Generation of ultraharmonics in surfactant based ultrasound contrast agents: use and advantages

A unique distinction between surfactant stabilized ultrasound contrast agent ST68 and water (or tissue), is the enhanced ability of the agent to generate non-linear frequencies such as sub-harmonics (f(0)/2), higher harmonics (2f(0), 3f(0), 4f(0),...), and ultraharmonics (3f(0)/2, 5f(0)/2, 7f(0)/2....). when insonated with fundamental frequency f(0). Currently, second harmonics (2f(0)) have been predominantly researched, to exploit the diagnostic benefits of the contrast-specific non-linear imaging. However, we found that at normal imaging pressures (100 kPa-1 MPa), ST68 agent-generated second harmonic enhancements dropped to similar to8 dB at 100 kPa and similar to2 dB at I MPa. Moreover, at these pressures water (or tissue) produced strong second harmonics due to non-linear propagation. Ultraharmonics and sub-harmonics on the other hand, were generated only by the agent, and were not produced due to the nonlinear propagation of ultrasound in either water or tissue. Additionally, ultraharmonic (3f(0)/2) enhancements of similar to 23 dB at 100 kPa, similar to 35 dB at 0.5 MPa and similar to 41 dB at 1.1 MPa for ST68-PFC, offer much greater signal to noise ratio than higher harmonics. (C) 2001 Published by Elsevier Science B.V.