Gharehaghaji Nahideh, Nazarpoor Mahmood, Saharkhiz Hodaiseh
Department of Radiology, Faculty of Paramedicine, Tabriz University of Medical Sciences, Tabriz, Iran.
Department of Medical Physics, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
Iran J Radiol. 2015 Apr 22;12(2):e22887. doi: 10.5812/iranjradiol.22887. eCollection 2015 Apr.
Ultrasmall superparamagnetic iron oxide nanoparticles have been used as a blood pool contrast agent for magnetic resonance angiography and perfusion studies. Linear relationship between signal intensity (SI) and nanoparticle concentration is essential for perfusion measurement.
The aim of this study was to investigate the effect of different flip angles on maximum SI and the linear relationship between SI and different concentrations of iron oxide nanoparticles using T1-weighted Turbo-FLASH (fast low angle shot) inversion recovery sequence to find the optimum flip angle for perfusion measurement.
This in vitro study was performed using carboxydextran coated iron oxide nanoparticles with 20 nm hydrodynamic size. Different concentrations of nanoparticles between 0 and 500 µmol Fe/L were prepared. MR imaging was performed using T1-weighted Turbo-FLASH inversion recovery sequence. Applied flip angles were 10-45º (interval of 5º). Then the maximum SI resulted by each concentration of nanoparticles was measured. Linear relationship between SI and nanoparticle concentration was evaluated regarding square correlations of 0.95 and 0.99. Coil non-uniformity was considered to obtain accurate SI of each image.
The maximum SI was obtained at the highest applied flip angle (45°). The linear relationship between SI and nanoparticle concentration was seen up to 112.21 and 98.83 μmol Fe/L for the short (10°) and the long (45°) flip angles, respectively (R(2) = 0.95). These values were reduced up to 48.54 and 42.73 μmol Fe/L for these flip angles with R(2) of 0.99.
The maximum SI will be increased at higher flip angles with non-linear relationship between SI and nanoparticle concentration. The result shows that an increase in the flip angle leads to a decrease in the range of the linearity. The optimum flip angle which is suitable for perfusion measurement was obtained at 10º for our imaging parameters and sequence. The results of this study may be used in in vivo perfusion measurements.
超小超顺磁性氧化铁纳米颗粒已被用作磁共振血管造影和灌注研究的血池造影剂。信号强度（SI）与纳米颗粒浓度之间的线性关系对于灌注测量至关重要。
本研究旨在使用T1加权Turbo-FLASH（快速低角度激发）反转恢复序列，研究不同翻转角对最大SI的影响以及SI与不同浓度氧化铁纳米颗粒之间的线性关系，以找到灌注测量的最佳翻转角。
本体外研究使用水动力尺寸为20 nm的羧基葡聚糖包被的氧化铁纳米颗粒。制备了0至500 μmol Fe/L之间的不同浓度纳米颗粒。使用T1加权Turbo-FLASH反转恢复序列进行磁共振成像。应用的翻转角为10 - 45°（间隔5°）。然后测量每种纳米颗粒浓度产生的最大SI。关于0.95和0.99的平方相关性评估SI与纳米颗粒浓度之间的线性关系。考虑线圈不均匀性以获得每个图像的准确SI。
在最高应用翻转角（45°）时获得最大SI。对于短翻转角（10°）和长翻转角（45°），SI与纳米颗粒浓度之间的线性关系分别在高达112.21和98.83 μmol Fe/L时可见（R² = 0.95）。对于这些翻转角，当R²为0.99时，这些值分别降至48.54和42.73 μmol Fe/L。
在较高翻转角下最大SI会增加，且SI与纳米颗粒浓度之间存在非线性关系。结果表明，翻转角的增加会导致线性范围减小。对于我们的成像参数和序列，适合灌注测量的最佳翻转角为10°。本研究结果可用于体内灌注测量。
