An intra-arterial electrode for intracranial electro-encephalogram recordings

Neuromodulation: What the neurointerventionalist needs to know

Neuromodulation is the alteration of neural activity in the central, peripheral, or autonomic nervous systems. Consequently, this term lends itself to a variety of organ systems including but not limited to the cardiac, nervous, and even gastrointestinal systems. In this review, we provide a primer on neuromodulation, examining the various technological systems employed and neurological disorders targeted with this technology. Ultimately, we undergo a historical analysis of the field's development, pivotal discoveries and inventions gearing this review to neuro-adjacent subspecialties with a specific focus on neurointerventionalists.

The brain nebula: minimally invasive brain-computer interface by endovascular neural recording and stimulation

A brain-computer interface (BCI) serves as a direct communication channel between brain activity and external devices, typically a computer or robotic limb. Advances in technology have led to the increasing use of intracranial electrical recording or stimulation in the treatment of conditions such as epilepsy, depression, and movement disorders. This indicates that BCIs can offer clinical neurological rehabilitation for patients with disabilities and functional impairments. They also provide a means to restore consciousness and functionality for patients with sequelae from major brain diseases. Whether invasive or non-invasive, the collected cortical or deep signals can be decoded and translated for communication. This review aims to provide an overview of the advantages of endovascular BCIs compared with conventional BCIs, along with insights into the specific anatomical regions under study. Given the rapid progress, we also provide updates on ongoing clinical trials and the prospects for current research involving endovascular electrodes.

Endovascular electroencephalography (eEEG) can detect the laterality of epileptogenic foci as accurately as subdural electrodes

Background

Traditional brain activity monitoring via scalp electroencephalography (EEG) offers limited resolution and is susceptible to artifacts. Endovascular electroencephalography (eEEG) emerged in the 1990s. Despite early successes and potential for detecting epileptiform activity, eEEG has remained clinically unutilized. This study aimed to further test the capabilities of eEEG in detecting lateralized epileptic discharges in animal models. We hypothesized that eEEG would be able to detect lateralization. The purpose of this study was to measure epileptiform discharges with eEEG in animal models with lateralization in epileptogenicity.

Materials and methods

We inserted eEEG electrodes into the transverse sinuses of three pigs, and subdural electrodes (SDs) on the surfaces of the left and right hemispheres. We induced epileptogenicity with penicillin in the left brain of pigs F00001 and F00003, and in the right brain of pig F00002. The resulting epileptiform discharges were measured by eEEG electrodes placed in the left and right transverse sinuses, and conducted comparisons with epileptiform discharges from SDs. We also had 12 neurological physicians interpret measurement results from eEEG alone and determine the side (left or right) of epileptogenicity.

Results

Three pigs were evaluated for epileptiform discharge detection using eEEG: F00001 (7 months old, 14.0 kg), F00002 (8 months old, 15.6 kg), and F00003 (8 months old, 14.4 kg). The eEEG readings were compared with results from SDs, showing significant alignment across all subjects (p < 0.001). The sensitivity and positive predictive values (PPV) were as follows: F00001 had 0.93 and 0.96, F00002 had 0.99 and 1.00, and F00003 had 0.98 and 0.99. Even though one of the neurological physicians got all sides incorrect, all other assessments were correct. Upon post-experimental dissection, no abnormalities were observed in the brain tissue or in the vascular damage at the site where the eEEG was placed, based on pathological evaluation.

Conclusion

With eEEG, lateralization can be determined with high sensitivity (>0.93) and PPV (>0.95) that appear equivalent to those of subdural EEG in the three pigs. This lateralization was also discernible by neurological physicians on visual inspection.

Endovascular Brain-Computer Interfaces in Poststroke Paralysis

Stroke is a leading cause of paralysis, most frequently affecting the upper limbs and vocal folds. Despite recent advances in care, stroke recovery invariably reaches a plateau, after which there are permanent neurological impairments. Implantable brain-computer interface devices offer the potential to bypass permanent neurological lesions. They function by (1) recording neural activity, (2) decoding the neural signal occurring in response to volitional motor intentions, and (3) generating digital control signals that may be used to control external devices. While brain-computer interface technology has the potential to revolutionize neurological care, clinical translation has been limited. Endovascular arrays present a novel form of minimally invasive brain-computer interface devices that have been deployed in human subjects during early feasibility studies. This article provides an overview of endovascular brain-computer interface devices and critically evaluates the patient with stroke as an implant candidate. Future opportunities are mapped, along with the challenges arising when decoding neural activity following infarction. Limitations arise when considering intracerebral hemorrhage and motor cortex lesions; however, future directions are outlined that aim to address these challenges.

