Imaging at high magnetic fields: initial experiences at 4 T.
This article reviews the preliminary experiences and the results obtained on the human brain at 4 T at the University of Minnesota. Anatomical and functional images are presented. Contrary to initial expectations and the early results, it is possible to obtain high-resolution images of the human brain with exquisite T1 contrast, delineating structures especially in the basal ganglia and thalamus, which were not observed clearly in 1.5-T images until now. These 4-T images are possible using a new approach that achieves maximal contrast for different T1 values at approximately the same repetition time and has built-in tolerance to variations in B1 magnitude. For functional images, the high field provides increased contribution from the venuoles and the capillary bed because the susceptibility-induced alterations in 1/T2* from these small-diameter vessels increase quadratically with the magnitude of the main field. Images obtained with short echo times at 4 T, and by implication at lower fields with correspondingly longer echo times, are expected to be dominated by contributions from large venous vessel or in-flow effects from the large arteries; such images are undesirable because of their poor spatial correspondence with actual sites of neuronal activity.
Uğurbil
K
K
Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis 55455.
Garwood
M
M
Ellermann
J
J
Hendrich
K
K
Hinke
R
R
Hu
X
X
Kim
S G
SG
Menon
R
R
Merkle
H
H
Ogawa
S
S
D001921:Brain / Q000033:anatomy & histology / Q000098:blood supply / Q000502:physiology; D017352:Echo-Planar Imaging / Q000379:methods; D005583:Fourier Analysis; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008280:Magnetics; D008954:Models, Biological; D008962:Models, Theoretical; D009044:Motor Cortex / Q000033:anatomy & histology / Q000502:physiology; D009048:Motor Skills / Q000502:physiology; D010775:Photic Stimulation; D013060:Speech / Q000502:physiology; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology