The use of pressure dependent subharmonic resonance to increase the signal to noise ratio of ultrasound contrast agent imaging.

Abstract

Conventional methods of subharmonic (SH) imaging of ultrasound contrast agents (UCAs) employ a frequency which is approximately twice the resonance frequency of the UCA (the SH resonance frequency). However, this approach may be limited by a low signal to noise ratio. To address this problem, the Hoff model was solved for several UCAs and the SH resonance frequencies of the bubble were calculated for different applied pressures (PAs). By increasing the PA above the pressure threshold for SH generation, the SH resonance frequency shifts toward lower values. Calculation of the scattered pressure in the regime of stable oscillations show that, if the bubble is sonicated with its pressure dependent SH resonance frequencies, the backscattered signal can be significantly stronger than when sonicating with the conventional SH resonance frequency (although the initiation of the SH occurs at a higher PA). The enhancement of the SH and ultraharmonic amplitudes can be up to 7 and 14 dB, respectively. This enhancement may lead to better UCA SH imaging, especially for molecular based imaging protocols.