Marc Fournelle

Purpose: This study explores how older adults with chronic back pain (CBP) evaluate different user interface (UI) designs and gamification elements for an ultrasound-based wearable providing real-time biofeedback during segmental stabilization exercises (SSE). The aim is to identify design preferences and motivational factors to enhance usability, engagement, and adherence in this specific population. Methods: We conducted a mixed-methods study with 15 older adults (aged ≥ 65) experiencing CBP. Participants interacted with three UI mockups (simple, anatomical, and playful) via a Wizard-of-Oz simulation and evaluated additional motivational elements (e.g., points, badges, progress charts). Semi-structured interviews and the Technology Usage Inventory (TUI) subscales were used to assess usability, acceptance, and intention to use. Results: Participants preferred the simple and anatomical UI designs, citing clarity, professionalism, and ease of interpretation. The playful design was viewed as less appropriate due to perceived infantilization. Game elements such as progress tracking, points, and levels were positively received, while competitive features like leaderboards were viewed critically. Most participants expressed interest in integrating pain education, favoring multimedia formats. Conclusions: Digital health tools for older adults must prioritize intuitive, medically reliable interfaces and allow personalization of motivational and educational components. The findings highlight the need for age-appropriate UI design and suggest that well-balanced gamification and educational features may enhance perceived acceptance and have the potential to support long-term use, which should be evaluated in longitudinal studies.

Introduction: Ultrasound is a promising new approach for noninvasive brain stimulation. Low-intensity focused ultrasound (LIFU) allows targeting the deep brain with high spatial and temporal resolution. For clinical use, ultrasound systems must fulfill specific requirements. Three-dimensional (3D) steering and focusing either requires mechanical displacement of (focused) transducers or multielement arrays and corresponding multichannel electronics. Since the waveform has an impact of the induced neurostimulation effect, electronics need sufficient flexibility for generating arbitrary temporal signal patterns. For compensation of skull aberration artifacts, elements must be excited with defined phase resulting of phase aberration correction (PAC) algorithms. Finally, for being clinically usable, systems must be combined with planning hardware and software. Methods: A versatile system for 3D steered LIFU based on two-dimensional matrix arrays was designed, fabricated, and characterized in terms of focusing, steering, and output of temporal patterns. Our PAC algorithm was validated on an ex vivo skull. The system was tested for compliance with defined medical device standard by accredited laboratories, and an initial Magnetic resonance imaging (MRI) phantom study was performed. Results: Our system allows 3D beam steering and focusing with lateral focus sizes down to 4 mm, which is less than the size of a human gyrus, such that detailed targeting is possible. Arbitrary temporal signal patterns (different wave forms, pulse length, duty cycle, and ramping) were generated. Different software interfaces allow patient-specific planning with a Magnetic resonance Tomograph (MR)- or neuronavigation-based workflow, in which a custom-developed PAC algorithm allows compensation of the skull bone. The absence of transducer susceptibility artifacts was shown in the MRI phantom study, and the acoustic focus was localized using magnetic resonance acoustic radiation force imaging. Discussion: Our new versatile ultrasound neuromodulation platform represents a compromise between conformal helmet-like systems and single element transducer setups. It is flexible in terms of spatiotemporal stimulation patterns and can be accommodated to different workflows. Impact Statement: Progress in the field of ultrasound neurostimulation is depending on the availability of suitable hardware fulfilling a range of practical, technical, safety, and regulatory requirements. Systems must fit in established clinical workflows (e.g., usable with MR and/or neuronavigation systems), allow accessing deep brain regions, and generate defined spatiotemporal ultrasound patterns. Furthermore, basic regulatory constraints (e.g., IEC 60601-1) must be fulfilled. Our new low-intensity focused ultrasound (LIFU) system addresses these requirements and is flexible enough for use in a research environment. It was developed for facilitating the clinical transfer of LIFU and helping to gain a better understanding of underlying effects in ultrasound neurostimulation.

