Magnetic tracking of instruments with respect to imaged anatomy is widely employed in medical practice.  Imaging systems that are enhanced with magnetic tracking may be used to track and display position and orientation of a diagnostic or therapeutic instrument relative to the imaging plane.  They can help the clinician guide the instrument to a chosen target with reduced error compared to an unguided instrument.  Furthermore, the visual representation of the tracked instrument is not necessarily constrained to the ultrasound imaging plane, thus enabling the clinician with more freedom of motion. 
For magnetic tracking of an instrument, an electromagnetic sensor can be included in a location of the instrument.  Electromagnetic sensors can be electromagnetic coils that surround or are close to the objects whose location is being tracked.  If an instrument with an included sensor is placed within a varying electromagnetic field, a voltage can be generated in the electromagnetic sensor.  This generated voltage can be used to determine and track the locations and relative positioning of the instrument within the electromagnetic field.  An ultrasound system enhanced with magnetic tracking of sensors can display a 3-dimensional merger of ultrasound generated anatomical features and the visual representation of the instrument position and orientation.