Information for patients
If you are a patient reading this and have a concern about an MRI scan you are scheduled to attend, we strongly recommend you contact the site where your scan is due to take place, you may also wish to refer to our ‘Information for Patients’ section. Please note local variations to the policies detailed on this website may apply, therefore please contact the hospital where your appointment is scheduled for clarification.
Disclaimer (MUST READ)
The MRI safety information contained within this webpage is intended for use by staff from NHS Greater Glasgow and Clyde (GGC) and associated health boards, namely: NHS Ayrshire and Arran, NHS Borders, NHS Dumfries & Galloway, NHS Forth Valley, NHS Golden Jubilee, and NHS Lanarkshire. Only staff from these health boards are approved to use this information and local variations to the policies detailed may apply. Non-approved users i.e. patients and staff from health boards other than those listed above, or staff from private medical organisations use this information at their own risk. We, NHS GGC, accept no responsibility for patient injury or adverse outcomes that may occur as a consequence of the information contained herein. If you have any questions regarding this disclaimer, please contact the NHS GGC MRI physics team on: ggc.MRSafetyExpert@nhs.scot.
MRI safety policy for scanning patients with metal objects or metal foreign bodies in their body
Must read: What this policy does not cover / notable exceptions
This policy does not relate to metal implants intended for patient implantation such as orthopaedic pins or screws
Must read: What the policy covers
This policy covers any erroneous metal foreign body which are typically not intended for patient implantation. For example: bullets, shrapnel, tools and so on…
Must read: The MR safety policy
For guidance on scanning of intra-orbital foreign bodies please follow this link.
There is no single, overarching policy that can be provided to ensure the safe MRI scanning of a patient who has an erroneous metal, foreign object within their body. Scanning of these patients must be considered on an individual basis as circumstances may vary.
What is provided here are some of the considerations one should take into account when considering the risk of scanning such a patient. Ultimately, the decision to scan should be made by the Radiologist who can offset the risk to the patient with the perceived benefit of scanning. The Radiologist may wish to consult with the referring clinician when considering the potential benefits of scanning and similarly, with the MR Safety Expert when considering the risk of scanning.
Examples (but not a comprehensive list) of metal foreign objects include: bullets or pellets, tools, weapons, metal fencing and shrapnel.
In considering the risks presented by the object, the following questions should be considered.
In regard to the risk to the patient from potential object migration:
- What is the object?
- How long has it been in its current position?
- Can we determine if it magnetic? Note that it may be possible for superficial objects to test if they are magnetic by using a handheld magnet.
- Is the object likely to be held in place by soft tissue or other piece of anatomy?
- What is in the immediate proximity of the object i.e. is the foreign object close to a sensitive piece of anatomy such as important vascular structures, organs or nerves?
For example, it is often the case that foreign objects such as pellets are embedded in soft tissue, far from any sensitive pieces of anatomy. Whilst there may be a risk that such an object might be ferrous, if the object has been well embedded in the soft tissue, the risk of migration may be considered low. Note that the picture of risk could change somewhat if the object was lying adjacent to, for example, the aorta.
In regard to the risk of heating or a burn to the patient as a result of object heating:
- Is the area of interest going to be exposed to the MRI RF field? If a local transmit – receive coil is available, would using this help to reduce the risk of heating? E.g. a foreign object in the abdomen would not be exposed to RF if the patient is referred for a brain scan and a brain T/R coil was used.
- What size and shape is the object? Long (>30cm) lengths of wire or metal may be more of a risk. Loops of metal are also more a concern.
- Is the patient able to respond to heating and press the buzzer? Please bear in mind that there may be a number of reasons why a person is not able to respond to heating (spinal injury, unconscious, anaesthetised, confused, mentally impaired).
Whilst considering the benefit that MRI scanning conveys to the patient, the Radiologist may also wish to consider, if there are safer, alternative means of addressing the clinical query rather than using MRI.
Further considerations: foreign metallic objects may cause imaging artefacts. A useful site for reference is the mrisafety.com section on Pellets, Bullets, and Shrapnel.
Overall, if the risk of migration and heating from MRI as a result of the foreign object is deemed to be low, the clinical benefit to the patient may well outweigh the perceived risk. However, given the variability involved with any given situation, the considerations above must be done on an individual basis.
Risk assessment: Note that a risk assessment cannot be accurately done in these circumstances as the picture of risk may vary from patient to patient depending on the nature and location of the foreign metal body