Higher order nonlinear ultrasonic imaging

Nonlinear imaging as conventionally applied in medical ultrasound separates the second harmonic response from the fundamental. Second harmonic images have better clutter rejection and transmit focusing but worse SNR compared with the fundamental. The authors propose using higher harmonic components to gain more tissue information and to improve SNR. The underlying idea is to model the nonlinear echo signal as a polynomial expansion of some basis waveform. When this model is excited by a number of transmit pulses with different amplitudes and phases then the coefficients of this model can be obtained through least squares inversion. Odd order nonlinearities are of particular interest since one of their spectral components is folded back into the system's transmission band. This component can be received without attenuation from the transducer's bandpass characteristic.