NEUROIMAGING / MAGNETIC RESONANCE

Magnetic resonance imaging contraindications

Created 23/05/2022, last revision 29/01/2023

  • MRI has gradually become one of the most important non-invasive imaging techniques in neurology
  • it uses a strong magnetic field, changing magnetic fields, radio waves, and a computer to acquire detailed images
  • healthcare professionals need to be aware of the potential risks and contraindications of MRI
  • there are four main potential hazard sources:
    • static magnetic field (most commonly 1.5 or 3T) attracts ferromagnetic objects and accelerate them toward the center of the device – can dislodge implants or affect the function of devices such as pacemakers and pumps
    • radiofrequency (RF) fields and variable gradient magnetic fields – can cause tissue heating, especially in the presence of implants (both ferromagnetic and non-ferromagnetic). These fields are a source of loud noise (the use of hearing protection – headphones or earplugs – is essential throughout the examination)
    • gadolinium contrast agents (GBCA)

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 obtain appropriate 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 safe
  • three major problems can occur with metal implants:
    • artifacts
    • the risk of implant migration
    • the risk of heating the implant and burning of adjacent tissue
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 may cause 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 must be removed and kept out of the MRI environment
    • with the implanted pumps, review the manufacturer´s 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 in or near 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 bodies must be performed by a radiologist before the patient enters the scanning room
  • implanted sternal device system (temporal use in children)
  • “Triggerfish” Contact Lens – this lens allows for an automated recording of continuous intraocular pressure. This device is MRI unsafe and can cause severe eye burns
  • gastric reflux device
    • The LINX Reflux Management System is implanted around the lower end of the esophagus – this implant is contraindicated
  • conventional (ferromagnetic) EEG electrodes
    • MRI safe electrodes have been developed – only the MRI-safe portion goes with the patient MR Conditional Quick Connect Electrodes
Relative contraindications
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  • fixed orthodontic devices pose no threat to the patient during the MRI scan
  • 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 stating 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,  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 personnel to immediately inform the MR operator of any discomfort in the oral cavity (pain, burning)
  • 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 medical conditions who are expected to have more frequent MRI scans
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Claustrophobia

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 a contrast study is necessary, the patient must give informed consent after the risks and benefits have been discussed

→ gadolinium in pregnancy and breastfeeding

Gadolinium contrast agents (GBCAs)

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Magnetic Resonance Imaging Contraindications
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