Magnetic Resonance Safety Seminar: An Introduction to the Potential Hazards Associated with MR Imaging KJ Jantzen, PhD

1. Magnetic Resonance Safety Seminar: An Introduction to the Potential Hazards Associated with MR Imaging KJ Jantzen, PhD The Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Florida Atlantic University Boca Raton Florida Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Center for Complex Systems and Brain Sciences

2. Safety concerns in MRI come from three major sources. • The existence of a static permanent high strength magnetic field (1.5 Tesla and above). • The rapid switching of gradients that occurs during MR image acquisition and provide spatial encoding information. (especially with functional MRI) • The radio frequency electromagnetic field used to excite the spins and produce a read out signal. Center for Complex Systems and Brain Sciences

3. Safety issues surrounding static field. • The magnetic field is always on and as such presents a • constant hazard. This is manifest in three general ways. • Magnetic effect on metal objects (projectile effect) • Magnetic effect on implanted metal devices. • Influence of static field on human physiology. Center for Complex Systems and Brain Sciences

4. Magnetic effect on metal objects (projectile effect) • Objects that are ferromagnetic (become magnetized in a magnetic field) have the potential to act as missiles flying into the bore. • Can cause obvious damage to EXPENSIVE equipment. • Have led to DEATH. • Oxygen Tanks • Tools • Equipment • Belts • Watches • Wallets • Safety issues surrounding static field. • Hair clips • Pens • Pagers • Phones • Lighters Center for Complex Systems and Brain Sciences

5. Safety issues surrounding static field. Center for Complex Systems and Brain Sciences

6. Implants devices • Any number of magnetic objects can exist inside the human body either for therapeutic reasons or by accident. • Pacemaker • Heart Valve • Aneurism Clips • TENS unit • Cochlear Implants • Shrapnel • Metal Filings in the eye • etc • Safety issues surrounding static field. Center for Complex Systems and Brain Sciences

7. Implants devices • Ferromagnetic devices in the body will attempt to align with the static field and can twist (can also cause irritation from tattoos and permanent eyeliner). • Ferromagnetic objects will also be attracted to the magnet with obvious negative effects. • Implanted devices use magnetic signals to change settings. If placed in a magnetic field the settings may change, the device may malfunction or stop altogether. • Safety issues surrounding static field. Center for Complex Systems and Brain Sciences

8. Influence of static field on human physiology No known long tern effects of exposure to fields strengths under 8.0T. Rapid movements in high field magnets may induce currents and cause artifacts such as phosphenes, vertigo or a metallic taste. There is no know risk to pregnant women or their infants. However due to the lack of ability to test for effects: PREGNANT WOMEN SHOULD NEVER BE ALLOWED TO ENTER THE SAFETY RESTRICTED AREA. • Safety issues surrounding static field. Center for Complex Systems and Brain Sciences

9. Safety concerns in MRI come from three major sources. • The existence of a static permanent high strength magnetic field (1.5 Tesla and above). • The rapid switching of gradients that occurs during MR image acquisition and provide spatial encoding information. (especially with functional MRI) • The radio frequency electromagnetic field used to excite the spins and produce a read out signal. Center for Complex Systems and Brain Sciences

10. 1.Bioeffects of Gradient Magnetic Fields Magnetic resonance (MR) imaging involves the rapid activation and switching gradient magnetic fields to code spatial location. According to Faraday's Law of Induction, exposure of any conductor to time-varying magnetic fields will induce a voltage in the conductor. MRI has the potential of inducing voltages within the tissues of the patient or any other conductive material. • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

11. 1. Bioeffects of Gradient Magnetic Fields Tissue Heating: Induced currents and voltages may result in power deposition and subsequent tissue heating. However, it is well accepted that the thermal effects that result from the gradient switching during MRI are negligible and are considered clinically insignificant (tattoos) Neuromuscular Stimulation: Both theory and practice have demonstrated that, when appropriately strong gradients are switched at a sufficiently fast rate, neuromuscular simulation may occur. This may partially result from direct stimulation or from induced voltages exceeding the threshold necessary for achieving neural action potential discharge. • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

12. 1. Bioeffects of Gradient Magnetic Fields • In the extreme, induction can result in: • seizures • magnetophosphenes (flashes of light) • peripheral nerve stimulation • skeletal muscular contractions • or even cardiac arrhythmias • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

