A new system for in vivo assessment of the degree of nonlinear generation using the second harmonic component in echo signals.

To assess the feasibility of a new system that uses the finite amplitude method and makes possible the assessment of the degree of nonlinear generation in vivo we adopted a method for agar-gel phantoms, using varying lipid concentrations and human livers in vivo. Instead of calculating the nonlinearity parameter B/A value, we evaluated the h value, which is determined by plotting the measured values of the ratio of the amplitude of the second harmonic component to that of the fundamental component. The agar-gel phantoms of various lipid concentrations and 20 cases of normal and 21 cases of fatty liver were studied in this investigation. There was an almost linear agreement between the h value and the lipid concentration of the phantom. The h value (mean +/- SD) was 0.25 +/- 0.03 in normal liver and 0.35 +/- 0.05 in fatty liver. A statistically significant difference was found between them (p < 0.0001). This new system was considered to be usable for evaluating h in vivo as an indicator of the lipid content of the liver.