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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2005;25:1408.)
© 2005 American Heart Association, Inc.

Vascular Biology

Blood Oxygen Level–Dependent MRI of Tissue Oxygenation

Relation to Endothelium-Dependent and Endothelium-Independent Blood Flow Changes

Wolfgang Utz; Jens Jordan; Thoralf Niendorf; Mandy Stoffels; Friedrich C. Luft; Rainer Dietz; Matthias G. Friedrich

From the Medical Faculty of the Charité (W.U., J.J., M.S., F.C.L., R.D., M.G.F.), Franz Volhard Klinik HELIOS Klinikum-Berlin at the Max Delbrück Center for Molecular Medicine, Berlin, Germany; GE Medical Systems (T.N.), Applied Science Laboratory, Boston, Mass; and Stephenson CHR Center, Departments of Cardiac Sciences and Radiology (M.G.F.), University of Calgary, Canada.

Correspondence to Matthias G. Friedrich, MD, FESC, Departments of Cardiac Sciences and Radiology, University of Calgary, 1403 29th St NW, Calgary, AB T2N 2T9, Canada. E-mail matthias.friedrich{at}ucalgary.ca

Objectives— The contribution of endothelial function to tissue oxygenation is not well understood. Muscle blood oxygen level–dependent MRI (BOLD MRI) provides data largely dependent on hemoglobin (Hb) oxygenation. We used BOLD MRI to assess endothelium-dependent signal intensity (SI) changes.

Methods and Results— We investigated mean BOLD SI changes in the forearm musculature using a gradient-echo technique at 1.5 T in 9 healthy subjects who underwent a protocol of repeated acetylcholine infusions at 2 different doses (16 and 64 µg/min) and N^G-monomethyl-L-arginine (L-NMMA; 5 mg/min) into the brachial artery. Sodium nitroprusside was used as a control substance. For additional correlation with standard methods, the same protocol was repeated, and forearm blood flow was measured by strain gauge plethysmography. We obtained a significant increase in BOLD SI during acetylcholine infusion (64 µg/min) and a significant decrease for L-NMMA infusion (P<0.005 for both). BOLD SI showed a different kinetic signal than did blood flow, particularly after intermittent ischemia and at high flow rates.

Conclusions— In standard endothelial function tests, BOLD MRI detects a dissociation of tissue Hb oxygenation from blood flow. BOLD MRI may be a useful adjunct in assessing endothelial function.

We used muscle blood oxygen level–dependent MRI (BOLD MRI) to study tissue Hb oxygenation in relation to postischemic hyperemia and endothelial stimulation. We found uncoupling of tissue Hb oxygenation from blood flow changes and conclude that BOLD MRI may provide additional information in assessing endothelial function.

Key Words: magnetic resonance imaging • endothelial function • BOLD • plethysmography

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