title: Feasibility of a fast method for B1-inhomogeneity correction for FSPGR sequences.
abstract: The Fast Spoiled Gradient Echo (FSPGR) sequence is often used in MRI to create T1-weighted images. The signal intensity generated by this sequence depends on the applied flip angle. Knowing the correct flip angle is essential for the determination of T1-maps by means of an FSPGR based Variable Flip Angle (VFA) approach. Also, quantitatively determining the concentration of contrast agent in case of Dynamic Contrast Enhanced MRI (DCE-MRI) requires knowledge of the applied flip angle. In both cases, the B1-field (in)homogeneity significantly affects the results. In this paper, we present a new method to obtain both the T1-map and B1-inhomogeneity map using scans that can each be acquired within a breath-hold. We combine two short sequences for T1 quantification: Variable Flip Angle and Look-Locker (LL). The T1-maps obtained from the LL data were used to estimate the B1-inhomogeneity inherently present in the VFA data, which was then used to correct for the VFA method's inaccurate flip angles. This way, a reliable T1-map could be computed, which was validated using both in vitro and in vivo scans. The in vitro results show that the procedure yields a substantially smaller mean deviation in T1 from the T1 measurement's gold standard (the Inversion Recovery method), while the in vivo results show both a more accurate estimation of T1 and a reduction of the influence of the B1-inhomogeneity on the signal intensity.
authors.affiliation: Quantitative Imaging Group, Department of Imaging Physics, Delft University of Technology, The Netherlands. Electronic address: j.j.n.vanschie@tudelft.nl.
authors.forename: Jeroen J N
authors.initials: JJ
authors.lastname: van Schie
authors.affiliation: Department of Radiology, Academic Medical Center Amsterdam, The Netherlands.
authors.forename: Cristina
authors.initials: C
authors.lastname: Lavini
authors.affiliation: Quantitative Imaging Group, Department of Imaging Physics, Delft University of Technology, The Netherlands.
authors.forename: Lucas J
authors.initials: LJ
authors.lastname: van Vliet
authors.affiliation: Quantitative Imaging Group, Department of Imaging Physics, Delft University of Technology, The Netherlands; Department of Radiology, Academic Medical Center Amsterdam, The Netherlands.
authors.forename: Frans M
authors.initials: FM
authors.lastname: Vos
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D003287:Contrast Media / Q000737:chemistry; D005240:Feasibility Studies; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016013:Likelihood Functions; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D012119:Respiration; D012984:Software
chemical_list: D003287:Contrast Media
keywords: B1-inhomogeneity correction; Look–Locker; T1-mapping; Variable flip angle