AN IN-VITRO STUDY ON THE INFLUENCE OF LIMITED FREQUENCY RESOLUTION ONCONTRAST AGENT-ENHANCED DOPPLER SIGNALS

Ultrasound contrast agents for vascular use are gas-filled microsphere s and will increase the backscatter from blood and therefore enhance t he Doppler signal. Studies have shown that Doppler enhancement may res ult in an increased maximum velocity when observed as the envelope of the spectral Doppler screen. Change in observed velocity may be due to biological or instrumentational effects. The purpose of this study wa s to investigate the possible instrumentational effects on the Doppler signal after injection of the contrast agent (Infoson(TM)). By perfor ming the measurements on a Doppler phantom, the biological effects was eliminated. Computer simulations of limited frequency resolution were compared to measurements. The conclusion was that the increase in det ected maximum velocity after Infoson injection is due to the combined effect of signal enhancement and limited frequency resolution. It is s hown that a large change in signal strength can change the estimated m aximum frequency from the spectral Doppler whether this is due to a co ntrast agent or instrument settings. It is therefore important in a cl inical situation to have an adequate, but not too strong or too weak s ignal in order to make the best velocity estimates.