Abstract: A guidance system for assisting with the insertion of a needle into a patient is disclosed. The guidance system utilizes ultrasound imaging or other suitable imaging technology. The guidance system can include an imaging device including a probe for producing an image of an internal body target, such as a vessel. One or more sensors can be included with the probe. The sensors sense a detectable characteristic related to the needle, such as a magnetic field of a magnet included with the needle. The system can include a processor that uses data relating to the sensed characteristic to determine a 3-D position of the needle, and a display for depicting the position of the needle. A needle assembly including a hub, cannula, and magnetic element is also disclosed, in which a magnetic axis of the magnetic element can be configured to be coaxially or otherwise aligned with the cannula axis.