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.

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The field of contrast-enhanced ultrasound (CEUS) combines nonlinearly oscillating microbubbles (MBs) with dedicated pulse sequences to reveal the vascular function of organs. Clinical ultrasound contrast agents consist of polydisperse MB suspensions with diameters ranging from 0.5 to 10 μ⁢m and resonance frequencies ranging from 1 to 15 MHz. As a result, just a small fraction of MBs resonates at a given ultrasound frequency. MB suspensions with narrow size distributions can be tuned for a specific imaging frequency, boost CEUS sensitivity, and enable deeper vascular imaging. However, their enhanced nonlinear behavior makes imaging susceptible to nonlinear-wave-propagation artifacts. Here we numerically investigate the impact of the acoustic wavefront shape on the imaging of nonlinearly oscillating, monodisperse MBs. Specifically, our approach relies on an extension of the iterative nonlinear-contrast-source method that accounts for all nonlinear effects in CEUS. We demonstrate that supersonic X-shaped wavefronts referred to as “X waves” can be used to generate ultrasound images of monodisperse MBs without nonlinear-wave-propagation artifacts. In contrast, imaging based on focused, planar, and diverging wavefronts leads to significant nonlinear artifacts. Taken together, our results show that X waves can harness the full potential of monodisperse MBs by enabling their sensitive and specific detection in a tissue context.@en

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.

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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.

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Desktop inkjet printers are ubiquitous and relatively inexpensive among the variety of available printers. These inkjet printers use an array of micro fluidic pumps, nozzles based on piezoelectric actuation, to dispense individual picoliter volume ink droplets at high speed. In this paper, we show that individual pumps in desktop printers can be accessed to dispense droplets on demand. Access was obtained using the printer’s command language programming. A detailed description of the access procedure is discussed. Droplets were printed on a paper as it rolled underneath the printhead, and with a minor hardware modification, they were also printed on a glass substrate. With this access, individual droplets were deposited, the smallest having an average diameter of 62 μm with a standard deviation of 6.9 μm, with a volume of ∼4 pL. From the intended position, the droplets had a standard deviation of 5.4 μm and 8.4 μm in the vertical and horizontal directions, respectively. The ink droplets were dispensed at a rate of 7.1 kHz. A circularity factor of 0.86 was obtained indicating that the dispensed droplets are of good quality. By replacing the ink in the cartridges with liquids of choice (e.g. cells, proteins, nanoparticles etc.), we believe it provides an opportunity for low-cost, high-speed, high-precision, picoliter volume printing for a variety of applications.@en