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.

Advances in 4D ultrasound imaging open new perspectives in biomedical research by reducing the long-standing challenge of operator dependency. Extensive research efforts are focused on developing next generation of 2D transducer arrays for 4D imaging. Here, we present a compact 2D array design based on hexagonal-shaped transducer elements. We demonstrate that 2D hexagonal arrays provide an optimal compact sampling, resulting in lower grating lobe levels and an improved imaging quality compared to conventional square-shaped transducer element arrays. A prototype array made of hexagonal transducer elements is presented, and its characterization is provided, demonstrating its imaging capabilities.

Light-sheet fluorescence microscopy has revolutionized biology by visualizing dynamic cellular processes in three dimensions. However, light scattering in thick tissue and photobleaching of fluorescent reporters limit this method to studying thin or translucent specimens. In this study, we applied nondiffractive ultrasound beams in conjunction with a cross-amplitude modulation sequence and nonlinear acoustic reporters to enable fast and volumetric imaging of targeted biological functions. We reported volumetric imaging of tumor gene expression at the cubic centimeter scale using genetically encoded gas vesicles and localization microscopy of cerebral capillary networks using intravascular microbubble contrast agents. Nonlinear sound-sheet microscopy provides a ~64× acceleration in imaging speed, ~35× increase in imaged volume, and ~4× increase in classical imaging resolution compared with the state of the art in biomolecular ultrasound.

The influence of the transducer lens on image reconstruction is often overlooked. Lenses usually exhibit a lower sound speed than soft biological tissues. In academic research, the exact lens sound speed and thickness are typically unknown. Here we present a simple and nondestructive method to characterize the lens sound speed and thickness as well as the time to peak of the round-trip ultrasound waveform, another key parameter for optimal image reconstruction. We applied our method to three transducers with center frequencies of 2.5, 7.5 and 15 MHz. We estimated the three parameters with an element-by-element transmission sequence that records internal reflections within the lens. We validated the retrieved parameters using an autofocusing approach that estimates sound speed in water. We show that the combination of our parameters estimation method with two-layer ray tracing outperforms standard image reconstruction. For all transducers, we successfully improved the accuracy of medium sound speed estimation, spatial resolution and contrast. The proposed method is simple and robust and provides an accurate estimation of the transducer lens parameters and of the time to peak of the ultrasound waveform which leads to improved ultrasound image quality.

Skeletal muscles generate force, enabling movement through a series of fast electro-mechanical activations coordinated by the central nervous system. Understanding the underlying mechanism of such fast muscle dynamics is essential in neuromuscular diagnostics, rehabilitation medicine and sports biomechanics. The unique combination of electromyography (EMG) and ultrafast ultrasound imaging (UUI) provides valuable insights into both electrical and mechanical activity of muscle fibers simultaneously, the excitation-contraction (E-C) coupling. In this feasibility study we propose a novel non-invasive method to simultaneously track the propagation of both electrical and mechanical waves in muscles using high-density electromyography and ultrafast ultrasound imaging (5000 fps). Mechanical waves were extracted from the data through an axial tissue velocity estimator based on one-lag autocorrelation. The E-C coupling in electrically evoked twitch contractions of the Biceps Brachii in healthy participants could successfully be tracked. The excitation wave (i.e. action potential) had a velocity of 3.9±0.5ms-1 and the subsequent mechanical (i.e. contraction) wave had a velocity of 3.5±0.9ms-1. The experiment showed evidence that contracting sarcomeres that were already activated by the action potential (AP) pull on sarcomeres that were not yet reached by the AP, which was corroborated by simulated contractions of a newly developed multisegmental muscle fiber model, consisting of 500 sarcomeres in series. In conclusion, our method can track the electromechanical muscle dynamics with high spatio-temporal resolution. Ultimately, characterizing E-C coupling in patients with neuromuscular diseases (e.g. Duchenne or Becker muscular dystrophy) may assess contraction efficiency, monitor the progression of the disease, and determine the efficacy of new treatment options.

Current methods to track the progression and evaluate treatment of muscular dystrophies are scarce. The electromechanical delay (EMD), defined as the time lag from muscle electrical activity to motion onset, has been proposed as a biomarker, but provides only limited insight in the pathophysiol-ogy of muscle function. This work proposes and evaluates a novel method to track the propagation of electromechanical waves in muscles, using high density electromyography and ultrafast ultrasound imaging. Muscle contractions in three healthy subjects were evoked by electrical stimulation, and the subsequent propagating action potentials were successfully tracked in all 90 trials. Contractile waves were detected in 83 recordings. Detection rate varied across muscle depth. Mean (SD) velocities for the action potential were 3.71 (0.08) m/s, 4.73 (0.35) m/s and 3.27 (0.09) m/s for participant 1, 2 and 3 respectively. Velocities for the contractile wave were 3.83 (1.07) m/s, 3.32 (0.78) m/s and 3.41 (0.69) m/s for participant 1, 2 and 3 respectively. In conclusion, our technique can track the fast muscular electromechanical dynamics with high spatiotemporal resolution by combining ultrafast ultrasound imaging and high-density electromyography.