Theoretical considerations for ultrasound contrast agent amplitude modulation techniques at high frequencies.

Abstract

Increasing the nonlinear response of ultrasound contrast agents (UCAs) in response to two consecutive pulses in amplitude modulation (AM) techniques can significantly increase the contrast to tissue ratio (CTR). It has been recently shown that one way to increase the nonlinearity is to take advantage of the buckling behavior of lipid shell bubbles. However, this method is limited to frequencies below the resonance of the bubble. To achieve enhanced nonlinearity at high frequencies, the oscillations of the UCAs should be optimized. In this work, the Hoff model was solved for a wide range of the parameters of the UCAs. Results showed that when the bubbles are sonicated with a frequency slightly less than the integer multiples of its resonance frequency (e.g., 2.7 and 3.6), and above a pressure threshold (PT), there is a significant increase in the UCA stable radial oscillations, which corresponds to a significant backscattered signal enhancement. If the sonication frequency of the AM technique is optimized according to the mentioned frequencies, and the amplitudes of the AM first and second pulses are smaller and greater than this PT, the CTR of the AM technique may be enhanced significantly.