Objective

Purely exponential decay is rarely observed in conventional mono-exponential T₂ mapping due to transmit field inhomogeneity and calibration errors, which collectively introduce stimulated and indirect echo pathways. Stimulated echo correction (SEC) requires an additional fit parameter for the transmit field, resulting in greater uncertainty in T₂ relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T₂ mapping using SEC.

Methods

The proposed method, called two-step SEC (tSEC), leverages spatial correlations in the transmit field to reduce the number of fully independent fitting parameters from three to two. The method involves a two-pass fit: the first pass involves a fast but standard SEC fit. The initially estimated transmit field is smoothed and provided as a fixed input to the second pass.

Results

Simulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T₂ variance with tSEC relative to SEC. Average T₂ values were unchanged between tSEC and SEC fits. The proposed method uses the same input data as SEC and exponential fits, so it is applicable to existing data.

Discussion

The proposed method generates reliable and reproducible quantitative T₂ maps and should be considered for future relaxometry studies.

中文翻译：

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具有发射场约束的受激回波补偿的横向弛豫法

客观的

由于传输场的不均匀性和校准误差，在传统的单指数T ₂映射中很少观察到纯指数衰减，这共同引入了受激和间接的回声路径。受激回波校正（SEC）需要针对发射场的附加拟合参数，相对于单指数拟合，T _2的不确定性更大。这项研究的目的是开发一种使用SEC进行T ₂映射的精确方法。

方法

所提出的方法称为两步SEC（tSEC），它利用发射场中的空间相关性将完全独立的拟合参数的数量从3个减少到2个。该方法涉及两次通过拟合：第一次通过涉及快速但标准的SEC拟合。初始估计的发射场被平滑并作为固定输入提供给第二遍。

结果

模拟和体内实验表明，相对于SEC，tSEC的相对T ₂方差分别降低了38％和27％。tSEC和SEC拟合之间的平均T ₂值不变。所提出的方法使用与SEC和指数拟合相同的输入数据，因此适用于现有数据。

讨论

所提出的方法可生成可靠且可重现的定量T ₂图，应考虑用于将来的弛豫法研究。