title: Residual magnetism in an MRI suite after field-rampdown: what are the issues and experiences?
abstract: OBJECTIVE
  To investigate residual magnetization at different locations in the MRI suite at several time points prior, during and after field-rampdown with the goal to determine if the MRI suites could be reused in a clinical environment after the field-rampdown of MR scanners of different field strengths.
  
  
  METHODS
  Residual magnetism was measured with two gaussmeters in the MRI suites of an 8 Tesla (T) and a 0.7T whole body magnet at several time points prior, during and after field-rampdown.
  
  
  RESULTS
  Residual magnetism, in the MRI suite after controlled rampdown of an 8T superconducting magnet, was not significantly elevated compared with magnetic fields in the environment. Through 40 days, no significant changes in magnetism could be seen compared with initial measurements directly after rampdown, as both gaussmeters consistently measured. Similar findings were also observed after the quenched shutdown of a 0.7T system but a remanence was observed.
  
  
  CONCLUSIONS
  A controlled rampdown of even an ultrahigh field MR system does not lead to retained magnetic contamination, while forced quenched rampdown of a mid-field system revealed temporary remanence. There is no need to degauss an MRI suite when an appropriate steel composition has been used in the iron shield.
authors.affiliation: Department of Radiology, The Ohio State University, Columbus, OH 43210, USA. sammet.5@osu.edu
authors.forename: Steffen
authors.initials: S
authors.lastname: Sammet
authors.forename: Regina Maria
authors.initials: RM
authors.lastname: Koch
authors.forename: Francisco
authors.initials: F
authors.lastname: Aguila
authors.forename: Michael Vinzenz
authors.initials: MV
authors.lastname: Knopp
mesh_terms: D004574:Electromagnetic Fields; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D011829:Radiation Dosage; D011874:Radiometry