Magnetic probe apparatus

A system and method for locating magnetic material. In one embodiment the system includes a magnetic probe; a power module in electrical communication with the magnetic probe to supply current to the magnetic probe; a sense module in electrical communication with the magnetic probe to receive signals from the magnetic probe; and a computer in electrical communication with the power module and the sense module. The computer generates a waveform that controls the supply of current from the power module and receives a signal from the sense module that indicates the presence of magnetic material. The magnetic probe is constructed from a material having a coefficient of thermal expansion of substantially 10−6/° C. or less and a Young's modulus of substantially 50 GPa or greater. In one embodiment magnetic nanoparticles are injected into a breast and the lymph nodes collecting the particles are detected with the probe and deemed sentinel nodes.