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

Abstract

Purpose: To validate single reference variable flip angle (SR-VFA) dynamic T₁ mapping with and without T₂ * 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-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.

Results: Both 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.

Conclusion: SR-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.

Keywords: MRI-compatible motor; accuracy and precision; agar phantom; dynamic T1 mapping; quantitative T1 mapping; single reference variable flip angle.