Simultaneous T₁ and B₁⁺ mapping using reference region variable flip angle imaging

Purpose To present a new method that can simultaneously and efficiently measure T₁ and B₁⁺ maps using reference region variable flip angle (RR-VFA) imaging. Methods Assuming T₁ relaxation time in a reference region such as fat is well characterized, and the reference region sufficiently covers smoothly varying B₁⁺ field inhomogeneity, B₁⁺ maps can be measured from VFA images, conventionally used for T₁ measurements. Fat-only images from two-point Dixon acquisitions were used to compute B₁⁺ maps, and the B₁⁺ maps were compared with ones using the double-angle method (DAM) in 22 breast MRI patients at 3T. Additionally, high spatial resolution VFA images were acquired to show T₁ measurements with and without the RR-VFA B₁⁺ correction in six patients. Results RR-VFA is able to generate reliable B₁⁺ maps, similar to those using the conventional DAM. This simultaneous T ₁ and B₁⁺ mapping can also be used to reduce T₁ estimation errors, where T₁ maps have more uniform fibroglandular tissue T₁ and better depiction of heterogeneous T ₁ of breast masses. Conclusion A new method that can measure both T₁ and B₁⁺ maps based on Dixon VFA images is described, offering improved T₁ quantification with no scan time penalty.