title: Induction of microcurrents in critically ill patients in magnetic resonance systems.
abstract: OBJECTIVE
  To determine whether electric current can be induced in intracardiac catheters, thermistor wires and pacing electrodes in patients during magnetic resonance imaging (MRI).
  
  
  METHODS
  Prospective laboratory study.
  
  
  METHODS
  Postgraduate medical school hospital.
  
  
  METHODS
  A sheep heart model.
  
  
  METHODS
  None.
  
  
  RESULTS
  Voltage generated by saline 0.9% flowing through a magnetic field and distribution of current from a catheter tip within a sheep heart model were measured in a 0.15 Tesla MRI system. Resistance of loops formed by pacing wires, a pacing electrode, and a thermistor wire were measured in saline 0.9%. Effects of rapidly changing magnetic fields and the movement of the beating heart on epicardial pacing wires were calculated theoretically. A flow of 200 mL/min of saline 0.9% induced a current of 0.1 microampere (microA) (at 0.15 Tesla). From magnetic resonance images we derived a current density of approximately 0.004 microA/mm2 (at 0.15 Tesla). Internal resistance of pacing catheters and thermistor wires was > 1 megaohm (M omega). The maximum currents calculated (for a higher field strength of 1.5 Tesla) in a circuit formed by epicardial pacing wires were 80 microA, induced by the beating heart moving the wires through the magnetic field and 46 microA, induced by the rapidly changing magnetic fields.
  
  
  CONCLUSIONS
  Current generated by flow of conducting fluid should be safe. Pacing catheters and thermistor wires should be safe if well insulated and disconnected from external electric connections. However, current induced in epicardial pacing wires may be a hazard, and precautions should be taken. External wire tips must be separated, insulated, and coiled to lie along the axis of the magnetic field. Electrocardiography is required, and defibrillation equipment should be available.
authors.affiliation: Department of Diagnostic Radiology, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Peden
authors.forename: A G
authors.initials: AG
authors.lastname: Collins
authors.forename: P C
authors.initials: PC
authors.lastname: Butson
authors.forename: J G
authors.initials: JG
authors.lastname: Whitwam
authors.forename: I R
authors.initials: IR
authors.lastname: Young
mesh_terms: D000818:Animals; D006328:Cardiac Catheterization / Q000295:instrumentation*; D002304:Cardiac Pacing, Artificial; D016638:Critical Illness; D004553:Electric Conductivity; D017097:Electric Impedance; D004567:Electrodes, Implanted; D004574:Electromagnetic Fields; D004869:Equipment Safety; D005069:Evaluation Studies as Topic; D008279:Magnetic Resonance Imaging; D009200:Myocardial Contraction; D012756:Sheep; D012965:Sodium Chloride / Q000009:adverse effects
chemical_list: D012965:Sodium Chloride