Accurate volumetric velocity estimation is crucial in ultrasound imaging for both diagnostic and therapeutic applications. Traditional ultrasound systems, though effective for two-dimensional imaging, face major limitations in 3D imaging due to hardware and computational demands. Row-column addressed (RCA) ultrasound probes offer a promising alternative by reducing hardware complexity, thereby reducing the gap between research prototypes and clinical systems. However, this typically comes at the expense of stronger sidelobes compared with fully populated matrix arrays, leading to reduced image contrast. Several approaches have been proposed to improve the contrast of power Doppler imaging, yet the accuracy and performance of velocity Doppler estimation have received comparatively little attention. In this study, we present a method that exploits the phase information from RCA row and column signals to derive a novel velocity estimator based on cross-correlation of orthogonal apertures. This extends the XDoppler scheme, initially developed for power Doppler imaging, to velocity estimation. The XDoppler estimator is shown to provide accurate measurements of axial velocities and to outperform the traditional phase-shift autocorrelator, while offering a theoretical Nyquist velocity twice as high. In vitro experiments further demonstrate enhanced sensitivity to slow flows and reduced bias in flow rate estimation. In vivo data from a carotid artery confirm the reduced sensitivity to aliasing and reveal the ability to track dynamic blood flow velocity changes associated with arterial pulsatility. These findings suggest that the XDoppler velocity estimator could improve volumetric velocity imaging in clinical contexts.

Microbubble contrast-enhanced ultrasound (CEUS) relies on discriminating nonlinear bubble signals from linear tissue backscattering. While Singular Value Decomposition (SVD) filtering improves this discrimination, existing techniques often fail to retain the slowly-moving microbubble signals from static clutter. Here, we present a novel multi-stage singular value decomposition (MS-SVD) framework for ultrafast CEUS imaging. Our method employs plane-wave transmissions at multiple angles and acoustic pressure levels (implemented via duty-cycle modulation) and alternating transmit polarity. The beamformed data are then processed by three sequential SVD filters: (1) spatial-angular SVD to extract coherent signals across all transmit angles, (2) spatial-pressure SVD to separate linear fundamental and nonlinear harmonic components, and (3) spatiotemporal SVD to isolate moving microbubble echoes from tissue clutter. In in vitro flow phantoms and in vivo rat brain through a cranial window, MS-SVD dramatically improves microbubble detection compared to conventional SVD filtering, MS-SVD yields much stronger vascular contrast and suppresses tissue clutter to a greater extent. In the in vitro phantom, MS-SVD yielded 2.3-fold more ULM localizations and 1.8-fold more tracked trajectories, a 3.5 dB higher vessel-to-background contrast and a 40 % lower background localization density, giving denser and more complete super-resolution maps. By capturing the full acoustic signature of microbubbles (both fundamental and harmonic), MS-SVD achieves higher contrast-to-noise and sensitivity in CEUS. These gains make it a powerful front-end for super-resolution ultrasound localization microscopy and other high-sensitivity microvascular imaging applications.

BACKGROUND:Cerebral complications in patients with infective endocarditis (IE) are common and worsen prognosis. Determining the optimal timing for cardiac surgery in this context remains challenging. In this study we describe the characteristics and outcomes of IE patients with cerebral complications who were managed either surgically or medically. METHODS:We analyzed all consecutive patients with IE-related cerebral complications enrolled in a prospective cohort study in Aquitaine, France (2013-2021). Patients were classified as operated or nonoperated. The primary outcome was all-cause mortality at 1 month; secondary outcomes included all-cause mortality up to 1 year and the impact of cerebral lesion type and surgical timing. RESULTS:Among 1230 IE patients, 288 had cerebral complications (age 65 ± 14 years, 74% male). Ischemic and hemorrhagic cerebral lesions occurred in 76% and 19% of patients, respectively. Severe valvular damages were present in 43% and cardiac surgery was indicated in 86% of cases. One-month mortality was significantly higher among nonoperated vs operated patients (27% vs 5.9%, P < 0.001). Multivariate analysis identified heart failure, coma, and cardiac surgery (odds ratio 0.24, 95% confidence interval 0.10-0.56, P < 0.001) as independent predictors of mortality. Neither the type of cerebral lesion nor surgical timing appeared to affect prognosis. CONCLUSIONS:When indicated, cardiac surgery should be systematically discussed in IE patients with cerebral complications. Early intervention guided by a multidisciplinary endocarditis team with neurology expertise may improve outcomes.

