Evaluating the accuracy of acoustic holograms for precise spatial targeting within the brain

Acoustic holography can reconstruct desired pressure fields and overcome phase aberrations caused by refractions in heterogeneous media, such as the skull. However, the accuracy of holographic targeting within the brain has not yet been thoroughly evaluated. We sought to characterize the holographic focusing limits for focused and unfocused single-element transducers. Holographic lenses enlarged the focal size by more than 4-fold. Bifocal lenses achieved foci separation of 7-68 mm and focal depths of 7-83 mm. Lenses were tested in silico and in free-field experiments, with RMS errors of 0.03-0.33. Focused transducers were preferable at low F numbers and were better-suited for murine brain targeting. However, planar transducers can focus over larger areas so have higher clinical relevance in the human brain. Finally, simulations with a human skull showed an RMS error < 0.01. This work provides valuable insight into the accuracy of acoustic holography, demonstrating that transducer design is essential for clinical brain applications.