Laser Ablation Of Hard Tissues Research Articles

Thermal damage and the prognostic evaluation of laser ablation of bone tissue-a review.

In recent years, an increasing number of scientists have focused on conducting experiments on laser ablation of bone tissue. The purpose of this study was to summarize the prognosis of tissue and the extent of thermal damage in past hard tissue ablation experiments, and review the evidence for the feasibility of laser osteotomy in surgery. An electronic search of PubMed, China National Knowledge Infrastructure (CNKI), and Web of Science (WOS) for relevant English-language articles published through June 2023 was conducted. This review includes 48 literature reports on laser ablation of hard tissues from medical and biological perspectives. It summarizes previous studies in which the ideal ablation rate, depth of ablation, and minimal damage to bone tissue and surrounding soft tissues were achieved by changing the laser type, optimizing the laser parameter settings, or adding adjuvant devices. By observing their post-operative healing and inflammatory response, this review aims to provide a better understanding of pulsed laser ablation of hard tissues. Previous studies suggest that laser osteotomy has yielded encouraging results in bone resection procedures. We believe that low or even no thermal damage can be achieved by experimentally selecting a suitable laser type, optimizing laser parameters such as pulse duration and frequency, or adding additional auxiliary cooling devices. However, the lack of clinical studies makes it difficult to conclusively determine whether laser osteotomy is superior in clinical applications.

Optimizing controlled laser cutting of hard tissue (bone)

Abstract Conventional bone surgery leads to unwanted damage to the surrounding tissues and a slow healing process for the patients. Additionally, physicians are not able to perform free cutting shapes due to the limitations of available systems. These issues can be overcome by robot-assisted contactless laser surgery since it provides less mechanical stress, allows precise functional cuts, and leads to faster healing. The remaining drawback of laser surgery is the low ablation rate that is not yet competitive with conventional mechanical piezo-osteotomes. Therefore, we aim at maximizing the efficiency in hard tissue laser ablation by optimizing the lateral movement speed for different irrigation conditions. The results of this study show a non-linear relationship between cutting rates, speeds, and depths that should be critically considered for integration in robotic laser surgery.

Ultrafast dynamics of hard tissue ablation using femtosecond-lasers.

Several studies on hard tissue laser ablation demonstrated that ultrafast lasers enable precise material removal without thermal side effects. Although the principle ablation mechanisms have been thoroughly investigated, there are still open questions regarding the influence of material properties on transient dynamics. In this investigation, we applied pump-probe microscopy to record ablation dynamics of biomaterials with different tensile strengths (dentin, chicken bone, gallstone and kidney stones) at delay times between 1 picosecond and 10 microseconds. Transient reflectivity changes, pressure and shock wave velocities and elastic constants were determined. The result revealed that absorption and excitation show the typical well-known transient behavior of dielectric materials. We observed for all samples a photomechanical laser ablation process, where ultrafast expansion of the excited volume generates pressure waves leading to fragmentation around the excited region. In addition, we identified tensile-strength-related differences in the size of ablated craters and ejected particles. The elastic constants derived were in agreement with literature values. In conclusion, pressure-wave-assisted material removal seems to be a general mechanism for hard tissue ablation with ultrafast lasers. This photomechanical process increases ablation efficiency and removes heated material, thus ultrafast laser ablation is of interest for clinical application where heating of the tissue must be avoided.

Laser cutting of bone tissue under bulk water with a pulsed ps-laser at 532nm.

