Laser Ablation Of Tissue Research Articles

Detection of Biological Molecules from Hard Biological Tissue Using Ion‐Beam‐Induced Desorption and Femtosecond Laser Ablation

AbstractSummary: In the last 10–15 years laser ablation became very popular for the analysis of solid samples. The study of laser‐matter interaction processes on different time scales – nano, pico, femto, and their application in different fields developed a thorough knowledge of the fundamental laws involved in this process. The intention in the current research was to determine the general features of different ablation processes (ns, fs) and ion beam desorption process. The aim was to perform a complete set of measurements of different target materials by means of mass spectrometry studies. More specifically, the mass spectra of ablated and sputtered particles from organic matter were studied. Time of flight mass spectrometer was used for detection. An investigation of the mechanism of laser ablation of biological tissue is a complicated problem due to the complexity of the examined organic material. In our experiments the main aim was to obtain optimal signal detection without the onset of considerable fragmentation. Comparison will be made between the mass spectra from biological samples obtained with laser ablation, and those obtained under bombardment with 9 keV‐accelerated Xe+ ions. As a general tendency in nanosecond ablation and in SIMS experiments the detection of higher mass molecular species is negligible in correspondence to femtosecond laser ablation mass spectra. This can be due to the process of heating that develops under ion bombardment. This work demonstrates the sensitivity of the TOF technique and the potential of using this method for exploring the dynamics of the laser ablation and ion beam desorption processes.An example of 20 µm holes drilled into vascular transplant‐grafts by 30 fs pulses.imageAn example of 20 µm holes drilled into vascular transplant‐grafts by 30 fs pulses.

XeCl Excimer Laser Ablation of Rabbit Tibia Bone: Morphology of the Irradiated Site and Self-Limiting Effect

The purpose of this work is to investigate the morphological changes of the rabbit tibia bone submitted to osteotomy with XeCl excimer laser. Laser ablation of tissue is a relevant clinical application of high-power lasers. Due to the variety of laser wavelengths and properties of biological targets, the subject has not yet been completely explored. In this study, four tibias were irradiated with six different durations. The applied energy density was 6.7 J/cm(2) per pulse at a 4-Hz repetition rate. The 24 samples had similar and well-defined craters that were free of carbonization. The ablation rates per pulse, at 60-120 seconds, were 3.8 and 1.9 microm at the compact bone and the marrow tissue, respectively. The ablation process ceased after 120 sec, with a 1.6-mm crater depth. In the present study, the laser used showed a self-limiting characteristic, which is a phenomenon that can be of great value in preserving important structures close to the working area, giving a margin of safety to the surgeon, in case of over-irradiation. This self-limiting effect is attributed to liquid filling the cavity by the bleeding and irrigation process.

In-situ Observation of Tissue Laser Ablation Using Optical Coherence Tomography

In laser ablation of biological tissue, tomography of the tissue surface is necessary for measurement of the crater shape and the crater depth. In this paper, we demonstrate in-situ observation of biological-tissue surface in laser ablation by optical coherence tomography (OCT). Depth of a crater of human tooth is measured by these OCT images, and then the ablation rate of 0.21 μm/pulse is determined.

Material ejection in nanosecond Er:YAG laser ablation of water, liver, and skin

We investigated the mechanisms of material ejection in Q-switched Er:YAG laser tissue ablation (70-ns pulse duration) where moderate and large radiant exposures are associated with large volumetric energy densities in the target material. For water, an initial phase of non-equilibrium surface vaporization is followed by an explosive vaporization of the superficial liquid volume from a supercritical state. The ablation of deeper layers with lower peak temperatures proceeds as phase explosion. For mechanically strong tissues, non-equilibrium surface vaporization is followed by a vapour explosion coupled with thermal dissociation of the biomolecules into volatile products. In deeper layers, ablation proceeds as confined boiling with mechanical tearing of the tissue matrix by the vapour pressure. The recoil stress induced at a radiant exposure of 5.4 J/cm2 is in the order of 500–900 MPa. For water and soft tissues such as liver, the recoil causes a powerful secondary material expulsion. For stronger tissues such as skin, no secondary expulsion was observed even though the recoil stress largely exceeds the static tensile strength of the tissue. Recoil-induced material expulsion results in an increase of both ablation efficiency and mechanical side effects of ablation. Theoretical modelling of the succession of phase transitions in nanosecond-laser tissue ablation and of recoil-induced material expulsion remain a major challenge for future work.

