Development of intravascular shock wave thrombolysis for cerebral embolism

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As advancing neurological images such as diffusion magnetic resonance imaging and single photon emission computed tomography, the patients having cerebral infarction within several hours after onset have been detectable. Since the therapeutic time window of cerebral infarction is generally thought to be within several hours, it is necessary to accomplish recanalization of occluded cerebral arteries with a little fibrinolytics as soon as possible.Fibrinolysis with a liquid jet induced by interaction between bubble and shock wave was succeeded in-vitro. In order to improve this technology for clinical application, A Q-switch pulsed Holmium : YAG laser was selected. This laser had 200 ns pulse duration and 2.1 mm wavelength. Energy range of this laser was variable from 36 to 150 mJ/pulse. The laser beam was transmitted through an optical fiber which diameter was 0.6 mm. In the present experiment, this laser irradiation at 86 mJ/pulse in water induced a strong shock wave over 100 atm and a … More transient spherical bubble, which can penetrate into an artificial thrombus forming a jet. In order to obtain a stronger shock wave and a larger bubble, optical fibers with three types of end surface ; a convex-lens, a coarse flat, and smooth flat were prepared and studied. The optical fiber with a convex lens-shaped end produced a shock wave with stronger overpressure and a larger bubble than that of the other ends. Regarding to two flat end surfaces, there was no difference in overpressure of a shock wave and bubble volume between smooth and coarse.A laser-induced bubble in a glass tube which diameter was 4mm was observed. The bubble gradually expanded and reached at maximum size at about 1 ms while a bubble in a large vessel did at about 300 μs. Based on this result, interaction between a shock wave induced by silver azide explosion and the laser-induced maximum bubble was attempted. The bubble was transformed to a liquid jet, which could penetrate into an artificial thrombus more deeply than only a laser-induced bubble did. Less