Quantifying the intra‐ and extravascular contributions to spin‐echo fMRI at 3 T

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Abstract
Functional MRI (fMRI) by means of spin‐echo (SE) techniques provides an interesting alternative to gradient‐echo methods because the contrast is based primarily on dynamic averaging associated with the blood oxygenation level‐dependent (BOLD) effect. In this article the contributions from different brain compartments to BOLD signal changes in SE echo planar imaging (EPI) are investigated. To gain a better understanding of the underlying mechanisms that cause the fMRI contrast, two experiments are presented: First, the intravascular contribution is decomposed into two fractions with different regimes of flow by means of diffusion‐weighting gradient schemes which are either flow‐compensated, or will maximally dephase moving spins. Second, contributions from the intra‐ and extravascular space are selectively suppressed by combining flow‐weighting with additional refocusing pulses. The results indicate two qualitatively different components of flowing blood which contribute to the BOLD contrast and a nearly equal share in functional signal from the intra‐ and extravascular compartments at TE ≈ 80 ms and 3 T. Combining these results, there is evidence that at least one‐half of the functional signal originates from the parenchyma in SE fMRI at 3 T. The authors suggest the use of flow‐compensated diffusion weighting for SE fMRI to improve the sensitivity to the parenchyma. Magn Reson Med 52:724–732, 2004.
Funding Information
  • Federal German Ministry of Education and Research (BMBF) within the framework of German-Israeli project cooperation (DIP)