title: Factors influencing flip angle mapping in MRI: RF pulse shape, slice-select gradients, off-resonance excitation, and B0 inhomogeneities.
abstract: To understand the various effects that influence actual flip angles, and correct for these effects, it is important to precisely quantify the MRI parameters (such as T1, T2, and perfusion). In this paper actual flip angle maps are calculated using a conventional gradient-echo (GRE) sequence with different radiofrequency (RF) pulse shapes (Gaussian, sinc, and truncated-sinc), slice-selection gradients, off-resonance excitations, and B0 field inhomogeneities. The experimental results demonstrate that RF pulse shapes significantly affect the flip angle distribution and calibration factors. Off-resonance RF excitations, B0 nonuniformities, and slice-selection gradients can lead to degradations in the signal intensities of the images used to map the flip angle, and potentially introduce a bias and increased variance in the measured flip angles.
authors.affiliation: Department of Diagnostic Radiology, Yale University School Medical Center, New Haven, Connecticut 06520-8042, USA. Jinghua.wang@yale.edu
authors.forename: Jinghua
authors.initials: J
authors.lastname: Wang
authors.forename: Weihua
authors.initials: W
authors.lastname: Mao
authors.forename: Maolin
authors.initials: M
authors.lastname: Qiu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Smith
authors.forename: R Todd
authors.initials: RT
authors.lastname: Constable
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves