Sz. Li et al., A COMPUTER-SIMULATION OF THE STATIC MAGNETIC-FIELD DISTRIBUTION IN THE HUMAN HEAD, Magnetic resonance in medicine, 34(2), 1995, pp. 268-275
Distortion of the static magnetic field inside the human head is depen
dent on regional tissue susceptibility variations and geometrical shap
e. These effects result in resonance line broadening and frequency shi
fts and consequently, intensity and spatial errors in both magnetic re
sonance imaging (URI) and magnetic resonance (MR) spectroscopy. To cal
culate the field distortion due to the susceptibility's geometry, two
dimensional (2D) finite element analysis was applied to simulate the f
ield distribution in a 2D model of the human head, placed in a uniform
magnetic field. The model contains air-filled cavities and sinuses, a
nd the remainder is treated as water. The magnetic field deviation was
evaluated using gray scale plots and histograms of the magnetic field
. The shifts in parts/million and broadening of the histograms corresp
ond to the NMR of the sampled region. The field distribution of the hu
man head was also experimentally mapped using the DANTE fagging sequen
ce. The calculated and experimental field maps are in good agreement.
Thus, geometric considerations with uniform susceptibilities are suffi
cient to explain most of the static magnetic field distribution in the
human head.