New approach for evaluating muscle function by using MR imaging

1)基本原理和目标。确定骨骼肌T2松弛时间是否受衰老影响，比较快肌和慢肌衰老的影响。方法。采用临床磁共振成像技术，对59例22 ~ 76岁健康人比目鱼肌和腓肠肌的T2松弛时间进行了研究。对小鼠进行T2松弛时间、脂肪比和腰肌细胞外间隙比的检测（老年组7只，24 ~ 26个月；年轻组7只，8 ~ 10周）。结果。腓肠肌T2松弛时间随年龄增长而明显增加（r=0.53, p<0.01）。而比目鱼肌则没有。老年大鼠腰肌T2松弛时间明显延长（p<0.05），腰肌细胞外间隙比明显变宽（p< 0.01）。老年小鼠和年轻小鼠的脂肪比例无显著差异。细胞外空间比与T2松弛时间呈显著正相关（r=0.84, p<0.01）。结论。随着年龄的增长，快缩肌T2松弛时间增加，这主要是由于细胞外空间增加，反映了年龄相关的II型纤维萎缩。2)为确定类固醇治疗（类固醇肌病）对肌肉T2弛豫时间的影响，测定兔注射类固醇前后比目鱼肌、腓肠肌和胫前肌T2弛豫时间。腓肠肌和胫前肌（快缩肌）的T2松弛时间明显增加，而比目鱼肌（慢缩肌）的T2松弛时间无明显变化。激素组腓肠肌和胫前肌细胞外间隙比显著大于对照组（p<0.01）。T2松弛时间是激素性肌病的一个潜在指标。

1) RATIONALE AND OBJECTIVES. To determine whether the T2 relaxation time of skeletal muscle is affected by aging and to compare the effects of aging between fast- and slow-twitch muscles. METHODS. T2 relaxation times of the soleus and gastrocnemius muscles were examined in 59 healthy human subjects 22 to 76 years of age, using a clinical magnetic resonance imaging. In mice, T2 relaxation times, fat ratios, and extracellular space ratios of the psoas muscles were examined (old group of 7 mice, 24 to 26 months; young group of 7 mice, 8 to 10 weeks). RESULTS. T2 relaxation time of the gastrocnemius muscle increased significantly with aging (r=0.53, p<0.01). While that of the soleus muscle did not. T2 relaxation time of the psoas muscle was significantly linger (p<0.05) and extracellular space ratio of the psoas muscle was significantly wider (P<0.01) in old than in young mice. No significant difference in fat ratio was observed between old and young mice. A significant positive correlation was seen between extracellular space ratio and T2 relaxation time (r=0.84, p<0.01). CONCLUSION. T2 relaxation time of fast-twitch muscle increases with aging, due mainly to increased extracellular space reflecting age-related type II fiber atrophy.2) To determine the T2 relaxation time of muscle was affected by steroid treatment (steroid myopathy), T2 relaxation time of the soleus, gastrocnemius and tibialis anterior muscles were measured before and after steroid injection in rabbit. The T2 relaxation time of the gastrocnemius and tibialis anterior muscles (fast-twitch) increased significantly but not in the soleus muscle (slow-twitch). Extracellular space ratio of the gastrocnemius and tibialis anterior muscles was significantly wider (p<0.01) in steroid-treated than in control. T2 relaxation time is a potential indicator for steroid-induced myopathy.