Quantifying magnetic nanoparticles in non-steady flow by MRI

Abstract

Objective

This 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 methods

The 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.

Results

The 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.

Conclusions

Under 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.