title: DTI at 7 and 3 T: systematic comparison of SNR and its influence on quantitative metrics.
abstract: Diffusion tensor imaging (DTI) and advanced related methods such as diffusion spectrum and kurtosis imaging are limited by low signal-to-noise ratio (SNR) at conventional field strengths. DTI at 7 T can provide increased SNR; however, B0 and B1 inhomogeneity and shorter T2⁎ still pose formidable challenges. The purpose of this study was to quantify and compare SNR at 7 and 3 T for different parallel imaging reduction factors, R, and TE, and to evaluate SNRs influences on fractional anisotropy (FA) and apparent diffusion coefficient (ADC). We found that R>4 at 7 T and R≥2 at 3 T were needed to reduce geometric distortions due to B0 inhomogeneity. For these R at 7 T, SNR was 70-90 for b=0 s/mm(2) and 22-28 for b=1000s/mm(2) in central brain regions. SNR was lower at 3 T (40 for b=0 s/mm(2) and 15 for b=1000 s/mm(2)) and in lateral brain regions at 7 T due to B1 inhomogeneity. FA and ADC did not change with MRI field strength, SENSE factor or TE in the tested range. However, the coefficient of variation for FA increased for SNR <15 and for SNR <10 in ADC, consistent with published theoretical studies. Our study demonstrates that 7 T is advantageous for DTI and lays the groundwork for further development. Foremost, future work should further address challenges with B0 and B1 inhomogeneity to take full advantage for the increased SNR at 7 T.
authors.affiliation: Department of Radiology, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Seongjin
authors.initials: S
authors.lastname: Choi
authors.forename: Dustin T
authors.initials: DT
authors.lastname: Cunningham
authors.forename: Francisco
authors.initials: F
authors.lastname: Aguila
authors.forename: John D
authors.initials: JD
authors.lastname: Corrigan
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bogner
authors.forename: W Jerry
authors.initials: WJ
authors.lastname: Mysiw
authors.forename: Michael V
authors.initials: MV
authors.lastname: Knopp
authors.forename: Petra
authors.initials: P
authors.lastname: Schmalbrock
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016880:Anisotropy; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged