field map
An MRI acquisition measuring magnetic field inhomogeneities used to correct distortions in functional imaging.
Full Definition
A field map is an essential calibration scan in MRI neuroinformatics that measures spatial variations in the static magnetic field (B0) across the brain. These field inhomogeneities, caused by tissue interfaces and magnetic susceptibility differences, create geometric distortions particularly problematic in echo-planar imaging sequences commonly used for fMRI. Field maps enable post-hoc correction of these distortions by providing a voxel-wise measurement of field deviation from the nominal field strength. The correction process involves unwarping distorted images based on the measured field map, significantly improving spatial accuracy of functional data. Modern neuroinformatics protocols routinely include field map acquisition as part of standard preprocessing pipelines to ensure accurate spatial localization of brain activity.
Usage
Usage note: Can be written as one word (fieldmap) or hyphenated (field-map); maintain consistency.
In Context
- "Field map correction reduced signal dropout in the orbitofrontal cortex characteristic of susceptibility artifacts." — Image quality improvement
- "The field map revealed significant B0 inhomogeneity near the auditory canals requiring careful correction." — Technical quality assessment