The Promise of Endovascular Neurotechnology: A Brain-Computer Interface to Restore Autonomy to People With Motor Impairment

ABSTRACT

This Joel A. DeLisa Lecture on endovascular brain-computer interfaces was presented by Dr Thomas Oxley on February 23, 2023, at the Association of Academic Physiatrists Annual Scientific Meeting. The lecture described how brain-computer interfaces replace lost physiological function to enable direct communication between the brain and external digital devices, such as computers, smartphones, and robotic limbs. Specifically, the potential of a novel endovascular brain-computer interface technology was discussed. The brain-computer interface uses a stent-electrode array delivered via the jugular vein and is permanently implanted in a vein adjacent to the motor cortex. In a first-in-human clinical trial, participants with upper limb paralysis who received the endovascular brain-computer interface could use the system independently and at home to operate laptop computers for various instrumental activities of daily living. A Food and Drug Administration-approved trial of the endovascular brain-computer interface in the United States is in progress. Future development of the system will provide recipients with continuous autonomy through digital access with minimal caregiver assistance. Physiatrists and occupational therapists will have a vital role in helping people with paralysis achieve the potential of implantable brain-computer interfaces.

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.

Cerebral venous disorders: Diagnosis and endovascular management

The role of the venous circulation in neurological diseases has been underestimated. In this review, we present an overview of the intracranial venous anatomy, venous disorders of the central nervous system, and options for endovascular management. We discuss the role the venous circulation plays in various neurological diseases including cerebrospinal fluid (CSF) disorders (intracranial hypertension and intracranial hypotension), arteriovenous diseases, and pulsatile tinnitus. We also shed light on emergent cerebral venous interventions including transvenous brain-computer interface implantation, transvenous treatment of communicating hydrocephalus, and the endovascular treatment of CSF-venous disorders.

Assessment of Safety of a Fully Implanted Endovascular Brain-Computer Interface for Severe Paralysis in 4 Patients: The Stentrode With Thought-Controlled Digital Switch (SWITCH) Study

Importance

Brain-computer interface (BCI) implants have previously required craniotomy to deliver penetrating or surface electrodes to the brain. Whether a minimally invasive endovascular technique to deliver recording electrodes through the jugular vein to superior sagittal sinus is safe and feasible is unknown.

Objective

To assess the safety of an endovascular BCI and feasibility of using the system to control a computer by thought.

Design, Setting, and Participants

The Stentrode With Thought-Controlled Digital Switch (SWITCH) study, a single-center, prospective, first in-human study, evaluated 5 patients with severe bilateral upper-limb paralysis, with a follow-up of 12 months. From a referred sample, 4 patients with amyotrophic lateral sclerosis and 1 with primary lateral sclerosis met inclusion criteria and were enrolled in the study. Surgical procedures and follow-up visits were performed at the Royal Melbourne Hospital, Parkville, Australia. Training sessions were performed at patients' homes and at a university clinic. The study start date was May 27, 2019, and final follow-up was completed January 9, 2022.

Interventions

Recording devices were delivered via catheter and connected to subcutaneous electronic units. Devices communicated wirelessly to an external device for personal computer control.

Main Outcomes and Measures

The primary safety end point was device-related serious adverse events resulting in death or permanent increased disability. Secondary end points were blood vessel occlusion and device migration. Exploratory end points were signal fidelity and stability over 12 months, number of distinct commands created by neuronal activity, and use of system for digital device control.

Results

Of 4 patients included in analyses, all were male, and the mean (SD) age was 61 (17) years. Patients with preserved motor cortex activity and suitable venous anatomy were implanted. Each completed 12-month follow-up with no serious adverse events and no vessel occlusion or device migration. Mean (SD) signal bandwidth was 233 (16) Hz and was stable throughout study in all 4 patients (SD range across all sessions, 7-32 Hz). At least 5 attempted movement types were decoded offline, and each patient successfully controlled a computer with the BCI.

Conclusions and Relevance

Endovascular access to the sensorimotor cortex is an alternative to placing BCI electrodes in or on the dura by open-brain surgery. These final safety and feasibility data from the first in-human SWITCH study indicate that it is possible to record neural signals from a blood vessel. The favorable safety profile could promote wider and more rapid translation of BCI to people with paralysis.

Trial Registration

ClinicalTrials.gov Identifier: NCT03834857.

Vascular remodeling in sheep implanted with endovascular neural interface

Objective.The aim of this work was to assess vascular remodeling after the placement of an endovascular neural interface (ENI) in the superior sagittal sinus (SSS) of sheep. We also assessed the efficacy of neural recording using an ENI.Approach.The study used histological analysis to assess the composition of the foreign body response. Micro-CT images were analyzed to assess the profiles of the foreign body response and create a model of a blood vessel. Computational fluid dynamic modeling was performed on a reconstructed blood vessel to evaluate the blood flow within the vessel. Recording of brain activity in sheep was used to evaluate efficacy of neural recordings.Main results.Histological analysis showed accumulated extracellular matrix material in and around the implanted ENI. The extracellular matrix contained numerous macrophages, foreign body giant cells, and new vascular channels lined by endothelium. Image analysis of CT slices demonstrated an uneven narrowing of the SSS lumen proportional to the stent material within the blood vessel. However, the foreign body response did not occlude blood flow. The ENI was able to record epileptiform spiking activity with distinct spike morphologies.Significance. This is the first study to show high-resolution tissue profiles, the histological response to an implanted ENI and blood flow dynamic modeling based on blood vessels implanted with an ENI. The results from this study can be used to guide surgical planning and future ENI designs; stent oversizing parameters to blood vessel diameter should be considered to minimize detrimental vascular remodeling.

Feasibility of using discrete Brain Computer Interface for people with Multiple Sclerosis

AIM

Brain-Computer Interfaces (BCIs) hold promise to provide people with partial or complete paralysis, the ability to control assistive technology. This study reports offline classification of imagined and executed movements of the upper and lower limb in one participant with multiple sclerosis and people with no limb function deficits.

