Correlation of ultrasonic attenuation (30 to 50 MHz and constituents of atherosclerotic plaque.

The ultrasonic integrated attenuation and the slope of attenuation (30-50 MHz) were measured in vitro at 20 degrees +/- 2 degrees C using radio frequency signals backscattered from human aortae. Ultrasonic measurements and histologic classifications were made in a total of 124 local regions from 58 independent segments of aortae. Values of the integrated attenuation were significantly higher in collagen-lipidic (142 +/- 51 dB cm-1, n = 18), and lipidic regions (139 +/- 53 dB cm-1, n = 11) compared to regions of normal media (97 +/- 20 dB cm-1, n = 44) and dense collagen (107 +/- 33 dB cm-1, n = 43). The most elevated integrated attenuation values were observed in calcified regions (245 +/- 93 dB cm-1, n = 8). The slope of attenuation was significantly higher in lipidic than in normal media (p = 0.002), dense collagen (p = 0.0007) or collagenlipidic (p = 0.04) regions. The correlation between attenuation and local tissue composition was used to establish ranges of values of integrated attenuation that are most likely to indicate specific tissue types. Images of the local tissue type were constructed. Comparison of these quantitative images with the corresponding histologic sections demonstrates that attenuation measurements offer promise for the in vivo characterization of plaque structure and composition.