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

Abstract

[EN] We present 3D printed holographic lenses that correct the aberrations of the skull and, simultaneously, 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 human hippocampi at once; a beam following an arbitrary curved trajectory, i.e., a self-bending beam; and a holographic plate producing a broad focus that overlaps with the left hippocampus (LH). Skull and LH geometries and acoustic properties are obtained from CT-scans and MRI, respectively. Time-reversal (TR) method is used to obtain the magnitude and phase of the back-propagated field from the target shape towards the lens surface. 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 accurately 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.