Ultrasound-assisted laser thrombolysis with endovascular laser and high-intensity focused ultrasound

Investigating the potential of catheter-assisted pulsed focused ultrasound ablation for atherosclerotic plaques

BACKGROUND

Atherosclerosis is a condition in which an adhesive substance called plaque accumulates over time inside the arteries. Plaque buildup results in the constriction of arteries, causing a shortage of blood supply to tissues and organs. Removing atherosclerotic plaques controls the development of acute ischemic stroke and heart diseases. It remains imperative for positive patient outcomes.

PURPOSE

This study sought to develop a minimally invasive technique for removing arterial plaques by applying focused ultrasound (FUS) energy on the metal surface of a nitinol catheter wire to induce inertial cavitation. The induced cavitation can deplete plaque mechanically inside the arteries, leading towards improved recanalization of blood vessels.

METHODS

The enhanced cavitation effect induced by combining FUS with a metal catheter was first verified by exposing agar phantom gels with or without a 0.9-mm diameter nitinol wire to an acoustic field produced by a 0.5-MHz FUS transducer. The phenomenon was further confirmed in pork belly fat samples with or without a 3-mm diameter nitinol catheter wire. Cavitation was monitored by detecting the peaks of emitted ultrasound signals from the samples using a passive cavitation detector (PCD). Cavitation threshold values were determined by observing the jump in the peak amplitude of signals received by the PCD when the applied FUS peak negative pressure (PNP) increased. To simulate arterial plaque removal, FUS with or without a catheter was used to remove tissues from pork belly fat samples and the lipid cores of human atherosclerotic plaque samples using 2500-cycle FUS bursts at 10% duty cycle and a burst repetition rate of 20 Hz. Treatment outcomes were quantified by subtracting the weight of samples before treatment from the weight of samples after treatment. All measurements were repeated 5 times (n = 5) unless otherwise indicated, and paired t-tests were used to compare the means of two groups. A p-value of <0.05 will be considered significant.

RESULTS

Our results showed that with a nitinol wire, the cavitation threshold in agar phantoms was reduced to 2.6 MPa from 4.3 MPa PNP when there was no nitinol wire in the focal region of FUS. For pork belly fat samples, cavitation threshold values were 1.0 and 2.0 MPa PNP, with and without a catheter wire, respectively. Pork belly fat tissues and lipid cores of atherosclerotic plaques were depleted at the interface between a catheter and the samples at 2 and 4 MPa FUS PNP, respectively. The results showed that with a catheter wire in the focal region of a 3-min FUS treatment session, 24.7 and 25.6 mg of lipid tissues were removed from pork belly fat and human atherosclerotic samples, respectively. In contrast, the FUS-only group showed no reduction in sample weight. The differences between FUS-only and FUS-plus-catheter groups were statistically significant (p < 0.001 for the treatment on pork belly samples, and p < 0.01 for the treatment on human atherosclerotic samples).

CONCLUSION

This study demonstrated the feasibility of catheter-assisted FUS therapy for removing atherosclerotic plaques.

Photobiomodulation and low-intensity pulsed ultrasound synergistically enhance dental mesenchymal stem cells viability, migration and differentiation: an invitro study

Novel methods and technologies that improve mesenchymal stem cells (MSCs) proliferation and differentiation properties are required to increase their clinical efficacy. Photobiomodulation (PBM) and low-intensity pulsed ultrasound (LIPUS) are two strategies that can be used to enhance the regenerative properties of dental MSCs. This study evaluated the cytocompatibility and osteo/odontogenic differentiation of dental pulp, periodontal ligament, and gingival MSCs after stimulation by either PBM or LIPUS and their combined effect. MTT assay, cell migration assay, osteo/odontogenic differentiation by AR staining and ALP activity, and expression of osteo/odontogenic markers (OPG, OC, RUNX2, DSPP, DMP1) by RT-qPCR were evaluated. Statistical analysis was performed using ANOVA, followed by Tukey's post hoc test, with a p-value of less than 0.05 considered significant. The results showed that combined stimulation by PBM and LIPUS resulted in significantly the highest viability of MSCs, the fastest migration, the most dense AR staining, the most increased ALP activity, and the most elevated levels of osteogenic and odontogenic markers. The synergetic stimulation of PBM and LIPUS can be utilized in cell-based regenerative approaches to promote the properties of dental MSCs.

