A reconstituted in vitro clot model for evaluating laser thrombolysis.

Background/objective: Laser thrombolysis is the selective removal of thrombus from occluded blood vessels using laser energy. A reconstituted clot model with reproducible optical absorption properties was developed to evaluate the effect of various laser parameters on thrombus removal rate.

Study Design/materials And Methods: Reconstituted clots were made with known fibrinogen concentrations and hematocrits. Ex vivo clots were collected from ten swine. Four red gelatin phantoms were prepared. Mass removal rates and ablation efficiencies were determined using a 577 nm, 1 microsec pulsed dye laser. The ablation efficiencies of the three clot models were compared at an energy of 25 mJ and a repetition rate of 4 Hz. In addition, the reconstituted clot model was ablated as pulse energy and repetition rate were varied with average power held constant at 100 mW.

Results: The mean ablation efficiency for ex vivo clots ranged from 0.4 +/- 0.1 to 3.4 +/- 0.7 microg/mJ/pulse, with significant differences between groups (ANOVA p < 0.05). Reconstituted clots of varied fibrinogen content had ablation efficiencies of 1.5 +/- 0.2 to 1.6 +/- 0.3 microg/mJ/pulse at this energy and repetition rate. Gelatin ablation efficiency was inversely proportional to protein content and ranged from 0.5 +/- 0.3 to 2.0 +/- 0.7 microg/mJ/pulse. Reconstituted clot mass removal rates (in microg/s) were clinically similar for settings ranging from 13 mJ at 8 Hz to 33 mJ at 3 Hz.

Conclusions: The reconstituted model clot is a reproducible and biologically relevant thrombolysis target. Ex vivo clot lacks reproducibility between individuals and gelatin phantoms lack clinical relevance. At a constant average power, varying laser parameters did not affect mass removal rates to a clinically significant degree.