BACKGROUND AND OBJECTIVES:Hemodynamic predictions by computational fluid dynamics (CFD) strongly depend on inlet boundary conditions (IBC). One-dimensional Doppler ultrasound (DUS) is typically used for estimating flow IBCs, despite its sensitivity to the operator, ultrasound hardware and assumptions in flow rate computation. An alternative is two-dimensional high-frame-rate ultrasound particle image velocimetry (echoPIV). This study investigated the differences between DUS and echoPIV-derived IBCs and their effect on wall shear stress parameters in the stented superficial femoral artery. METHODS:CFD simulations using DUS and echoPIV-derived IBCs were performed for three patients with a superficial femoral artery stenosis that were treated with a stent. Spatiotemporal velocity profiles were compared at 0 - 50 mm from the inlet. Differences were quantified with the root-mean-square error (RMSE). Regions of low time-averaged wall shear stress (TAWSS) and high oscillatory shear index (OSI) using a literature-based threshold of 0.4 Pa and 0.2, respectively, and an IBC-specific threshold (lower third and upper third, respectively) were determined. Co-localization was quantified using the Jaccard similarity index. RESULTS:The DUS and echoPIV-derived IBCs differed in flow rate and velocity profile, with the largest difference found at peak systole (RMSE: > 50 cm/s). Using the literature-based threshold, similarity in low TAWSS was high for two patients (0.85 - 0.88) and low for one (0.57). Agreement in high OSI was low in two patients (0.45 - 0.48) and high in one patient (0.83). The IBC-specific threshold increased the agreement for both low TAWSS and high OSI (≥0.75). CONCLUSIONS:Differences in DUS and echoPIV-derived IBCs affected the TAWSS and OSI magnitudes. Regions of low TAWSS and high OSI corresponded well using an IBC-specific threshold. The literature-based threshold resulted in lower similarity values and different interpretations of restenosis risk that may cause differences in follow-up intensity or medical management.

Spectral computed tomography derived virtual monoenergetic imaging (VMI) reconstructions have been shown to reduce stent-induced blooming artifacts thus minimizing in-stent lumen underestimation. We have investigated the use of VMI reconstructions to reduce the blooming artifact for stent markers, single and double stent configurations. Two partially overlapping covered stents were deployed in a superficial femoral artery phantom. A conventional and twelve VMI reconstructions (40–100 keV and 120–200 keV with 10 and 20 keV increments, respectively) were created. Contrast-to-noise ratio, signal-to-noise ratio, attenuation difference between native and in-stent vessel lumen and full width at half maximum (FWHM) of the stent peaks were evaluated. The in-stent lumen diameter was measured, and the stent evaluated using a 5-point scale by three interventional radiologists. The 80–100 keV VMI reconstructions for the single stent configuration and the 140 keV VMI reconstruction for the other configurations resulted in the smallest lumen underestimation and best quality score on blooming. The underestimation was reduced from 21.5–29.1

Microbubble contrast agents are well-known in the biomedical field for their ability to enhance the contrast in ultrasound imaging and to facilitate targeted drug delivery within the body. Upon injection into the vasculature, these bubbles are strongly influenced by the viscoelastic properties of surrounding soft tissues. Here, we simulate the scattered pressure from a single phospholipid-coated microbubble placed in a uniform viscoelastic medium. We use a modified Rayleigh-Plesset equation that incorporates the viscoelastic response of the phospholipid shell and a Kelvin-Voigt model to represent tissue viscoelasticity. Our simulations aim to investigate the relationship between the viscoelasticity of the medium and that of the bubble shell, and its influence on bubble dynamics as a function of driving pressure, bubble radius, and medium elastic modulus. Results show that the frequency of maximum scatter response increases with the elastic modulus of the medium. While the radial excursion of a 2.0μm radius bubble can decrease by as much as 45% in a medium with an elastic modulus of 200 kPa as compared to that in water, the scattered pressure can increase by 50%. In contrast, the change in harmonic scattering is negligible: simulations predict a increase of only 5% for a 2.0μm bubble when increasing the medium elasticity from 0 to 200 kPa at a driving pressure of 120 kPa. Furthermore, subharmonics generated by driving the bubble at its resonance frequency (TR) are comparable to the subharmonics generated at twice the resonance frequency at lower driving pressures. For elevated pressures the TR/T2R subharmonic ratio increases with increasing elastic modulus. This is in sharp contrast with the resonance behavior of a microbubble in water. These results bear consequences for strategies that exploit the fundamental, harmonic, and subharmonic response of microbubble contrast agents.

