Optimizing signal-to-noise ratio of high-resolution parallel single-shot diffusion-weighted echo-planar imaging at ultrahigh field strengths

• Published in: Magnetic resonance in medicine 2012-03, Vol.67 (3), p.679-690
• Main Authors: Reischauer, Carolin, Vorburger, Robert S., Wilm, Bertram J., Jaermann, Thomas, Boesiger, Peter
• Format: Article
• Language: English
• Subjects: Adult; Brain Mapping - methods; Computer Simulation; Diffusion Magnetic Resonance Imaging - methods; echo-planar imaging; Echo-Planar Imaging - methods; Female; high-resolution diffusion-weighted imaging; Humans; Image Processing, Computer-Assisted; Male; Models, Theoretical; parallel imaging; Phantoms, Imaging; Signal-To-Noise Ratio; ultrahigh field strengths
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.23057

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 T2 and T2* relaxation times and increased B0 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. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.