Fig. 6

Impact of region of interest (ROI) size on measured flow volumes. The underestimation of flow caused by an ROI smaller than actual vessel size is relatively greater than the overestimation of flow caused by an ROI larger than the vessel. Thus, the ROI should contain the vessel or be slightly larger, but not smaller, than actual vessel size. Flow volumes for ROI sizes 50, 75, 125 and 150% diameter were expressed as percent of flow volume of the 100% vessel diameter. Data are shown for the descending aorta (DAo; a-d) and umbilical vein (UV; e-h) using the Doppler-ultrasound gating (DUS; left) and metric optimized gating (MOG; right) methods both without and with linear background correction. Median and range error bars are indicated