Extensive heterogeneity in white matter intensity in high-resolution T2*-weighted MRI of the human brain at 7.0 T

MRI at high magnetic field strength potentially allows for an increase in resolution and image contrast. The gains are particularly dramatic for T2*-weighted imaging, which is sensitive to susceptibility effects caused by a variety of sources, including deoxyhemoglobin, iron concentration, and tissue microstructure. On the other hand, the acquisition of high quality whole brain MRI at high field is hampered by the increased inhomogeneity in Bo and B1 fields. In this report, high-resolution gradient echo MRI was performed using an 8-channel detector to obtain T2*-weighted images over large brain areas. The high SNR achieved with the multi-channel array enabled T2*-weighted images of the brain with an unprecedented spatial resolution of up to 0.2 × 0.2 × 0.5 mm3. This high resolution greatly facilitated the detection of microscopic susceptibility effects. In addition to the expected contrast between gray, white matter, cerebral spinal fluid, and veins, a large degree of heterogeneity in contrast was observed throughout the white matter of normal brain. The measured T2* values in white matter varied as much as 30% with some of the variation apparently correlating with the presence of large fiber bundles.