Strongly modulating pulses for counteracting RF inhomogeneity at high fields.
TLDR
A new pulse technique for counteracting RF inhomogeneity at high fields is reported, which makes use of the detailed knowledge of the voxels' B1 and B0 amplitude 2D histogram to generate gates where the flip angle is made uniform.Abstract:
A new pulse technique for counteracting RF inhomogeneity at high fields is reported. The pulses make use of the detailed knowledge of the voxels' B(1) and B(0) amplitude 2D histogram to generate, through an optimization procedure, gates where the flip angle is made uniform. Although most approaches to date require the use of parallel transmission, this method does not and therefore offers several advantages. The data necessary for the algorithm to determine an irradiation scheme requires only one transmit B(1) along with a B(0) inhomogeneity measurement. The use of a B(1) and B(0) amplitude 2D histogram instead of their spatial distribution also decreases substantially the complexity of the optimization problem, allowing the algorithm to find an RF solution in less than 30 s. Finally, the optimization procedure is based on an exact calculation and does not use any linear approximation. In this article, the theory behind the method in addition to spoiled gradient echo experimental data at 3T for 3D brain imaging are reported. The images obtained yield a reduction of the standard deviation of the sine of the flip angle by a factor of up to 15 around the desired value, compared to when a standard square pulse calibrated by the scanner is used.read more
Citations
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Journal ArticleDOI
kT -points: short three-dimensional tailored RF pulses for flip-angle homogenization over an extended volume.
Martijn A. Cloos,Martijn A. Cloos,Nicolas Boulant,Michel Luong,Guillaume Ferrand,Eric Giacomini,D. Le Bihan,Alexis Amadon +7 more
TL;DR: Application of kT‐point‐based excitations demonstrated excellent flip angle uniformity for a small target flip angle and with sub‐millisecond durations, making them good candidates for short‐repetition time 3D sequences at high field.
Journal ArticleDOI
Universal pulses: A new concept for calibration-free parallel transmission.
TL;DR: A calibration‐free parallel transmission method is investigated to mitigate the radiofrequency (RF) field inhomogeneity problem in brain imaging at 7 Tesla (T).
Journal ArticleDOI
On Variant Strategies to Solve the Magnitude Least Squares Optimization Problem in Parallel Transmission Pulse Design and Under Strict SAR and Power Constraints
TL;DR: Various two-stage strategies consisting of different initializations and nonlinear programming approaches are investigated, and these incorporate directly the strict SAR and hardware constraints, allowing the use of the proposed approach in routine.
Journal ArticleDOI
Homogeneous non-selective and slice-selective parallel-transmit excitations at 7 Tesla with universal pulses: A validation study on two commercial RF coils.
Vincent Gras,Markus Boland,Alexandre Vignaud,Guillaume Ferrand,Alexis Amadon,Franck Mauconduit,Denis Le Bihan,Tony Stöcker,Nicolas Boulant +8 more
TL;DR: The universal pulses designed in this work confirm their relevance in 3D and 2D protocols with commercially available equipment and become accessible to exploit with more flexibility the potential of UHF for brain imaging.
Journal ArticleDOI
Safety Considerations of 7-T MRI in Clinical Practice.
Michael N. Hoff,Alexander M. McKinney,Frank G. Shellock,Ulrich A. Rassner,Tobias Gilk,Robert E. Watson,Todd D. Greenberg,Jerry W. Froelich,Emanuel Kanal +8 more
TL;DR: The rationale for safety concerns at this field strength are discussed as well as potential approaches to mitigate risk to patients and health care professionals.
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Michael Garwood,Lance Delabarre +1 more
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