Sonothrombolysis for acute ischemic stroke: a systematic review of randomized controlled trials

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.

Research progress in ultrasound use for the diagnosis and treatment of cerebrovascular diseases

Cerebrovascular diseases pose a serious threat to human survival and quality of life and represent a major cause of human death and disability. Recently, the incidence of cerebrovascular diseases has increased yearly. Rapid and accurate diagnosis and evaluation of cerebrovascular diseases are of great importance to reduce the incidence, morbidity and mortality of cerebrovascular diseases. With the rapid development of medical ultrasound, the clinical relationship between ultrasound imaging technology and the diagnosis and treatment of cerebrovascular diseases has become increasingly close. Ultrasound techniques such as transcranial acoustic angiography, doppler energy imaging, three-dimensional craniocerebral imaging and ultrasound thrombolysis are novel and valuable techniques in the study of cerebrovascular diseases. In this review, we introduce some of the new ultrasound techniques from both published studies and ongoing trials that have been confirmed to be convenient and effective methods. However, additional evidence from future studies will be required before some of these techniques can be widely applied or recommended as alternatives.

Combination of ultrasound and rtPA enhances fibrinolysis in an In Vitro clot system

BACKGROUND

Catheter-based lysis with recombinant tissue plasminogen activator (rtPA) is a well-established therapy for spontaneous intracerebral hemorrhage (ICH). The effectiveness of this therapy can be increased with ultrasound, but the optimal conditions are not yet clearly established. Using a novel in vitro system of blood clots previously developed by our group, we investigated various parameters of intralesional sonothrombolysis using an endosonography catheter in combination with rtPA.

METHODS

Standardized human blood clots were equipped with a drainage catheter and weighed before and after 4 treatments: control (drainage only), rtPA only, ultrasound only and the combination of rtPA+ultrasound. The effectiveness of ultrasound was further analysed in terms of optimal frequency, duration and distance to the probe. Temperature and acoustic peak rarefaction pressure (APRP) were assessed to analyse potential adverse effects and quantify lysis. Histo-morphological analysis of the treated clots was performed by H&E staining and confocal laser scanning microscopy using fluorescent fibrinogen.

RESULTS

The combined treatment rtPA+ultrasound achieved the highest lysis rates with a relative weight of 30.3%±5.5% (p≤0.0001) compared to all other groups. Similar results were observed when treating aged clots. Confocal fluorescent microscopy of the treated clots revealed a rarefied fibrin mesh without cavitations. No relevant temperature increase occurred (0.53±0.75°C). The optimal insonation treatment time was 1 hour. APRP measurements showed a lysis threshold of 515.5±113.4 kPa. Application of 10 MHz achieved optimal lysis and lysis radius, while simultaneously proving to be the best frequency for morphologic imaging of the clot and surrounding tissue.

CONCLUSIONS

These promising data provide the basis for an individualized minimal invasive ICH therapy by rtPA and sonothrombolysis independent of ICH age.

Effect of pulse repetition frequency of high-intensity focused ultrasound on in vitro thrombolysis

Vascular occlusion by the thrombi is the main reason for ischemic stroke and deep vein thrombosis. High-intensity focused ultrasound (HIFU) and histotripsy or microtripsy pulses can effectively dissolve the blood clot with no use of thrombolytic agent and ultrasound contrast agent (microbubbles). In this study, HIFU bursts at the same duty cycle (2%) but varied pulse repetition frequency (PRF) from 1Hz to 1000Hz were delivered to in vitro porcine blood clot for 30s. Thrombolysis efficiency initially increases slightly with the PRF, 86.4±10.3%, 89.9±11.9, and 92.9±12.8% at the PRF of 1Hz, 10Hz, and 100Hz, respectively, without significant difference (p>0.05), but then drops dramatically to 37.9±6.9% at the PRF of 1000Hz (p<0.05). The particle size in the supernatant of dissolution is 547.1±129.5nm, which suggests the disruption of thrombi into the subcellular level. Thrombi motion during HIFU exposure shows violent motion and significant curling at the low PRF, rotation about its axis with occasional curling at the moderate PRF, and localized vibration at the high PRF due to the generation of acoustic radiation force and streaming. Quantitative analysis of recorded motion shows the axial displacement decreases with the PRF of delivered HIFU bursts, from 3.9±1.5mm at 1Hz to 0.7±0.4mm at 1000Hz. Bubble cavitation during HIFU exposure to the blood clot was also monitored. The increase of PRF led to the increase of inertial cavitation but the decrease of stable cavitation. In summary, the PRF of delivered HIFU bursts at the same output energy has a significant effect on the thrombi motion, bubble cavitation activities, and subsequently thrombolysis efficiencies.

