Orientation Dependence of White Matter T 2 * Contrast at 7 T : A Direct Demonstration

Recently a great deal of interest at fields of 7T or more has been high resolution T2 -weighted images [1,2]. A FLASH-like sequence [3] can easily generate very high resolution (e.g. 0.2x0.2x1.0mm voxels) images in a reasonable time frame (<10 minutes), with relatively low distortion and SAR load. An impressive level of structure can be seen, not just due to the resolution but also because of increased contrast between tissues, especially around blood vessels. However, as explored by Li and colleagues [4], there is also considerable contrast in white matter areas that is not properly understood. Li suggests various contrast mechanisms including differences in iron concentration and/or organization/orientation, variation in myelin density, and variation in density and orientation of venous micro-vascular elements. This study attempts to directly address the question of possible orientation components to the contrast.