Venous blood effects in spin-echo fMRI of human brain.
The spin-echo response to visual activation was studied as a function of spatial resolution at a field of 1.5 T. The results showed that the increase in absolute T(2) upon activation was as large as 22.8 +/- 3.1% (P < 0.05) at the highest resolution (5.3 mm(3)), while it was as small as 3.5 +/- 0.2% (P < 0.05) at the lowest resolution (42.2 mm(3)). In addition, upon increasing resolution, the spin-echo signal decay as a function of echo time changed from monoexponential to nonexponential. These data indicate that, when using the standard resolution for fMRI studies at 1.5 T, the effects of spin-echo changes in the draining veins are of major contribution to the total blood oxygenation level-dependent (BOLD) signal changes measured in voxels encompassing the activated brain areas. The data can be quantitatively accounted for using a model based on the intravascular origin of the spin-echo effect including both macrovascular and microvascular effects. Existing theories for the spin-echo BOLD effect based on diffusion through field gradients predict negligible spin-echo effects inside the large vessels and are therefore incompatible with the data. Magn Reson Med 42:617-626, 1999.
Oja
J M
JM
Department of Radiology, Johns Hopkins University Medical School, Baltimore, Maryland. oja@messi.uku.fi
Gillen
J
J
Kauppinen
R A
RA
Kraut
M
M
van Zijl
P C
PC
D001921:Brain / Q000502:physiology; D002550:Cerebral Veins / Q000033:anatomy & histology / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008833:Microcirculation / Q000502:physiology; D010100:Oxygen / Q000097:blood; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology
D010100:Oxygen