Power Doppler sonography: clinical applications

Abstract

Objective: Color Doppler imaging (CD) has had a great impact on ultrasonography (US). This technique depicts local flow by encoding an estimate of the mean Doppler frequency shift at a particular position in color. However, the choice of the mean frequency shift as the parameter for representing flow in color Doppler is somewhat arbitrary. Power Doppler ultrasound is a technique that encodes the power in the Doppler signal in color. This parameter is fundamentally different from the mean frequency shift. The frequency is determined by the velocity of the red blood cells, while the power depends on the amount of blood present. Providing an image of a different property of blood flow, power Doppler has shown several key advantages over colour Doppler, including higher sensitivity to flow, better edge definition and depiction of continuity of flow. In this paper we review the results of power Doppler clinical studies.

Materials and methods: All relevant information available in the literature on the potential clinical applications of this technique was revised to give a detailed survey.

Results: The increased flow sensitivity and better vascular detailing of power Doppler have been used to detect flow presence and characteristics in vessels that are poorly imaged with conventional color Doppler. The improved depiction of tissue vasculature has shown potential advantages, especially in some areas, such as the cortex of native kidneys and renal allografts, the prepuberal testis, the infant hip and the bowel wall, in which color Doppler is not sensitive enough to detect clinically important, slow and poor flow in small vessels. In inflammatory conditions, power Doppler was valuable in depicting increased flow in vessels that are dilated because of inflammatory response. In this field, advantages have been reported in acute cholecystitis and in inflammatory states of musculoskeletal tissues. The higher sensitivity to slow flow and the improved detailing of the course of tortuous and irregular vessels made power Doppler a promising technique to image intratumoral vessels and, thereby, to ameliorate the accuracy of color Doppler in predicting the likelihood of benign versus malignant nature of nodules. Specific flow patterns, missed at color Doppler studies, have been indicated with power Doppler in some tumors of the liver and breast. In different settings, power Doppler also permitted to monitor serial blood flow changes after therapy and to display them as color intensity, allowing the observer to distinguish flow changes.

Conclusion: Although the actual role of power Doppler in changing patient management has not been assessed yet, this technique can depict flow which was previously undetectable, and thus permits an easier and more confident diagnosis in body regions where the ultrasound signal is weak because blood vessels are small.