On the role of physiological fluctuations in quantitative gradient echo MRI: implications for GEPCI, QSM, and SWI.

PURPOSE Physiological fluctuations in biological tissues adversely affect MR images if present during signal acquisition. This problem is especially important for quantitative MRI. The goal of the studies reported in this study was to reduce the contributions of physiological fluctuations in quantitative MRI based on T2* tissue relaxation properties. Specifically, in this study we deal with GEPCI, QSM, and SWI techniques and propose methods allowing for substantial improvement of their results. METHODS We used a navigator imbedded in a multi-gradient-echo sequence to record and correct MR signal phase fluctuations at each phase encoding step. All GEPCI, QSM, and SWI images were then reconstructed from a single acquisition. We used a keyhole-type approach to further average out effects of physiological fluctuations. Voxel spread function technique was used to correct for macroscopic field inhomogeneities. RESULTS Brains of normal subjects and subjects with multiple sclerosis were studied. We demonstrated that our used strategies substantially reduced the width of the R2* = 1/T2* distribution within human brains and significantly improved quantification of tissue damage in multiple sclerosis. We also showed improved quality of the SWI and QSM images. CONCLUSION The strategies used in this study greatly reduced physiologically induced artifacts in GEPCI, QSM, and SWI, improving the reliability of these techniques.