A COMPUTER-SIMULATION OF THE STATIC MAGNETIC-FIELD DISTRIBUTION IN THE HUMAN HEAD

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.