Laser Ablation Of Soft Tissues Research Articles

Methodology for the Implementation of Internal Standard to Laser-Induced Breakdown Spectroscopy Analysis of Soft Tissues.

The improving performance of the laser-induced breakdown spectroscopy (LIBS) triggered its utilization in the challenging topic of soft tissue analysis. Alterations of elemental content within soft tissues are commonly assessed and provide further insights in biological research. However, the laser ablation of soft tissues is a complex issue and demands a priori optimization, which is not straightforward in respect to a typical LIBS experiment. Here, we focus on implementing an internal standard into the LIBS elemental analysis of soft tissue samples. We achieve this by extending routine methodology for optimization of soft tissues analysis with a standard spiking method. This step enables a robust optimization procedure of LIBS experimental settings. Considering the implementation of LIBS analysis to the histological routine, we avoid further alterations of the tissue structure. Therefore, we propose a unique methodology of sample preparation, analysis, and subsequent data treatment, which enables the comparison of signal response from heterogenous matrix for different LIBS parameters. Additionally, a brief step-by-step process of optimization to achieve the highest signal-to-noise ratio (SNR) is described. The quality of laser–tissue interaction is investigated on the basis of the zinc signal response, while selected experimental parameters (e.g., defocus, gate delay, laser energy, and ambient atmosphere) are systematically modified.

Mechanisms for soft‐tissue ablation and the development of alternative medical lasers based on investigations with mid‐infrared free‐electron lasers

AbstractExperimental evidence indicating the potential biomedical advantages of using a Mark‐III Free‐Electron Laser (FEL) for the ablation of soft tissue were first reported in 1994. Research progress since that time is reviewed, including: 1) successful human surgery using the Mark‐III FEL; 2) advances in understanding the physical mechanism for infrared tissue ablation and how these mechanistic features correlate with the preferential ablative properties; 3) the pursuit of table‐top, nanosecond‐pulsed laser technology that mimics the preferential ablation properties of the Mark‐III FEL with the aim of improving clinical acceptance of mid‐infrared laser ablation of soft tissue; and 4) current research challenges.

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.

Theoretical model of CO2 laser ablation of soft-tissue phantoms

A model of thermal laser ablation of soft tissues is developed taking into consideration two mechanisms: evaporation and liquid moving, due to vapour pressure gradient. Usually a soft tissue is modelled as a single-component material with thermal and optical properties very similar to those of water. We examined the non-stable kinetics of the evaporation process, for short-pulse infrared laser ablation of soft tissues, and we also calculated the average liquid velocity and the ablation rates under vapour pressure gradient. The theoretical results are in good agreement with previous reported experimental data on gelatin and polyacrylamide tissue phantoms

Pulsed laser ablation of soft tissues, gels, and aqueous solutions at temperatures below 100 degrees C.

It is desirable for laser microsurgical procedures to remove tissue accurately and with minimal thermal and mechanical damage to adjacent non-irradiated tissues. Pulsed laser ablation can potentially remove biological tissue with microprecision if appropriate irradiation conditions are applied. The major goal of this study was to determine whether laser ablation is possible at temperatures below 100 degrees C. Another aim was to test thermoelastic and recoil stress magnitudes and to estimate their effects on phantom and biological tissue. Pulsed laser ablation of water (aqueous solution of potassium chromate) and water containing soft tissues (collagen gel and pig liver) irradiated under confined stress conditions was studied. The ablation mechanism and stages of the ablation process were determined based on time-resolved measurements of laser-induced acoustic waves with simultaneous imaging of the ablation process by laser-flash photography. This study reveals the important role of tensile thermoelastic stress, which produces efficient cavitation that drives material ejection at temperatures substantially below 100 degrees C. Ablation thresholds for the aqueous solution, collagen gel, and liver were 20, 38, and 55 J/cm3, respectively, which correspond to temperature jumps of 5, 10, and 15 degrees C. Two distinct stages of material ejection were observed: (1) initial removal of small volumes of material due to the rupture of single subsurface bubbles, (2) bulk material ablation in the form of jets produced by intense hydrodynamic motions formed upon collapse of large bubbles after coalescence of smaller bubbles. The duration of material ejection upon short-pulse ablation may vary from microseconds to submilliseconds, and depended on the mechanical properties of materials and the incident laser fluence. Nanosecond laser ablation of water, gels, and soft tissue under confined-stress conditions of irradiation may occur at temperatures below 100 degrees C. This ablation regime minimizes thermal injury to adjacent tissues and involves thermoelastic stress and recoil pressure magnitudes, which may be tolerated by tissues adjacent to an ablated crater.

