Fullerton G D, Cameron I L, Ord V A
Radiology. 1985 May;155(2):433-5. doi: 10.1148/radiology.155.2.3983395.
In vitro studies of spin-spin relaxation times of the protons or hydrogen nuclei which make up the tendon demonstrated significant dependence of T2 on orientation at physiological levels of hydration. T2 varied from approximately 250 mu sec. with the tendon aligned with the magnetic field to 22 msec. at an angle of 55 degrees or 125 degrees and 4 msec. at deviations of +/- 15 degrees from 55 degrees and 125 degrees. 55 degrees and 125 degrees are the so-called "magic angles" at which 3 cos2 theta - 1 = 0. As a result, the signal from human tendons in vivo will depend on their orientation; however, T2 is generally short enough that the signal intensity will approach 0 in MR images regardless of the orientation of the tendons, thereby preventing this phenomenon from being observed in most studies.
对构成肌腱的质子或氢核的自旋-自旋弛豫时间进行的体外研究表明，在生理水合水平下，T2对取向有显著依赖性。T2随肌腱与磁场对齐时约为250微秒，到55度或125度角时为22毫秒，在与55度和125度相差±15度时为4毫秒。55度和125度是所谓的“魔角”，此时3cos2θ - 1 = 0。因此，体内人体肌腱的信号将取决于其取向；然而，T2通常足够短，以至于在磁共振图像中，无论肌腱的取向如何，信号强度都将接近0，从而在大多数研究中无法观察到这种现象。
