Leroy-Willig A, Carlier P, Morvan D, Duboc D, Fardeau M
Institut de Myologie, Groupe Hospitalier Pitié-Salpétrière, Paris.
Rev Neurol (Paris). 1998 Jun;154(5):379-88.
Medical imaging is now giving access not only to anatomy but also to functions of organs in the human body. Functional imaging may yield a direct appreciation of the function of a given organ, as is the case when measuring ejection fraction of heart with SPECT. Alternately the approach is indirect. This is the case of cerebral functional imaging, either with PET or NMR, where the perfusion increase induced by neuronal activity is detected. Recent developments of NMR, combining imaging and spectroscopy, allow now to detect modification of physiological parameters induced by muscular activity. Indirect detection of muscle activity is very rich in information alternately requiring invasive techniques. Water shifts resulting from intense exercise are detected either from muscle volume increase or water signal modifications, using simple NMR sequences. Then it is easy to identify which muscle is involved in a given protocol. These water shifts, studied in various muscles and several types of exercise protocols, reflect the perfusion increase induced by exercise, and the contribution of metabolic products such as lactate. In some patients with metabolic myopathies a decreased adaptation of perfusion has been detected. Perfusion measurements, previously performed by using venous occlusion plethysmography or radioactive tracers, now benefit from recently developed MR techniques. Oxygenation of muscle may be measured either by spectroscopy of myoglobin, allowing a time resolution of 1 second, or by spectroscopic imaging allowing a spatial resolution of 1-2 cm in a few minutes. Muscle temperature may be non invasively monitored by diffusion-weighted MR. Direct detection of muscle activity is useful only in those muscles that cannot be directly observed. Ultrafast MR imaging may be used to study vocal cords or oculomotor muscles. More interesting is the measurement of contractility, either in myocardium or skeletal muscle, allowed by MR with spin-tagging. Another contribution of MR to muscle studies is the possibility to quantify muscle cross section and muscle volume, in order to normalize strength or metabolism measurements. Sequences using T1 or T2 differences between muscular and adipose tissue allow to quantify the true muscular volume in patients with neuromuscular disorders. Protocols combining several of these parameters by interleaved NMR measurements of perfusion, phosphorylated metabolites, lactate, myoglobin, now open the way to many comprehensive non-invasive pathophysiological studies.
医学成像如今不仅能呈现人体器官的解剖结构，还能揭示其功能。功能成像可以直接评估特定器官的功能，比如用单光子发射计算机断层扫描（SPECT）测量心脏射血分数时的情况。或者，这种方法是间接的。脑功能成像就是如此，无论是正电子发射断层扫描（PET）还是核磁共振成像（NMR），都是通过检测神经元活动引起的灌注增加来实现的。核磁共振成像的最新进展，将成像与光谱学相结合，现在能够检测肌肉活动引起的生理参数变化。间接检测肌肉活动蕴含着丰富的信息，不过以往需要采用侵入性技术。通过使用简单的核磁共振序列，从肌肉体积增加或水信号变化中可以检测到剧烈运动导致的水转移。这样就很容易确定在特定运动方案中涉及哪些肌肉。在不同肌肉和多种运动方案中研究这些水转移，能反映出运动引起的灌注增加以及乳酸等代谢产物的作用。在一些患有代谢性肌病的患者中，已检测到灌注适应性下降。灌注测量以前是通过静脉阻塞体积描记法或放射性示踪剂进行的，现在受益于最近开发的磁共振技术。肌肉的氧合作用可以通过肌红蛋白光谱法测量，时间分辨率为1秒，也可以通过光谱成像测量，几分钟内就能实现1 - 2厘米的空间分辨率。肌肉温度可以通过扩散加权磁共振成像进行非侵入性监测。直接检测肌肉活动仅在那些无法直接观察到的肌肉中有用。超快磁共振成像可用于研究声带或动眼肌。更有意思的是，利用磁共振自旋标记技术可以测量心肌或骨骼肌的收缩性。磁共振对肌肉研究的另一个贡献是能够量化肌肉横截面积和肌肉体积，以便对力量或代谢测量结果进行标准化。利用肌肉组织和脂肪组织之间的T1或T2差异的序列，可以量化神经肌肉疾病患者的真实肌肉体积。通过对灌注、磷酸化代谢产物、乳酸、肌红蛋白进行交错核磁共振测量，将这些参数中的几个参数结合起来的方案，现在为许多全面的非侵入性病理生理学研究开辟了道路。
