Published Online
on February 10, 2005

A more recent version of this article appeared on April 1, 2005

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Submitted on July 16, 2004
Revised on December 3, 2004
Accepted on December 21, 2004

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; and 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.

^* To whom correspondence should be addressed. 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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