The rheology of soft materials is routinely measured at low strain rates to extract constitutive laws necessary for understanding and modeling their behavior. High-frequency rheology, however, remains difficult to access. Consequently, the mechanical properties of soft materials at MHz strain rates are largely unknown. Ultrasound-driven microbubbles, widely used in biomedical imaging, drug delivery, and therapy, act as efficient mechanical actuators at MHz frequencies. Their dynamics depend on nonlinear resonance behavior, the viscoelasticity of their stabilizing shells, and the viscoelastic properties of the surrounding medium. Here, we make use of (nonlinear) bubble dynamics to characterize the rheology of polyacrylamide (PAM) hydrogels at strain rates exceeding 106 s-1. Narrow resonance curves of single coated microbubbles embedded in PAM, obtained through high-speed imaging, were compared to a Rayleighâ€"Plesset-type model. The results show that the shear modulus is similar in both the Hz and MHz regimes, while the loss modulus behaves very differently, exhibiting an effective shear viscosity at MHz frequencies comparable to that of water. These findings demonstrate a new approach for probing the high-frequency rheology of viscoelastic media.

Performing adjunctive intravascular imaging during femoropopliteal endovascular intervention could improve treatment planning and outcome. This systematic review assessed how imaging findings of intravascular ultrasound (IVUS) and optical coherence tomography (OCT) can contribute to improving treatment planning and outcomes of patients with femoropopliteal arterial disease. Scopus and PubMed databases were searched from January 2011 to July 2023 for all studies reporting on the use of IVUS or OCT imaging findings in the treatment of femoropopliteal disease. The effect of IVUS and OCT imaging findings on treatment plan and outcome, as well as the predictive ability of IVUS and OCT for treatment outcome, were analyzed. A total of 42 studies (one randomized-controlled trial, 17 prospective, 20 retrospective, and four descriptive studies), 34 involving IVUS, seven OCT, and one both, were included. IVUS-assessed diameters were significantly larger, and lesion length was longer compared to angiography, which affected treatment planning. OCT-measured diameters were significantly larger than angiography at follow-up and did not differ significantly from IVUS except for one location. Both IVUS and OCT identified more dissections, calcifications, residual stenoses, and inadequate stent expansion than angiography, impacting treatment planning. IVUS-assessed imaging findings were associated with reduced restenosis at 1 and 2-year follow-up compared to angiography alone, while for OCT, data was limited. IVUS and OCT can visualize complementary imaging features compared to angiography alone that change the treatment plan of patients with femoropopliteal disease, both pre- and post-treatment. IVUS has the potential to improve treatment outcomes, whereas there is still limited evidence for OCT.

Hypothesis: Monodisperse phospholipid-coated microbubbles, with a size and resonance frequency tuned to the ultrasound driving frequency, have strong potential to enhance sensitivity, efficiency, and control in emerging diagnostic and therapeutic applications involving bubbles and ultrasound. A key requirement is that they retain their gas volume and shell material during physiologic pressure changes and withstand the overpressure during intravenous injection. The shell typically comprises a mixture of a phospholipid (e.g., DSPC) mixed with a PEGylated phospholipid (e.g., DPPE-PEG5000). We hypothesize that (i) lipid-coated microbubbles destabilize when shell buckling occurs under pressurization, (ii) the overpressure at which buckling occurs (buckling pressure) is linked to the molar fraction of PEGylated lipid in the shell, and (iii) PEGylated lipid can be selectively expelled from the shell by fluidizing it at elevated temperatures.Experiments: The buckling pressure was measured using ultrasound attenuation spectroscopy while the ambient pressure was varied. When the ambient pressure increased, the microbubble resonance frequency dropped sharply due to shell buckling and the associated loss of elasticity. The buckling pressure Pb was obtained for monodisperse microbubbles formed by microfluidic flow-focusing, with DPPE-PEG5000 mixed with DSPC at molar fractions from 1.5% to 10%. Additionally, Pb was quantified for microbubbles containing 10 mol% PEG after heating at temperatures ranging from 40∘C to 70∘C. The molar PEG content of the microbubbles was analyzed using high-performance liquid chromatography.Findings: Quasi-static compression of a microbubble above its buckling pressure leads to its destabilization. Lowering the PEG molar fraction from 10 to 1.5% increased the buckling pressure from 3 kPa to 27 kPa. Similarly, heating the 10 mol% bubble suspension at 60∘C for one hour raised the buckling pressure by 20 kPa, due to the selective loss of PEGylated lipid from the shell, without affecting the monodispersity of the bubbles. The higher buckling pressure significantly improved microbubble stability, allowing them to withstand pressurization cycles of up to 45 kPa, nearly three times the systolic blood pressure in vivo.

