Quantifying magnetic nanoparticles in non-steady flow by MRI

ObjectiveThis work compares the measured $${{R}_{2}^*}$$ of magnetic nanoparticles to their corresponding theoretical values in both gel phantoms and dynamic water flows on the basis of the static dephasing theory.Materials and methodsThe magnetic moment of a nanoparticle solution was measured by a magnetometer. The $${{R}_{2}^*}$$ of the nanoparticle solution doped in a gel phantom was measured at both 1.5 and 4.7 T. A total of 12 non-steady state flow experiments with different nanoparticle concentrations were conducted. The $${{R}_{2}^*}$$ at each time point was measured.ResultsThe theoretical $${{R}_{2}^*}$$ on the basis of the magnetization of nanoparticles measured by the magnetometer agree within 11% of MRI measurements in the gel phantom study, a significant improvement from previous work. In dynamic flow experiments, the total $${{R}_{2}^*}$$ calculated from each experiment agrees within 15% of the theoretical $${{R}_{2}^*}$$ for 10 of the 12 cases. The MRI phase values are also reasonably predicted by the theory. The diffusion effect does not seem to contribute significantly.ConclusionsUnder certain situations with known $${{R}_{2}^*}$$ , the static dephasing theory can be used to quantify the susceptibility or concentration of nanoparticles in either a static or dynamic flow environment at a given time point. This approach may be applied to in vivo studies.