MR Safety

1. MR Safety

2. Bioeffects • Static Magnetic Fields • Varying Magnetic Fields • RF Exposure, Acoustic Noise, SAR • Implants • Missile Effect • Pregnancy • Pediatric

3. MR-Related Injuries • Missile Effect/Projectile injury • Dislodged ferromagnetic implants • Burns • Failure of internal/external devices • Failure of patient support systems • Acoustic injury • Contrast agent adverse effects • Cryogen handling related injuries

4. Relative Proportions Reported 2005, injuries occurred over 10 year span

5. Reported Deaths • 9 deaths out of 389 reported events • 3 due to pacemaker failure • 2 due to insulin pump failure • Remaining 4 due to • Projectile • Implant disturbance • Asphyxiation (due to cryogenic mishap during install) • Escaped He gas displaces O2

6. Static Fields • No deleterious bioeffects have been shown for typical clinical magnet strengths • ECG traces have shown enhanced T wave amplitude • Very high magnet strengths (4 T +) anecdotal reports • Dizziness/nausea • Disorientation • Metallic taste • When moving through field • Mild sensory effects • Visual sensations (magnetophosphenes)

7. Bioeffects Studied • Alterations in cell growth/morphology • DNA structure & gene expression • Pre- & post-natal reproduction & development • Visual functions • Animal Behavior • Visual response to photic stimulation • Nerve bioelectric activity • Cardiovascular dynamics, hematological indices • Physiological regulation & circadian rhythms • Immune response

8. Study Results • Often contradictory • Cannot be reliably reproduced • Data based on animal models • Cannot be readily extrapolated to humans

9. Varying Fields • Gradient switching • Rapidly oscillating magnetic fields • Induces current in conductors • Produces loud banging • Earplugs necessary • Very high gradient fields • Magnetophosphenes • Peripheral nerve stimulation • Most likely with EPI sequences • Most common effect is heating • Epicardial or retained intracardiac pacer wires • More often heating attributable to RF fields

10. RF Fields • Major cause of tissue heating • Ferromagnetic implants esp. susceptible • Temperatures < 42° C body does a good job of self regulation • FDA limits core temperature rise to 1° C • Specific Absorption Rate (SAR) • Watts/Kg • Measured by MR • Enter correct patient’s weight! • FDA limits • ECG gating studies requires MRI compatible leads • Otherwise skin burns could result

11. Limiting SAR To reduce SAR: Decrease Power & Duty Cycle of RF Pulses • SAR depends on: • [Magnetic field strength]² • [Flip angle]² • Size of patient • Duty cycle of RF pulses • Minimize heat deposition by: • Controlling flip angle • ↑ repetition time • ↓ # of sections • ↑ echo spacing in FSE • ↓ # echoes in FSE • ↓ refocusing flip angle in FSE

12. FDA Limits

13. Projectiles

14. Wheelchair

15. Office Chair

16. Firearms

17. O2 Tank

18. Bed

19. Floor Polisher

20. Other Metal Objects

21. Screening Options • Written screening form • Verbal screening • Screening devices • Hand-held magnets • Metal detectors • CAUTION • Device sensitivity may not guarantee no metal present

22. Portable Item Labels MR Safe Wholly nonmetallic items Composition known MR Conditional No/negligible attractive forces observed Not MR Safe Clearly ferromagnetic

23. Screening Form

24. Form Cont’d

25. Implants & Prostheses • Intracranial Vascular clips • Intravascular coils, filters, stents • Extra-cranial vascular clips • Vascular access ports • Heart valves • Dental devices & materials • Penile implants • Otologic implants • Ocular implants • Intra-occular ferrous foreign bodies • Bullets, pellets & shrapnel • Orthopedic implants, materials & devices • Halo vest & other similar externally applied devices

26. Electrically, Magnetically, orMechanically-Activated or Electrically Conductive Implants • Cardiac pacemakers • May be possible to scan assuming: • Non-dependent pacer patient • Clinically fit to scan • Radiologist, cardiologist, rep from pacer company present • Or Newer MR safer pacemaker implanted • Cochlear implants • Tissue expanders • Ocular prostheses • Dental implants • Neurostimulators • Bone growth stimulators • Implantable cardiac defibrillators • Implantable drug infusion pumps

