  The development of neurologically active drugs faces a challenge in treating
brain diseases due to the blood-brain barrier's impermeability. High-intensity
focused ultrasound can open the barrier in a targeted manner, expanding
treatment options. However, this procedure risks brain damage and off-target
effects without proper monitoring. Current monitoring methods have limitations.
We present Equivalent Time Active Cavitation Imaging, a novel ultrasound
modality that characterizes the ultrasound pressure field during treatment.
This system utilizes a unique plane wave sequence and an algorithm to filter
the microbubble signal for pressure field mapping. We conducted pressure
measurements in vitro for comparison with hydrophones and in vivo during
blood-brain barrier opening in mice. Our modality successfully spatiotemporally
characterizes the pressure field with an active imaging setup, demonstrating
good correlation with hydrophone measurements. Experimental in vivo results are
promising, establishing the feasibility of this monitoring method. In
conclusion, this proof of concept represents a significant step toward a new
ultrasound modality for monitoring blood-brain barrier opening using focused
ultrasound. This approach offers a safer and more precise monitoring method,
opening new possibilities for treating brain diseases.
