磁共振强磁场中保持稳定悬浮及超顺磁性的微粒粒度研究

Study on the Size of Particals Keep Stable and Uperparamagnetism in MRI High Magnetic Fields

用超顺磁性氧化铁制备磁共振造影剂的多篇报道中，Fe3O4磁粒的尺寸大致在15～50nm之间。根据超顺磁性理论推导出显示超顺磁现象的临界尺寸理论值为25nm，在1．5T磁共振磁场中的临界值为7．1nm。分析了在强磁场中包覆有表面活性剂的Fe3O4磁粒的粒径在大于理论计算的临界尺寸时，仍有可能保持超顺磁状态。根据磁学理论，分析了磁共振造影剂稳定的机理；推导出在磁共振磁场中，Fe3O4磁粒在造影剂中稳定悬浮的极限尺寸为13．3nm。指出造影剂中的Fe3O4磁粒既能稳定悬浮又具有超顺磁性的合适尺寸为10nm左右。

Superparamagnetic iron oxide contrast agents have been reported by many researches. The diameter of Fe3O4 in these agents is 15 -50 nm. The critical size which developed based on superparamagnetic theory is 25 nm. And the critical size is 7. 1 nm in 1.5 T MRI high magnetic fields, the diameter of Fe3O4 coating suspending agents on the surface would remain superparamagnetic state is analyzed when their particle size is larger than the size theoretically in MRI high magnetic fields. Based on magnetic theory, the mechanism of stability of contrast agent was analyzed, and the critical size which Fe3O4 magnetic microparticles keep stable in the contrast agent is 13.3 nm developed. The proper occluder size which Fe3O4 magnetic microparticles keep stable and Uperparamagnetism in the contrast agent is 10nm reported.