A Feasibility Study on Femtosecond Laser Thrombolysis

Objective: In this feasibility study, we investigate possible femtosecond laser thrombolysis. Background data: Because of low pulse energies, femtosecond laser surgery inherently minimizes side effects on the surrounding tissue. Moreover, current femtosecond laser sources as well as fiber technology allow consideration of catheter-based treatments. Methods: Two femtosecond laser systems (=800nm, =1030nm) along with a three dimensional (3D) scanner system (NA approximate to 0.1) were used in this study. In vitro experiments were performed on porcine thrombi and blood vessels. Ablation thresholds were determined in air, by determining the pulse energy at which single shot ablation was visible under the optical microscope. Ablation rates were determined in physiological saline. Additionally, ablation of thrombi and blood vessels was monitored by means of a fiber spectrometer. Results: Depending upon the scan velocity, typical ablation rates for thrombi were approximate to 0.04mm(3)/sec. Ablation thresholds of thrombi and blood vessels differ by factors of 3 and 1.5 at laser wavelengths of 800 and 1030nm, respectively. At a distance of 5mm above the surface, second harmonic generation was observed in blood vessels, but not within thrombi. Conclusions: The results show that a typical thrombus volume can be destroyed within a reasonable time frame. Because of the higher threshold difference of thrombi and blood vessels, the use of a laser wavelength of 800nm is preferable. Furthermore, the detection of the second harmonic could provide a feedback mechanism to protect the vascular wall from mechanical and laser damage.