A computational framework for the multiphysics simulation of microbubble-mediated sonothrombolysis using a forward-viewing intravascular transducer

Enhancing sonothrombolysis outcomes with dual-frequency ultrasound: Insights from an in silico microbubble dynamics study

Sonothrombolysis is a technique that employs the ultrasound waves to break down the clot. Recent studies have demonstrated significant improvement in the treatment efficacy when combining two ultrasound waves of different frequencies. Nevertheless, the findings remain conflicted on the ideal frequency pairing that leads to an optimal treatment outcome. Existing experimental studies are constrained by the limited range of frequencies that can be investigated, while numerical studies are typically confined to spherical microbubble dynamics, thereby restricting the scope of the analysis. To overcome this, the present study investigated the microbubble dynamics caused by the different combinations of ultrasound frequencies. This was carried out using computational modelling as it enables the visualisation of the microbubble behaviour, which is difficult in experimental studies due to the opacity of blood. The results showed that the pairings of two ultrasound waves with low frequencies generally produced stronger cavitation and higher flow-induced shear stress on the clot surface. However, one should avoid the frequency pairings that are integer multipliers of each other, i.e., frequency ratio of 1/3, 1/2 and 2, as they led to resultant wave with low pressure amplitude that weakened the cavitation. At 0.5 + 0.85 MHz, the microbubble caused the highest shear stress of 60.5 kPa, due to its large translational distance towards the clot. Although the pressure threshold for inertial cavitation was reduced using dual-frequency ultrasound, the impact of the high-speed jet can only be realised when the microbubble travelled close to the clot. The results obtained from the present study provide groundwork for deeper understanding on the microbubble dynamics during dual-frequency sonothrombolysis, which is of paramount importance for its optimisations and the subsequent clinical translation.

Numerical modeling of ultrasound-triggered microneedle-mediated delivery of drug particles into bacterial biofilms

Ultrasonic microneedle patches, a class of ultrasound-driven transdermal drug delivery systems, are promising in addressing bacterial biofilms. This device has been proven to be more effective in treating Staphylococcus aureus biofilms than drug in free solution. However, there exists a notable gap in understanding how various excitation conditions and material parameters affect drug delivery efficiency. This study aims to fill this void by conducting an comprehensive multi-physics numerical analysis of ultrasonic microneedle patches, with the ultimate goal of enhancing drug delivery. First, we investigate the impact of various ultrasound frequencies on drug penetration depths. The findings reveal that local resonance can accelerate drug release within a shorter time window (first 1.5 h), whereas non-resonant frequencies enable more profound and prolonged diffusion. This information is crucial for medical professionals in selecting the most effective frequency for optimal drug administration. Furthermore, our investigation extends to the effects of applied voltage on temperature distribution, a critical aspect for ensuring medical safety during the application of these patches. Additionally, we examine how particles of different sizes respond to acoustic pressure and streaming fields, providing valuable insights for tailoring drug delivery strategies to specific therapeutic needs. Overall, our findings offer comprehensive guidelines for the effective use of ultrasonic microneedle patches, potentially shifting the paradigm in patient care and enhancing the overall quality of life.

Feasibility of in vitro calcification plaque disruption using ultrasound-induced microbubble inertial cavitation

Percutaneous transluminal coronary angioplasty (PTCA) is a clinical method in which plaque-narrowed arteries are widened by inflating an intravascular balloon catheter. However, PTCA remains challenging to apply in calcified plaques since the high pressure required for achieving a therapeutic outcome can result in balloon rupture, vessel rupture, and intimal dissection. To address the problem with PTCA, we hypothesized that a calcified plaque can be disrupted by microbubbles (MBs) inertial cavitation induced by ultrasound (US). This study proposed a columnar US transducer with a novel design to generate inertial cavitation at the lesion site. Experiments were carried out using tubular calcification phantom to mimic calcified plaques. After different parameters of US + MBs treatment (four types of MBs concentration, five types of cycle number, and three types of insonication duration; n = 4 in each group), inflation experiments were performed to examine the efficacy of cavitation for a clinically used balloon catheter. Finally, micro-CT was used to investigate changes in the internal structure of the tubular plaster phantoms. The inflation threshold of the untreated tubular plaster phantoms was > 11 atm, and this was significantly reduced to 7.4 ± 0.7 atm (p = 5.2E-08) using US-induced MBs inertial cavitation at a treatment duration of 20 min with an acoustic pressure of 214 kPa, an MBs concentration of 4.0 × 108 MBs/mL, a cycle number of 100 cycles, and a pulse repetition frequency of 100 Hz. Moreover, micro-CT revealed internal damage in the tubular calcification phantom, demonstrating that US-induced MBs inertial cavitation can effectively disrupt calcified plaques and reduce the inflation threshold of PTCA. The ex vivo histopathology results showed that the endothelium of pig blood vessels remained intact after the treatment. In summary, the results show that US-induced MBs inertial cavitation can markedly reduce the inflation threshold in PTCA without damaging blood vessel endothelia, indicating the potential of the proposed treatment method.

Sonothrombolysis: State-of-the-Art and Potential Applications in Children

In recent years, advances in ultrasound therapeutics have been implemented into treatment algorithms for the adult population; however, the use of therapeutic ultrasound in the pediatric population still needs to be further elucidated. In order to better characterize the utilization and practicality of sonothrombolysis in the juvenile population, the authors conducted a literature review of current pediatric research in therapeutic ultrasound. The PubMed database was used to search for all clinical and preclinical studies detailing the use and applications of sonothrombolysis, with a focus on the pediatric population. As illustrated by various review articles, case studies, and original research, sonothrombolysis demonstrates efficacy and safety in clot dissolution in vitro and in animal studies, particularly when combined with microbubbles, with potential applications in conditions such as deep venous thrombosis, peripheral vascular disease, ischemic stroke, myocardial infarction, and pulmonary embolism. Although there is limited literature on the use of therapeutic ultrasound in children, mainly due to the lower prevalence of thrombotic events, sonothrombolysis shows potential as a noninvasive thrombolytic treatment. However, more pediatric sonothrombolysis research needs to be conducted to quantify the safety and ethical considerations specific to this vulnerable population.

Numerical investigation of ultrasound focusing and bubble collapse

Ultrasound focusing and microbubble collapse are numerically investigated using a level-set interface tracking method for two-phase flows with multiple interfaces. The computations for ultrasound propagating through a spherical lens demonstrate the ultrasound refraction and pressure intensification at the rear of the lens. The focusing of the initial negative pressure wave through the lens induces a converging flow and the focusing of the subsequent positive pressure wave further intensifies the pressure at the lens. Computations are extended to bubble oscillations near the focusing lens and compared with the no-lens case. The lens not only amplifies the bubble expansion and contraction rates significantly but also generates a larger pressure gradient across the bubble. This ultrasound focusing effect contributes to the asymmetric collapse of the bubble and the formation of a liquid jet that penetrates the bubble. The effects of lens size, initial bubble radius and bubble-lens distance on bubble expansion and liquid jet are further investigated.