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 DeltaR2* 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* (DeltaR2*), 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, DeltaR2* was derived in two different ways: 1) by subtraction of R2* values obtained from monoexponential decay functions, 2) by computing DeltaR2* 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 DeltaR2* was derived from method (1). CONCLUSION: Similar results were observed for the two methods, with a slightly higher detection sensitivity of responding voxels when DeltaR2* was obtained from monoexponential approximation.