High-Power Thulium Fiber Laser Ablation of Urinary Tissues at 1.94 µm

This paper describes the preliminary testing of a new laser, the thulium fiber laser, as a potential replacement for the holmium:YAG laser for multiple applications in urology. A 40 W thulium fiber laser operating at a wavelength of 1.94 microm delivered radiation in a continuous-wave or pulsed mode (10 msec) through either 300-microm- or 600-microm-core low-OH silica fibers for vaporization of canine prostate and incision of animal ureter and bladder-neck tissues. The thulium fiber laser vaporized prostate tissue at a rate of 0.21+/-0.02 g/min. The thermal-coagulation zone measured 500 to 2000 microm, demonstrating the potential for hemostasis. Laser incisions were also made in bladder tissue and ureter, with coagulation zones of 400 to 600 microm. The thulium fiber laser has several potential advantages over the holmium laser, including smaller size, more efficient operation, more precise incision of tissues, and operation in either the pulsed or the continuous-wave mode. However, before clinical use will be possible, development of higher-power thulium fiber lasers and shorter pulse lengths will be necessary for rapid vaporization of the prostate and more precise incision of urethral/bladder-neck strictures, respectively.

Hollow-waveguide-based nanosecond, near-infrared pulsed laser ablation of tissue

Short-pulse solid-state lasers have recently received much attention as new coherent light sources for medical applications, but steady transmission of their high-energy output pulses through a solid quartz fiber is difficult because of the onset of laser-induced breakdown. We previously demonstrated that hollow waveguides could be used to deliver nanosecond laser pulses for tissue ablation. The aim of this study was to determine the optimum laser pulse energy and range of defocused distance for obtaining a deep and sharp ablation channel in myocardial tissue with laser pulses transmitted through a hollow waveguide. Cyclic-olefin-polymer-coated silver hollow waveguides of 1 mm in inner diameter and 1 m in length were used. A vacuum-cored scheme was applied to the waveguides to suppress laser-induced air breakdown. Porcine myocardial tissue was irradiated with 300 laser pulses that were delivered through the waveguide in vitro at various laser energy levels and defocused distances, and depths and diameters of channels were measured. Histological analysis of the ablated tissues was also performed. At an ablation energy of approximately 60 mJ/pulse, deep (>4.5 mm) and sharp (depth-to-diameter ratio of > 6) channels were created in tissue in the range of defocused distances of -4 approximately + 0.5 mm. Under these conditions, waveguide bending did not cause a remarkable change in ablation characteristics. Histological analysis of ablated tissue showed limited thermal damage but suggested a certain extent of mechanical effects in the tissue. With near-infrared, nanosecond laser pulses delivered through a cyclic-olefin-polymer-coated silver hollow waveguide, efficient and sharp ablation of myocardial tissue can be achieved, suggesting the usefulness of the hollow waveguide as a new flexible delivery system for high-intensity laser pulses.

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.

Mechanisms of Pulsed Laser Ablation of Biological Tissues

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mechanisms of Pulsed Laser Ablation of Biological Tissues (Chem. Rev. 2003, 103, 577−644. Published on the Web 02/12/03.)

Mechanisms of Pulsed Laser Ablation of Biological Tissues (<i>Chem. Rev.</i> <b>2003</b>, <i>103</i>, 577−644. Published on the Web 02/12/03.)

Mechanisms of pulsed laser ablation of biological tissues.

Author(s): Vogel, Alfred; Venugopalan, Vasan | Abstract: The mechanisms of pulsed laser ablation of biological tissues were studied. The transiently empty space created between the fiber tip and the tissue surface improved the optical transmission to the target and thus increased the ablation efficiency. It was found that the structure and morphology also affect the energy transport among tissue constituents.

