THEORY OF 1/T-1 AND 1/T-2 NMRD PROFILES OF SOLUTIONS OF MAGNETIC NANOPARTICLES
THEORY OF 1/T-1 AND 1/T-2 NMRD PROFILES OF SOLUTIONS OF MAGNETIC NANOPARTICLES
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DOI：
10.1002/mrm.1910340214
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发表时间：
1995-08-01
影响因子：
3.3
通讯作者：
KELLAR, KE
中科院分区：
文献类型：
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作者：
KOENIG, SH;KELLAR, KE
直径为5-50纳米的有机涂层氧化铁晶体（“纳米颗粒”）是潜在的磁共振成像造影剂。磁性相互作用使溶剂水质子的1/T-1和1/T-2在纳米粒子的“外球”环境中显著增加；随后的扩散混合将这种弛豫分布到整个溶剂中。已发表的理论适用于溶质磁能比热能小的情况，适用于一般可达场（小于或等于50t）下的小磁性溶质（如钆和锰二乙烯三氨基五乙酸，以及氮氧化物自由基）。对于类似于0.05 T以上的场，即在大多数成像场中，纳米颗粒失效。作者重新制定了外球弛豫理论，以纳入溶质纳米颗粒的渐进磁饱和，此外，还指出了如何在实际颗粒的磁性不理想时使用经验磁化数据。有效地处理纳米粒子的快速热诱导磁化重定向（它们的“超顺磁性”）的影响是很重要的，包括它们对粒径的敏感性。理论结果以1/T-1和1/T-2的磁场依赖关系（NMRD曲线）表示，并将其归一化为Fe含量，然后与现有有限的表征良好的材料数据进行比较。
Organically coated iron oxide crystallites with diameters of 5-50 nm (''nanoparticles'') are potential magnetic resonance imaging contrast agents. 1/T-1 and 1/T-2 of solvent water protons are increased dramatically by magnetic interactions in the ''outer sphere'' environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g,, gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (less than or equal to 50 T). It fails for nanoparticles at fields above similar to 0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their ''superparamagnetism'') effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T-1 and 1/T-2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well-characterized material.