Detection of Fibrous Cap in Atherosclerotic Plaque by Intravascular Ultrasound by Use of Color Mapping of Angle-Dependent Echo-Intensity Variation

Abstract

Background-The thickness of the fibrous cap is a major determinant in the vulnerability of atherosclerotic plaque to rupture. It has been demonstrated that intravascular ultrasound (IVUS) backscatter from fibrous tissue is strongly dependent on the ultrasound beam angle of incidence. This study investigated the feasibility of using a new IVUS color mapping technique representing the angle-dependent echo-intensity variation to determine the thickness of the fibrous cap in atherosclerotic plaque. Methods and Results-Nineteen formalin-fixed noncalcified human atherosclerotic plaques from necropsy were imaged in vitro with a 30-MHz IVUS catheter. The IVUS catheter was moved coaxially relative to the plaque. The images showing maximum and minimum echo intensity of the plaque surface were selected to calculate the angle-dependent echo-intensity variation. A colorized representation of the echo-intensity variation in the plaque was obtained from the 2 IVUS images. A clearly bordered area with large variation in echo intensity was revealed for each plaque surface in the colorized IVUS image. The thickness (x, mm) of this area correlated significantly with that of fibrous cap (y, mm) measured from histologically prepared sections as yϭ1.05xϪ0. 01 (rϭ0.81, PϽ0.0001). Bland-Altman analysis also supported the reliability of this method (mean difference, 0.00Ϯ0.10 mm). Conclusions-This novel technique for color mapping the echo-intensity variation in IVUS provided an accurate representation of the thickness of the fibrous cap in atherosclerotic plaque. This method may be useful in assessing plaque vulnerability to rupture in atherosclerosis.

Volumetric Quantitative Analysis of Tissue Characteristics of Coronary Plaques After Statin Therapy Using Three-Dimensional Integrated Backscatter Intravascular Ultrasound

“…Recently, mathematical analysis of RF signals from IVUS and color mapping of angle-dependent echo-intensity variation have been developed for detecting vulnerable plaques (6,7). In addition, IVUS elastography has been shown to distinguish different plaque morphologies in vivo (9).…”

Ultrasonic Tissue Characterization of the Atherosclerotic Carotid Artery-Histological Correlates of Carotid Integrated Backscatter-

“…Hiro et al attempted to assess the thickness of the fibrous cap in vitro with an angledependent echo intensity variation using intravascular ultrasound. 14 We also attempted to set the ultrasound beam as perpendicular as possible to the surface of the plaque, and the echo reflection was quantified with IBS. IBS was greater in the thick fibrous cap than in the thin fibrous cap.…”

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“…However, the sensitivity to identify fatty plaque components remains low [8,9]. Recent rf-(radiofrequency) based tissue identification strategies appear to have better performance [9,10]. With palpography, the local strain of the tissue is obtained.…”