Improved common carotid elasticity and intima-media thickness measurements from computer analysis of sequential ultrasound frames.

B-mode ultrasound has gained popularity as a non-invasive method for direct visualization of superficial vessels. With B-mode ultrasound, arterial stiffness can be directly measured since image acquisition of the arterial wall thickness and vessel diameter can be obtained simultaneously in a dynamic fashion throughout the cardiac cycle. Recently, a method was developed to measure carotid arterial diameter and intima-media thickness (IMT) from B-mode images that utilizes computerized edge tracking-multiframe image processing that automatically measures arterial diameter and IMT in multiple sequential frames spanning several cardiac cycles. To evaluate this method, replicate B-mode common carotid artery ultrasound examinations and blood pressure measurements were obtained in 24 subjects 1-2 weeks apart. Approximately 80 sequential frames spanning two cardiac cycles were analyzed from each ultrasound examination to obtain maximum arterial diameter (D(max)), minimum arterial diameter (D(min)), and IMT using a computerized edge detection method. The intraclass correlations of D(max), D(min), and IMT were 0.97-0.99 and the mean absolute difference for these measurements were 0.03-0.11 mm. The coefficient of variation for D(max) and D(min) were 1.28 and 1.18%, respectively. The intraclass correlation for several standard arterial stiffness indices, Peterson's elastic modulus, Young's modulus, arterial distensibility, compliance, and the beta stiffness index ranged between 0.84 and 0.89. Additionally, it was determined that averaging IMT over five frames centered at D(min) reduced single frame IMT measurement variability by 27% (P=0.005) compared with IMT measured from a single frame corresponding to D(min). Comparison of the phasic relationship of D(max) and D(min) measured from the B-mode ultrasound image with the simultaneously recorded electrocardiogram (ECG) signal in the 24 subjects, provided a more accurate method of frame selection for arterial diameter extrema independent of the ECG signal. The method of computerized edge detection-sequential multiframe image processing presented in this paper represents a technological advance for image analysis of B-mode ultrasound images of common carotid arterial dimensions that is highly reproducible and directly applicable to noninvasive imaging of atherosclerosis.