Christina M Lewis1, Samuel A Hurley1, M Elizabeth Meyerand1,2, Cheng Guan Koay1. 1. Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA. 2. Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Abstract
PURPOSE: Define criteria for selection of optimal flip angle sets for T1 estimation and evaluate effects on T1 mapping. THEORY AND METHODS: Flip angle sets for spoiled gradient echo-based T1 mapping were selected by minimizing T1 estimate variance weighted by the joint density of M0 and T1 in an initial acquisition. The effect of optimized flip angle selection on T1 estimate error was measured using simulations and experimental data in the human and rat brain. RESULTS: For two-point acquisitions, optimized angle sets were similar to those proposed by other groups and, therefore, performed similarly. For multipoint acquisitions, optimal angle sets for T1 mapping in the brain consisted of a repetition of two angles. Implementation of optimal angles reduced T1 estimate variance by 30-40% compared with a multipoint acquisition using a range of angles. Performance of the optimal angle set was equivalent to that of a repetition of the two-angle set selected using criteria proposed by other researchers. CONCLUSION: Repetition of two carefully selected flip angles notably improves the precision of resulting T1 estimates compared with acquisitions using a range of flip angles. This work provides a flexible and widely applicable optimization method of particular use for those who repeatedly perform T1 estimation. Magn Reson Med 76:792-802, 2016.
PURPOSE: Define criteria for selection of optimal flip angle sets for T1 estimation and evaluate effects on T1 mapping. THEORY AND METHODS: Flip angle sets for spoiled gradient echo-based T1 mapping were selected by minimizing T1 estimate variance weighted by the joint density of M0 and T1 in an initial acquisition. The effect of optimized flip angle selection on T1 estimate error was measured using simulations and experimental data in the human and rat brain. RESULTS: For two-point acquisitions, optimized angle sets were similar to those proposed by other groups and, therefore, performed similarly. For multipoint acquisitions, optimal angle sets for T1 mapping in the brain consisted of a repetition of two angles. Implementation of optimal angles reduced T1 estimate variance by 30-40% compared with a multipoint acquisition using a range of angles. Performance of the optimal angle set was equivalent to that of a repetition of the two-angle set selected using criteria proposed by other researchers. CONCLUSION: Repetition of two carefully selected flip angles notably improves the precision of resulting T1 estimates compared with acquisitions using a range of flip angles. This work provides a flexible and widely applicable optimization method of particular use for those who repeatedly perform T1 estimation. Magn Reson Med 76:792-802, 2016.
Authors: Fang Liu; Rajeev Chaudhary; Samuel A Hurley; Alejandro Munoz Del Rio; Andrew L Alexander; Alexey Samsonov; Walter F Block; Richard Kijowski Journal: J Magn Reson Imaging Date: 2013-09-23 Impact factor: 4.813
Authors: Nikola Stikov; Mathieu Boudreau; Ives R Levesque; Christine L Tardif; Joëlle K Barral; G Bruce Pike Journal: Magn Reson Med Date: 2014-02-27 Impact factor: 4.668