Intraarterial encephalography from an acutely implanted aneurysm embolization device in awake humans

OBJECTIVE

Endovascular electroencephalography (evEEG) uses the cerebrovascular system to record electrical activity from adjacent neural structures. The safety, feasibility, and efficacy of using the Woven EndoBridge Aneurysm Embolization System (WEB) for evEEG has not been investigated.

METHODS

Seventeen participants undergoing awake WEB endovascular treatment of unruptured cerebral aneurysms were included. After WEB deployment and before detachment, its distal deployment wire was connected to an EEG receiver, and participants performed a decision-making task for 10 minutes. WEB and scalp recordings were captured.

RESULTS

All patients underwent successful embolization and evEEG with no complications. Event-related potentials were detected on scalp EEG in 9/17 (53%) patients. Of these 9 patients, a task-related low-gamma (30-70 Hz) response on WEB channels was captured in 8/9 (89%) cases. In these 8 patients, the WEB was deployed in 2 middle cerebral arteries, 3 anterior communicating arteries, the terminal internal carotid artery, and 2 basilar tip aneurysms. Electrocardiogram artifact on WEB channels was present in 12/17 cases.

CONCLUSIONS

The WEB implanted within cerebral aneurysms of awake patients is capable of capturing task-specific brain electrical activities. Future studies are warranted to establish the efficacy of and support for evEEG as a tool for brain recording, brain stimulation, and brain-machine interface applications.

Making a case for endovascular approaches for neural recording and stimulation

There are many electrode types for recording and stimulating neural tissue, most of which necessitate direct contact with the target tissue. These electrodes range from large, scalp electrodes which are used to non-invasively record averaged, low frequency electrical signals from large areas/volumes of the brain, to penetrating microelectrodes which are implanted directly into neural tissue and interface with one or a few neurons. With the exception of scalp electrodes (which provide very low-resolution recordings), each of these electrodes requires a highly invasive, open brain surgical procedure for implantation, which is accompanied by significant risk to the patient. To mitigate this risk, a minimally invasive endovascular approach can be used. Several types of endovascular electrodes have been developed to be delivered into the blood vessels in the brain via a standard catheterization procedure. In this review, the existing body of research on the development and application of endovascular electrodes is presented. The capabilities of each of these endovascular electrodes is compared to commonly used direct-contact electrodes to demonstrate the relative efficacy of the devices. Potential clinical applications of endovascular recording and stimulation and the advantages of endovascular versus direct-contact approaches are presented.

Endovascular Electroencephalogram Records Simultaneous Subdural Electrode-Detectable, Scalp Electrode-Undetectable Interictal Epileptiform Discharges

Introduction: We hypothesized that an endovascular electroencephalogram (eEEG) can detect subdural electrode (SDE)-detectable, scalp EEG-undetectable epileptiform discharges. The purpose of this study is, therefore, to measure SDE-detectable, scalp EEG-undetectable epileptiform discharges by an eEEG on a pig. Methods: A pig under general anesthesia was utilized to measure an artificially generated epileptic field by an eEEG that was able to be detected by an SDE, but not a scalp EEG as a primary outcome. We also compared the phase lag of each epileptiform discharge that was detected by the eEEG and SDE as a secondary outcome. Results: The eEEG electrode detected 113 (97%) epileptiform discharges (97% sensitivity). Epileptiform discharges that were localized within the three contacts (contacts two, three and four), but not spread to other parts, were detected by the eEEG with a 92% sensitivity. The latency between peaks of the eEEG and right SDE earliest epileptiform discharge ranged from 0 to 48 ms (mean, 13.3 ms; median, 11 ms; standard deviation, 9.0 ms). Conclusion: In a pig, an eEEG could detect epileptiform discharges that an SDE could detect, but that a scalp EEG could not.

The Future of Endovascular Therapy

PURPOSE OF THE REVIEW

This article summarizes a broad range of the most recent advances and future directions in stroke diagnostics, endovascular robotics, and neuromodulation.

RECENT FINDINGS

In the past 5 years, the field of interventional neurology has seen major technological advances for the diagnosis and treatment of cerebrovascular diseases. Several new technologies became available to aid in complex prehospital stroke triage, stroke diagnosis, and interpretation of radiologic findings. Robotics and neuromodulation promise to expand access to established treatments and broaden neuroendovascular indications.

SUMMARY

Mobile applications offer a solution to simplify prehospital diagnostic and transfer decisions. Several prehospital devices are also under development to improve the accuracy of detection of large vessel occlusion (LVO). Artificial intelligence is now routinely used in early diagnosis of LVO and for detecting salvageability of the affected brain parenchyma. Technological advances have also paved the way to incorporate endovascular robotics and neuromodulation into practice. This may expand the deliverability of established treatments and facilitate the development of cutting-edge treatments for other complex neurologic diseases.