METHODS

We collected neural signals using electroencephalography (EEG) while participants performed executed and imagined motor tasks as directed by prompts shown on a screen.

RESULTS

Participants with no limb function attained >70% decoding accuracy on their best-imagined task compared to rest and on at-least one task comparison. The participant with multiple sclerosis also achieved accuracies within the range of participants with no limb function loss.Clinical Relevance - While only one case study is provided it was promising that the participant with MS was able to achieve comparable classification to that of the seven healthy controls. Further studies are needed to assess whether people suffering from MS may be able to use a BCI to improve their quality of life.

Racial and Socioeconomic Disparities in the Use and Outcomes of Endovascular Thrombectomy for Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Racial and socioeconomic disparities in the incidence, treatment, and outcomes of acute ischemic stroke exist and have been described. We aimed to characterize disparities in the use of endovascular thrombectomy in a nationally representative analysis.

MATERIALS AND METHODS

Discharge data from the Nationwide Inpatient Sample between 2006 and 2016 were queried using validated International Classification of Disease codes. Patients admitted to US hospitals with acute ischemic stroke were included and stratified on the basis of race, income, and primary payer. Trends in endovascular thrombectomy use, good outcome (discharge to home/acute rehabilitation), and poor outcome (discharge to skilled nursing facility, hospice, in-hospital mortality) were studied using univariate and multivariable analyses.

RESULTS

In this analysis of 1,322,162 patients, endovascular thrombectomy use increased from 53/111,829 (0.05%) to 3054/146,650 (2.08%) between 2006 and 2016, respectively. Less increase was observed in black patients from 4/12,733 (0.03%) to 401/23,836 (1.68%) and those in the lowest income quartile from 10/819 (0.03%) to 819/44,984 (1.49%). Greater increase was observed in the highest income quartile from 18/22,138 (0.08%) to 669/27,991 (2.39%). Black race predicted less endovascular thrombectomy use (OR = 0.79; 95% CI, 0.72-0.86). The highest income group predicted endovascular thrombectomy use (OR = 1.24; 95% CI, 1.13-1.36) as did private insurance (OR = 1.30; 95% CI, 1.23-1.38). High income predicted good outcome (OR = 1.10; 95% CI. 1.06-1.14), as did private insurance (OR = 1.36; 95% CI, 1.31-1.39). Black race predicted poor outcome (OR = 1.33; 95% CI, 1.30-1.36). All results were statistically significant (P < .01).

CONCLUSIONS

Despite a widespread increase in endovascular thrombectomy use, black and low-income patients may be less likely to receive endovascular thrombectomy. Future effort should attempt to better understand the causes of these disparities and develop strategies to ensure equitable access to potentially life-saving treatment.

Motor neuroprosthesis implanted with neurointerventional surgery improves capacity for activities of daily living tasks in severe paralysis: first in-human experience

BACKGROUND

Implantable brain-computer interfaces (BCIs), functioning as motor neuroprostheses, have the potential to restore voluntary motor impulses to control digital devices and improve functional independence in patients with severe paralysis due to brain, spinal cord, peripheral nerve or muscle dysfunction. However, reports to date have had limited clinical translation.

METHODS

Two participants with amyotrophic lateral sclerosis (ALS) underwent implant in a single-arm, open-label, prospective, early feasibility study. Using a minimally invasive neurointervention procedure, a novel endovascular Stentrode BCI was implanted in the superior sagittal sinus adjacent to primary motor cortex. The participants undertook machine-learning-assisted training to use wirelessly transmitted electrocorticography signal associated with attempted movements to control multiple mouse-click actions, including zoom and left-click. Used in combination with an eye-tracker for cursor navigation, participants achieved Windows 10 operating system control to conduct instrumental activities of daily living (IADL) tasks.

RESULTS

Unsupervised home use commenced from day 86 onwards for participant 1, and day 71 for participant 2. Participant 1 achieved a typing task average click selection accuracy of 92.63% (100.00%, 87.50%-100.00%) (trial mean (median, Q1-Q3)) at a rate of 13.81 (13.44, 10.96-16.09) correct characters per minute (CCPM) with predictive text disabled. Participant 2 achieved an average click selection accuracy of 93.18% (100.00%, 88.19%-100.00%) at 20.10 (17.73, 12.27-26.50) CCPM. Completion of IADL tasks including text messaging, online shopping and managing finances independently was demonstrated in both participants.

CONCLUSION

We describe the first-in-human experience of a minimally invasive, fully implanted, wireless, ambulatory motor neuroprosthesis using an endovascular stent-electrode array to transmit electrocorticography signals from the motor cortex for multiple command control of digital devices in two participants with flaccid upper limb paralysis.

Neurological implications of COVID-19: a review of the science and clinical guidance

COVID-19 is a significant global health burden. The pulmonary morbidity and mortality of COVID-19 is well described, however, there is mounting evidence of neurological manifestations of SARS-CoV-2, which may be of prognostic significance. This paper summarises the available evidence in order to provide clinicians with a concise summary of the peripheral and central neurological manifestations of COVID-19, discusses specific issues regarding the management of chronic neurological disease in the context of the pandemic, and provides a summary of the thrombotic implications of the disease for the neurologist.

Mobile Interventional Stroke Team Model Improves Early Outcomes in Large Vessel Occlusion Stroke

Background and Purpose:

Triage of patients with emergent large vessel occlusion stroke to primary stroke centers followed by transfer to comprehensive stroke centers leads to increased time to endovascular therapy. A Mobile Interventional Stroke Team (MIST) provides an alternative model by transferring a MIST to a Thrombectomy Capable Stroke Center (TSC) to perform endovascular therapy. Our aim is to determine whether the MIST model is more time-efficient and leads to improved clinical outcomes compared with standard drip-and-ship (DS) and mothership models.