Mechanism study of skin tissue ablation by nanosecond laser pulses

Understanding the fundamental mechanisms in laser tissue ablation is essential to improve clinical laser applications by reducing collateral damage and laser pulse energy requirements. In this dissertation, skin tissue ablation by nanosecond laser pulses has been studied from near infrared to ultraviolet for a clear understanding of the mechanism that can be used to enhance future design of pulsed lasers for dermatology and plastic surgery. Multiple laser and optical configurations have been constructed to generate 9–12 ns laser pulses at 1064, 532, 266, and 213 nm. Through histology and optical transmission measurements of ablation depth as a function of laser pulse energy, the 589 nm spectral line in the secondary radiation from ablated skin tissue samples was identified as the signature of the occurrence of ablation. Subsequently, this spectral signature has been used to investigate the probabilistic process of the ablation near the threshold at the four wavelengths. In addition, optical breakdown and backscattering in water were investigated along with a nonlinear refraction index measurement using a z‐scan technique. Preliminary studies on ablation of a gelatin based tissue phantom are also presented. The current theoretical models describing soft tissue ablation by short laser pulses were critically reviewed. A new plasma‐mediated model has subsequently been developed and a laser‐induced localized thermal ionization pathway has been investigated. It was found to have significant influence on the initial free electron density during plasma formation due to the combination of strong light absorption and subsequent confined temperature rise in chromophores. Good agreement has been found between the model and experimental results.

Laser ablation of soft tissue using a cryogenically cooled ablation cell

A cryogenically cooled ablation cell enables the direct analysis of thin sections from fresh soft tissue samples, such as liver or kidney, for trace elements using laser ablation ICP-MS. We show here, for the first time, that reproducibilities of about 2–6% can be achieved if the tissue sample can be ablated at a temperature below −60 °C. All ablation and detection parameters, such as energy, spot size, focus, fire frequency and integration time at the ICP-TOF-MS, were optimised. A calibration method using three different tissue samples (sheep kidney, pig liver and sheep liver), from which the bulk element concentrations were determined, was validated with CRM Pig Liver (LGC 7112), which was pressed and frozen in the form of a thin slice. Good recoveries (86–124% for the certified values) were achieved for Cd (0.31 mg kg−1; 0.25 ± 0.04 certified), Cu (101 mg kg−1; 117 ± 8 certified), Zn (43.0 mg kg−1; 43.0 ± 2.7 certified) and Mo (1.8 mg kg−1; ∼1 indicative value). Therefore this CRM can be used for the quantification of other tissues with similar C-content using a one-point calibration. Detection limits in the lower µg kg−1 range (Cd: 15 µg kg−1, Cu: 50 µg kg−1, Zn: 20 µg kg−1, Mo: 10 µg kg−1 and Pb: 2 µg kg−1) were determined based on 3σ of the blank signal with a spatial resolution of less than 200 μm. Using the CRM Pig Liver, it was shown that the use of an internal standard (13C) can account for fluctuations in the ablated material during a line scan. Instead of 12% RSD without internal standard, the stability of the signal was improved using the normalized signal (5.2%) compared to 2.5–3.5% precision when a NIST 610 Glass standard was ablated. Hence, LA coupled to ICP-MS with a cryogenically cooled ablation chamber is the ideal technique for 2D mapping of trace elements in soft tissues. Depending on the concentration of element present, it may be possible to determine trace elements directly in tissue samples at a spatial resolution of <20 µm.

What's new in pediatric obstructive sleep apnea

Obstructive sleep apnea syndrome (OSAS) is a common problem in children that may go unrecognized for several years. Although severe sequelae of OSAS may occur such as cor pulmonale and right-sided heart failure, the more common problems seen with OSAS are behavioral, including irritability, mood disturbances, inattentiveness, and daytime somnolence. Recent evidence suggests the potential for sustained adverse neurocognitive outcomes in snoring children. Most children with sleep apnea present with snoring, restless sleep, apneic spells, and have adenotonsillar hypertrophy. The diagnosis of OSAS is most accurately made by polysomnography, although overnight video or audio recording or pulse oximetry may be helpful. Nonsurgical treatment of OSAS includes the use of nasal steroids, oxygen, and continuous positive airway pressure or bilevel continuous positive airway pressure. The most common surgical treatment remains tonsillectomy and adenoidectomy, which is successful in resolving symptoms and physiologic changes due to OSAS. Alternatives include the use of radiofrequency or laser ablation of tissue, tongue suspension procedures, and skeletal surgery. Careful postoperative monitoring for complications is important in children with severe OSAS.

Nanosecond, high-intensity pulsed laser ablation of myocardium tissue at the ultraviolet, visible, and near-infrared wavelengths: in-vitro study.

