鷹野 譲¹, 水重 克文¹, 森田 久樹¹, 藤田 憲弘¹, 千田 彰一², 松尾 裕英¹

Yuzuru TAKANO¹, Katsufumi MIZUSHIGE¹, Hisaki MORITA¹, Norihiro FUJITA¹, Shoichi SENDA², Hirohide MATSUO¹

¹香川医科大学第2内科, ²香川医科大学総合診療部

¹The Second Department of Internal Medicine Kagawa Medical School, ²The Department of Primary Care (Internal) Medicine Kagawa Medical School

キーワード : Intravascular ultrasound, Radio frequency signals, Integrated backscatter, Ultrasonic tissue characterization, Atherosclerosis

Although intravascular ultrasound (IVUS) is a feasible method for evaluating vessel anatomy, inter-or intraobserver variations are known to occur in interpretations of vessel wall structure. Additionally, IVUS images are affected by instrumental conditions. We therefore analyzed ultrasonic Radio Frequency (RF) signals reflected directly from the arterial wall, and attempted to quantify the histology of atherosclerotic lesions. For our observations, we used an ALOKA USI-122KG IVUS system equipped with a 20 MHz center frequency catheter probe. RF signals were obtained from 51 segments of formalin-fixed aorta in a 37°C water bath. A region of interest (ROI) measuring 0.2 mm in depth×1.0 mm in width was positioned within the atherosclerotic lesions in various stage. Integrated backscatter (IB) was calculated by integrating the power spectrum from 15 MHz to 25 MHz, which was drawn by analysis of RF signal using fast Fourier transform algorithm. Arterial sections, including the ROI, were stained by the hematoxylin eosin and elastica van Gieson, and were classified into 4 groups; normal(Norm., n=12), fatty(Fat., n=9), fibrous(Fib., n=17) and calcified(Calc., n=13) lesions. In each group, we made a preliminary assessment of the influence on IB value of distance between the transducer and ROI, and of the angle between the ultrasonic beam and inner surface echo. The IB values were found to be unaffected by distance or angle under the experimental conditions. Mean IB values for the four groups were 32.9±4.2 dB in Norm., 19.0±5.3 dB in Fat., 44.5±5.9 dB in Fib. and 66.7±9.1 dB in Calc.. The IB value of Norm. was significantly higher than that of Fat., and significantly lower than that of Fib. and Calc. (all; p