A 7T Coil System for Imaging Humans in the Sphinx Position to Evaluate the Effect of Head Orientation Relative to B0 for MR Imaging

Introduction: At 7T the B0 field has a strong effect on MR imaging. T2* weighted gradient echo scans have revealed surprising variation in image intensity in white matter [1]. Various mechanisms have been proposed, including differences in iron concentration or myelin density in various white matter fiber bundles or variation in density and orientation of venous micro-vascular elements [1]. Tissue orientation relative to the main magnetic field has been demonstrated to be a major component of the white matter contrast variation in high field animal brain T2 imaging [2]. Although the effect is smaller at lower field, it has been evaluated in 3T human brain imaging, where it is suggested that T2* varies according to sin(θz) in fiber bundles [3]. In addition, strong B0 gradients at air-tissue interfaces such as under the frontal lobe make it difficult to image some regions.