In vitro ultrasonic tissue characterization for evaluation of hepatic diseases

The objective of this study is to explore the potential of attenuation and ultrasonic (US) velocity estimates (6 to 30 MHz) to discriminate healthy and diseased human liver. Echoes from 47 fresh in vitro samples of human liver and a planer reflector were obtained using a 20-MHz central frequency transducer (scan plane parallel to the reflector placed beneath the liver approximately). Comparisons of echo times-of-flights and echo spectra with and without intervening liver were normalized by local liver thickness to calculate the US velocity and attenuation, respectively (substitution method). Projection parameter images were constructed, and measurements from selected regions of interest were compared with histological classification. The average US velocities were 1540.4 ± 35.5 m/s, 1579.9 ± 25.2 m/s, 1584.4 ± 35.1 m/s for normal (N = 13), cancerous (N = 8) and fibrotic (N = 26) groups, respectively. Significant velocity differences were found between the normal group and both pathological groups, (p<0.01). However, US velocity failed to differentiate fibrotic and cancerous groups. Average attenuation slopes were 0.074 ± 0.016 dB.mm^-1 MHz^-1, 0.098 ± 0.029 dB.mm^-1 MHz^-1, 0.063 ± 0.015 dB.mm^-1 MHz^-1 for normal, fibrotic and cancerous groups, respectively and were significantly different between normal and fibrotic (p<0.005) groups and between cancerous and fibrotic groups (p < 10^-4) but not between cancerous and normal groups. However, an outlier was found in the cancerous group. Removing this outlier resulted in a significant difference between cancerous and normal groups (p<0.005). Such high frequency measurements (20 MHz) could potentially be used intra-operatively to identify suspicious focal lesions otherwise difficult to classify with other imaging modalities.