Methods:

This is a prospective observational cohort study with 3-month follow-up between June 2016 and December 2018 at a multicenter health system, consisting of one comprehensive stroke center, 4 TSCs, and several primary stroke centers. A total of 228 of 373 patients received endovascular therapy via 1 of 4 models: mothership with patient presentation to a comprehensive stroke center, DS with patient transfer from primary stroke center or TSC to comprehensive stroke center, MIST with patient presentation to TSC and MIST transfer, or a combination of DS with patient transfer from primary stroke center to TSC and MIST. The prespecified primary end point was initial door-to-recanalization time and secondary end points measured additional time intervals and clinical outcomes at discharge and 3 months.

Results:

MIST had a faster mean initial door-to-recanalization time than DS by 83 minutes ( P <0.01). MIST and mothership had similar median door-to-recanalization times of 192 minutes and 179 minutes, respectively ( P =0.83). A greater proportion had a complete recovery (National Institutes of Health Stroke Scale of 0 or 1) at discharge in MIST compared with DS (37.9% versus 16.7%; P <0.01). MIST had 52.8% of patients with modified Rankin Scale of ≤2 at 3 months compared with 38.9% in DS ( P =0.10).

Conclusions:

MIST led to significantly faster initial door-to-recanalization times compared with DS, which was comparable to mothership. This decrease in time has translated into improved short-term outcomes and a trend towards improved long-term outcomes.

Registration:

URL: https://www.clinicaltrials.gov . Unique identifier: NCT03048292.

Emergent Large Vessel Occlusion Stroke During New York City's COVID-19 Outbreak: Clinical Characteristics and Paraclinical Findings

BACKGROUND AND PURPOSE

The 2019 novel coronavirus outbreak and its associated disease (coronavirus disease 2019 [COVID-19]) have created a worldwide pandemic. Early data suggest higher rate of ischemic stroke in severe COVID-19 infection. We evaluated whether a relationship exists between emergent large vessel occlusion (ELVO) and the ongoing COVID-19 outbreak.

METHODS

This is a retrospective, observational case series. Data were collected from all patients who presented with ELVO to the Mount Sinai Health System Hospitals across New York City during the peak 3 weeks of hospitalization and death from COVID-19. Patients' demographic, comorbid conditions, cardiovascular risk factors, COVID-19 disease status, and clinical presentation were extracted from the electronic medical record. Comparison was made between COVID-19 positive and negative cohorts. The incidence of ELVO stroke was compared with the pre-COVID period.

RESULTS

Forty-five consecutive ELVO patients presented during the observation period. Fifty-three percent of patients tested positive for COVID-19. Total patients' mean (±SD) age was 66 (±17). Patients with COVID-19 were significantly younger than patients without COVID-19, 59±13 versus 74±17 (odds ratio [95% CI], 0.94 [0.81-0.98]; P=0.004). Seventy-five percent of patients with COVID-19 were male compared with 43% of patients without COVID-19 (odds ratio [95% CI], 3.99 [1.12-14.17]; P=0.032). Patients with COVID-19 were less likely to be White (8% versus 38% [odds ratio (95% CI), 0.15 (0.04-0.81); P=0.027]). In comparison to a similar time duration before the COVID-19 outbreak, a 2-fold increase in the total number of ELVO was observed (estimate: 0.78 [95% CI, 0.47-1.08], P≤0.0001).

CONCLUSIONS

More than half of the ELVO stroke patients during the peak time of the New York City's COVID-19 outbreak were COVID-19 positive, and those patients with COVID-19 were younger, more likely to be male, and less likely to be White. Our findings also suggest an increase in the incidence of ELVO stroke during the peak of the COVID-19 outbreak.

Distinct Neural Correlates Underlie Inhibitory Mechanisms of Motor Inhibition and Motor Imagery Restraint

There is evidence to suggest that motor execution and motor imagery both involve planning and execution of the same motor plan, however, in the latter the output is inhibited. Currently, little is known about the underlying neural mechanisms of motor output inhibition during motor imagery. Uncovering the distinctive characteristics of motor imagery may help us better understand how we abstract complex thoughts and acquire new motor skills. The current study aimed to dissociate the cognitive processes involved in two distinct inhibitory mechanisms of motor inhibition and motor imagery restraint. Eleven healthy participants engaged in an imagined GO/NO-GO task during a 7 Tesla fMRI experiment. Participants planned a specific type of motor imagery, then, imagined the movements during the GO condition and restrained from making a response during the NO-GO condition. The results revealed that specific sub-regions of the supplementary motor cortex (SMC) and the primary motor cortex (M1) were recruited during the imagination of specific movements and information flowed from the SMC to the M1. Such condition-specific recruitment was not observed when motor imagery was restrained. Instead, general recruitment of the posterior parietal cortex (PPC) was observed, while the BOLD activity in the SMC and the M1 decreased below the baseline at the same time. Information flowed from the PPC to the SMC, and recurrently between the M1 and the SMC, and the M1 and the PPC. These results suggest that motor imagery involves task-specific motor output inhibition partly imposed by the SMC to the M1, while the PPC globally inhibits motor plans before they are passed on for execution during the restraint of responses.

Call to Action: SARS-CoV-2 and CerebrovAscular DisordErs (CASCADE)

Background and purpose

The novel severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2), now named coronavirus disease 2019 (COVID-19), may change the risk of stroke through an enhanced systemic inflammatory response, hypercoagulable state, and endothelial damage in the cerebrovascular system. Moreover, due to the current pandemic, some countries have prioritized health resources towards COVID-19 management, making it more challenging to appropriately care for other potentially disabling and fatal diseases such as stroke. The aim of this study is to identify and describe changes in stroke epidemiological trends before, during, and after the COVID-19 pandemic.

