|MRI of Cerebral Ischemia in Animals & Humans|
Morphological and Functional Characterization of a
New Model of Hypoxic-Ischemic Encephalopathy in Neonatal Rat Using a
Bilateral Carotid Artery Occlusion
Rebecca Recker1, Arash Adami1, Beatriz Tone1, Rich Hartman1, Jerome Badaut2, Hui Tian1, Stephen Ashwal1, Andre Obenaus1
1Loma Linda University School of Medicine, Loma Linda, California , USA; 2Centre Hospitalier Universitaire Vadois, Lausanne, Switzerland
Neonatal hypoxic-ischemic encephalopathy clinically presents with global diffuse injury. However, the most popular rat pup models of neonatal HIE induce a focal unilateral injury. The bilateral carotid artery occlusion (BCAO) model has been shown to induce bilateral injury in 10d old rat pups, an age that developmentally correlates with the term neonate. T2 and DWI assessment of gradation of injury was obtained that allows for candidate selection for future therapeutic treatment. Injury stratification was performed using a novel rat pup scoring system (RPSS) system which correlated with lesion volume.
Susceptibility Weighted MRI for Detection and Staging
of Angiogenesis After Stroke in Rats
Quan Jiang1, 2, Lakshman Gollapalli2, Mark E. Haack2, 3, Guang Liang Ding1, Zheng Gang Zhang1, Li Zhang1, Lian Li1, Ying Wang1, James R. Ewing1, Jia Ni Hu2, Hassan Bagher-Ebadian1, Michael Chopp1
1Henry Ford Health System, Detroit, Michigan, USA; 2Wayne State University, Detroit, Michigan, USA; 3MRI Institute for Biomedical Research, Detroit, Michigan, USA
We investigated the evolution of angiogenesis using high-resolution susceptibility-weighted imaging incorporating phase information (SWI) after sildenafil treatment of embolic stroke. We demonstrate that SWI can detect and identify cerebral angiogenesis after ischemic stroke. By combining information from blood-to-brain transfer constant of Gd-DTPA (Ki) measurement, SWI can stage the progress of angiogenesis. SWI provides a direct measurement of angiogenesis, unlike indirect measurements of cerebral blood flow (CBF) and cerebral blood volume (CBV).
Edge Location of Sodium Accumulation in
Focal Cerebral Ischemia in the Rat: ADC and 23Na MRI
Victor E. Yushmanov1, Alexander Kharlamov1, Boris Yanovski1, George LaVerde2, Fernando E. Boada2, Stephen C. Jones1, 2
1Allegheny-Singer Research Institute, Pittsburgh, Pennsylvania, USA; 2University of Pittsburgh, Pittsburgh, Pennsylvania, USA
ADC and 23Na twisted projection MRI were compared and confirmed by histology and flame photometry in the rat brain after MCAO. Within an ADC-homogeneous infarct region, sites with an elevated rate of 23Na increase (slope, 22±4%/h, p<0.005 compared to 14%/h±1%/h in other ischemic regions) were observed. In the ischemic regions, there was no slope/ADC correlation between and within brains (P>0.4). Maximum slope was located near the stroke periphery in 7 animals. Differences in collateral circulation in the cortex and caudate putamen were not slope determinants (P>0.3). 23Na MRI is more sensitive than ADC for assessing regional ischemic damage.
Imaging Macrophage Infiltration of Ischemic Tissue is
Not Possible Following Transient Middle Cerebral Artery Occlusion
Tracy Deanne Farr1, Jörg Seehafer2, Mathias Hoehn2
1Max-Plack Institute for Neurological Research , Cologne, Germany; 2Max-Plack Institute for Neurological Research, Cologne, Germany
There is concern that contrast in the ischemic brain, following systemic administration of iron oxide to label blood born macrophages, accumulates non-specifically. The results of this study support that. We administered contrast during a time of high peripheral macrophage activity following transient middle cerebral artery occlusion; an optimal model due to the delay in blood brain barrier breakdown, and the lack of erythrocyte accumulation and cerebral spinal fluid disruption. No changes in signal intensity that could be attributed to macrophage accumulation were observed in T2* or T1-weighted images and there were few iron positive macrophages in the histological sections.
