Quantifying iron-oxide nanoparticles at high concentration based on longitudinal relaxation using a three-dimensional SWIFT look-locker sequence

Abstract

Purpose: Iron-oxide nanoparticles (IONPs) have proven utility as contrast agents in many MRI applications. Previous quantitative IONP mapping has been performed using mainly T2* mapping methods. However, in applications requiring high IONP concentrations, such as magnetic nanoparticles based thermal therapies, conventional pulse sequences are unable to map T 2* because the signal decays too rapidly. In this article, sweep imaging with Fourier transformation (SWIFT) sequence is combined with the Look-Locker method to map T1 of IONPs in high concentrations. Methods: T1 values of agar containing IONPs in different concentrations were measured with the SWIFT Look-Locker method and with inversion recovery spectroscopy. Precisions of Look-Locker and variable flip angle (VFA) methods were compared in simulations. Results: The measured R 1 (=1/T1) has a linear relationship with IONP concentration up to 53.6 mM of Fe. This concentration exceeds concentrations measured in previous work by almost an order of magnitude. Simulations show SWIFT Look-Locker method is also much less sensitive to B1 inhomogeneity than the VFA method. Conclusion: SWIFT Look-Locker can accurately measure T1 of IONP concentrations ≤53.6 mM. By mapping T 1 as a function of IONP concentration, IONP distribution maps might be used in the future to plan effective magnetic nanoparticle hyperthermia therapy. © 2014 Wiley Periodicals, Inc.