Methods

This is an international, multicenter, hospital-based study on stroke incidence and outcomes during the COVID-19 pandemic. We will describe patterns in stroke management, stroke hospitalization rate, and stroke severity, subtype (ischemic/hemorrhagic), and outcomes (including in-hospital mortality) in 2020 during COVID-19 pandemic, comparing them with the corresponding data from 2018 and 2019, and subsequently 2021. We will also use an interrupted time series (ITS) analysis to assess the change in stroke hospitalization rates before, during, and after COVID-19, in each participating center.

Conclusion

The proposed study will potentially enable us to better understand the changes in stroke care protocols, differential hospitalization rate, and severity of stroke, as it pertains to the COVID-19 pandemic. Ultimately, this will help guide clinical-based policies surrounding COVID-19 and other similar global pandemics to ensure that management of cerebrovascular comorbidity is appropriately prioritized during the global crisis. It will also guide public health guidelines for at-risk populations to reduce risks of complications from such comorbidities.

Endovascular Neuromodulation: Safety Profile and Future Directions

Endovascular neuromodulation is an emerging technology that represents a synthesis between interventional neurology and neural engineering. The prototypical endovascular neural interface is the Stentrode^TM, a stent-electrode array which can be implanted into the superior sagittal sinus via percutaneous catheter venography, and transmits signals through a transvenous lead to a receiver located subcutaneously in the chest. Whilst the Stentrode^TM has been conceptually validated in ovine models, questions remain about the long term viability and safety of this device in human recipients. Although technical precedence for venous sinus stenting already exists in the setting of idiopathic intracranial hypertension, long term implantation of a lead within the intracranial veins has never been previously achieved. Contrastingly, transvenous leads have been successfully employed for decades in the setting of implantable cardiac pacemakers and defibrillators. In the current absence of human data on the Stentrode^TM, the literature on these structurally comparable devices provides valuable lessons that can be translated to the setting of endovascular neuromodulation. This review will explore this literature in order to understand the potential risks of the Stentrode^TM and define avenues where further research and development are necessary in order to optimize this device for human application.

Abstract 95: The Mobile Interventional Stroke Team (MIST) Model Improves Early Outcomes in Elvo Stroke: The NYC Mist Trial

Introduction: Endovascular therapy (EVT) has become the standard of care for treatment of emergent large vessel occlusion (ELVO) in ischemic stroke. It is a time sensitive procedure that has previously only been performed at comprehensive stroke centers (CSC). Transfer was required for patients presenting at a primary stroke center (PSC). PSCs with interventional capacity (PSCI) have emerged to increase access to EVT. We have developed a Mobile Interventional Stroke Team (MIST) model, in which a MIST transfers from a CSC to PSCI to perform EVT.

Hypothesis: The delivery of care by the MIST at PSCIs is more time efficient and leads to improved clinical outcomes in comparison to transferring patients from a PSC to PSCI or CSC and comparable to direct presentation to a CSC.

Methods: Analysis of prospectively collected data from 228 patients who received EVT for ELVO at a CSC or 4 PSCIs between June 2016 - December 2018 was performed. The cohorts include: Mothership with patient presentation to CSC (n=20), Drip-and-Ship with patient transfer from PSC or PSCI to CSC (DS) (n=114), MIST and patient presentation to PSCI (n=64), and DS with patient transfer from PSC to PSCI and MIST (DS/MIST) (n=30). The primary outcome was initial door-to-recanalization. Secondary outcomes measured other time intervals and clinical outcomes at discharge and 3 months.

Results: MIST had a faster mean initial door-to-recanalization time than DS by 83 minutes (p < 0.05). MIST and Mothership had similar median times of 192 minutes and 181 minutes, respectively (p = 0.84). A greater proportion of patients reached a discharge NIHSS of 0 or 1 in MIST compared to DS (34% vs. 17%; p < 0.01). MIST led to 53% with a mRS of ≤ 2 at 3 months compared to 39% in DS, although not statistically significant (p = 0.10).

Conclusions: MIST has led to significantly faster initial door-to-recanalization times compared to DS. This decrease in time has translated into improved short-term outcomes and a trend towards improved long-term outcomes.

Variant ascending pharyngeal artery maintaining flow in a subocclusive internal carotid artery

Ectopic branches of the external carotid artery are rare but have critical diagnostic and therapeutic implications. We present a case involving a 70-year-old man who presented with recurrent left hemispheric strokes in the setting of a subocclusive left internal carotid stenosis. A left ascending pharyngeal artery with variant origin from the internal carotid artery helped maintain flow distal to the area of stenosis and allowed for safe and successful internal carotid artery stenting. Identification of this variant and recognition of the anastomotic network involving this connection were crucial to determine the safety of stenting. The patient had no further recurrent events and had sustained improvement on his 90-day follow-up.

Removing the need for invasive brain surgery: the potential of stent electrodes

Over the last decade, significant advances in brain–machine interfaces have demonstrated that people with paralysis can control assistive technology such as computers, wheelchairs and bionic arms with their minds. However, due to the invasive surgery required to access the brain and implant electrodes, to date, no device has received commercial US FDA approval, and consequently there is no existing solution to return independence and mobility for the hundreds-of-millions of people paralyzed by stroke, spinal cord injury and motor neuron disease. But there is hope. We have developed a minimally invasive brain–machine interface that can access the brain using cortical vessels which mitigates the risks associated with open brain surgery.