A large number of clinical trials of transmyocardial laser revascularization (TMLR) have been conducted to treat severe ischemic heart diseases. A variety of laser sources have been used or tested for this treatment, however, no comprehensive study has been performed to reveal the mechanism and the optimum laser irradiation condition for the myocardium tissue ablation. There have been reported limited experimental data of the high-intensity pulsed laser ablation of myocardium tissues. A 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics were used for ablation experiments. At each wavelength, 25 laser pulses irradiated the porcine myocardium tissue samples at a constant laser intensity (peak laser power divided by laser spot area) of approximately 2 GW/cm(2) and the ablation depths were measured. During ablation, laser-induced optical and acoustic emissions were measured to investigate the ablation mechanism at each laser wavelength. For the ablated tissues, histological observation was made with a polarization optical microscope. It was shown that the ablation efficiency did not directly depend on the linear absorption coefficient of the tissue; the ablation depth was maximized at 355 and 1064 nm, and minimized at 532 nm. Strong laser-induced optical and acoustic emissions were observed for the 266- and 1064-nm laser irradiations. The histology showed that thermal denaturation of the tissue near the ablation walls decreased with decreasing wavelength for 266, 355, and 532 nm, but it was limited for 1064 nm. At the laser intensity of approximately 2 GW/cm(2), ablation characteristics were drastically changed for the different laser wavelengths. The results indicated that for 266, 355, and 532 nm, the tissue removal was achieved mainly through a photothermal process, but for 266 nm the intense laser-induced plasma formation would result in a reduced laser energy coupling to the tissue. For 1064 nm, a photodisruption was most probable as a dominant tissue removal process. Because of the high ablation rate and limited thermal denaturation, the 355- and 1064-nm lasers could be potential laser sources for TMLR, although further investigation is needed to discuss the clinical issues.

Nanosecond, high-intensity pulsed laser ablation of myocardium tissue at the ultraviolet, visible, and near-infrared wavelengths: In-vitro study

Background and Objective A large number of clinical trials of transmyocardial laser revascularization (TMLR) have been conducted to treat severe ischemic heart diseases. A variety of laser sources have been used or tested for this treatment, however, no comprehensive study has been performed to reveal the mechanism and the optimum laser irradiation condition for the myocardium tissue ablation. There have been reported limited experimental data of the high-intensity pulsed laser ablation of myocardium tissues. Study Design/Materials and Methods A 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics were used for ablation experiments. At each wavelength, 25 laser pulses irradiated the porcine myocardium tissue samples at a constant laser intensity (peak laser power divided by laser spot area) of ∼2 GW/cm2 and the ablation depths were measured. During ablation, laser-induced optical and acoustic emissions were measured to investigate the ablation mechanism at each laser wavelength. For the ablated tissues, histological observation was made with a polarization optical microscope. Results It was shown that the ablation efficiency did not directly depend on the linear absorption coefficient of the tissue; the ablation depth was maximized at 355 and 1064 nm, and minimized at 532 nm. Strong laser-induced optical and acoustic emissions were observed for the 266- and 1064-nm laser irradiations. The histology showed that thermal denaturation of the tissue near the ablation walls decreased with decreasing wavelength for 266, 355, and 532 nm, but it was limited for 1064 nm. Conclusion At the laser intensity of ∼2 GW/cm2, ablation characteristics were drastically changed for the different laser wavelengths. The results indicated that for 266, 355, and 532 nm, the tissue removal was achieved mainly through a photothermal process, but for 266 nm the intense laser-induced plasma formation would result in a reduced laser energy coupling to the tissue. For 1064 nm, a photodisruption was most probable as a dominant tissue removal process. Because of the high ablation rate and limited thermal denaturation, the 355- and 1064-nm lasers could be potential laser sources for TMLR, although further investigation is needed to discuss the clinical issues. Lasers Surg. Med. 29:464–473, 2001. © 2001 Wiley-Liss, Inc.

Dynamics of laser-induced cavitation bubbles near an elastic boundary

The interaction of a laser-induced cavitation bubble with an elastic boundary and its dependence on the distance between bubble and boundary are investigated experimentally. The elastic boundary consists of a transparent polyacrylamide (PAA) gel with 80% water concentration with elastic modulus E = 0.25 MPa. At this E-value, the deformation and rebound of the boundary is very pronounced providing particularly interesting features of bubble dynamics. It is shown by means of high-speed photography with up to 5 million frames s−1 that bubble splitting, formation of liquid jets away from and towards the boundary, and jet-like ejection of the boundary material into the liquid are the main features of this interaction. The maximum liquid jet velocity measured was 960 m s−1. Such high-velocity jets penetrate the elastic boundary even through a water layer of 0.35 mm thickness. The jetting behaviour arises from the interaction between the counteracting forces induced by the rebound of the elastic boundary and the Bjerknes attraction force towards the boundary. General principles of the formation of annular and axial jets are discussed which allow the interpretation of the complex dynamics. The concept of the Kelvin impulse is examined with regard to bubble migration and jet formation. The results are discussed with respect to cavitation erosion, collateral damage in laser surgery, and cavitation-mediated enhancement of pulsed laser ablation of tissue.

