Yoojin Lee1, Yeji Han1, HyunWook Park1, Hidehiro Watanabe2, Michael Garwood3, Jang-Yeon Park4. 1. Department of Electrical Engineering, Korean Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea. 2. Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, Japan. 3. The Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA. 4. School of Biomedical Engineering, College of Biomedical and Health Science, Research Institute of Biomedical Engineering, Konkuk University, Chungju, Korea (ROK).
Abstract
PURPOSE: To propose a new phase-based B1-mapping method that exploits phase information created by hyperbolic secant (HS) pulses in conventional 2D spin-echo imaging. METHODS: In this B1-mapping method, HS pulses are used to accomplish π/2 excitation and π refocusing in standard multislice spin-echo imaging. When setting the ratio of pulse lengths of the π/2 and π HS pulses to 2:1, the spin-echo phase is independent of offset frequency and varies as a function of B1 strength. To eliminate undesired phase accumulations induced by unknown factors other than the B1 strength, two spin-echo images are acquired using HS pulses applied with opposite frequency-sweep directions, and the resulting phase images are subtracted from each other. To demonstrate the performance of the proposed method, phantom and in vivo experiments were performed using a surface coil and a volume coil. RESULTS: The B1 maps obtained by using the proposed method were in accordance with the B1 maps obtained using previous methods in both phantom and in vivo experiments. CONCLUSION: The proposed method is easy to implement without any sequence modification, is insensitive to B0 inhomogeneity and chemical shift, and is robust in a reasonably wide range of B1 field strength.
PURPOSE: To propose a new phase-based B1-mapping method that exploits phase information created by hyperbolic secant (HS) pulses in conventional 2D spin-echo imaging. METHODS: In this B1-mapping method, HS pulses are used to accomplish π/2 excitation and π refocusing in standard multislice spin-echo imaging. When setting the ratio of pulse lengths of the π/2 and π HS pulses to 2:1, the spin-echo phase is independent of offset frequency and varies as a function of B1 strength. To eliminate undesired phase accumulations induced by unknown factors other than the B1 strength, two spin-echo images are acquired using HS pulses applied with opposite frequency-sweep directions, and the resulting phase images are subtracted from each other. To demonstrate the performance of the proposed method, phantom and in vivo experiments were performed using a surface coil and a volume coil. RESULTS: The B1 maps obtained by using the proposed method were in accordance with the B1 maps obtained using previous methods in both phantom and in vivo experiments. CONCLUSION: The proposed method is easy to implement without any sequence modification, is insensitive to B0 inhomogeneity and chemical shift, and is robust in a reasonably wide range of B1 field strength.
Authors: Efraín Torres; Taylor Froelich; Paul Wang; Lance DelaBarre; Michael Mullen; Gregory Adriany; Daniel Cosmo Pizetta; Mateus José Martins; Edson Luiz Géa Vidoto; Alberto Tannús; Michael Garwood Journal: Magn Reson Med Date: 2021-09-09 Impact factor: 4.668
Authors: Lucia I Navarro de Lara; Laleh Golestanirad; Sergey N Makarov; Jason P Stockmann; Lawrence L Wald; Aapo Nummenmaa Journal: Magn Reson Med Date: 2020-01-23 Impact factor: 4.668