| Andreas Schäfer 1 2, Harald E. Möller 1 * |
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
2University of Nottingham, School of Physics and Astronomy, Sir Peter Mansfield Magnetic Resonance Centre, University Park, Nottingham, United Kingdom
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| email: Harald E. Möller (moeller@cbs.mpg.de) |
*Correspondence to Harald E. Möller, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany
| BOLD contrast • correlation distance • distant dipolar field • intermolecular double-quantum coherence (iDQC) |
A functional MRI (fMRI) study with visual stimulation of healthy subjects was performed at 3T exploiting intermolecular double-quantum coherences. The correlation distance, dc, was varied between 60 and 300  m for different evolution times,  . Robust activation was obtained in all experiments with average signal changes ([bar  S2 ]) = 8.4 ± 0.7% and 9.4 ± 0.8% for = 15 and 20 ms, respectively) exceeding those normally associated with conventional blood oxygen level-dependent (BOLD) fMRI. Relaxation-rate changes (R2 = 0.33 ± 0.36 s-1 and R2* = 0.77 ± 0.54 s-1) were similar to those commonly obtained for the extravascular BOLD effect. The number of activated voxels increased with increasing dc until a plateau was reached at  120 m. Similar trends were observed for the activation-induced percent signal change and for the maximal Z-scores. These effects were quantitatively explained by a reduced sensitivity at short dc due to increasing signal attenuation related to diffusion and an increasing amount of signal fluctuations in the fMRI time series due to imperfect suppression of unwanted coherence pathways. Consistent indications of a preferential selection of susceptibility changes in blood vessels of a particular size were not obtained. Magn Reson Med 58:696-704, 2007. © 2007 Wiley-Liss, Inc. |
Received: 16 March 2007; Revised: 30 July 2007; Accepted: 6 August 2007
