Extravascular proton-density changes as a non-BOLD component of contrast in fMRI of the human spinal cord

• Published in: Magnetic resonance in medicine 2002-07, Vol.48 (1), p.122-127
• Main Authors: Stroman, P.W., Krause, V., Malisza, K.L., Frankenstein, U.N., Tomanek, B.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; blood oxygen level-dependent (BOLD); functional MRI; human; Humans; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging; Mathematics; Medical sciences; Miscellaneous. Technology; Models, Theoretical; Radiodiagnosis. Nmr imagery. Nmr spectrometry; spinal cord; Spinal Cord - physiology; spinal fMRI
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.10178

The fractional signal intensity change (ΔS/S) observed during activation in T2‐weighted fMRI of the spinal cord has previously been shown to depend linearly on the echo time (TE) but to have a positive value of roughly 2.5% extrapolated to zero TE. In this study we investigated the origin of this finding by measuring the ΔS/S in spinal fMRI with very short TEs. Our results demonstrate that the ΔS/S does not approach zero, but has a value as high as 3.3% at TE = 11 ms. At TEs > 33 ms we observed the linear relationship between ΔS/S and TE as in previous studies. These data demonstrate that there is a non‐BOLD contribution to signal changes observed in spinal fMRI. We hypothesize that this contribution is a local proton density increase due to increased water exudation from capillaries with increased blood flow during neuronal activation, and term this effect “signal enhancement by extravascular protons” (SEEP). Magn Reson Med 48:122–127, 2002. © 2002 Wiley‐Liss, Inc.