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 ( rho(c) = 0.74 > rho(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.