Minimization of Cavitation Effects in Pulsed Laser Angioplasty

Abstract

In pulsed laser angioplasty, ablation goes along with explosive evaporation in the blood filled vessel. This generates a cavitation bubble whose expansion leads to a microsecond dilatation of the vessel wall¹. The subsequent bubble collapse leads to an invagination of the vessel wall which further adds to the mechanical trauma². It is likely that the mechanical damage and the subsequent healing response contribute to the relatively high rate of restenosis observed after laser angioplasty which has prevented a widespread clinical acceptance of the method. We suggest to avoid cavitation by displacing the liquid from the vicinity of the ablation site. This can be accomplished in two ways: 1. Injection of CO ₂ gas. The gas can displace the blood around the ablation site for several seconds without causing an embolism, because it quickly dissolves in blood 2. Double pulses. The laser pulse energy is divided into a pre-pulse with low energy, and an ablation pulse with higher energy. The pre-pulse creates a small cavitation bubble, and the ablation pulse is applied when this bubble is maximally expanded and can be filled by the ablation products of the main pulse. The energy of the pre-pulse must be small enough to keep the cavitation effects below the damage threshold for the vessel walls. If the energy ratio of both pulses is chosen appropriately, the ablation products will not lead to a further expansion of the bubble generated by the pre-pulse, and the maximal bubble size remains much smaller than after a single ablation pulse. This technique avoids the injection of an exogenous gas.