<title>Visualization of microsecond laser ablation of porcine clot and gelatin under a clear liquid</title>

Laser thrombolysis uses microsecond laser pulses to remove thrombus-blocked arteries in the heart and the brain. Rapidly expanding and collapsing vapor bubbles are formed upon absorption of the laser energy by the thrombus. The goal of this study was to visualize the process of ablation and assess the effects of pulse repetition rate. The differences between contact versus non-contact of the laser delivery device with the thrombus were also investigated. Initial experiments were conducted with a gel-based clot model confined in 3 mm inner diameter silicone tubes. Subsequent experiments used 24 hour old porcine blood clots. Laser pulses of 50 mJ pulse energy were delivered via a quartz fiber contained in a flushing catheter. Pulse repetition rates of 1 Hz, 3 Hz, and 6 Hz were used. Wavelengths of 506 nm and 577 nm were used to ablate clot. Bubble action was captured by flash photography using a CCD camera and recorded on video. The amount of material removed was measured using a spectrophotometric technique. Bubble action was similar on clot and the clot model. No significant differences in bubble action or mass removal were observed at the three pulse repetition rates and the two wavelengths. Contact between the catheter and the clot did not result in a pistoning effect of the catheter at the pulse energy used.