27. Safety Zones Zone 1 General Public Zone 2 Interface between public & strictly controlled access areas Zone 3 Access strictly controlled by MR personnel Serious injury could result from interaction between ferromagnetic materials & static/time-varying magnetic fields Zone 4 Magnet room Within Zone 3

28. Personnel Definitions • Non-MR personnel • Patients • Visitors • Facility staff • Not undergone formal training in MR Safety in previous 12 months • Level 1 personnel • Passed minimal safety education efforts • MR department office staff • Patient aides • Level 2 personnel • More extensively trained/educated in broader aspects of MR safety issues • MR techs • Radiologists • Radiology department nursing staff • Level 1 & 2 may move about in all zones

29. Quench • Superconducting magnet suddenly becomes resistive • Wires formerly offering no resistance to large currents suddenly have resistance • Rapidly heat • Liquid He quickly boils • Converts to gaseous state • Rapidly expands • Typical cryostat volume ~1500 Liters • Produces 1 million liters of gas • Rapid expansion causes large ↑ in volume • Large ↑ in pressure • May have to break control room window to allow entry if venting fails • Must be vented to outside

30. Magnet Quench

31. Vented Inside Damaged stack Case in which stack was unable to handle amount of venting gases during a quench while patient was being scanned Room filled with cloud of escaped gases & condensed water vapors Pressure increased to the point where door could not be opened After breaking glass, patient was removed Separated ceiling & walls

32. Installation Planning

34. Before Installing • Is floor strong enough? • What is the delivery path for magnet? • Evaluate possible electromagnetic interference • Moving metal-cars, elevators • Evaluate vibrations • Examine fringe field extent vs. planned controlled areas • Within 5 gauss line, posted & controlled access • Within 1 gauss line exclude sensitive equipment • CT scanners • CRTs • If not possible, add magnetic shielding • Consider adding Ferrous metal detectors • Sound penetration into adjacent areas

35. RF Shielding Walls, floors & ceilings covered with copper sheeting Door perimeter lined with continuous pneumatic RF seal Stainless steel frame/hinges View window includes wire mesh

36. Fringe Fields FDA recommends limiting personnel access to 5 gauss line

37. Fringe field: Any field outside magnet bore Active shielding ensures fringe field contained w/in magnet room Active Shielding 1 documented case fringe field fatality (torque on ferromagnetic aneurism clip)

38. Pregnancy • To date no deleterious effects seen in fetus • Single Shot FSE sequences can be used • Pregnant healthcare workers • No restrictions • Should not remain in magnet room however • Pregnant patients • No restrictions on scans • Many facilities prefer to delay scan until after 1st trimester • Written consent • Review on case-by-case basis • Use of contrast agents should not routinely be used • Agents do cross placental barrier & enter amniotic fluid • Ingested by fetus, passed via urinary tract & re-ingested

39. Establish, Implement, & Maintain Current MR Safety Policies & Procedures All clinical & research MR sites, irrespective of magnet format / field strength, including installations for diagnostic, research, interventional, and/or surgical applications, should maintain MR safety policies. 2. These PAP should also be reviewed concurrently w/ introduction of any significant changes in safety parameters of MR environment of site (e.g., adding faster /stronger gradient capabilities or higher RF duty cycle studies) & updated as needed. In this review process, national & international standards & recommendations should be taken into consideration prior to establishing local guidelines, PAP. 3. Each site will name an MR medical director whose responsibilities will include ensuring that MR safe practice guidelines are established & maintained as current & appropriate for the site. It is the responsibility of site’s administration to ensure that PAP that result from these guidelines are implemented & adhered to at all times by all of the site’s personnel. 4. Procedures should be in place to ensure that any & all adverse events, MR safety incidents, or “near incidents” that occur in the MR site are reported to the medical director in a timely fashion (e.g., within 24 hours or 1 business day of their occurrence) & used in continuous quality improvement efforts. It should be stressed that the FDA states that it is incumbent upon the sites to also report adverse events & incidents to them via their MedWatch program. The ACR supports this requirement & feels that it is in the ultimate best interest of all MR practitioners to create & maintain this consolidated database of such events to help us all learn about them & how to better avoid them in future ACR White Paper

40. FDA Recommendation ‘If non-ionizing imaging (like sonography) is sub-optimal, or if the information to be gained by MR would have required more invasive testing (like radiography, CT, angiography to name a few), MRI is acceptable.’

41. Pediatric • Special consideration mainly due to: • Sedation • Monitoring

42. End MRI Safety