Study participants were 10 healthy male volunteers with a mean age of 26 years (range, 25 to 28 years) and a mean body mass index of 22.4 (range, 18.6 to 26.8). None of the subjects had a reported history of previous intravenous accesses or indwelling catheter use. To determine method reproducibility, all subjects were assessed on days 1 and 14, at the same time of day, and under standardized conditions. All B-mode images were acquired by a single observer with 2 year’s experience in superficial vein mapping. Before each session, the subjects were instructed to fast and abstain from exercise, nicotine, caffeine, and alcohol ≤12 hours preceding the examination. The local medical ethics committee approved the study, and all subjects were required to sign informed consent.