1. US6595925 - In or relating to contrast agents

Ultrasound imaging using gas microbubble-containing contrast agents may be performed in the recirculating phase following admixture of the contrast agent with the blood pool, thereby prolonging the useful imaging time window compared to that conventionally obtained during the backscatter signal peak resulting from first pass of a contrast agent bolus. The length of the time window may further be increased by imaging at ultrasound frequencies of 2 MHz or less, particularly by harmonic imaging at transmit frequencies less than the resonance frequencies of the gas microbubbles.