A method for targeting a blood vessel comprises acquiring ultrasound data, automatically determining a target sample volume, acquiring Doppler ultrasound data, and communicating an indicator of flow characteristics in the target sample volume. The ultrasound data is for a plane within a body. The target sample volume is determined at an intersection of a trajectory of an insertable instrument with the plane. The Doppler ultrasound data is acquired for at least the target sample volume at the intersection. The indicator of flow characteristics is based on the Doppler ultrasound data. An associated apparatus is also described.
