ISME—incoherent sampling of multi‐echo data to minimize cardiac‐induced noise in brain maps of R2* R₂^ and magnetic susceptibility

Abstract Purpose Maps of the MRI parameters and magnetic susceptibility () enable the investigation of microscopic tissue changes in brain disease. However, cardiac‐induced signal instabilities increase the variability of brain maps of and . In this study, we introduce incoherent sampling of multi‐echo data (ISME)—a sampling strategy that minimizes the level of cardiac‐induced instabilities in brain maps of and . Methods ISME uses phase‐encoding gradients to shift the k‐space frequency of the acquired data between consecutive readouts of a multi‐echo train. As a result, the multi‐echo data at a given k‐space index are acquired at different phases of the cardiac cycle. We compare the variability of and maps acquired with ISME and with standard multi‐echo trajectories in N = 10 healthy volunteers. We investigate the effect of both trajectories on the spatial aliasing of pulsating MR signals and propose a weighted least‐squares approach for the estimation of that accounts for the increase of the residuals with echo time. Results ISME reduces the variability of and maps across repetitions by 25%/26%/21% and 24%/32%/23% in the cerebellum/brainstem/whole brain, respectively. With ISME, the spatial aliasing of pulsating MR signals is incoherent between raw echo images, leading to visually sharper maps. The proposed weighted least‐squares approach for the estimation of reduces the dependence of the fitting residuals on echo time and the variability of by an additional 3%/2%/1% in the cerebellum/brainstem/whole brain. Conclusion ISME allows the mitigation of cardiac‐induced signal instabilities in brain maps of and , improving reproducibility.