Advantages of paramagnetic chemical exchange saturation transfer (CEST) complexes having slow to intermediate water exchange properties as responsive MRI agents.
Advantages of paramagnetic chemical exchange saturation transfer (CEST) complexes having slow to intermediate water exchange properties as responsive MRI agents.
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DOI：
10.1002/nbm.2874
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发表时间：
2013-07
影响因子：
2.9
通讯作者：
Dean Sherry, A.
中科院分区：
文献类型：
--
作者：
Soesbe, Todd C.;Wu, Yunkou;Dean Sherry, A.
顺磁饱和转移化学交换（PARACEST）复合物是外源性造影剂，具有进一步扩展磁共振功能和分子成像能力的巨大潜力。由于螯合物中存在中心顺磁性镧系离子（Ln 3+、La 3+、Gd 3+、Lu 3+），结合到PARACEST试剂的质子和水分子的共振频率远离本体水频率偏移。这种大的化学位移加上对化学交换速率的极端敏感性，使PARACEST试剂非常适合报告重要的生物指标，如温度，pH值和代谢物的存在。此外，使用频率选择性饱和脉冲将PARACEST试剂“关闭”和“打开”的能力使其具有优于基于Gd 3+的造影剂的明显优势。PARACEST研究目前面临的挑战是将有希望的体外结果转化为体内系统。这篇简短的综述文章首先介绍了PARACEST造影剂背后的基本理论，它们相对于其他造影剂的优势，以及它们在磁共振成像中的应用。然后介绍了一些最近的PARACEST研究结果。具体而言，使用水分子交换速率调制的pH测量，由于水分子交换的T2交换对比，使用超短回波时间（TE<10 μs）克服T2交换谱线增宽，以及T2交换作为磁共振成像的新对比机制的潜在应用。
Paramagnetic saturation transfer chemical exchange (PARACEST) complexes are exogenous contrast agents that have great potential to further extend the functional and molecular imaging capabilities of magnetic resonance. Due to the presence of a central paramagnetic lanthanide ion (Ln3+ ≠ La3+, Gd3+, Lu3+) within the chelate, the resonance frequencies of protons and water molecules bound to the PARACEST agent are shifted far away from the bulk water frequency. This large chemical shift combined with an extreme sensitivity to the chemical exchange rate make PARACEST agents ideally suited for reporting significant biological metrics such as temperature, pH, and the presence of metabolites. Also, the ability to turn PARACEST agents “off” and “on” using a frequency selective saturation pulse gives them a distinct advantage over Gd3+-based contrast agents. A current challenge for PARACEST research is translating the promising in vitro results into in vivo systems. This short review article first describes the basic theory behind PARACEST contrast agents, their benefits over other contrast agents, and their applications to magnetic resonance imaging. It then describes some of the recent PARACEST research results. Specifically, pH measurements using water molecule exchange rate modulation, T2-exchange contrast due to water molecule exchange, the use of ultra-short echo times (TE<10 μs) to overcome T2-exchange line-broadening, and the potential application of T2-exchange as a new contrast mechanism for magnetic resonance imaging.
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