Anatomical brain imaging at 7T using two‐dimensional GRASE

Abstract

GRASE is highly suitable for structural scanning at ultra-high field strengths and is a valid alternative to the commonly used TSE sequence.

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.…”

“…The obtained contrast of the 3D TSE appears reduced when compared to standard 2D TSE [5]. This can be both due to the increased magnetization transfer contrast present on resonance 2D T 2 weighted imaging [6] or to the mixed T 2 − T 1 contrast in the presence of the long echo trains used in 3D TSE imaging.…”

“…The T 2 -weighted images were acquired with a commercially available variable flip-angle 3D TSE sequence known as the sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) sequence [5]. This sequence optimizes the signal evolution of the flip angle train for specified T 1 /T 2 relaxation times and allows longer RF-pulse trains to be used making it possible to efficiently acquire 3D TSE images.…”

“…This imaging technique should benefit from the increased signal-to-noise ratio (SNR) available at high field strengths (B 0 ≥ 3T), allowing acquisitions with higher spatial resolution and hence better visualization of small brain structures. While most clinical applications using TSE contrast are based on 2D TSE and anisotropic voxels (to ensure whole brain coverage within SAR constraints and in clinical acceptable times), remarkable image quality at quasiisotropic spatial resolution has been demonstrated at 7T using various 2D TSE implementations [5], but these have been limited to small z-coverage (~21 mm). One approach to overcome these limitations is the use of simultaneous multi-slice imaging combined with PINS pulses to reduce Abstract Objectives For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B 1 + inhomogeneity.…”

Clinical Neuroimaging Using 7 T MRI: Challenges and Prospects

“…Furthermore, new methods were developed lately to overcome SAR limitation for TSE implementation. For instance, reduction of SAR level on 2‐dimensional TSE can be achieved using gradient and spin echo (GRASE) or RF subpulses . Three‐dimensional T2‐weighted sequences are also promising; however, these different methods are not yet sufficiently developed to be used in clinical routine.…”