Validation of single reference variable flip angle (SR-VFA) dynamic T1 mapping with T 2* correction using a novel rotating phantom
Michael A. Malmberg, Henrik Odéen, Lorne W. Hofstetter, J. Rock Hadley, Dennis L. Parker
Abstract
Purpose
To validate single reference variable flip angle (SR-VFA) dynamic T1 mapping with and without T 2* correction against inversion recovery (IR) T1 measurements.
Methods
A 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-T 2* 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.
Results
Both VFA and SR-VFA-T 2* 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-T 2* and VFA methods at low TEs (˜<2 ms), whereas accuracy degraded strongly with later TEs. T 2* correction of the SR-VFA T1 maps was found to consistently improve accuracy and precision, especially at later TEs.
Conclusion
SR-VFA-T 2* 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.