The aim of the study was to compare the histological results after complete osteotomies of the sheep tibia using either the prototype carbon dioxide (CO2) laser osteotome ‘OsteoLAS’ (n = 12) or an oscillating saw (n = 12). The laser parameters were as follows: wavelength 10.6 µm; energy of laser pulses 75–85 mJ; pulse duration 80 μs; pulse repetition rate 200 Hz; spot diameter 460 μm (1/e2 level); radiant exposure 45–51 J/cm2; peak irradiance 0.56–0.64 MW/cm2. Both groups were divided into two subgroups (n = 6), and the animals were killed after 4 weeks or 12 weeks, respectively. Light and fluorescence microscopy with semiquantitative analysis and histomorphometry were performed to compare bone healing. Charring-free laser osteotomies were possible up to a depth of 20 mm with the short-pulsed CO2 laser. The laser, however, required a significantly longer time to perform, and a wedge-shaped gap was present on the cis-cortex. After 4 weeks the osteotomy gaps were almost unchanged in both groups and filled with connective tissue. After 12 weeks the gaps were filled with newly formed bone in both groups. Primary gap healing was predominant in the laser group and longitudinal cortical remodelling in the control group. On a cellular level, no fundamental differences were observed for early and late stages of bone healing. Further research has to be focussed on improving the CO2 laser ostetome in order to reduce the long duration of the laser osteotomy and the necessity of creating a wedge-shaped cut in thick bones.

OBJECTIVE:The purpose of this study was to examine for the first time the feasibility of performing complete osteotomy of sheep tibia using a computer-guided CO2-laser osteotome, and to examine bone healing under functional loading.BACKGROUND DATA:Bone cutting without aggravating thermal side effects has been demonstrated with scanning CO2-laser osteotomy. Further research is necessary to develop a clinically usable laser osteotome, which may allow new types of bone surgical procedures.MATERIALS AND METHODS:The scanning parameters for performing tibial osteotomies were determined in preliminary ex vivo trials. Osteotomies were performed in the mid-diaphysis of sheep tibia using either the prototype laser osteotome (osteoLAS, study group; n = 12), or an oscillating saw (control group; n = 12). Both groups were divided into two subgroups each (n = 6), and the two groups were sacrificed after 4 and 12 wk. Radiographs were taken postoperatively and after 4, 8, and 12 wk to compare the course of bone healing.RESULTS:Laser osteotomies of sheep tibia up to a depth of 20 mm were possible without visible thermal damage to the bone. A sequential PC-controlled cut geometry with artificial widening of the osteotomy gap was required for a complete osteotomy. Both clinically and radiologically, the laser and control groups showed undisturbed primary gap healing. Bone healing was similar and undelayed after both laser osteotomy and osteotomy done by mechanical saw.CONCLUSIONS:Osteotomy of multi-layered bones with a scanning CO2-laser demonstrates clinical and radiological healing patterns comparable to those seen with osteotomy done by standard mechanical instruments. It is, however, a technically demanding procedure, and complete laser osteotomies of long bones are only reasonable in bones with a diameter <20 mm, which will likely restrict the use of this technique to bones 7-10 mm thick. Through the use of computer guidance, extremely precise osteotomies and sophisticated cut geometries are possible using this technique. For practical applications, precise control of the depth of laser cutting and easier manipulation of the osteotome are required.

The advantages of laser osteotomy are free cut geometry and minimal thermal damage. Due to the lack of haptic feedback there is need for an alternate feedback method for accurate Laser Osteotomy. Based on the frequency analysis of the acoustic signal, generated by the ablation process, we are developing a feedback system to obtain in situ information on the ablation and for differentiation between different sorts of biological tissue. We used a pulsed slab CO2-laser (wavelength 10.6 µm, pulse length 80 µs) and piezoelectric sensors for sound detection. We studied the correlation of the ablation signal of different kinds of tissue in the frequency domain.