Objective. Coronary microvascular dysfunction plays a central role in major cardiovascular diseases, yet non-invasive imaging of the human coronary microcirculation remains an unresolved challenge in clinical practice. ultrasound localization microscopy (ULM) enables microvascular imaging beyond the diffraction limit, but whole-heart volumetric ULM is hindered by cardiac motion, rib-induced acoustic aberrations, limited control over microbubble (MB) dynamics, and hardware-related field-of-view constraints. Experimental optimization under clinical conditions is therefore challenging.Approach. We developed a dedicated simulation framework for three-dimensional coronary ULM by extending a previously validated brain ULM simulation framework to the human coronary circulation. A synthetic coronary vascular network with physiologically realistic hemodynamics was generated using a space-colonization algorithm combined with Murray's law and Poiseuille flow assumptions. Ground-truth MB dynamics were simulated and convolved with experimentally measuredin vitropoint spread functions, including configurations with human ribs to reproduce acoustic aberrations. The framework generates realistic four-dimensional (x, y, z, t) ultrasound datasets for quantitative benchmarking of MB detection, localization, and tracking performance.Main results. Systematic simulations demonstrated that both cardiac motion and rib-induced aberrations significantly degrade coronary ULM performance, particularly in small vessels, leading to reduced precision, sensitivity, and Jaccard index. Cardiac gating partially restored performance but increased acquisition time, underscoring critical trade-offs between robustness and efficiency.Significance.This simulation framework provides a realistic and flexible benchmarking platform for the evaluation of volumetric coronary ULM under controlled conditions. It enables quantitative assessment of acquisition strategies, probe designs and image-processing algorithms, thereby supporting the development and clinical translation of three-dimensional coronary ULM.

Objective To extend the use of a large multi-lens probe technology to 4D ultrafast Doppler imaging and validate its performance both in vitro using a flow phantom and in vivo on the human carotid artery. Methods Radio-frequency data were acquired using a 1MHz large-aperture multi-lens probe on a tilted flow phantom with two tubes perfused by a water-cellulose mixture, and on a human carotid artery in vivo with contrast agents. 3D delay-and-sum beamforming with coherent compounding of 10 to 12 diverging waves, lens correction, and dynamic focusing was performed, followed by singular value decomposition (SVD) filtering to obtain Power Doppler data, Color and spectral Doppler data. Tube diameters were measured from Power Doppler volumes and compared with reference measurements taken with a conventional linear probe. Results Tube diameters measured with the probe were consistent with those using a premium image quality commercial echographic device (Aixplorer, Supersonic Imagine), demonstrating the capability to retrieve structural information. The multi-lens system showed sensitivity to flow orientation and successfully detected opposite flow directions within the phantom. Doppler spectra captured carotid pulsatility, illustrating the ability to quantify physiologically relevant flow dynamics. The large-aperture design achieved an extended field of view of 41 × 69 × 41 mm³ in the phantom and 39 × 103 × 32 mm³ in vivo, with penetration depths of up to 8 cm and 6 cm, respectively. Conclusion The large multi-lens probe enables a wide-field of view 4D ultrafast Doppler imaging of the carotid in humans and holds strong potential to improve vascular mapping in a clinical setting.

OBJECTIVE:Non-invasive focused ultrasound therapies of abdominal organs, including the heart and the liver, have emerged in the last decades. Transthoracic focusing of ultrasound poses challenges such as pressure loss and aberrations. Numerical models of ultrasonic propagation have been developed to study the focalization in heterogeneous tissues, particularly for transcranial applications. However, ribcage models were less studied than skull models, and no experimental validation of ribcage models has been performed so far. METHODS:Both linear and nonlinear k-space simulations were used to model the ultrasonic propagation from a clinical system dedicated to transthoracic cardiac therapy. Tissue acoustic properties were determined from computed tomography scans. Experimental model validation was performed with hydrophone measurements of pressure fields through in vitro human ribs and in vitro porcine flail chest. RESULTS:An excellent agreement of pressure distribution between the acquired and simulated pressure fields was found for the linear propagation model with a mean correlation coefficient between the measured and simulated pressure fields of R2 = 0.89±0.07. For the nonlinear propagation, the mean correlation coefficient was R2 = 0.91±0.06. The feasibility of the simulations through the human thorax was demonstrated on 9 patients who underwent non-invasive therapy of the aortic valve. The global attenuation estimated numerically was correlated with the amplitude at the focus necessary to nucleate cavitation (R2 = 0.64). CONCLUSION:The numerical model of transthoracic ultrasound propagation was validated and used on a human patient's thorax. SIGNIFICANCE:With further development, this model could be used as a treatment planning tool for non-invasive ultrasonic cardiac therapy.

