1. A flexible needle comprising: a flexible elongate needle body with a channel and a needle lumen extending therein, the needle lumen defined by an interior surface of a wall of the flexible elongate needle body, the channel extending within the wall, the flexible elongate needle body including a distal tip portion, wherein the distal tip portion of the flexible elongate needle body is configured to pierce or puncture target tissue, wherein the channel comprises a groove; a shape sensor coupled to the flexible elongate needle body, wherein the shape sensor extends into the distal tip portion of the flexible elongate needle body and wherein the shape sensor is at least partially positioned within the groove; and a connector adapted for connecting the shape sensor to a processor for determining the shape of the flexible elongate needle body based on data from the shape sensor.