Purpose: To measure and quantify changes of R2* relaxation rates in the brain during breathing of Carbogen and CO2/air and to demonstrate clinical application of the proposed method.
Materials and Methods: In nine healthy volunteers and in two patients with a meningioma and a glioblastoma, respectively, cerebral tissue response to respiratory challenges using Carbogen and CO2/air was monitored with a dynamic R2* weighted multi-gradient-echo sequence with high temporal and spatial resolution. The breathing protocol consisted of 3/4/3 minutes of breathing air/gas/air, respectively. The ΔR2* response was analysed voxel-by-voxel. From all voxels with significant changes a global ΔR2* response function was obtained by averaging all voxel time series.
Results: In volunteers, almost all voxels showed a negative ΔR2* response as physiologically expected, showing the high sensitivity of the method. The maximum change of the ΔR2* response function during Carbogen breathing was almost twice as high as during CO2/air breathing (-2.4±0.3s-1 vs. -1.5±0.3s-1). For both gases, the ΔR2* response to the respiratory challenge was about three times slower (40–50s) than the response to normalization (14–15s). All measured ΔR2* response curves showed the same dynamic behavior.
In both patients, the examination was well tolerated and ΔR2* could be successfully determined, which allowed the assessment of tumor tissue responses.
Conclusion: The determination of ΔR2* in response to elevated levels of O2 and CO2 in blood provides a robust and reproducible method to assess oxygenation changes and vasoreactivity non-invasively. Initial examinations of tumor patients demonstrate the feasibility in clinical applications.
