Rüdiger Stirnberg1, Philipp Ehses1, Eberhard Daniel Pracht1, and Tony Stöcker1,2
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, 2Department of Physics and Astronomy, University of Bonn, Bonn, Germany
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, 2Department of Physics and Astronomy, University of Bonn, Bonn, Germany
We propose fast 3D Actual Flip angle
Echo Planar Imaging (AFEPI) with CAIPIRINHA acceleration and arbitrary
EPI factor. In-vivo experiments at 7T show that 2.5mm isotropic whole-head FA
maps obtained in about 10s are feasible with negligible signal dropouts and negligible
distortions.
Fig.
3 Sagittal example slice of S(TR1) magnitude images and
corresponding FA maps for 5mm isotropic AFI (A, top) and AFEPI protocols at
2.5mm (B,C) and 5mm (D,E) isotropic resolution without distortion correction. Regardless of TE and
segmentation factor, major signal dropouts in the FA maps of 5mm AFEPI scans
with anterior-posterior PE direction make those FA maps unreliable above the
sphenoid sinus. The 2.5mm AFEPI maps match well with the AFI reference maps,
again regardless of TE and segmentation. [Open figure to see both PE directions as animated GIF.]
Fig. 1 Schematic sequence diagram of the AFI sequence (top) with optional
multi-echo extension (dotted outlines), and the proposed AFEPI sequence with y-
and a z-blips (red) to achieve skipped-CAIPI sampling (bottom). Spoiler
gradient pulses (shaded gray) correspond to 6π/2π/2π
(RO/PE/3D) and n times increased voxel dephasing at the end of TR1 and TR2,
respectively2. For simplicity, an example EF=5 and n=TR2/TR1=3 is displayed.
