Pacemaker lead wires, ECG, and plethysmographic cables can also as surface-coil connections act as antennae. Usually the materials of such wires are not ferromagnetic.

Gradient and radio frequency fields may induce current into these wires and thus cause fibrillations and burns. This presents a risk to the patient and must be eliminated before the examination. The risk of heating during the MRI scan is dependent on the length and the material of these wires as well as the used field strength. If these wires are outside the RF field there is no risk of heating to expect.

The principal contraindications of the MRI procedure are mostly related to the presence of metallic implants in a patient. The risks of MRI scans increase with the used field strength. In general, implants are becoming increasingly MR safe and an individual evaluation is carried out for each case.

Some patients should not be examined in MRI machines, or come closer than the 5 Gauss line to the system.

Absolute Contraindications for the MRI scan:
Patients with absolute contraindications should not be examined or only with special MRI safety precautions. Patients with an implanted cardiac pacemaker have been scanned on rare occasions, but pacemakers are generally considered an absolute contraindication. Relative contraindications may pose a relative hazard, and the type and location of an implant should be assessed prior to the MRI examination.

Relative Contraindications for the MRI scan:
Osteosynthesis material is usually anchored so well in the patients that no untoward effect will result. Another effect on metal parts in the patient's body is the heating of these parts through induction. In addition, image quality may be severely degraded. The presence of other metallic implants such as surgical clips etc. should be made known to the MRI operators. Most of these materials are non-magnetic, but if magnetic, they can pose a hazard.

See also MRI safety, Pregnancy, Claustrophobia and Tattoos.