Brain perfusion relies on a complex vascular network of arteries, veins, and capillaries to meet its constant demand for oxygen and nutrients. Disruption of this microvascular system is a hallmark of many neurological disorders, including small vessel disease, stroke, and brain tumors. As such, high-resolution in vivo imaging of cerebral microvascular flow and structure remains critical to understanding these pathologies. Among them, ultrasound localization microscopy (ULM) allows noninvasive imaging of microvascular network down to small arterioles and venules at subwavelength resolution using injected microbubbles, but the approach remains mainly limited to 2D imaging with few volumetric implementations. In this study, we explore in vivo transcranial 3D ULM of the mouse brain using row-column arrays (RCA) and introduce an analysis framework to build a flow-directed vascular graph from the ULM microbubble tracking data, allowing to differentiate between subgraphs of artery-like and vein-like vascular segments. Using this framework, we are able to quantify flow and radius relationships for each subgraph in different anatomical regions. This high-sensitivity framework enables in vivo microvascular imaging and quantification in mice and provides a scalable platform for preclinical neurovascular studies in health and disease.

Objective.Ultrafast nonlinear ultrasound imaging of gas vesicles (GVs) promises high-sensitivity biomolecular visualization for applications such as targeted molecular imaging and real-time tracking of gene expression. However, separating GV-specific signals from tissue remains challenging due to tissue clutter and limitations of current methods, which require complex transmit schemes and suffer from incomplete tissue suppression. This study aims to develop and validate harmonic amplitude-modulated singular value decomposition (HAM-SVD), a novel technique that represents a shift from current GV imaging methods by exploiting the unique nonlinear pressure-dependence of the GV harmonic signature.Approach.HAM-SVD employs single-cycle plane waves transmitted at 9.6 MHz across five tilted angles at a pulse repetition frequency of 2500 Hz, under four duty cycles (DCs) with alternating polarity. Beamformed data are reshaped into a space-pressure Casorati matrix and decomposed via SVD. Tissue background is suppressed by discarding the first (weakly nonlinear tissue) and lowest (noise) singular modes, yielding images comprised solely of pressure-dependent second-harmonic GV signals. The method was validated through numerical simulations,in vitrophantom experiments, andin vivorat lower limb imaging.Main results.HAM-SVD achieved a signal-to-background ratio of 19.16 ± 1.63 dBin vivo, significantly outperforming pulse inversion (14.19 ± 1.41 dB) and amplitude modulation (AM-SVD) (15.79 ± 1.38 dB). Simulation and phantom studies demonstrated superior spatial coherence in singular vector decomposition and reduced nonlinear artifacts compared to AM-SVD. HAM-SVD enables wide-field, ultrafast imaging without complex transmit sequences while maintaining robust tissue clutter suppression across varying pressure levels.Significance.By combining harmonic imaging with AM-SVD's adaptive clutter filtering, HAM-SVD overcomes limitations of conventional nonlinear techniques, including depth restrictions in xAM and incomplete tissue cancellation in pulse inversion. This approach enhances molecular imaging specificity for GVs and holds translational potential for ultrasound localization microscopy of slow-flowing contrast agents and preclinical disease-targeted molecular imaging.

