Investigation into the effectiveness of ultrasound SHI imaging according to static and dynamic parameters of contrast agents
Résumé
Second harmonic inversion (SHI) is a new method to improve contrast to tissue ratio (CTR) of ultrasound contrast images through reducing tissue-generated 2nd harmonics during wave propagation. Two 90° phase-shifted pulses with the same frequencies and amplitudes are transmitted. The two received RF data are summed and filtered around 2nd harmonic frequency to create SHI image. However, after experimental evaluation on SHIs effectiveness, we found that movements and destruction of contrast agent bubbles strongly affect the results of SHI. Using CREANUIS software, SHI is simulated with various bubble movements (\Delta d), reflective amplitude (Amp) and mediums nonlinear parameter (\beta) changes. Amp and \beta decreasing are two different ways to describe the bubble cloud evolution. The influences are quantified by CTR of SHI images. Simulation results show that CTR improves by 11dB for 100% \beta destruction and 13dB for 100% Amp destruction. In lateral direction, CTR rises until reaching a stable value when bubble movement increases between the two pulses. In axial direction, CTR exhibits oscillations with increasing movements with respect to transmitted pulse wavelength. The maximum increases are both 16dB. So SHI is expected to be optimized by increasing the power and adjusting pulse repetition frequency (PRF) of transmitted pulses.
Domaines
Acoustique [physics.class-ph]
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