Differences in definity and optison microbubble destruction rates at a similar mechanical index with different real-time perfusion systems

The purpose of this study was to determine microbubble responses to different pulse sequence schemes that exist on low mechanical index (MI) real-time perfusion imaging systems using either intravenous albumin-coated (Optison) or lipid-encapsulated (Definity) microbubbles. A tissue-mimicking phantom was created that permitted insonation of microbubbles at 3 cm (near field) and 9 cm (far field) from the diagnostic transducer face. Differences in effluent microbubble concentration were measured after they passed through vessels being insonified with pulse sequence schemes that transmitted alternating polarity (pulse inversion Doppler), alternating amplitude (power modulation), or both (contrast pulse sequencing) at a similar MI, frame rate, and transmit frequency. Normalized contrast signal intensity within a recirculating chamber was also measured in the near and far field. Pulse inversion Doppler produced less initial normalized contrast signal intensity and greater destruction rates than amplitude varying pulse sequence schemes like power modulation or contrast pulse sequencing at both the 0.1- and 0.2-MI settings. These differences indicate that the same MI setting on different real-time perfusion imaging techniques will produce different microbubble responses.