OBJECTIVE:Calcific aortic valve disease advances via increased fibrosis and calcification deposition, leading to progressive narrowing of the outflow tract, left ventricular hypertrophy and cardiac failure. Currently, surgical repair and replacement are the only strategies for intervention. While transcatheter aortic valve replacement offers a less invasive alternative to surgical intervention, implanted bioprosthetic valves have limited durability. Non-invasive ultrasound therapy was shown to not damage normal porcine aortic valve, and successfully reduced stenosis of calcified bioprosthetic valves in vivo, as well as decrease stenosis of native severely calcified aortic stenosis in a first-in-human study. However, critical questions regarding the effect of ultrasound therapy on valvular cells remain. In this study, we aimed to optimize pulsed ultrasound cavitation (PUC) treatment for cell culture studies and evaluate the acute and persistent effects on human valvular interstitial cells (hVICs) in calcifying conditions. METHODS:We utilized viability, metabolism and calcification assays as well as mass spectrometry-based proteomics to holistically characterize the effects of PUC treatment in hVICs. RESULTS:hVICs viability and metabolism were not significantly altered as a function of PUC treatment at short- (48 hour) or long-term (21 day) time points. Furthermore, PUC treatment did not increase hVICs calcification in vitro. Proteomic profiling of hVICs showed that PUC treatment had limited persistent changes to protein profiles compared with the acute effects of PUC treatment. CONCLUSION:These studies suggest that ultrasound therapy, currently limited to very severe aortic stenosis, could be of interest at an earlier stage of the disease.

Background. Pediatric hypertrophic cardiomyopathy (HCM) is associated with significant morbidity and mortality. While identified as a genetic disease mainly involving sarcomeric genes, the association between genotypical variation and phenotypic expression is not fully established. Developments in Ultrafast ultrasound imaging allows quantifying myocardial stiffness using shear waves elastography (SWE). When combined with strain measurements, myocardial work can be computed, offering new insights into phenotype myocardial properties. Methods. An age-matched population of 20 Healthy volunteers (HVs, mean age=11.1 ± 4.5years), 20 HCM (genotype- and phenotype-positive, mean age=11.6 ± 5.3years) and 20 Genotype (genotype-positive, phenotype-negative, mean age=11.1 ± 4.8years) were included in the study. Each participant underwent conventional echocardiography and a full cardiac-cycle exploration of the basal anteroseptal segment consisting of: (1) myocardial stiffness by SWE, (2) segmental strain and thickness, which are used to compute one-beat work, the stress-strain loop area, contributive and dissipative work. Results. Mean diastolic myocardial stiffness (DMS) and peak myocardial strain (PMS) distinguished the HCM group (DMS=23.7 ± 8.7kPa; PMS= -6.64 ± 5.9%) from HV group (DMS=7.2 ± 0.7kPa, p<0.01; PMS= -19.9 ± 4.1%, p<0.01). No significant differences were observed in DMS and PMS between HVs and Genotype groups. One-beat work and stress-strain loop areas showed significant differences among all 3 groups (p<0.01) and could distinguish the Genotype group (one-beat work= 318.2 ± 100.2µJ/mm; stress-strain loop area=33.2 ± 10.6kPa.%) from HVs (one-beat work= 582.4 ± 137µJ/mm; stress-strain loop area= 66.8 ± 19.8 kPa.%), and the HCM group (one-beat work= 38.2 ± 107.1µJ/mm, stress-strain loop area=5.8 ± 6.5kPa.%), p<0.01. Conclusion. Combining Ultrafast ultrasound with speckle-tracking echocardiography, we demonstrate that one-beat work and stress-strain relationship, obtained by combining myocardial stiffness, strain, and thickness have the potential to distinguish genotype-positive, phenotype-negative patients from healthy controls. Clinical outcome studies are needed to determine the prognostic value of these parameters in phenotype-positive HCM patients. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was supported by Canadian Institutes of Health Research (CIHR), 202203PJT- 183888; Canada Foundation for Innovation (CFI) and the Ministry of Research and Innovation, Canada; and the Labatt Family Heart Center at the Hospital for Sick Children, Toronto, Canada. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. This work was supported by the European Research Council (ERC) under the European Union?s Horizon Europe research and innovation program (5D ULTRAFAST HCM project, grant agreement # 101220327) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All subjects gave informed written consent, and the study was approved by The Hospital for Sick Children Research Ethics Board (REB # 1000074747). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data referenced and analyzed in this manuscript are available from the corresponding author upon reasonable request. All datasets generated during the current study are archived in secure institutional storage and will be shared in de-identified form for academic research purposes.

