Knowledge of the physical properties of atherosclerotic plaque is essential when evaluating its vulnerability in a clinical setting. Such knowledge, however, is still difficult to obtain with the various approaches developed to date. This paper describes a novel noninvasive method (phased tracking method) for measuring minute change in thickness of each of the multiple layers of the arterial wall during one cardiac cycle. Such minute change in thickness less than 100 microns of the arterial wall cannot be measured by conventional ultrasound B-mode or M-mode images. A method for evaluation of the regional elastic modulus in the circumference direction, E theta, from the resultant change in wall thickness is also described. This method was applied to in vivo experiments in subjects with hyperlipemia and normal subjects. The spatial distribution of the regional elastic moduli, E theta, was evaluated for the carotid atherosclerotic plaques. By comparing the pathological findings with the distribution of elasticity, average elasticity of lipid and that of a mixture of smooth muscle and collagen fiber could be determined. Based on these reference parameters, each point was statistically categorized as lipid, mixture, or other. Thus, the plaque was electronically stained using transcutaneous ultrasound. By applying this method to the common carotid arteries, the presence of thin collagen fiber was clarified along the arterial axis for normal subjects, while soft inclusion of lipid was found for every plaque in subjects with hyperlipidemia. This novel method offers potential as a diagnostic technique for detection of plaque vulnerability with high spatial resolution.