Reduced slab boundary artifact in multi-slab 3D fast spin-echo imaging

136

Purpose To develop an acquisition scheme for generating magnetic resonance elastography (MRE) displacement data with whole-brain coverage, high spatial resolution, and adequate signal-to-noise ratio (SNR) in a short scan time. Theory and Methods A 3D multislab, multishot acquisition for whole-brain MRE with 2.0 mm isotropic spatial resolution is proposed. The multislab approach allowed for the use of short repetition time to achieve very high SNR efficiency. High SNR efficiency allowed for a reduced acquisition time of only six minutes while the minimum SNR needed for inversion was maintained. Results The mechanical property maps estimated from whole-brain displacement data with nonlinear inversion (NLI) demonstrated excellent agreement with neuroanatomical features, including the cerebellum and brainstem. A comparison with an equivalent 2D acquisition illustrated the improvement in SNR efficiency of the 3D multislab acquisition. The flexibility afforded by the high SNR efficiency allowed for higher resolution with a 1.6 mm isotropic voxel size, which generated higher estimates of brainstem stiffness compared with the 2.0 mm isotropic acquisition. Conclusions The acquisition presented allows for the capture of whole-brain MRE displacement data in a short scan time, and may be used to generate local mechanical property estimates of neuroanatomical features throughout the brain.

Section: Fig 4 Comparison Of T 2 -Weighted Anatomical Images Withmentioning

confidence: 94%

3D multislab, multishot acquisition for fast, whole‐brain MR elastography with high signal‐to‐noise efficiency

Johnson

Holtrop

McGarry

et al. 2013

136

“…Second, interleaved multislab acquisitions are highly sensitive to slab selection profiles and can lead to signal loss at the edges of each slab, which was visible on reformatted images. Such multislab acquisitions can be improved by performing overlapping slab or sliding slab acquisitions. Third, the effect of magnetization transfer and rotating‐frame relaxation in SAMPA T 2 ‐prep need to be further evaluated to improve accuracy of the technique.…”

Section: Discussionmentioning

confidence: 99%

Slice‐selective adiabatic magnetization T₂‐preparation (SAMPA) for efficient T₂‐weighted imaging at ultrahigh field strengths

Dyvorne

Balchandani

2015

Purpose At high field, T2-weighted (T2w) imaging is limited by transmit field inhomogeneity and increased radiofrequency power deposition. In this work we introduce SAMPA (Slice-selective Adiabatic Magnetization T2 PrepAration) and demonstrate its use for efficient brain T2w imaging at 7T. Methods SAMPA was designed by subsampling an optimized B1 insensitive rotation (BIR4) waveform with small tip angle linear subpulses. In order to perform T2w imaging, SAMPA was inserted before a fast gradient echo acquisition. The off-resonance behavior, B1 robustness and slice selectivity of the novel T2 preparation module were analyzed using Bloch simulations. The performance of SAMPA for T2w imaging was demonstrated in phantom experiments as well as in the brains of healthy volunteers at 7T. Results Based on simulations, the proposed design operates at peak B1 of 15 μT and higher, within a 400 Hz bandwidth. T2 values were in strong agreement with spin echo-based T2 mapping in phantom experiments. Whole brain, interleaved multislab 3D imaging could be acquired with 0.8 mm3 isotropic resolution in 5:36 min per T2 weighting. Conclusion Compared with previous adiabatic T2 preparation techniques, SAMPA allows for slice-selectivity, which can lead to efficient and robust acquisitions for T2w imaging at high field.

“…These methods work well in dMRI if long TRs (∼4 s) are used together with large amounts of slab overlap, but they exhibit residual artifacts in shorter TR acquisitions . A variation of the overlapping method shifts the slab by one slice position once all k z phase encoding steps for a designated subset of k y phase encoding steps are acquired to transform the signal modulation in the slice direction to the k y phase encoding direction, using signal demodulation to reduce ghosting artifacts . This method has also been demonstrated in non‐Cartesian sequences .…”

Section: Introductionmentioning

confidence: 99%

Reducing slab boundary artifacts in three‐dimensional multislab diffusion MRI using nonlinear inversion for slab profile encoding (NPEN)

Koopmans

Frost

et al. 2015

PurposeTo propose a method to reduce the slab boundary artifacts in three-dimensional multislab diffusion MRI.MethodsBloch simulation is used to investigate the effects of multiple factors on slab boundary artifacts, including characterization of residual errors on diffusion quantification. A nonlinear inversion method is proposed to simultaneously estimate the slab profile and the underlying (corrected) image.ResultsCorrection results of numerical phantom and in vivo data demonstrate that the method can effectively remove slab boundary artifacts for diffusion data. Notably, the nonlinear inversion is also successful at short TR, a regimen where previously proposed methods (slab profile encoding and weighted average) retain residual artifacts in both diffusion-weighted images and diffusion metrics (mean diffusion coefficient and fractional anisotropy).ConclusionThe nonlinear inversion for removing slab boundary artifacts provides improvements over existing methods, particularly at the short TRs required to maximize SNR efficiency.