Measurement of magnetic resonance T2 for physiological experiments.

The proton transverse relaxation time (T2) of human skeletal muscles has been increasingly used in magnetic resonance imaging experiments to examine muscle physiology and neuromuscular control. However, little attention has been paid to the experimental factors affecting the accuracy or sensitivity of the T2 measurement. We have explored theoretically and experimentally the structure of several magnetic resonance pulse sequences for measuring T2 of the first dorsal interosseous muscle and found that a multiecho imaging technique using non-slice-selective refocusing pulses (MENSS) produces more accurate T2 estimates than multiecho slice-selective (MESS) imaging methods that are commonly used. Using either technique we acquired four 5-mm-thick transverse images of the first dorsal interosseous muscle with a spatial resolution of 0.6 mm within 5 min. The T2 measured by the MENSS method was closer to the true T2 than was the T2 estimated by the MESS method. After a given amount of exercise, the MENSS technique revealed an average 28 +/- 10% increase in T2 compared with a 13 +/- 3% increase measured with an equivalent MESS technique. We conclude that the MENSS method is a more accurate and sensitive procedure for studying neuromuscular physiology compared with the more commonly used MESS method.