Superheated nanodroplets (NDs) are proposed for in vivo radiation dose sensing applications, based on their ability to vaporize into echogenic microbubbles when exposed to ionizing radiation. Combined with Ultrasound Localization Microscopy (ULM), the ultrafast detection of radiation-induced ND vaporization produces super-resolved vaporization maps that match the radiation field with sub-millimeter accuracy. However, in the presence of flow, discriminating between microbubbles moving in the field of view and radiation-induced vaporization events is not trivial. As an alternative, sparse acoustic signatures emitted by vaporizing NDs can be super-localized by passive ULM, i.e. P-ULM. In this work, we extend our previous 2D implementation of P-ULM to 3D, using a large aperture matrix array probe. We exposed perfluorobutane NDs to a proton beam and recorded their vaporization signatures during irradiation. The events were extracted from the radiofrequency channel data using a spatiotemporal filtering approach and super-localized by fitting the time differences of arrival between channels to a one-way time of flight model. The vaporization maps were overlaid on the proton beam distribution and estimated the proton range and beam dispersion within 0.98 ± 0.04 mm and 0.03 ± 0.02 mm of the reference range measurement (depth-dose distribution in water measured with a diode), respectively. These results pave the way for volumetric dose mapping using radiosensitive nanodroplets and passive imaging.

Reliable acoustic coupling in a non-handheld mode and reducing the form factor of electronics are specific challenges in making ultrasound wearable. Applications relying on a large field of view (such as tracking of large muscles) induce a need for a large element count to achieve high image quality. In our work, we developed a 256-element linear array for imaging of abdominal muscles with four integrated custom-developed 8:32 multiplexer Integrated Circuits (ICs), allowing the array to be driven by our compact 32 ch electronics. The system is optimized for flexible use in R&D applications and allows adjustable transmit voltages (up to +/−100 V), arbitrary delay patterns, and 12-bit analog-to-digital conversion (ADC) with up to 50 MSPS and wireless (21.6 MBit/s) or USB link. Image metrics (SLL, FWHM) were very similar to a fully populated array driven with a 256 ch system. The contrast allowed imaging of lesions down to 7 cm in the phantom. In a first in-vivo study, we demonstrated reliable acoustic contact even during exercise and were able to visualize deep abdominal muscles such as the TrA. In combination with a muscle tracking algorithm, the change of thickness of the TrA during SSE could be monitored, demonstrating the potential of the approach as biofeedback for physiotherapy training.

For the more efficient application of ultrasound in future therapies, fundamental research is needed on the mode of action of ultrasound on biological systems using therapeutic frequencies. To address this need, a new versatile high-throughput platform for focused ultrasound in vitro application was designed, developed, and characterized. The applicator was aligned with the dimensions of a 96-well plate and frequencies commonly used in the therapeutic ultrasound range (0.5–2.0 MHz). Two different platform configurations were developed: (a) a low-intensity version with 96 individual transducers allowing dry coupling of the well plate; and (b) a high-intensity version with water cooling, supporting parallel sonication of 32 out of 96 wells. The platforms were characterized by performing an analysis of the homogeneity of the sound pressure and intensity, the impact of filled volume per well, the cross-coupling effect between the wells, and the influence of the well plate. The low-intensity design delivers pressure levels up to 605 kPa inside the well with maximum I_SPPA values between 0.78 and 12.38 W/cm². In contrast, the high-intensity system achieves pressures up to 1460 kPa and a maximum I_SPPA of 72 W/cm² inside the wells. The successfully developed high-throughput platform supports parallelized sonication in standard, well-plate formats and is suitable for focused ultrasound applications in vitro.

Fully populated matrix arrays typically require a very high number of electronic channels for allowing real-time volumetric imaging. Reducing the element count by sparse approaches will either lead to smaller elements (large opening angle but low sensitivity) or densely packed arrays with large elements (small opening angle, better SNR). We investigated the possibility to apply defocusing micro-lenses on a 2D spiral array based on a 4 MHz piezocomposite material for improving the opening angle and thereby increasing the FOV. We showed that our microlens structure can increase the opening angle from 16 to 37°. First phantom measurements showed the suitability of the array for optoacoustic imaging by reconstruction a point targets with a FWHM of 420 µm.

