Objective: To determine accurate quantitative transverse relaxation times (T2) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain.
Methods: A method for T2 mapping from retrospective proton density (PD) and T2-weighted fast spin echo images was recently introduced, but requires measurement of flip angles. We examined whether 1.5T flip angle variation in brain can be predicted, thus enabling T2 analysis of historical PD and T2-weighted images without a concurrent flip angle map. After method validation in healthy volunteers, retrospective longitudinal T2 analysis was performed in 14 MS subjects over seven years. Changes in patient T2 values were compared with brain atrophy, T2 lesion load and disability score in MS.
Results: Similar flip angle maps across volunteers enabled retrospective T2 from PD and T2-weighted images even when different refocusing angles were used. Over seven years, significant T2 changes of 2-4% were observed when using T2 modelling and the 7-year effect size for globus pallidus T2 was 0.56, which was more significant than brain atrophy. No significant T2 results were found when using exponential fit, which cannot account for refocusing angle variation. Moreover, change is T2 in globus pallidus and internal capsule correlated with MS disability score over time when using T2 modelling.
Conclusions: Accurate quantitative T2 can be extracted from standard clinical 1.5T MRI exams that include PD and T2-weighted imaging even when no flip angle map is available. This method was applied retrospectively to examine seven year changes in MS.
Keywords: Atrophy; B(1) mapping; Brain iron; Multiple sclerosis; Proton density; T(2) mapping; T(2)-weighting.
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