Fluid attenuated inversion recovery (FLAIR) MRI at 7.0 Tesla: comparison with 1.5 and 3.0 Tesla

Abstract

PurposeTo assess fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) at three field strengths, regarding signal-to-noise ratio (SNR), contrast and signal homogeneity, in order to determine the potential gain and current challenges of FLAIR at ultra-high field strength (7 T).MethodsFLAIR images of five healthy volunteers (age 24 ± 4 years, 4 male) were acquired at 1.5 T, 3 T and 7 T. Image homogeneity and visibility of normal brain structures were evaluated. SNR of grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF) were measured in regions not affected by transmit field heterogeneity.ResultsThe SNR (mean ± SD) at 7 T (GM 168 ± 15, WM 125 ± 11) increased slightly more than proportionally, compared with at 1.5 T (GM 30 ± 3, WM 22 ± 2) and 3 T (GM 62 ± 7, WM 44 ± 4). Relative contrast between GM and WM at 7 T (1.35 ± 0.07) was slightly less than at 3 T (1.42 ± 0.14) or 1.5 T (1.37 ± 0.07). Several major fibre bundles became visible at 7 T. One incidentally observed white matter lesion was well visible at all field strengths.ConclusionImage homogeneity remains challenging and should be improved by future technical developments. FLAIR imaging at 7 T yields a high SNR,with better contrast for WM substructures and the iron-bearing basal ganglia, and has potential for good conspicuity of WM lesions.

Generalized Multiple-Layer Appearance of the Cerebral Cortex with 3D FLAIR 7.0-T MR Imaging

“…Similarly, with diffusion-weighted imaging at 3.0 T, a hypointense layer was observed for the primary motor cortex but was not observed in the superior frontal cortex (14). The 3D magnetization-prepared FLAIR sequence at 7.0 T uses long turbo spin-echo trains with low refocusing angles, which results in strong T2 weighting and sensitivity to diffusion (15)(16)(17). The higher SNR at 7.0 T as compared with that at 1.5 or 3.0 T enables SNR to be traded for stronger T2 weighting and, thus, more contrast.…”

Morphology-Specific Discrimination between MS White Matter Lesions and Benign White Matter Hyperintensities Using Ultra-High-Field MRI

“…[14][15][16][17] While advantageous due to the associated higher SNR, imaging at a high field also presents challenges. 18 Susceptibility artifacts near the air-tissue interfaces are amplified at higher fields, rendering information in the phase image unusable in extreme cases.…”

3D T 2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems

“…Results The improvement provided by the dynamic k Tpoints over the static k T -point design and conventional hard 1 3 SAR [6] or 3D-TSE implementations with long RF pulse trains. The presence of spatial B 1 + inhomogeneities at high field results in signal voids and different degrees of contrast between tissues throughout the volume as has been reported and is visible in several studies [5,[7][8][9]. Sequences involving a 3D TSE readout such as the fluid-attenuated inversion recovery (FLAIR) and the double inversion recovery (DIR) are now frequently used in clinical routines; however, usefulness of such sequences is limited by the non-uniform B 1 + profile that propagates throughout the train of RF pulses.…”