Shortened T2 after exercise in ischemic skeletal muscle

Purpose To detect skeletal muscle ischemia with transverse relaxometry after ischemic exercise. Materials and Methods Ten subjects with intermittent claudication were studied. T2 was measured in the gastrocnemius and soleus muscles (m. gastrocnemius and m. soleus) at rest and repeatedly after exercise during 45 minutes of recovery. Prior to MRI a symptom-limited treadmill exercise was performed, and the ankle-arm blood pressure index (AAI) was measured at rest and after exercise. Results In the 14 legs with ischemic pain, a diverging response was found in the calf: T2 increased in m. gastrocnemius by 5.6% ± 4.9%, but decreased in m. soleus by –1.2% ± 4.4% (P < 0.001). Moreover, 13 regions in legs with ischemic pain and reduced AAI (from 0.7 ± 0.2 at rest to 0.31 ± 0.15 after exercise) had shortened T2 (–3.6% ± 1.8%) immediately after exercise. This finding was most frequent in m. soleus and two regions of m. gastrocnemius. Recovery was delayed in the latter two regions. Conclusion T2 may identify ischemic muscles after hypoxic exercise. Shortened T2 suggests a reduced water content (e.g., distribution volume of water) and may affect the upslope kinetics of an extravascular perfusion tracer. The different responses to ischemia by the soleus and gastrocnemius muscle may be due in part to their different fiber type compositions. J. Magn. Reson. Imaging 2006. © 2005 Wiley-Liss, Inc.