Alternating Look-Locker for quantitative T 1, T 1ρ and B 1 3D MRI mapping
Lin Wu, Chris Carchi, Shalom Michaeli, Silvia Mangia, Djaudat Idiyatullin
Abstract
Purpose
To develop a new MRI method, entitled alternating Look-Locker (aLL), for quantitative T1, T1ρ, and B1 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 B1 and T1 mapping are demonstrated on an agar/saline phantom and on an in-vivo rat head. T1ρ relaxation was achieved by cyclically applying magnetization preparation (MP) modules consisting of two adiabatic pulses. T1ρ 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 T1 and T1ρ maps. Conversely, without it, the method can be used for simultaneous T1 and B1 mapping. T1ρ values were similar with both aLL and SS techniques. However, the aLL method resulted in more robust quantitative mapping compared to the SS method. Unlike the SS method, the aLL method does not require additional scans for generating T1 maps.
Conclusion
The proposed method offers a new flexible tool for quantitative mapping of T1, T1ρ, and B1. The aLL method can also be used with readout schemes different from MB-SWIFT.