Cepstral analysis of ultrasound in chronic liver disease--a preliminary study in the non-invasive evaluation of structural change

To evaluate the morphological changes in chronic liver disease non-invasively we used the frequency-domain analysis of ultrasound. We assumed that liver tissue is a collection of semi-regularly arrayed small scatterers of ultrasound. We applied cepstral analysis to ultrasonic waveforms and evaluated the periodicity of scalloping of the power spectrum, caused by an interference effect among liver scatterers of a given spacing. In a phantom experiment, we could correctly measure the space among scatterers of a phantom consisting of a regularly spaced distribution of nylon filaments. In an experiment involving a freshly excised porcine liver, the distribution of the space among scatterers (SAS) determined on cepstral analysis reflected the size distribution of the hepatic lobules. In a human study, two statistical parameters, mode and kurtosis, were determined from the distribution of the SAS for each patient. In a previous study, we collected ultrasonic data during peritoneoscopy with a 10 MHz transducer directly contacting the liver and showed that we could evaluate morphological changes in chronic liver disease using cepstral analysis. In the present study, we obtained data in two ways: with a 3.5 MHz transducer through the abdominal wall and with a 10 MHz transducer directly contacting the liver during peritoneoscopy. The mode and kurtosis of the SAS obtained with the 3.5 MHz transducer were both well correlated with the mode and kurtosis of the SAS obtained with the 10 MHz transducer. These results suggest that we can evaluate morphological changes in chronic liver disease non-invasively.