Methodology for determination of contrast agent relaxivity using MRI

Abstract

Abstract Knowledge of the longitudinal and transverse relaxivities (r1 and r2) of a contrast agent (CA) is essential for its magnetic characterization. These parameters can be measured using Magnetic Resonance Imaging (MRI) clinical scanners with the advantage of characterizing the CA under the same experimental conditions where it will be employed. Nevertheless, when using MRI, there are several limitations to be considered, and we provide ways to compensate for them to obtain more accurate results. Here, we present a fast and robust methodology to determine the relaxivity of CA solutions using a 3T MRI clinical scanner with a birdcage coil. Relaxivity measurements were performed on a phantom consisting of 5 samples of copper sulfate at different concentrations. We optimized image acquisition for total scan time using three different pulse sequences. Post-processing steps following image acquisition were implemented in a semiautomatic MATLAB toolbox. Relaxation times were estimated using the three-parameter model with the Levenberg-Marquardt algorithm. Statistical comparisons demonstrate good reproducibility and robustness in the relaxivity estimation by each method.