Excimer laser ablation of soft tissue: a study of the content of rapidly expanding and collapsing bubbles

Both holmium (/spl lambda/=2.09 /spl mu/m) and excimer (/spl lambda/=308 nm) lasers are used for ablation of tissue. In a previous study, excimer laser ablation of aorta produced rapidly expanding and collapsing vapor bubbles. To investigate whether the excimer-induced bubble is caused by vaporization of (tissue) water, the threshold fluence for bubble formation at a bare fiber tip in water and on tissue was compared between the excimer laser (pulse length 115 ns) and the Q-switched and free-running holmium lasers (pulse length 1 /spl mu/s and 250 /spl mu/s, respectively). To induce bubble formation by excimer laser light in water, the absorber Oxybuprocaine-hydrochloride (OBP-HCl) was added to the water. Fast flash photography was used to measure the threshold fluence as a function of the water temperature (6-90/spl deg/C) at ambient pressure and as a function of the boiling temperature of water (100-184/spl deg/C) at augmented environmental pressures (1-11 bar). For both the holmium and excimer laser, the threshold fluence for bubble formation decreased proportionally with increasing water temperature (correlation coefficient r=0.95-0.99). Correspondingly, the threshold fluence for bubble formation increased with increasing boiling temperature of water. A similar correlation was found for the excimer laser-induced bubble formation on tissue. Furthermore, for both the holmium and the excimer laser, the threshold fluence for water vaporization was much lower than theoretically predicted values. It is concluded that the principal content of the large (up to 3 mm), short lived ( >

XeCl laser ablation of atherosclerotic aorta: Luminescence spectroscopy of ablation products

XeCl laser ablation of atherosclerotic aorta tissue was investigated. Luminescence spectra of ablation products were measured for soft and hard arterial tissues. A pronounced difference observed between plume luminescence for various plaques and normal vessel wall correlates with the chemical composition of the tissue. The mechanism of plume luminescence appeared to be thermochemical excitation ablation products (particles, atoms, molecules, etc.) in the air. The process of soft tissue ablation was delayed with respect to the exciting laser pulse at relatively low laser fluences close to the ablation threshold. The kinetics of the ablation process as a function of laser-pulse energy fluence is reported. The data indicate that tissue ejection mechanism, which involves vapor bubbles formation, expansion and explosion, is suitable for the description of the XeCl excimer laser ablation of soft tissues.

XeCl laser ablation of atherosclerotic aorta: optical properties and energy pathways.

The energetics of 308-nm excimer laser irradiation of human aorta were studied. The heat generation that occurred during laser irradiation of atherosclerotic aorta equaled the absorbed laser energy minus the fraction of energy for escaping fluorescence (0.8-1.6%) and photochemical decomposition (2%). The absorbed laser energy is equal to the total delivered light energy minus the energy lost as specular reflectance (2.4%, air/tissue) and diffuse reflectance (11.5-15.5%). Overall, about 79-83.5% of the delivered light energy was converted to heat. We conclude that the mechanism of XeCl laser ablation of soft tissue involves thermal overheating of the irradiated volume with subsequent explosive vaporization. The optical properties of normal wall of human aorta and fibrous plaque, both native and denatured were determined. The light scattering was significant and sufficient to cause a subsurface fluence (J/cm2) in native aorta that equaled 1.8 times the broad-beam radiant exposure, phi o (2.7 phi o for denatured aorta). An optical fiber must have a diameter of at least 800 microns to achieve a maximum light penetration (approximately 200 microns for phi o/e) in the aorta along the central axis of the beam.