Bulte J W, Vymazal J, Brooks R A, Pierpaoli C, Frank J A
Diagnostic Radiology Department, Warren G. Magnuson Clinical Center National Institutes of Health, Bethesda, MD 20892.
J Magn Reson Imaging. 1993 Jul-Aug;3(4):641-8. doi: 10.1002/jmri.1880030414.
The frequency dependence of T1 and T2 was measured for homogeneous suspensions of magnetite and iron oxyhydroxide particles in water with various concentrations of gelatin. The transverse relaxivity showed two types of behavior: (a) For magnetic particles, there was a rapid increase in T2 relaxivity with frequency, followed by a saturation plateau, which accorded with the Langevin magnetization function. From these curves, the magnetic moment of the particle domains was estimated to range from 0.8 to 6.3 x 10(4) Bohr magnetons. (b) For iron oxyhydroxide (ferritin, ferrihydrite, and akaganéite) particles, T2 relaxivity increased linearly with frequency, the slope of the increase characteristic for each particle. T2 relaxivity generally increased with increasing gelatin concentration, corresponding to the measured decrease in the water diffusion coefficient. For iron oxides, homogeneously distributed either as iatrogenic agents or endogenous biominerals, these findings may aid in the interpretation of in vivo relaxivity and the effect on MR imaging.
在含有不同浓度明胶的水中，对磁铁矿和羟基氧化铁颗粒的均匀悬浮液测量了T1和T2的频率依赖性。横向弛豫率表现出两种行为：(a) 对于磁性颗粒，T2弛豫率随频率迅速增加，随后出现饱和平台，这与朗之万磁化函数一致。根据这些曲线，颗粒畴的磁矩估计在0.8至6.3×10⁴玻尔磁子范围内。(b) 对于羟基氧化铁（铁蛋白、水铁矿和赤铁矿）颗粒，T2弛豫率随频率线性增加，每种颗粒增加的斜率具有特征性。T2弛豫率通常随明胶浓度的增加而增加，这与测得的水扩散系数降低相对应。对于作为医源性物质或内源性生物矿物质均匀分布的铁氧化物，这些发现可能有助于解释体内弛豫率以及对磁共振成像的影响。
