Hagberg Gisela E, Mamedov Ilgar, Power Anthony, Beyerlein Michael, Merkle Hellmut, Kiselev Valerij G, Dhingra Kirti, Kubìček Vojtĕch, Angelovski Goran, Logothetis Nikos K
Department for Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
Contrast Media Mol Imaging. 2014 Jan-Feb;9(1):71-82. doi: 10.1002/cmmi.1535.
Calcium-sensitive MRI contrast agents can only yield quantitative results if the agent concentration in the tissue is known. The agent concentration could be determined by diffusion modeling, if relevant parameters were available. We have established an MRI-based method capable of determining diffusion properties of conventional and calcium-sensitive agents. Simulations and experiments demonstrate that the method is applicable both for conventional contrast agents with a fixed relaxivity value and for calcium-sensitive contrast agents. The full pharmacokinetic time-course of gadolinium concentration estimates was observed by MRI before, during and after intracerebral administration of the agent, and the effective diffusion coefficient D* was determined by voxel-wise fitting of the solution to the diffusion equation. The method yielded whole brain coverage with a high spatial and temporal sampling. The use of two types of MRI sequences for sampling of the diffusion time courses was investigated: Look-Locker-based quantitative T(1) mapping, and T(1) -weighted MRI. The observation times of the proposed MRI method is long (up to 20 h) and consequently the diffusion distances covered are also long (2-4 mm). Despite this difference, the D* values in vivo were in agreement with previous findings using optical measurement techniques, based on observation times of a few minutes. The effective diffusion coefficient determined for the calcium-sensitive contrast agents may be used to determine local tissue concentrations and to design infusion protocols that maintain the agent concentration at a steady state, thereby enabling quantitative sensing of the local calcium concentration.
钙敏磁共振成像造影剂只有在组织中的造影剂浓度已知时才能得出定量结果。如果有相关参数，造影剂浓度可以通过扩散模型来确定。我们已经建立了一种基于磁共振成像的方法，能够测定传统造影剂和钙敏造影剂的扩散特性。模拟和实验表明，该方法适用于具有固定弛豫率值的传统造影剂和钙敏造影剂。在脑内注射造影剂之前、期间和之后，通过磁共振成像观察钆浓度估计值的完整药代动力学时间进程，并通过对扩散方程解的体素拟合确定有效扩散系数D*。该方法以高空间和时间采样实现了全脑覆盖。研究了使用两种类型的磁共振成像序列对扩散时间进程进行采样：基于Look-Locker的定量T(1)映射和T(1)加权磁共振成像。所提出的磁共振成像方法的观察时间很长（长达20小时），因此覆盖的扩散距离也很长（2-4毫米）。尽管存在这种差异，但基于几分钟的观察时间，体内的D*值与先前使用光学测量技术的结果一致。为钙敏造影剂确定的有效扩散系数可用于确定局部组织浓度，并设计将造影剂浓度维持在稳态的输注方案，从而实现对局部钙浓度的定量传感。
