Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 46, Issue 1, Pages 114-125Publisher
WILEY
DOI: 10.1002/mrm.1166
Keywords
fMRI; neuroimaging; brain; physiological noise; BOLD contrast
Funding
- NCI NIH HHS [CA41464] Funding Source: Medline
- NCRR NIH HHS [M01 RR00008-GCRC] Funding Source: Medline
- NIMH NIH HHS [MH51358] Funding Source: Medline
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The premises of this work are: 1) the limit of spatial resolution in fMRI is determined by anatomy of the microcirculation; 2) because of cortical gray matter tortuosity, fMRI experiments should tin principle) be carried out using cubic voxels; and 3) the noise in fMRI experiments is dominated by row-frequency BOLD fluctuations that are a consequence of spontaneous neuronal events and are pixel-wise dependent. A new model is proposed for fMRI contrast which predicts that the contrast-to-noise ratio (CNR) tends to be independent of voxel dimensions tin the absence of partial voluming of activated tissue), TE, and scanner bandwidth. These predictions have been tested at 3 T, and results support the model. Scatter plots of fMRI signal intensities and low-frequency fluctuations for activated pixels in a finger-tapping paradigm demonstrated a linear relationship between signal and noise that was independent of TE. The R-2 value was about 0.9 across eight subjects studied. The CNR tended to be constant across pixels within a subject but varied across subjects: CNR = 3.2 +/- 1.0. fMRI statistics at 20- and 40-ms TE values were indistinguishable, and TE values as short as IO ms were used successfully. Robust fMRI data were obtained across all subjects using 1 x 1 x 1 mm(3) cubic voxels with 10 contiguous slices, although 1.5 x 1.5 x 1.5 mm(3) was found to be optimum. Magn Reson Med 46:114-125, 2001, (C) 2001 Wiley-Liss, Inc.
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