TH-AB-207-04: Active Implants in MRI: The MR Technologist's Perspective

The continued growth of Magnetic Resonance Imaging (MRI) in the last decades requires MRI safety programs to protect patients and healthcare workers from the hazards of MRI. Especially, a detailed knowledge about the MR safety status and applicable conditions is necessary before patients with implantable devices can be scanned in an MRI system. This course focuses on the evaluation of MRI safety programs and the MRI safety of implants from the perspective of the MR Industry, the implantable device industry and the MRI technologists. Auditing and Evaluating MRI Facility Safety Programs MRI safety programs have come under increased attention from the ACR and Joint Commission accreditation programs. The ACR in particular now requires that the medical physicist review the safety program annually. An effective audit for content and implementation can be performed using published guidance and techniques adapted from auditing radiation safety programs. This presentation provides practical guidance for the physicist tasked with conducting annual MRI safety program evaluations. Learning Objectives: 1. Describe resources and references that provide benchmarks for the content of a facility’s MRI safety program 2. Evaluate implementation of MRI safety programs through observation and review of documentation Implants Historically MRI vendors have contra-indicated the scanning of patients with implants due to concerns such as displacement and heating. Concerted engineering efforts by implant vendors to improve understanding of the MRI fields and potential implant interactions has resulted in labeling for some devices that allow safe patient examinations in MRI scanners within specific scanning conditions. The challenge is at least three-fold: 1) the precise definition of the conditions that, if followed, permit the safe scanning of the patient, 2) conditions and instructions that are reasonable to implement in typical clinical setting, 3) device test methods that support the MRI condition/exposure claims. The net Result of this ongoing effort is the benefit of providing limited scanning services to many (though not all) patients with implanted devices, at the cost of additional complexity for medical device and scan service providers. To recognize the range of implant imaging scenarios, terminology was developed (MR Safe, MR Conditional, and MR Unsafe) to identify the implant categorization and clarify the relevant issues. The purpose of the three implant presentations in this session is to provide understanding and experiences about the emerging opportunity and challenge of scanning patients with active implants from the perspective of the MR vendors, active implant device vendors and the MR technologists/radiographers. Over the last ten years there has been a concerted effort among the many stakeholders to understand issues, learn what MRI scanner engineering information is relevant, and develop testing methodologies that substantiate active and passive implant device MR Conditional labeling claims and instructions. As a Result of this cross-industry effort, better quality, higher performing products are being produced with more precise labeling and instructions for use. It is important to understand that as engineering understanding continues to improve, safety margins can decrease in order to extend better MRI access to patients, and consequently it is only more important to follow the labeling instructions. By understanding this background, the medical physicist community can support this emerging practice of medicine. Publicly available outputs have included: 1) A new technical specification for implant vendors (ISO/IEC TS1094 ed. 1) concerning MRI/active device interactions. Edition 2 is anticipated to publish end of 2015 and work will commence shortly thereafter on a full international standard. Additional standards work related to the specific needs of individual active device categories is underway. 2) Enhancements to the MR Safety standard (IEC 60601-2-33 ed. 3.1) concerning additional MRI system information outputs and revisions to MRI system labeling as needed for safe patient scanning. Publication of ed. 3.2 is imminent and will include “Fixed Parameter Option: Basic” (FPO:B) which is a new technical specification of scanner magnetic fields output control that coordinates with current active implant vendor design capabilities to simultaneously simplify the MR scanning process and improve scanner performance for safe scanning of patients. 3) Advances in device labeling through consultation with regulatory bodies (e.g. FDA), MR technologist/radiographers (SMRT) and both MRI and active implant industries. Revisions to numerous other standards (e.g. ASTM standards) are also supporting efforts towards improved, practical, clear labeling. 4) Ongoing educational efforts through presentations and publications to the larger MRI and active implant communities. Learning Objectives: 1. Learn about the new information MR vendors are releasing to support MR conditional scanning of implants and pending changes to scanner controls to further the optimize MR conditional scanning of implants. 2. Explain the workflow and issues involved in scanning patients with implanted device. Explore ideas that might make this easier. 3. Learn the fundamental interactions between implantable devices and each MRI field type (static, switched gradient, and RF)—and how each can cause safety hazards. 4. Learn about how the potential for patient harm due to device interactions depends on a variety of complex factors that are not easy to extrapolate between device models or makes—careful identification and usage of device MR Conditional labeling is imperative to protect patient safety. NIH/NCI grant 5R25CA132822, NIH/NINDS grant 5R25NS080949 and Philips Healthcare research grant C32