Carlsson Asa, Starck Göran, Ljungberg Maria, Ekholm Sven, Forssell-Aronsson Eva
Radiation Physics, Göteborg University, SE-413 45, Göteborg, Sweden.
Magn Reson Imaging. 2006 Nov;24(9):1179-85. doi: 10.1016/j.mri.2006.07.005. Epub 2006 Sep 15.
Susceptibility differences are common causes for artifacts in magnetic resonance (MR); therefore, it is important to choose phantom materials in a way that these artifacts are kept at a minimum. In this study, a previously proposed MR imaging (MRI) method [Beuf O, Briguet A, Lissac M, Davis R. Magnetic resonance imaging for the determination of magnetic susceptibility of materials. J Magn Reson 1996; Series B(112):111-118] was improved to facilitate sensitive in-house measurements of different phantom materials so that such artifacts can more easily be minimized. Using standard MRI protocols and distilled water as reference, we measured magnetic volume susceptibility differences with a clinical MR system. Two imaging techniques, echo planar imaging (EPI) and spin echo, were compared using liquid samples whose susceptibilities were verified by MR spectroscopy. The EPI sequence has a very narrow bandwidth in the phase-encoding direction, which gives an increased sensitivity to magnetic field inhomogeneities. All MRI measurements were evaluated in two ways: (1) manual image analysis and (2) model fitting. The narrow bandwidth of the EPI made it possible to detect very small susceptibility differences (equivalent susceptibility difference, Deltachi(e)> or =0.02 ppm), and even plastics could be measured. Model fitting yielded high accuracy and high sensitivity and was less sensitive to other image artifacts as compared with manual image analysis.
敏感性差异是磁共振（MR）成像中伪影的常见原因；因此，以将这些伪影降至最低的方式选择体模材料非常重要。在本研究中，对先前提出的磁共振成像（MRI）方法[Beuf O, Briguet A, Lissac M, Davis R. Magnetic resonance imaging for the determination of magnetic susceptibility of materials. J Magn Reson 1996; Series B(112):111 - 118]进行了改进，以利于对不同体模材料进行灵敏的内部测量，从而能更轻松地将此类伪影降至最低。使用标准MRI协议并以蒸馏水作为参考，我们用临床MR系统测量了磁体积极化率差异。使用通过磁共振波谱验证其敏感性的液体样本，比较了两种成像技术，即回波平面成像（EPI）和自旋回波。EPI序列在相位编码方向上具有非常窄的带宽，这使其对磁场不均匀性的敏感性增加。所有MRI测量通过两种方式进行评估：（1）手动图像分析和（2）模型拟合。EPI的窄带宽使得能够检测到非常小的敏感性差异（等效敏感性差异，Deltachi(e)>或 =0.02 ppm），甚至可以测量塑料。与手动图像分析相比，模型拟合具有更高的准确性和灵敏度，并且对其他图像伪影不太敏感。