Uncertainty estimation for temperature measurement with diagnostic ultrasound

Background

Ultrasound therapies are promising, non-invasive applications with potential to significantly improve, e.g. cancer therapies like viro- or immunotherapy or surgical applications. However, a crucial step towards their breakthrough is still missing: affordable and easy-to-handle quality assurance tools for therapy devices and ways to verify treatment planning algorithms. This deficiency limits the safety and comparability of treatments.

Methods

To overcome this deficiency accurate spatial and temporal temperature maps could be used. In this paper, the suitability of temperature calculation based on time-shifts of diagnostic ultrasound backscattered signals (echo-time-shift) is investigated and associated uncertainties are estimated. Different analysis variations were used to calculate the time-shifts: discrete and continuous methods as well as different frames as a reference for temperature calculation (4 s before, 16 s before the frame of interest, base frame). A sigmoid function was fitted and used to calculate temperatures. Two-dimensional temperature maps recorded during and after therapeutic ultrasound sonication were examined. All experiments were performed in agar-graphite phantoms mimicking non-fatty tissue, with high-intensity focused ultrasound being the source of heating.

Results

Continuous methods are more accurate than discrete ones, and uncertainties of calculated temperatures are in general lower, the earlier the reference frame was recorded. Depending on the purpose of the measurement, a compromise has to be made between the following: calculation accuracy (early reference frame), tolerance towards small movements (late reference frame), reproducing large temperature changes or cooling processes (reference frame at a certain point in time), speed of the algorithm (discrete (fast) vs. continuous (slower) shift calculation), and spatial accuracy (interval size for index-shift calculation). Within the range from 20 °C to 44 °C, uncertainties as low as 12.4 % are possible, being mainly due to medium properties.

Conclusions

Temperature measurements using the echo-time-shift method might be useful for validation of treatment plan algorithms. This might also be a comparatively accurate, fast, and affordable method for laboratory and clinical quality assessment. Further research is necessary to improve filter algorithms and to extend this method to multiple foci and the usage of temperature-dependent tissue quantities. We used an analytical approach to investigate the uncertainties of temperature measurement. Different analysis variations are compared to determine temperature distribution and development over time.

Meta-analysis of Vascular Imaging Features to Predict Outcome Following Intravenous rtPA for Acute Ischemic Stroke

Background

The present review investigated which findings in vascular imaging techniques can be used to predict clinical outcome and the risk of symptomatic intracerebral hemorrhage (sICH) in patients who underwent intravenous thrombolytic treatment.

Methods

Publications were searched, and the inclusion criteria were as follows: (1) published manuscripts, (2) patients with acute ischemic stroke managed with intravenous recombinant tissue plasminogen activator (rtPA), and (3) availability of imaging assessment to determine vessel patency or the regulation of cerebral blood flow prior to, during, and/or after thrombolytic treatment. Clinical outcomes were divided into neurological outcome [National Institutes of Health Stroke Scale (NIHSS) within 7 days] and functional outcome (modified Rankin score in 2–3 months). sICH was defined as rtPA-related intracerebral bleeding associated with any worsening of NIHSS.

Results

Thirty-nine articles were selected. Recanalization was associated with improved neurological and functional outcomes (OR = 7.83; 95% CI, 3.71–16.53; p < 0.001 and OR = 11.12; 95% CI, 5.85–21.14; p < 0.001, respectively). Both tandem internal carotid artery/middle cerebral artery (ICA/MCA) occlusions and isolated ICA occlusion had worse functional outcome than isolated MCA occlusion (OR = 0.26, 95% CI, 0.12–0.52; p < 0.001 and OR = 0.24, 95% CI, 0.07–0.77; p = 0.016, respectively). Reocclusion was associated with neurological deterioration (OR = 6.48, 95% CI, 3.64–11.56; p < 0.001), and early recanalization was associated with lower odds of sICH (OR = 0.36, 95% CI, 0.18–0.70; p = 0.003).

