Intracranial tumor response to respiratory challenges at 3.0 T: Impact of different methods to quantify changes in the MR relaxation rate R2*

Purpose: To compare two ΔR2* quantification methods for analyzing the response of intracranial tumors to different breathing gases. The determination of changes in the magnetic resonance imaging (MRI) relaxation rate R2* (ΔR2*), induced by hyperoxic and hypercapnic respiratory challenges, enables the noninvasive assessment of blood oxygenation changes and vasoreactivity. Materials and Methods: Sixteen patients with various intracranial tumors were examined at 3.0 T. The response to respiratory challenges was registered using a dynamic multigradient‐echo sequence with high temporal and spatial resolution. At each dynamic step, ΔR2* was derived in two different ways: 1) by subtraction of R2* values obtained from monoexponential decay functions, 2) by computing ΔR2* echo‐wise from signal intensity ratios. The sensitivity for detection of responding voxels and the behavior of the “global” response were investigated. Results: Significantly more responding voxels (about 4%) were found for method (1). The “global” response was independent from the chosen quantification method but showed slightly larger changes (about 6%) when ΔR2* was derived from method (1). Conclusion: Similar results were observed for the two methods, with a slightly higher detection sensitivity of responding voxels when ΔR2* was obtained from monoexponential approximation. J. Magn. Reson. Imaging 2010;32:17–23. © 2010 Wiley‐Liss, Inc.