Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602, USA.
Magn Reson Imaging. 2012 Jan;30(1):26-35. doi: 10.1016/j.mri.2011.09.005. Epub 2011 Nov 8.
Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is performed by obtaining sequential MRI images, before, during and after the injection of a contrast agent. It is usually used to observe the exchange of contrast agent between the vascular space and extravascular extracellular space (EES), and provide information about blood volume and microvascular permeability. To estimate the kinetic parameters derived from the pharmacokinetic model, accurate knowledge of the arterial input function (AIF) is very important. However, the AIF is usually unknown, and it remains very difficult to obtain such information noninvasively. In this article, without knowledge of the AIF, we applied a reference region (RR) model to analyze the kinetic parameters. The RR model usually depends on kinetic parameters found in previous studies of a reference region. However, both the assignment of reference region parameters (intersubject variation) and the selection of the reference region itself (intrasubject variation) may confound the results obtained by RR methods. Instead of using literature values for those pharmacokinetic parameters of the reference region, we proposed to use two pharmacokinetic parameter ratios between the tissue of interest (TOI) and the reference region. Specifically, one parameter K(R) is calculated as the ratio between the volume transfer constant K(trans) of the TOI and RR. Similarly, another parameter V(R) is calculated as the ratio between the extravascular extracellular volume fraction v(e) of the TOI and RR. To investigate the consistency of the two ratios, the K(trans) of the RR was varied ranging from 0.1 to 1.0 min(-1), covering the cited literature values. A simulated dataset with different levels of Gaussian noises and an in vivo dataset acquired from five canine brains with spontaneous occurring brain tumors were used to study the proposed ratios. It is shown from both datasets that these ratios are independent of K(trans) of the RR, implying that there is potentially no need to obtain information about literature values from the reference region for future pharmacokinetic modeling and analysis.
动态对比增强磁共振成像（DCE-MRI）通过在注射对比剂之前、期间和之后获取连续的 MRI 图像来进行。它通常用于观察对比剂在血管空间和细胞外间隙（EES）之间的交换，并提供有关血容量和微血管通透性的信息。为了估计药代动力学模型得出的动力学参数，准确了解动脉输入函数（AIF）非常重要。然而，AIF 通常是未知的，并且仍然很难非侵入性地获得此类信息。在本文中，在不知道 AIF 的情况下，我们应用参考区域（RR）模型来分析动力学参数。RR 模型通常依赖于以前在参考区域的研究中找到的动力学参数。但是，参考区域参数的分配（个体间变化）和参考区域本身的选择（个体内变化）都可能使 RR 方法得出的结果产生混淆。我们提出不使用参考区域的那些药代动力学参数的文献值，而是使用感兴趣的组织（TOI）和参考区域之间的两个药代动力学参数比。具体来说，一个参数 K(R)是通过计算 TOI 和 RR 的体积转移常数 K(trans)的比值得到的。同样，另一个参数 V(R)是通过计算 TOI 和 RR 的细胞外间隙体积分数 v(e)的比值得到的。为了研究这两个比值的一致性，RR 的 K(trans)从 0.1 变化到 1.0 min(-1)，涵盖了文献中的值。使用具有不同水平高斯噪声的模拟数据集和从五个患有自发性脑肿瘤的犬脑中采集的体内数据集来研究所提出的比值。从这两个数据集可以看出，这些比值与 RR 的 K(trans)无关，这意味着在未来的药代动力学建模和分析中，可能无需从参考区域获取文献值的信息。
