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8. Implantable medical and non-medical objects

The use of MRI continues to expand in the UK, alongside advances in device technology.  In order to ensure good patient management and patient safety, departments should implement robust procedures to ensure the MRI safety status of any implanted device.  The SCoR and BAMRR recommend that departments obtain a copy of the annually updated publication by Shellock,F Reference Manual for Magnetic Resonance Safety, Implants and Devices.10  This contains safety advice and guidance and a comprehensive list of implants alongside the field strength under which they have been tested.  The list can also be viewed on the website hosted by Shellock F: http://www.mrisafety.com/  11 (accessed 27th February 2013)

However, as these are both American hosted publications, they may not always contain information on a particular device.  In this instance, contact should be made directly to the device manufacturer to ascertain its MRI safety status.

Departments should be aware that the MR compliancy listing of an implant may be changed and should ensure that their information is kept up to date.

13695342-exclamation-point.jpg All visitors and patients should be adequately screened by means of a safety questionnaire prior to entering the controlled area and no-one should be allowed to enter within the area if there is any doubt regarding the compliancy of any implants. Please also see section 17.1

An example safety questionnaire can be viewed on the BAMRR Website at the following link: http://www.bamrr.org/mri-safety  (accessed 27th February 2013)

Departments should have a mechanism for recording and storing details obtained regarding an implant’s MR compliancy.

13695342-exclamation-point.jpgFor MR conditional devices, departments should liaise with their MR safety advisor and equipment manufacturer to ensure that the conditions can safely be met.

13695342-exclamation-point.jpg Departments should proceed with caution.  The SCoR and BAMRR recommend that written evidence regarding an implant’s compliancy be obtained prior to scanning.  If a department is unable to obtain the required information, then scanning should not take place.

NB.  Manufacturers of implants and devices have a duty to supply safety information.  If you are unable to obtain such information, please report it to the MHRA.

8.1  Active devices

Mechanically, electrically and magnetically operated devices may malfunction in the presence of a strong magnetic field.  This malfunction may not be obvious at the time of examination but may subsequently have serious consequences.
Examples include:

  • cardiac  pacemakers
  • cochlear implants
  • programmable hydrocephalus shunts
  • implanted neurostimulation systems
  • implanted drug infusion pumps

NB: this is not an exhaustive list of examples.

13695342-exclamation-point.jpg Departments should ensure that their local rules contain information about active device implants which are contraindicated.  For those which are MR conditional, a process for scanning patients with such implants should be clearly documented.

Most cardiac pacemakers are contra-indicated in MRI.  Field strengths as low as 1mT may be sufficient to cause deflection, programming changes or to close reed switches.  Such patients should not enter the MR controlled area.  Departments should also be aware of patients who have had a pacemaker removed and should check for any remaining pacemaker wires which can act as antennae and cause induced currents.  However, there are now a number of manufacturers in the UK that have developed MR conditional pacemakers and leads, see 8.2.

13695342-exclamation-point.jpg The field strengths and other relevant operating parameters at which specific implants have been tested should be noted when assessing the safety of implants.  Safety at one field strength may change at another.

13695342-exclamation-point.jpgIt should be noted that many implants and devices have NOT been assessed at field strengths of 3T and above.

8.2  MR Conditional Pacemakers

Certain manufacturers have now developed MR Conditional pacemakers, allowing for patients with these to undergo MRI scanning under certain stated conditions for safe operation.

Current examples include:

BIOTRONIK Pro MRI Pacing systems. Further information available at:

http://www.biotronik.com/wps/wcm/connect/en_promri/biotronik/home/12      (accessed 28th February 2013)

MEDTRONIC Sure Scan- Advisa MRI Pacemaker and Ensura MRI Pacemaker systems.  Further information available at:  http://www.medtronic.com/surescan/index.html13     (accessed 28th February 2013)

ST JUDE MEDICAL Accent MRI Pacemaker. Further information available at:

http://www.sjmprofessional.com/Products/Intl/Pacing-Systems/Accent-MRI-Pacemaker.aspx14  (accessed 28th February 2013)

The MHRA states ‘Exceptionally, a person fitted with an MR conditional pacemaker may enter the MR controlled area for scanning only if the MR operator has confirmed that all of the manufacturer’s stated conditions for safe operation are met’. 2

In addition to complying with the manufacturers’ conditions for safe operation, the SCoR advises that departments formulate a local policy to be included within the local rules. Such a policy should include: a patient pathway; clearly defined roles and responsibilities of the radiology department, radiographic staff and the cardiology department; a list of any contraindications, potential adverse events and emergency procedures; the manufacturers’ specific operating instructions and any local specific instructions.

