Development of Intravascular Acoustic Microscopy System

急性冠脉综合征的病因，如急性心肌梗死或不稳定心绞痛，已被揭示为冠状动脉中易受伤害的斑块的破裂。该研究项目的目的是开发一种适用于临床环境的血管内声学显微镜系统。资助期间的具体目标是建立一个频率为40 MHz的超声诊断系统，与传统的血管内超声系统相比，可以提供更多的信息。传统的血管内超声仪器的射频信号通过采样频率为500mSA/S的高速A/D转换器进行数字化，心电和冠状动脉内压同时数字化并存储在工作站中。来自自动灵敏度时间补偿的常规IVUS图像和集成背向散射成像。对连续帧中相同部分的射频信号进行分析，计算相关系数和位移。组织速度成像定义为1/30秒内移位的二维分布，其中相关系数为0.7或更高。组织应变成像是在考虑冠状动脉内压力变化的情况下，根据两点间的组织速度差得出的。该系统可显示正常冠状动脉、软斑块和硬斑块。软斑块的应变大于正常冠状动脉，且在一个心动周期内应变变化较大。临床结果提示该系统对急性冠脉综合征的病理生理学评估是有效的。

The cause of acute coronary syndromes such as acute myocardial infarction or unstable angina has been revealed as the rupture of a vulnerable plaque in a coronary artery. The objective of the research project was to develop an intravascular acoustic microscope system applicable to clinical settings. The concrete purpose during the term of Grant-in Aid for Scientific Research was to establish an ultrasonic diagnostic system with 40 MHz frequency which can provide greater information compared with a conventional intravascular ultrasound (IVUS) system.The radio-frequency (RF) signal from a conventional IVUS apparatus was digitized by a high speed A/D converter with a sampling frequency of 500 MSa/s. The ECG and intracoronary pressure were simultaneously digitized and stored in a workstation. Conventional IVUS images and Integrated Backscatter Imaging derived from automatic sensitivity time compensation. RF signals of the same portion in consecutive frames were analyzed and correlation and displacement were calculated. Tissue Velocity Imaging was defined as two-dimensional distribution of the displacement in 1/30 sec where the correlation was 0.7 or more. Tissue Strain Imaging was derived from the tissue velocity difference between two points considering intracoronary pressure change. Normal coronary artery, soft plaque and hard plaque were visualized by the system. The strain of the soft plaque was larger than that of normal coronary artery and the strain was greatly changed during one cardiac cycle. The clinical results suggest the efficiency of the system to assess the pathophysiology of acute coronary syndromes.