Examples of field-map correction
The magnitude of the field-map correction depends on the magnitude of the susceptibility artifact. For regions with a large field-variation due to suseptibility, such as orbital-frontal cortex, signal can be completely lost, so the distortion is of no value. For subjects with small sinuses and correspondingly small field-variations the correction might be insignficant. In every cohort of subjects, however, there will be a subgroup with significant distortion that can be corrected. The images below were obtained from the first three subjects who volunteered for a study. Although the corrections aren't huge, they are significant in some regions of the frontal lobe. The images below are from three randomly chosen subjects demonstrating the degree of correction (Note: This page doesn't quite work yet: it only shows two images. Click to flip between them.<\p>
