Neurovascular Research: Waleed Brinjikji, Ramanathan Kadirvel, David F. Kallmes

Projects

Basic research

The Neurovascular Research Laboratory's basic research is primarily focused on better understanding the mechanisms of aneurysm growth and rupture and the healing of aneurysms. New therapeutic approaches for treating intracranial saccular aneurysms also are being researched, including some under good laboratory practice (GLP) standards, the most stringent preclinical testing conditions approved by the Food and Drug Administration.

1. Animal modeling of aneurysms

The Neurovascular Research Lab has developed an animal model of intracranial saccular aneurysms at the right common carotid artery in rabbits. This elastase model of saccular aneurysm has been widely applied as a preclinical example for testing endovascular devices and is routinely accepted by the Food and Drug Administration. Several endovascular devices that are commercially available have been tested this way, as the rabbit aneurysm is similar to the human aneurysm histologically and morphologically. In addition, this model shares many molecular and hemodynamic features with human intracranial aneurysms.

The rabbit elastase model has achieved widespread application with advantages including a curved vessel anatomy that simulates human aneurysms such as those in the ophthalmic region, demonstrated long-term patency and aneurysm sizes similar to the mean size of human aneurysms. Histopathologic studies show that after embolization with platinum coils, the lab's model mimics the healing seen in human aneurysms. This preclinical model is ideally suited for studying endovascular devices for aneurysm treatment as well as aneurysm growth.

The lab continues to improve the animal modeling of aneurysms that are more relevant to human intracranial aneurysms through continued development and testing.

2. Improving treatment of aneurysms

A noninvasive and reliable form of treatment has yet to be discovered for the clinical management of intracranial saccular aneurysms. The lab aims to improve existing methods of minimally invasive treatments, such as flow diverters or microcoils, while also exploring alternative nonendovascular procedures. To improve the stabilization and healing process after treatment, systemic therapies using disease modifiers and local delivery of proteins and stem cells also are being tested.

These discoveries will lead to an increased understanding of the mechanisms involved in the healing process and benefit patients who have intracranial aneurysms. The long-term goal is to diminish or eradicate the risk of devastating aneurysm rupture.

3. Computational fluid dynamics and particle image velocimetry of brain aneurysms

Given the high mortality rate associated with ruptured intracranial aneurysms, determining the risk of rupture is critical to management decisions. Advanced imaging techniques available today enable the physician to view the blood flow through arteries, but do not provide meaningful quantitative assessment of in vivo hemodynamics. Computational fluid dynamics studies can identify various physical flow phenomena that have been implicated in causing rupture.

The purpose of this research is to find correlations between hemodynamic variables and clinical events to better understand aneurysm development and improve patient evaluation and treatment. In collaboration with Mayo Clinic's Division of Engineering and Technology Services, the lab is validating companion computation fluid dynamics simulations on patient-specific aneurysm models using particle image velocimetry. The data are also being used to experimentally compare fluid mechanics behavior in aneurysms treated with different therapeutic devices.

4. Stroke Thromboembolism Registry of Imaging and Pathology (STRIP)

With the arrival of mechanical thrombectomy for the treatment of acute ischemic stroke, there has been growing interest in the histopathological and imaging characteristics of retrieved thromboemboli. Past studies propose that studying clot composition can provide insights into stroke etiology, as well as demonstrate association recanalization success with intravenous thrombolysis and mechanical thrombectomy. Furthermore, improved characterization of clot composition regarding imaging and histopathologic features could help in device selection prior to the mechanical thrombectomy procedure itself.

STRIP is a multicenter project that aims to:

Characterize the histopathologic features of thromboemboli of various etiologies using a combination of histology (hematoxylin and eosin and Martius scarlet blue) and immunostaining methods
Examine the correlation between clot composition and degree and ease of revascularization using mechanical thrombectomy techniques
Review the association between device selection (aspiration versus stent retriever), technique selection (balloon guide catheter versus standard catheter), clot subtype (RBC rich, platelet rich, fibrin rich, WBC rich) and angiographic outcomes
Study the association between the presence of a hyperdense artery sign (on imaging) and clot histological characteristics