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CLINICAL RESEARCH: CARDIAC IMAGING

Evaluation of Cuff-Induced Ischemia in the Lower Extremity by Magnetic Resonance Oximetry

Michael C. Langham, PhD^_*, Thomas F. Floyd, MD, Emile R. Mohler, III, MD, Jeremy F. Magland, PhD^_* and Felix W. Wehrli, PhD^_*,_*

^_* Department of Radiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

Manuscript received April 28, 2009; revised manuscript received August 20, 2009, accepted August 30, 2009.

^_* Reprint requests and correspondence: Dr. Felix W. Wehrli, 1 Founders, University of Pennsylvania Medical Center, 3400 Spruce Street, Philadelphia, Pennsylvania 19104 (Email: wehrli{at}mail.med.upenn.edu).

Objectives: The aim of this study was to evaluate vascular function in the lower extremities by making direct time-course measurement of oxygen saturation in the femoral/popliteal arteries and veins during cuff-induced reactive hyperemia with magnetic resonance imaging-based oximetry.

Background: Magnetic resonance imaging-based oximetry is a new calibration-free technique taking advantage of the paramagnetic nature of blood that depends on the volume fraction of deoxyhemoglobin in red blood cells.

Methods: We compared post-occlusive blood oxygenation time-course of femoral/popliteal vessels in: 1) young healthy subjects (YH) (n = 10; mean ankle-brachial index [ABI] 1.0 ± 0.1, mean age 30 ± 7 years); 2) peripheral arterial disease (PAD) patients (n = 12; mean ABI 0.6 ± 0.1, mean age 71 ± 9 years); and 3) age-matched healthy control subjects (AHC) (n = 8; mean ABI 1.1 ± 0.1, mean age 68 ± 9 years). Blood oxygenation was quantified at 3.0-T field strength with a field mapping pulse sequence yielding the magnetic susceptibility difference between blood in the vessels and surrounding muscle tissue from which the intravascular blood oxygen saturation is computed as %HbO₂.

Results: Significantly longer washout time (42 ± 16 s vs. 14 ± 4 s; p < 0.0001) and lower upslope (0.60 ± 0.20 %HbO₂/s vs. 1.32 ± 0.41 %HbO₂/s; p = 0.0008) were observed for PAD patients compared with healthy subjects (YH and AHC combined). Furthermore, greater overshoot was observed in YH than in AHC (21 ± 8 %HbO₂ vs. 10 ± 5 %HbO₂; p = 0.0116).

Conclusions: Post-occlusive transient changes in venous blood oxygenation might provide a new measure of vascular competence, which was found to be reduced in subjects with abnormal ABI, manifesting in prolonged recovery during the early phase of hyperemia.

Key Words: blood oxygen saturation • magnetic resonance oximetry • peripheral arterial disease • phase image • reactive hyperemia

Abbreviations and Acronyms   ABI = ankle-brachial index   AHC = age-matched control subjects   FMD = flow-mediated dilation   NIRS = near-infrared spectroscopy   PAD = peripheral artery disease   SvO2 = venous oxygen saturation   YH = young healthy subjects

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