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  • Title: Improving T2 -weighted imaging at high field through the use of kT -points.
    Author: Eggenschwiler F, O'Brien KR, Gruetter R, Marques JP.
    Journal: Magn Reson Med; 2014 Apr; 71(4):1478-88. PubMed ID: 23788025.
    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.
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