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

Mürtz, Petra; Flacke, Sebastian; Müller, Andreas; Soehle, Martin; Wenningmann, Ingobert; Kovacs, Attila; Träber, Frank; Willinek, Winfried A.; Gieseke, Jürgen; Schild, Hans H.; Remmele, Stefanie

The consistent determination of changes in the transverse relaxation rate R2* (ΔR2*) 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 ΔR2* quantification from dynamic multigradient-echo data: (A) subtraction of R2* values calculated from monoexponential decay functions; and (B) computation of ΔR2* 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 ΔR2* quantification obtained by the two methods were compared with respect to the quality of the voxel-wise ΔR2* response, the number of responding voxels and the behaviour of the 'global' response of all voxels with significant R2* changes. For the two ΔR2* quantification methods, we found no differences in the temporal variation of the voxel-wise ΔR2* responses or in the detection sensitivity. The maximum change in the 'global' response was slightly smaller when ΔR2* was derived from signal intensity ratios. In conclusion, this first methodological comparison shows that both ΔR2* quantifications, from monoexponential approximation as well as from signal intensity ratios, are applicable for the monitoring of R2* changes during respiratory challenges. Copyright © 2010 John Wiley & Sons, Ltd.

NMR in Biomedicine, 2010, Vol 23, Issue 9, p1053

0952-3480

Academic Journal

10.1002/nbm.1532