Hard-tissue ablation was already investigated for a broad variety of pulsed laser systems, which cover almost the entire range of available wavelengths and pulse parameters. Most effective in hard-tissue ablation are Er:YAG and CO2 lasers, both utilizing the effect of absorption of infrared wavelengths by water and so-called explosive vaporization, when a thin water film or water–air spray is supplied. The typical flow rates and the water layer thicknesses are too low for surgical applications where bleeding occurs and wound flushing is necessary. We studied a 20 W ps-laser with 532 nm wavelength and a pulse energy of 1 mJ to effectively ablate bones that are submerged 14 mm under water. For these laser parameters, the plasma-mediated ablation mechanism is dominant. Simulations based on the blow-off model predict the cut depth and cross-sectional shape of the incision. The model is modified considering the cross section of the Gaussian beam, the incident angle, and reflections. The ablation rate amounts to 0.2 mm3/s, corresponding to an increase by at least 50% of the highest values published so far for ultrashort laser ablation of hard tissue.

Characterization of multiphoton microscopy in the bone marrow following intravital laser osteotomy.

The bone marrow is an important site where all blood cells are formed from hematopoietic stem cells and where hematologic malignancies such as leukemia emerge. It is also a frequent site for metastasis of solid tumors such as breast cancer and prostate cancer. Intravital microscopy is a powerful tool for studying the bone marrow with single cell and sub-cellular resolution. To improve optical access to this rich biological environment, plasma-mediated laser ablation with sub-microjoule femtosecond pulses was used to thin cortical bone. By locally removing a superficial layer of bone (local laser osteotomy), significant improvements in multiphoton imaging were observed in individual bone marrow compartments in vivo. This work demonstrates the utility of scanning laser ablation of hard tissue with sub-microjoule pulses as a preparatory step to imaging.

Measurements of erbium laser-ablation efficiency in hard dental tissues under different water cooling conditions

Laser triangulation measurements of Er:YAG and Er,Cr:YSGG laser-ablated volumes in hard dental tissues are made, in order to verify the possible existence of a "hydrokinetic" effect that has been proposed as an alternative to the "subsurface water expansion" mechanism for hard-tissue laser ablation. No evidence of the hydrokinetic effect could be observed under a broad range of tested laser parameters and water cooling conditions. On the contrary, the application of water spray during laser exposure of hard dental material is observed to diminish the laser-ablation efficiency (AE) in comparison with laser exposure under the absence of water spray. Our findings are in agreement with the generally accepted principle of action for erbium laser ablation, which is based on fast subsurface expansion of laser-heated water trapped within the interstitial structure of hard dental tissues. Our measurements also show that the well-known phenomenon of ablation stalling, during a series of consecutive laser pulses, can primarily be attributed to the blocking of laser light by the loosely bound and recondensed desiccated minerals that collect on the tooth surface during and following laser ablation. In addition to the prevention of tooth bulk temperature buildup, a positive function of the water spray that is typically used with erbium dental lasers is to rehydrate these minerals, and thus sustaining the subsurface expansion ablation process. A negative side effect of using a continuous water spray is that the AE gets reduced due to the laser light being partially absorbed in the water-spray particles above the tooth and in the collected water pool on the tooth surface. Finally, no evidence of the influence of the water absorption shift on the hypothesized increase in the AE of the Er,Cr:YSGG wavelength is observed.

Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation

Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788±0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses.

Research advances in laser ablation of hard tissue

Laser ablation of hard tissue allows very precise pre-programmed incisions with complete free geometry and it has advantage of leaving no tissue damages. Those disadvantages of thermal side effects and low cutting rates had been overcome by introducing ultra-short pulses and ultra-power laser systems. This review highlights the recent advances in the laser ablation of hard tissues. Key words: Laser; Hard tissue; Ablation; Advances

Planning and simulation of microsurgical laser bone ablation

Laser ablation of hard tissue is not completely understood until now and not modeled for computer-assisted microsurgery. A precise planning and simulation is an essential step toward the usage of microsurgical laser bone ablation in the operating room. Planning the volume for laser bone ablation is based on geometrical definitions. Shape and volume of the removed bone by single laser pulses were measured with a confocal microscope for modeling the microsurgical ablation. To remove the planned volume and to achieve smooth surfaces, a simulation of the laser pulse distribution is developed. The confocal measurements show a clear dependency from laser energy and resulting depth. Two-dimensional Gaussian functions are fitting in these craters. Exemplarily three ablation layers were planned, simulated, executed and verified. To model laser bone ablation in microsurgery the volume and shape of each laser pulse should be known and considered in the process of ablation planning and simulation.

