Validation of single reference variable flip angle (SR-VFA) dynamic T mapping with T * correction using a novel rotating phantom.

Purpose: To validate single reference variable flip angle (SR-VFA) dynamic T mapping with and without T * correction against inversion recovery (IR) T measurements.

Methods: A custom cylindrical phantom with three concentric compartments was filled with variably doped agar to produce a smooth spatial gradient of the T relaxation rate as a function of angle across each compartment. IR T , VFA T , and B 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. B -corrected SR-VFA and SR-VFA-T * T maps were computed from the sliding window reconstructed images and compared against rotationally registered IR and VFA T maps to determine the percentage error.

Results: Both VFA and SR-VFA-T * T maps fell within 10% of IR T 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 T change had a nonconstant slope. SR-VFA T mapping was found to have similar accuracy as the SR-VFA-T * and VFA methods at low TEs (˜<2 ms), whereas accuracy degraded strongly with later TEs. T * correction of the SR-VFA T maps was found to consistently improve accuracy and precision, especially at later TEs.

Conclusion: SR-VFA-T * dynamic T mapping was found to be accurate against reference IR T measurements within 10% in an agar phantom. Further validation is needed in mixed fat-water phantoms and in vivo.