# Ultrasound-transparent neural interfaces for multimodal interaction

## TL;DR

This paper introduces neural interfaces that are transparent to ultrasound, allowing for better integration with brain imaging and therapy.

## Contribution

The novel contribution is a framework for designing acoustically transparent neural interfaces using flexible materials.

## Key findings

- Flexible interfaces with practical metal thicknesses can achieve high acoustic transparency.
- Design guidelines were validated through experiments showing successful ultrasound transmission.
- The approach can be extended to therapeutic applications using focused ultrasound.

## Abstract

Neural interfaces that unify diagnostic and therapeutic functionalities hold particular promise for advancing both fundamental neuroscience and clinical neurotechnology. Functional ultrasound imaging (fUSI) has recently emerged as a powerful modality for high-resolution, non-invasive monitoring of brain function and structure. However, conventional metal-based microelectrodes typically impede ultrasound propagation, limiting compatibility with fUSI. Here, we present flexible, ultrasound-transparent neural interfaces that retain practical metal thicknesses while achieving high acoustic transparency. We introduce a theoretical and simulation-based framework to investigate the conditions under which commonly used polymers and metals in neural interfaces can become acoustically transparent. Based on these insights, we propose design guidelines that maximise ultrasound transmission through soft neural interfaces. We experimentally validate our approach through immersion experiments and by demonstrating the acoustic transparency of a suitably engineered interface using fUSI in phantom and in vivo experiments. Finally, we discuss the potential extension of this approach to therapeutic focused ultrasound (FUS). This work establishes a foundation for the development of multimodal neural interfaces with enhanced diagnostic and therapeutic capabilities, enabling both scientific discovery and translational impact.