The MHRA defines implanted medical devices in two main categories: Active and Non-active. Active implants contain metallic components and require an energy source, whereas non-active implants contain metallic components and do not require an energy source in order to function, these are sometimes referred to as “passive implants”.
Implantable devices can contain electrical and metallic components which are affected by the static magnetic field, time varying magnetic field gradients and radio frequency electromagnetic fields in MRI. Some implants are not compatible with MRI and are therefore contraindicated by the implant manufacturer, or they may cause artefacts that can affect image quality. Many active and non-active implants are MR Safe or MR Conditional and as part of carrying out good MR safety checks this information should be obtained before the patient attends for their scan. Specific implant information should be documented in the patient’s permanent records, and some patients are given documentation and information about their implant by their surgeon.
The MHRA recommends that the hospital should develop a policy for the identification, documentation, imaging and provision of any necessary aftercare for patients with implantable medical devices undergoing an MR examination (section 4.11 Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use, 2015).
‘Off label’ scanning of implants
‘Off label’ scanning is a term that has only been recently used in the MRI community. This process is followed when it has not been possible to check implant or device safety for one or more reasons, but where MRI has been indicated as clinically valuable for the patient. MHRA guidance – section 4.11.4 ‘Scanning patients with implants where MRI may be contraindicated’
Functionality of these implants is dependent upon an energy source such as electrical, mechanical or pneumatic power. Examples of active implants include pacemakers and defibrillators, cochlear implants and auditory brainstem implants, neurostimulators and drug infusion pumps.
Relevant links and articles:
- BIR Safety week 2019 – Safety advice sheet: cardiac pacemakers
- BJR ‘Off-Label’ MRI examination of an MR Conditional Pacemaker
Leadless cardiac pacemakers: used for implantation in adults with bradyarrhythmias. This involves inserting a device into the heart that helps it beat at a normal rate.
- Article: Case report: Safety and Utility of Spinal Magnetic Resonance Imaging in Patients with High-Frequency Spinal Cord Stimulators: A Prospective Single-Centre Study March 2019
- MRI Safety week 2019 safety advice sheet – Neurostimulators
Deep Brain Stimulators
These implants do not require a power source in order to function. Examples of non-active implants include joint replacements, heart valves, aneurysm clips, programmable shunts, breast implants and intravascular stents.
Relevant links and articles
- Article: Programmable CSF Shunt Valves: Radiographic Identification and Interpretation, 1997
- Radiopaedia: Programmable cerebrospinal fluid shunt
- BBC article on dad who gets tattoo of shunt to help his daughter
- Magnetic Resonance Imaging is a safe technique in patients with prosthetic heart valves and coronary stents
- National Institute for Health and Care Excellence (NICE) website
- MED_EL website
- Cochlear Ltd
- Advanced Bionics Ltd
- BIR Safety week 2019 safety advice sheet: cochlear implants
- Magnet dislocation during 3T magnetic resonance imaging in a pediatric case with cochlear implant, Brazilian Journal of Otorhinolaryngology, April 2016
- Magnetic Resonance Imaging With Cochlear Implant Magnet in Place: Safety and Imaging Quality, Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology, April 2015
- Magnetic resonance imaging in patients with magnetic hearing implants : Overview and procedural management, October 2013