Laser thrombolysis using long pulse frequency-doubled Nd:YAG lasers

Laser thrombolysis is a means for clearing blood clots in occluded arteries. Many researchers have studied the mechanisms of clot ablation, and research clinicians have used the technique to treat myocardial infarction with a number of different laser systems. Specifically, a 1-microsec pulsed dye laser has been used clinically to remove blood clots in coronary arteries. As a comparative study, the ablation characteristics of lasers with pulse durations in the ranges of 50-150 microsec and 2-10 msec were investigated. Two frequency-doubled Nd:YAG lasers at 532 nm were used in this study. Ablation threshold and ablation efficiency of gel phantoms and thrombus using these two lasers were measured and compared with the results of the pulsed dye laser. The pulsed dye laser in this study operated at 522 nm.

Gelatin samples with 150 cm(-1) absorption coefficient at 532 nm and animal clot were confined to 3-mm silicone tubes to measure ablation parameters. Additional samples with 150 cm(-1) absorption coefficient at 522 nm were prepared for use with the pulsed dye laser. A fluorescence technique and photographic bubble detection were used to determine ablation threshold. A spectrophotometric technique was used to determine ablation efficiency.

The ablation threshold of the gel phantoms for all three lasers was determined to be 17 +/- 2 mJ/mm(2). Ablation efficiency for the gel phantoms was 1.7 +/- 0.1 microg/mJ. Clot had an ablation efficiency of 2.9 +/- 1.0 microg/mJ.

Ablation threshold and efficiency are independent of laser pulse duration for 1-microsec, 50-150-microsec, and 2-10-msec pulses (P < 0.05).