Calculation of MRI artifacts caused by static field disturbances

Abstract

Theory indicates that in magnetic resonance imagining, according to the spin-wrap method, the distortions in the image caused by a locally disturbed static magnetic field should show up as displacements in the slice-selection and read-out directions, proportional to the magnitude of the field disturbance and inversely proportional to the strengths of the imagining gradients. In phase-contrast images, phase effects may be described by the product of field disturbance, gyromagnetic ratio and data collection delay. To test this theory spheres with aberrant permeability (steel, air) were imaged immersed in water. The resulting images showed good agreement with simulated images calculated under the above assumptions. The implications of the above assumptions. The implications of these results concerning contrast media consisting of magnetic particles are discussed.