Secondary cavitation bubble dynamics during laser-induced bubble formation in a small container

We investigated secondary cavitation bubble dynamics during laser-induced bubble formation in a small container with a partially confined free surface and elastic thin walls. We employed high-speed photography to record the dynamics of sub-mm-sized laser-induced bubbles and small secondary bubble clouds. Simultaneous light scattering and acoustic measurements were used to detect the oscillation times of laser-induced bubbles. We observed that the appearance of secondary bubbles coincides with a prolonged collapse phase and with re-oscillations of the laser-induced bubble. We observed an asymmetric distribution of secondary bubbles with a preference for the upstream side of the focus, an absence of secondary bubbles in the immediate vicinity of the laser focus, and a migration of laser-induced bubble toward secondary bubbles at large pulse energies. We found that secondary bubbles are created through heating of impurities to form initial nanobubble nuclei, which are further expanded by rarefaction waves. The rarefaction waves originate from the vibration of the elastic thin walls, which are excited either directly by laser-induced bubble or by bubble-excited liquid-mass oscillations. The oscillation period of thin walls and liquid-mass were Twall = 116 µs and Tlm ≈ 160 µs, respectively. While the amplitude of the wall vibrations increases monotonically with the size of laser-induced bubbles, the amplitude of liquid-mass oscillation undulates with increasing bubble size. This can be attributed to a phase shift between the laser-induced bubble oscillation and the liquid-mass oscillator. Mutual interactions between the laser-induced bubble and secondary bubbles reveal a fast-changing pressure gradient in the liquid. Our study provides a better understanding of laser-induced bubble dynamics in a partially confined environment, which is of practical importance for microfluidics and intraluminal laser surgery.

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.

Angioscopy-Guided Selective Pulmonary Thrombectomy and Angioscopy-Monitored Systemic Thrombosis for a Pulmonary Embolism

Few modalities have the capacity to demonstrate massive or fragmented thrombi to evaluate the effect of catheter-based or systemic thrombosis for pulmonary embolism (PE). We herein present a patient who underwent a thrombectomy for PE using a non-obstructive general angioscopy (NOGA) system. Small floating mobile thrombi were aspirated using the original method, and massive thrombi were aspirated using the NOGA system. Systemic thrombosis was also monitored via NOGA for 30 minutes. Detachment of thrombi from the wall of the pulmonary artery began two minutes after infusion of a recombinant tissue plasminogen activator (rt-PA). Six minutes after thrombolysis, the thrombi lost their erythematous color, and the white thrombi gradually floated and dissolved. NOGA-guided selective pulmonary thrombectomy and NOGA-monitored systemic thrombosis contributed to improved patient survival. Rapid systemic thrombosis for PE using rt-PA was also demonstrated by NOGA.

A review on photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel therapeutic technique based on the combination of ultrasound and laser. The underlying mechanism of PUT is the enhanced cavitation effect inside blood vessels. The enhanced cavitation activity can result in bio-effects such as reduced perfusion in microvessels. The reduced perfusion effect in microvessels in the eye has the potential to control the progression of eye diseases such as diabetic retinopathy and age-related macular degeneration. Several in vivo studies have demonstrated the feasibility of PUT in removing microvasculature in the eye using rabbit eye model and vasculature in the skin using rabbit ear model. Numerical studies using a bubble dynamics model found that cavitation is enhanced during PUT due to the dramatic increase in size of air/vapor nuclei in blood. In addition, the study conducted to model cavitation dynamics inside a blood vessel during PUT found stresses induced on the vessel wall during PUT are higher than that at normal physiological levels, which may be responsible for bio-effects. The concentration of vasodilators such as nitric oxide and prostacyclin were also found to be affected during PUT in an in vitro study, which may limit blood perfusion in vessels. The main advantage of PUT over conventional techniques is non-invasive, precise, and selective removal of microvessels with high efficiency at relatively low energy levels of ultrasound and laser, without affecting the nearby structures. However, the main limitation of vessel rupture/hemorrhage needs to be overcome through the development of real-time monitoring of treatment effects during PUT. In addition to the application in removing microvessels, PUT-based techniques were also explored in treating other diseases. Studies have found a combination of ultrasound and laser to be effective in removing blood clots inside veins, which has the potential to treat deep-vein thrombosis. The disruption of atherosclerotic plaque using combined ultrasound and laser was also tested, and the feasibility was demonstrated.

