The relationship between vascular wall shear stress and flow-mediated dilation: endothelial function assessed by phase-contrast magnetic resonance angiography
Harry A. Silber, MD, PhDa,
David A. Bluemke, MD, PhDa,
Pamela Ouyang, MD, FACCa,
Yiping P. Du, PhDa,
Wendy S. Post, MD, MS, FACCa and
Joao A. C. Lima, MD, FACC*,a
a Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
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Figure 1 Phase-contrast images of the brachial artery cross-section in a normal subject. Each image consists of a magnitude (anatomic) and a phase (velocity) component. Images were acquired at baseline, during arterial occlusion by cuff inflation (the magnitude component shows the flattened cross-section; the phase component shows absence of flow), during peak hyperemia immediately after cuff release and at 1 min after cuff release, when flow-mediated dilation had occurred. The images are smoothed (but the raw data used for measurements and calculations are unaffected).
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Figure 2 Blood flow velocity profile at baseline and at peak hyperemia for three subjects with different bluntness factor n: the subject with smallest n (least blunt profile, top row), a subject with n close to the average (middle row) and the subject with greatest n (bluntest profile, bottom row).
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Figure 4 Bland-Altman plot: difference between diameter by phase-contrast magnetic resonance angiography (PCMRA) and ultrasound (U/S) plotted against average diameter by PCMRA and U/S. Also shown are 95% limits of agreement (mean ± 2 SD). Diameter is greater by PCMRA. Solid square = baseline; open square = 1 min. after release of occlusion. MRI = magnetic resonance imaging.
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WSS, change from baseline to peak hyperemia immediately after cuff release). FMD = 2.5 (