The protection of soft tissue structures behind the ablated bone in skull base surgery is mandatory. As the destruction of the membrane lining the inner ear can lead to a damage of organ functions (e.g. deafness or vertigo) a precise bone tissue removal by a laser ablation setup is investigated. For the detection of the boundary between soft tissue and bone the ablation area and rate are monitored by a video camera. Through this the laser is guided across the ablation area by image processing technologies. An aim of this project is a defined, navigated-controlled and laser based bone removal for the future buildup of a robot based surgical laser instrument. This publication describes the setup of our video controlled laser ablation system, initial experiments and results.

As the anatomic structures, for example bone thickness, are different and the destruction of the membrane lining the inner ear can lead to a damage of organ functions, for example deafness or vertigo, the protection of soft tissue structures behind the ablated bone in skull base surgery is mandatory. Consequently, a safer and more accurate Cochlear Implantation technology need to be developed urgently. For the detection of the boundary between soft tissue and bone the laser bone ablation system which was based on the combination of laser, robotics, coaxial monitoring and vision navigation was developed for a micro surgery at the skull base. Through this the laser is guided across the ablation area by vision navigation technologies. In this paper our laser bone ablation system and the first results of the boundary detection are described.

Background and Objectives: We report first results of animal trials using an improved laser osteotomy technique. This technique allows effective bone cutting without the usual thermal tissue damage.Study Design/Materials and Methods: A comparative in vivo study on mandibles of seven canines was done with a mechanical saw and a CO2 laser based osteotome with a pulse duration of 80 microseconds. The laser incisions were performed in a multipass mode using a PC-controlled galvanic beam scanner and an assisting water spray.Results: A complete healing through a whole bony rearrangement of the osteotomy gap with newly build lamellar Haversian bone was observed 22 days after the laser operations under optimal irradiation conditions.Conclusions: An effective CO2 laser osteotomy without aggravating thermal side effects and healing delay is possible using the described irradiation technique. It allows an arbitrary cut geometry and may result in new advantageous bone surgery procedures.

Systematic investigations on ablation of compact bone tissue with different CO2 laser systems are presented. Main attention is paid to the influence of the laser wavelength and pulse duration on the efficiency of the ablation.

The paper presents the project goals and first results of the network project ROLANDI (Robotic and Laser-Aided Navigation for Dental Implants). The combination of image guidance and laser surgery is a promising approach in dental implantology. The main advantage compared to conventional drilling is the contactless ablation process that diminishes residual movements of the patient. However, the accuracy of the entire registration chain - from the CT imaging via optical navigation to the positioning precision of the robotic laser tool holder - has to be investigated in the course of the project. We will present the methodology for the error propagation estimation and a novel laser-based procedure to obtain a ground truth.

The purpose of this study was to determine the laser side effects of cutting bone with a short-pulsed (80 μs) CO2 laser. To approximate living conditions, 10 samples of cortical bone and 10 rib segments were prepared immediately after sacrificing the pigs. The laser incisions were not accompanied with carbonization. At the border of the incisions, two narrow zones of damage were noted: an amorphous, intensively stained zone of 1–3 μm width and a wider, also sharply demarcated but faintly stained zone of 7–10 μm. A broader zone of about 50 μm was characterized by empty lacunae and osteocyte damage. The histological results indicated only minimal damage to bone ablated at the specified parameters.

Novel methods of laser measurements and interventions in the framework of image-guided surgery are presented. The first innovation concerns the basis of error propagation studies in registration chains from CT via OR navigator to the surgical laser tool holder. Here, we propose a holographic ground truth. The second innovation concerns a laser-based inherent sound-guidance principle for burr hole depth measurement.

Haemostatic and aseptic effects and intricate cut geometry are beneficial aspects of non-contact laser osteotomy. Collateral thermal damage, however, has severely limited the use of conventional lasers. The purpose of this study was to test the side effects on bone after cutting it with short CO 2 laser pulses and simultaneous application of a fine air–water spray. The 10.6 μm CO 2 laser emitted 80-μs pulses of 46 mJ energy, f=100 Hz, focused to a spot diameter of 130 ìm. Scan rate amounted to 40 mm/s. To approximate live conditions 10 samples of cortical bone and 10 rib segments were prepared immediately after sacrificing of pigs. A reference cut with a bandsaw and three laser cuts with an increasing number of beam passes (4, 16, 64) were performed on each sample. Half of the samples were decalcified in EDTA. The others were embedded in plastic to cut non-decalcified sections. The laser incisions were not accompanied by carbonisation. The incisions with slightly convergent walls were 150 ìm wide. The depths of the cavities increased with the number of the beam passes from approximately 0.5 mm (4 passes) to 3 mm (64 passes). At the border of the incisions two narrow zones of damage were noted: an amorphous intensively stained zone of 1–3 μm width and a wider, also sharply demarcated but faintly stained zone of 7–10 μm. A broader zone of about 50 μm was characterised by empty lacunae and osteocyte damage. These effects were not predictable; intact osteocytes were also observed near to the cut surface. Polarised light microscopy showed no alterations in the inorganic structure of the bone at the cut borders. The histological results indicated only minimal damage to bone ablated at the specified parameters. The described laser procedure might have advantages over mechanical instruments.

The purpose of this study was to determine the laser side effects of cutting bone with a short-pulsed (80 μs) CO2 laser. To approximate living conditions, 10 samples of cortical bone and 10 rib segments were prepared immediately after sacrificing the pigs. The laser incisions were not accompanied with carbonization. At the border of the incisions, two narrow zones of damage were noted: an amorphous, intensively stained zone of 1–3 μm width and a wider, also sharply demarcated but faintly stained zone of 7–10 μm. A broader zone of about 50 μm was characterized by empty lacunae and osteocyte damage. The histological results indicated only minimal damage to bone ablated at the specified parameters.

