Premium
Experimental determination of the BOLD field strength dependence in vessels and tissue
Author(s) -
Gati Joseph S.,
Me Ravi S.,
Uǧurbil Kǎmil,
Rutt Brian K.
Publication year - 1997
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910380220
Subject(s) - voxel , nuclear magnetic resonance , field strength , physics , chemistry , materials science , nuclear medicine , magnetic field , medicine , radiology , quantum mechanics
High resolution functional MRI (fMRI) experiments were performed in human visual cortex at 0.5, 1.5, and 4 T to determine the blood oxygenation level dependent (BOLD) field strength response within regions of obvious venous vessels and cortical gray matter (“tissue”). T 2 *‐weighted FLASH images were collected in single‐ and multi‐echo mode and used to determine the intrinsic BOLD parameters, namely, signal‐to‐noise ratio (Ψ), the apparent transverse relaxation rate (R 2 *) and the change in R 2 * (ΔR 2 *) between the activated and baseline states. The authors find the average percentage signal change (ΔS/S, measured at TE = T 2 *) to be large in vessels (13.3 ± 2.3%, 18.4 ± 4.0%, and 15.1 ± 1.2%) compared with that in tissue (1.4 ± 0.7%, 1.9 ± 0.7%, and 3.3 ± 0.2%) at 0.5, 1.5, and 4 T, respectively. The signal‐to‐noise ratio in optimized, fully relaxed proton density weighted gradient echo images was found to increase linearly with respect to the static magnetic field strength (B 0 ). The predicted upper bound on BOLD contrast‐to‐noise ratio (ΔS/R) max as a function of field strength was calculated and found to behave less than linearly in voxels containing vessels larger than the voxel itself and greater than linearly in voxels containing a mixture of capillaries and veins/venules with a diameter less than that of the voxel.