High-resolution fMRI using multislice partial k-space GR-EPI with cubic voxels

The premises of this work are: 1) the limit of spatial resolution in fMRI i s determined by anatomy of the microcirculation; 2) because of cortical gra y matter tortuosity, fMRI experiments should tin principle) be carried out using cubic voxels; and 3) the noise in fMRI experiments is dominated by ro w-frequency BOLD fluctuations that are a consequence of spontaneous neurona l events and are pixel-wise dependent. A new model is proposed for fMRI con trast which predicts that the contrast-to-noise ratio (CNR) tends to be ind ependent of voxel dimensions tin the absence of partial voluming of activat ed tissue), TE, and scanner bandwidth. These predictions have been tested a t 3 T, and results support the model. Scatter plots of fMRI signal intensit ies 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 st udied. The CNR tended to be constant across pixels within a subject but var ied 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 s uccessfully. 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 W iley-Liss, Inc.