MR Safety-Basic Introduction Vera Kimbrell BSRT MR R FSMRT
Educational Objectives:
1. Outline the major safety issue facing MR professionals
2. Explore the causes and potential problems in a MR environment
3. Review the mechanisms in place to mitigate harm during a MR exam
MR Safety is an active and constant process to protect out patients, staff and the scanner itself from both internal and external events that could cause harm. In this presentation we will explore the areas for concern and the detail the safeguards in place to mitigate those events. The Safety concerns in a MR environment are typically divided into 4 categories · Static Field · Gradient Field · RF Field · Implant safety Those major categories are then subdivided into more narrow topics: · Ferrous Metal attractive forces · Torque when trans versing the field (Spatial Gradients) · Induced current (Peripheral Nerve stimulation) · Acoustic Noise (gradient function) · RF burns · Both function and potential for magnetic field interaction and burns for pts with implanted devices · Cryogen safety Those issues and the programs and policies in place to prevent accidents are the topic of countless lectures, books, and discussions. The field of MR has evolved rapidly and those tasked with maintaining MR safety have struggled to keep up and ahead of those advancements. Unfortunately accidents in the MR environment continue to happen and the industry is responding with a new wave of education, tools, and policies. We will deal with each of the Major topics and their subtopics to review the safety concerns and address mitigating policies and processes. The static magnetic field is comprised of the main magnet and the “fringe field” surrounding the device. Magnets can be permanent, resistive or superconductive. For our purposes today we will deal with only the permanent and super-conductive, as resistive magnets are a small part of the population of devices. The largest difference between permanent and superconductive magnets from a MR safety prospective is cryogens and the ability to “ramp down” or quench the device. A permanent magnet has no way for the field to be easily reduced while the superconductive magnet has the added safety concerns involving cryogens. Liquid Helium is very cold and has the capacity to expand about 760 to 1 when converting to a gas or “boiling” as is the case with a “quench”. This can be a very dangerous situation and all personnel in the MR environment must be trained to understand these issues. Site design, access control and education are the primary safety tools that prevent projectile incidents. It’s important to hold frequent educational sessions with anyone needing access to Zone 3 and monitor and control all equipment needed to accomplish patient care. Training and education is the cornerstone of a comprehensive MR Safety program. Work must be done designing policies, procedures and follow up drills that instill good safe workflows. Gradients pose a dual safety issue. First is the potential for induction of current and peripheral nerve stimulation. This can cause pain or discomfort and the FDA dictates the scan must be stopped if the pt feels discomfort. The other issue with gradient fields is acoustic noise. The decibel level can reach about 120 db with modern scanners and hardware. Radiofrequency can be an issue if there are potential loops in which a current can be induced. This can lead to RF burns of which the mechanism is poorly understood. In order to prevent this occurrence attention must be paid to any wires, leads and patient positioning during the procedure. Implanted devices have several issues when in a magnetic field and exposed to RF and gradient fields. They may move, torque, heat or have functionality issues. The same goes for conditional equipment like Ventilator, monitors, respirators, etc. Safety protocols must be in place to mitigate concerns and issues involving patients who have implanted devices MR Safety is a complex and at times difficult process. In the MR environment it’s not a choice and policies must be strictly followed. Education, Access and constant vigilance are the keys to success
Michael Steckner PhD Toshiba Medical
ISMRM/SMRT Safety Committee
www.mrsafety.com
http://hyperphysics.phy-astr.gsu.edu
Anne Sawyer BSRT R MR FSMRT-Stanford University
Mriquestions.com
ACR white paper on MR Safety FDA guidelines