Fig. 2

Dynamic needle tip positioning schematic. a The needle tip is visualized as a high-echoic point between the skin surface and the anterior wall of the target vessel on the ultrasound image. b The probe is advanced toward slightly until the high-echoic point disappears from the image. c The needle tip is advanced further toward the anterior wall, and the high-echoic point is visualized just over the target vessel. d The needle tip penetrates the anterior wall under ultrasound guidance, and the high-echoic point is visualized in the target vessel. e The probe is further advanced until the high-echoic point disappears from the image. f The needle tip is advanced further slightly with a reduced puncture angle until the high-echoic point appears on the image