Ultrasonic devices for preventing microbubbles and/or microparticles from reaching the brain during a PCI or cardiovascular surgery. Devices 27 and 77 are designed for implantation in the chest cavity and operate in combination with needle vents or other vent systems for removing diverted microbubbles. Systems 77 and 83 are designed for noninvasive employment. Devices 57 and 87 are particularly designed to prevent microbubbles from reaching the great origins of the carotid arteries and/or for diverting bubbles that might reach the vicinity and otherwise pass through. Improved devices 11 and 94 separate microbubbles from a flowing bloodstream and produce a cleansed stream.