Haemostatic and aseptic effects and intricate cut geometry are beneficial aspects of non-contact laser osteotomy. Collateral thermal damage, however, has severely limited the use of conventional lasers. The purpose of this study was to test the side effects on bone after cutting it with short CO2 laser pulses and simultaneous application of a fine air-water spray. The 10.6 microm CO2 laser emitted 80 micros pulses of 46 mJ energy, f=100 Hz, focused to a spot diameter of 130 ìm. Scan rate amounted to 40 mm/s. To approximate live conditions 10 samples of cortical bone and 10 rib segments were prepared immediately after sacrificing of pigs. A reference cut with a bandsaw and three laser cuts with an increasing number of beam passes (4, 16, 64) were performed on each sample. Half of the samples were decalcified in EDTA. The others were embedded in plastic to cut non-decalcified sections. The laser incisions were not accompanied by carbonisation. The incisions with slightly convergent walls were 150 ìm wide. The depths of the cavities increased with the number of the beam passes from approximately 0.5 mm (4 passes) to 3 mm (64 passes). At the border of the incisions two narrow zones of damage were noted: an amorphous intensively stained zone of 1-3 microm width and a wider, also sharply demarcated but faintly stained zone of 7-10 microm. A broader zone of about 50 microm was characterised by empty lacunae and osteocyte damage. These effects were not predictable; intact osteocytes were also observed near to the cut surface. Polarised light microscopy showed no alterations in the inorganic structure of the bone at the cut borders. The histological results indicated only minimal damage to bone ablated at the specified parameters. The described laser procedure might have advantages over mechanical instruments.

The isotope-selective multiphoton dissociation of CHClF2 in a multipass refocusing Herriott cell was used to enrich more than 4 moles of chlorodifluoromethane to 99.99% of12C isotopic purity. It is the largest isotope quantity ever separated by a laser process. A cw excited mechanically Q-switched CO2 laser, which delivers 16 mJ pulses at 5 kHz was used. The enrichment controlled by a mass-spectrometer and guided by a PC was run with a rate of 25 g12C per 24 h.

By photochemical dissociation of the rare carbon isotope component of CHClF2 by means of a CO2 laser with an average power of 150 W, Q-switched at 10 kHz, we have demonstrated the separation of more than 1 mol of C-13, enriched to 50% (2 mol of total carbon). It is contained in about 1 mol (101 g) of the product C2F4. The total throughput of the starting material was 29 kg. The experiment was run day and night for 2 weeks, almost only controlled by a computer. We obtained production rates of 5 mmol/h, corresponding to about 0.5 kg C-13 per year.

C-13 isotope separation by multiphoton dissociation of CHClF2 was studied by a continous-discharge CO2 laser Q-switched at 8 kHz. This laser can easily emit two or more wavelengths with good spatial and temporal overlap. The best irradiation results were obtained by the line pair 9P16 + 9P28. After optimizing also the pressures of CHClF2 and of buffer gases (He and Ar), the energy density and the gas speed, the process is now much less nonlinear than in previous experiments with a single wavelength. Differences to the TEA laser induced process were observed, and generally the pressure influence on yield and selectivity showed a variety of phenomena. They were interpreted in terms of collisional changes of spectra during the laser pulse.

13C isotope separation by multiphoton dissociation of CHClF2 was studied by a continuous-discharge CO2 laserQ-switched at 8 kHz. This laser can easily emit two or more wavelengths with good spatial and temporal overlap. The best irradiation results were obtained by the line pair 9P16 + 9P28. After optimizing also the pressures of CHClF2 and of buffer gases (He and Ar), the energy density and the gas speed, the process is now much less nonlinear than in previous experiments with a single wavelength. Differences to the TEA laser induced process were observed, and generally the pressure influence on yield and selectivity showed a variety of phenomena. They were interpreted in terms of collisional changes of spectra during the laser pulse.

A low-pressure (20 mbar) CO2 laser allows to extract pulses at several selected wavelengths simultaneously from the same active medium. We demonstrated this, using an industrial laser modified by a Q-switch and a resonator with two branches. In one branch the wavelengths are spatially separated, whereas in the other they oscillate in one common transverse mode. We designed a multiwavelength resonator which requires a single additional reflector compared to usual laser cavities. It provided tunable oscillation at six wavelength simultaneously.

Laser osteotomy offers remarkable advantages, e.g. free cut geometry, over the conventional mechanical saw. Unlike the saw, however, the laser lacks haptic feedback during cutting. Based on ablation noise analysis, we are developing an acoustic-feedback system for laser osteotomy to obtain in situ information on the ablation within the tissue. We used a pulsed TEA CO2 laser (wavelength 9.57µm, pulse length 1µs/50ns FWHM, pulse energy 25 mJ) and piezoelectric transducers for sound detection. Various bone specimens as well as reference materials were stud- ied. For the determination of the ablation crater depth, we analyzed the time delay between the laser-induced acoustic signal from the surface of the specimen and the bottom of the ablation crater. The possibility of control- ling the cut depth in material with known acoustical properties with high precision is demonstrated. For acoustic tissue differentiation, we analyzed acoustic spectra initiated by laser pulses in different materials. The spectra show specific material-based features. This will prompt surgeons with information about the transi- tion from compact bone to other materials, e.g. soft tissue. An acoustic feedback system will eventually provide online control over the depth of the incision and ancillary recognition of the tissue exposed to the laser.