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To determine the feasibility of quantitative ultrasonic techniques to define the composition of atherosclerotic plaques, samples of freshly excised human aortas were sewn to a sample holder and immersed in a saline bath for ultrasonic interrogation. Integrated backscatter of a 2-microsecond portion of the backscattered radiofrequency signal was measured with a 10 MHz focused transducer. Integrated backscatter was calculated by normalizing the root-mean-square voltage of the gated signal to the root-mean-square voltage obtained by replacing the tissue sample with a nearly perfect reflector. Microscopic examination of the 124 interrogated sites allowed differentiation of normal, fibrous, fibrofatty, and calcified regions. A site was considered calcified if it contained any histochemically detectable calcium. Values of integrated backscatter were markedly elevated from calcified regions (-30.0 +/- 6.4 dB, n = 25; mean +/- SD; p less than 0.001) compared to normal (-43.2 +/- 2.4 dB, n = 20) and fibrofatty (-43.9 +/- 3.4 dB, n = 43) sites. Values from fibrous regions (-40.7 +/- 3.8 dB, n = 36) were also significantly different compared with the calcified and fibrofatty regions (p less than 0.001). Thus, we have demonstrated that quantitative ultrasonic backscatter identifies and differentiates calcification and fibrosis in atherosclerotic sites offering promise for the noninvasive assessment of the pathologic status of the arterial wall.
Barzilai et al. (Sun,) studied this question.