Er:YAG laser ablation of cerebellar and cerebral tissue.

With the availability of suitable fibres, the Er:YAG laser has become an indispensable tool for invasive neurosurgical applications as a source of precise ablation. The aim of this study was to investigate the ablative effects of the Er:YAG laser on brain tissue. The response of neuronal tissue to 2.94 microns Er:YAG laser irradiation was investigated on excised rat brain specimens. Ablation craters were created in cerebral and cerebellar tissues using 0.3, 0.5 and 1.0 J single pulses of 150 microseconds duration. The corresponding average irradiances were 37.7 J/cm2, 62.9 J/cm2 and 125.8 J/cm2, respectively. Craters were checked qualitatively, crater dimensions were measured and compared, and volume of ablated tissue was estimated. Laser-induced crater dimensions were found to be significantly different at different energy levels applied. Moreover, dimensions of craters on cerebral and cerebellar tissues were significantly different in terms of dimensions. We observed that with the Er:YAG laser ablation craters were created with practically no thermal damage to adjacent tissues. The differences observed in the response of cerebral and cerebellar cortical tissues were dependent on the anatomical and chemical differences.

Clinical application of laser-induced breakdown spectroscopy to the analysis of teeth and dental materials.

The luminous plasma generated during laser ablation of dental tissue and dental materials has been analyzed to determine qualitative and quantitative elemental composition. The use of pulsed lasers for controlled material ablation now is frequently suggested as an alternative to mechanical drilling for the removal of caries and in tooth modification. Spectral analysis of the ablated plasma can be exploited to monitor precisely the laser drilling process in vivo and in real time. Teeth samples and dental materials were ablated using pulses from a Nd:YAG laser. The line positions and intensities in the spectra, recorded in real time, were used to identify elements and to determine their relative concentrations. From the spectra of horizontally and vertically cut tooth slices, profiles of elemental distribution were determined; these were used in a range of monitoring applications. We showed that the transition from caries to healthy tooth material could be identified through the decrease in calcium (Ca) and phosphorus (P) concentrations, whereas nonmineralizing elements and organic materials increased in concentration. We also could relate the spatial distribution of elements to their migration or accumulation over time, for example, the migration of aluminium (Al) from dental restorative materials to the tooth matrix. The plasma existing during laser ablation (in vitro/in vivo) can be analyzed spectrally in real time. From the spectra, one can pinpoint high/low levels of element concentrations within the tooth matrix. Thus, this analysis could be used to monitor the ablation of material during laser dental treatment.

The predictability of corneal flap thickness and tissue laser ablation in laser in situ keratomileusis

Objective To evaluate the relationship between predicted flap thickness and actual flap thickness and between predicted tissue ablation and actual tissue ablation. Design Prospective, nonrandomized comparative (self-controlled) trial. Participants A total of 60 patients (102 eyes) who underwent laser in situ keratomileusis (LASIK). Main outcome measures Subtraction pachymetry was used to determine actual corneal flap thickness and corneal tissue ablation depth. Other measurements included flap diameter and keratometry readings. Results Actual flap thickness was significantly different ( P < 0.0001) from predicted flap thickness. Fifteen eyes had a predicted flap thickness of 160 μm and a mean actual flap of 105 μm (standard deviation [SD], ±24.3 μm; range, 48–141 μm). Sixty-four had a predicted flap of 180 μm with an actual flap mean of 125 μm (SD, ±18.5 μm; range, 82–155 μm). Seventeen eyes had a predicted flap of 200 μm, with an actual flap mean of 144 μm (SD, ±19.3 μm; range, 108–187 μm). In addition, we found that significantly more tissue ( P < 0.0001) was ablated than predicted. Linear regression of the observed ablation on predicted ablation yielded the following relationship: actual ablation = 14.5 + 1.5 (predicted ablation). Neither flap diameter nor flap thickness were found to increase with respect to steeper corneal curvatures. Conclusions Actual corneal flap thickness was consistently less than predicted regardless of the depth plate used; actual tissue ablation was consistently greater than predicted tissue ablation for the laser used in this study.

Laser ablation of granulation tissue at the tracheoesophageal puncture site

Laser ablation of granulation tissue at the tracheoesophageal puncture site