An image-guided focused ultrasound system for generating acoustic shock waves that induce traumatic brain injury in wild-type zebrafish

We have developed an image-guided focused ultrasound system that generates acoustic shock waves to induce traumatic brain injury (TBI) in wild-type zebrafish.  This system permits the development of a TBI model for zebrafish that adequately recapitulates mild (closed-head) traumatic brain injury and subsequent secondary injury mechanisms.  Acoustic shock waves of short pulses (pulse length = 50 ms) of intense focused ultrasound (pressure = 11 MPa) within a 7.5 mm x 1.2 mm focal zone cause brain injury by inducing mechanical stress and transient cavitation.  Since zebrafish have a high degree of genetic homology and cell signalling pathways relative to mammalian species, this research may provide insight into shockwave-induced dysfunction and disruption of the blood-brain barrier in humans. The shock wave generation system incorporates a 1 MHz focused ultrasound transducer (focal length = 10 cm in water), which is excited by pulsed 1 MHz signals that are amplified and transmitted via an impedance-matching transformer.  A calibrated radiation force balance is used to correlate input electrical power with output acoustic power, which is subsequently correlated with focal-zone pressure using measurements from a calibrated hydrophone.  An imaging probe embedded within the focused transducer generates confocal B-mode images to enable visualization of the zebrafish location, and to locate the zebrafish brain consistently within the focal zone.  Zebrafish are anaesthetized using 100 ppm clove oil, and then individually positioned in a holder within a water tank.  The holder contains a 3 mm hole covered by a thin layer of ultrasound-transparent mylar membrane, which is located under the zebrafish head to ensure that ultrasound signals are delivered only to the head.  Post-TBI studies show that shocked zebrafish experience longer recovery times, decreased swim distances and velocities, heightened anxiety, and altered group social dynamics.