In vitro characterization of carotid plaque using a clinical ultrasound imaging system

The goal of this work is to demonstrate the feasibility of objective noninvasive methods for in vivo characterization of carotid plaque content. Using a clinical ultrasonic imager connected to a radiofrequency (RF) signal acquisition system, both RF signals and grayscale (GS) images were obtained from a tissue-mimicking reference phantom and from 26 independent segments of formalin-fixed human carotid endarterectomy specimens. Integrated backscatter (IBS) images of each segment were constructed from an FFT-based analysis on individual RF lines using a sliding Hamming window technique (32 point length, 1 point shift). For 82 matched ROIs, average IBS from parameter images was compared to average GS values normalized with respect to GS in the reference phantom. For 70 of the ROIs, plaque content was assessed by histology in terms of collagen, lipid, hemorrhage and calcification content. The current GS and IBS approaches were not found to be equivalent. The IBS values (mean standard error) for collagen, lipid and hemorrhage were 8.1, 1.1, 5.3 ± 1.0 and 4.9 ± 0.7 dB, respectively