Conclusion

Brain circulation data before, during, and after thrombolysis may be useful for predicting the clinical outcome. Cerebral arterial recanalization, presence and site of occlusion, and reocclusion are all important in predicting the clinical outcome.

Pierre Curie: the anonymous neurosurgical contributor

Pierre Curie, best known as a Nobel Laureate in Physics for his co-contributions to the field of radioactivity alongside research partner and wife Marie Curie, died suddenly in 1906 from a street accident in Paris. Tragically, his skull was crushed under the wheel of a horse-drawn carriage. This article attempts to honor the life and achievements of Pierre Curie, whose trailblazing work in radioactivity and piezoelectricity set into motion a wide range of technological developments that have culminated in the advent of numerous techniques used in neurological surgery today. These innovations include brachytherapy, Gamma Knife radiosurgery, focused ultrasound, and haptic feedback in robotic surgery.

Safety of thrombolytic therapy with rt-PA and transcranial color Doppler ultrasound (TCCS) combined with microbubbles: a histopathologic study on rabbit brain tissues

OBJECTIVE

To evaluate effect of thrombolytic therapy with rt-PA (recombinant tissue plasminogen activator) and transcranial color Doppler ultrasound (TCCS) combined with microbubbles on histology of brain tissue.

METHODS

New Zealand rabbits were subjected to TCCS based thrombolytic therapy, in 8 groups depending on dose of rt-PA, exposure duration of TCCS and presence of attenuation by skull bone window, 2 animals/group: (1) skull+1/2 rt-PA+TCCS+MBs, 10 min, (2) skull+rt-PA+TCCS+MBs, 10 min, (3) skull+1/2 rt-PA+TCCS+MBs, 20 min, (4) skull+rt-PA+TCCS+MBs, 20 min, (5) skull+1/2 rt-PA+TCCS+MBs, 30 min, (6) skull+rt-PA+TCCS+MBs, 30 min, (7) 1/2 rt-PA+TCCS+MBs, 10 min, (8) 1/2 rt-PA+TCCS+MBs, 20 min. The brain tissues were harvested after therapies and submitted for microscopic, electronic microscope and immunohistochemical examination. The histological changes were scored.

RESULTS

TCCS caused exposure duration dependent brain tissue damage. With attenuation by bone window, TCCS based therapies for 10-20 min caused minimal tissue damage. However, significant tissue damage was observed upon TCCS for 30 min in presence of skull bone window, presenting as hemorrhage, misdistribution of organelles, demyelination of nerve fibers, and thinning of basement membrane in blood-brain barrier, which was milder than that after 20 min of exposure to TCCS in absence of bone window. Dose of rt-PA did not affect brain histology in all groups.

CONCLUSION

Short treatment of brain tissue with TCCS through a bone window is relative safe. And skull bone window protected brain tissue from TCCS induced damage.

Focused ultrasound: relevant history and prospects for the addition of mechanical energy to the neurosurgical armamentarium

Although the concept of focused ultrasonography emerged more than 70 years ago, the need for a craniectomy obviated its development as a noninvasive technology. Since then advances in phased array transducers and magnetic resonance imaging technology have resurrected the ultrasound as a noninvasive therapeutic for a plethora of neurological conditions ranging from embolic stroke and intracranial hemorrhage to movement disorders and brain neoplasia. In the same way that stereotactic radiosurgery has fundamentally changed the scope and treatment paradigms of tumor and specifically skull base surgery, focused ultrasound has a similar potential to revolutionize the field of neurological surgery. In addition, focused ultrasound comes without the general complexity or the risks of ionizing radiation that accompany radiosurgery. As the quest for minimally invasive and noninvasive therapeutics continues to define the new neurosurgery, the focused ultrasound evolves to join the neurosurgical armamentarium.