Background/Objectives: Chronic low back pain (CLBP) is prevalent among older adults and leads to significant functional limitations and reduced quality of life. Segmental stabilization exercises (SSEs) are commonly used to treat CLBP, but the selective activation of deep abdominal muscles during these exercises can be challenging for patients. To support muscle activation, physiotherapists use biofeedback methods such as palpation and ultrasound imaging. This randomized controlled pilot study aimed to compare the effectiveness of these two biofeedback techniques in older adults with CLBP. Methods: A total of 24 participants aged 65 years or older with CLBP were randomly assigned to one of two groups: one group performed self-palpation biofeedback, while the other group used real-time ultrasound imaging to visualize abdominal muscle activation. Muscle activation and thickness were continuously tracked using a semi-automated algorithm. The preferential activation ratio (PAR) was calculated to measure muscle activation, and statistical comparisons between groups were made using ANOVA. Results: Both groups achieved positive PAR values during all repetitions of the abdominal-draw-in maneuver (ADIM) and abdominal bracing (AB). Statistical analysis revealed no significant differences between the groups in terms of PAR during ADIM (F(2, 42) = 0.548, p = 0.58, partial η² = 0.025) or AB (F(2, 36) = 0.812, p = 0.45, partial η² = 0.043). Both groups reported high levels of exercise enjoyment and low task load. Conclusions: In conclusion, both palpation and ultrasound biofeedback appear to be effective for guiding older adults with CLBP during SSE. Larger studies are needed to confirm these results and examine the long-term effectiveness of these biofeedback methods.

Three-dimensional passive acoustic mapping (PAM) with matrix arrays typically suffers from high demands on the receiving electronics and high computational load. In our study, we investigated, both numerically and experimentally, the influence of matrix array aperture size, element count, and beamforming approaches on defined image metrics. With a numerical Vokurka model, matrix array acquisitions of cavitation signals were simulated. In the experimental part, two 32 × 32 matrix arrays with different pitches and aperture sizes were used. After being reconstructed into 3D cavitation maps, defined metrics were calculated for a quantitative comparison of experimental and numerical data. The numerical results showed that the enlargement of the aperture from 5 to 40 mm resulted in an improvement of the full width at half maximum (FWHM) by factors of 6 and 13 (in lateral and axial dimension, respectively). A larger array sparsity influenced the point spread function (PSF) only slightly, while the grating lobe level (GLL) remained more than 12 dB below the main lobe. These results were successfully experimentally confirmed. To further reduce the GLL caused by array sparsity, we adapted a non-linear filter from optoacoustics for use in PAM. In combination with the delay, multiply, sum, and integrate (DMSAI) algorithm, the GLL was decreased by 20 dB for 64-element reconstructions, resulting in levels that were identical to the fully populated matrix reconstruction levels.

Objective: Non-invasive human machine interfaces (HMIs) have high potential in medical, entertainment, and industrial applications. Traditionally, surface electromyography (sEMG) has been used to track muscular activity and infer motor intention. Ultrasound (US) has received increasing attention as an alternative to sEMG-based HMIs. Here, we developed a portable US armband system with 24 channels and a multiple receiver approach, and compared it with existing sEMG- and US-based HMIs on movement intention decoding. Methods: US and motion capture data was recorded while participants performed wrist and hand movements of four degrees of freedom (DoFs) and their combinations. A linear regression model was used to offline predict hand kinematics from the US (or sEMG, for comparison) features. The method was further validated in real-time for a 3-DoF target reaching task. Results: In the offline analysis, the wearable US system achieved an average ${{\bm{R}}}^2$ of 0.94 in the prediction of four DoFs of the wrist and hand while sEMG reached a performance of ${{\bm{R}}}^2{\bm{\ }}$ = 0.60. In online control, the participants achieved an average 93% completion rate of the targets. Conclusion: When tailored for HMIs, the proposed US A-mode system and processing pipeline can successfully regress hand kinematics both in offline and online settings with performances comparable or superior to previously published interfaces . Significance: Wearable US technology may provide a new generation of HMIs that use muscular deformation to estimate limb movements. The wearable US system allowed for robust proportional and simultaneous control over multiple DoFs in both offline and online settings.