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
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- 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
- external pumps must be removed and kept out of the MRI environment
- 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
- MRI safe electrodes have been developed – only the MRI-safe portion goes with the patient
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)
- 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
- 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
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- claustrophobic patients might require sedation
- using larger and open MRI systems might be helpful → claustrophobia and MRI
MRI during pregnancy
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- MRI (for maternal or fetal reasons) is the leading imaging modality in pregnancy
- use a 1.5 T scanner
- to date, there are no known adverse effects or specific consequences for fetuses exposed to non-contrast MRI
- published data show no increased risk of fetal malformations, even in the first trimester [Ray, 2016]
- there is growing experience with fetal MRI (detection of brain 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
- if a contrast study is necessary, the patient must give informed consent after the risks and benefits have been discussed