Drilling of bone and tooth tissue belongs to recurrent medical procedures (screw- and pin-bores, bores for implant inserting, trepanation etc.). Small round bores can be in general quickly produced with mechanical drills. Problems arise however by angled drilling, by the necessity to fulfill the drilling without damaging of sensitive soft tissue beneath the bone, or by the attempt to mill precisely noncircular small cavities. We present investigations on laser hard tissue "milling", which can be advantageous for solving these problems. The "milling" is done with a CO2 laser (10.6 &mgr;m) with pulse duration of 50 - 100 &mgr;s, combined with a PC-controlled galvanic beam scanner and with a fine water-spray, which helps to avoid thermal side-effects. The damaging of underlying soft tissue can be prevented through control of the optical or acoustical ablation signal. The ablation of hard tissue is accompanied with a strong glowing, which is absent during the laser beam action on soft tissue. The acoustic signals from the diverse tissue types exhibit distinct differences in the spectral composition. Also computer image analysis could be a useful tool to control the operation. Laser "milling" of noncircular cavities with 1 - 4 mm width and about 10 mm depth is particularly interesting for dental implantology. In ex-vivo investigations we found conditions for fast laser "milling" of the cavities without thermal damage and with minimal tapering. It included exploration of different filling patterns (concentric rings, crosshatch, parallel lines and their combinations), definition of maximal pulse duration, repetition rate and laser power, optimal position of the spray. The optimized results give evidences for the applicability of the CO2 laser for biologically tolerable "milling" of deep cavities in the hard tissue.

Non-contact laser osteotomy offers new opportunities in various surgical fields, since it allows very precise pre-programmed incisions with completely free geometry. However laser osteotomy is a demanding task, because bone is a tough composite material, which is at the same time a living tissue and sensitive to temperature increases. Besides thermal side effects, practical laser applicability was limited until now because of very low cutting rates and limited incision depths. We discuss how to overcome these disadvantages by means of an optimal arrangement of thermo-mechanical ablation with a pulsed CO2 laser and with a water-spray as an assisting media. To this arrangement belong optimal pulse duration, irradiance and radiant exposure of the laser pulses, as well as multi-pass cutting procedures. Effective ablation of hard bone tissue with minimal thermal damage is possible with relatively long CO2 laser pulses of 80 mu s duration and an average laser power of up to 40 W. To overcome the depth limitation special scanning techniques, which allow deep incisions even in thick multi-layer bones in feasible irradiation times, were developed in our group.

Drilling and surface processing of bone and tooth tissue belongs to standard medical procedures (bores and embeddings for implants, trepanation etc.). Small circular bores can be generally quickly produced with mechanical drills. However problems arise at angled drilling, the need to execute drilling procedures without damaging of sensitive soft tissue structures underneath the bone or the attempt to mill small non-circular cavities in hard tissue with high precision. We present investigations on laser hard tissue "milling", which can be advantageous for solving these problems. The processing of bone is done with a CO2 laser (10.6 &mgr;m) with pulse durations of 50 - 100 &mgr;s, combined with a PC-controlled fast galvanic laser beam scanner and a fine water-spray, which helps keeping the ablation process effective and without thermal side-effects. Laser "milling" of non-circular cavities with 1 - 4 mm width and about 10 mm depth can be especially interesting for dental implantology. In ex-vivo investigations we found conditions for fast laser processing of these cavities without thermal damage and with minimised tapering. It included the exploration of different filling patterns (concentric rings, crosshatch, parallel lines, etc.), definition of maximal pulse duration, repetition rate and laser power, and optimal water spray position. The optimised results give evidence for the applicability of pulsed CO2 lasers for biologically tolerable effective processing of deep cavities in hard tissue.

Non-contact laser osteotomy brings new opportunities in maxillofacial and other surgical fields, since it allows very precise pre-programmed incisions of arbitrary geometries. Laser osteotomy is however difficult, because bone is a tough composite material, which is at the same time sensitive to a temperature increase. Besides thermal side effects, practical laser applicability was limited until now because of very low cutting rates and limited incision depths. We discuss how to overcome these disadvantages by means of an optimal arrangement of thermo-mechanical ablation with a pulsed CO2 laser and with a water-spray as an assisting media. To the arrangement belong optimal duration, intensity and energy density of the laser pulses, as well as a multi-pass cutting procedure. We show that effective ablation of hard tissue with minor thermal damage is possible with relatively long CO2 laser Pulses of 80 mu s duration and average laser power up to 40 - 50 W. To overcome the depth limit we have developed a special scanning technique, which allows cutting of massive multilayer bones with a feasible rate.

