Corbin Nadège, Callaghan Martina F
Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom.
Magn Reson Med. 2021 Aug;86(2):693-708. doi: 10.1002/mrm.28720. Epub 2021 Mar 1.
The variable flip angle (VFA) approach to T mapping assumes perfectly spoiled transverse magnetisation at the end of each repetition time (TR). Despite radiofrequency (RF) and gradient spoiling, this condition is rarely met, leading to erroneous T estimates ( ). Theoretical corrections can be applied but make assumptions about tissue properties, for example, a global T time. Here, we investigate the effect of imperfect spoiling at 7T and the interaction between the RF and gradient spoiling conditions, additionally accounting for diffusion. We provide guidance on the optimal approach to maximise the accuracy of the T estimate in the context of 3D multi-echo acquisitions.
The impact of the spoiling regime was investigated through numerical simulations, phantom and invivo experiments.
The predicted dependence of on tissue properties, system settings, and spoiling conditions was observed in both phantom and in vivo experiments. Diffusion effects modulated the dependence of on both efficiency and T times.
Error in can be minimized by using an RF spoiling increment and gradient spoiler moment combination that minimizes T -dependence and safeguards image quality. Although the diffusion effect was comparatively small at 7T, correction factors accounting for this effect are recommended.
T 映射的可变翻转角（VFA）方法假定在每个重复时间（TR）结束时横向磁化完全被破坏。尽管有射频（RF）和梯度破坏，但这种情况很少满足，从而导致错误的 T 估计（ ）。可以应用理论校正，但这些校正对组织特性做出了假设，例如全局 T 时间。在此，我们研究了 7T 时不完全破坏的影响以及 RF 和梯度破坏条件之间的相互作用，此外还考虑了扩散。我们为在 3D 多回波采集的背景下最大化 T 估计准确性的最佳方法提供指导。
通过数值模拟、体模和体内实验研究了破坏机制的影响。
在体模和体内实验中均观察到了预测的 对组织特性、系统设置和破坏条件的依赖性。扩散效应调节了 对 效率和 T 时间的依赖性。
通过使用最小化 T 依赖性并保障图像质量的 RF 破坏增量和梯度扰相矩组合，可以将 中的误差最小化。尽管在 7T 时扩散效应相对较小，但建议使用考虑此效应的校正因子。
