Acoustic Holograms Allow the Generation of Complex Fields Inside the Central Nervous System

Focused ultrasound is currently used in many emerging therapeutic applications for the non-invasive treatment of neurological disorders and pathologies inside the central nervous system. However, the accurate focusing of ultrasound beams at the central nervous system is mainly limited due to the strong phase aberrations produced by refraction and attenuation of the skull. We present 3D-printed acoustic holographic lenses for the generation of ultrasonic fields of complex spatial distribution inside the skull. Using holographic lenses with an aperture of 50 mm and working frequency of 1.1 MHz, we experimentally, numerically and theoretically produce acoustic beams whose spatial distribution match target structures of the central nervous system. In particular, we present three configurations of increasing complexity: a set of points, a curved trajectory and an arbitrary volume. Results show that, using low-cost 3D-printed lenses, ultrasonic beams can be focused not only at a single point, but overlapping at one or various target structures simultaneously, e.g., left and right hippocampi. These results open new paths to spread emerging therapeutic ultrasound applications including blood-brain barrier opening or neuromodulation using low-cost systems.