B1 Field inhomogeneity correction for qDESS T2 mapping: application to rapid bilateral knee imaging.

Purpose: T 2 mapping is a powerful tool for studying osteoarthritis (OA) changes and bilateral imaging may be useful in investigating the role of between-knee asymmetry in OA onset and progression. The quantitative double-echo in steady-state (qDESS) can provide fast simultaneous bilateral knee T 2 and high-resolution morphometry for cartilage and meniscus. The qDESS uses an analytical signal model to compute T 2 relaxometry maps, which require knowledge of the flip angle (FA). In the presence of B 1 inhomogeneities, inconsistencies between the nominal and actual FA can affect the accuracy of T 2 measurements. We propose a pixel-wise B 1 correction method for qDESS T 2 mapping exploiting an auxiliary B 1 map to compute the actual FA used in the model. Methods: The technique was validated in a phantom and in vivo with simultaneous bilateral knee imaging. T 2 measurements of femoral cartilage (FC) of both knees of six healthy participants were repeated longitudinally to investigate the association between T 2 variation and B 1 . Results: The results showed that applying the B 1 correction mitigated T 2 variations that were driven by B 1 inhomogeneities. Specifically, T 2 left–right symmetry increased following the B 1 correction ( ρ c = 0.74 > ρ c = 0.69). Without the B 1 correction, T 2 values showed a linear dependence with B 1 . The linear coefficient decreased using the B 1 correction (from 24.3 ± 1.6 ms to 4.1 ± 1.8) and the correlation was not statistically significant after the application of the Bonferroni correction (p value > 0.01). Conclusion: The study showed that B 1 correction could mitigate variations driven by the sensitivity of the qDESS T 2 mapping method to B 1 , therefore, increasing the sensitivity to detect real biological changes. The proposed method may improve the robustness of bilateral qDESS T 2 mapping, allowing for an accurate and more efficient evaluation of OA pathways and pathophysiology through longitudinal and cross-sectional studies. [ABSTRACT FROM AUTHOR]