Mean scatterer spacing estimation using the complex cepstrum

This paper presents a new method of estimating the distance between regularly-spaced coherent scatterers within soft tissue from backscattered radio-frequency (RF) signals. This scatterer spacing has been used successfully to classify tissue type, diagnose diffuse liver and kidney disease, and to diagnose Hodgkin's disease involvement in the spleen. This new method makes use of the complex cepstrum to identify periodic structure in the backscattered ultrasound signals. Periodic components in the time domain RF signal manifest themselves as peaks in the quefrency (cepstral) domain. The task of estimating the scatterer spacing is then reduced to identifying peaks in the cepstrum. Using simulation data, we show that peaks in the quefrency domain (corresponding to known periodic components in the RF signal) are easier to detect when the cepstrum is computed using the complex cepstrum rather than the commonly used power cepstrum. Similar improvements are seen using phantom and in vivo liver data.