A system and method for determining a center of a blood vessel. An ultrasonic probe includes a midline marker. A computing system includes a processor, a memory, a user interface, and an imaging screen. The processor displays imagery from the ultrasonic probe on the imaging screen, receives a selection of a desired blood vessel displayed on the imaging screen via the user interface, determines a center of the desired blood vessel, and produces an alert when the midline marker of the ultrasonic probe is disposed over the center of the desired blood vessel.
