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Keywords:

  • intracranial hemorrhage;
  • magnetic resonance-guided focused ultrasound;
  • noninvasive;
  • stroke;
  • thrombolysis

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 (1·1 MHz) and brain (220 kHz) magnetic resonance-guided focused ultrasound systems (InSightec Ltd, Tirat Carmel, Israel) were used to treat tube-like (4 cc), round (10 cc), and bulk (300 cc) 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 1200 W. 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 500–1200 W). Liquefaction efficiency was calculated for brain unit sonications (duration of one-second, duty cycle of 10%, power of 600 W, and burst length between 0·1 ms and 100 ms).

Results

Liquified lesion volume increased as power was raised, without a thermal rise. For brain unit sonications, a power setting of 600 W and ultrashort sonications (burst length between 0·1 and 1·0 ms) 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.