Reducing inhomogeneity artifacts in functional MRI of human brain activation-thin sections vs gradient compensation

J Magn Reson. 2000 Aug;145(2):184-91. doi: 10.1006/jmre.2000.2105.


We evaluated two methods for correcting inhomogeneity-induced signal losses in magnetic resonance gradient-echo imaging that either use gradient compensation or simply acquire thin sections. The strategies were tested in the human brain in terms of achievable quality of T2*-weighted images at the level of the hippocampus and of functional activation maps of the visual cortex. Experiments were performed at 2.0 T and based on single-shot echo-planar imaging at 2. 0 x 2.0 mm(2) resolution, 4 mm section thickness, and 2.0 s temporal resolution. Gradient compensation involved a sequential 16-step variation of the refocusing lobe of the slice-selection gradient (TR/TE = 125/53 ms, flip angle 15 degrees ), whereas thin sections divided the 4-mm target plane into either four 1-mm or eight 0.5-mm interleaved multislice acquisitions (TR/TE = 2000/54 ms, flip angle 70 degrees ). Both approaches were capable of alleviating the inhomogeneity problem for structures in the base of the brain. When compared to standard 4-mm EPI, functional mapping in the visual cortex was partially compromised because of a lower signal-to-noise ratio of inhomogeneity-corrected images by either method. Relative to each other, consistently better results were obtained with the use of contiguous thin sections, in particular for a thickness of 1 mm. Multislice acquisitions of thin sections require minimal technical adjustments.

Publication types

  • Clinical Trial

MeSH terms

  • Adult
  • Artifacts*
  • Brain / physiology*
  • Brain Mapping
  • Cerebrovascular Circulation / physiology
  • Fourier Analysis
  • Hippocampus / physiology
  • Humans
  • Magnetic Resonance Imaging / methods*
  • Photic Stimulation