Quantitative T₁ and proton density mapping with direct calculation of radiofrequency coil transmit and receive profiles from two-point variable flip angle data

Quantitative T₁ mapping of brain tissue is frequently based on the variable flip angle (VFA) method, acquiring spoiled gradient echo (GE) datasets at different excitation angles. However, accurate T₁ calculation requires a knowledge of the sensitivity profile B₁ of the radiofrequency (RF) transmit coil. For an additional derivation of proton density (PD) maps, the receive coil sensitivity profile (RP) must also be known. Mapping of B₁ and RP increases the experiment duration, which may be critical when investigating patients. In this work, a method is presented for the direct calculation of B₁ and RP from VFA data. Thus, quantitative maps of T₁, PD, B₁ and RP can be obtained from only two spoiled GE datasets. The method is based on: (1) the exploitation of the linear relationship between 1/PD and 1/T₁ in brain tissue and (2) the assumption of smoothly varying B₁ and RP, so that a large number of data points can be fitted across small volume elements where B₁ and RP are approximately constant. The method is tested and optimized on healthy subjects.