Resolving arterial flows is essential for understanding cardiovascular pathologies, improving diagnosis, and monitoring patient condition. Ultrasound contrast imaging uses microbubbles to enhance the scattering of the blood pool, allowing for real-time visualization of blood flow. Recent developments in vector flow imaging further expand the imaging capabilities of ultrasound by temporally resolving fast arterial flow. The next obstacle to overcome is the lack of spatial resolution. Super-resolved ultrasound images can be obtained by deconvolving radiofrequency (RF) signals before beamforming, breaking the link between resolution and pulse duration. Convolutional neural networks (CNNs) can be trained to locally estimate the deconvolution kernel and consequently super-localize the microbubbles directly within the RF signal. However, microbubble contrast is highly nonlinear, and the potential of CNNs in microbubble localization has not yet been fully exploited. Assessing deep learningbased deconvolution performance for non-trivial imaging pulses is therefore essential for successful translation to a practical setting, where the signal-to-noise ratio is limited, and transmission schemes should comply with safety guidelines. In this study, we train CNNs to deconvolve RF signals and localize the microbubbles driven by harmonic pulses, chirps, or delay-encoded pulse trains. Furthermore, we discuss potential hurdles for in-vitro and in-vivo super-resolution by presenting preliminary experimental results. We find that, whereas the CNNs can accurately localize microbubbles for all pulses, a short imaging pulse offers the best performance in noise-free conditions. However, chirps offer a comparable performance without noise, but are more robust to noise and outperform all other pulses in low-signal-to-noise ratio conditions.

Context Radiofrequency ablation (RFA) is used as treatment for symptomatic thyroid nodules. Factors influencing the volume reduction ratio (VRR) at 12 months are not yet fully understood.Objective The primary objective of this work was evaluating the VRR at 12 months after RFA. Secondary objectives were the assessment of a learning curve and factors influencing the VRR at 12 months.Methods A retrospective observational cohort study was conducted at 3 Dutch referral hospitals of patients who underwent RFA for symptomatic thyroid nodules with available ultrasound (US) follow-up. Main outcome measures included US-based VRR at 12 months and chronologically numbered RFA procedures. All patients' baseline, treatment, and early follow-up factors were assessed for correlation with VRR at 12 months.Results A total of 337 patients with 356 nodules were included in the learning curve analysis. VRR at 12 months increased for the first 20 treatments per center and stabilized thereafter, indicating a plateau phase after a learning curve. These initial cases were removed from further analysis. In the remaining 299 nodules, median VRR at 3, 6, and 12 months was 57.1%, 65.6%, and 70.8%. Baseline nodule volume negatively correlated with VRR at 12 months but VRR was high for every volume category. Energy delivered per volume did not correlate with VRR.Conclusion In RFA for thyroid nodules, a stable treatment efficacy is achieved after 20 treatments, with a median VRR of 70.8%. Baseline nodule volume, energy delivered, and prolonged follow-up 6 months after treatment may not be clinically relevant to predict treatment success.

OBJECTIVE:Sonoporation employs ultrasound-driven microbubble oscillations to permeabilize cell membranes, offering the potential for intracellular drug delivery. However, its clinical adaption remains limited, primarily due to an incomplete understanding of the mechanisms through which oscillating bubbles disrupt cell membranes. Most mechanistic sonoporation studies have focused on cell monolayers cultured on rigid plastic scaffolds. METHODS:Here we investigated the influence of scaffold stiffness on sonoporation outcome using simultaneous ultra-high-speed imaging (10 million frames/s) to capture bubble dynamics and high-resolution confocal microscopy to assess cell membrane response and model drug uptake. Monodisperse 2.3 μm radius microbubbles were used to sonoporate single human umbilical vein endothelial cells cultured on either a soft hydrogel scaffold or a rigid polymer membrane. Ultrasound driving frequency and acoustic pressure amplitude were varied, while the pulse length was fixed at 15 cycles. RESULTS:Our results show that the slope of sonoporation efficiency versus microbubble radial excursion curve decreased by a factor of 30 when using the soft scaffold versus the rigid one, despite no apparent differences in microbubble dynamics. Furthermore, the nearly identical sonoporation efficiency versus radial excursion curves across the employed ultrasound frequencies of 0.5, 1.0 and 2.0 MHz suggest that acoustic radiation forces and normal or shear stresses are unlikely to be the primary mechanisms driving the observed differences. Additionally, membrane pore size increased with frequency for the rigid scaffold but decreased for the soft scaffold. CONCLUSION:Our findings highlight the critical role of mechanical scaffold properties in determining sonoporation outcomes, where softer scaffolds result in reduced membrane disruption and altered pore formation dynamics despite unchanged bubble oscillation behavior.