Thulium fiber laser lithotripsy: An in vitro analysis of stone fragmentation using a modulated 110-watt Thulium fiber laser at 1.94 µm

The high-power Thulium fiber laser has previously been shown to rapidly vaporize and coagulate soft urinary tissues (e.g., prostate). This is the first preliminary study of a high-power Thulium fiber laser for fragmentation of urinary stones. A continuous-wave, high-power Thulium fiber laser operating at a wavelength of 1.94 microm, was modulated to operate in pulsed mode with an output pulse energy of 1 J through a 300-microm-core silica fiber at a 20 milliseconds pulse length and repetition rate of 10 Hz. The fragmentation time to reduce uric acid (UA) (n = 13) and calcium oxalate monohydrate (COM) (n = 6) stones into particles < 2 mm was measured. Mean initial mass of the UA and COM stones measured 860+/-211 and 763 +/- 204 mg. Fragmentation rates measured 388 +/- 49 and 25 +/- 2 mg/minute. Average time needed to fragment the UA and COM stones into particles < 2 mm was 2.25 +/- 0.63 and 30.7 +/- 8.4 minutes, respectively. The high-power Thulium fiber laser, when operated in pulsed mode, is capable of fragmenting both soft (UA) and hard (COM) urinary stones. The Thulium fiber laser may be useful as a single laser system for use in multiple soft and hard tissue laser ablation applications in urology.

Measurement of Acoustic Transients During Pulsed Holmium:YAG Laser Ablation of Cadaveric Human Temporal Bone

Pulsed infrared (IR) and ultraviolet (UV) lasers have been suggested for use in middle ear surgery due to potential fiberoptic delivery, decreased thermal trauma and precise ablation characteristics. Although attention has been focused on the thermal and photoacoustic events that occur during pulsed laser ablation of hard tissue, there are few studies which evaluate the acoustic energy generated from these devices from an audiological standpoint. In this study, the mastoid cavities of cadaveric human temporal bones were irradiated with a holmium: yttrium aluminium garnet (Ho:YAG) laser (λ=2.12 µm) using the following parameters: 5, 10, and 15 Hz pulse repetition rate and 1, 2, 4, 6, 8, and 10 W average power. During ablation, acoustic measurements were made using a sound level meter positioned 5 cm away from the target site. With each set of laser parameters, the sound intensity exceeded 85 dB (dBA scale). Peak intensities of 125 dB were measured, and a saturation effect noted above 4 W or 500 mJ/pulse. The clinical significance of these findings is discussed and the acoustical aspects of middle ear function and noise trauma are reviewed.

Mechanism Associated with Excimer Laser Ablation of Hard-Tissue.

The mechanism associated with excimer laser ablation of hard tissue has been studied using fast photography and an electron probe micro analyzer (EPMA). A bovine femur was adopted as a modelof hard tissue. The ArF and KrF excimer lasers were used in this study. Time-resolved photographs of ablation plume were obtained using a microscope-mounted camera together with pulsed illumination from a XeCl excimer laser pumped dye solution. Ablation velocity and the start time of ablation were estimated. In addition, change in composition of bone surface was investigated by EPMA. The ratio of Calcium to Phosphor, which is an important parameter for determining the chemical characteristics of Hydroxyapatite, was estimated. Possible mechanisms to explain laser ablation were examined. The results indicated that theArF and KrF excimer lasers promoted primarily photothermal ablation. Photochemical ablation had occurred only in ArF excimer laser irradiation. Photomechanical ablation appeared to be negligible during ArF and KrF excimer laser ablation of bone.

