Sinha Usha, Csapo Robert, Malis Vadim, Xue Yanjie, Sinha Shantanu
Department of Physics, San Diego State University, San Diego, California, USA.
J Magn Reson Imaging. 2015 Apr;41(4):941-53. doi: 10.1002/jmri.24641. Epub 2014 Apr 28.
To investigate age related changes in diffusion tensor indices and fiber architecture of the medial and lateral gastrocnemius (MG and LG) muscles using diffusion tensor imaging (DTI).
The lower leg of five young and five senior subjects was scanned at 3 Tesla and DTI indices extracted using three methods: region of interest, histogram, and tract based. Tracked fibers were automatically edited to ensure physiologically relevant tracks. Pennation angles were measured with respect to the deep and superficial aponeuroses of both muscles.
The three methods provided internally consistent measures of the DTI indices (correlation coefficient in the range of 0.90-0.99). The primary, secondary, and tertiary eigenvalues in the MG and LG increased significantly in the senior cohort (P < 0.05), while the small increase in fractional anisotropy with age was not significant (MG/LG: P = 0.39/0.85; 95% confidence interval: [-0.059/-0.056, 0.116/0.064]). Fiber lengths of MG fibers originating distally were significantly decreased in seniors (P < 0.05) while pennation angles decreased with age in the MG and LG but this was not significant.
Fiber atrophy and increased fibrosis have opposing effects on the diffusion indices resulting in a complicated dependence with aging. Fiber architectural changes could play a role in determining aging muscle function.
使用扩散张量成像（DTI）研究内侧和外侧腓肠肌（MG和LG）肌肉的扩散张量指数和纤维结构与年龄相关的变化。
对5名年轻受试者和5名老年受试者的小腿进行3特斯拉扫描，并使用三种方法提取DTI指数：感兴趣区域法、直方图法和基于纤维束的方法。对追踪到的纤维进行自动编辑，以确保其生理相关性。测量了两块肌肉相对于深浅腱膜的羽状角。
三种方法对DTI指数的测量结果具有内部一致性（相关系数在0.90 - 0.99范围内）。老年组中MG和LG的第一、第二和第三特征值显著增加（P < 0.05），而随着年龄增长各向异性分数的小幅增加并不显著（MG/LG：P = 0.39/0.85；95%置信区间：[-0.059/-0.056, 0.116/0.064]）。老年人中，起源于远端的MG纤维长度显著缩短（P < 0.05），而MG和LG的羽状角随年龄减小，但不显著。
纤维萎缩和纤维化增加对扩散指数有相反的影响，导致与衰老的复杂相关性。纤维结构变化可能在决定衰老肌肉功能中起作用。
