NEUROIMAGING / MAGNETIC RESONANCE

Magnetic resonance imaging contraindications

Created 23/05/2022, last revision 06/06/2022

  • Magnetic Resonance Imaging (MRI) has become a mainstay of non-invasive diagnostic modality since the 1980s
  • it uses a powerful magnetic field, changing magnetic fields, radio waves, and a computer to get detailed images
  • healthcare professionals must know potential risks of MRI
  • there are three major potential safety risks:
    • the magnetic field of MRI scanners attracts and accelerates ferromagnetic objects toward the center of the machine. This effect can displace implants or affect the function of devices such as pacemakers and pumps
    • the radiofrequency (RF) field created by RF coils can cause tissue heating, especially in the presence of implants. Even non-ferromagnetic implants and wires can cause heating
    • the time-varying fast-switching gradient magnetic field function can stimulate muscles or peripheral nerves and induce implant heating. They also produce noise in the MRI scanner space, which can damage the hearing system. Using hearing protection (headphones or earplugs) is essential during an MRI examination

Metallic devices and objects

  • all devices require investigation through a certified MRI safety website or the individual manufacturers’ website. If there is no evidence or information about the MRI safety of a device/implant, it has to be considered MRI unsafe
  • it is the referring physician’s responsibility to get proper information about the implant! With a relative contraindication, the referring physician must weigh the benefits of the examination and inform the patient of the risks (after consultation with a radiologist)
  • all removable metal prostheses (dental bridges) and electronic devices (e.g., hearing aids) must be removed before entering the MRI room
  • dental implants are usually made of titanium or zirconium and are therefore safe
  • three major problems can be encountered with metal implants:
    • artifacts
    • the danger of implant movement
    • the risk of the implant heating and burning the adjacent tissues
Absolute contraindications
  • the MRI non-approved cardiac implantable electronic devices (CIED)  → see more here
    • pacemaker (PM), cardioverter-defibrillator (ICD), cardiac resynchronization therapy (CRT) device
  • temporary external transvenous pacing leads and abandoned intracardiac pacing leads
    • radiofrequency pulses can induce currents that could lead to thermal injuries
  • implantable neurostimulation systems with unknown MR compatibility
  • cochlear implants, unless MR compatibility is documented
    • several implants have received the conditional status for MRI
    • use a 1.5T scanner only
    • pre-MRI CT of the temporal bone is required for bone thickness
  • drug infusion pumps (insulin delivery, analgesic drugs, or chemotherapy pumps)
    • external pumps need to be removed and kept out of the MRI environment
    • with the implanted pumps, review the manufacturer guidelines for the specific pump before MRI
  • aneurysmal vascular clips unless their MR compatibility is documented
    • the examination may be performed if the clips or coils were placed after the year 2000
    • > 6-8 weeks after the procedure
  • catheters with metallic components (Swan-Ganz catheter)
  • magnetic dental implants
  • artificial limb unless MR compatibility is documented
  • metal foreign bodies within or adjacent to the globe
    • fragment in the eye could move or be displaced and cause injury to the eye or surrounding tissue
    • a screening radiograph or CT of the orbits for the foreign body must be performed by a radiologist before the patient enters the scan room
  • implanted sternal device system (temporal use in children)
  • “Triggerfish” Contact Lens – this lens allows for an automated recording of continuous intraocular pressures. This device is MRI unsafe and can cause severe eye burn
  • gastric reflux device
    • The LINX Reflux Management System is implanted around the lower end of the esophagus – this implant is totally contraindicated
  • traditional (ferromagnetic) EEG electrodes
    • MRI conditional electrodes have been developed – only the MRI safe portion goes with the patient MR Conditional Quick Connect Electrodes
Relative contraindications
Content available only for logged-in subscribers (registration will be available soon)
  • fixed orthodontic devices do not pose a threat to the patient during the MRI examination
  • metal components cause artifacts, but these can be avoided by changing the scanning plane
  • before the MR examination, the orthodontist should remove the detachable wires and check the strength of the fixation and write a report that the device is MRI ready
    • devices with retained wire arches can sometimes present a closed, electrically conductive loop that can become heated during the MR examination; therefore, in practice, the possibility of thermal damage to the oral mucosa during the MR examination cannot be expunged. Prior to the examination, the patient must be instructed by the MR staff that in the event of discomfort in the oral cavity (pain, burning), the patient must immediately inform the MR operator
  • fixed orthodontic devices (locks and rings) must be completely removed before the MRI examination in the jaw area – consider an alternative imaging method
  • ceramic, plastic, or titanium locks should be preferred for patients with health problems where more frequent MR examinations can be expected
Content available only for logged-in subscribers (registration will be available soon)

Claustrophobia

  • claustrophobic patients might need sedation
  • using larger and open MRI systems might be helpful

MRI during pregnancy

  • MRI (for maternal or fetal reasons) is the leading imaging technique during pregnancy
  • use a 1.5 T scanner
  • to date, there is no known adverse effect or specific consequence for fetuses exposed to non-contrast MRI
    • published data did not show a higher risk of fetal malformations even in the first trimester  [Ray, 2016]
    • there is a growing experience with MRI of the fetus (detection of CNS developmental defects, placental abnormalities, etc.) [Griffiths, 2005]
  • gadolinium should be avoided when examining a pregnant patient
    • if contrast examination is essential, the patient must provide informed consent after a discussion of risks and benefits

→ gadolinium during pregnancy and breastfeeding

Gadolinium contrast agents (GBCAs)

icon-angle icon-bars icon-times