The relationship between the nonlinear coefficient and parameter values of Nakagami distribution from the envelopes of fundamental and second harmonic signals are investigated to obtain more accurate nonlinear quantitative characteristics of tissue.The envelopes of fundamental and second harmonic signals are separated from the whole echoed RF signals using Butterworth high-pass filter.Then the Nakagami distribution parameters of the envelope signals are calculated and compared.The simulation results show that for different values of the nonlinear coefficients

the values of di

stribution parameters of the fundamental envelope signals are aliasing.On the contrary

the parameter values of second harmonic are mutually separating

especially for the nonlinear coefficients ranged from 3 to 6.In vitro experiments

compared with fat tissue

the relative differences of Nakagami parameter

and

of the fundamental envelope signals for liver and brain tissue are 7.3%

0.03% and 2.0%

4.3%

respectively;however the relative differences of 2

nd

harmonic envelope signals are 8.3%

19.4% and 7.0%

34.0%

respectively.The results of vitro experiments verify the effectiveness and correctness of the simulation results.In conclusion

the parameter values of Nakagami distribution for the second harmonic envelope signals from different degrees of nonlinearity in tissue are significantly different.According to this

we can quantitatively analyze the nonlinear characteristics of biological tissue.