Dataset Information

A generalized slab-wise framework for parallel transmit multiband RF pulse design.

ABSTRACT:

Purpose

We propose a new slab-wise framework to design parallel transmit multiband pulses for volumetric simultaneous multislice imaging with a large field of view along the slice direction (FOVs).

Theory and methods

The slab-wise framework divides FOVs into a few contiguous slabs and optimizes pulses for each slab. Effects of relevant design parameters including slab number and transmit B1 (B1+) mapping slice placement were investigated for human brain imaging by designing pulses with global or local SAR control based on electromagnetic simulations of a 7T head RF array. Pulse design using in vivo B1+ maps was demonstrated and evaluated with Bloch simulations.

Results

RF performance with respect to SAR reduction or B1+ homogenization across the entire human brain improved with increasing slabs; however, this improvement was nonlinear and leveled off at ∼12 slabs when the slab thickness reduced to ∼12 mm. The impact of using different slice placements for B1+ mapping was small.

Conclusion

Compared with slice-wise approaches where each of the many imaging slices requires both B1+ mapping and pulse optimization, the proposed slab-wise design framework attained comparable RF performance while drastically reducing the number of required pulses; therefore, it can be used to increase time efficiency for B1+ mapping, pulse calculation, and sequence preparation.

SUBMITTER: Wu X

PROVIDER: S-EPMC4654723 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Publications

A generalized slab-wise framework for parallel transmit multiband RF pulse design.

Wu Xiaoping X Schmitter Sebastian S Auerbach Edward J EJ Uğurbil Kâmil K Van de Moortele Pierre-François PF

Magnetic resonance in medicine 20150520 4

<h4>Purpose</h4>We propose a new slab-wise framework to design parallel transmit multiband pulses for volumetric simultaneous multislice imaging with a large field of view along the slice direction (FOVs).<h4>Theory and methods</h4>The slab-wise framework divides FOVs into a few contiguous slabs and optimizes pulses for each slab. Effects of relevant design parameters including slab number and transmit B1 (B1+) mapping slice placement were investigated for human brain imaging by designing pulses ...[more]

PMID: 25994797

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Project description:PurposeChemical exchange saturation transfer (CEST) measurements at ultra-high field (UHF) suffer from strong saturation inhomogeneity. Retrospective correction of this inhomogeneity is possible to some extent, but requires a time-consuming repetition of the measurement. Here, we propose a calibration-free parallel transmit (pTx)-based saturation scheme that homogenizes the saturation over the imaging volume, which we call PUlse design for Saturation Homogeneity utilizing Universal Pulses (PUSHUP).TheoryMagnetization transfer effects depend on the saturation B1rms$$ {\mathrm{B}}_1^{\mathrm{rms}} $$ . PUSHUP homogenizes the saturation B1rms$$ {\mathrm{B}}_1^{\mathrm{rms}} $$ by using multiple saturation pulses with alternating B1$$ {\mathrm{B}}_1 $$ -shims. Using a database of B1$$ {\mathrm{B}}_1 $$ maps, universal pulses are calculated that remove the necessity of time-consuming, subject-based pulse calculation during the measurement.MethodsPUSHUP was combined with a whole-brain three-dimensional-echo planar imaging (3D-EPI) readout. Two PUSHUP saturation modules were calculated by either applying whole-brain or cerebellum masks to the database maps. The saturation homogeneity and the group mean CEST amplitudes were calculated for different B1$$ {\mathrm{B}}_1 $$ -correction methods and were compared to circular polarized (CP) saturation in five healthy volunteers using an eight-channel transmit coil at 7 Tesla.ResultsIn contrast to CP saturation, where accurate CEST maps were impossible to obtain in the cerebellum, even with extensive B1$$ {\mathrm{B}}_1 $$ -correction, PUSHUP CEST maps were artifact-free throughout the whole brain. A 1-point retrospective B1$$ {\mathrm{B}}_1 $$ -correction, that does not need repeated measurements, sufficiently removed the effect of residual saturation inhomogeneity.ConclusionThe presented method allows for homogeneous whole-brain CEST imaging at 7 Tesla without the need of a repetition-based B1$$ {\mathrm{B}}_1 $$ -correction or online pulse calculation. With the fast 3D-EPI readout, whole-brain CEST imaging with 45 saturation offsets is possible at 1.6 mm resolution in under 4 min.

Dataset Information

A generalized slab-wise framework for parallel transmit multiband RF pulse design.

Purpose

Theory and methods

Results

Conclusion

Publications

A generalized slab-wise framework for parallel transmit multiband RF pulse design.

Similar Datasets

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