  • Departments must ensure a robust process for checking that both the pacemaker and the leads are MR conditional.
  • Departments should ensure that they obtain the manufacturers’ guidelines relevant to the United Kingdom.

8.3  Non-active devices

There is a risk that implanted ferro-magnetic devices will undergo attractive forces such that they can dislodge, causing serious injury or discomfort to the person concerned.  Such devices will be labelled as MR unsafe, MR conditional or MR safe.

13695342-exclamation-point.jpg Departments should ensure that their local rules contain information about non-active device implants which are MR unsafe.  For those which are MR conditional a process for scanning patients with such implants should be clearly documented.

Examples include:

  • Coils, stents and filters
  • Aneurysm clips
  • Heart valves
  • Orthopaedic implants

NB: this is not an exhaustive list of examples.

8.3.1   Aneurysm clips

13695342-exclamation-point.jpg Numerous aneurysm clips are contraindicated, namely those made of certain stainless steels.10

The majority are listed as either MR conditional or MR safe.10

If your department has a policy to scan MR conditional and MR safe aneurysm clips, a clearly defined process for ensuring accurate MR compliancy details of the clip and the process for scanning these clips should be documented within the local rules.

8.3.2   Management of Post Operative Patients

Great care must be taken with regard to recently implanted MR safe or MR conditional ferro-magnetic implants or clips which are not anchored into bone, before they become embedded with fibrous tissue.  Local rules should specify the time which should elapse prior to scanning, but it should be not be less than six weeks.  Those objects, such as bone screws or joint replacements which are firmly anchored, may safely be scanned but should be monitored carefully because the object may be subject to temperature rise: scanning should be discontinued if discomfort occurs.  Image quality around the site will, in any case, be seriously degraded and the examination may not be of diagnostic quality.

8.4  Intra Orbital Foreign Bodies

8.4.1   Patients

Intra orbital foreign bodies (IOFB) are of particular concern and any patient  presenting with a history of an IOFB should be treated with caution.  SCoR and BAMRR recommend that departments initiate a clinical screening process.  This should be documented within the local rules and must comply with IR(ME)R Schedule 1. The MR operator may be a named IR(ME)R Referrer who is also a registered healthcare professional and is entitled by the IR(ME)R Employer to refer for plain film radiography of orbits.

13695342-exclamation-point.jpg Departments should also investigate the existence of any previous orbital imaging prior to the patient undergoing an X-ray to exclude an IOFB.

8.4.2   Staff or carers accompanying a patient

Staff or carers accompanying a patient should not enter the MR controlled area, nor should they undergo an X-Ray if they have a history of an IOFB.  In such an instance the department should make alternative arrangements if the patient requires a carer within the scan-room.

8.4.3   Volunteers

Volunteers who present with a history of an IOFB should not generally be scanned (although they should be advised that this would not necessarily preclude them for a clinical scan if they were to require one in future).  However, if there has been provision made within the ethical approval for exposure to ionising radiation then the volunteer may proceed and undergo the clinical screening procedure for IOFB as outlined in 8.4.1.

NB. All volunteers participating in experimental trials should be screened before exposure and should have given informed consent.  The scanning of volunteers requires approval from local ethics committees.  It is recommended that all examinations are reported and suitable processes be in place for onward referral for those found to have abnormal scans.

8.5  Non- medical objects

8.5.1   Bullets and Shrapnel

Metallic objects in the body (such as shrapnel or a bullet) become fibrosed in tissue within six weeks.  Beyond that time it may be safe for scanning.  However, consideration must be given to the likelihood of heating effects and also the potential for larger, ferro-magnetic objects to experience significant forces while being positioned within the bore of the magnet.

Any large (>1 cm3) metallic fragments should be assessed on a case by case basis.  Such objects are of greater concern if they are located near significant soft tissue or vascular structures.  Therefore, obtaining current and previous imaging is essential in the assessment of risk versus benefit required before the MR scan may proceed.  Involvement of the patient, the referring clinician and a radiologist or consultant radiographer who can review and comment on related imaging is recommended in such cases.

8.5.2   Make up, piercings, tattoos

Non-medical objects such as piercings and make-up which has a high iron oxide content may cause burning and, wherever possible, should be removed both for patient safety and diagnostic image quality.  Some tattoos also have a high ferrous content and patients should be counselled regarding the possibility of local burns and asked to report any discomfort immediately and scanning stopped.  Consideration should also be given to patients who have hair extensions as there are certain types that are bonded or tied to the hair using metal components.

8.5.3    Transdermal Patches

Some transdermal patches contain metal within the backing which could potentially become conductive, leading to skin burns.

13695342-exclamation-point.jpg Transdermal patches should be removed prior to the patient entering the scan room if they contain, or may possibly contain, metal within the backing.

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