An investigation of the relationship between ultrasound echo enhancement and Doppler frequency shift using a pulsatile arterial flow phantom.

RATIONALE AND OBJECTIVES Based on the echo-enhancing effect of microbubbles, various agents have been developed to improve the diagnostic confidence in patients with inadequate Doppler signals. In the clinical trials of the echo enhancer Levovist, there were a few isolated cases in which the maximum flow velocities of the enhanced Doppler spectra appeared to higher than the velocities in the nonenhanced baseline spectra. This raised the concern that echo enhancement could give a false indication of maximum flow velocity. This study investigated whether a systematic association between echo enhancement and velocity shift exists. METHODS A pulsatile flow phantom that simulated the elasticity of blood vessels and the acoustic attenuation of extravascular tissue was used to compare enhanced with unenhanced Doppler spectra under accurately reproducible flow conditions. The experiments were carried out with varied sound attenuation and evaluated with dedicated spectral analysis software that included a special averaging tool. RESULTS Levovist enhanced the Doppler signal by 16 to 31 dB, and the enhanced and unenhanced power spectra presented identical distribution of spectral power density under all flow conditions. CONCLUSIONS The measurements gave no evidence that echo enhancement with Levovist falsifies the Doppler measurement of flow velocity.