Occurrence, extent, and implications of pressure waves during excimer laser ablation of normal arterial wall and atherosclerotic plaque

Abstract

Ablation of atherosclerotic plaque and normal arterial wall was performed using a Xenon-Chloride Excimer laser with a wave-length of 308 nm and a pulse duration of 115 ns. The light was transmitted via a 600 microns bare fibre and adjusted to an energy density of 3.5J/cm2. The acoustic signals generated by the laser pulse were measured with two types of hydrophones consisting of polyvinylidenefluoride with active diameters of 0.3 mm and 0.5 mm and recorded on a dual channel digital storage oscilloscope using either a 0.5 m coaxial cable or a broadband fibre-optic transmission system. Tissue was retrieved from nine cadaver human aortas and macroscopically classified as either normal or calcified atherosclerotic plaque. Histological analysis (Haematoxylin eosin, elastica van Gieson, and immunohistochemical staining) was carried out after the experiments to verify the macroscopic diagnosis and to correlate the acoustic responses with the tissue characteristics. For normal arterial wall, maximum peak pressure was 1.28 MPa +/- 0.85 MPa, rise time 163 ns +/- 43 ns, and pressure increase 8.2k Pa +/- 5.4k Pa/ns. For calcified, atheromatous segments, a maximum peak pressure of 2.02 MPa +/- 1.16 MPa, a rise time of 69.9 ns +/- 25.8 ns, and a pressure increase of 32.3 kPa +/- 21.3 kPa/ns was found. Statistical analysis showed a significant shorter rise time (P < 0.0001) and a higher pressure increase (P < 0.0001) for calcified tissue in comparison to normal arterial wall, whereas maximum pressures alone did not allow a differentiation of tissue characteristics. Several hundred kPa are generated during Excimer laser ablation.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoacoustic fibrinolysis: Pulsed-wave, mid-infrared laser-clot interaction

“…It has been shown that several hundred bars of pressure are generated during pulsed-wave laser ablation of atherosclerotic plaque [12]. Apparently, the induction and radial distribution of a shock-wave front creates local tissue fragmentation [13]. Thus, it is likely that the nonselective yet significant mechanical destruction of lased clots that we observed in our experiment was due in large part to the formation and propagation of shock waves.…”

Perspectives of coronary excimer laser angioplasty: Multiplexing, saline flushing, and acoustic ablation control

“…The theoretical background for multiplexing goes back to the early 1980s and is based on the assumption that excimer laser ablation induces a mass explosion of the irradiated atherosclerotic target rather than cutting it slice by slice by molecular photodecomposition [11,12]. As we have shown, pressure waves do accompany each laser pulse below and above the ablation threshold.…”

Formation of pressure waves during in vitro excimer laser irradiation in whole blood and the effect of dilution with contrast media and saline

“…However, the concept of tissue ablation without injury to adjacent vessel wall structures 2141 seems to be limited because intimal dissections and perforations were documented following laser angioplasty [ 13,15,161. The observation of a rapidly expanding and then collapsing vapour bubble [61 and the occurrence of pressure waves [1,4,17,181, both of which are associated with the ablation of vascular tissue, may explain the trauma to vessel wall structures next to the irradiated area [4,6,191. Excimer laser light with a wavelength of 308 nm is absorbed in blood.…”

“…For the detection of acoustic signals generated by the laser pulse, hydrophones with active diameters of 0.5 mm were used as previously described [1,2]. Briefly, the hydrophones are fabricated from a 0.5 mm diameter, 9-Fm-thick polyvinilidenefluoride piezoelectric film bonded onto a 0.5-mm-thick metal needle (Instiute for Semicinductor Technology, Stuttgart, Germany).…”