Sonothrombolysis: an emerging modality for the treatment of acute ischemic and hemorrhagic stroke

The efficacy of hyperbaric oxygen in hemorrhagic stroke: experimental and clinical implications

Hemorrhagic stroke, accounting for 10-30% of stroke cases, carries high rates of morbidity and mortality. This review presents the current knowledge on the efficacy of hyperbaric oxygen (HBO)-based modalities in the preclinical research on hemorrhagic stroke. Both preconditioning and post-treatment with HBO are considered as prospective therapeutic options. High efficacy of HBO therapy (HBOT) for brain hemorrhage has been noted. We found that moderate hyperbaric pressures appear optimal for therapeutic effect, while the therapeutic window of opportunity is short. HBO preconditioning offers more modest neuroprotective benefit as compared to HBO post-treatment for experimental intracerebral hemorrhage. We advocate for mandatory calculations of percent changes in the experimentally investigated indexes of HBO effectiveness and stress the need to design new clinical trials on HBO for hemorrhagic stroke.

[The use of transcranial focused ultrasound in CNS diseases]

Transcranial focused ultrasound is a modern medical technique, which provides non-invasive impact on the brain. Current development stage of this technique is no longer than 20 years and many possible applications of this technique are still at pre-clinical stage. The greatest progress has been made in the field of functional neurosurgery. Focused ultrasound enables non-invasive MRI-guided formation of small destruction foci in the relevant targets, providing therapeutic neuromodulating effects in patients with Parkinson's disease, essential tremor, pain syndromes, obsessive-compulsive disorders, and other diseases. So far, this treatment was carried out in more than 300 patients. Several cases of ultrasound thermal destruction of intracranial neoplasms were published. There are attempts to perform third ventriculostomy using ultrasound in animals. A separate area focuses on the enhancement of the permeability of the blood-brain barrier to various substances driven by focused ultrasound. The possibilities of enhancing the permeability to chemotherapeutic agents, immune drugs, and other substances are being investigated in laboratories. A large number of studies focus on treatment of Alzheimer's disease. clinical trials aimed at enhancing the permeability of the blood-brain barrier to chemotherapeutic agents have been initiated. Reversible neuromodulating, stimulating, and inhibiting effect of focused ultrasound on the nervous system structures is another non-destructive effect, which is currently being actively investigated in animals. Furthermore, laboratory studies demonstrated the ability of focused ultrasound to destroy blood clots and thrombi. Transcranial focused ultrasound provides numerous unique possibilities for scientific and practical medicine. Large-scale research is required prior to the widespread clinical implementation. Nevertheless, we can already state that implementation of this technique will significantly enhance diagnostic and therapeutic potential of neurosurgery and neurology.

Efficacy and spatial distribution of ultrasound-mediated clot lysis in the absence of thrombolytics

Ultrasound and microbubble (MB) contrast agents accelerate clot lysis, yet clinical trials have been performed without defining optimal acoustic conditions. Our aim was to assess the effect of acoustic pressure and frequency on the extent and spatial location of clot lysis. Clots from porcine blood were created with a 2-mm central lumen for infusion of lipid-shelled perfluorocarbon MBs (1×10(7) ml(-1)) or saline. Therapeutic ultrasound at 0.04, 0.25, 1.05, or 2.00 MHz was delivered at a wide range of peak rarefactional acoustic pressure amplitudes (PRAPAs). Ultrasound was administered over 20 minutes grouped on-off cycles to allow replenishment of MBs. The region of lysis was quantified using contrast-enhanced ultrasound imaging. In the absence of MBs, sonothrombolysis did not occur at any frequency. Sonothrombolysis was also absent in the presence of MBs despite their destruction at 0.04 and 2.00 MHz. It occurred at 0.25 and 1.05 MHz in the presence of MBs for PRAPAs > 1.2 MPa and increased with PRAPA. At 0.25 MHz the clot lysis was located in the far wall. At 1.05 MHz, however, there was a transition from far to near wall as PRAPA was increased. The area of clot lysis measured by ultrasound imaging correlated with that by micro-CT and quantification of debris in the effluent. In conclusion, sonothrombolysis with MBs was most efficient at 0.25 MHz. The spatial location of sonothrombolysis varies with pressure and frequency indicating that the geometric relation between therapeutic probe and vascular thrombosis is an important variable for successful lysis clinically.