NEUROIMAGING / MAGNETIC RESONANCE
Magnetic resonance imaging contraindications
Created 23/05/2022, last revision 06/11/2023
- 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 associated with MRI
- there are four main potential hazard sources:
- static magnetic field (most commonly 1.5 or 3T) attracts ferromagnetic objects and accelerates 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 induce tissue heating, especially in the presence of implants (both ferromagnetic and non-ferromagnetic). These fields are a source of loud noise; hence, 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! In cases of 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 composed of titanium or zirconium and are deemed safe
- three principal issues may arise with metal implants:
- artifacts
- the risk of implant migration
- the risk of implant heating leading to adjacent tissue burn
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 conditional status for MRI
- use a 1.5T scanner only
- pre-MRI CT of the temporal bone is required for assessing bone thickness
- drug infusion pumps (insulin delivery, analgesic drugs, or chemotherapy pumps)
- external pumps must be removed and kept out of the MRI environment
- for implanted pumps, review the manufacturer´s guidelines for the specific pump before the MRI
- external pumps must be removed and kept out of the MRI environment
- aneurysmal vascular clips unless their MR compatibility is documented
- 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
- an 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 MRI-contraindicated
- conventional (ferromagnetic) EEG electrodes
- MRI-safe electrodes have been developed – only the MRI-safe portion goes with the patient to the scanner
- MRI-safe electrodes have been developed – only the MRI-safe portion goes with the patient to the scanner
Relative contraindications
- joint replacements, osteosynthetic material < 6 weeks after implantation or with signs of loosening
- prosthetic heart valves or annuloplasty rings < 6-8 weeks since implantation
- if the surgery was performed after the year 2000, the examination can be safely done with a 1.5T scanner
- stents < 6 weeks after implantation (in an emergency, there is no need to wait for 6 weeks – check the manufacturer’s instructions)
- inferior vena cava (IVC) filter < 6 weeks after implantation (use 1.5T)
- neurostimulation devices
- MRI should be performed only in strict accordance with the manufacturer’s conditional guidelines
- metal embolization material and occluders < 6 weeks after implantation unless their MR compatibility is documented
- ocular prosthesis
- medication patch should be removed before the procedure
- tattoos (including permanent makeup) in the area of interest
- tattoo must be healed; if <6 weeks old, reschedule the patient
- iron particles (especially red ink) will cause the tattoo to heat up – use ice packs on any tattoo that is in contact with the bore of the scanner or the MRI coil; encourage the patients to squeeze the communication ball if they experience warmth around their tattoo
- if the tattoo is within the scan area, a metal artifact may appear on the MRI image
- gastrointestinal tubes
- tubes containing no metal components are, by definition, MRI-Safe
- a unique device in this category is the Edi Catheter, which is considered MRI Unsafe
- colonoscopy clips (endoclips) < 8 weeks
- clips are made of titanium, tantalum, or non-ferromagnetic stainless steel and are labeled as MR Conditional
- cardiac loop recorders
- specific product details should be reviewed before MRI; consult the cardiologist managing the loop recorder
- data stored on the device may be altered or erased – download them before the MRI examination
- metallic fragments of uncertain origin located near the examined area
- most pellets and bullets tested for MR compatibility are composed of non-ferromagnetic materials
- consider the risks/benefits of performing an MRI
- radiographic screening (plain film radiographs or CT) is recommended for patients with a history of gunshot wounds
- spinal fixation hardware – the main issue is an artifact and possible heating; prefer a 1.5T scanner
- piercings/microdermal piercings
- piercings should be removed or replaced with metal-free alternatives before the examination
- surgical metal piercings outside the examination area are allowed
- piercings should be removed or replaced with metal-free alternatives before the examination
- some other devices and implants may be contraindicated – the radiologist and MRI technologist must assess the type of device
- 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, check the strength of the fixation, and write a report stating that the device is MRI-ready
- devices with retained wire arches may 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, MR personnel must instruct the patient to immediately notify the MR operator of any discomfort in the oral cavity (pain, burning).
- devices with retained wire arches may 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 undergo more frequent MRI scans
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Claustrophobia |
- claustrophobic patients may 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 during the examination of a pregnant patient
- if a contrast study is necessary, the patient must provide informed consent after the risks and benefits have been discussed
- if a contrast study is necessary, the patient must provide informed consent after the risks and benefits have been discussed
Gadolinium contrast agents (GBCAs) |
