Tracking oxygen effects on MR signal in blood and skeletal muscle during hyperoxia exposure

Blood and muscle T-1 and T-2 relaxivity was examined under normoxic (air; 2 0.8% O-2) and hyperoxic (100% O-2) conditions to determine whether the oxyg enation state of blood in the large vessels and in the microcirculation can be monitored in vivo. The femoral artery/vain and the soleus and gastrocne mius muscles were examined in healthy human male volunteers. Arterial blood T1 decreased with hyperoxia, while venous blood T-2 increased, due to incr eased dissolved Oz and decreased deoxyhemoglobin, respectively. A biexponen tial T-2 model of muscle is proposed, where the short T-2 component reflect s primarily the intracellular and interstitial compartments (in fast exchan ge), and the long Ta reflects blood. In this model, the long T-2 component increased with hyperoxia exposure, This was more evident in slow twitch (so leus) than in fast twitch (gastrocnemius) muscle. It is concluded that chan ges in the long T-2 component reflect change in the microcirculation oxygen ation state. (C) 1999 Wiley-Liss, Inc.