Effect of Implant Duration, Anatomical Location and Electrode Orientation on Bandwidth Recorded with a Chronically Implanted Endovascular Stent-Electrode Array

Access to the brain to implant recording electrodes has conventionally required a craniotomy. To mitigate risks of open brain surgery, we previously developed a stent-electrode array that can be delivered to the cortex via cerebral vessels. Following implantation of a stent-electrode array (Stentrode) in a large animal model, we investigated the longevity of highquality signals, by measuring bandwidth in animals implanted for up to six months; no signal degradation was observed. We also investigated whether bandwidth was influenced by implant location with respect to the superior sagittal sinus and branching cortical veins; it was not. Finally, we assessed whether electrode orientation had an impact on recording quality. There was no significant difference in bandwidths from electrodes facing different orientations. Interestingly, electrodes facing the skull (180°) were still able to record neural information with high fidelity. Consequently, a minimally invasive surgical approach combined with a stent-electrode array is a safe and efficacious technique to acquire neural signals over a chronic duration.

Cortical Brain Stimulation with Endovascular Electrodes

Electrical stimulation of neural tissue and recording of neural activity are the bases of emerging prostheses and treatments for spinal cord injury, stroke, sensory deficits, and drug-resistant neurological disorders. Safety and efficacy are key aspects for the clinical acceptance of therapeutic neural stimulators. The cortical vasculature has been shown to be a safe site for implantation of electrodes for chronically recording neural activity, requiring no craniotomy to access high-bandwidth, intracranial EEG. This work presents the first characterization of endovascular cortical stimulation measured using cortical subdural surface recordings. Visual stimulation was used to verify electrode viability and cortical activation was compared with electrically evoked activity. Due to direct activation of the neural tissue, the latency of responses to electrical stimulation was shorter than for that of visual stimulation. We also found that the center of neural activation was different for visual and electrical stimulation indicating an ability of the stentrode to provide localized activation of neural tissue.

Feasibility of identifying the ideal locations for motor intention decoding using unimodal and multimodal classification at 7T-fMRI

Invasive Brain-Computer Interfaces (BCIs) require surgeries with high health-risks. The risk-to-benefit ratio of the procedure could potentially be improved by pre-surgically identifying the ideal locations for mental strategy classification. We recorded high-spatiotemporal resolution blood-oxygenation-level-dependent (BOLD) signals using functional MRI at 7 Tesla in eleven healthy participants during two motor imagery tasks. BCI diagnostic task isolated the intent to imagine movements, while BCI simulation task simulated the neural states that may be yielded in a real-life BCI-operation scenario. Imagination of movements were classified from the BOLD signals in sub-regions of activation within a single or multiple dorsal motor network regions. Then, the participant's decoding performance during the BCI simulation task was predicted from the BCI diagnostic task. The results revealed that drawing information from multiple regions compared to a single region increased the classification accuracy of imagined movements. Importantly, systematic unimodal and multimodal classification revealed the ideal combination of regions that yielded the best classification accuracy at the individual-level. Lastly, a given participant's decoding performance achieved during the BCI simulation task could be predicted from the BCI diagnostic task. These results show the feasibility of 7T-fMRI with unimodal and multimodal classification being utilized for identifying ideal sites for mental strategy classification.

In Vivo Impedance Characterization of Cortical Recording Electrodes Shows Dependence on Electrode Location and Size

OBJECTIVE

Neural prostheses are improving the quality of life for those suffering from neurological impairments. Electrocorticography electrodes located in subdural, epidural, and intravascular positions show promise as long-term neural prostheses. However, chronic implantation affects the electrochemical environments of these arrays.

METHODS

In the present work, the effect of electrode location on the electrochemical properties of the interface was compared. The impedances of the electrode arrays were measured using electrochemical impedance spectroscopy in vitro in saline and in vivo four-week postimplantation.

RESULTS

There was not a significant effect of electrode location (subdural, intravascular, or epidural) on the impedance magnitude, and the effect of the electrode size on the impedance magnitude was frequency dependent. There was a frequency-dependent statistically significant effect of electrode location and electrode size on the phase angles of the three arrays. The subdural and epidural arrays showed phase shifts closer to -90° indicating the capacitive nature of the interface in these locations. The impact of placing electrodes within a blood vessel and adjacent to the blood vessel wall was most obvious when looking at the phase responses at frequencies below 10 kHz.

CONCLUSION

Our results show that intravascular electrodes, like those in subdural and epidural positions, show electrical properties that are suitable for recording. These results provide support for the use of intravascular arrays in clinically relevant neural prostheses and diagnostic devices.

SIGNIFICANCE

Comparison of electrochemical impedance of the epidural, intravascular, and subdural electrode array showed that all three locations are possible placement options, since impedances are in comparable ranges.

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.

Spatially dynamic recurrent information flow across long-range dorsal motor network encodes selective motor goals

Performing voluntary movements involves many regions of the brain, but it is unknown how they work together to plan and execute specific movements. We recorded high-resolution ultra-high-field blood-oxygen-level-dependent signal during a cued ankle-dorsiflexion task. The spatiotemporal dynamics and the patterns of task-relevant information flow across the dorsal motor network were investigated. We show that task-relevant information appears and decays earlier in the higher order areas of the dorsal motor network then in the primary motor cortex. Furthermore, the results show that task-relevant information is encoded in general initially, and then selective goals are subsequently encoded in specifics subregions across the network. Importantly, the patterns of recurrent information flow across the network vary across different subregions depending on the goal. Recurrent information flow was observed across all higher order areas of the dorsal motor network in the subregions encoding for the current goal. In contrast, only the top-down information flow from the supplementary motor cortex to the frontoparietal regions, with weakened recurrent information flow between the frontoparietal regions and bottom-up information flow from the frontoparietal regions to the supplementary cortex were observed in the subregions encoding for the opposing goal. We conclude that selective motor goal encoding and execution rely on goal-dependent differences in subregional recurrent information flow patterns across the long-range dorsal motor network areas that exhibit graded functional specialization.