Background: Cardiac Amyloidosis (CA), particularly transthyretin amyloidosis (ATTR) is characterized by the deposit of amyloid proteins in the extracellular matrix of myocardium leading to increased myocardial stiffness (MS) and impaired diastolic function. Previous studies have shown that 2D ultrasound shear wave elastography (SWE) can quantify non-invasively myocardial shear wave velocity (SWV) characterizing its stiffness. However, myocardium is a tri-dimensional tissue with a helicoidal fiber structure associated to anisotropic mechanical properties that vary over cardiac cycle. Therefore, accurately measuring MS in diastasis phase, under passive stiffness, requires a 3D approach with ECG gating. Purpose: We aim to demonstrate the feasibility of 3D-SWE for the quantification of diastolic MS in ATTR-CA patients. Methods: This prospective cohort study included 12 patients with diagnosed ATTR-CA (primary exposure variable) patients that received a standard echocardiographic examination and 3D-SWE. A customized ultrasound device based on a matrix transducer was used to perform 3D-SWE (Fig A) measuring SWV, primary outcome variable, in a myocardial volume of 10x16x16mm 3 (Fig C). Positioning was guided by real-time 2D B-mode and acquisitions were trigged during diastasis phase using ECG gating (Fig B). SWV was assessed in 3 myocardial regions: anterior free wall of the right ventricle (RV), basal antero-septal wall (AS) and apex, with 10 acquisitions per segment, totaling 360 transthoracic 3D-SWE acquisitions. Inter-operator variability was evaluated in 3 patients by two sonographers. Results: 3D-SWE was successfully performed in all patients (82±6 years; 85% men; LVEF: 60±9%; E/E’: 14±7; IVS: 16±3mm and GLS: -11±4%), in the 3 myocardial regions. Median SWV (Q1-Q3) values were 2.85m/s (2.35–3.03) in RV, 5.24 m/s (4.71–5.72) in AS, and 1.24 m/s (1.04–1.56) at the apex. Mean absolute difference over measurements performed by the two sonographers was 0.22m/s (RV), 0.75m/s (AS) and 0.23m/s (apex) and Intra-Correlation Coefficient was 0.96. Conclusion: Feasibility and good reproducibility of 3D-SWE on ATTR-CA patients was demonstrated. SWV of AS and RV segments were higher than apex segment and MS values reported on healthy volunteer. This distribution of MS among the 3 segments is consistent with apical sparing reported using strain measurement. 3D-SWE has the potential to provide accurate MS assessment for early diagnosis and follow-up of CA patients.

Visualizing the arterial tree using ultrasound, from the aorta to the small vessels, has significantly improved over time due to advances in ultrasound imaging technology. Initially limited to exploring the major vessels, ultrasound analysis has made considerable progress with enhanced image quality. While injecting microbubbles as a contrast agent partially addresses this limitation, its use is constrained by the need for intravenous injection, making the examination more complex and time-consuming. To address these drawbacks, new commercial modes have emerged, distinct from conventional color- and power-Doppler modes, offering the ability to analyze slow flows and, consequently, microvascularization. These dedicated imaging modes include B-flowTM, E-flowTM, Superb Microvascular Imaging (SMITM), Micro Flow Imaging (MFITM), MV-FlowTM, Detective Flow Imaging (DFITM), Micro-VTM, and Angio PLUS imagingTM. Although these modes share similar objectives, they are based on different technologies, each with its own specific characteristics. The exact algorithms behind these modes vary and are proprietary but rely on a combination of approaches to reduce tissue clutter and electronic noise while improving sensitivity to slower-flow Doppler signals. This review aims to explain the technological basis of these "microvascular flow imaging modes" (MVFI) currently clinically available in vascular imaging to the physician and sonographer specialized in vascular ultrasound, discussing their current limitations and potential applications in vascular medicine.

Ultrasound Localization Microscopy (ULM) has emerged as a promising technique for imaging microvascular networks at subwavelength resolution. However, its 3D translation in clinics for complex organs like the brain remains limited due to technological and experimental challenges, including probe design constraints, motions artifacts, and both acoustic attenuation and aberrations caused by the skull. In this study, we present a fast and versatile simulation framework for 3D ULM based on a realistic human brain vasculature model that includes small vessels down to the precapillary scale, along with its hemodynamics driven by conservation and Murray's law. This novel framework enables comparison of ultrasound probe configurations, ULM algorithm performance, and experimental parameters such as microbubble (MB) concentration, subpixel motion, and skull-induced aberrations in transcranial imaging conditions. To illustrate a range of case scenarios, three matrix array probes were evaluated including a matrix probe with large elements combined with diverging lenses. We evaluated localization accuracy, tracking performance, velocity distribution and the extent of the field of view. As expected, the simulations also highlighted the negative impact of high MB concentration and motions artifacts on detection performance, as well as the significant effect of skull-induced aberrations. The proposed framework provides a robust interface for developing, testing and optimizing 3D ULM systems, with potential applications extending to other organs and clinical scenarios.

