can be employed for drilling and operating in hard tissues (bone, tooth). The essential factor which made this device possible for use as Er-YAG laser energy delivery system is based on the known data from the CO2 waveguide research was the control over the thickness and the index of refraction of the dielectric layer (AgI). Another important factor was to avoid the roughness of the plastic substrate and of the Ag/AgI layers. Reducing the roughness enabled us to reduce the scattering of the transmitted radiation to a low value, which is essential for the good functioning of the waveguide. The performed experiments have shown that an energy of up to 900 mJ could be coupled into the flexible waveguide and delivered to a target in straight or bent trajectory. The transmission was 55% in straight and 40% in bent trajectory (waveguide length 1 m, internal diameter 1.9 mm minimum radius of bending 20 cm).

Endoscopically controlled laser lithotripsy of sialoliths

Among the diseases of the major salivary glands, sialolithiasis is a frequent clinical picture. Until now the condition has nearly always had to be treated surgically. In rare cases, discharge can be achieved by acid stimulation of secretion. If located distally in the excretory duct, concrements may be removed by enoral lancing. If it is close to glands, e.g., in the knee of Whartons duct or in the ductal part of the submandibular gland, extirpation of the gland including the stone is unavoidable. Besides wound healing problems and the occurrence of salivary fistulas, the main risk of surgery is injury to the nerves around the major salivary glands, e.g., the n. facialis or one of its branches, the n. hypoglossus, or the n. lingualis with consecutive paresis. Based on the clinical results of lithotripsy by laser-induced shock waves (LIL) applied to renal stones and ureteroliths as well as bilary duct and pancreas stones, we investigated the suitability of endoscopically controlled laser therapy for sialolithiasis.

Infrared laser power transmission through silver halide crystals and polycrystalline fibers

Laser-induced breakdown (LIB) thresholds in AgClxBr1-x crystals and fibers were studied under CO2 pulse and cw laser excitation. The dependence of the LIB and IR absorption on composition and temperature treatment suggests, that the LIB in silver halide crystals and fibers is due to the absorption at 10.6 micrometers caused by cation vacancies bound with charged dislocation silver halides. The lower optical stability of the fibers is due to defects induced by the heating under pressure, applied during the production of the fibers by extrusion and the subsequent fast quenching to RT. A simple method for reduction of the IR absorption is proposed.

Er:YAG laser flexible waveguides

Flexible plastic waveguides (WG) were devised for the delivery of Er-YAG laser energy in curved trajectories. The WG were optically characterized. The WG transmitted energy could drill a hole in teeth enamel hence it can be used as a substitute for a pneumatic drill.

IR fiber radiometry for high-temperature measurements during laser tissue interaction

The temperature of the reaction zone is one of the main parameters for the characterization of laser-tissue-interaction. IR-radiometry, a noncontact temperature measurement method, is used to determine the temperature of the reaction zone. To be able to measure the inside of cavities, especially of hollow organs, we used IR-fibers to guide the temperature radiation to the complex receiver device. During the laser-tissue interaction the IR-radiation field of the reaction zone is focused on an IR-optical fiber made of AgClxBr1-x. The temperature is measured for Nd:YAG laser application with different power densities and compared with standard thermographic equipment.