Journal
NEUROIMAGE
Volume 24, Issue 4, Pages 1164-1169Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.neuroimage.2004.11.011
Keywords
effective transverse relaxation rate; brain rotation; susceptibility effects
Funding
- NIMH NIH HHS [R01 MH61427] Funding Source: Medline
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Several modern MRI techniques, such as functional MRI (fMRI), rely on the detection of microscopic changes in magnetic susceptibility. However, differences in magnetic susceptibility between brain tissue, bone, and air also produce local magnetic field gradients that may interfere with the contrast of interest, particularly at high field strengths. Since the magnetic field distribution depends on the orientation of the human head in the MRI scanner, head rotations can change the effective transverse relaxation rate (R-2*) and confound fMRI studies. The size of the R-2* changes produced by small head rotations was estimated from a brain-shaped gel-phantom at 4 T, by measuring the signal decay at 96 different echo times. Similar measurements were carried out in a human study. Rotations larger than 2degrees changed R-2* more than 1.5 Hz in the phantom, and indicate that even small rotations may compromise fMRI results. (C) 2004 Elsevier Inc. All rights reserved.
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