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

Purpose: T2 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 T2 and high-resolution morphometry for cartilage and meniscus.
The qDESS uses an analytical signal model to compute T2 relaxometry maps, which require knowledge of the flip angle (FA). 
In the presence of B1 inhomogeneities, inconsistencies between the nominal and actual FA can affect the accuracy of T2 measurements.
We propose a pixel-wise B1 correction method for qDESS T2 mapping exploiting an auxiliary B1 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. 
T2 measurements of femoral cartilage (FC) of both knees of six healthy participants were repeated longitudinally to investigate the association between T2 variation and B1.

Results: The results showed that applying the B1 correction mitigated T2 variations that were driven by B1 inhomogeneities. 
Specifically, T2 left-right symmetry increased following the B1 correction (rc = 0.74 > rc = 0.69). Without the B1 correction, T2 values showed a linear dependence with B1. The linear coefficient decreased using the B1 correction (from 24.3 \(\pm\) 1.6 ms to 4.1 \(\pm\) 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 B1 correction could mitigate variations driven by the sensitivity of the qDESS T2 mapping method to B1, therefore increasing the sensitivity to detect real biological changes. The proposed method may improve the robustness of bilateral qDESS T2 mapping, allowing for an accurate and more efficient evaluation of OA pathways and pathophysiology through longitudinal and cross-sectional studies.

This repository contains the raw data for reproducing the results reported in the paper. The data are provided in NIFTI format.

研究目的：T2 mapping是研究骨关节炎（osteoarthritis, OA）病变的有力工具，而双侧膝关节成像可用于探究膝关节间不对称在OA发病与进展中的作用。定量双回波稳态成像（quantitative double-echo in steady-state，简称qDESS）能够快速同时获取双侧膝关节的T2 mapping数据，并实现软骨与半月板的高分辨率形态计量学分析。
定量双回波稳态成像采用解析信号模型计算T2弛豫测绘图，该模型需要知晓翻转角（flip angle, FA）。当存在B1场不均匀性时，名义翻转角与实际翻转角之间的不一致会影响T2测量的准确性。
本研究提出一种逐像素B1校正方法用于qDESS的T2 mapping，利用辅助B1图计算模型中使用的实际翻转角。
研究方法：本技术通过体模实验与在体双侧膝关节同时成像进行了验证。对6名健康受试者双侧膝关节的股骨软骨（femoral cartilage, FC）进行了纵向重复T2测量，以探究T2变化与B1之间的关联。
研究结果：结果表明，施加B1校正可减轻由B1场不均匀性导致的T2变化。具体而言，经B1校正后，左右侧膝关节的T2对称性有所提升（相关系数rc=0.74 > rc=0.69）。未进行B1校正时，T2值与B1呈线性相关；经B1校正后，线性系数从24.3±1.6 ms降至4.1±1.8 ms，且经Bonferroni校正后，该相关性无统计学意义（P值>0.01）。
研究结论：本研究表明，B1校正可减轻qDESS T2 mapping方法对B1的敏感性所导致的变化，从而提升检测真实生物学变化的灵敏度。所提出的方法可提升双侧qDESS T2 mapping的鲁棒性，使得通过纵向与横断面研究能够更准确、高效地评估OA的发病机制与病理生理学过程。
本仓库包含用于复现论文中报告结果的原始数据，数据以NIFTI格式提供。