A systematic review of endovascular stent-electrode arrays, a minimally invasive approach to brain-machine interfaces

OBJECTIVE

The goal of this study was to systematically review the feasibility and safety of minimally invasive neurovascular approaches to brain-machine interfaces (BMIs).

METHODS

A systematic literature review was performed using the PubMed database for studies published between 1986 and 2019. All studies assessing endovascular neural interfaces were included. Additional studies were selected based on review of references of selected articles and review articles.

RESULTS

Of the 53 total articles identified in the original literature search, 12 studies were ultimately selected. An additional 10 articles were included from other sources, resulting in a total of 22 studies included in this systematic review. This includes primarily preclinical studies comparing endovascular electrode recordings with subdural and epidural electrodes, as well as studies evaluating stent-electrode gauge and material type. In addition, several clinical studies are also included.

CONCLUSIONS

Endovascular stent-electrode arrays provide a minimally invasive approach to BMIs. Stent-electrode placement has been shown to be both efficacious and safe, although further data are necessary to draw comparisons between subdural and epidural electrode measurements given the heterogeneity of the studies included. Greater access to deep-seated brain regions is now more feasible with stent-electrode arrays; however, further validation is needed in large clinical trials to optimize this neural interface. This includes the determination of ideal electrode material type, venous versus arterial approaches, the feasibility of deep brain stimulation, and more streamlined computational decoding techniques.

Over the Horizon: The Present and Future of Endovascular Neural Recording and Stimulation

The past decade has witnessed an explosion in applications for neural recording and stimulation in the treatment of clinical disorders. Neuromodulatory approaches are now a mainstay of care for essential tremor and Parkinson's disease, and are expanding rapidly into a wide range of other neurological and psychiatric diseases. In parallel, advancements in endovascular approaches to cerebrovascular diseases have resulted in minimally invasive techniques that deliver devices to neural tissue in the central and peripheral nervous systems, with significantly improved safety and efficacy. In this review, we discuss the history of endovascular neural recording and stimulation, its current progress, and applications for neurological disease.

Signal quality of simultaneously recorded endovascular, subdural and epidural signals are comparable

Recent work has demonstrated the feasibility of minimally-invasive implantation of electrodes into a cortical blood vessel. However, the effect of the dura and blood vessel on recording signal quality is not understood and may be a critical factor impacting implementation of a closed-loop endovascular neuromodulation system. The present work compares the performance and recording signal quality of a minimally-invasive endovascular neural interface with conventional subdural and epidural interfaces. We compared bandwidth, signal-to-noise ratio, and spatial resolution of recorded cortical signals using subdural, epidural and endovascular arrays four weeks after implantation in sheep. We show that the quality of the signals (bandwidth and signal-to-noise ratio) of the endovascular neural interface is not significantly different from conventional neural sensors. However, the spatial resolution depends on the array location and the frequency of recording. We also show that there is a direct correlation between the signal-noise-ratio and classification accuracy, and that decoding accuracy is comparable between electrode arrays. These results support the consideration for use of an endovascular neural interface in a clinical trial of a novel closed-loop neuromodulation technology.

The evolution of endovascular electroencephalography: historical perspective and future applications

Current standard practice requires an invasive approach to the recording of electroencephalography (EEG) for epilepsy surgery, deep brain stimulation (DBS), and brain-machine interfaces (BMIs). The development of endovascular techniques offers a minimally invasive route to recording EEG from deep brain structures. This historical perspective aims to describe the technical progress in endovascular EEG by reviewing the first endovascular recordings made using a wire electrode, which was followed by the development of nanowire and catheter recordings and, finally, the most recent progress in stent-electrode recordings. The technical progress in device technology over time and the development of the ability to record chronic intravenous EEG from electrode arrays is described. Future applications for the use of endovascular EEG in the preoperative and operative management of epilepsy surgery are then discussed, followed by the possibility of the technique's future application in minimally invasive operative approaches to DBS and BMI.

Technical Aspects of Intra-Arterial Electroencephalogram Recording

The purpose of this prospective study is to show a technique for recording electroencephalographic activity via an endovascular approach in presurgical evaluation of epileptic patients. Technical aspects and insertion strategy are outlined. Advantages of intra-arterial electroencephalography have been demonstrated. It is a semi-invasive procedure that provides information in temporal lobe and extratemporal epilepsy. It allows a dynamic electroencephalographic recording and patient tolerance is excellent. Risks are practically absent. Disadvantages are: in comparison to ovale electrodes, chronic and multicontact recording is not possible and the recording is only intercritical.

