Array-Based Beamforming to the Vertebral Canal: Demonstration of Feasibility

Focused ultrasound blood-spinal cord barrier opening is a promising new method for improving the non-invasive delivery of therapeutic agents to the spinal cord. A custom 64-element phased array was built, based on the design of a component of a spine-specific array for focusing ultrasound through vertebral laminae and correcting vertebra-induced distortions. Geometric and hydrophone delays were tested in each thoracic vertebra in an ex vivo spine (n=12). Pressure fields were measured in each canal to measure focal aberrations. Geometric delays produced foci shifted by 2.4±1.7 mm from the target, while hydrophone delays produced foci 1.3±1.1 mm from the target. Simulation showed good correlation with hydrophone delays and may be a viable non-invasive method for phase corrections. This work demonstrates the feasibility of transvertebral ultrasound beamforming with a phased-array.