Changes in the MR relaxation rate R2* induced by respiratory challenges at 3.0 T: a comparison of two quantification methods

The consistent determination of changes in the transverse relaxation rate R-2* (Delta R-2*) is essential for the mapping of the effect of hyperoxic and hypercapnic respiratory challenges, which enables the noninvasive assessment of blood oxygenation changes and vasoreactivity by MRI The purpose of this study was to compare the performance of two different methods of Delta R-2* quantification from dynamic multigradient-echo data (A) subtraction of R-2* values calculated from monoexponential decay functions, and (B) computation of Delta R-2* echo-wise from signal intensity ratios A group of healthy volunteers (n = 12) was investigated at 3 0 T, and the brain tissue response to carbogen and CO2-air inhalation was registered using a dynamic multigradient echo sequence with high temporal and spatial resolution Results of the Delta R-2* quantification obtained by the two methods were compared with respect to the quality of the voxel-wise Delta R-2* response, the number of responding voxels and the behaviour of the 'global' response of all voxels with significant R-2* changes For the two Delta R-2* quantification methods, we found no differences in the temporal variation of the voxel-wise Delta R-2* responses or in the detection sensitivity The maximum change in the 'global' response was slightly smaller when Delta R-2* was derived from signal intensity ratios In conclusion, this first methodological comparison shows that both Delta R-2* quantifications, from monoexponential approximation as well as from signal intensity ratios, are applicable for the monitoring of R-2* changes during respiratory challenges Copyright (C) 2010 John Wiley & Sons, Ltd