Center for Biomedical Imaging (CBI), Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, USA.
NMR Biomed. 2019 Nov;32(11):e4135. doi: 10.1002/nbm.4135. Epub 2019 Jul 26.
To investigate the feasibility of using multiple flip angles in dynamic contrast enhanced (DCE) MRI to reduce the uncertainty in estimation of intracellular water lifetime (τ ).
Numerical simulation studies were conducted to assess the uncertainty in estimation of τ using dynamic contrast enhanced MRI with one or two flip angles. In vivo experiments with a murine brain tumor model were conducted at 7T using two flip angles. The in vivo data were used to compare τ estimation using the single-flip-angle (SFA) protocol with that using the double-flip-angle (DFA) protocol. Data analysis was conducted using the two-compartment exchange model combined with the three-site-two-exchange model for water exchange.
In the numerical simulation studies with a range of contrast kinetic parameters and signal-to-noise ratio = 20, the median bias of τ estimation decreased from 72 ms with SFA to 65 ms with DFA, and the corresponding median inter-quartile range reduced from 523 ms to 156 ms. In the in vivo studies, τ estimation with SFA was not successful in most voxels in the tumors, as the estimated τ values reached the upper limit of the parameter range (2 s). In contrast, the estimated τ values with DFA were mostly between 0.2 and 1.5 s and homogeneously distributed spatially across the tumor. The τ estimation with DFA was less sensitive to arterial input function scaling but more sensitive to pre-contrast T than the other contrast kinetic parameters.
This study results demonstrate the feasibility of using multiple flip angles to encode the post-contrast time-intensity curve with different weighting of water exchange effect to reduce the uncertainty in τ estimation.
研究在动态对比增强磁共振成像（DCE MRI）中使用多个翻转角以降低细胞内水寿命（τ）估计不确定性的可行性。
通过数值模拟研究评估了使用一个或两个翻转角的 DCE MRI 对 τ 估计的不确定性。在 7T 下使用两种翻转角进行了脑肿瘤模型的体内实验。使用双翻转角（DFA）方案和单翻转角（SFA）方案比较了体内数据中 τ 的估计。数据分析使用结合水交换的三部位二交换模型的两室交换模型进行。
在一系列对比动力学参数和信噪比=20 的数值模拟研究中，τ 估计的中位数偏差从 SFA 的 72ms 降低到 DFA 的 65ms，相应的中位数四分位间距从 523ms 降低到 156ms。在体内研究中，由于估计的 τ 值达到参数范围（2s）的上限，SFA 中的 τ 估计在大多数肿瘤体素中都不成功。相比之下，DFA 中的估计 τ 值大多在 0.2 和 1.5s 之间，并且在肿瘤中空间上均匀分布。DFA 中的 τ 估计对动脉输入函数缩放的敏感性较低，但对预对比 T 比对其他对比动力学参数更敏感。
本研究结果表明，使用多个翻转角对后对比时间-强度曲线进行编码以降低 τ 估计的不确定性是可行的，方法是对水交换效应进行不同加权。
