THE INFLUENCE OF ACOUSTIC-IMPEDANCE MISMATCH ON POSTSTENOTIC PULSED-DOPPLER ULTRASOUND MEASUREMENTS IN A CORONARY-ARTERY MODEL

Acoustic impedance mismatch at the fluid-wall interface was shown to a ffect the spectra from an intravascular Doppler device in an in vitro model with a diameter typical of human coronary arteries. Measurements were obtained first under Poiseuille flow conditions with impedance m ismatches of 0%, 7% and 12%, and then under stenosed conditions for th e 0% and 7% mismatch cases. For the zero mismatch case, the Doppler sp ectra could be readily interpreted in terms of fluid mechanical phenom ena. When mismatch was present, the spectra from Poiseuille flow exhib ited multiple peaks which could not be directly related to the velocit y profile. Also, the spectra from stenosed flow with a mismatch of 7% were similar to those from the zero mismatch case but did not exhibit the specific flow-related features as clearly. These results indicate that the impedance mismatch alters the acoustic environment inside the model and that this causes artifact in the Doppler spectra.