Analytical Modeling of Noise in MRI Scanners

Acoustic noise generated by MRI scanners is sometimes a significant problem for patients by heightening their anxiety and even causing temporary and permanent hearing impairment. This noise is caused by the Lorentz forces acting on the gradient coils of MRI scanner bound within an epoxy resin cylinder. Some acoustic analytical models were developed to describe the sound radiation characteristics of the gradient coil system. The gradient coil was modeled as a finite cylindrical duct with vibrating walls. The sound field in the duct satisfied both the boundary conditions at the wall and at the open ends. The wave reflection phenomenon at the open ends of the finite duct was described by general radiation impedance. Comparisons between the results obtained by these analytical models and calculated by a commercial (boundary element method) BEM code are presented in this paper. Both the advantages and disadvantages of both methods are discussed. The comparisons show that the results calculated by all these models reached good agreement especially at the cut-off frequencies (resonance frequencies). Corresponding experimental data have also shown a similar trend at the cut-off frequencies.Copyright © 2007 by ASME