Safety Considerations in Magnetic Resonance Imaging of Patients with Implanted Medical Devices (Neuroimaging 2016)

Educational Objectives

The goal of this lecture is to improve patient care through the appropriate and safe use of neuroimaging. After hearing and assimilating this lecture, the clinician will be better able to:

1. Assess the risks of MRI for a patient who has an implanted medical device.

Summary

MRI: Scanners create several types of magnetic fields; any ferromagnetic item (and in some cases, nonferromagnetic items) can produce magnetic fields and induce currents; interaction of scanner’s magnetic field with medical device may lead to three types of potential complications; these include thermal effects (heating), magnetic effects (which may lead to movement or shifting of device), and electromagnetic effects (which may change field or function of device).

Thermal effects: Commonly encountered devices include implanted cardiac devices, cochlear implants, and, in neurologic practice, deep brain stimulators; all of these devices contain ferromagnetic materials, and some contain batteries; studies show subclinical effects and damage to tissue when cardiac devices undergo heating within MRI scanner; scanner may induce current in leads of device; patient may experience sensation of warmth or heat near or overlying device.

Mechanical effects: Small studies have demonstrated shifting of cochlear devices in scanner; in study of <35 patients, four experienced movement of cochlear device during scanning; in three patients, manual repositioning of device possible; in one case, surgical replacement required; firm external wrapping of device often prevents this complication; some devices become endothelialized or epithelialized with time and therefore present less risk for movement.

Electromagnetic effects: Every device at risk for electromagnetic effects because of presence of ferromagnetic materials; with advances in technology, smaller ferromagnetic parts and substitution with nonferromagnetic parts increasing; scanning might turn device off, shorten life of battery, or alter settings of device; in some cases, devices interrogated immediately after scan, with revision of settings as needed; programmable ventriculoperitoneal shunts subject to these types of complications.

Terminology: Devices no longer referred to as MRI compatible or incompatible; new categories magnetic resonance (MR) safe, MR conditional, and MR unsafe; MR safe — device has no potential for causing shift in field or inducing current when placed in MR scanner; no implantable devices currently labeled as MR safe; MR conditional — device poses no known hazards under specific MRI conditions and specific device conditions; implies that, with certain device settings and MRI field strengths, device not altered; most devices labeled MR conditional and have undergone testing; such devices should be placed in specified setting before going into scanner; MR unsafe — devices pose potential hazards in any MR device; eg, wristwatch; caveats — although newer aneurysm clips usually MR conditional, safety of previously tested devices become concern as scanners increase in strength and undergo changes in design (ie, device labeled MR conditional may have been tested using magnet of lower strength); MR conditional label associated with specific set of circumstances (setting of device and strength of magnet); per Food and Drug Administration, device considered safe in one type of scanner should not be assumed safe in other scanners.

Practical considerations for neurologists: Before performing MRI, radiology department researches manufacturer code and details of implanted device, and assesses safety of scanning and need for interrogation after procedure; elective MRI may need to be rescheduled to ensure that resources for interrogating device available.

Emergent MRI: Most MR conditional devices can withstand scanning in 1.5-T or 3-T scanner; MR unsafe devices should not be scanned; however, even when devices inadvertently scanned, adverse events rare; in most cases, changes in settings do not disable device.

Readings

Ponce de Leon M. Safety considerations in magnetic resonance imaging of patients with implanted medical devices. Continuum (Minneap Minn) 2016;22(5 Neuroimaging).

Disclosures

For this program, the following was disclosed: Dr. Ponce de Leon reported nothing to disclose. Unlabeled Use of Products/Investigational Use Disclosure: Dr. Ponce de Leon reports nothing to disclose. To view disclosures of planning committee members with relevant financial relationships, visit: audiodigest.org/continuumaudio/committee. All other members of the planning committee report nothing to disclose.

Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

CA051704

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.