The choice of the optimal ultrasonic frequency for vascular studies is
determined by the required resolution and penetration. Anatomical rea
ltime two-dimensional imaging and blood flow studies provide complemen
tary information. Intravascular scanning allows high-frequency ultraso
und to be used, with correspondingly good spatial resolution. Contrast
resolution is degraded by beam side lobes and the limited dynamic ran
ge of the ultrasonic pulse. The physics of ultrasonic scattering by bl
ood, pulsed Doppler and duplex scanning and colour flow imaging perfor
mances determines the limits of clinical applications. Contrast agents
enhance the echogenicity of blood, improving sensitivity and, through
second harmonic detection, suppressing solid tissue echoes. Three-dim
ensional display, with segmentation by the presence of the flow signal
, facilitates spatial perception. Clinical applications in vascular pa
thologies are summarised.