AIMS:Myocardial work assessment has emerged as a promising tool for left ventricular (LV) performance evaluation. Existing non-invasive methods for assessing it rely on assumptions on LV pressure and geometry. Recently, shear wave elastography allowed to quantify changes in myocardial stiffness throughout the cardiac cycle. Based on Hooke's law, it becomes theoretically possible to calculate myocardial stress and work from myocardial stiffness and strain measurements. The main objective of this study is to demonstrate the feasibility of this comprehensive ultrasound approach and to compare myocardial work values between populations where variations are anticipated. METHODS AND RESULTS:Children with hypertrophic cardiomyopathy (HCM), aortic stenosis (AS) and healthy volunteers (HV) were included in this study. Segment dimensions, strain, thickness, and segmental myocardial stiffness were assessed in the basal antero-septal segment throughout the cardiac cycle. One-beat segmental work, the stress-strain loop area, and contributive and dissipative work were compared between groups. Twenty HV (9.8 ± 5.3 years of age), 20 HCM (10.0 ± 6.1 years of age), and 5 AS (5.3 ± 4.3 years of age) subjects were included. One-beat segmental work was significantly higher in AS (272.0 ± 102.9 µJ/mm) and lower in HCM (38.2 ± 106.9 µJ/mm) compared with HV (131.1 ± 83.3 µJ/mm), P = 0.02 and P = 0.01, respectively. Desynchronized work was prevailing in HCM with dissipative work during systole measured at 17.3 ± 28.9 µJ/mm and contributive work during diastole measured at 15.3 ± 18.0 µJ/mm. The stress-strain loop area was higher in AS (95.2 ± 31.1 kPa%) and HV (66.2 ± 35.9 kPa%) than in HCM (5.8 ± 13.0 kPa%), P < 0.01. CONCLUSION:Calculating segmental myocardial work based on myocardial stiffness and strain measurements is technically feasible. This approach overcomes the inherent limitations of current methods by introducing a direct quantitative measure of myocardial stress.

This work details the design and fabrication of a 24 Fr ultrasound catheter sheath with >90 degrees mechanical steering and forward-looking imaging for minimally invasive cardiac procedures. A 16 Fr lumen accommodates therapy catheters, while a 2D annular array provides real-time imaging: wide-view 3D for navigation and high-res 2D for precise monitoring. Field-II simulations were performed to optimize the array-256 trapezoidal elements (7.5 MHz) arranged in four rings-maintaining a 22.5 Fr outer diameter. The fabrication involved a piezocomposite stack on a flexible PCB integrated into the sheath. In vitro testing using a therapy catheter and a CIRS054 phantom demonstrated potential for both 3D guidance and high-resolution 2D imaging, meeting application requirements. This advanced sheath aims to improve cardiac surgery workflow, eliminating the need for an auxiliary ultrasound imaging pathway and providing 3D real-time information while reducing fluoroscopy. This solution was further validated in a porcine preclinical cardiac interventional procedure.

Mapping microcirculation at the whole-organ scale in 3D is crucial for understanding vascular pathologies and improving diagnostics. Although 3D ultrasound localization microscopy (ULM) enables microscopic resolution by localizing intravenously injected microbubbles in small animal models, visualizing entire organs in large animals or humans remains challenging due to limited field of view, low sensitivity, and probe technological complexity. Here, we demonstrate how a multi-lens array method overcomes these limitations. Combined with 3D ULM, it maps and quantifies large vascular volumes (up to 120 × 100 × 82 mm³) at high spatial resolution (125-200 µm) with a volumetric acquisition rate of 312 Hz, using low-cost technology. This approach enables deeper insights into hemodynamics from large vessels to pre-capillary arterioles, by providing vast and rich datasets of whole-organ vascularization. It could also facilitate diagnosis of microcirculation disorders and monitoring of small-vessel disease treatments by addressing key limitations of current imaging modalities.

