Harmonic Magnification by Time Reversal based on a Hammerstein Decomposition

Sébastien Ménigot (1) , Jean-Marc Girault (1)

1 iBraiN - Imaging, Brain & Neuropsychiatry

In tissue harmonic imaging, the contrast has been increased by using nonlinearities. However, enhancing the contrast requires a good harmonic level. Time reversal process is well-known to enhance the backscattered signal by optimizing the transmitted wave. However, it is not well-adjusted for second harmonics, since the nonlinearities of the time reversed harmonic signal will be double the frequency and will be removed by the transducer. To take into account the harmonics, one way consists in modelling the ultrasound system by parallel subsystems with a Hammerstein model. Therefore finding the optimal wave for harmonic generation means to create a matched filter for the subsystem describing the nonlinearity. As described by the time reversal, the first wave propagates to the medium. The backscattered second harmonic components are extracted from a Hammerstein model. The second harmonic signal is time reversed, frequency shifted by a demodulation and sent in the medium. In this study, the nonlinear components could be increased by 15 dB in comparison to the time reversal process and conventional imaging. Moreover, the SNR can be increased by 7 dB. The second harmonic time reversed waves focus better on the inclusion and wave coherence is preserved. From this point of view, the optimization process can be viewed as an extension of the matched filtering feature of the time reversal principle to second harmonics.

Mots clés: Time Reversal; Harmonic imaging; Hammerstein model; Waveform design

Domaines: Traitement du signal et de l'image [eess.SP]; Acoustique [physics.class-ph]; Imagerie

Sébastien Ménigot, Jean-Marc Girault. Harmonic Magnification by Time Reversal based on a Hammerstein Decomposition. IEEE International Ultrasonic Symposium 2016, IEEE UFFC, Sep 2016, Tours, France. ⟨10.1109/ULTSYM.2016.7728742⟩. ⟨hal-01371264⟩