Saijo Yoshifumi, Tanaka Akira, Owada Naoki, Akino Yoshihisa, Nitta Shinichi
Department of Medical Engineering and Cardiology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryomachi, Aoba-ku, Sendai 980-8575, Japan.
Ultrasonics. 2004 Apr;42(1-9):753-7. doi: 10.1016/j.ultras.2003.11.022.
Intravascular ultrasound (IVUS) provides not only the dimensions of coronary artery but the information of tissue components. In catheterization laboratory, soft and hard plaques are classified by visual inspection of echo intensity. So-called soft plaque contains lipid core or thrombus and it is believed to be more vulnerable than a hard plaque. However, it is not simple to analyze the echo signals quantitatively. When we look at a reflection signal, the intensity is affected by the distance of the object, the medium between transducer and objects and the fluctuation caused by rotation of IVUS probe. The time of flight is also affected by the sound speed of the medium and Doppler shift caused by tissue motion but usually those can be neglected. Thus, the analysis of RF signal in time domain can be more quantitative than intensity of RF signal. In the present study, a novel imaging technique called "intravascular tissue velocity imaging" was developed for searching a vulnerable plaque. Radio-frequency (RF) signal from a clinically used IVUS apparatus was digitized at 500 MSa/s and stored in a workstation. First, non-uniform rotation was corrected by maximizing the correlation coefficient of circumferential RF signal distribution in two consecutive frames. Then, the correlation and displacement were calculated by analyzing the radial difference of RF signal. Tissue velocity was determined by the displacement and the frame rate. The correlation image of normal and atherosclerotic coronary arteries clearly showed the internal and external borders of arterial wall. Soft plaque with low echo area in the intima showed high velocity while the calcified lesion showed the very low tissue velocity. This technique provides important information on tissue character of coronary artery.
血管内超声（IVUS）不仅能提供冠状动脉的尺寸，还能提供组织成分信息。在导管实验室中，软斑块和硬斑块通过回声强度的视觉检查进行分类。所谓的软斑块含有脂质核心或血栓，被认为比硬斑块更易破裂。然而，对回声信号进行定量分析并不简单。当我们观察反射信号时，其强度受物体距离、换能器与物体之间的介质以及IVUS探头旋转引起的波动影响。飞行时间也受介质声速和组织运动引起的多普勒频移影响，但通常可以忽略不计。因此，在时域中对射频信号进行分析比射频信号强度分析更具定量性。在本研究中，为寻找易损斑块开发了一种名为“血管内组织速度成像”的新型成像技术。来自临床使用的IVUS设备的射频（RF）信号以500 MSa/s的速率数字化并存储在工作站中。首先，通过最大化两个连续帧中圆周射频信号分布的相关系数来校正不均匀旋转。然后，通过分析射频信号的径向差异来计算相关性和位移。组织速度由位移和帧率确定。正常和动脉粥样硬化冠状动脉的相关图像清晰显示了动脉壁的内边界和外边界。内膜中低回声区域的软斑块显示出高速度，而钙化病变显示出非常低的组织速度。该技术提供了关于冠状动脉组织特征的重要信息。
