Nuclear magnetic resonance systems and methods of use thereof are provided. The systems employ implantable radiofrequency coils (105) and optionally implantable magnets (101). The systems can employ weak permanent magnets and/or permanent magnets that provide magnetic fields that are much less homogeneous than in conventional systems. This allows, for example, for inexpensive and simple probeheads for nuclear magnetic resonance relaxometry with suitable biosensors. The methods of the present invention allow in- vivo magnetic resonance measurements and, in particular, monitoring of analytes and determination of medical diagnostic information, for example, based on determined magnetic resonance parameters.
