doi:10.1016/j.ultrasmedbio.2007.08.006 ● Original Contribution ULTRASOUND MEASUREMENT OF THE BRACHIAL ARTERY FLOW-MEDIATED DILATION WITHOUT ECG GATING VINCENZO GEMIGNANI,* ELISABETTA BIANCHINI,* FRANCESCO FAITA,* CHIARA GIANNARELLI, † YVONNE PLANTINGA, † LORENZO GHIADONI, † and MARCELLO DEMI* ‡ *Institute of Clinical Physiology, National Research Council, Pisa, Italy; † Department of Internal Medicine, University of Pisa, Pisa, Italy; and ‡ Esaote S.p.A, Genova, Italy (Received 5 June 2007; revised 27 July 2007; in final form 11 August 2007) Abstract—The methods commonly used for noninvasive ultrasound assessment of endothelium-dependent flow-mediated dilation (FMD) require an electrocardiogram (ECG) signal to synchronize the measurements with the cardiac cycle. In this article, we present a method for assessing FMD that does not require ECG gating. The approach is based on temporal filtering of the diameter-time curve, which is obtained by means of a B-mode image processing system. The method was tested on 22 healthy volunteers without cardiovascular risk factors. The measurements obtained with the proposed approach were compared with those obtained with ECG gating and with both systolic and end-diastolic measurements. Results showed good agreement between the methods and a higher precision of the new method due to the fact that it is based on a larger number of measurements. Further advantages were also found both in terms of reliability of the measure and simplification of the instrumentation. (E-mail: gemi@ifc.cnr.it) © 2008 World Federation for Ultrasound in Medicine & Biology. Key Words: Flow-mediated dilation, Ultrasound, ECG gating, Image processing. INTRODUCTION Flow-mediated dilation (FMD) of the brachial artery is an established noninvasive method used to assess endo- thelial function (Celermajer et al. 1992). Over the last 15 y, this examination has gained increasing importance since several studies have shown that an impaired FMD response is related to cardiovascular risk factors, such as smoking (Celermajer et al. 1993; Corretti et al. 1998), hypercholesterolemia (Vogel et al. 1996; Toikka et al. 1999), hypertension (Park et al. 2001; Ghiadoni et al. 2001), diabetes (Lambert et al. 1996; Kawano et al. 1999) and aging (Celermajer et al. 1994, Ghiadoni and Virdis 2006) and is an independent predictor of cardio- vascular events (Lerman and Zeiher 2005; Deanfield et al. 2007). The technique most commonly used to assess the FMD is based on ultrasound imaging and was de- scribed in the guidelines of the International Brachial Artery Reactivity Task Force (Corretti et al. 2002). The examination consists in measuring the brachial artery diameter at rest and after reactive hyperemia induced by ischemia of the forearm. The measurement is taken on a B-mode section of the artery, which is imaged above the antecubital fossa in the longitudinal plane. In the past, the diameter values were obtained by manual analysis, where the borders of the vessel were identified by means of electronic calipers. More recently, automatic methods have been developed and these have increased the ob- jectivity of the examination and largely reduced the time needed for analysis (Beux et al. 2001; Craiem et al. 2007; Frangi et al. 2003; Gemignani et al. 2007; Newey et al. 2002; Sonka et al. 2002). In FMD measurements, the timing, with respect to the cardiac cycle, is very important. In fact, vasodilations induced by reactive hyperemia are not much larger than the diameter variations between systole and diastole (Chuang et al. 2002). Guidelines suggest using electro- cardiogram (ECG) gating during image acquisition, where the onset of the R-wave is used to identify the end diastole, and this is currently the method most commonly used both for manual and automatic analyses. This re- quirement, however, influences the complexity of the ultrasound equipment adopted for the examination. Now- adays, high frequency linear array transducers are also available in less expensive hand-carried ultrasound de- vices, which are being used more and more in research and clinical practice. Although such devices produce Address correspondence to: Vincenzo Gemignani, IFC-CNR, via Moruzzi 1, 56124 Pisa, Italy. E-mail: gemi@ifc.cnr.it Ultrasound in Med. & Biol., Vol. 34, No. 3, pp. 385–391, 2008 Copyright © 2008 World Federation for Ultrasound in Medicine & Biology Printed in the USA. All rights reserved 0301-5629/08/$–see front matter 385