Computational modeling of an endovascular approach to deep brain stimulation

OBJECTIVE

Deep brain stimulation (DBS) therapy currently relies on a transcranial neurosurgical technique to implant one or more electrode leads into the brain parenchyma. In this study, we used computational modeling to investigate the feasibility of using an endovascular approach to target DBS therapy.

APPROACH

Image-based anatomical reconstructions of the human brain and vasculature were used to identify 17 established and hypothesized anatomical targets of DBS, of which five were found adjacent to a vein or artery with intraluminal diameter ≥1 mm. Two of these targets, the fornix and subgenual cingulate white matter (SgCwm) tracts, were further investigated using a computational modeling framework that combined segmented volumes of the vascularized brain, finite element models of the tissue voltage during DBS, and multi-compartment axon models to predict the direct electrophysiological effects of endovascular DBS.

MAIN RESULTS

The models showed that: (1) a ring-electrode conforming to the vessel wall was more efficient at neural activation than a guidewire design, (2) increasing the length of a ring-electrode had minimal effect on neural activation thresholds, (3) large variability in neural activation occurred with suboptimal placement of a ring-electrode along the targeted vessel, and (4) activation thresholds for the fornix and SgCwm tracts were comparable for endovascular and stereotactic DBS, though endovascular DBS was able to produce significantly larger contralateral activation for a unilateral implantation.

SIGNIFICANCE

Together, these results suggest that endovascular DBS can serve as a complementary approach to stereotactic DBS in select cases.

Frameless stereotactic endoscope-assisted transoccipital hippocampal depth electrode placement: cadaveric demonstration of a new approach

PURPOSE

Hippocampal recording using depth electrodes is indicated in a small subgroup of patients with medically intractable seizures. There are several conventional techniques for implantation of hippocampal depth electrodes. We describe a new method for hippocampal depth electrode placement using an image-guided endoscopic transoccipital route. This technique is simple and effective, eliminating several drawbacks of conventional techniques.

METHODS

One silicone-injected cadaver head was used. A rigid endoscope sheath was inserted through a transoccipital corridor into the atrium of the lateral ventricle and then advanced to the temporal horn. Each of the hemispheres was cannulated. The hippocampus was identified visually, and a depth electrode was inserted into the substance of the hippocampus along its long axis under direct vision.

RESULTS

In both hemispheres we were able to successfully implant the depth electrode within the hippocampus. The advantages of our technique over conventional approaches are (1) there is no need for frame-based stereotaxy, thus reducing operating time and patient discomfort, (2) the electrodes are inserted into the hippocampus under direct endoscopic visualization, reducing the chance of injury to vascular structures, (3) there is no need to insert a larger cannula into the hippocampus before placement of the electrodes, reducing trauma to the hippocampus, and (4) the number of electrodes within the hippocampus can be assessed at the end of the procedure, reducing malposition.

CONCLUSION

We believe that image-guided endoscopic transoccipital hippocampal depth electrode placement can be performed with precision equal or superior to conventional techniques but without their major disadvantages.

Intraventricular monitoring for temporal lobe epilepsy: report on technique and initial results in eight patients

OBJECTIVE AND IMPORTANCE

Resective surgery is an effective treatment for refractory temporal lobe epilepsy. In difficult cases, invasive monitoring may be needed to precisely lateralise and localise seizure foci of mesial temporal origin. The authors present a modified technique for image guided, endoscopic placement of an intraventricular electrode array (IVE) that abuts the amygdalo-hippocampal complex.

METHODS

Eight patients with suspected mesial temporal lobe epilepsy had placement of an IVE in conjunction with other invasive electrodes. Seven of these patients also had subdural grid or strip electrodes and four had foramen ovale electrodes. Frameless image guidance was used to place a custom 10-contact depth electrode through a rigid neuroendoscope within the atrium of the lateral ventricle. Once proper orientation towards the temporal horn was confirmed, the IVE array was advanced into the temporal horn to the temporal tip. The endoscope was removed and electrode placement was confirmed through an intraoperative lateral skull radiograph and on visual inspection at the time of resection in two cases.

RESULTS

The IVE was crucial for localisation in one patient and helped localisation in four others. Surgery was offered to seven patients. The only serious complication of IVE placement was a thalamic contusion presumably from an errant electrode tip. One electrode was inadvertently placed into the frontal horn. There were no deaths and no permanent morbidity associated with the procedure.

CONCLUSION

Endoscopically placed temporal horn, intraventricular electrodes provide an alternative to transcortical depth electrode placement. The technique hopefully can avoid complications associated with multiple depth electrode placements, especially when bilateral amygdalo-hippocampal electrical recordings are desired, although there may be a steep learning curve.