@phdthesis{sathyam96d,
  author = {U. S. Sathyam},
  title = {Laser Thrombolysis: Basic Ablation Studies},
  school = {Oregon Graduate Institute of Science and Technology},
  year = {1996},
  abstract = {Laser thrombolysis is a procedure that is being developed to treat cardiovascular disease and stroke by removing clots occluding arteries of the heart and the brain. This thesis presents studies of pulsed ablation phenomena that take place during during laser thrombolysis. The main goals were to optimize laser parameters for efficient ablation, and to investigate the ablation mechanism. Most of the studies described here used a gel-based clot model, and selected results were verified using porcine clot. \vskip2mm A parametric study was performed to identify the optimal wavelength, spot size, pulse energies, and repetition rate for maximum material removal. The minimum radiant exposures to achieve ablation at any wavelength were measured. The results suggest that most visible wavelengths were equally efficient at removing material at radiant exposures above threshold. Larger catheters are likely to ablate more efficiently. Ablation was initiated at surface temperatures just above 100$^\circ$C. A vapor bubble was formed during ablation. The vapor bubbles expanded and collapsed within 500\,$\mu$s after the laser pulse. Less than 5\% of the total pulse energy is coupled into the bubble energy. A large part of the delivered energy is unaccounted for and is likely released partly as acoustic transients from the vapor expansion and partly wasted as heat. When the ablation process was studied within the cylindrical confines of a tube, dilation of the vessel due to bubble expansion was observed at clinically relevant energies. \vskip2mm The thesis concludes by summarizing the relevance of the gel results to the implementation of laser thrombolysis. It proposes optimal laser parameters for the design of a next generation laser system; a doubled Nd:YAG laser is suggested. It also suggests that the current laser and delivery systems may not be able to completely remove large clot burden that is sometimes encountered in heart attacks. However, laser thrombolysis may emerge as a favored treatment for strokes where the occlusion is generally smaller and rapid recanalization is of paramount importance. A final hypothesis is that laser thrombolysis should be done at radiant exposures close to threshold to minimize any damaging effects of the bubble dynamics on the vessel wall.},
}