J. Powers 1, R. Seip 2, W. Shi 2
1 Philips Ultrasound, Bothell – WA, USA,
2 Philips Research, Briarcliff – NY, USA
For many years existing ultrasound devices have been used for sonothrombolysis (STL) research in-vitro, in animals, and even in humans. These have included laboratory transducers, physiotherapy devices, and diagnostic ultrasound systems.
None of these are optimal for STLsince they were designed for different applications. Therefore, we have been investigating the clinical requirements for an STL device for ischemic stroke and the influence of various system parameters on the lytic capabilities of ultrasound and microbubbles (MB).
The safety and efficacy of an STL treatment are influenced by the following key factors, among others: thromboembolic occlusion locations, temporal bone window sizes, transcranial beam patterns, steering coverage, power deposition, MB concentration and replenishment time, total treatment time, workflow, etc. These multiple dimensional factors present unique challenges to the system designer: for example, the cerebral bone window confines the available aperture size and bone attenuation limits the useable frequency range, which then constrain the ability to focus and steer the beam. Therefore, a system approach is needed for an integrated design of therapeutic array, pulsing (frequency, pulse length, amplitude, duty cycle etc.), scanning sequence, and array fixture. Additional system design considerations include the ability of the system to mesh with the existing stroke workflow for easier and faster adoption by clinicians, or in a point-of- care setting to start the treatment as soon as possible.
In designing such a system “Safety First” must be the guiding mantra. tPA, the only approved therapy for ischemic stroke increases the risk of hemorrhage ten-fold, so clearly some risk is unavoidable. This talk will describe some of these tradeoffs so that researchers may make more educated choices in their proposed research.
Key words: microbubbles, sonothrombolysis, ultrasound.