Photoablation in atherosclerotic plaque at 9.5 μm with the free-electron laser FELIX

Abstract

So far, laser angioplasty in minimally invasive cardiac surgery has been performed with the Excimer laser in the UV, and experimentally with IR lasers, at 2.1 micrometers (Holmium laser) and 2.94 micrometers (Erbium laser), using water as the prevailing absorber. Plaques are inhomogeneous, composed of various materials (fibrous tissue, cholesterol, hydroxyapatite calcifications) absorbing off the water absorption bands. The Free-Electron Laser FELIX (FOM, Nieuwegein/NL) was tuned to 9.5 micrometers wavelength (absorption maximum of hydroxyapatite and cholesterol) and to wavelengths with low absorption in plaque. Ablation was performed in vitro at an energy per pulse between 10 and 20 mJ and a laserpulse length (macropulse) of 4 micrometers . Ablation rates, ablation thresholds and collateral thermal damage were assessed by histologic micrometry for plaque and for normal vessel wall. The ablation rates were found to be higher in water containing plaque than in calcified plaque. With the high absorption of hydroxyapatite at 9.5 micrometers , the ablation thresholds for (calcified) plaque and vessel wall differ by 50% at least. Thus, accidental perforation is almost impossible, adding an element of selectivity and inherent safety not available so far. Collateral thermal damage at all applied wavelengths was of the same order as known from other IR sources (15 - 30 micrometers ).