[Power Doppler signals produced by static structures: a frequent cause of interpretation errors in the study of slow flows].

INTRODUCTION: The main characteristic of power Doppler US is its high sensitivity in showing blood vessels with small caliber and slow flow. However, artifacts are a common problem with this technique and they lead to impaired and subjective image reading. We analyzed the artifacts from Power Doppler signals from static structures both in vitro and in vivo. MATERIAL AND METHODS: Some samples of different tissues (liver, muscle, fat) positioned into a water bath were studied with Power Doppler in vitro. The static structures were imaged with a 10 MHz transducer (Esaote AU4, Genoa, Italy) both through water and with the transducer resting directly on the tissue. PRF and WF were set differently every time and their individual/combined role in causing artifacts was assessed. Then we examined different organs in vivo to investigate if the same setting as in vitro would cause the same artifacts. RESULTS: All our tissue samples exhibited strong and persistent color signals at low PRF and WF settings, with stronger signals at the solid/liquid interface and no signals from the liquid color box. Comparison of images acquired with same setting, particularly color gain, but different PRF (750 Hz to 3 KHz) or WF (50 to 600 Hz) showed that artifacts are mainly related to the latter. In vivo examinations showed similar findings, especially relative to the liquid/solid and solid hypoechoic/solid hyperechoic interfaces. CONCLUSIONS: Persistent and fairly strong Power Doppler signals can be produced by echogenic structures with no flow; these artifacts are frequent at low PRF, but are mainly caused by incorrect WF setting. They are most frequent along interfaces with specular reflection. To conclude, we would like to stress that, in addition to motion artifacts, which are easier to recognize, other potentially misleading signals may come from static structures.