A Multi-Resolution Comparison of Single-Shot EPI, 3DFFE and PRESTO for fMRI at 7T

INTRODUCTION Single-shot Echo-Planar Imaging (EPI) is the sequence most commonly used for fMRI experiments. At high field, e.g. 7T, magnetic field inhomogeneities cause spins to become out of phase quickly, and distortion and signal dropout become severe [1]. Consequently, single-shot EPI fMRI suffers technical limitations at high field. Here we consider two alternatives to EPI for high field fMRI: 3D Fast Field Echo (FFE), a multi-shot EPI sequence, and 3D PRESTO (Principles of Echo-Shifting with a Train of Observations), a 3DFFE-based sequence that uses echo-shifting to achieve efficient T2* weighting [2][3][4]. Recently Neggers et al. (2008) have demonstrated increased fMRI sensitivity in 3D PRESTO-SENSE compared with single-shot EPI for a low-resolution, full-brain scan at 3T [5]. Even though the observed percent signal change was lower for 3D PRESTO-SENSE compared with EPI, the time course was more stable, leading to better fMRI sensitivity [5]. In light of the SNR benefits associated with increasing B0 and the difficulties facing full-brain single-shot echo planar fMRI at high field, a detailed comparison of EPI and alternate sequences for high field fMRI is warranted. Here we consider the fMRI performance of EPI, 3DFFE, and 3D PRESTO at four different resolutions for a visual and motor fMRI task at 7T.