BACKGROUND:Current, invasive cerebral oxygenation monitors require either retrograde jugular venous bulb cannulation or intraparenchymal probe insertion. There is no accurate, noninvasive, continuous monitor of cerebral blood oxygenation.METHODS:The authors designed, built, and tested novel optoacoustic instrumentation that continuously measures blood oxygenation in the superior sagittal sinus (SSS) in vivo in 12 anesthetized sheep. In this technique, laser pulses generate acoustic signals, the amplitudes and slopes of which are proportional to oxyhemoglobin saturation in the SSS. Optoacoustic signals from the SSS measured through the scalp and cranium were compared with directly measured oxyhemoglobin saturation in blood withdrawn from the cannulated SSS.RESULTS:In the first experiments (feasibility), FIO2 changes produced rapid corresponding changes in optoacoustic signals and arterial oxygen saturation. In the second experiments (validation), the authors correlated oxyhemoglobin saturation in the SSS with optoacoustic signals and developed quantifying algorithms. In eight of nine validation experiments, the authors quantified optoacoustic signals by subtracting the temporal profile at low FIO2 (0.08-0.1) from profiles at higher FIO2 and integrating those signals in the range from 3 to 5 micros. In each validation experiment, optoacoustic signals showed tight temporal association and good linear correlation with measured oxyhemoglobin saturation (r2 0.75 to 0.99 for eight individual experiments).CONCLUSIONS:The optoacoustic system detects signals induced in the SSS and optoacoustic signals from the SSS linearly correlate with oxyhemoglobin saturation. The data suggest that the optoacoustic technique merits clinical evaluation.

Results of systematic measurements of the ablation parameters for hard bone tissue by application of different CO2 lasers with wavelength of 9.6 and 10.6μm, pulse durations from 40ns up to 225μs and diverse focusing conditions are described. Influence of thermal diffusion, absorption in ablation debris and other physical processes on the ablation characteristics and preconditions for effective ablation with minimal thermal side effects are discussed. The main features of the mobile system for laser osteotomy and first results with this system are presented.

The optoacoustic technique was tested in vivo for noninvasive monitoring of cerebral blood oxygenation. Linear correlation of optoacoustic signals with actual blood oxygenation in the superior sagittal sinus in sheep was demonstrated.

We proposed to monitor cerebral blood oxygenation by measuring optoacoustic waves induced in the superior sagittal sinus (SSS), a large central cerebral vein. We performed in vitro and in vivo in sheep testing of the optoacoustic technique that accurately measures blood oxygenation by using the well-established differences in the optical absorption coefficients of oxy- and deoxyhemoglobin in the near IR spectral range. Laser optoacoustics overcomes the problem of loss of diagnostic information due to strong light scattering that inevitably complicates pure optical techniques.

Non-contact laser osteotomy offers new opportunities in various surgical fields, since it allows very precise pre-programmed incisions with completely free geometry. However laser osteotomy is a demanding task, because bone is a tough composite material, which is at the same time a living tissue and sensitive to temperature increases. Besides thermal side effects, practical laser applicability was limited until now because of very low cutting rates and limited incision depths. We discuss how to overcome these disadvantages by means of an optimal arrangement of thermo-mechanical ablation with a pulsed CO2 laser and with a water-spray as an assisting media. To this arrangement belong optimal pulse duration, irradiance and radiant exposure of the laser pulses, as well as multi-pass cutting procedures. Effective ablation of hard bone tissue with minimal thermal damage is possible with relatively long CO2 laser pulses of 80 �s duration and an average laser power of up to 40 W. To overcome the depth limitation special scanning techniques, which allow deep incisions even in thick multi-layer bones in feasible irradiation times, were developed in our group.