Identification of photoacoustic transients during pulsed laser ablation of the human temporal bone: an experimental model.

Laser ablation of hard tissues during neurotologic operations has been accomplished with continuous-wave (CW) lasers in the visible and midinfrared spectrum. The mechanism of ablation at these wavelengths is secondary to photothermal-induced tissue destruction. As a result, significant thermal damage to surrounding tissue may occur. Pulsed ultraviolet (UV) lasers have been suggested as an alternative to the argon, KTP-532, and CO2 lasers currently used in clinical practice. The pulse length of Excimer lasers are considerably shorter than the thermal diffusion time of bone tissue, and as a consequence thermal injury is minimal. This makes pulsed lasers an attractive tool for tissue ablation in the ear: in essence a "cold knife." However, the short pulse width of Excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen. This study identifies the presence of these photoacoustic waves during the Excimer laser treatment of the cadaveric human temporal bone. A XeCl (lambda = 308 nm, tau p = 12 ns) excimer laser was used to ablate hard tissue surrounding the oval window and facial ridge with energies of 75, 45, 25, and 12 mJ/pulse. Spot size was estimated to be 0.5 mm2. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the promontory, round window niche, and facial ridges. The signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope. Photoacoustic waves were clearly identified. Notably, large acoustic waves were measured on the promontory and on both sides of the facial ridge. The implications and clinical relevance of these findings is discussed and compared to findings obtained from a model system.

Mechanism of dye-enhanced pulsed laser ablation of hard tissues: implications for dentistry

Alexandrite laser ablation of enamel enhanced by an indocyanine green dye was studied. A microjet system was employed to deliver precisely measured small amounts of absorbing dye solution to the site of irradiation. A sequence of physical phenomena involved in dye-enhanced laser ablation of dental enamel was revealed when laser pulse profiles were compared with the profiles of laser-induced pressure, laser-induced plasma, and ablation plume kinetics. To understand photomechanical effects on the enamel ablation, the absolute values of pressure waves were measured by a calibrated wide-band acoustic transducer. Absolute amplitude and temporal profile of pressure waves, plasma emission, ablation plume kinetics, ablation efficiency, and crater quality under free-running and and Q-switched ablation of enamel were studied. It was found that there is an optimal dye solution volume (100-200 nL) when the maximum ablation efficiency (30 μm/pulse) can be obtained. It was shown that the ablation efficiency under Q-switched laser irradiation is approximately one order of magnitude lower than that under free-running ablation. It was shown that Q-switched enamel ablation with dye solution is caused by the powerful recoil pressure wave with an amplitude 3-6.5 kbar. In contrast, dye-enhanced free-running enamel ablation is caused by plasma-mediated evaporation of enamel and accompanied by recoil pressure waves of lower amplitude (0.5-1 kbar) that is below mechanical damage threshold in enamel. Uneven crater walls after Q-switched ablation were observed by scanning electron microscopy (SEM). Free-running ablation makes precise craters with smooth and even crater walls.

Morphological study of Holmium : YAG laser ablation of hard tissue

Morphological study of Holmium : YAG laser ablation of hard tissue

Hard tissue laser ablation mechanisms

The aim of this work is the experimental and theoretical investigation of the influence of variable laser parameters (wavelength, fluence, pulse repetition rate) and of the optical and thermophysical properties of bone tissue (absorption coefficient, tissue inhomogeneity) as well as of the sample thickness on ablation thresholds and ablation rate. Ablation and perforation experiments were conducted using a semiconductively pre-ionized transverse excitation atmospheric pressure (TEA) carbon dioxide (CO2) laser (10.6Μm and a sliding discharge TEA [hydrogen fluoride (HF)] laser (2.9Μm). The experimental data are discussed with respect to the following ablation mechanisms: thermal melting and vaporization process, pressure oscillation of gases released by the thermal decomposition of collagen and/or apatite, stresses due to the expansion of superheated water.

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.