LTS SQUID gradiometer system for in vivo magnetorelaxometry

A system for spatially resolved magnetorelaxometry in spatially expanded objects (e.g. for in vivo investigations) in a disturbed environment is presented. The system is based on an LTS SQUID gradiometer with a field gradient sensitivity of 30 fT cm^-1 Hz^-1/2 and an intrinsic balance of some 10^-5. A Helmholtz coil of 80 cm diameter allows the magnetization of the samples with fields up to 7 mT. A nonmagnetic x-y stage (driven by step motors) covers a scanning area of 40 cm × 25 cm. We present spatially resolved measurements of the Néel relaxation of samples (dried ferrofluid) and compare them with model calculations. The data acquisition and monitoring as well as the filtering and fitting procedure are discussed.