Kai Desinger

Interstitial bipolar RF-thermotherapy (RFITT) therapy planning by computer simulation and MRI-monitoring : A new concept for minimally invasive procedures

In addition to the laser, microwave or other energy sources, interstitial thermotherapy with radio-frequency current (RFITT) in bipolar technique has already been shown in vitro to be a safe and an economical alternative energy source with a comparable operating performance. The therapeutical application efficiency of these bipolar RF-needle applicators was evaluated using 3 different types of probes: standard, flushed and high performance cooled RF-probes (3 mm). These can be used to create large coagulation volumes in tissue such as for the palliative treatment of liver metastases or the therapy of the benign prostate hyperplasia. It was shown that the achievable lesion size resulting from the cooled RF-probes could be increased by a factor of three compared to a standard bipolar probe. With these bipolar power RF-applicators, coagulation dimensions of 5 cm length and 4 cm diameter with a power input of 40 watt could be achieved within 20 minutes. No carbonization and electrode tissue adherence was observed. Investigations in vitro with adapted RFITT-probes, using paramagnetic materials such as titanium alloys and high performance plastic, have shown that monitoring under MRI (Siemens Magnetom, 1.5 Tesla) allows visualization of the development of the spatial temperature distribution in tissue using an intermittent diagnostic and therapeutical application. This is no loss in performance compared to continuous applications. A ratio of 1:4 (15 s Thermal Flash MRI, 60 s RF-energy) has shown to be feasible. A computer simulation of the temperature and damage distribution during a bipolar RFITT application has been developed. The simulation works on-line with a RF-generator and measures the output power continuously. The electric power density (heat generating term) and the damage distribution is displayed graphically in real time.

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.

Interstitial thermotherapy with bipolar rf applicators: computer-aided therapy control and monitoring

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.

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.

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.

High-frequency current application in bipolar technique for interstitial thermotherapy (HF-ITT)

For a minimally invasive treatment of pathologic tissue, e.g. tumors, the benign prostate hyperplasia (BPH) or the concha hyperplasia in otorhinolaryngology (ENT), next to the laser- induced interstitial thermotherapy (LITT) or the monopolar HF- surgery the interstitial thermotherapy with high-frequency alternating current (HF-ITT) in bipolar technique is a good alternative. Investigation results are presented which prove the feasibility and show the performance of this technique. Bipolar needles of different geometries, adapted to the various application fields, such as palliative treatment of metastatic carcinomas in liver and concha hyperplasia, were built and tested. Basic investigations of the thermal field distribution in in vitro samples were performed. The efficiency of the developed applicators were examined in in vitro experiments with porcine liver, turkey breast and porcine concha. Coagulation volumes of different needle diameters and power settings are show. Carbonization and dehydration can be avoided by irrigation of the tissue during treatment through integrated flushing ports and thus the performance is increased. For the treatment of concha hyperplasia special designs are presented which could probably offer an additional increase of safety and a simplification of performing a concha coagulation procedure. The new design of a bipolar needle electrode permits the surgeon the use of a partial application of high frequency current for ITT. Less power is needed due to the limited current distribution at the immediate operation site, which means that it is not necessary to fix the neutral electrode to the patient. Thus an easy to handle and a highly safe procedure can be performed by the surgeon.

Interstitial thermotherapy with bipolar electrosurgical devices

In addition to the laser, microwave or other energy sources, interstitial thermotherapy with radio-frequency current (RFITT) in bipolar technique has already been shown in vitro to be a safe and economical alternative energy source with a comparable operating performance. The bipolar technique is, from the technical point of view, completely without risk whereas with monopolar devices, where a neutral electrode has to be applied, an uncontrolled current flow passes through the patients body. The therapeutical application efficiency of these bipolar RF-needle applicators was evaluated using newly designed high performance flushed and cooled probes (qq 3 mm). These can be used to create large coagulation volumes in tissue such as for the palliative treatment of liver metastases or the therapy of the benign prostate hyperplasia. As a result, the achievable lesion size resulting from these flushed and internally cooled RF- probes could be increased by a factor of three compared to a standard bipolar probe. With these bipolar power RF- applicators, coagulation dimensions of 5 cm length and 4 cm diameter with a power input of 40 watt could be achieved within 20 minutes. No carbonization and electrode tissue adherence was found. Investigations in vitro with adapted RFITT-probes using paramagnetic materials such as titanium alloys and high performance plastic have shown that monitoring under MRI (Siemens Magnetom, 1.5 Tesla), allows visualization of the development of the spatial temperature distribution in tissue using an intermittent diagnostic and therapeutical application. This does not lead to a loss in performance compared to continuous application. A ratio of 1:4 (15 s Thermo Flash MRI, 60 s RF-energy) has shown to be feasible.

Computer simulation to model interstitial bipolar rf coagulation

A computer simulation has been developed of the temperature and damage distribution during a bipolar RFITT (radio- frequency current induced interstitial thermotherapy) application. The electric field and the heat transfer is calculated by the Finite Difference Method. The model considers the change of tissue parameters due to the heating process and the variation of power during an RFITT procedure. The simulation works on-line with an RF-generator and measures the output power continuously. The electric power density (heat generating term) and the damage distribution can be displayed graphically in real time.

Longitudinal vibration response of a curved fiber used for laser ultrasound surgical therapy (LUST)

A theoretical study of the longitudinal vibration response of a bent fiber used as an active element of a medical applicator for laser ultrasound surgical therapy (LUST) is presented. An important problem concerns taking into account fiber bending which may appear due to applications in endoscopy. NIR laser radiation and low frequency ultrasound (20 - 50 kHz) with amplitudes of up to 100 micrometers can be transmitted by silica glass fibers. The fiber cross- section is much smaller than the longitudinal wavelength. Wave propagation in the bent fiber is described by the governing second-order equations of motion which neglect the flexure effect. In contest to numerous works on bent rods, the case of an arbitrary continuous curvative distribution along the fiber is investigated. A simple analytical formula for the transfer function (the ratio of displacements at the working end of the fiber divided by those at the driven end) is obtained. The transfer function depends on frequency, fiber length, output impedance, loss factor, and the mean- square curvative of the fiber. The behavior of this function is investigated applied to some fibers whose lengths are of the order 1 m. If the displacement at the driven end of the fiber is known, the acoustical power output of the applicator can be found from the known values of the tissue impedance and the transfer function.

Die akustischen Übertragungseigenschaften von Lichtwellenleitern und deren Nutzbarkeit in der Medizintechnik

In der modernen Medizintechnik findet Ultraschall eine breite Anwendung. Niederfrequenter Ultraschall (20 50 kHz) wird in der Chirurgie zum selektiven Trennen von Gewebe (sog. CUSA-Technik) und zum Reinigen von Instrumenten eingesetzt. Hochfrequenter Ultraschall (bis 100 MHz wird für die Diagnostik (A-, B-Scan, Farbdoppler etc.) verwendet. Darüber hinaus gibt es eine Reihe anderer Anwendungen. Die für die Steinzertrümmemng extraund intrakorporal induzierten Stoßwellen besitzen Frequenzanteile bis zu 1 MHz. Der kommerzielle Einsatz des Ultraschalls wird bis heute unter anderem dadurch begrenzt, daß es für ihn keinen verlustarmen flexiblen Wellenleiter gibt. So führt z.B. die mikrokristalline Struktur von Titandrähten zu hohen Reibungsverlusten.