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(Stroke. 2005;36:751.)
© 2005 American Heart Association, Inc.

Original Contributions

Blood Oxygen Level–Dependent MRI of Cerebral CO₂ Reactivity in Severe Carotid Stenosis and Occlusion

Sargon Ziyeh, MD; Jochen Rick; Matthias Reinhard, MD; Andreas Hetzel, MD; Irina Mader, MD Oliver Speck, PhD

From the Section of Neuroradiology (S.Z., I.M.), Neurocenter, Medical Physics (J.R., O.S.), Department of Radiology, Department of Neurology (M.R., A.H.), University Hospital of Freiburg D-79106 Freiburg, Germany.

Correspondence to Dr Sargon Ziyeh, Section of Neuroradiology, University Hospital of Freiburg, Neurocenter Breisacher Str. 64 D-79106 Freiburg, Germany. E-mail ziyeh{at}nz.ukl.uni-freiburg.de

Background and Purpose— Impaired cerebrovascular reserve capacity (CVC) is a risk factor for ischemic events in patients with high-grade carotid stenosis and occlusion. In this study, the CVC in response to a CO₂ challenge was evaluated with blood oxygen level–dependent (BOLD) MRI and the results compared with those of a transcranial Doppler CO₂ tests.

Methods— A T₂*-weighted single-shot multigradient echo-planar imaging sequence was used to determine cerebral CO₂ reactivity. T₂* values were calculated for each pixel at rest and during a challenge with 7% CO₂, and a reference function was fitted to the T₂* time courses. Whole-brain color-coded T₂* parameter maps were calculated and visually evaluated for regional differences. Additionally, a region-of-interest analysis was undertaken. Average values for T₂* normalized to changes in end-tidal PCO₂ were calculated. Results were correlated with a transcranial Doppler CO₂ tests in 20 patients with high-grade stenosis or occlusion of the carotid artery.

Results— Color parameter maps showed areas of decreased BOLD effect within the internal carotid artery territory in 12 of 13 hemispheres with impaired CVC in transcranial Doppler CO₂ test. Regional normalized T₂* was highly correlated with changes of middle cerebral artery blood flow velocity in transcranial Doppler CO₂ test. Normalized T₂* was significantly reduced in hemispheres with impaired CVC in transcranial Doppler (P<0.0001).

Conclusions— BOLD MRI can easily be included in routine MRI exams. The technique is robust and yields diagnostic information concerning the cerebrovascular reserve.

Key Words: carotid stenosis • hemodynamics • magnetic resonance imaging • ultrasonography, Doppler, transcranial

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