Juergen Helfmann

A new system for a combined laser and ultrasound application in neurosurgery.

A new combined Laser and Ultrasound Surgical Therapy (LUST) device suitable for endoscopical coagulation and tissue fragmentation has been developed at the LMTB. The new feature is the simultaneous transmission of laser radiation and ultrasound via flexible silica glass fibers. The ultrasound tissue interaction is based on the well-known CUSA-technology which enables the surgeon to cut various types of tissue with different degrees of effectiveness. Application fields are in oncology, neurosurgery and angioplasty. The laser radiation can be used, for example, for tissue coagulation purposes. With a fiber based LUST-system working at a frequency of 30 kHz, a displacement of 100 microns could be attained at the distal end. (The usual standard CUSA displacement is 10-350 microns.) During in vitro experiments the following tissue fragmentation rates could be achieved: brain tissue 50 mg sec-1, liver 4.5 mg sec-1 and kidney 4 mg sec-1 (displacement of the tip 60 microns; phi 1.3 mm; suction setting: 5 W). Laser radiation up to 25 W was sufficient to coagulate soft tissue. This technology offers new possibilities in minimal invasive surgery. The flexible opto-acoustic waveguide (phi 400-1700 microns) can be bent making areas accessible that were previously inaccessible. Without changing the instrumentation the surgeon can use the laser radiation for tissue coagulation or cutting and the ultrasound for tissue fragmentation and tissue reduction.

New application system for simultaneous laser and ultrasonic transmission in endoscopic surgery (LUST)

A new combined Laser and Ultrasound Surgical Therapy (LUST) device for an endoscopically suitable coagulation and tissue fragmentation based on the transmission of laser radiation and ultrasound via flexible silica glass fibers was developed at the LMTB. The ultrasound tissue interaction is based on the well-known CUSA-technology, which enables the surgeon to cut various types of tissue with different degrees of effectiveness. This selective cutting performance is a very useful feature, e.g. for a brain tumor extirpation, where it must be guaranteed that vessels and nerves are not affected while ensuring a fast reduction of the tumor mass. Application fields are in oncology, neurosurgery and angioplasty. The laser radiation can be used for tissue coagulation purposes and homeostasis. With a fiber based LUST-system working at a resonance frequency of 30 kHz, using a laser-vibrometer, velocity amplitudes of up to 20 m/s could be detected at the distal end which corresponds to an elongation of more than 100 micrometers . The investigations have shown that the velocity amplitude, next to suction, frequency and cross section of the active fiber tip, has the greatest impact on the fragmentation rate. With a suction setting of 5 W, the following tissue fragmentation rates could be achieved with a 1.3 mm2 fiber cross section and a tip amplitude velocity of 12 m/s: brain tissue 50 mg/s, liver 4,5 mg/s and kidney 4 mg/s. Laser radiation up to 25 watt was sufficient to coagulate soft tissue. This new approach in developing an application system for the therapeutical use of laser radiation and ultrasound via optical waveguides offers new possibilities in minimally invasive surgery, providing a complete new working sphere for the surgeon. The flexible opto-acoustic waveguide (400 - 1700 micrometers ) can be bent making areas accessible which were inaccessible before. The surgeon can use the laser radiation for tissue coagulation or cutting and the ultrasound for tissue fragmentation and tissue reduction without changing the instrumentation.

