Minimization of cavitation effects in pulsed laser ablation illustrated on laser angioplasty

Cavitation effects in pulsed laser ablation can cause severe deformation of tissue near the ablation site. In angioplasty, they result in a harmful dilatation and invagination of the vessel walls. We suggest to reduce cavitation effects by dividing the laser pulse energy into a pre-pulse with low and an ablation pulse with high energy. The pre-pulse creates a small cavitation bubble which can be filled by the ablation products of the main pulse. For suitable energy ratios between the pulses, this bubble will not be enlarged by the ablation products, and the maximal bubble size remains much smaller than after a single ablation pulse. The concept was analyzed by numerical calculations based on the Gilmore model of cavitation dynamics and by high-speed photography of the effects of single and double pulses performed with a silicone tube as vessel model. The use of double pulses prevents the deformation of the vessel walls. The concept works with an energy ratio of up to about 1:30 between the pulses. For the calculated optimal ratio of 1:14.6, the bubble volume is reduced by a factor of 17.7. The ablation pulse is best applied when the pre-pulse bubble is maximally expanded, but the timing is not very critical.