In piezoacoustic drop-on-demand inkjet printing, a single droplet is produced for each piezoelectric actuator driving pulse. This droplet is typically multicomponent, including surfactants to control the spreading and drying of the droplet on the substrate. However, the role of these surfactants in the droplet formation process remains rather elusive. Surfactant concentration gradients may manifest themselves across microsecond-to-second timescales, spanning both the rapid ejection of ink from the nozzle exit and the comparatively slower idling timescale governing the firing of successive droplets. In the present work, we study the influence of surfactants on droplet formation across 6 orders of magnitude in time. To this end, we visualize the microsecond droplet formation process using stroboscopic 8 ns laser-induced fluorescence microscopy while we vary the nozzle idle time. Our results show that increasing the idle time up to O(1) s affects only the breakup dynamics of the inkjet but not its velocity. By contrast, for idle times greater than O(1) s, both the breakup dynamics are altered and the velocity of the inkjet increases. We show that the increased velocity results from a decreased surface tension of the ejected droplet, which we observed from the shape oscillations of the jetted droplets in flight. The measured decrease in surface tension is surprising as the microsecond timescale of droplet formation is much faster than the typical millisecond-to-second timescale of surfactant adsorption. By varying the bulk surfactant concentration, we show that the fast decrease in surface tension results from a local surfactant concentration increase to more than 200 times the critical micelle concentration. Numerical simulations then show that the evaporation-driven increased surfactant concentration present at the nozzle exit results in the surface of the droplet being fully coated during its ejection. Altogether, our results suggest that a local high concentration of surfactant allows surfactant adsorption to the interface of an inkjet on the microsecond-to-millisecond timescale, which is much faster than the typical millisecond-to-second timescale associated with surfactant adsorption.

Ultrasound contrast agents (UCAs) have been used as vascular reporters for the past 40 years. The ability to enhance vascular features in ultrasound images with engineered lipid-shelled microbubbles has enabled breakthroughs such as the detection of tissue perfusion or super-resolution imaging of the microvasculature. However, advances in the field of contrast-enhanced ultrasound are hindered by experimental variables that are difficult to control in a laboratory setting, such as complex vascular geometries, the lack of ground truth, and tissue nonlinearities. In addition, the demand for large datasets to train deep learning-based computational ultrasound imaging methods calls for the development of a simulation tool that can reproduce the physics of ultrasound wave interactions with tissues and microbubbles. Here, we introduce a physically realistic contrast-enhanced ultrasound simulator (PROTEUS) consisting of four interconnected modules that account for blood flow dynamics in segmented vascular geometries, intravascular microbubble trajectories, ultrasound wave propagation, and nonlinear microbubble scattering. The first part of this study describes the numerical methods that enabled this development. We demonstrate that PROTEUS can generate contrast-enhanced radio-frequency (RF) data in various vascular architectures across the range of medical ultrasound frequencies. PROTEUS offers a customizable framework to explore novel ideas in the field of contrast-enhanced ultrasound imaging. It is released as an open-source tool for the scientific community.

The acoustic response of phospholipid-coated microbubbles is strongly affected by the viscoelastic properties of their stabilizing shell, which depend on surface dilatation through the lipid packing density. However, no fast, reliable, and user-friendly method currently exists to probe the surface dilatation-dependent shell rheology, similar to the Langmuir trough used for macroscopic flat lipid monolayers. In this work, we present a novel quasi-static method to measure the shell parameters of lipid-coated monodisperse microbubbles as a function of surface dilatation. The method relies on the combination of acoustic attenuation spectroscopy and optical attenuation spectroscopy. Acoustic attenuation spectra, measured as a function of ambient pressure, probes the microbubble resonance, while optical attenuation spectra are fitted with a Mie scattering model to provide an accurate measure of both modal bubble radius and polydispersity index (PDI). This integrated approach enables ultrafast sample characterization within a single second. We demonstrate the potential of the method by reporting shell viscosity, shell elasticity, and the corresponding surface tension curve for several cases including different concentrations of palmitic acid in the shell, and varying medium salinity and medium acidity.

