Assessment of muscle oxygenation with balanced SSFP: A quantitative signal analysis

Purpose To investigate the feasibility of balanced steady‐state free precession (b‐SSFP) for blood oxygenation level–dependent (BOLD) MRI during a short‐term ischemia/reactive hyperemia (RH) experiment on human calf muscles. Materials and Methods To investigate contributions to the b‐SSFP signal during an RH experiment, the relaxation times T 1 , T 2 , and T   2 *were quantified in an interleaved fashion. Data from soleus, gastrocnemius, and tibialis muscle groups of five healthy subjects were evaluated. Results During ischemia a decreased b‐SSFP signal amplitude as well as a decrease in T 2 , T   2 * , and the initial intensity I 0 was observed. RH provoked an overshoot of T 2 , T   2 * , and the b‐SSFP signal. No paradigm‐related changes in T 1 were observed. Comparing the evolution of transverse relaxation times, initial intensity, and b‐SSFP signal amplitude, we concluded that the measured b‐SSFP signal in muscle tissue is not only determined by T 2 variations but also significantly influenced by I 0 changes. These I 0 changes are attributed to spin density variations since inflow effects were suppressed by saturation bands. Conclusion b‐SSFP signal changes during a RH paradigm cannot unambiguously be assigned to oxygenation changes. Therefore, care has to be taken with their interpretation. J. Magn. Reson. Imaging 2008;27:1169–1174. © 2008 Wiley‐Liss, Inc.