Mirza Pasovic, François Varray, Olivier Basset, Christian Cachard

Aim of the study Nonlinearity of the tissue distorts the US wave in propagation: Rise of higher harmonics and Energy of fundamental frequency is shifted to higher harmonics

Effects based on nonlinear ultrasound offer new possibilities for:

• Imaging nonlinear parameter B/A
• Tissue characterization
• Enhanced Ultrasound Contrast Imaging [1]

Model The model  of non linear propagation is based on a KZK parabolic solution for unfocused transducer

a).	b).

c).

Illustration of the fundamental diminution and the rise of the n-harmonics. a) is the intial pressure wave (z=0m) and b) is the same wave after 15cm of propagation. The nonlinear effect are clearly visible. c) is the evolution of the fundamental and the first harmonics of the signal.

Methods and applications

1 - B/A imaging

In nonlinear contrast imaging, there is "competition" between 2nd harmonic generated by Ultrasound Contrast agent (UCA) and surrounding medium. To increase "Agent to Tissue Ratio", second harmonic generated by tissue must be reduced [2].

2 - Frequency focalisation

Transmission of Second Harmonic Reduction Signal (SHRS) [3]

a).	b).

a) the initial time frequency image is diplayed, b) the resulting time frequency image is displayed after SHRS applications. The second harmonic component is completely reduced at the region of interest.

References