Doppler ultrasonography of peripheral vascular disease: The potential for ultrasound contrast agents

Noninvasive diagnosis of peripheral vascular disease started with the intro duction of Doppler technology. The development of high frequency ultrasound and color Doppler imaging allows continuous assessment of vascular disorde rs along the arterial tree. However, the technique remains operator depende nt. It also suffers from anatomic limitations, such as bowel gas and ultras ound attenuation due to depth or wall calcification. Ultrasound contrast ag ents increase the Doppler signal intensity and should therefore reduce the rate of technical failures. They are useful for detecting the flux in cases of attenuated ultrasound beam and reduced blood flow. Their administration using continuous infusion protocols increases the duration of the effect. New imaging modalities such as harmonic imaging and pulse inversion imaging reduce Doppler artifacts and allow real time detection of the microbubbles flowing in the blood stream. Future directions include ultrasound-guided t herapy of occlusion using encapsulated drugs targeted to the thrombus.