Purpose

To correct with post-processing effects of incomplete recovery of the longitudinal magnetization before a new inversion pulse in the Modified Look-Locker Inversion recovery sequence (MOLLI) sequence.

Theory and methods

We model such effects as a temporal shift (\(\tau\)) of the signal of the Look-Locker block following next inversion pulses. After using the following equation \(S\left( t \right) = A - B \times \exp \left( { - \left( {t + \tau } \right)/T1^{*} } \right)\), a temporal registration of \(\tau\) is applied to the signal of the affected block to adjust the sampling time of the recovery signal and correct the underlying effect on quantitative T1. To test our approach, simulations, phantoms, and five volunteers’ data were used while applying different MOLLI sampling schemes at different heart rates and compared to the reference three-parameter fit.

Results

The temporal registration of the affected signals allows to reach higher accuracy on long T1 when compared to the reference three parameters fit (10.15 vs 22.12% for T1 = 1785 ms; 8.22 vs 14.65% for T1 = 1278 ms), and lower average variation in case of rest-period deletion (62 vs 231 ms).

Conclusion

The proposed approach leads to more accurate T1 in case of incomplete recovery. It is less sensitive to parameters affecting the recovery such as the rest period or the sampling scheme; and, therefore, supports multi-center studies with different MOLLI protocols.

中文翻译：

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时间配准：一种管理心脏 T1 映射的改良 Look-Locker 反转恢复序列 (MOLLI) 中纵向磁化不完全恢复的新方法。

目的

在修改 Look-Locker 反转恢复序列 (MOLLI) 序列中的新反转脉冲之前纠正纵向磁化不完全恢复的后处理效果。

理论与方法

我们将此类效应建模为紧随下一个反转脉冲后 Look-Locker 模块的信号的时间偏移 ( \(\tau\) )。使用以下等式后\(S\left( t \right) = A - B \times \exp \left( { - \left( {t + \tau } \right)/T1^{*} } \right) \) ，将\(\tau\)的时间配准应用于受影响块的信号，以调整恢复信号的采样时间并纠正对定量T 1 的潜在影响。为了测试我们的方法，模拟，模型，并且使用了五名志愿者的数据，同时在不同的心率下应用了不同的 MOLLI 采样方案，并与参考三参数拟合进行了比较。

结果

与参考三个参数拟合相比，受影响信号的时间配准允许在长T 1上达到更高的准确度（ T 1 = 1785 ms 为 10.15 对 22.12%； T 1 = 1278 ms为 8.22 对 14.65% ），并且更低休息期删除的平均变化（62 vs 231 ms）。

结论

在不完全恢复的情况下，所提出的方法会导致更准确的T 1 。它对影响恢复的参数（例如休息期或采样方案）不太敏感；因此，支持使用不同 MOLLI 协议的多中心研究。