Issa Bashar, Obaidat Ihab M, Hejasee Rola H, Qadri Shahnaz, Haik Yousef
Department of Physics, College of Sciences, United Arab Emirates University, Al Ain, UAE; Centre of Research Excellence in Nanobioscience 203, University of North Carolina, Greensboro North Carolina, USA.
J Magn Reson Imaging. 2014 Mar;39(3):648-55. doi: 10.1002/jmri.24197. Epub 2013 May 29.
To measure and model nuclear magnetic resonance (NMR) relaxation enhancement due to the presence of gadolinium (Gd)-substituted Zn-Mn ferrite magnetic nanoparticles (MNP) at different temperatures.
Relaxation rates were measured at 1.5 T using fast spin echo (FSE) sequences in samples of agarose gel doped with uncoated and polyethylene glycol (PEG)-coated Mn0.5 Zn0.5 Gd0.02 Fe1.98 O4 nanoparticles over the temperature range 8-58°C. Physical characterization of the MNPs synthesized using chemical coprecipitation included scanning (SEM) and transmission (TEM) electron microscopy, inductively coupled plasma (ICP), dynamic light scattering (DLS), and magnetometry.
Relaxivity (in s(-1) mM(-1) Fe) for the uncoated and coated particles, respectively, increased as follows: from 2.5 to 3.2 and 0.4 to 0.7 for T1, while for T2 it increased from 162.3 to 253.7 and 59.7 to 82.2 over the temperature range 8-58°C. T2 data were fitted to the echo limited motional regime using one fitting parameter that reflects the degree of agglomeration of particles into a cluster. This parameter was found to increase linearly with temperature and was larger for the PEG-coated particles than the uncoated ones.
The increase of 1/T2 with temperature is modeled successfully using echo limited motional regime where both diffusion of the protons and nanoparticle cluster size increase with temperature. Both transverse and longitudinal relaxation efficiencies are reduced by PEG coating at all temperatures. If prediction of relaxation rates under different particle concentrations and operating temperatures is possible then the use of MNP in temperature monitoring and hyperthermia applications may be achieved.
测量并建立模型，以研究在不同温度下，钆（Gd）取代的锌锰铁氧体磁性纳米颗粒（MNP）的存在对核磁共振（NMR）弛豫增强的影响。
在1.5 T磁场下，使用快速自旋回波（FSE）序列，对掺杂有无涂层和聚乙二醇（PEG）涂层的Mn0.5Zn0.5Gd0.02Fe1.98O4纳米颗粒的琼脂糖凝胶样品在8 - 58°C温度范围内进行弛豫率测量。采用化学共沉淀法合成的磁性纳米颗粒的物理特性表征包括扫描电子显微镜（SEM）、透射电子显微镜（TEM）、电感耦合等离子体（ICP）、动态光散射（DLS）和磁强计测量。
在8 - 58°C温度范围内，未涂层和涂层颗粒的弛豫率（以s(-1) mM(-1) Fe为单位）分别如下增加：T1弛豫率从2.5增加到3.2，从0.4增加到0.7；而T2弛豫率从162.3增加到253.7，从59.7增加到82.2。T2数据使用一个反映颗粒聚集成簇程度的拟合参数，拟合到回波受限运动状态。发现该参数随温度线性增加，且PEG涂层颗粒的该参数大于未涂层颗粒。
利用回波受限运动状态成功建立了1/T2随温度变化的模型，其中质子扩散和纳米颗粒簇尺寸均随温度增加。在所有温度下，PEG涂层均降低了横向和纵向弛豫效率。如果能够预测不同颗粒浓度和工作温度下的弛豫率，那么磁性纳米颗粒在温度监测和热疗应用中的使用将成为可能。
