従来の超音波断層像において，心臓壁領域内部rnは心内腔領域と同様に輝度が小さく表示されるこrnとが多い．さらに心臓の超音波断層優には，サイrnドローブの肋骨による反射に起因するアーチファrnクトが多数存在する．したがって，輝度のみを用いrnて心臓壁領域を自動同定することは難しい．一方，rn心臓からの反射RF信号の周波数特性は，S/Nがrn悪くない限り，エコーの振幅と比べて多くの情報rn（周波数ごとの振幅，位相）を含んでいる．%In the conventional ultrasonic tomographic images, the heart wall cannot be distinguished from the cardiac lumen automatically using only the echogenicity. One of the largest problems is that echogenicity, which corresponds to the amplitude of the RF echo, in the heart wall is as low as that in the lumen. In this paper, ultrasonic RF echoes from the heart wall and lumen were analyzed in frequency domain in order to distinguish the heart wall from the lumen automatically. Temporal changes in complex frequency spectra were evaluated using the magnitude-squared coherence function. The coherence function of the RF signal scattered from the interventricular septum (IVS) was high. In contrast, the coherence function in the right ventricle (RV) and left ventricle (LV) was low because the scatterers (blood cells) slipped off from the focal area of the ultrasonic beam by blood flow. For automated identification of the heart wall using the coherence function, the optimal threshold T_0(f) for the coherence function should be determined. In this study, based on the Bayes decision rule, the optimum value of T_0(f) was determined. In-vivo experimental results show that the differentiation of the heart wall from the lumen was improved significantly using the proposed method.
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