A feasibility study on removing lipid deposition in atherosclerotic plaques with ultrasound-assisted laser ablation

Objective. Atherosclerosis is the buildup of fats, cholesterol, and other substances on the inner walls of arteries. It can affect arteries of heart, brain, arms, legs, pelvis and kidney, resulting in ischemic heart disease, carotid artery disease, peripheral artery disease and chronic kidney disease. Laser-based treatment techniques like laser atherectomy can be used to treat many common atherosclerostic diseases. However, the use of laser-based treatment remains limited due to the high risk of complications and low efficiency in removing atherosclerostic plaques as compared with other treatment methods. In this study, we developed a technology that used high intensity focused ultrasound to assist laser treatment in the removal of the lipid core of atherosclerotic plaques.Approach. The fundamental mechanism to disrupt atherosclerostic plaque was to enhance the mechanical effect of cavitation during laser/ultrasound therapy. To promote cavitation, spatiotemporally synchronized ultrasound bursts of 2% duty cycle at 0.5 MHz and nanosecond laser pulses at 532 nm wavelength were used. Experiments were first performed on pig belly fat samples to titrate ultrasound and laser parameters. Then, experiments were conducted on human plaque samples, where the lipid depositions of the plaques were targeted.Main results. Our results showed that fat tissue could be removed with an ultrasound peak negative pressure (PNP) of 2.45 MPa and a laser radiant exposure as low as 3.2 mJ mm^-2. The lipid depositions on the atherosclerostic plaques were removed with laser radiant exposure of 16 mJ mm^-2in synchronizing with an ultrasound PNP of 5.4 MPa. During all the experiments, laser-only and ultrasound-only control treatments at the same energy levels were not effective in removing the lipid.Significance. The results demonstrated that the addition of ultrasound could effectively reduce the needed laser power for atherosclerotic plaque removal, which will potentially improve treatment safety and efficiency of current laser therapies.

Estimating Thrombus Elasticity by Shear Wave Elastography to Evaluate Ultrasound Thrombolysis for Thrombus With Different Stiffness

OBJECTIVE

There is uncertainty about deep vein thrombosis standard treatment as thrombus stiffness alters each case. Here, we investigated thrombus' stiffness of different compositions and ages using shear wave elastography (SWE). We then studied the effectiveness of ultrasound-thrombolysis on different thrombus compositions.

METHODS

Shear waves generated through mechanical shaker and traveled along thrombus of different hematocrit (HCT) levels, whereas 18-MHz ultrasound array used to detect wave propagation. Thrombus' stiffness was identified by the shear wave speed (SWS). In thrombolysis, a 3.2 MHz focused transducer was applied to different thrombus compositions using different powers. The thrombolysis rate was defined as the percentage of weight loss.

RESULTS

The estimated average SWS of 20%, 40%, and 60% HCT thrombus were 0.75 m/s, 0.44 m/s, and 0.32 m/s, respectively. For Thrombolysis, the percentage weight loss at 8 MPa Negative pressure for the same HCT groups were 23.1%, 35.29%, and 39.66% respectively.

CONCLUSION

SWS is inversely related to HCT level and positively related to thrombus age. High HCT thrombus had higher weight loss compared to low HCT. However, the difference between 20% and 40% HCT was more significant than between 40% and 60% HCT in both studies. Our results suggest that thrombus with higher SWS require more power to achieve the same thrombolysis rate as thrombus with lower SWS.

SIGNIFICANCE

Characterizing thrombus elastic property undergoing thrombolysis enables evaluation of ultrasound efficacy for fractionating thrombus and reveals the appropriate ultrasound parameters selection to achieve a certain thrombolysis rate in the case of a specific thrombus stiffness.

Laser thrombolysis and in vitro release kinetics of tPA encapsulated in chitosan polysulfate-coated nanoliposome

A major challenge in managing coronary artery disease is to find an effective thrombolytic therapy with minimal side effects. Laser thrombolysis is a practical procedure to remove the thrombus from inside blocked arteries, although it can cause embolism and re-occlusion of the vessel. The present study aimed to design a liposome drug delivery system for the controlled release of tissue plasminogen activator (tPA) and delivery of drug system into the thrombus by Nd:YAG laser at a wavelength of 532 nm for the treatment of arterial occlusive diseases. In this study, tPA encapsulated into the chitosan polysulfate-coated liposome (Lip/PSCS-tPA) was fabricated by a thin-film hydration technique. The particle size of Lip/tPA and Lip/PSCS-tPA was 88 and 100 nm, respectively. The release rate of tPA from Lip/PSCS-tPA was measured to be 35 % and 66 % after 24 h and 72 h, respectively. Thrombolysis through the delivery of Lip/PSCS-tPA into the thrombus during the laser irradiation was higher compared to irradiated thrombus without the nanoliposomes. The expression of IL-10 and TNF-α genes was studied by RT-PCR. The level of TNF-α for Lip/PSCS-tPA was lower than that of tPA, which can lead to improved cardiac function. Also, in this study, the thrombus dissolution process was studied using a rat model. After 4 h, the thrombus area in the femoral vein was significantly lower for groups treated with Lip/PSCS-tPA (5 %) compared to the groups treated with tPA alone (45 %). Thus, according to our results, the combination of Lip/PSCS-tPA and laser thrombolysis can be introduced as an appropriate technique for accelerating thrombolysis.

