Extravascular proton-density changes as a non-BOLD component of contrast in fMRI of the human spinal cord.
The fractional signal intensity change (Delta S/S) observed during activation in T(2)-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 Delta S/S in spinal fMRI with very short TEs. Our results demonstrate that the Delta S/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 Delta S/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).
Stroman
P W
PW
MR Technology Group, Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada. Patrick.Stroman@nrc.ca
Krause
V
V
Malisza
K L
KL
Frankenstein
U N
UN
Tomanek
B
B
D006801:Humans; D008279:Magnetic Resonance Imaging; D008433:Mathematics; D008962:Models, Theoretical; D013116:Spinal Cord / Q000502:physiology*