A 63-year-old male with a history of hypertension, hyperlipidemia, and BPH presents to the ED for evaluation of 2 days of intermittent right arm numbness and difficulty moving the right arm. Episodes last around 20 to 30 minutes at a time. These episodes have occurred 2-3 times per day. Initial head CT is negative. Neurology recommends MRI for further evaluation. The patient is a retired mechanic. How do you briefly but safely screen this patient for MRI? (note, this patient should also fill out a full MRI safety screening form if it is part of your hospital's protocol, but a brief screening tool will give you reassurance to put the order in and decrease blind clicking-through of the safety prompt in the order).
The 5 questions of a brief but comprehensive MRI safety screening:
1. Do you have any metal in your body? (obviously)
General MRI mechanics: Very briefly, an MRI machine will apply forces to ferromagnetic metals that produce both heat and torque. This is dangerous for obvious reasons and can result in burns and local tissue disruption.
2. Have you had any surgeries, procedures, or implants?
The safety of implanted devices in MRI machines is extremely variable. It is important to consider all implanted devices including, but not limited to, pacemaker/AICD, neurostimulators, medication pumps, cochlear implant, ocular implants, aneurysm clips, artificial heart valves, coils, stents, filters, tissue expanders, and penile implants.
An excellent resource is MRISafety.com which is a website that contains a comprehensive list of device MRI compatibility which can be searched based on device serial numbers. This requires the patient to have the card related to the device in hand or they are able to contact the primary surgeon who placed the device.
The majority of metallic implants currently are either non-ferromagnetic or weakly ferromagnetic. Weakly ferromagnetic devices can pose a potential issue with MRI as they may be subject to forces that can cause heating or movement despite being considered "safe for MRI". This is especially relevant in coils, stents, and filters. It is recommended that, if possible, patients with weakly ferromagnetic coils, stents, or filters not undergo MRI for the first 6 to 8 weeks after implantation to ensure that these devices are adhered to the vessel wall and will not be subjected torque forces by the MRI magnet.
Un-fun fact: There is a documented case in literature of the patient dying from disruption of an aneurysm clip after entering an MRI suite. The aneurysm clip was documented as non-ferromagnetic but turned out to have been a magnetic clip and it was dislodged from the vessel causing a massive brain bleed.
3. Have you ever been shot? What about by a BB gun?
Retained bullets, shrapnel, or other projectiles are a common cause of injury in an MRI. The majority of these are ferromagnetic and pose significant risk in the MRI machine. Patients will sometimes forget until prompted that they were shot by a BB gun as a child and have a retained BB in an extremity or elsewhere.
4. Have you ever worked in automotive, metal grinding, or gotten metal into your eye?
Ocular metallic foreign bodies pose a risk of blindness when exposed to MRI due to both heat and torque. Patients who have worked in high risk careers such as automotive, steel working, or metal grinding are especially high risk as they may not know they have a small fragment in their eye. At Stony Brook, it is our radiology policy here that patients who have work-related risk factors should undergo a orbit x-ray to evaluate for retained metallic bodies.
5. Do you have any medication patches or old/amateur tattoos?
Again, both of these pose a risk of burns inside the MRI machine due to micro-particles of ferromagnetic metals which heat up when exposed to MRI. Patients will sometimes forget that they have a medication patch when listing medications. Same goes for all tattoos, especially home or amateur tattoos. Practitioners will often use ink that contains metallic fragments which will also cause burns in the MRI machine.
Disclaimer: This is not a substitute for having the patient fill out the full MRI safety screening form. However, this is a brief verbal screening you can perform with the patient and know that when you click the safe-for-MRI order, you can be confident that you have not poorly assessed their risk.
Laura Saltzman, MD is a current third year resident at Stony Brook Emergency Medicine.
Resources
Edited by Bassam Zahid, MD