Overview

Medical implants represent a 3 billion € market in the EU. Approximately 50 million EU citizens carry a medical implant and a majority of these will need a magnetic resonance imaging (MRI) scan during the lifetime of their device. However, the powerful magnetic field of MRI systems still represents a unique safety hazard for these patients. Therefore, it is vital for both patient safety and the success of a medical implant on the market, that implant manufactures can demonstrate safety compliance in an MRI environment. This project will improve the competitiveness of European implant manufacturers by providing innovative, metrologically sound and legally safe methods to demonstrate the compatibility of their products with MRI safety regulations.

Need

With more than 30 million scans per year in EURAMET countries, MRI safety is an ongoing concern. Carriers of medical implants, making up almost 10 % of the EU population, are particularly at risk as fatal accidents have occurred due to the interference of the device with the electromagnetic fields (EMF) from the scanner. As the majority of these patients will need an MRI scan at one point in their lives, MRI compatibility of an implant is a key factor for the competitiveness of a manufacturer. This was exemplified in 2011 when Medtronic Inc. achieved the first ever MRI approval for a cardiac pacemaker and within a few years virtually all noncompatible devices disappeared from the market.

The currently applied procedures to demonstrate MRI compatibility are either outdated (ASTM F2182) or incomplete (ISO/IEC TS10974). The applications of those are costly and lengthy since a mistake can be fatal
for both patient and manufacturer. While large producers of high-end active implantable medical devices are facing technological challenges to demonstrate MRI compatibility, SMEs manufacturing passive medical
implants are overburdened by the necessity to demonstrate MRI safety for each new size and shape of a particular device, therefore limiting their innovation potential.

Numerical modelling of field distributions in human subjects is an established state of the art technique. However, even though this technique has been used to include the presence of metallic implants there were limitations as mostly generic or simplified implants with non-detailed features were modelled and there was limited experimental verification of the results.

Parallel-transmit (pTx) radiofrequency systems can be used in MRI scanners to steer, within certain limits, the electromagnetic field as well as temperature distributions in and around the implant. The use of pTx for risk mitigation has enormous potential to ensure safety for a wide range of different implants and boundary conditions, and these systems can be combined with sensor-equipped implants to provide real-time feedback. However, currently such pTx methodology is still in early development and further work is needed to prove its use.

In the EMRP project HLT06 MRI safety it was discovered that heating of metallic implants due to switched magnetic-field gradients is an underestimated hazard in MRI. Some normative documents ignore this effect
completely, whilst others mention the possibility of such effects only in the context of protecting the device rather than the patient. Recently, an experimental investigation of these effects hinted at the possibility that
the induced heating effect might not scale with the root-mean-square averaged field changes, which would be in contrast to the assumptions of existing standards on this subject. Therefore, more work is needed to
investigate the hazards associated with the interaction between bulk metallic implants and switched magnetic fields.