Alternating Look-Locker for quantitative T1, T1? and B1 3D MRI mapping

Purpose: To develop a new MRI method, entitled alternating Look-Locker (aLL), for quantitative T-1, T-1?, and B-1 3D mapping.Methods: A Look-Locker scheme that alternates magnetization from +Z and -Z axes of the laboratory frame is utilized in combination with a 3D Multi-Band Sweep Imaging with Fourier Transformation (MB-SWIFT) readout. The analytical solution describing the spin evolution during aLL, as well as the correction required for segmented acquisition were derived. The simultaneous B-1 and T-1 mapping are demonstrated on an agar/saline phantom and on an in-vivo rat head. T-1? relaxation was achieved by cyclically applying magnetization preparation (MP) modules consisting of two adiabatic pulses. T-1? values in the rat brain in-vivo and in a gadobenate dimeglumine (Gd-DTPA) phantom were compared to those obtained with a previously introduced steady-state (SS) method.Results: The accuracy and precision of the analytical solution was tested by Bloch simulations. With the application of MP modules, the aLL method provides simultaneous T(1 )and T-1? maps. Conversely, without it, the method can be used for simultaneous T-1 and B-1 mapping. T-1? values were similar with both aLL and SS techniques. However, the aLL method resulted in more robust quantita-tive mapping compared to the SS method. Unlike the SS method, the aLL method does not require additional scans for generating T-1 maps.Conclusion: The proposed method offers a new flexible tool for quantitative map-ping of T-1, T-1?, and B-1. The aLL method can also be used with readout schemes different from MB-SWIFT.