13. 2.Gradient Field-Induced Acoustic Noise During the operation of MR systems various types of acoustic noises are produced. The primary source of noise in fMRI results from the extremely fast gradient shifts required to collect EPI images. These currents, in the presence of the strong static magnetic field of the MR system, produce significant forces that act upon the gradient coils. Acoustic noise, manifested as loud tapping, knocking, or chirping sounds, is produced when the forces cause motion or vibration of the gradient coils as they impact against their mountings. • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

14. 2. Gradient Field-Induced Acoustic Noise • Some of these sounds may present minor or substantial problems to patients and health workers including: • simple annoyance • difficulties in verbal communication • heightened anxiety • temporary hearing loss • permanent hearing impairment • This is particularly true during fMRI when the noise is substantially louder. • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

15. 2. Gradient Field-Induced Acoustic Noise • Safety Stategies: • All subjects must be fitted with sound attenuation equipment in the form of • Ear plugs (available at UMRI) • Approved Protective headphones • Safety issues surrounding gradient field. Center for Complex Systems and Brain Sciences

16. Safety concerns in MRI come from three major sources. • The existence of a static permanent high strength magnetic field (1.5 Tesla and above). • The rapid switching of gradients that occurs during MR image acquisition and provide spatial encoding information. (especially with functional MRI) • The radio frequency electromagnetic field used to excite the spins and produce a read out signal. Center for Complex Systems and Brain Sciences

17. Safety issues surrounding RF EM field • The main safety concern with radio frequency electromagnetic fields is tissue heating and burns. • Energy transmitted by RF coil can be absorbed by superficial layers of the body and dissipated in the form of heat through convection, conduction, radiation or evaporation. • SAR: specific absorption rate: rate of absorption of EM energy in the body. • This is measured as a function of time and energy; W/min/kg Center for Complex Systems and Brain Sciences

18. Safety issues surrounding RF EM field • Effects of RF on metal bodies and implanted devices • Metal objects also absorb RF and can become heated as a result • May result in burns to the skin if the object comes in contact with the subject. • RF signals may interact with implanted electrical devices such as pacemakers and cause them to function abnormally. Center for Complex Systems and Brain Sciences

19. D. Other Safety Concerns Psychological Distress Psychological reactions such as claustrophobia anxiety panic attacks are commonly reported in patients who undergo MRI Solution: Try to make the subject as comfortable as possible without compromising your experimental design. Otherwise, discontinue the experiment. Center for Complex Systems and Brain Sciences

20. Safety Restricted Area N Waiting Room MRI Suite To CCS&BS Restricted Access Point Control room Screening areas!! Safety Strategies: Zone map for 1.5T Center for Complex Systems and Brain Sciences

21. Safety Strategies • The best safety strategy is to follow carefully and fully the Procedures and Guidelines manual. • No Magnetic Objects are allowed inside the Safety Restricted Area • Neverleave the door to the safety restricted area open. • Any objects to be brought into the safety restricted area MUSTbe tested first. • Subject Screening: Prior to entering the safety restricted area of the MRI every patient must: • Complete an Eligibility Checklist • Remove all metallic or otherwise susceptible material • Undergo a visual and verbal screening • This goes for experimenters too!! Center for Complex Systems and Brain Sciences

22. Safety Strategies • Subjects must always wear ear protection during scanning. • Pregnant women are NEVER allowed in the safety restricted area. • Pay attention to subject reports of heating, tingling, strange sensations, etc. • Maintain a line of communication with your subject, • Check with subject often to see if they are OK. Center for Complex Systems and Brain Sciences

23. Safety Strategies When in doubt: Err on the side of caution!!!! If there is any question as to the safety of an object or person, do not allow it inside the Safety Restricted Area! Remember: You are first and best line of defense and should exert the necessary control to assure the participants safety! Center for Complex Systems and Brain Sciences

24. What to do if someone is injured in an MRI • Remove them from the Safety Restricted Area • Alert a physician or technician at UMRI. • Call 911. You should know or have ready access to the UMRI address and phone number. For detailed safety information: www.mrisafety.com Center for Complex Systems and Brain Sciences