Advanced Imaging of Intracranial Atherosclerosis: Lessons from Interventional Cardiology

Intracranial atherosclerosis is a major cause of ischemic stroke. Patients with a high degree of stenosis have a significant rate of stroke despite medical therapy. Two randomized trials of stenting have failed to show benefit. Improving periprocedural complication rates and patient selection may improve stenting outcomes. Fractional flow reserve (FFR), intravascular ultrasound (IVUS), and optical coherence tomography (OCT) are intravascular imaging techniques employed to improve patient selection and stent placement in interventional cardiology. FFR has been shown to improve cardiovascular outcomes when used in patient selection for intervention. Studies of FFR in intracranial atherosclerosis show that the measure may predict which plaques lead to stroke. IVUS is used in cardiology to quantify stenosis and assist with stent placement. Comparisons with histology show that it can reliably characterize plaques. Several case reports of IVUS in intracranial arteries show the technique to be feasible and indicate it may improve stent placement. Plaque characteristics on IVUS may help identify vulnerable plaques. In interventional cardiology, OCT provides excellent visualization of vessel geometry and is useful periprocedurally. Images reliably identify thin-capped fibroatheromas and other plaque features. Case reports indicate that OCT is safe for use in intracranial arteries. OCT can be used to identify perforator vessels and so may be useful in avoiding perforator strokes, a common complication of stenting. Plaque characteristics on OCT may be useful in patient selection.

Novel and emerging technologies for endovascular thrombectomy

Endovascular thrombectomy device improvements in recent years have served a pivotal role in improving the success and safety of the thrombectomy procedure. As the intervention gains widespread use, developers have focused on maximizing the reperfusion rates and reducing procedural complications associated with these devices. This has led to a boom in device development. This review will cover novel and emerging technologies developed for endovascular thrombectomy.

Suitability of nitinol electrodes in neural prostheses such as endovascular neural interfaces

A major challenge facing neural prostheses is the development of electrodes that are well tolerated by the brain and body. A novel way to circumvent the need to perform an invasive craniotomy and penetration of the blood-brain barrier to implant electrodes, is to guide electrodes up into the cerebral veins and place electrodes on the vessel walls adjacent to neuronal populations. To aid in the development of these stent based devices, microelectrodes manufactured from Nitinol would allow electrodes to be implanted via a catheter and then once deployed, alter their shape to conform to the vessel walls. However, there is a paucity of data on whether Nitinol is a suitable material to record neural signals. Here we show that Nitinol is tolerated by the body and that it can effectively measure neural signals. Specifically, we electrochemically evaluate Nitinol electrodes in blood and record visually evoked potentials from sheep.

Republished: The bumper technique for advancing a large profile microcatheter

Operators commonly encounter difficulty maneuvering a microcatheter beyond the distal lip of wide neck aneurysms and aneurysms in challenging locations. Few techniques have been described to guide operators in these particular situations. In this case report of a 56-year-old woman with a 16 mm ophthalmic artery aneurysm, the microcatheter continually snagged the distal aneurysm lip, preventing delivery of a flow diverter into the distal parent vessel. In troubleshooting this obstacle, a second microguidewire was introduced alongside the microcatheter and was used to cover the distal lip of the aneurysm to prevent further snagging. The second guidewire successfully deflected the microcatheter into the distal vessel, a technique that we have aptly dubbed the ‘bumper technique’.

7T-fMRI: Faster temporal resolution yields optimal BOLD sensitivity for functional network imaging specifically at high spatial resolution

Recent developments in accelerated imaging methods allow faster acquisition of high spatial resolution images. This could improve the applications of functional magnetic resonance imaging at 7 Tesla (7T-fMRI), such as neurosurgical planning and Brain Computer Interfaces (BCIs). However, increasing the spatial and temporal resolution will both lead to signal-to-noise ratio (SNR) losses due to decreased net magnetization per voxel and T₁-relaxation effect, respectively. This could potentially offset the SNR efficiency gains made with increasing temporal resolution. We investigated the effects of varying spatial and temporal resolution on fMRI sensitivity measures and their implications on fMRI-based BCI simulations. We compared temporal signal-to-noise ratio (tSNR), observed percent signal change (%∆S), volumes of significant activation, Z-scores and decoding performance of linear classifiers commonly used in BCIs across a range of spatial and temporal resolution images acquired during an ankle-tapping task. Our results revealed an average increase of 22% in %∆S (p=0.006) and 9% in decoding performance (p=0.015) with temporal resolution only at the highest spatial resolution of 1.5×1.5×1.5mm³, despite a 29% decrease in tSNR (p<0.001) and plateaued Z-scores. Further, the volume of significant activation was indifferent (p>0.05) across spatial resolution specifically at the highest temporal resolution of 500ms. These results demonstrate that the overall BOLD sensitivity can be increased significantly with temporal resolution, granted an adequately high spatial resolution with minimal physiological noise level. This shows the feasibility of diffuse motor-network imaging at high spatial and temporal resolution with robust BOLD sensitivity with 7T-fMRI. Importantly, we show that this sensitivity improvement could be extended to an fMRI application such as BCIs.

The bumper technique for advancing a large profile microcatheter

Operators commonly encounter difficulty maneuvering a microcatheter beyond the distal lip of wide neck aneurysms and aneurysms in challenging locations. Few techniques have been described to guide operators in these particular situations. In this case report of a 56-year-old woman with a 16 mm ophthalmic artery aneurysm, the microcatheter continually snagged the distal aneurysm lip, preventing delivery of a flow diverter into the distal parent vessel. In troubleshooting this obstacle, a second microguidewire was introduced alongside the microcatheter and was used to cover the distal lip of the aneurysm to prevent further snagging. The second guidewire successfully deflected the microcatheter into the distal vessel, a technique that we have aptly dubbed the 'bumper technique'.

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.

Abstract WMP22: Multiparametric CT Perfusion to Determine the Collaterals Status in Patients With Acute Ischemic Stroke: A New Perfusion Index

Introduction: Good collateral flow is an independent predictor of reperfusion that can be used to extend the treatment window in the new era of endovascular therapies for patients with acute ischemic stroke (AIS). Using a multiparametric approach, we aimed to identify perfusion parameter/s that can represent the extent of collaterals in comparison to CTA.

