Flow index evaluation of 3-d volume flow images: An in vivo and in vitro study

Three-dimensional (3-D) ultrasound imaging has improved evaluation of organ circulation and might contribute new information on maternal and fetal blood supply. Flow index (FI) of 3-D color images has been proposed as a measure of perfusion. The aim of this study was to evaluate whether the 3-D FI is a parameter of volume flow and flow velocity in a human vessel and in a flow phantom. A 1-cm-long strip of the uterine artery was recorded in 3-D power Doppler (3D-PD) mode in a cross-sectional study of 170 normal singleton pregnancies between 26 and 42 weeks' gestation. A fixed ultrasound system installation was used during the examination. The VOCAL™ software integrated in the ultrasound unit calculated vessel volume and FI. Reproducibility of the measurements was tested. The method was also tested on a commercially available flow phantom. Reproducibility measurements gave satisfactory results, both in terms of inter- and intraobserver variation. Unexpectedly, in normal pregnancy, the uterine artery FI decreased slightly with gestation. Uterine artery vessel volume increased, however, with gestational age. A poor correlation was found between the FI and both flow velocity and volume flow in the flow phantom. In conclusion, 3D-PD imaging can give impressive anatomical pictures of organ vascular tree. However, the new FI is poorly related to flow velocity or volume of flow. (E-mail: saemundur.gudmundsson@med.lu.se)