Sensitivity of 2D-Selective RF Excitations for Inner-Field-of-View Diffusion-Weighted Imaging to Field Inhomogeneities

Inner-field-of-view techniques based on 2D-selective RF (2DRF) excitations reduce geometric distortions of echo-planar imaging and improve diffusion-weighted imaging of the human spinal cord. A comparison of two common approaches revealed that a setup with the 2DRF excitation collinear to the image plane suffers from a reduced signal-to-noise ratio (SNR) for tall slice stacks. In this study, it is shown that the SNR loss is related to the larger sensitivity of the corresponding 2DRF excitation to frequency offsets caused by field inhomogeneities and is particularly pronounced for the large fields-of-excitation and 2DRF pulse durations needed for tall slice stacks.