The Effects of Voxel Size and Image Smoothing on R2* Measurements of the Human Brain

Christian Denk¹, Alexander Rauscher¹

Quantitative imaging of the R2* relaxation rate employing multiple echoes can be used to assess blood oxygenation and iron content in neural structures. However, R2* is not a strictly intrinsic tissue property, as it also depends on the spatial relationship between voxel geometry and background field inhomogeneities. These background field inhomogeneities cause additional signal decay. To investigate the influence of spatial resolution and smoothing on R2* values, we acquired images with high spatial resolution and applied spatial smoothing to the complex data, which simulates acquisition at lower spatial resolution, and to the magnitude data. We found that both changes in spatial resolution and spatial smoothing of magnitude of high resolution data leads to strong changes in R2*, which suggests that R2* values should be interpreted in the light of data acquisition parameters as well as data smoothing.