Ultrasound contrast agents (UCAs) are improving the signal-to-noise ratio of the reflected ultrasound so that Doppler frequency spectra can be recorded even under poor sonographic conditions. This is of particular diagnostic value in transcranial Doppler sonography. Dependhrg on speci6c pharmacologic properties, echocontrast agents may cause diierent increase and duration in Doppler signal amplitude. We used a dog model to study the temporal profile of Doppler signal amplitude after application of a phosphollpid-containing echocontrast agent (BY %3). In addition, we compared it with a contrast agent containhtg albmnin (Albunex). Spherosome suspension BY 963 resulted in a dose-dependent increase in the duration of ultrasound ampligcation (Doppler enhancement of 1 mL, 3 mL and 10 mL of BY 963 per animal: 62.4 2 8.4, 72.8 t 9.2 and 67.7 t 4.2 s, respectively, n = 6). Detection of BY 963 in the extracranial jugular vein demonstrated that the UCA passes through the cerebral microcirculation (cerebral transit time was 2.2 2 0.2 s, n = 4). The signal enhancement lasted longer using the spherosome suspension compared with the albumin-containing solution (77.2 ~fr 11.6 and 31.1 2 3.7 s, respectively, n = 6), and the maximum increase in intensity was more pronounced (27.0 k 2.0 and 17.5 5 2.2 dB, respectively, n = 6).