Erich Reichel

First Clinical Experience with a Q-Switched Neodymium: YAG Laser for Urinary Calculi

Animal studies using a high intensity nanosecond pulsed neodymium:YAG laser did not reveal any serious tissue damage. Following these investigations patient treatment was begun in June 1987. Laser energy of a neodymium:YAG laser with an 8 nsec. pulse duration and a repetition rate of up to 50 Hz. was coupled into a flexible 600 resp. 400 micron. quartz fiber. Laser-induced breakdown was created with 35 to 50 mJ. at the fiber tip, resulting in a shock wave that disintegrated the calculus into tiny fragments. A total of 56 patients with 58 calculi (54 ureteral and 4 kidney stones) was treated from June 1987 to March 1988. Of the calculi 48 could be fragmented completely, while 6 others were reduced to a size small enough to be removed with forceps. Four stones composed of calcium oxalate monohydrate could not be disintegrated. The combination of laser stone disintegration with flexible ureterorenoscopy implies the possibility of an atraumatic, 1-step procedure for fragmentation of ureteral and kidney calculi.

Study of different ablation models by use of high-speed-sampling photography

In our study we investigated the ablation characteristics of an aqueous dye solution with a defined absorption coefficient, irradiated by short (8 ns) and long (100 microsecond(s) ) pulses from a Nd:YAG laser (wavelength: 1064 nm). The experimental technique was schlieren photography with a second Nd:YAG laser at 532 nm as a light source and with a variable delay between the two laser pulses. With a special arrangement of the laser beams and the sample effects below and above the surface of the liquid could be simultaneously observed. We could distinguish three ablation mechanisms, depending on the pulse duration and the incident fluence. With short pulses and a fluence below the vaporization threshold the tensile pulse from the bipolar thermoelastic wave, propagating from the liquid-air interface into the sample, caused rupture and spallation of the liquid. At fluences generating a surface temperature in excess of 100 degree(s)C the short pulses caused explosive vaporization, characterized by shock wave emission both in air and in liquid. At the same fluence the long pulses caused slow vaporization, meaning that vapor and liquid ejection started during the laser pulse and was less violent than with the 8 ns pulses.

Contact Probes for Intravascular Laser Recanalization Experimental Evaluation

Experimental laser ablation of atheromatous plaques was performed with a bare quartz glass fiber, a metal probe, and a sapphire probe. The tissue response after irradiation with increasing energies was evaluated by means of light and scanning electron microscopy. Laser emission through the bare fiber caused a narrow, deep crater with an irregular surface surrounded by a zone of thermal necrosis. After tissue ablation with the metal probe, a disproportion between the small tissue defect and the large zone of thermal necrosis was observed. The largest tissue defect was vaporized by the sapphire contact probe. A small zone of thermal necrosis surrounded the laser crater.

Laser-induced shock wave lithotripsy

SummaryWith a high intensity Q-switched Nd-YAG laser shock waves can be generated in a liquid close to the calculus. Up to 80 mJ single pulse energy with 8 nsec pulse duration can be transmitted through flexible quartz fibers. Energy conversion and enhancement can be accomplished at the fiber tip with optical focussing of the light at the quartz tip, with irrigation solutions and with high pulse energies. Iron-III-dextran solutions (1 mg Fe3+/1) and magnesium chloride (50 mmol/l) increased the pressure in the laser induced breakdown up to ten times (8,000–10,000 bar). Smaller stone particles and higher efficacy in stone fragmentation could be achieved.

Morphologische Untersuchungen des Urothels nach Einwirkung intensiver Nanosekunden-Laserpulse

The energy of a Nd-YAG laser (1,064 nm wave length, 8 ns pulse duration) was used to irradiate the urothelium of the ureter or bladder and kidney parenchyma in pigs. Single pulse energy was 50-120 mJ with a 20-Hz repetition rate. The horizontal laser beam was reflected 90 degrees down by a 100% mirror and with a specially designed apparatus focussed on the surface of the tissue. Laser light from a quartz glass fiber was also focussed directly onto the tissue. Urothelium and kidney parenchyma were irradiated in 7 pigs. Tissue samples were examined histologically and raster electron microscopically 2, 4, 8 and 12 days after irradiation. No macroscopic lesion could be found. Maximum energy caused a small cone of 40 micron depth. No thermic effects or necrosis resulted, so that no harm is to be expected with unintentional irradiation.

