Biomedical Physics Unit, UMONS, Mons, Belgium.
Faculty of Medicine, UMONS, Mons, Belgium.
Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2017 Nov;9(6). doi: 10.1002/wnan.1468. Epub 2017 Apr 11.
Superparamagnetic nanoparticles are used as contrast agents in magnetic resonance imaging and allow, for example, the detection of tumors or the tracking of stem cells in vivo. By producing magnetic inhomogeneities, they influence the nuclear magnetic relaxation times, which results in a darkening, on the image, of the region containing these particles. A great number of studies have been devoted to their magnetic properties, to their synthesis and to their influence on nuclear magnetic relaxation. The theoretical and fundamental understanding of the behavior of these particles is a necessary step in predicting their efficiency as contrast agents, or to be able to experimentally obtain some of their properties from a nuclear magnetic resonance measurement. Many relaxation models have been published, and choosing one of them is not always easy, many parameters and conditions have to be taken into account. Relaxation induced by superparamagnetic particles is generally attributed to an outersphere relaxation mechanism. Each model can only be used under specific conditions (motional averaging regime, static regime, high magnetic field, etc.) or for a particular sequence (Carr-Purcell-Meiboom-Gill, spin echo, free-induction decay, nuclear magnetic relaxation dispersion profile, etc.). The parameters included in the equations must be carefully interpreted. In some more complex conditions, simulations are necessary to be able to predict the relaxation rates. A good agreement is usually observed between the theoretical predictions and the experimental results, although some data still cannot be fully understood, such as the dependence of the transverse relaxation on the magnetic field. WIREs Nanomed Nanobiotechnol 2017, 9:e1468. doi: 10.1002/wnan.1468 For further resources related to this article, please visit the WIREs website.
超顺磁纳米颗粒可用作磁共振成像中的造影剂，例如，可以检测肿瘤或在体内追踪干细胞。通过产生磁场不均匀性，它们会影响核磁弛豫时间，从而导致含有这些颗粒的区域在图像上变暗。大量的研究致力于研究它们的磁性能、合成以及对核磁弛豫的影响。这些粒子行为的理论和基础理解是预测其作为造影剂效率的必要步骤，或者能够从核磁共振测量中实验获得它们的一些特性。已经发表了许多弛豫模型，选择其中一个并不总是容易的，需要考虑许多参数和条件。超顺磁粒子引起的弛豫通常归因于外球弛豫机制。每个模型只能在特定条件下（运动平均化状态、静态状态、强磁场等）或特定序列下（Carr-Purcell-Meiboom-Gill、自旋回波、自由感应衰减、核磁弛豫弥散谱等）使用。方程中包含的参数必须仔细解释。在一些更复杂的条件下，需要进行模拟才能预测弛豫率。理论预测与实验结果通常吻合较好，尽管有些数据仍然无法完全理解，例如横向弛豫对磁场的依赖性。WIREs Nanomed Nanobiotechnol 2017, 9:e1468. doi: 10.1002/wnan.1468 如需了解本文相关资源，请访问 WIREs 网站。
