title: Optimizing signal-to-noise ratio of high-resolution parallel single-shot diffusion-weighted echo-planar imaging at ultrahigh field strengths.
abstract: The potential signal-to-noise ratio (SNR) gain at ultrahigh field strengths offers the promise of higher image resolution in single-shot diffusion-weighted echo-planar imaging the challenge being reduced T(2) and T(2) * relaxation times and increased B(0) inhomogeneity which lead to geometric distortions and image blurring. These can be addressed using parallel imaging (PI) methods for which a greater range of feasible reduction factors has been predicted at ultrahigh field strengths-the tradeoff being an associated SNR loss. Using comprehensive simulations, the SNR of high-resolution diffusion-weighted echo-planar imaging in combination with spin-echo and stimulated-echo acquisition is explored at 7 T and compared to 3 T. To this end, PI performance is simulated for coil arrays with a variable number of circular coil elements. Beyond that, simulations of the point spread function are performed to investigate the actual image resolution. When higher PI reduction factors are applied at 7 T to address increased image distortions, high-resolution imaging benefits SNR-wise only at relatively low PI reduction factors. On the contrary, it features generally higher image resolutions than at 3 T due to smaller point spread functions. The SNR simulations are confirmed by phantom experiments. Finally, high-resolution in vivo images of a healthy volunteer are presented which demonstrate the feasibility of higher PI reduction factors at 7 T in practice.
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland. reischauer@biomed.ee.ethz.ch
authors.forename: Carolin
authors.initials: C
authors.lastname: Reischauer
authors.forename: Robert S
authors.initials: RS
authors.lastname: Vorburger
authors.forename: Bertram J
authors.initials: BJ
authors.lastname: Wilm
authors.forename: Thomas
authors.initials: T
authors.lastname: Jaermann
authors.forename: Peter
authors.initials: P
authors.lastname: Boesiger
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio