Transcranial acoustic holograms for arbitrary fields generation using focused ultrasound into the brain

Abstract

We present 3D-printed holographic lenses that correct the aberrations of the skull and produce arbitrary ultrasonic fields with the geometry of brain structures. Using experimental techniques on a human skull phantom (HSP), a multiple-point focusing lens is designed to focus at both hippocampi; a beam following a curved trajectory and a holographic plate producing a focus that overlaps the left hippocampus (LH). Skull and LH geometries and acoustic properties are obtained from CT-MRI scans. Time-reversal method is used to obtain the magnitude and phase of the back-propagated field. The holographic lenses are designed assuming each pixel of the lens vibrates as a Fabry-Pérot resonator. The resulting lenses are 3D-printed using SLA techniques. The three studied cases show similar results in simulation and experiment with and without the HSP: for the bi-focal beam, the reconstructed field matches the target foci; for the curved trajectory beam, the target acoustic image is reconstructed by the designed holographic lens; for the broad focus beam, results present the same qualitative performance providing a similar overall covering of the LH. The reported holographic lenses can be used to control the spatial features of ultrasonic beams inside the skull in an unprecedented manner using single-element ultrasonic sources.