Potential of magnetic resonance-guided focused ultrasound for intracranial hemorrhage: an in vitro feasibility study

Background Intracranial hemorrhage has a mortality rate of up to 40-60% due to the lack of effective treatment. Magnetic resonance-guided focused ultrasound may offer a breakthrough noninvasive technology, by allowing accurate delivery of focused ultrasound, under the guidance of real-time magnetic resonance imaging. Aim The purpose of the current study was to optimize the acoustic parameters of magnetic resonance-guided focused ultrasound for effective clot liquefaction, in order to evaluate the feasibility of magnetic resonance-guided focused ultrasound for thrombolysis. Methods Body (11MHz) and brain (220kHz) magnetic resonance-guided focused ultrasound systems (InSightec Ltd, Tirat Carmel, Israel) were used to treat tube-like (4cc), round (10cc), and bulk (300cc) porcine blood clots in vitro, using burst sonications of one-second to five-seconds, a duty cycle of 5-50%, and peak acoustic powers between 600 and 1200W. Liquefied volumes were measured as hyperintense regions on T2-weighted magnetic resonance images for body unit sonications (duration of one-second, duty cycle of 10%, and power of 500-1200W). Liquefaction efficiency was calculated for brain unit sonications (duration of one-second, duty cycle of 10%, power of 600W, and burst length between 01ms and 100ms). Results Liquified lesion volume increased as power was raised, without a thermal rise. For brain unit sonications, a power setting of 600W and ultrashort sonications (burst length between 01 and 10ms) resulted in liquefaction efficacy above 50%, while longer burst duration yielded lower efficacy. Conclusions These results demonstrate the feasibility of obtaining reproducible, rapid, efficient, and accurate blood clot lysis using the magnetic resonance-guided focused ultrasound system. Further in vivo studies are needed to validate the feasibility of magnetic resonance-guided focused ultrasound as a treatment modality for intracranial hemorrhage.