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Magn Reson Med. 2014 Apr;71(4):1478-88. doi: 10.1002/mrm.24805. Epub 2013 Jun 20.

Improving T2 -weighted imaging at high field through the use of kT -points.

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  • 1Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.

Abstract

PURPOSE:

At high magnetic field strengths (B(0) ≥ 3 T), the shorter radiofrequency wavelength produces an inhomogeneous distribution of the transmit magnetic field. This can lead to variable contrast across the brain which is particularly pronounced in T(2) -weighted imaging that requires multiple radiofrequency pulses. To obtain T(2) -weighted images with uniform contrast throughout the whole brain at 7 T, short (2-3 ms) 3D tailored radiofrequency pulses (kT -points) were integrated into a 3D variable flip angle turbo spin echo sequence.

METHODS:

The excitation and refocusing "hard" pulses of a variable flip angle turbo spin echo sequence were replaced with kT -point pulses. Spatially resolved extended phase graph simulations and in vivo acquisitions at 7 T, utilizing both single channel and parallel-transmit systems, were used to test different kT -point configurations.

RESULTS:

Simulations indicated that an extended optimized k-space trajectory ensured a more homogeneous signal throughout images. In vivo experiments showed that high quality T(2) -weighted brain images with uniform signal and contrast were obtained at 7 T by using the proposed methodology.

CONCLUSION:

This work demonstrates that T(2) -weighted images devoid of artifacts resulting from B(1)(+) inhomogeneity can be obtained at high field through the optimization of extended kT -point pulses.

Copyright © 2013 Wiley Periodicals, Inc.

KEYWORDS:

B1+ inhomogeneity correction; T2-weighted imaging; TSE sequence; kT-points

PMID:
23788025
[PubMed - indexed for MEDLINE]
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