Improving T2-Weighted Imaging at High Field Through the Use of kT-Points

PurposeAt 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 (k(T)-points) were integrated into a 3D variable flip angle turbo spin echo sequence. MethodsThe excitation and refocusing hard pulses of a variable flip angle turbo spin echo sequence were replaced with k(T)-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 k(T)-point configurations. ResultsSimulations 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. ConclusionThis 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 k(T)-point pulses. Magn Reson Med 71:1478-1488, 2014. (c) 2013 Wiley Periodicals, Inc.