The influence of pulse sequence on the relaxation effects of superparamagnetic iron oxide contrast agents

The effects of different pulse sequences and timing parameters on the increase in transverse relaxation rate produced by superparamagnetic iron oxide particles have been studied. Gradient-echo, single spin-echo, and multiple-echo images recorded at 2.0 T were used to evaluate the reduction in signal intensity per unit concentration of iron oxide for different echo times and in different media. For the same echo time, gradient-echo sequences were found to be more than twice as sensitive to the effects of the agent as single spin-echo imaging sequences, while multiple-echo sequences were much less affected than either. Using measurements of the relative effects on different sequences, the contributions of different relaxation mechanisms have been quantified.