Validation of single reference variable flip angle (SR‐VFA) dynamic T1 mapping with T2* correction using a novel rotating phantom

Abstract

AbstractPurposeTo validate single reference variable flip angle (SR‐VFA) dynamic T1 mapping with and without T2* correction against inversion recovery (IR) T1 measurements.MethodsA custom cylindrical phantom with three concentric compartments was filled with variably doped agar to produce a smooth spatial gradient of the T1 relaxation rate as a function of angle across each compartment. IR T1, VFA T1, and B1+ measurements were made on the phantom before rotation, and multi‐echo stack‐of‐radial dynamic images were acquired during rotation via an MRI‐compatible motor. B1+‐corrected SR‐VFA and SR‐VFA‐T2* T1 maps were computed from the sliding window reconstructed images and compared against rotationally registered IR and VFA T1 maps to determine the percentage error.ResultsBoth VFA and SR‐VFA‐T2* T1 maps fell within 10% of IR T1 measurements for a low rotational speed, with a mean accuracy of 2.3% ± 2.6% and 2.8% ± 2.6%, respectively. Increasing rotational speed was found to decrease the accuracy due to increasing temporal smoothing over ranges where the T1 change had a nonconstant slope. SR‐VFA T1 mapping was found to have similar accuracy as the SR‐VFA‐T2* and VFA methods at low TEs (˜<2 ms), whereas accuracy degraded strongly with later TEs. T2* correction of the SR‐VFA T1 maps was found to consistently improve accuracy and precision, especially at later TEs.ConclusionSR‐VFA‐T2* dynamic T1 mapping was found to be accurate against reference IR T1 measurements within 10% in an agar phantom. Further validation is needed in mixed fat–water phantoms and in vivo.