Chappell Karyn E, Robson Matthew D, Stonebridge-Foster Amanda, Glover Alan, Allsop Joanna M, Williams Andreanna D, Herlihy Amy H, Moss Jill, Gishen Philip, Bydder Graeme M
Department of Imaging, Hammersmith Hospital NHS Trust, London, England, UK.
AJNR Am J Neuroradiol. 2004 Mar;25(3):431-40.
Magic angle effects are well recognized in MR imaging of tendons and ligaments, but have received virtually no attention in MR neurography. We investigated the hypothesis that signal intensity from peripheral nerves is increased when the nerve's orientation to the constant magnetic induction field (B(0)) approaches 55 degrees (the magic angle).
Ten volunteers were examined with their peripheral nerves at different orientations to B(0) to detect any changes in signal intensity and provide data to estimate T2. Two patients with rheumatoid arthritis also had their median nerves examined at 0 degrees and 55 degrees.
When examined with a short TI inversion-recovery sequence with different TEs, the median nerve showed a 46-175% increase in signal intensity between 0 degrees and 55 degrees and an increase in mean T2 from 47.2 to 65.8 msec. When examined in 5 degrees to 10 degrees increments from 0 degrees to 90 degrees, the median nerve signal intensity changed in a manner consistent with the magic angle effect. No significant change was observed in skeletal muscle. Ulnar and sciatic nerves also showed changes in signal intensity depending on their orientation to B(0). Components of the brachial plexus were orientated at about 55 degrees to B(0) and showed a higher signal intensity than that of nerves in the upper arm that were nearly parallel to B(0). A reduction in the change in signal intensity in the median nerve with orientation was observed in the two patients with rheumatoid arthritis.
Signal intensity of peripheral nerves changes with orientation to B(0). This is probably the result of the magic angle effect from the highly ordered, linearly orientated collagen within them. Differences in signal intensity with orientation may simulate disease and be a source of diagnostic confusion.
魔角效应在肌腱和韧带的磁共振成像中已得到充分认识，但在磁共振神经成像中几乎未受到关注。我们研究了这样一个假设：当外周神经与恒定磁感应场（B(0)）的夹角接近55度（魔角）时，神经的信号强度会增加。
对10名志愿者的外周神经在与B(0)不同的夹角下进行检查，以检测信号强度的任何变化，并提供数据来估计T2。两名类风湿性关节炎患者的正中神经也分别在0度和55度下进行了检查。
当使用具有不同回波时间（TE）的短TI反转恢复序列进行检查时，正中神经在0度至55度之间信号强度增加了46% - 175%，平均T2从47.2毫秒增加到65.8毫秒。当从0度到90度以5度至10度的增量进行检查时，正中神经的信号强度变化符合魔角效应。骨骼肌未观察到明显变化。尺神经和坐骨神经的信号强度也根据它们与B(0)的夹角而变化。臂丛神经的组成部分与B(0)的夹角约为55度，其信号强度高于上臂中几乎与B(0)平行的神经。在两名类风湿性关节炎患者中，观察到正中神经信号强度随夹角的变化有所减少。
外周神经的信号强度随与B(0)的夹角而变化。这可能是由于神经内高度有序、线性排列的胶原产生魔角效应的结果。信号强度随夹角的差异可能会模拟疾病，成为诊断混淆的一个来源。
