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Objective: To determine accurate quantitative transverse relaxation times (T 2 ) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain., Methods: A method for T 2 mapping from retrospective proton density (PD) and T 2 -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 T 2 analysis of historical PD and T 2 -weighted images without a concurrent flip angle map. After method validation in healthy volunteers, retrospective longitudinal T 2 analysis was performed in 14 MS subjects over seven years. Changes in patient T 2 values were compared with brain atrophy, T 2 lesion load and disability score in MS., Results: Similar flip angle maps across volunteers enabled retrospective T 2 from PD and T 2 -weighted images even when different refocusing angles were used. Over seven years, significant T 2 changes of 2-4% were observed when using T 2 modelling and the 7-year effect size for globus pallidus T 2 was 0.56, which was more significant than brain atrophy. No significant T 2 results were found when using exponential fit, which cannot account for refocusing angle variation. Moreover, change is T 2 in globus pallidus and internal capsule correlated with MS disability score over time when using T 2 modelling., Conclusions: Accurate quantitative T 2 can be extracted from standard clinical 1.5T MRI exams that include PD and T 2 -weighted imaging even when no flip angle map is available. This method was applied retrospectively to examine seven year changes in MS., (Copyright © 2016 Elsevier Inc. All rights reserved.)

High-pass filtering is required for the removal of background field inhomogeneities in magnetic resonance phase images. This high-pass filtering smooths across boundaries between areas with large differences in phase. The most prominent boundary is the surface of the brain where areas with large phase values inside the brain are located close to areas outside the brain where the phase is, on average, zero. Cortical areas, which are of great interest in brain MRI, are therefore often degraded by high-pass filtering. Here, we propose the use of the bilateral filter for the high-pass filtering step. The bilateral filter is essentially a Gaussian filter that stops smoothing at boundaries. We show that the bilateral filter improves image quality at the brain's surface, without sacrificing contrast within the brain., (Copyright © 2011 Elsevier Inc. All rights reserved.)