Laser-light induced chromosome aberrations in Chinese hamster cells.

Wild-type Chinese hamster cells CHO K1 and their radiosensitive mutant xrs5 were irradiated at 308 nm, using light pulses of a XeCl excimer laser with total energy fluences of 0.1 kJ/m2 to 4.08 kJ/m2. Chromosome-type and chromatid-type chromosome aberrations have been observed at pulse irradiances of 2.5 x 10(7) W/m2 and 1.7 x 10(8) W/m2, indicating that in mammalian cells DNA double-strand breaks occur already in this irradiance range. The results obtained with laser irradiation are compared with X-ray irradiation.

Double-pulse technique for optical emission spectroscopy of ablation plasmas of samples in liquids.

Sharp atomic and ionic line spectra of excimer-laser-induced ablation plasmas of samples in liquids were observed. A new double-pulse technique employing quartz fibers facilitates spectral analysis of samples in liquids in which spectral lines normally are strongly broadened and quenched. The first pulse generates a cavitation bubble on the sample surface, which provides a gaseous environment for optical emission spectroscopy on the ablation plasma induced by a second pulse fired into the bubble.

Macroscopic and microscopic findings after excimer laser treatment of different tissue.

In reported tests, the interaction of excimer laser radiation with bone, meniscus, and tendon tissue was observed. Depending on various laser parameters, different tissue reactions were observed in all procedures. Ablation was performed in a liquid medium to ensure extended carbonizations even at low application energy and repetition rate. Our studies revealed that the longer the pulse, the lower the destruction rate of fibers. However, a longer pulse caused lower ablation rates than a shorter one. An increase of repetition rate instead of an increase of application energy resulted in higher heat accumulation in the adjacent tissue. Differentiation of the single parameters on various tissue allows flexibility of thermal effects from the laser procedure.

[Ablation of hard biological tissue with the excimer laser]. / Abtragung von biologischem Hartgewebe mit dem Excimerlaser.

Cutting and drilling of bone- and meniscus tissue were performed using a XeCl-excimer laser combined with a tapered fiber. Ablation speed on meniscus tissue is already sufficient, the thermal damage of the adjacent tissue is minimal. Increasing of energy transmission through special fibers promises higher ablation rates also on hard biological tissue and that promoted the interest in lasers again for accident surgeons.

New tool combination: XeCl-excimer laser and tapered fiber enhances potential for atraumatic hard tissue operations.

XeCl excimer lasers have already been used to ablate bone, however, until now the results have been unsatisfactory until now. First, ablation of bone in air produced macroscopic noticeable carbonizations similar to those produced by thermal infrared lasers. Second, ablation rates were very low even on meniscus tissue. A new tool combination, XeCl excimer laser and tapered fibers, obtain higher ablation rates, because of its efficient light guiding capability. Using a liquid medium (water, normal saline solution) during laser application prevents macroscopic noticeable carbonizations.

Ultrafast imaging of tissue ablation by a XeCl excimer laser in saline.

To determine the temporal evolution of laser induced tissue ablation, arterial wall specimens with either hard calcified or fatty plaques and normal tissue were irradiated in a 0.9% saline solution using a XeCl excimer laser (wavelength 308 nm, energy fluence 7 J/cm2, pulse width 30 ns) through a 600 microns fused silica fiber pointing perpendicular either at a 0.5 mm distance or in direct contact to the vascular surface. Radiation of a pulsed dye laser (wavelength 580 nm) was used to illuminate the tissue surface. The ablation process and the arising bubble above the tissue surface were recorded with a CCD camera attached to a computer based image-processing system. Spherical cavitation bubbles and small tissue particles emerging from the irradiated area have been recorded. The volume of this bubble increased faster for calcified plaques than for normal tissue.

Studies in fiber guided excimer laser surgery for cutting and drilling bone and meniscus.

Our experiments on transmitting high-power excimer laser pulses through optical fibers and our investigations on excimer laser ablation of hard tissue show the feasibility of using the excimer laser as an additional instrument in general and accident surgery involving minimal invasive surgery. By combining XeCl-excimer lasers and tapered fused silica fibers we obtained output fluences up to 32 J/cm2 and ablation rates of 3 microns/pulse of hard tissue. This enables us to cut bone and cartilage in a period of time which is suitable for clinical operations. Various experiments were carried out on cadavers in order to optimize the parameters of the excimer laser and fibers: e.g., wavelength, pulse duration, energy, repetition rate, fiber core diameter. The surfaces of the cut tissue are comparable to cuts with conventional instruments. No carbonisation was observed. The temperature increase is below 40 degrees C in the tissue surrounding the laser spot. The healing rate of an excimer laser cut is not slower than mechanical treatments; the quality is comparable.

[Ablation of the trabecular meshwork]. / Die Ablation des Trabekelwerks.

In an experimental investigation we examined the possibility to create an open pathway between the anterior chamber and Schlemm's canal by excimer laser ablation of the trabecualr meshwork (AT) in enucleated eyes. A quartzfiber was directed through the anterior chamber to the opposite chamber angle. With an energy of 0.3-1.5 mJ and wavelengths of 248 and 308 nm pores were easily made into the trabecular meshwork leading to a direct connection between the anterior chamber and Schlemm's canal. This result was confirmed by histologic examination of the globes. The trabecular meshwork has disappeared completely. The surrounding tissue reveals only minimal thermal effects due to the laser burns. With the same method cyclodialysis and basal iridectomy may be performed. The operation is simple and effects can be placed with great accuracy.