Effects of varying duty cycle and pulse width on high-intensity focused ultrasound (HIFU)-induced transcranial thrombolysis.

The goal was to test the effects of various combinations of pulse widths (PW) and duty cycles (DC) on high-intensity focused ultrasound (HIFU)-induced sonothrombolysis efficacy using an in vitro flow model. An ExAblate™ 4000 HIFU headsystem (InSightec, Inc., Israel) was used. Artificial blood clots were placed into test tubes inside a human calvarium and exposed to pulsatile flow. Four different duty cycles were tested against four different pulse widths. For all study groups, an increase in thrombolysis efficacy could be seen in association with increasing DC and/or PW (p < 0.0001). Using transcranial HIFU, significant thrombolysis can be achieved within seconds and without the use of lytic drugs in vitro. Longer duty cycles in combination with longer pulse widths seem to have the highest potential to optimize clot lysis efficacy.

Transcranial sonothrombolysis using high-intensity focused ultrasound: impact of increasing output power on clot fragmentation.

BACKGROUND: The primary goal of this study was to investigate the relationship between increasing output power levels and clot fragmentation during high-intensity focused ultrasound (HIFU)-induced thrombolysis. METHODS: A HIFU headsystem, designed for brain applications in humans, was used for this project. A human calvarium was mounted inside the water-filled hemispheric transducer. Artificial thrombi were placed inside the skull and located at the natural focus point of the transducer. Clots were exposed to a range of acoustic output power levels from 0 to 400 W. The other HIFU operating parameters remained constant. To assess clot fragmentation, three filters of different mesh pore sizes were used. To assess sonothrombolysis efficacy, the clot weight loss was measured. RESULTS: No evidence of increasing clot fragmentation was found with increasing acoustic intensities in the majority of the study groups of less than 400 W. Increasing clot lysis could be observed with increasing acoustic output powers. CONCLUSION: Transcranial sonothrombolysis could be achieved in vitro within seconds in the absence of tPA and without producing relevant clot fragmentation, using acoustic output powers of <400 W.

Introduction of a rabbit carotid artery model for sonothrombolysis research.

The goal of this study was to develop an in vivo sonothrombolysis model for stroke research. The rabbit carotid artery has average vessel diameters similar to human M1/M2 segments and allows generation of a thrombotic occlusion using various kinds of thrombus material as well as thrombus placement under visual control. It further allows real-time monitoring of flow and clot mechanics during the sonothrombolysis procedure using high-frequency diagnostic ultrasound. In the present study, the model will be introduced and first results to show feasibility using diagnostic as well as high-intensity focused ultrasound will be presented.