Benedikt A. Poser1, Soeren Johst2, Weiran Deng1, Stephan Orzada2, Mark E. Ladd2, 3, Victor Andrew Stenger1
1John A Burns School of Medicine, University of Hawaii, Honolulu, HI, United States; 2Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany; 3Department of Diagnostic and Interventional Radiology and Neuroradiology,, University Hospital Essen, Essen, Germany
Gradient-echo BOLD fMRI suffers signal voids in regions of strong susceptibility variation e.g. near ear canals and frontal sinuses. z-shimming can correct this by applying a z-gradient moment to counteract the local background gradient. The global correction affects all spins and dephases originally intact signal, hence an intermediate compromise is required.