Single-shot EPI with signal recovery from the susceptibility-induced losses.
A major problem in the gradient-recalled echo-planar imaging (EPI) method that also uses a long echo time (TE) is the severe signal loss in regions with large static field inhomogeneities. These regions include the ventral frontal, medial temporal, and inferior temporal lobes, which experience inhomogeneities induced by susceptibility effects commonly found near air/tissue interfaces. For functional magnetic resonance imaging (fMRI) studies that use both gradient-recalled EPI at relatively long TE and high-field scanners, this signal loss is severe, preventing investigation of certain human cognitive processes that involve these regions, such as memory and attention. Methods have been developed to recover this signal loss; however, most of them require multiple excitations and thus compromise temporal resolution. In this report, a new technique is described which achieves good signal recovery within a single excitation. It is anticipated that this technique will prove useful for fMRI studies in inhomogeneous areas that require high temporal resolution.
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