Microbubbles are of great interest both for ultrasound imaging and for ultrasound-assisted therapy due to their nonlinear scattering, which is enhanced by the viscoelastic shell. A full characterization of this nonlinear response is therefore crucial to fully exploit their potential. Current microbubble characterization techniques rely on assumptions regarding the microbubble shell rheology. Here, a stress-strain method is proposed to characterize the viscoelastic shells of single microbubbles with minimal underlying assumptions, which mainly entail separable viscous and elastic contributions. Detailed knowledge of the acoustic driving pressure and frequency, combined with a precise measurement of the bubble oscillations obtained through high-frequency ultrasound scattering, allows to derive the viscoelastic contribution of single microbubbles. To account for experimental uncertainties, we employed a fitting procedure of the surface tension in the buckled and ruptured regimes, which currently limits the applicability of the method to phospholipid-shelled microbubbles. The method was validated through simulations, and used to experimentally characterize 275 individual microbubbles from a monodisperse population, revealing a shell elasticity of (0.49 +/- 0.10) N m(-1), and initial surface tension of (28.7 +/- 3.94) mN m(-1). Besides providing detailed information on single bubble dynamics, this analysis paves the way for the characterization of the viscous dissipation mechanisms of individual microbubble shells.

Ultrasound contrast imaging utilizes microbubbles to enhance echogenicity of the blood pool. Produced B-mode images are often composed of randomly overlapping and interfering point-spread-functions (PSFs) resulting from collective microbubble scatter. Microbubble localization techniques such as Ultrasound Localization Microscopy (ULM) super-resolve these images through centroid localization of sparse PSFs. While ULM can increase the resolution by up to 20 times, it struggles at high concentrations where PSFs overlap. Another inherent limitation lies in the use of conventional beamforming algorithms that discard the underlying physics of microbubble scatter. Recent deep learning-based super-resolution approaches address this limitation by deconvolving radiofrequency signals before image reconstruction, thereby leveraging microbubble and ultrasound physics for resolution enhancement. Given the highly non-linear nature of microbubble scattering, non-trivial imaging pulses may enhance these deconvolution strategies and increase localization performance. Here, we assess the performance of convolutional neural networks for localizing microbubbles across different transmit pulses. Our results show that the networks can accurately localize microbubbles for all investigated transmits, and that networks trained on chirps are significantly more robust to noise. Additionally, we show that incorporating bubble physics in the deep learning algorithms enhances ultrasound contrast imaging super-resolution performance.

OBJECTIVE:Accurate sizing of ultrasound contrast agent microbubbles is crucial for understanding their behavior through a direct comparison between models and experimental data. However, a gold standard method for microbubble sizing has yet to be established. METHODS:We introduced optical attenuation spectroscopy (OAS) for the sizing of monodisperse microbubble suspensions. This method employs a spectrophotometer to obtain an optical attenuation spectrum, to which a Mie scattering model is fitted, yielding the modal bubble radius and polydispersity index. We compared OAS sizing with the most common methods: Coulter Counter, brightfield microscopy and fluorescence microscopy. RESULTS:OAS measurements were in excellent agreement (±1.5%) with fluorescence microscopy. In contrast, the Coulter Counter over-estimated the modal microbubble radius compared with OAS by 4% for 3.0 μm radius microbubbles, increasing up to 11% for 4.0 μm radius microbubbles. Brightfield microscopy systematically over-estimated the microbubble radius by 0.45 μm compared with fluorescence microscopy. CONCLUSION:OAS has proven to be a versatile method for sizing monodisperse microbubble suspensions due to its convenient, label-free, and rapid acquisition within seconds.

