A random phased-array for MR-guided transcranial ultrasound neuromodulation in non-human primates

TL;DR

This paper presents a novel 128-element MR-guided transducer for non-invasive brain stimulation in primates, demonstrating precise focus and effective targeting through the skull using advanced acoustic and optical measurement techniques.

Contribution

The study introduces a new randomized phased-array transducer optimized for transcranial ultrasound neuromodulation in non-human primates, with detailed characterization and modeling.

Findings

Effective focus beyond skull bone with slight broadening and shift

Accurate 3D pressure mapping within cortical regions

Optimized transducer geometry for targeted neuromodulation

Abstract

Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650kHz. The array is randomized with 128 elements, radius of curvature 7.2cm, and opening diameter 10.3cm (focal ratio 0.7). Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques.