Pixel T2 distribution in functional magnetic resonance images of muscle.
Pixel T2 distribution in functional magnetic resonance images of muscle.
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肌肉功能磁共振图像中的像素 T2 分布。
DOI：
10.1152/jappl.1999.87.6.2107
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Meyer,RA
中科院分区：
文献类型：
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作者：
Prior,BM;Foley,JM;Jayaraman,RC;Meyer,RA
通过磁共振成像观察到的骨骼肌1H-NMR横向弛豫时间（T2）的增加已被用于绘制运动期间的整个肌肉活动。一些研究进一步表明，运动后T2的肌内变化可用于通过定义活动T2阈值并将超过阈值的像素计数为“活动肌肉”来逐像素地映射活动。这意味着运动单位在肌肉中的分布是非随机的，因此，中等强度运动后像素T2值的分布应该比休息时或更高强度运动后的分布要宽得多，因为中等强度运动应该会招募一些运动单位，因此会招募一些像素，而不是其他像素。本研究检查了健康受试者（5名男性和2名女性，18-46岁）在休息时、运动至疲劳后（50% 1次重复最大值，20次/min至失效= Max）和1/2 Max时（25% 1次重复最大值，重复次数与Max相同）的三块肌肉（四头肌、胫骨前肌和二头肌/肱肌）中像素T2值的分布。虽然对于每一块肌肉，运动强度和平均像素T2之间存在线性关系，但在1/2 Max和Max运动之间像素T2的方差没有显著差异。与休息相比，两次锻炼后像素T2的方差适度增加（10-43%），但这与肌肉活动的蒙特卡罗模拟一致，该模拟假设运动单元区域在肌肉上的随机分布以及每个运动单元区域内肌肉细胞的随机分布。此外，40%的像素到像素的肌肉T2变化被证明是由于成像噪声。结果表明，磁共振成像T2无法可靠地逐像素映射正常受试者的活动肌肉。
Increases in skeletal muscle1H-NMR transverse relaxation time (T2) observed by magnetic resonance imaging have been used to map whole muscle activity during exercise. Some studies further suggest that intramuscular variations in T2 after exercise can be used to map activity on a pixel-by-pixel basis by defining an active T2 threshold and counting pixels that exceed the threshold as “active muscle.” This implies that motor units are nonrandomly distributed across the muscle and, therefore, that the distribution of pixel T2 values ought to be substantially broader after moderate exercise than at rest or after more intense exercise, since moderate-intensity exercise should recruit some motor units, and hence some pixels, but not others. This study examined the distribution of pixel T2 values in three muscles (quadriceps, anterior tibialis, and biceps/brachialis) of healthy subjects (5 men and 2 women, 18–46 yr old) at rest, after exercise to fatigue (50% 1 repetition maximum at 20/min to failure = Max), and at ½Max (25% 1 repetition maximum, same number of repetitions as Max). Although for each muscle there was a linear relationship between exercise intensity and mean pixel T2, there was no significant difference in the variance of pixel T2 between ½Max and Max exercise. There was a modest (10–43%) increase in variance of pixel T2 after both exercises compared with rest, but this was consistent with a Monte Carlo simulation of muscle activity that assumed a random distribution of motor unit territories across the muscle and a random distribution of muscle cells within each motor unit's territory. In addition, 40% of the pixel-to-pixel muscle T2 variations were shown to be due to imaging noise. The results indicate that magnetic resonance imaging T2 cannot reliably map active muscle on a pixel-by-pixel basis in normal subjects.