Studies of acoustical and shock waves in the pulsed laser ablation of biotissue

Abstract

Quantitative studies are conducted into the absolute pressure values of the acoustical and shock waves generated and propagating in a biotissue under pulsed (tau p = 50 ns) UV (lambda = 308 nm) laser irradiation (below and above the ablation threshold). Powerful (several hundreds of bars in pressure) high-frequency (f approximately 10(7) Hz) acoustic compression and rarefaction pulses are found to be generated in the biotissue. The amplitudes and profiles of the acoustic pulses developing in atherosclerotic human aorta tissues and an aqueous CuCl2 solution under laser irradiation are investigated as a function of the laser pulse energy fluence. The results obtained point to the absence of the cold spallation of the objects of study by rarefaction waves. Based on experimental data, the rise rates, pressure gradients, and propagation velocities of shock waves in the biotissue are calculated. The experimental data are found to agree well with the theoretical estimates.

Time and Frequency Resolved XeCl Laser-Induced Mechanical Transients in Otic Capsule Bone

“…The positive values for rarefaction waves seen at high fluence reflect the recoil momentum created by the violent release of ablation products. This is in good agreement with Esenaliev et al, 19 who used a model with CuCl 2 solution and atherosclerotic blood vessels.…”

“…The generation of the rarefaction wave occurs due to the large impedance mismatch between the bone and air, and its peak magnitude can be calculated knowing the acoustic impedance of both media. 19 In a constrained surface (such as water), the bipolar shape is neither observed nor predicted from theory. 22 The magnitude of the stress component increases with fluence, but this is not accompanied by a matching increase in the magnitude of the rarefaction wave (Fig.…”

“…The precise measurement of a thermal-elastic wave created by laser irradiation below the threshold for ablation permits the estimation of all these parameters. 19 Above the threshold for ablation, these equations are no longer valid, as the recoil stress momentum imparted to the target site by ablation products cancels out the rarefaction wave. This contributes to the overall broadening of the stress wave component.…”

“…Attenuation of the acoustic wave proceeds exponentially as a function of the damping coefficient. 19 In turn the damping coefficient increases proportionally with the square of the frequency, though this dependence is highly variable in tissue. Significant attenuation of an acoustic wave at 10 MHz occurs in about 1 cm in tissue.…”

Optodynamic energy-conversion efficiency during an Er:YAG-laser-pulse delivery into a liquid through different fiber-tip geometries

“…The expansion, driven by rapid heating, can generate thermo-elastic stress waves. 35 This happens when the laser energy is deposited into a medium within a time that is shorter than the characteristic time t s for the propagation of stress waves across the irradiated volume: 41,43 …”