Quantitative R2∗ MRI of the liver with rician noise models for evaluation of hepatic iron overload: Simulation, phantom, and early clinical experience

Abstract

Purpose To compare Rician and non-Rician noise models for quantitative R2∗ magnetic resonance imaging (MRI), in a simulation, phantom, and human study. Materials and Methods Synthetic 12-echo spoiled GRE (SGRE) datasets were generated with various R2∗ rates (0-2000 sec-1) at a signal-to-noise ratio (SNR) of 50, 20, 10, and 5. Phantoms of different MnCl2 concentrations (0-25 mM) were constructed and imaged using a 12-echo 3D SGRE sequence at 1.5T. Increasing levels of synthetic noise was added to the original data to simulate sequentially lower SNR conditions. Sixteen patients with suspected or known iron overload were imaged using 12-echo 3D SGRE at 1.5T. Various R2∗ quantification methods, based on Rician and non-Rician noise models, were compared in the simulation, phantom, and human datasets. Results Non-Rician R2∗ estimates were variably inaccurate in the high R2∗ range (>500 sec-1), with SNR-dependent linear goodness-of-fit statistic (R2) of 0.373-0.999. Rician R2∗ estimates were accurate even in the high R2∗ range, with high R2 of 0.940-0.999 regardless of SNR. Non-Rician R2∗ estimates were variably nonlinear at high MnCl2 concentrations, with SNR-dependent R2 of 0.345-0.994. Rician R2∗ estimates were linear even at high MnCl2 concentrations, with high R2 of 0.923-0.994 regardless of SNR. Between-method agreement of the R2∗ estimates was excellent in patients with low ferritin but poor in patients with high ferritin. Rician R2∗ estimates had excellent correlation with ferritin (r = 0.966 P < 0.001). Conclusion Rician R2∗ estimates were most consistent in the high R2∗ conditions and under varying SNR, and may be more reliable when high iron load is suspected.