Brian W. Chong

Finite element modeling of embolic coil deployment: multifactor characterization of treatment effects on cerebral aneurysm hemodynamics.

Endovascular coiling is the most common treatment for cerebral aneurysms. During the treatment, a sequence of embolic coils with different stiffness, shapes, sizes, and lengths is deployed to fill the aneurysmal sac. Although coil packing density has been clinically correlated with treatment success, many studies have also reported success at low packing densities, as well as recurrence at high packing densities. Such reports indicate that other factors may influence treatment success. In this study, we used a novel finite element approach and computational fluid dynamics (CFD) to investigate the effects of packing density, coil shape, aneurysmal neck size, and parent vessel flow rate on aneurysmal hemodynamics. The study examines a testbed of 80 unique CFD simulations of post-treatment flows in idealized basilar tip aneurysm models. Simulated coil deployments were validated against in vitro and in vivo deployments. Among the investigated factors, packing density had the largest effect on intra-aneurysmal velocities. However, multifactor analysis of variance showed that coil shape can also have considerable effects, depending on packing density and neck size. Further, linear regression analysis showed an inverse relationship between mean void diameter in the aneurysm and mean intra-aneurysmal velocities, which underscores the importance of coil distribution and thus coil shape. Our study suggests that while packing density plays a key role in determining post-treatment hemodynamics, other factors such as coil shape, aneurysmal geometry, and parent vessel flow may also be very important.

Validation and Initial Clinical Use of Automatic Peak Skin Dose Localization with Fluoroscopic and Interventional Procedures

PURPOSE To assess the accuracy and initial clinical use of a software tool that automatically maps and records values of skin dose, including peak skin dose (PSD), administered to patients undergoing fluoroscopically guided interventional procedures. MATERIALS AND METHODS In this retrospective study, the institutional review board determined that this HIPAA-compliant study met the criteria as a quality assurance investigation. Informed consent was waived. After the initial validation and accuracy tests, distributed skin dose and PSD estimates were obtained for fluoroscopically guided interventional procedures performed in the radiology, cardiology, and gastroenterology practice areas between January and October 2011. A total of 605 procedures were performed in 520 patients (64% men; age range, 20-95 years). The accuracy of a skin dose tool to estimate patient dose distribution was verified with phantom studies by using an external dosimeter and direct exposure film. PSD distribution, PSD according to procedure type, and PSD for individual physician operators were assessed. RESULTS Calculated PSD values agreed within ±9% of that measured by using film dosimetry under the condition of matched-phantom geometry. The area receiving the highest dose (greater than 95% of peak) agreed within ±17%. Of 605 patient procedures, 15 demonstrated PSD greater than 2 Gy, with a maximum PSD of 5.6 Gy. CONCLUSION Knowledge of the patient skin dose can help direct treatment of patients who were administered relatively high skin dose and may be used to plan future procedures. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112295/-/DC1.

Hemodynamic Characterization of Geometric Cerebral Aneurysm Templates Treated With Embolic Coils

Embolic coiling is one of the most effective treatments for cerebral aneurysms (CAs), largely due to the hemodynamic modifications that the treatment effects in the aneurysmal environment. However, coiling can have very different hemodynamic outcomes in aneurysms with different geometries. Previous work in the field of biofluid mechanics has demonstrated on a general level that geometry is a driving factor behind aneurysmal hemodynamics. The goal of this study was to relate two specific geometric factors that describe CAs (i.e., dome size (DS) and parent-vessel contact-angle (PV-CA)) and one factor that describes treatment (i.e., coil packing density (PD)) to three clinically relevant hemodynamic responses (i.e., aneurysmal root-mean-square velocity (Vrms), aneurysmal wall shear stress (WSS), and cross-neck flow (CNF)). Idealized models of basilar tip aneurysms were created in both virtual and physical forms to satisfy two-level multifactorial experimental designs. Steady and pulsatile flow hemodynamics were then evaluated in the virtual models using computational fluid dynamics (CFD) (before and after virtual treatment with finite element (FE) embolic coil models), and hemodynamics were also evaluated in the physical models using particle image velocimetry (PIV) (before and after treatment with actual embolic coils). Results showed that among the factors considered, PD made the greatest contributions to effects on hemodynamic responses in and around the aneurysmal sac (i.e., Vrms and WSS), while DS made the greatest contributions to effects on hemodynamics at the neck (i.e., CNF). Results also showed that while a geometric factor (e.g., PV-CA) may play a relatively minor role in dictating hemodynamics in the untreated case, the same factor can play a much greater role after coiling. We consider the significance of these findings in the context of aneurysmal recurrence and rupture, and explore potential roles for the proposed methods in endovascular treatment planning.

