A medical system tracks the position of a portion of a medical instrument within a body of a patient. In some embodiments, the medical instrument includes a needle, a syringe, and a needle-position-tracking element positioned between the needle and the syringe and in fluid communication with both. The needle-position-tracking element includes an electromagnet structure that includes a core, a conductive coil wrapped around the core, and ancillary circuitry configured to pass a current through the conductive coil to thereby generate a magnetic field. A sensor device senses the magnetic field and generates corresponding sensor signals. A control circuit calculates the position of a portion of the medical instrument based on the sensor signals.