Quantification of Cerebral Perfusion using Laser Speckle Imaging and Infarct Volume using MRI in a Pre-clinical Model of Posterior Circulation Stroke

Published: November 17, 2020

doi:

Surya C. Gnyawali, Debra G. Wheeler, Allyson L. Huttinger, Cole Anderson, Ian Mandybur, Catherine Lee, Caitlin Hatten, Jenna Boue, Matthew Joseph, Shahid M. Nimjee^2,4

¹Department of Neurological Surgery,The Ohio State University Medical Center, ²Department of Anatomy,The Ohio State University Medical Center, ³Department of Internal Medicine,The Ohio State University Medical Center, ⁴Department of Radiology,The Ohio State University Medical Center

Summary

A canine model of LVO stroke was utilized to develop laser speckle imaging to monitor cerebral perfusion in real-time. Diffusion-weighted MRI was optimized to image infarct volume utilizing a high b-value, enabling ADC and MRA, correlated with DSA at the time of stroke. Finally, ADC reconstructions correlated with histological findings.

Abstract

Background: Basilar artery occlusion (BAO) is a subset of posterior circulation stroke that carries a mortality as high as 90%. The current clinical standard to diagnose ischemic stroke include computerized tomography (CT), CT angiography and perfusion and magnetic resonance imaging (MRI). Large animal pre-clinical models to accurately reflect the clinical disease as well as methods to assess stroke burden and evaluate treatments are lacking.

Methods: We describe a canine model of large vessel occlusion (LVO) stroke in the posterior circulation, and developed a laser speckle imaging (LSI) protocol to monitor perfusion changes in real time. We then utilized high b-value DWI (b=1800s/mm²) MRI to increase detection sensitivity. We also evaluated the ability of magnetic resonance angiography (MRA) to assess arterial occlusion and correlate with DSA. Finally, we verified infarct size from apparent diffusion coefficient (ADC) mapping with histology.

Results: Administration of thromboembolism occluded the basilar artery as tracked by DSA (n=7). LSI correlated with DSA, demonstrating a reduction in perfusion after stroke onset that persisted throughout the experiment, allowing us to monitor perfusion in real time. DWI with an optimized b-value for dogs illustrated the stroke volume and allowed us to derive ADC and magnetic resonance angiography (MRA) images. The MRA performed at the end of the experiment correlated with DSA performed after occlusion. Finally, stroke burden on MRI correlated with histology.

Conclusions: Our studies demonstrate real time perfusion imaging using LSI of a canine thromboembolic LVO model of posterior circulation stroke, which utilizes multimodal imaging important in the diagnosis and treatment of ischemic stroke.

Introduction

The prevalence of stroke worldwide is almost 25.7 million, the majority of which are ischemic¹. Posterior circulation stroke accounts for 20% of all strokes of which basilar artery occlusion is the most severe, approaching 90% mortality¹^,². In 1995, recombinant tissue plasminogen activator (rtPA) was the first acute therapy developed for ischemic stroke in patients who presented within 3 hours from stroke onset³. More recently, mechanical thrombectomy has demonstrated benefit in treating acute ischemic stroke in patients who present with large vessel occlusion (LVO), which includes the intracranial portion of the internal carotid artery or the first segment of the anterior and middle cerebral arteries⁴. None of the recent clinical trials included posterior circulation stroke and its outcomes remain dismal despite utilizing mechanical thrombectomy for basilar artery occlusion⁵^,⁶.

Advances in assessment techniques in stroke patients have an impact on predicting the chance of functional recovery and survival⁷. Pre-clinical models of posterior circulation stroke have been previously described⁸^,⁹^,¹⁰, however assessing stroke burden and revascularization remain suboptimal. Smaller species such as rodents offer several advantages including ease of genetic manipulation, inexpensive animal purchase, and low per diem housing costs¹¹^,¹². However, small animal experiments sometimes do not fully represent large animal and human vasculature, physiological conditions, or related inflammatory responses⁷. Large animals more closely mimic human stroke²^,⁷^,¹³^,¹⁴. Moreover, serial blood sampling can be performed for blood analysis of thrombotic and inflammatory markers.

In this study, we describe a canine model of basilar artery occlusion verified by digital subtraction angiography (DSA) from the onset of stroke. We utilize laser speckle perfusion imaging (LSI) to monitor perfusion in real time. We then utilize a novel microvascular enhancement algorithm based on laser speckle perfusion imaging (LSI) acquisition as well as a high b-value magnetic resonance imaging (MRI) technique to optimize infarct imaging¹⁵. These techniques allow us to monitor and quantify local and global ischemia. Finally, we correlate these imaging findings to histology. Understanding prognosis and the need to study posterior circulation stroke in pre-clinical models is critical in order to improve therapies.

Protocol

All procedures were performed in compliance with the Animal Welfare Act and the Guide for Care and Use of Laboratory Animals (NRC 2011), as approved by the Ohio State University’s Institutional Animal Care and Use Committee (IACUC). 1. Step 1 Animal Preparation and Surgical Protocol A canine model of basilar artery occlusion (BAO) stroke was used as previously described9,10. Fast adult beagles (8-13 kg, 14-21 months o…

Representative Results

Laser Speckle Perfusion Recording and Imaging: Perfusion recording was performed continuously until the animal was transported to MRI, and again at sacrifice (Figure 1A). Data showed that cerebral perfusion decreased by ~15% to 83 ± 10% at the time point before basilar artery occlusion (pre-BAO). This nominal decline is likely the result of a microcatheter insertion in the distal vertebral artery. After injecting the prepare thromboembolus, the post-BAO perfusion d…

Discussion

The most common causes of posterior circulation stroke include embolism, large-artery atherosclerosis, and small artery disease⁵. Basilar arterial occlusion (BAO) represents a subset of posterior circulation strokes, carrying significant morbidity and mortality¹³. In this context, a canine model of acute posterior stroke was utilized and we developed an LSI protocol to monitor perfusion of the occluded region in real time. Laser speckle perfusion imaging was performed throu…

Disclosures

The authors have nothing to disclose.

Acknowledgements

This work was supported in part from the Mayfield Education and Research Foundation grant #GRT00049047 and Ohio Department of Services Agency Accelerator Award #TECG20180269 to SMN.

Materials

2% 2,3,5-triphenyltetrazolium chloride (TTC in PBS, pH 7.4)	Sigma Aldrich	T8877
EDTA K3 vacutainers	Becton Dickinson	BD455036
Eosin	Surgipath	3801602
Formalin, neutral buffered, 10%	Richard-Allan Scientific	5701
Hematoxylin 560	Surgipath	3801570
HUG-U-VAC positioning system	DRE Veterinary	1320
LabChart Software	ADInstruments Inc.
Laser Speckle Imaging camera	Perimed Inc., Jarfalla, Sweden	PeriCam PSI HR System
Lithium heparin vacutainer, 4.5%	Becton Dickinson	BD 368056
Matlab	The MathWorks, Inc., Natick, MA
OsiriX MD v.5.0 software	Pixmeo Inc, Geneva
Paraformaldehyde 4% in PBS	Alfa Aesar	AAJ61899AP
PimSoft v1.4 software	Perimed Inc.	software that accompanies LSI equipment
Prisma Fit 3 tesla (3T) magnet	Siemen's Diagnostics
Sodium heparin for injection (to coat blood gas syringe)	NovaPlus	402525D

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