Standards for medical devices in MRI: Present and future

Abstract

The purpose of this review is to define the current standards addressing safety of medical devices in MRI and to describe ongoing standards development efforts. The American Society for Testing and Materials (ASTM International) began developing standard test methods for determining the MR safety of medical devices in MRI in 1997. To date, five ASTM standards addressing testing and marking medical devices and other items for use in the MR environment have been published. International Standards Organization (ISO) 14630, the general requirements standard for nonactive surgical implants, is currently being revised to include information about MR safety of passive implants and to reference the ASTM standards. To address the unique safety issues of active implants, and in particular, active implants with leads, like pacemakers and neurostimulators, a joint working group between ISO TC150/ SC6 on active implants and International Electrotechnical Commission (IEC) SC 62B MT40 on magnetic resonance equipment for medical diagnosis is working to develop a technical specification for active implantable medical devices (AIMDs) in MRI. While much progress has been made, work still needs to continue to develop a complete body of test methods to allow the evaluation of the safety of medical devices in the MR environment.

Safety of Ultra-High Field MRI: What are the Specific Risks?

“…Some sites required proper testing according to the ASTM guidelines, whereas others relied on their local testing procedures. The ASTM guidelines include testing procedures for displacement force, torque, RF heating, and the influence on image quality [53,54]. Whereas the first two testing procedures are rather straightforward, as outlined earlier positioning of the implant at the worst case location for RF-heating testing is much more challenging at UHF than for lower fields, due to the substantially increased non-uniformity and asymmetric nature of the EM fields in conducting samples, i.e., how does one verify that the location of maximum heating is actually being probed?…”

Magnetic resonance imaging and gynecological devices

“…According to this terminology, testing "MRI safety" required in vitro tests in order to assess static magnetic field interactions, MRrelated heating and, in some cases, induced electrical currents. In order to test "MR compatibility," the assessment and description of artifacts are also required, in addition to the above-mentioned tests [4,9].…”

“…After a while, the CDRH's classification method proved confusing, which could potentially lead to accidents and injured patients; therefore, as of August 2005, the ASTM published the classification method currently in use, which defines three groups [4,9] Each group was represented graphically (Fig. 1).…”

Equipment changes and magnetic resonance imaging compatibility

“…At the centre of the field, implants are subject to torque and may rotate, loosening them [1]. Implants may also be heated, in extreme cases causing burns [2]. These problems are magnified as the magnetic field strength increases.…”

“…We read with great interest the recent editorial and paper regarding new connectors in neuraxial anaesthesia [1,2]. Our institution recently replaced all epidural kits with a new product (Flex Tip Plus Ò Epidural Catheter; Arrow International UK Ltd., Uxbridge, Middlesex, UK).…”