Ultrasound measurement of brachial flow-mediated vasodilator response

Brachial artery flow-mediated vasodilation is increasingly used as a measur e of endothelial function. High resolution ultrasound provides a noninvasiv e method to observe this flow-mediated vasodilation by monitoring the diame ter of the artery over time following a transient flow stimulus. Since hund reds of ultrasound images are required to continuously monitor brachial dia meter for the 2-3 min during which the vasodilator response occurs, an auto mated diameter estimation is desirable. However, vascular ultrasound images suffer from structural noise caused by the constructive and destructive in terference of the backscattered signals, and the true boundaries of interes t that define the diameter are frequently obscured by the multiple-layer st ructure of the vessel wall, These problems make automated diameter estimati on strategies based on the detection of the vessel wall boundary difficult. We obtain a robust automated measurement of the vasodilator response by au tomatically locating the artery using a variable window method, which gives both the lumen center and width. The vessel wall boundary is detected by a global constraint deformable model, which is insensitive to the structural noise in the boundary area, The ambiguity between the desired boundary and other undesired boundaries is resolved by a spatiotemporal strategy. Our m ethod provides excellent reproducibility both for interreader and intraread er analyzes of percent change in diameter, and has been successfully used i n analyzing over 4000 brachial flow-mediated vasodilation scans from severa l medical centers in the United States.