Methods: AIS patients with anterior circulation large vessel occlusion who had baseline CTA and CT perfusion were included. CT perfusion data were processed by Bayesian method to generate arterial tissue delay (ATD) maps at thresholds of 2 & 6 seconds. The volume of mild delayed perfusion (Vol-ATD >2sec ), moderate delayed (Vol-ATD 2-6sec ) and critical delayed perfusion (Vol-ATD >6sec ) in addition to corresponding rCBV and rCBF were calculated. Baseline CTA collaterals were scored using an established scoring scale1 and dichotomized to poor or good. The association of perfusion parameters and status of collaterals was assessed by repeated measure of analyses and receiver operating characteristic (ROC).

Results: In 28 patients included, 16 had good collaterals on CTA. After controlling for age, sex, baseline NIHSS and type of treatment, multivariate logistic regression analysis identified rCBV (p<0.001) and ATD 2-6sec (p=0.003), but not rCBF, Vol-ATD > 2sec or Vol-ATD >6sec , as independent predictors of good collaterals. ROC analysis showed AUC of 0.88 (sensitivity/specificity: 75%/100%) for rCBV and AUC of 0.84 (sensitivity/specificity: 93%/67%) for Vol-ATD 2-6sec . We defined a perfusion collateral index (PCI) calculated from Vol-ATD 2-6sec x its rCBV, that remained an independent predictor of good collaterals with improved diagnostic accuracy over each measure alone resulting in nominal AUC of 1 (sensitivity/specificity: 100%/100%).

Conclusions: Multiparametric CT perfusion can be used to assess the status of collaterals in patients with AIS. Perfusion collateral index (PCI) defined as Vol-ATD 2-6sec x rCBV is a new perfusion index with a nominal diagnostic accuracy of 100% compared to baseline CTA to predict status of collaterals in our small cohort. Our results need to be validated in a larger prospective cohort.

A technical consideration when using flow diversion for recurrent aneurysms following stent-assisted coiling

Flow diversion (FD) is a treatment option for recurrent aneurysms including following stent-assisted coiling (SAC), although this approach is both 'off-label' and unproven. A technical challenge of FD placement may involve the microwire catching on the tines of the previously placed stent or potentially going 'in-out-in' from the central axis of the stent. We report a case and technique that assures the wire has safely remained within the central axis of the stent. The procedure was performed in standard fashion except that the intermediate catheter was passed completely through the previously placed stent after the microwire/microcatheter had crossed. The large diameter of the intermediate catheter assured that the microwire did not go 'in-out-in'. The intermediate catheter was completely withdrawn from the stent and the FD was placed in standard fashion. This technique may help to achieve complete FD opening and prevent thromboembolic complications associated with incomplete FD opening.

A technical consideration when using flow diversion for recurrent aneurysms following stent-assisted coiling

Flow diversion (FD) is a treatment option for recurrent aneurysms including following stent-assisted coiling (SAC), although this approach is both 'off-label' and unproven. A technical challenge of FD placement may involve the microwire catching on the tines of the previously placed stent or potentially going 'in-out-in' from the central axis of the stent. We report a case and technique that assures the wire has safely remained within the central axis of the stent. The procedure was performed in standard fashion except that the intermediate catheter was passed completely through the previously placed stent after the microwire/microcatheter had crossed. The large diameter of the intermediate catheter assured that the microwire did not go 'in-out-in'. The intermediate catheter was completely withdrawn from the stent and the FD was placed in standard fashion. This technique may help to achieve complete FD opening and prevent thromboembolic complications associated with incomplete FD opening.

Feasibility of a chronic, minimally invasive endovascular neural interface

Development of a neural interface that can be implanted without risky, open brain surgery will increase the safety and viability of chronic neural recording arrays. We have developed a minimally invasive surgical procedure and an endovascular electrode-array that can be delivered to overlie the cortex through blood vessels. Here, we describe feasibility of the endovascular interface through electrode viability, recording potential and safety. Electrochemical impedance spectroscopy demonstrated that electrode impedance was stable over 91 days and low frequency phase could be used to infer electrode incorporation into the vessel wall. Baseline neural recording were used to identify the maximum bandwidth of the neural interface, which remained stable around 193 Hz for six months. Cross-sectional areas of the implanted vessels were non-destructively measured using the Australian Synchrotron. There was no case of occlusion observed in any of the implanted animals. This work demonstrates the feasibility of an endovascular neural interface to safely and efficaciously record neural information over a chronic time course.

Chronic impedance spectroscopy of an endovascular stent-electrode array

OBJECTIVE

Recently, we reported a minimally invasive stent-electrode array capable of recording neural signals from within a blood vessel. We now investigate the use of electrochemical impedance spectroscopy (EIS) measurements to infer changes occurring to the electrode-tissue interface from devices implanted in a cohort of sheep for up to 190 days.

APPROACH

In a cohort of 15 sheep, endovascular stent-electrode arrays were implanted in the superior sagittal sinus overlying the motor cortex for up to 190 days. EIS was performed routinely to quantify viable electrodes for up to 91 days. An equivalent circuit model (ECM) was developed from the in vivo measurements to characterize the electrode-tissue interface changes occurring to the electrodes chronically implanted within a blood vessel. Post-mortem histological assessment of stent and electrode incorporation into the wall of the cortical vessels was compared to the electrical impedance measurements.

