Early experience of paramagnetic tracers in ultra low magnetic fields.

Preliminary results on small gadolinium chelates, superparamagnetic particles and protein conjugated paramagnetic agents used at ultra low field imaging are reported. Ultra low magnetic field was found to be highly sensitive to ferromagnetic particles and signal intensity was decreased at 0.03 mg/ml. Small gadolinium complexes caused similar shortening of relaxation time T1 as in higher field strengths. The magnitude of T1 relaxivity was 1.4 to 2.0 times higher when Gd-DTPA was conjugated to proteins.