XeCl laser ablation of atherosclerotic aorta: Optical properties and energy pathways

Abstract

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.

Excimer Laser–Assisted Removal of Embedded Inferior Vena Cava Filters

“…This finding coincides with prior research on laser tissue interaction using the xenon chloride excimer laser system. [22][23][24][25] A combination of photothermal ablation with photochemolysis disintegrates tissue into particles ≤5 μm in diameter. Because 308-nm wavelength penetrates only 50 to 100 μm through vascular tissue, precise tissue ablation is achieved immediately adjacent to the laser tip, with minimal risk of collateral tissue damage.…”

Physical aspects of excimer laser angioplasty for undilatable lesions

“…Protein and nucleic acid chromophores absorb ultraviolet light at 308 nm and transfer heat to tissue water [12]. Intracellular water vaporizes, causing cells to explode, and generates bubbles three times greater than the diameter of the laser catheter [6,7,[9][10][11]. Adjacent tissue temperatures rise to more than 858C [11], but carbonization is not commonly seen [6,10,12].…”

“…Original experiments carried out in air [8] attributed the mechanism of tissue ablation to the nonthermal process of photochemical bond breaking, but this was later disputed by studies in aqueous media showing that the predominant effect of excimer laser angioplasty involves a thermomechanical process of rapidly expanding and imploding vapor bubbles [6,7,[9][10][11]. Protein and nucleic acid chromophores absorb ultraviolet light at 308 nm and transfer heat to tissue water [12].…”

Large laser sheaths for pacing and defibrillator lead removal

“…Advancement increases with fluence, up to the highest fluence tested (80 mJ/mm 2 ). Previous detailed work on the laser-tissue interaction for ELCA has shown that the ablation mechanism combines photochemical decomposition of cellular structures with explosive photothermal vaporization of cellular water [9,10]. The latter effect produces a transient steam bubble at the tip of the device, with a lifetime of approximately 100 s and a size 1-3 times the diameter of the fiber.…”