Estimates of Relative Contrast Recirculation Obtained
from Perfusion MRI: A Potential Tool for Guiding Treatment Decision in
Acute Ischemic Stroke
Sheng-Ping Wu1, Logi Vidarsson1, Jeff Winter1, David Mikulis2, Andrea Kassner1
1The Hospital for Sick Children and the University of Toronto, Toronto, Canada; 2The Toronto Western Hospital, Toronto, Canada
Permeability MRI has the potential to objectively guide rt-PA treatment of stroke and thereby reducing the risk of hemorrhagic transformation (HT). However, one limitation is the long scan time (~5 min), which is problematic for stroke patients. In contrast, perfusion MRI is part of the routine stroke protocol and allows extraction of a parameters called relative recirculation (rR). The purpose of this study was to determine the relative efficacy of rR, compared with permeability (KPS), for prediction of HT. Our results demonstrated that KPS (p<0.01) and rR (p<0.01) were significantly increased in patients with HT, compared with patients without HT. Furthermore, a significant correlation was observed between KPS and rR (r=0.85, p<0.001). Both parameters effectively predict HT, although, rR is more clinically feasible
Diagnostic Impact of Aortic MRI at 3Tesla in Patients
with Acute Cryptogenic Stroke
Andreas Harloff1, Patrick Dudler1, Alex Frydrychowicz1, Christoph Strecker1, Anna Lena Stroh1, Annette Geibel1, Andreas Hetzel1, Cornelius Weiller1, Jürgen Hennig1, Michael Markl1
1Albert-Ludwigs Universität , Freiburg, Germany
The purpose of this study was to evaluate a new 3D MRI protocol for the reliable detection of aortic high-risk plaques compared to transesophageal echocardiography (TEE) and to test the reliability of additional MRI in stroke of undetermined etiology
Does Local AIF Improve Prediciton of
Soren Christensen1, 2, Fernando Calamante3, Ona Wu4, Thomalla Götz5, Jens Fiehler5, Jachim Rother5, Thomas Kucinski5, Leif Ostergaard2, Patricia Desmond1, Stephen Davis1
1University of Melbourne, Parkville, Australia; 2University of Aarhus, Aarhus, Denmark; 3Brain Research Institute, Melbourne, Australia; 4Massachusetts General Hospital, Boston, USA; 5University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Two local AIF methods were compared to conventional processing (manual AIF selection from the contra lateral hemisphere) by ROC analysis in a retrospective study of 104 acute (<6h) stroke patients. The final infarct lesion was delineated on the follow up MRI and used as infarct/no infarct classifier on the acute PWI maps. Both local AIF techniques performed marginally inferior to conventional processing. We speculate that: 1) AIFs selected on distal branches signals of the arterial tree might not represent the true AIF. 2) Delay and dispersion provide predictive information that should not be discarded from local AIF estimates.
Prediction of Hemorrhagic Transformation in Acute
Ischemic Stroke: MRI Texture Analysis Versus Visual Inspection of Gd
Fang Liu1, George Tomlinson2, David Mikulis3, Frank Silver3, Andrea Kassner1
1The Hospital for Sick Children and the University of Toronto, Toronto, Canada; 2The University of Toronto, Toronto, Canada; 3The Toronto Western Hospital, Toronto, Canada
Hemorrhagic transformation (HT) is a potentially fatal complication of thrombolytic therapy in acute ischemic stroke (AIS). Early prediction of HT could substantially improve the safety of this therapy, thereby improving patient outcome. Early Gadolinium (Gd) enhancement on post-contrast T1-weighted MRI has been used to predict HT in subacute stroke. However, assessment at earlier time points (< 4 hours from symptom onset) did not reliably predict HT. An alternative to visual inspection is texture analysis, which discriminates textural information related to higher-order statistics and spectral properties not obvious to even an expert eye (trained radiologist). This method can quantify dependencies between neighboring pixels as well as patterns of variation within a region-of-interest. In this study we performed texture analysis,based on a co-occurrence matrix of post-contrast T1w images, to assess the prediction of HT in AIS patients and to compare it with visual inspection of Gd enhancement. Our results show that texture analysis of post T1-weighted images is superior to visual inspection for the prediction of HT in early AIS. To our knowledge, this is the first application of texture analysis in AIS. Further studies are needed to validate our results.
BOLD MR Mapping of Cerebrovascular Reactivity in
Patients with Arterial Steno-Occlusive Disease: Validation by Arterial
Spin Labeling MRI
Daniel M. Mandell1, 2, Jay S. Han, 23, Julien Poublanc1, Adrian P. Crawley1, Jeff A. Stainsby, 1, Joseph A. Fisher, 23, David J. Mikulis1, 2
1Toronto Western Hospital, Toronto, Canada; 2University of Toronto, Toronto, Canada; 3Toronto General Hospital, Toronto, Canada
An emerging technique for mapping cerebrovascular reserve uses inhaled CO2 as a vasodilatory stimulus, and BOLD MR as an index of CBF changes. While BOLD MR signal reflects CBF, it also depends on cerebral blood volume, cerebral metabolic rate, arterial oxygenation, and hematocrit. We performed both BOLD and arterial spin labelling MR mapping of reserve in 25 patients with arterial steno-occlusive disease. ASL MR acted as a reference standard for measurement of CBF changes. BOLD and ASL MR measurements were highly correlated, suggesting BOLD MR is a reasonable surrogate for CBF imaging to map cerebrovascular reserve in this patient population.
Asymmetry and Flow Dynamics in the Vertebrobasilar
System as Assessed by Vessel Encoded Arterial Spin Labeling
Akash P. Kansagra1, Eric C. Wong1
1University of California, San Diego, La Jolla, California , USA
Vessel encoded ASL allows quantitative and efficient imaging of cerebral vascular territories. Here, we discuss the application of vessel encoded ASL to reveal vertebral artery territories in five healthy subjects. In particular, we depict examples of vertebral artery territories and comment on unusual territorial morphology, with particular attention to asymmetry and mixing within the vertebrobasilar system.