Considerations for precise sonication of distal cortical targets in the macaque

Transcranial ultrasound is a noninvasive tool for brain therapies including ablation, neuromodulation, and blood-brain barrier opening. Sonication of cortical targets in macaques is challenging due to absorption and aberration from the skull. Because of this, transcranial ultrasound is largely limited to deep brain targets where the geometry of the skull is less prohibitive. Here, we address this limitation by designing a system which targets distal cortical regions and achieves a near free-field spot size at the target while minimizing pressure in the skull. We compare the focal volume and skull pressure performance with proximal sonication using two common therapeutic transducers and characterize the focal spot size at varied frequency while considering standing waves.