Shapiro Mikhail G, Atanasijevic Tatjana, Faas Henryk, Westmeyer Gil G, Jasanoff Alan
Division of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Magn Reson Imaging. 2006 May;24(4):449-62. doi: 10.1016/j.mri.2005.12.033. Epub 2006 Mar 20.
Time-resolved MRI has had enormous impact in cognitive science and may become a significant tool in basic biological research with the application of new molecular imaging agents. In this paper, we examine the temporal characteristics of MRI contrast agents that could be used in dynamic studies. We consider "smart" T1 contrast agents, T2 agents based on reversible aggregation of superparamagnetic nanoparticles and sensors that produce changes in saturation transfer effects (chemical exchange saturation transfer, CEST). We discuss response properties of several agents with reference to available experimental data, and we develop a new theoretical model that predicts the response rates and relaxivity changes of aggregation-based sensors. We also perform calculations to define the extent to which constraints on temporal resolution are imposed by the imaging methods themselves. Our analysis confirms that some small T1 agents may be compatible with MRI temporal resolution on the order of 100 ms. Nanoparticle aggregation T2 sensors are applicable at much lower concentrations, but are likely to respond on a single second or slower timescale. CEST agents work at high concentrations and temporal resolutions of 1-10 s, limited by a requirement for long presaturation periods in the MRI pulse sequence.
时间分辨磁共振成像在认知科学领域产生了巨大影响，并且随着新型分子成像剂的应用，它可能会成为基础生物学研究中的一项重要工具。在本文中，我们研究了可用于动态研究的磁共振成像造影剂的时间特性。我们考虑了“智能”T1造影剂、基于超顺磁性纳米颗粒可逆聚集的T2造影剂以及会引起饱和转移效应（化学交换饱和转移，CEST）变化的传感器。我们参照现有的实验数据讨论了几种造影剂的响应特性，并开发了一种新的理论模型来预测基于聚集的传感器的响应速率和弛豫率变化。我们还进行了计算，以确定成像方法本身对时间分辨率的限制程度。我们的分析证实，一些小型T1造影剂可能与大约100毫秒量级的磁共振成像时间分辨率兼容。纳米颗粒聚集T2传感器在低得多的浓度下适用，但可能在单个秒级或更慢的时间尺度上响应。CEST造影剂在高浓度下工作，时间分辨率为1 - 10秒，这受到磁共振成像脉冲序列中长预饱和期要求的限制。
