Classification of flow-limiting thrombus in acute coronary syndrome by acoustic microscopy

Virtual histology (VH), based on a power spectral analysis of radio-frequency signal from intravascular ultrasound (IVUS) with neural network, can detect an unstable plaque from all the regions of coronary atherosclerosis. However, it provides limited information on plaque vulnerability because the resolution is larger than 100 m and thrombus is not classified precisely. The objective of the present study is to measure the acoustic properties of flow-limiting thrombus responsible for acute coronary syndrome (ACS) at the microscopic level. A newly developed acoustic microscope with 100-MHz pulsed ultrasound was equipped to measure two-dimensional distribution of attenuation and sound speed. The tissues were obtained from coronary arteries of 26 patients with ACS by intracoronary aspiration catheter. They were sectioned at 5-mm thickness and mounted onto glass slides without cover slips or staining and used acoustic microscopy study. The values of attenuation and sound speed of the red thrombus were significantly higher than those of the platelets-rich thrombus. Both acoustic parameters of old red thrombus were significantly lower than those of the organized thrombus. The acoustic properties provided by acoustic microscopy can classify the flow-limiting thrombus at different pathological stages. The criteria will provide further information for development of a VH-IVUS algorithm.