New application system for laser and ultrasonic therapy in endoscopic surgery

Flexible acoustic waveguides for selective tissue fragmentation are not yet commercially available. Experimental studies have shown the possibility of transmission of acoustical transients via optical silica glass fibers. The aim of this project is the development of a new endoscopic application system that would enable surgeons to use the laser and the ultrasound technique for therapy simultaneously. The concept of this application system is based on the transmission of laser radiation and ultrasound power via flexible silica glass fibers. Theoretical and experimental results on the feasibility of such an application system for an ultrasonic power delivery system are presented. Piezo-electric transducers are used to provide a high efficiency in generating the ultrasonic power. With reference to the CUSA-technique, a special flexible guiding system has been designed for providing aspiration at the tip and for protection of the fiber. The system transmits via an optical fiber up to 100 Watt Nd:YAG laser radiation. The axial oscillation of the fiber tip is +/- micrometers at a frequency of 27 kHz. First results of in vitro experiments are presented. The parenchymatous cells of liver can be fragmented without destruction of the collagenous matrix. The laser can be optionally used to coagulate bleedings or to cut collagenous tissues in contact. Applications for an acoustical and optical waveguide in ultrasonic surgery are demonstrated. This new approach in developing a first application system for the therapeutical use of laser radiation and power ultrasound in minimal invasive surgery via optical waveguides offers new possibilities in surgery. The laser ultrasonic surgical therapy (LUST) with its thin and flexible applicator provides new working fields especially for neuro or liver surgery. The tip can be bent and thus areas which could not be treated before have now been made accessible. Without changing the instrumentation, the surgeon can use the laser for tissue coagulation or cutting, next to the selective ultrasonic tissue fragmentation, where nerves or vessels will not be affected. Such a LUST-application system could be ready for clinical use in two to four years.

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.

Efficiency of stone fragmentation by long pulses of a Q-switched Nd:YAG laser

The effect of long pulsed Nd:YAG laser (pulse duration 300 ns) with the fundamental and second harmonic wavelength on the fragmentation of different urological and gall stones has been investigated. With 200 and 400 micrometers fibers in a contact application, all types of stones could be fragmented with energies less than 120 mJ (400 micrometers fiber) or 45 mJ (200 micrometers fiber). By use of a double pulse-simultaneous application of second harmonic and fundamental radiation the efficiency of fragmentation could be increased and the energy threshold decreased.

Imaging of xenofluorescent objects in strongly scattering media: first results

This paper presents an ongoing investigation of laser induced xenofluorescence using a fluorescent marker to detect objects in turbid media. The aim is the development and validation of a method for imaging vessels using near infrared fluorescence angiography techniques in strongly scattering media. The main purpose is to show the course of blood and lymph vessels in the head and neck region of tumor patients. The first step was the selection of the best method and a suitable fluorescence dye to image these vessels. Using a phantom with the optical parameters similar to skin and fat tissue different methods of fluorescence excitation and detection were investigated. The following experiments were performed: whole area two-dimensional excitation and detection (CCD camera) as well as a focused excitation with scanned detection (photo diode). Furthermore investigations of the improvement of the vessel detection using a phase demodulation technique were performed. The measurements were simultaneously accompanied by analytic calculations using diffusion approximation. The photophysical investigations of several dyes have led to the use of tsAlClPc as fluorescence dye for the technical comparison of the investigated methods. Since this phthalocyanine is phototoxic a clinical certified dye (probably Indocyanine green) will be used for future experiments. The methods with focused excitation and scanned detection have shown the best resolution, but they are slow and expensive in comparison to the CCD camera technique. Further experiments should give more information about the application dependent decision which method is best suited.

New alternative for laser lithotropsy-long pulse passively q-switched solid-state laser with fiber-based resonator

This paper presents an overview of the important processes which are responsible for stone fragmentation. The efficiency of these processes in dependence of wavelength and laser pulse duration is discussed. Beside shockwaves and cavitation phenomena the role of a compressional shock acting on the stone and the plasma confinement is emphasized. As a conclusion the concept of a passively Q-switched solid state laser with a fiber-based resonator which prolongs the pulse duration is presented.

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.

Tissue differentiation using laser-induced shock waves by detection of acoustic transients through an optical wave-guide

Some physical phenomena which occur during the fragmentation of calculi by laser induced optical break down are presented. With in vitro experiments it could be shown that the energy of the laser induced plasma and of the cavitation bubble (induced by the plasma) depends by the nature of the tissue. The laser induced plasma and the cavitation bubble generate shock waves. These sound waves are transferred via the laser fiber and detected with a piezo- electrical sensor at the proximal end. The acoustic signal contains information on the potential energy of the bubble, which depends on the energy of the plasma. The possibility of measuring the energy dependent acoustic transients allows to distinguish between hard and soft tissue and by this it is suitable for controlling the laser lithotripsy process. The transmission of acoustic transients through silica glass fibers is investigated by theoretical calculations. It shows the feasibility of silica glass fibers as an acoustic wave guide.