American Telemedicine Association: Telestroke Guidelines

The following telestroke guidelines were developed to assist practitioners in providing assessment, diagnosis, management, and/or remote consultative support to patients exhibiting symptoms and signs consistent with an acute stroke syndrome, using telemedicine communication technologies. Although telestroke practices may include the more broad utilization of telemedicine across the entire continuum of stroke care, with some even consulting on all neurologic emergencies, this document focuses on the acute phase of stroke, including both pre- and in-hospital encounters for cerebrovascular neurological emergencies. These guidelines describe a network of audiovisual communication and computer systems for delivery of telestroke clinical services and include operations, management, administration, and economic recommendations. These interactive encounters link patients with acute ischemic and hemorrhagic stroke syndromes with acute care facilities with remote and on-site healthcare practitioners providing access to expertise, enhancing clinical practice, and improving quality outcomes and metrics. These guidelines apply specifically to telestroke services and they do not prescribe or recommend overall clinical protocols for stroke patient care. Rather, the focus is on the unique aspects of delivering collaborative bedside and remote care through the telestroke model.

What is the Role for Intra-Arterial Therapy in Acute Stroke Intervention?

Intravenous recombinant tissue plasminogen activator continues to be first-line therapy for patients with acute ischemic stroke presenting within the appropriate time window, but one potential limitation is the low rate of recanalization in the setting of large artery occlusions. Intra-arterial (IA) treatment is effective for emergency revascularization of proximal intracranial arterial occlusions, but proof of benefit has been lacking until recently. Our goal is to outline the history of endovascular therapy and review both IA thrombolysis and mechanical interventions. In addition, we will discuss the impact of important trials such as the Third Interventional Management of Stroke (IMS3) trial, and the more recent trials Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands (MR CLEAN), Endovascular Treatment for Small Core and Proximal Occlusion Ischemic Stroke (ESCAPE), Extending the Time for Thrombolysis in Emergency Neurological Deficits—Intra-Arterial (EXTEND-IA), and Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment (SWIFT PRIME) on acute stroke management and the implications for the practicing neurohospitalist.

Hemodynamic characterization of geometric cerebral aneurysm templates

Hemodynamics are currently considered to a lesser degree than geometry in clinical practices for evaluating cerebral aneurysm (CA) risk and planning CA treatment. This study establishes fundamental relationships between three clinically recognized CA geometric factors and four clinically relevant hemodynamic responses. The goal of the study is to develop a more combined geometric/hemodynamic basis for informing clinical decisions. Flows within eight idealized template geometries were simulated using computational fluid dynamics and measured using particle image velocimetry under both steady and pulsatile flow conditions. The geometric factor main effects were then analyzed to quantify contributions made by the geometric factors (aneurysmal dome size (DS), dome-to-neck ratio (DNR), and parent-vessel contact angle (PV-CA)) to effects on the hemodynamic responses (aneurysmal and neck-plane root-mean-square velocity magnitude (Vrms), aneurysmal wall shear stress (WSS), and cross-neck flow (CNF)). Two anatomical aneurysm models were also examined to investigate how well the idealized findings would translate to more realistic CA geometries. DNR made the greatest contributions to effects on hemodynamics including a 75.05% contribution to aneurysmal Vrms and greater than 35% contributions to all responses. DS made the next greatest contributions, including a 43.94% contribution to CNF and greater than 20% contributions to all responses. PV-CA and several factor interactions also made contributions of greater than 10%. The anatomical aneurysm models and the most similar idealized templates demonstrated consistent hemodynamic response patterns. This study demonstrates how individual geometric factors, and combinations thereof, influence CA hemodynamics. Bridging the gap between geometry and flow in this quantitative yet practical way may have potential to improve CA evaluation and treatment criteria. Agreement among results from idealized and anatomical models further supports the potential for a template-based approach to play a useful role in clinical practice.

Hemicraniectomy for Ischemic and Hemorrhagic Stroke: Facts and Controversies

Malignant large artery stroke is associated with high mortality of 70% to 80% with best medical management. Decompressive craniectomy (DC) is a highly effective tool in reducing mortality. Convincing evidence has accumulated from several randomized trials, in addition to multiple retrospective studies, that demonstrate not only survival benefit but also improved functional outcome with DC in appropriately selected patients. This article explores in detail the evidence for DC, nuances regarding patient selection, and applicability of DC for supratentorial intracerebral hemorrhage and posterior fossa ischemic and hemorrhagic stroke.