Recent Advances in Targeted Nanotherapies for Ischemic Stroke

Ischemic stroke (IS) is a severe neurological disease caused by the narrowing or occlusion of cerebral blood vessels and is known for high morbidity, disability, and mortality rates. Clinically available treatments of stroke include the surgical removal of the thrombus and thrombolysis with tissue fibrinogen activator. Pharmaceuticals targeting IS are uncommon, and the development of new therapies is hindered by the low bioavailability and stability of many drugs. Nanomedicine provides new opportunities for the development of novel neuroprotective and thrombolytic strategies for the diagnosis and treatment of IS. Numerous nanotherapeutics with different physicochemical properties are currently being developed to facilitate drug delivery by accumulation and controlled release and to improve their restorative properties. In this review, we discuss recent developments in IS therapy, including assisted drug delivery and targeting, neuroprotection through regulation of the neuron environment, and sources of endogenous biomimetic specific targeting. In addition, we discuss the role and neurotoxic effects of inorganic metal nanoparticles in IS therapy. This study provides a theoretical basis for the utilization of nano-IS therapies that may contribute to the development of new strategies for a range of embolic diseases.

Optimized acoustic streaming generated at oblique incident angles to improve ultrasound thrombolysis effect

BACKGROUND

Combined with thrombolytic drugs and/or microbubbles (MBs), ultrasound (US) has been regarded as a useful tool for thrombolysis treatment by taking its advantages of non-invasive, non-ionization, low cost and accurate targeting of tissues deep in body. Recently, low-intensity pulsed ultrasound (LIPUS), which can cause fewer complications by stable cavitation and acoustic streaming other than more violent effects, has attracted broad attention.

PURPOSE

However, the thrombolysis effect in practice might not achieve expectation because there is not an ideal parallel multilayer structure between the skin and the targeted vessel. Therefore, the current work aims to better elucidate the influence of US incident angle on the generation of acoustic streaming and thrombolysis effect.

METHODS

Systemic numerical and experimental studies, viz., finite element modeling (FEM), particle image velocimetry (PIV) and in vitro thrombolysis measurements, were performed to estimate the acoustical/streaming field pattern, maximum flow velocity and shear stress on the surface of thrombus, as well as the lysis rate generated at different conditions. These methods aim at verifying the hypothesis that streaming-induced vortices can further accelerate the dissolution of the thrombus and optimized thrombolysis effected can be achieved by adjusting US incident angles.

RESULTS

The pool data results showed that the variation trends of the flow velocity and shear stress obtained from FEM simulation and PIV experiments are qualitatively consistent with each other. There exists an optimal incident angle that can maximize the flow velocity and shear stress on the surface of thrombus, so that superior stirring and mixing effect can be generated. Furthermore, as the flow velocity and shear stress on thrombus surface are both highly correlated with the thrombolysis effect (the correlation coefficient R1 = 0.988, R2 = 0.958, respectively), the peak value of lysis rate (increase by at least 5.02%) also occurred at 10°.

CONCLUSIONS

The current results demonstrated that, with appropriately determined incident angle, higher thrombolysis rate could be achieved without increasing the driving pressure. It may shed the light on future US thrombolysis planning strategy that, if combined with other advanced technologies (e.g., machine-learning-based image analysis and image-guided adaptive US emission modulation), more efficient thrombolytic effect could be realized while minimizing undesired side-effects caused by excessively high pressure. This article is protected by copyright. All rights reserved.

The Updated Role of Transcranial Ultrasound Neuromodulation in Ischemic Stroke: From Clinical and Basic Research

Ischemic stroke is a common cause of death and disability worldwide, which leads to serious neurological and physical dysfunction and results in heavy economic and social burdens. For now, timely and effective dissolution of thrombus, and ultimately improvement in the recovery of neurological functions, is the treatment strategy focus. Recently, many studies have reported that transcranial ultrasound stimulation (TUS), as a non-invasive method, can dissolve thrombus, improve cerebral blood circulation, and exert a neuroprotective effect post-stroke. TUS can promote functional recovery and improve rehabilitation efficacy among patients with ischemic stroke. This mini-review summarizes the potential mechanism and limitation of TUS in stroke aims to provide a new strategy for the future treatment of patients with ischemic stroke.

