PLANET: An Ellipse Fitting Approach for Simultaneous T1 and T2 Mapping Using Phase-Cycled Balanced Steady-State Free Precession

Purpose: To demonstrate the feasibility of a novel, ellipse fitting approach, named PLANET, for simultaneous estimation of relaxation times T1 and T2 from a single 3D phase-cycled balanced steady-state free precession (bSSFP) sequence. Methods: A method is presented in which the elliptical signal model is used to describe the phase-cycled bSSFP steadystate signal. The fitting of the model to the acquired data is reformulated into a linear convex problem, which is solved directly by a linear least squares method, specific to ellipses. Subsequently, the relaxation times T1 and T2, the banding free magnitude, and the off-resonance are calculated from the fitting results. Results: Maps of T1 and T2, as well as an off-resonance and a banding free magnitude can be simultaneously, quickly, and robustly estimated from a single 3D phase-cycled bSSFP sequence. The feasibility of the method was demonstrated in a phantom and in the brain of healthy volunteers on a clinical MR scanner. The results were in good agreement for the phantom, but a systematic underestimation of T1 was observed in the brain. Conclusion: The presented method allows for accurate mapping of relaxation times and off-resonance, and for the reconstruction of banding free magnitude images at realistic signalto- noise ratios. Magn Reson Med 000:000–000, 2017. VC 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made