Histological distinction of mechanical and thermal defects produced by nanosecond laser pulses in striated muscle at 1064 nm

For the therapeutic application of laser light it is necessary to minimize defects in the non-irradiated tissue. These defects depend on the primary mechanism of interaction which is determined by the duration of laser action. In the case of continuous wave laserlight a tissue layer surrounding the irradiated volume is thermally affected. On using laser pulsed with a certain energy this layer becomes smaller with decreasing pulse duration. With the pulses of a Q-switched laser tissue cutting will be obtained by the laser-induced breakdown (LIB). Thereby shockwaves are emitted which stress the tissue mechanically. Even in this case thermal lesions can be found. To be able to distinguish between thermal and mechanical effects by histological examination, experiments were performed with ns- and microsecond(s) -laserpulses under the same conditions. A Nd:YAG-laser at 1064 nm was used either Q-switched (pulse duration: 8 ns) or flashlamp-pulsed (100 microsecond(s) ) with a pulse repetition rate of 10 Hz. The beam was focused through air below the tissue surface (focal length in air: 80 mm). The beam geometry in the focal region was identical for both cases. The position of the focal plane relative to the surface was exactly controlled, as it influences extension and kind of the defect. To produce evaluable defects in the microsecond(s) experiments 200 laserpulses with an energy of 340 mJ per pulse had to be applied. The unfixed striated muscle samples of Sprague Dawley rats were immediately dissected prior to laser exposure. For the microsecond(s) experiments the defect region could be divided into 4 zones surrounding a crater, which was found at a focal plane position 2 mm below the surface. Zone 1 shows vacuoles and intensive staining. In zone 2 the myofibrils were displaced and torn apart. Zone 3 represents a sharply bordered intensively stained region. In zone 4 muscle cells are contracted. The zones are all of thermal origin, which could be derived from experiments, wherein an electrically heated wire was fixed inside the samples. In the ns experiments in general larger craters were found. Even a single laser pulse already produces a crater which did not happen in the microsecond(s) experiments. After the application of 5 to 10 pulses only some vacuoles could be found outside the crater. Increasing the number of pulse to 200 the picture is similar to that produced with microsecond(s) pulses. These results show that a few ns pulses suffice to form a crater. Additional ns-pulses lead to heat accumulation and produce thermal lesions like those of the microsecond(s) case and mechanical changes produced by shockwaves may be concealed.

Shock Wave Detection by Use of Hydrophones

Piezoelectric polyvinylidene-fluoride (PVDF-) foils are nowadays commonly utilised as transducer materials in shock wave detectors. The only few urn thick foils are excited in the thickness vibrational mode where the resolution in time is sufficiently high for ns phenomena. PVDF is only partially crystalline and therefore flexible as well as acoustically (nearly) transparent. Its piezoelectric constant amounts to 15 pC/N, yielding a sensitivity high enough for shock wave measurements without additional amplifiers.

Bifunctional irrigation liquid as an ideal energy converter for laser lithotripsy with nanosecond laser pulses

The intracorporal lithotripsy of ureter stones using laser pulses with a duration of 8 to 20 ns is carried out by means of energy converters. These devices have the purpose to transform the optical energy of the laserlight into mechanical energy of shockwaves, which cause the intended stone fragmentation. Therefore this method is independent of any optical property of the stone. For the endoscopic lithotripsy a continuous flow of irrigation liquid must be supplied to ensure a clear field of view and to transport the small stone fragments out of the body. In the case of the method developed by us, a second function is appointed to this liquid: the energy conversion. In transparent liquids, conversion of the optical energy is done by the laser-induced breakdown (LIB), which produces mechanical shockwaves. To release such a LIB, the laserpulse intensity must exceed a certain threshold. To achieve a LIB in the liquid at the fiber exit there are two possibilities. First, the fiber exit is spherically shaped, which leads to a kind of focus between fiber and stone. Second, the threshold intensity of the liquid is lowered. This is performed by addition of minimal amounts of Fe+++-ions. To obtain a stable and physiologically applicable irrigation solution the Fe+++-ions were added to isotonic saline solution in form of a dextran complex.

Effects of Laser Pulses on Cells and Tissue

Laser-induced shock wave lithotripsy with a Q-switched Nd-YAG laser was developed in Graz /1,2/ and, after thorough preliminary experiments, has been successfully introduced into clinical care. In vivo studies on pigs /3,4/ and in vitro studies on rat organs /5,6/ and human cell cultures have been done to investigate the effects of laser pulses on biologic material.

Intracorporeal Laser-Induced Shock-Wave Lithotripsy

Extracorporeal shock-wave lithotripsy (ESWL) has introduced a tremendous change in the management of patients with urinary stones. Patient morbidity has decreased as compared to other methods of stone removal, and only 10–25% of all patients need subsequent stone-particle manipulation by secondary percutaneous or transurethral methods. Impacted or very hard calculi in the ureter, especially when they are not surrounded by fluid, can only be crushed in about 40–50% of cases in situ, while the rest of the stone material has to be flushed up to the kidney and be disintegrated there. This procedure has to be done with small catheters or an endoscope since direct access to the stone is mandatory. Thus, there is still need for ureteroscopic manipulation.