A minimally invasive strategy to evacuate hematoma by synergy of an improved ultrasonic horn with urokinase: an in-vitro study

OBJECTIVES

In this study, Ultrasound Needle-an improved minimally invasive ultrasonic horn device was used to explore its potential of synergizing with urokinase in enhancing clots lysis in an in-vitro intracranial hematoma model.

MATERIALS AND METHODS

10 ml bovine blood was incubated for 3 h at 37 ℃, and coagulated into clot to mimic intracranial hematoma in-vitro. Ultrasound Needle was an improved ultrasonic horn with a fine tip (1.80 mm) and metallic sheath, and had a frequency of 29.62 kHz. 10000 IU urokinase was injected through the metallic sheath during the vibration of Ultrasound Needle tip to lyse the clots for 8 minutes under different working parameter settings (n = 8) to explore the influence of parameters Amplitude (%) and Duty (%) on clot lysis weight (W₀ ). The maximum temperatures were measured by an infrared thermometer during the treatment process. The W₀ of different treatment groups (US (Ultrasound Needle), US+NS (normal saline), UK (urokinase), US+UK, n = 8) were compared to verify the synergistic lysis effect of Ultrasound Needle combined with urokinase at optimal working parameters (40% Amplitude, 20% Duty; input power 4.20 W; axial tip-vibration amplitude 69.17 μm). Clots samples after treatment were fixed overnight for macroscopic examination. And fluorescent frozen sections and scanning electron microscopy examination were performed to show microscopic changes in clots and evaluate the cavitation effect of Ultrasound Needle on promoting drug diffusion within the clots.

RESULTS

The clot lysis weight W₀ increased with the parameters Amplitude (%) and Duty (%), reached a peak (2.435±0.137 g) at 40% Amplitude and 20% Duty (input power 4.20 W), and then decreased. Higher Amplitude (%) and Duty (%) led to higher maximum temperature, and W₀ was negatively correlated with the maximum temperature after the peak (r = -0.958). At the optimal parameter setting, the maximum temperature was 33.8±0.9 ℃, and the W₀ of the US+UK group was more than 4 times of UK alone group (2.435±0.137 g vs 0.607±0.185 g). Fluorescent frozen sections confirmed that the ultrasound energy of Ultrasound Needle could mechanically damage the clot tissues and promote the intra-clots drug diffusion. Macroscopic examination showed that US+UK group caused larger clots lysis area than UK alone group (2.08 cm² vs 0.65 cm² ). In addition, electron microscopy examination exhibited that the fibrin filaments of the clots in US+UK group were lysed more thoroughly compared to single treatment groups.

CONCLUSIONS

Ultrasound Needle, an improved ultrasonic horn device, can mechanically damage the clot tissues and exhibit an excellent synergistic lysis effect with thrombolytic drugs. Therefore, Ultrasound Needle has great potential in providing a new minimally invasive strategy for rapid intracranial hematoma evacuation. This article is protected by copyright. All rights reserved.

The feasibility of ultrasound-assisted endovascular laser thrombolysis in an acute rabbit thrombosis model

PURPOSE

This study aimed to test the feasibility of combined ultrasound and laser technique, namely, ultrasound-assisted endovascular laser thrombolysis (USELT), for thrombolysis by conducting in vivo tests in a rabbit thrombosis model.

MATERIALS AND METHODS

An acute thrombus was created in the right jugular vein of rabbit and then was treated with ultrasound only, laser only, and USELT to dissolve the blood clot. A total of 20 rabbits were used. Out of which, the first three rabbits were used to titrate the laser and ultrasound parameters. Then, five rabbits were treated with ultrasound only, five rabbits were treated with laser only, and seven rabbits were treated with USELT. During USELT, 532-nm laser pulses were delivered endovascularly directly to the clot through a fiber optic, and 0.5 MHz ultrasound pulses were applied noninvasively to the same region. A laser fluence of 4 to 12 mJ/cm² and ultrasound amplitude of 1 to 2 MPa were used. Recanalization of the jugular vein was assessed by performing ultrasound Doppler imaging immediately after the treatment. The maximum blood flow speed after the treatment as compared to its value before the treatment was used to calculate the blood flow recovery in vessel.

RESULTS

The blood flow was fully recovered (100%) in three rabbits, partially recovered in two rabbits (more than 50% and less than 100%) with mean percentage recovery of 69.73% and poorly recovered in two rabbits (<50%) with mean percentage recovery of 6.2% in the USELT group. In contrast, the treatment group with ultrasound or laser alone did not show recanalization of vein in any case, all the five rabbits were poorly/not recovered with a mean percentage recovery of 0%.

CONCLUSIONS

The USELT technology was shown to effectively dissolve the blood clots in an acute rabbit jugular vein thrombosis model.