A characterization of cardiac‐induced noise in R2* maps of the brain

Abstract

AbstractPurposeCardiac pulsation increases the noise level in brain maps of the transverse relaxation rate R2*. Cardiac‐induced noise is challenging to mitigate during the acquisition of R2* mapping data because its characteristics are unknown. In this work, we aim to characterize cardiac‐induced noise in brain maps of the MRI parameter R2*.MethodsWe designed a sampling strategy to acquire multi‐echo 3D data in 12 intervals of the cardiac cycle, monitored with a fingertip pulse‐oximeter. We measured the amplitude of cardiac‐induced noise in this data and assessed the effect of cardiac pulsation on R2* maps computed across echoes. The area of k‐space that contains most of the cardiac‐induced noise in R2* maps was then identified. Based on these characteristics, we introduced a tentative sampling strategy that aims to mitigate cardiac‐induced noise in R2* maps of the brain.ResultsIn inferior brain regions, cardiac pulsation accounts for R2* variations of up to 3 s−1 across the cardiac cycle (i.e., ∼35% of the overall variability). Cardiac‐induced fluctuations occur throughout the cardiac cycle, with a reduced intensity during the first quarter of the cycle. A total of 50% to 60% of the overall cardiac‐induced noise is localized near the k‐space center (k < 0.074 mm−1). The tentative cardiac noise mitigation strategy reduced the variability of R2* maps across repetitions by 11% in the brainstem and 6% across the whole brain.ConclusionWe provide a characterization of cardiac‐induced noise in brain R2* maps that can be used as a basis for the design of mitigation strategies during data acquisition.