Fibrosis, lipids, and calcium in human atherosclerotic plaque. In vitro differentiation from normal aortic walls by ultrasonic attenuation

Abstract

This study was designed to determine whether attenuation of ultrasound by the aortic wall is potentially useful in characterizing the atherosclerotic lesion. Measurements were made on fresh specimens taken from a human aorta at autopsy. Four hundred different sites, 4 mm in diameter each, corresponding to the dimension of the ultrasonic beam at the focal zone, were ultrasonically analyzed and histologically studied. Attenuation of ultrasound in each site was assessed by Fourier analysis of the echo produced by a specular reflector placed behind the specimen. Two parameters were measured over the range 7-11 MHz: the integrated attenation index (per cm), and slope (per cm per MHz) of the best fit straight line relating attenuation and frequency. Histological examination - performed for each of the 400 sites where attenuation had been measured - identified four subsets (100 samples each): normal aortic walls, fibrous plaques, fibrofatty plaques, and calcified plaques. Results obtained from ultrasonic and histological analyses showed that the integrated attenuation index was lowest in normal walls (24 ± 2.1, mean ± SE) and progressively increased in fibrous (32 ± 3.1), fibrofatty (82 ± 6.5), and calcific (185 ± 8.7) subsets (all intergroup differences were significant, except for the normal vs. fibrous comparison). The slope value was significantly lower in the fibrous than in the normal subsets: (10-3) 31.9 ± 4.5 vs. (10-3) 99.5 ± 9.1, respectively. Values of fibrofatty and calcific plaques overlapped: (10-3) 383 ± 21 vs. (10-3) 320 ± 23, respectively. Both were significantly different from normal and fibrous groups. Thus, alterations in ultrasonic indices related to attenuation characterize the different pathological patterns of atherosclerosis in the human arterial wall, providing a distinction between normal specimens and fibrous, fibrofatty, and calcified plaques.