MAIN RESULTS

EIS could be used to infer electrode viability and was consistent with x-ray analysis performed in vivo, and post-mortem evaluation. Viable electrodes exhibited consistent 1 kHz impedances across the 91 day measurement period, with the peak resistance frequency for the acquired data also stable over time. There was a significant change in 100 Hz phase angles, increasing from -67.8° ± 8.8° at day 0 to -43.8° ± 0.8° at day 91, which was observed to stabilize after eight days. ECM's modeled to the data suggested this change was due to an increase in the capacitance of the electrode-tissue interface. This was supported by histological assessment with >85% of the implanted stent struts covered with neointima and incorporated into the blood vessel within two weeks.

CONCLUSION

This work demonstrated that EIS could be used to determine the viability of electrode implanted chronically within a blood vessel. Impedance measurements alone were not observed to be a useful predictor of alterations occurring at the electrode tissue interface. However, measurement of 100 Hz phase angles was in good agreement with the capacitive changes predicted by the ECM and consistent with suggestions that this represents protein absorption on the electrode surface. 100 Hz phase angles stabilized after 8 days, consistent with histologically assessed samples.

SIGNIFICANCE

These findings demonstrate the potential application of this technology for use as a chronic neural recording system and indicate the importance of conducting EIS as a measure to identify viable electrodes and changes occurring at the electrode-tissue interface.

Micro-CT and Histological Evaluation of an Neural Interface Implanted Within a Blood Vessel

OBJECTIVE

Recently, we reported the development of a stent-mounted electrode array (Stentrode) capable of chronically recording neural signals from within a blood vessel with high fidelity. Preliminary data suggested incorporation of the Stentrode into the blood vessel wall was associated with improved recording sensitivity. We now investigate neointimal incorporation of the Stentrode, implanted in a cohort of sheep for up to 190 days.

METHODS

Micro-CT, obtained from the Imaging and Medical Beamline at the Australian Synchrotron, and histomorphometic techniques developed specifically for evaluation of cerebral vasculature implanted with a stent-electrode array were compared as measures to assess device incorporation and vessel patency.

RESULTS

Both micro-CT analysis and histomorphometry, revealed a strong correlation between implant duration and the number of incorporated stent struts. <10% (26/268) of stent struts were covered in neointima in sheep implanted for <2 weeks, increasing to >78% (191/243) between 2 and 4 weeks. Average strut-to-lumen thickness from animals implanted >12 weeks was comparable across both modalities, 339 ±15 μm measured using micro-CT and 331 ±19 μm ( n = 292) measured histologically. There was a strong correlation between lumen areas measured using the two modalities ( ), with no observation of vessel occlusion observed from any of the 12 animals implanted for up to 190 days.

CONCLUSION

Micro-CT and the histomorphometric techniques we developed are comparable and can both be used to identify incorporation of a Stentrode implanted in cerebral vessels.

SIGNIFICANCE

This study demonstrates preliminary safety of a stent-electrode array implanted in cerebral vasculature, which may facilitate technological advances in minimally invasive brain-computer interfaces.

Endovascular therapy for ischemic stroke with perfusion-imaging selection

BACKGROUND

Trials of endovascular therapy for ischemic stroke have produced variable results. We conducted this study to test whether more advanced imaging selection, recently developed devices, and earlier intervention improve outcomes.

METHODS

We randomly assigned patients with ischemic stroke who were receiving 0.9 mg of alteplase per kilogram of body weight less than 4.5 hours after the onset of ischemic stroke either to undergo endovascular thrombectomy with the Solitaire FR (Flow Restoration) stent retriever or to continue receiving alteplase alone. All the patients had occlusion of the internal carotid or middle cerebral artery and evidence of salvageable brain tissue and ischemic core of less than 70 ml on computed tomographic (CT) perfusion imaging. The coprimary outcomes were reperfusion at 24 hours and early neurologic improvement (≥8-point reduction on the National Institutes of Health Stroke Scale or a score of 0 or 1 at day 3). Secondary outcomes included the functional score on the modified Rankin scale at 90 days.

RESULTS

The trial was stopped early because of efficacy after 70 patients had undergone randomization (35 patients in each group). The percentage of ischemic territory that had undergone reperfusion at 24 hours was greater in the endovascular-therapy group than in the alteplase-only group (median, 100% vs. 37%; P<0.001). Endovascular therapy, initiated at a median of 210 minutes after the onset of stroke, increased early neurologic improvement at 3 days (80% vs. 37%, P=0.002) and improved the functional outcome at 90 days, with more patients achieving functional independence (score of 0 to 2 on the modified Rankin scale, 71% vs. 40%; P=0.01). There were no significant differences in rates of death or symptomatic intracerebral hemorrhage.

CONCLUSIONS

In patients with ischemic stroke with a proximal cerebral arterial occlusion and salvageable tissue on CT perfusion imaging, early thrombectomy with the Solitaire FR stent retriever, as compared with alteplase alone, improved reperfusion, early neurologic recovery, and functional outcome. (Funded by the Australian National Health and Medical Research Council and others; EXTEND-IA ClinicalTrials.gov number, NCT01492725, and Australian New Zealand Clinical Trials Registry number, ACTRN12611000969965.).

Antiplatelet resistance and thromboembolic complications in neurointerventional procedures

Antiplatelet resistance is emerging as a significant factor in effective secondary stroke prevention. Prevalence of aspirin and clopidogrel resistance is dependent upon laboratory test and remains contentious. Large studies in cardiovascular disease populations have demonstrated worse ischemic outcomes in patients with antiplatelet resistance, particularly in patients with coronary stents. Thromboembolism is a complication of neurointerventional procedures that leads to stroke. Stroke rates related to aneurysm coiling range from 2 to 10% and may be higher when considering silent ischemia. Stroke associated with carotid stenting is a major cause of morbidity. Antiplatelet use in the periprocedure setting varies among different centers. No guidelines exist for use of antiplatelet regimens in neurointerventional procedures. Incidence of stroke in patients post procedure may be partly explained by resistance to antiplatelet agents. Further research is required to establish the incidence of stroke in patients with antiplatelet resistance undergoing neurointerventional procedures.