Real‐time motion and retrospective coil sensitivity correction for CEST using volumetric navigators (vNavs) at 7T

PURPOSE: To explore the impact of temporal motion‐induced coil sensitivity changes on CEST‐MRI at 7T and its correction using interleaved volumetric EPI navigators, which are applied for real‐time motion correction. METHODS: Five healthy volunteers were scanned via CEST. A 4‐fold correction pipeline allowed the mitigation of (1) motion, (2) motion‐induced coil sensitivity variations, [Formula: see text] , (3) motion‐induced static magnetic field inhomogeneities, ΔB(0), and (4) spatially varying transmit RF field fluctuations, [Formula: see text]. Four CEST measurements were performed per session. For the first 2, motion correction was turned OFF and then ON in absence of voluntary motion, whereas in the other 2 controlled head rotations were performed. During post‐processing [Formula: see text] was removed additionally for the motion‐corrected cases, resulting in a total of 6 scenarios to be compared. In all cases, retrospective ∆B(0) and ‐ [Formula: see text] corrections were performed to compute artifact‐free magnetization transfer ratio maps with asymmetric analysis (MTR(asym)). RESULTS: Dynamic [Formula: see text] correction successfully mitigated signal deviations caused by head motion. In 2 frontal lobe regions of volunteer 4, induced relative signal errors of 10.9% and 3.9% were reduced to 1.1% and 1.0% after correction. In the right frontal lobe, the motion‐corrected MTR(asym) contrast deviated 0.92%, 1.21%, and 2.97% relative to the static case for Δω = 1, 2, 3 ± 0.25 ppm. The additional application of [Formula: see text] correction reduced these deviations to 0.10%, 0.14%, and 0.42%. The fully corrected MTR(asym) values were highly consistent between measurements with and without intended head rotations. CONCLUSION: Temporal [Formula: see text] cause significant CEST quantification bias. The presented correction pipeline including the proposed retrospective [Formula: see text] correction significantly reduced motion‐related artifacts on CEST‐MRI.