MR-guided focused ultrasound: a new generation treatment of Parkinson's disease, essential tremor and neuropathic pain

The application of high intense focused ultrasound (HIFU) is currently the subject of many experimental and clinical trials. The combination of HIFU with MRI guidance known as MR-guided focused ultrasound (MRgFUS) appears to be particularly promising to ablate tissues located deep in the brain. The method can be the beginning of interventional neurology and an important alternative to neurosurgery. Studies conducted to date show the effectiveness of the method both in chronic diseases and in emergency cases. The safety and effectiveness of this method have been observed in parkinsonian and essential tremor as well as in neuropathic pain. The procedure does not require anaesthesia. Ionizing radiation is not used and there is no risk of cumulative dose. Such advantages may result in low complication rates and medical justification for further development of MRgFUS.

Cardiovascular drug delivery with ultrasound and microbubbles

Microbubbles lower the threshold for cavitation of ultrasound and have multiple potential therapeutic applications in the cardiovascular system. One of the first therapeutic applications to enter into clinical trials has been microbubble-enhanced sonothrombolysis. Trials were conducted in acute ischemic stroke and clinical trials are currently underway for sonothrombolysis in treatment of acute myocardial infarction. Microbubbles can be targeted to epitopes expressed on endothelial cells and thrombi by incorporating targeting ligands onto the surface of the microbubbles. Targeted microbubbles have applications as molecular imaging contrast agents and also for drug and gene delivery. A number of groups have shown that ultrasound with microbubbles can be used for gene delivery yielding robust gene expression in the target tissue. Work has progressed to primate studies showing delivery of therapeutic genes to generate islet cells in the pancreas to potentially cure diabetes. Microbubbles also hold potential as oxygen therapeutics and have shown promising results as a neuroprotectant in an ischemic stroke model. Regulatory considerations impact the successful clinical development of therapeutic applications of microbubbles with ultrasound. This paper briefly reviews the field and suggests avenues for further development.

Transcranial Doppler ultrasound: a review of the physical principles and major applications in critical care

Transcranial Doppler (TCD) is a noninvasive ultrasound (US) study used to measure cerebral blood flow velocity (CBF-V) in the major intracranial arteries. It involves use of low-frequency (≤2 MHz) US waves to insonate the basal cerebral arteries through relatively thin bone windows. TCD allows dynamic monitoring of CBF-V and vessel pulsatility, with a high temporal resolution. It is relatively inexpensive, repeatable, and portable. However, the performance of TCD is highly operator dependent and can be difficult, with approximately 10-20% of patients having inadequate transtemporal acoustic windows. Current applications of TCD include vasospasm in sickle cell disease, subarachnoid haemorrhage (SAH), and intra- and extracranial arterial stenosis and occlusion. TCD is also used in brain stem death, head injury, raised intracranial pressure (ICP), intraoperative monitoring, cerebral microembolism, and autoregulatory testing.

Unanswered questions in thrombolytic therapy for acute ischemic stroke

This article reviews some of the current literature in support or against extension of the intravenous tissue plasminogen activator window, use of intra-arterial therapy or devices, as well alternative pharmacologic therapies that may extend the window for treatment of patients with acute ischemic stroke, with consideration of the relative risk of thrombolytic complications, factors for worse outcomes, and unclear stroke onset, as seen in patients with wake-up stroke. The issue of newer concomitant antithrombotic therapies as they affect the decision for acute ischemic stroke thrombolytic therapy is also explored.

Transcranial Doppler ultrasound: technique and application

Transcranial Doppler (TCD) ultrasound provides rapid, noninvasive, real-time measures of cerebrovascular function. TCD can be used to measure flow velocity in the basal arteries of the brain to assess relative changes in flow, diagnose focal vascular stenosis, or to detect embolic signals within these arteries. TCD can also be used to assess the physiologic health of a particular vascular territory by measuring blood flow responses to changes in blood pressure (cerebral autoregulation), changes in end-tidal CO2 (cerebral vasoreactivity), or cognitive and motor activation (neurovascular coupling or functional hyperemia). TCD has established utility in the clinical diagnosis of a number of cerebrovascular disorders such as acute ischemic stroke, vasospasm, subarachnoid hemorrhage, sickle cell disease, as well as other conditions such as brain death. Clinical indication and research applications for this mode of imaging continue to expand. In this review, the authors summarize the basic principles and clinical utility of TCD and provide an overview of a few TCD research applications.