OBJECTIVE:Local flow dynamics impact atherosclerosis yet are difficult to quantify with conventional ultrasound techniques. This study investigates the performance of ultrasound vector flow imaging (US-VFI) with and without ultrasound contrast agents in the healthy femoral bifurcation. METHODS:High-frame-rate ultrasound data with incremental acoustic outputs were acquired in the femoral bifurcations of 20 healthy subjects before (50V) and after contrast injection (2V, 5V and 10V). 2-D blood-velocity profiles were obtained through native blood speckle tracking (BST) and contrast tracking (echo particle image velocimetry [echoPIV]). As a reference, 4-D flow magnetic resonance imaging (4-D flow MRI) was acquired. Contrast-to-background ratio and vector correlation were used to assess the quality of the US-VFI acquisitions. Spatiotemporal velocity profiles were extracted, from which peak velocities (PSV) were compared between the modalities. Furthermore, root-mean-square error analysis was performed. RESULTS:US-VFI was successful in 99% of the cases and optimal VFI quality was established with the 10V echoPIV and BST settings. A good correspondence between 10V echoPIV and BST was found, with a mean PSV difference of -0.5 cm/s (limits of agreement: -14.1-13.2). Both US-VFI techniques compared well with 4-D flow MRI, with a mean PSV difference of 1.4 cm/s (-18.7-21.6) between 10V echoPIV and MRI, and 0.3 cm/s (-23.8-24.4) between BST and MRI. Similar complex flow patterns among all modalities were observed. CONCLUSION:2-D blood-flow quantification of femoral bifurcation is feasible with echoPIV and BST. Both modalities showed good agreement compared to 4-D flow MRI. For the femoral tract the administration of contrast was not needed to increase the echogenicity of the blood for optimal image quality.

In arterial disease, the presence of two or more serial stenotic lesions is common. For mild lesions, it is difficult to predict whether their combined effect is hemodynamically significant. This study assessed the hemodynamic significance of idealized serial stenotic lesions by simulating their hemodynamic interaction in a computational flow model. Flow was simulated with SimVascular software in 34 serial lesions, using moderate (15 mL/s) and high (30 mL/s) flow rates. Combinations of one concentric and two eccentric lesions, all 50

Over the past decade, ultrasound (US) has gathered significant attention and research focus in the realm of medical treatments, particularly within the domain of anti-cancer therapies. This growing interest can be attributed to its non-invasive nature, precision in delivery, availability, and safety. While the conventional objective of US-based treatments to treat breast, prostate, and liver cancer is the ablation of target tissues, the introduction of the concept of immunogenic cell death (ICD) has made clear that inducing cell death can take different non-binary pathways through the activation of the patient's anti-tumor immunity. Here, we investigate high-intensity focused ultrasound (HIFU) to induce ICD by unraveling the underlying physical phenomena and resulting biological effects associated with HIFU therapy using an automated and fully controlled experimental setup. Our in-vitro approach enables the treatment of adherent cancer cells (B16F10 and CT26), analysis for ICD hallmarks and allows to monitor and characterize in real time the US-induced cavitation activity through passive cavitation detection (PCD). We demonstrate HIFU-induced cell death, CRT exposure, HMGB1 secretion and antigen release. This approach holds great promise in advancing our understanding of the therapeutic potential of HIFU for anti-cancer strategies.

The study of vapor bubble growth following droplet vaporization in a superheated liquid involves research areas such as hydrodynamics, heat transfer, mass transfer, and thermodynamics. The interplay between these multiscale aspects is strongly dependent on the geometry, the thermodynamic response, and the local physical properties of the system. To understand the role of each aspect of this complex mechanism we model super-heated droplet vaporization by coupling the equation of motion for bubble growth with the thermodynamics of phase change and heat transfer through the convection-diffusion equation. The semi-analytical model is validated with the analytical description for vapor bubble growth dominated either by inertia (Rayleigh) or by thermal diffusion (Plesset-Zwick), depending on droplet radius and degree of superheat. The effect of a mismatch of the thermal properties between the host liquid and the droplet is shown to be relevant only for low superheating, above which an increase in thermal diffusivity leads to a reduction in the rate of vaporization. At medium to high superheating, the droplet vaporizes completely without relying on thermal diffusion. At the point of complete vaporization, the potential energy within the system drives the bubble overshoots, which vary based on the droplet size and degree of superheat.

Understanding the ultrasound pressure-driven dynamics of microbubbles confined in viscoelastic materials is relevant for multiple biomedical applications, ranging from contrast-enhanced ultrasound imaging to ultrasound-assisted drug delivery. The volumetric oscillations of spherical bubbles are analyzed using the Rayleigh-Plesset equation, which describes the conservation of mass and momentum in the surrounding medium. Several studies have considered an extension of the Rayleigh-Plesset equation for bubbles embedded into viscoelastic media, but these are restricted to a particular choice of constitutive model and/or to small deformations. Here, we derive a unifying equation applicable to bubbles in viscoelastic media with arbitrary complex moduli and that can account for large bubble deformations. To derive this equation, we borrow concepts from finite-strain theory. We validate our approach by comparing the result of our model to previously published results and extend it to show how microbubbles behave in arbitrary viscoelastic materials. In particular, we use our viscoelastic Rayleigh-Plesset model to compute the bubble dynamics in benchmarked viscoelastic liquids and solids.