Magnetic probe apparatus

A system for locating a magnetic marker in a patient comprising:

• a magnetic probe comprising;
• a drive coil for producing an alternating magnetic field;
• and
• a sense coil for detecting a magnetic field as generated by the magnetic marker in response to the alternating magnetic field produced by the drive coil,
• wherein the drive coil and sense coil having different radii, and being spaced axially from each other;
• and
• wherein the axial spacing between the drive coil and the sense coils is such that as the radius of the larger coil varies from an initial radius the change in the mutual inductance between the sense coil and the drive coil caused by the change in radius of the larger coil is zero,
• a power module in electrical communication with the magnetic probe to supply current to the magnetic probe;
• an amplifier in electrical communication with the magnetic probe to receive signals from the magnetic probe;
• a processing module in electrical communication with the power module and the amplifier;
• and
• a plurality of magnetic nanoparticles,
• wherein the processing module generates a waveform that controls the supply of current from the power module to the magnetic probe;
• wherein the processing module receives a signal from the amplifier that indicates the proximity to the injectable magnetic nanoparticles;
• and
• wherein the magnetic nanoparticles have a mean diameter size of greater than 200 nm thereby not to migrate but remain positioned at the site of introduction.