Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10712415 | Magnetic Resonance Imaging | 2016 | 11 Pages |
Abstract
This study aims to quantify the mean change of the effective transverse relaxation time T2â in active brain regions of human volunteers at field strengths of B0 = 3 T and 7 T. Besides the mono-exponential signal decay model an extended model is tested that considers mesoscopic field gradients across imaging voxels. Both models are checked for cross-talk and correlations between the parameters. A visual checkerboard-stimulation experiment with pause and stimulation periods of 50 s and six repetitions was performed on healthy volunteers. Eleven contrasts were acquired in about 1.47 s/1.43 s at 3 T/7 T using a segmented multi-contrast echo-planar imaging (EPI) sequence. Average BOLD-signal time courses were calculated in a multi-step (non-)linear least-squares process. Baseline T2â values of 37.72 ms/24.99 ms (47.34 ms/33.71 ms) with stimulus-correlated changes â T2â of 1.32 ms/0.74 ms (1.99 ms/1.43 ms) resulted from the mono-exponential (extended) model for 3 T/7 T. A dependence of those values on the initial intensity S0 was observed. Stimulus-correlated changes of S0 in the order of 1% were measured at both field strengths. The mono-exponential model was found to be less prone to instabilities in the regression of both parameters. Signal alterations due to inflow were observed. Measured relaxation times agree with values from literature using repetitive stimulation. A strong dependence of the measured relaxation times on the inflow-related model parameter was found for both models. The extended model is applicable to dynamic neurofunctional measurements, but is currently limited due to the low number of contrasts acquired.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Condensed Matter Physics
Authors
Moritz C. Berger, Peter Bachert, Jens Gröbner, Armin M. Nagel,