Over the last decade, 3D ultrafast ultrasound imaging has been used in different applications including Elastic Tensor Imaging (ETI) based on 3D Shear Wave Elastography and Backscatter Tensor Imaging (BTI). BTI and ETI can provide important biomechanical and structural parameters of fibrous soft tissues such as the skeletal muscles or the myocardium. However, 3D ultrafast imaging requires 2D transducers arrays with a large number of elements, which mainly limits their use to laboratory research settings. This study aims to develop a clinically transposable ultrasound system combining 3D-ETI and BTI to characterize anisotropic tissues. A low channel count system with 128 channels based on a vantage system and a dedicated matrix transducer driven at 2.5MHz was developed. The performance of the approach was demonstrated on anisotropic and fibrous phantoms. In-vivo feasibility was performed on the brachii biceps of 4 healthy volunteers at controlled contractions levels using weights held in the hand. Using this approach, we could investigate the functional change of muscle stiffness during contraction (shear wave speed from 3.2±0.20m/s to 6.6±0.58m/s, and elastic fractional anisotropy from 0.26±0.04 to 0.49±0.07). Structural characterization was performed with BTI, fiber organization and coherence fractional anisotropy remained constant with contraction (0.27±0.05). This novel device enables non-invasive characterization of anisotropic tissues, discerning stress and structural anisotropy in promising applications in musculoskeletal and myocardial pathologies.

Introduction: Mitral regurgitation (MR) severity is assessed by measuring the regurgitant volume (RVol) with echocardiography using the proximal iso-velocity surface area (PISA) method. The low temporal resolution of focused ultrasound, the assumption of perfect hemispheric iso-velocity contours, and the use of a single point to assess the velocity are the pitfalls inherent to this method. This study aimed to evaluate a method using ultrafast ultrasound with higher temporal resolution, and multiple point for velocity assessment to provide a more accurate volume measurement. Methods: A custom left heart mock circulatory system, comprised of a left atrium and a left ventricle connected by an orifice simulating MR, was filled with demineralized water mixed with cellulose. Pulsatile flow was generated using predefined RVols of 20mL, 30mL and 40 mL. Data were acquired at 6000 frames/s by a conventional cardiac phased array probe (central frequency at 2.75MHz) emitting ultrafast diverging waves, connected to an ultrafast scanner. RVols were computed as the surface integral of the velocity through a planar disk at the input of the orifice and with the PISA method at this same point. The root mean squared error (RMSE), mean absolute percentage error (MAPE) and accuracy of the two methods was compared with a t-test to evaluate the performances of PISA and the planar disk method. Results: RVol estimation using the planar disk method showed a much lower absolute error values than the clinical standard PISA method (15 +/- 9% vs 81 +/- 5%, p<0.001). Conclusion: This study demonstrates that ultrafast ultrasound can provide accurate estimate of RVol in a model of MR by leveraging the complete axial velocity mapping at high temporal resolution. Its complementary role to PISA method should be evaluated in future clinical studies.

Objectives: Monitoring cavitation during ultrasound therapy is crucial for assessing the procedure safety and efficacy. This work aims to develop a self-sensing and low-complexity approach for robust cavitation detection in moving organs such as the heart. Methods: An analog-to-digital converter was connected onto one channel of the therapeutic transducer from a clinical system dedicated to cardiac therapy, allowing to record signals on a computer. Acquisition of successive echoes backscattered by the cavitation cloud on the therapeutic transducer was performed at a high repetition rate. Temporal variations of the backscattered echoes were analyzed with a Singular-Value Decomposition filter to discriminate signals associated to cavitation, based on its stochastic nature. Metrics were derived to classify the filtered backscattered echoes. Classification of raw backscattered echoes was also performed with a machine learning approach. The performances were evaluated on 155 in vitro acquisitions and 110 signals acquired in vivo during transthoracic cardiac ultrasound therapy on 3 swine. Results: Cavitation detection was achieved successfully in moving tissues with high signal to noise ratio in vitro (cSNR = 25±5) and in vivo (cSNR = 20±6) and outperformed conventional methods (cSNR = 11±6). Classification methods were validated with spectral analysis of hydrophone measurements. High accuracy was obtained using either the clutter filter-based method (accuracy of 1) or the neural network-based method (accuracy of 0.99). Conclusion: Robust self-sensing cavitation detection was demonstrated to be possible with a clutter filter-based method and a machine learning approach. Significance: The self-sensing cavitation detection method enables robust, reliable and low complexity cavitation activity monitoring during ultrasound therapy.