Unusual Presentation of a Dural Arteriovenous Fistula of the Superior Sagittal Sinus and Single Modality Therapy with Onyx

Superior sagittal sinus (SSS) dural arteriovenous fistulas (DAVF) are rare and present unique challenges to treatment. Complex, often bilateral, arterial supply and involvement of large volumes of eloquent cortical venous drainage may necessitate multimodality therapy. We report a case of a DAVF of the SSS in a patient who presented uniquely with increasing dizziness and disequilibrium who was treated with a single modality, endovascular embolization with ethyl vinyl alcohol co-polymer (Onyx, EV3, Irvine, CA). The patient underwent staged embolization in 2 sessions with no complications. An angiographic cure was achieved and the patients symptoms were ameliorated. Single modality therapy with endovascular embolization of a SSS DAVF can be achieved. Careful attention to technique during embolization with Onyx is required, but complete obliteration is possible without the need for adjunctive surgical resection.

E-061 Towards the Pre-Surgical Treatment Planning of Cerebral Aneurysms Using High Fidelity Simulations

Over the last decade, advances in medical imaging have led to a 75% increase in early diagnosis of cerebral aneurysms (CAs) along with a growing arsenal of medical devices that can now treat a wider range of CA cases. Endovascular treatment planning has shown limited progress. Current treatment planning is driven by prior training, convention and experience. Despite the best of plans, the process can involve an element of trial and error during treatment that increases procedural time, treatment costs, and the risk of procedural complications. Further, treatment planning can be unsuccessful in many cases with recurrence rates as high as 21.9% and retreatment rates of 11.0%. Therefore, there is a critical need to improve endovascular treatment planning. Here we present a novel simulation algorithm that enhances clinical capabilities for personalised pre-surgical treatment planning. In the first step of the algorithm, a computational anatomy is generated from MR or CT image data. Next, the computational anatomy is used to simulate treatment using novel device-specific finite element (FE) models that consider the structural properties of the treatment device, its mechanics, and the clinical deployment strategy. Changes in blood flow are then simulated using computational fluid dynamics (CFD). Lastly, mechanical and fluid dynamic simulation results are used to evaluate the outcomes of different treatment options. The simulation algorithm was validated against in-vitro deployments of embolic coils, stents, and the Pipeline embolization device in 3 idealised and 2 anatomical CA models. Results showed excellent agreement between FE device simulations and physical device deployments. Fluid dynamics were also compared between CFD simulations and in-vitro flow velocity and pressure measurements in the treated CA models. Results showed good agreement in mean aneurysmal velocity magnitude and intra-aneurysmal pressure. Detailed 3D structural validations against microCT data will also be presented. The value of the simulation algorithm for treatment planning is demonstrated for 3 patient cases. In case 1, stent-assisted coiling (Figure 1a) and flow diverter treatment options (Figure 1b) are evaluated for a wide-neck posterior communicating artery (PCA) aneurysm (Figure 1). In case 2, the simulation algorithm is used to predict changes in fluid dynamics after 12 coil deployments in a large basilar-tip aneurysm. Clinical and simulations results of that case showed a persisting flow jet into the aneurysmal sac after treatment. In case 3, the simulation algorithm is used to compare stent-assisted coiling and coiling-alone in a basilar tip aneurysm. Abstract E-061 Figure 1 Disclosures B. Chong: 1; C; Mayo Clinic Center for Individualised Medicine, Arizona State University. 4; C; Endovantage LLC. H. Babiker: 4; C; Endovantage LLC. D. Frakes: 4; C; Endovantage, LLC. J. Ryan: 5; C; Endovantage LLC. F. Gonzalez: 4; C; Endovantage LLC.

Turf wars and silos--the effect of disruptive technologic innovation in the treatment of cerebral and peripheral vascular disease.

It is with interest and enthusiasm that we read the editorial comment authored by Hopkins et al [1]. The authors describe the traditional organization of medicine, which has led to the creation of department silos. They very elegantly play out the problem of turf wars because of this silo system and correctly point out that this approach led to tremendous advantages and expertise in that physicians were able to concentrate their energy and efforts and become true specialists. The authors note that turf wars continue to exist today driven by a number of factors including actual and potential declining reimbursement, changes in training programs with increased interest in organ system rather than specific organs, development of miniaturization techniques and less invasive approaches, and the advances of imaging, which allow subspecialty physicians to perform and interpret images. We define all of these factors as disruptive technical innovations. These changes are not limited solely to health care. The business literature is laced with many classic case reports of companies that have both floundered and flourished because of disruptive technical innovations. One of the classic cases described in business schools is that of the company that transformed a disruptive technology to their advantage [2]. Crown Cork and Seal was a major producer of cork-lined bottle caps at the turn of the century. As disruptive technological innovations continued in the bottling business, this corporation had to make numerous decisions on how to proceed. Were they simply to remain a bottle cap maker or were they in the business of manufacturing containers—metal cans, glass bottles, bottle caps, and plastic bottles? They chose to respond to a changing market place and have evolved into a corporation with operations in 42 countries employing over 24,000 people and net sales of