Xie He, Cheng Yu-Chung N, Kokeny Paul, Liu Saifeng, Hsieh Ching-Yi, Haacke E Mark, Palihawadana Arachchige Maheshika, Lawes Gavin
Department of Physics and Astronomy, Wayne State University, Detroit, Michigan, USA.
Department of Radiology, Wayne State University, Detroit, Michigan, USA.
Magn Reson Med. 2016 Oct;76(4):1263-9. doi: 10.1002/mrm.26035. Epub 2015 Oct 31.
This work quantifies magnetic susceptibilities and additional frequency shifts derived from different samples.
Twenty samples inside long straws were imaged with a multiecho susceptibility weighted imaging and analyzed with two approaches for comparisons. One approach applied our complex image summation around a spherical or cylindrical object method to phase distributions outside straws. The other approach utilized phase values inside each straw from two orientations. Both methods quantified susceptibilities of each sample at each echo time. The R2* value of each sample was measured too. Uncertainty of each measurement was also estimated.
Quantified susceptibilities from complex image summation around a spherical or cylindrical object are consistent within uncertainties between different echo times. However, this is not the case for the other method. Nonetheless, most quantified susceptibilities are consistent between these two methods. Phase values due to additional frequency shifts in some of ferritin and nanoparticle samples have been identified. Only R2* values quantified from low concentration nanoparticle samples agree with the predictions from the static dephasing theory.
This work suggests that using the sample sizes and phase values only outside samples can correctly quantify the susceptibilities of those samples. With the presence of a possible additional frequency shift inside a material, it will not be suitable to obtain susceptibility maps without taking that into account. Magn Reson Med 76:1263-1269, 2016. © 2015 Wiley Periodicals, Inc.
本研究对来自不同样本的磁化率和额外的频率偏移进行量化。
使用多回波磁化率加权成像对长吸管内的20个样本进行成像，并采用两种方法进行分析以作比较。一种方法是将我们的围绕球形或圆柱形物体的复图像求和方法应用于吸管外部的相位分布。另一种方法利用来自两个方向的每个吸管内部的相位值。两种方法都在每个回波时间量化每个样本的磁化率。还测量了每个样本的R2*值。同时也估计了每次测量的不确定性。
围绕球形或圆柱形物体的复图像求和所量化的磁化率在不同回波时间的不确定性范围内是一致的。然而，另一种方法并非如此。尽管如此，这两种方法所量化的大多数磁化率是一致的。已识别出一些铁蛋白和纳米颗粒样本中由于额外频率偏移导致的相位值。只有从低浓度纳米颗粒样本量化得到的R2*值与静态去相位理论的预测相符。
本研究表明，仅使用样本外部的样本大小和相位值可以正确量化这些样本的磁化率。如果材料内部存在可能的额外频率偏移，在未考虑这一点的情况下获取磁化率图将不合适。《磁共振医学》76:1263 - 1269, 2016。© 2015威利期刊公司。
