Abstract
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 T1, T2, and Tmath image 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 T2, Tmath image, and the initial intensity I0 was observed. RH provoked an overshoot of T2, Tmath image, and the b-SSFP signal. No paradigm-related changes in T1 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 T2 variations but also significantly influenced by I0 changes. These I0 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.
