MRI safety from A to Z

2. S.Shokoofeh.Mousavi.G Razi Hospital 2

3. Table of
Content
 Introduction
 Physics
 Safety issues
 Biological Effect
 Flying Objects
 Induced Current
 Auditory Damage
 Power Deposition
 Heating &Burn
 Contrast Agent
 Pregnancy
 Phobia
 Emergency & Quench
 Safety Approaches
 Zones
 Signage
 Screening Form
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4. Introductio
n
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5. What is MRI?
o Stands for Magnetic Resonance Imaging
o The MRI scanner: a very large and powerful magnet
o Our clinical scanner: 1.5 Tesla
• 1.5 Tesla = 15,000 gauss
• Earths magnetic field ~ 0.5 gauss
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6. Why Safety Issues Are So
Important ?
o The magnet is always ON (24/7/365)
o Safe Modality, important safety issues though!
Non-invasive
No ionizing radiation
Potential for serious accidents
High cost maintenance
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7. Safety
Targets
MRI
Staff
MRI
Machine
Patients
& Public
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8. Physics
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9. Characteristics of the Magnetic
Field
o The force of the field is measured in tesla (T)
o The force INCREASES as you move closer to the magnet
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10. Electromagnetic Fields in MRI
oStatic
oGradient
oRF
oFringe Magnetic Field
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11. Fringe Magnetic Field
o Vitally important for flying objects
o 5 Gauss Exclusion Zone around magnet for patients
having pacemaker
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12. Magnetic Properties of the
Materials
Diamagnetic
• Fat
• Water
• Calcium
Paramagnetic
• Molecular O2
• Metal Chelate
Ferromagnetic
• Iron
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13. Forces in the MR
Environment
Missile
effect
TRANSLATION
Torque
effect
ROTATION
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14. Safety
Issues
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15. Safety Issues
Static magnetic
field
biological effects
mechanical effects
Gradient Field
induced currents
auditory damage
RF Field
RF power
deposition
heating
Other
Contrast Agents
Pregnancy
Phobia
EmergenciesS.Shokoofeh.Mousavi.G Razi Hospital 15

16. Biological
Effects
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17. Biological Effects of Magnetic
Fields
o Static Field
o No evidence of mutagenic effects
o No evidence of an effect on organ development
o RF Field
o Tissue Heating
o Gradient Field
o Eddy current formation
o Nerve Stimulation
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18. Biological Effects of Stronger
Magnets
o Electrical stimulation of peripheral and cutaneous nerves
o Electrical stimulation of the retina, delusion
o Vertigo, nausea, headaches, metallic taste
o Cardiovascular effects
o Bone healing
o Itching
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19. Mechanical Effects
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20. Magnetic Field & Environment
Interactions
o Environment effect on Magnetic Field:
Image degradation
o Magnetic Field effect on Environment:
Broken devices, Projectile accidents
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21. Foreign Materials in the Body
o Is a concern in MRI, can be fatal
o Several cases of Death, lost sight, serious injuries have been
reported
o Magnetic field might move/dislodge the ferromagnetic implants
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22. Foreign Materials in the Body
Any device electrically or mechanically activated
• Pacemaker
• Insulin pump
• Aneurism clips
• Pacing wires
• Cochlear/Ocular implants
• Neurostimulators
• Hydrocephalus shunts
• Metallic foreign body in the eye
• Shrapnel, bullets
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23. Foreign Materials in the Body
o Stent/grafts/valves
o Orthopedic implants
o Contraceptive device
o Dental implants
o Permanent cosmetics
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24. Check this out!
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www.mrisafety.com

25. Projectile Accidents
o The MRI magnets are ALWAYS on
o The fringe magnetic field can cause ferrous metal objects to fly into
the bore of the magnet with great force and speed
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27. S.Shokoofeh.Mousavi.G
Razi Hospital
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28. Disasters in MRI
o India
A guy sticking between Oxygen Cylinder and bore -> Quench
o USA
A little boy was hit by Oxygen Cylinder -> Death
o Iran
Several significant injuries (burning, sight loose,…)
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Still happening …

29. Oxygen cylinder
Infusion pump
Tools
Clipboards
Trolley
Coach
Badges
Ventilator
Wheelchair
Vacuum cleaner
Walking cane
Stethoscopes
Monitoring equipment
IV stands
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30. Cell phone
Keys
Glasses
Hair pins / barrettes
Jewelry
Paper clips
Coins
Pens
Pocket knife
Nail clippers
Scissors
Credit cards
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31. Induced Currents
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32. Induced Currents
o Biological effects of time varying (gradient) magnetic fields
o Faraday’s Law: Induction of electric fields and currents in tissues
o depends on tissue conductivity, gradient strength, rise time,
wave shape, polarity, repetition time TR and duration of the scan
o Possible effects: Nerve stimulation, Magnetophosphenes
o No evidence for irreversible or significant biological effects
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33. Auditory Damage
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34. Auditory safety
• Activation of gradient magnetic fields produces significant vibrations
• MRI acoustical noise: reversible hearing impairment , even permanent damage
• Hearing protection is recommended for all patients
• Noise attenuating ear-plugs or head phones are routinely used
• Advanced protocols are available
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35. Acoustic Noise
o The stronger magnet, the louder noise
o Sound intensity can reach 120 dB
o Hearing protection mandatory for 90dB:
• patients
• staff remaining in the scanner room
• relatives accompanying children or patients
o FDA Safety Guidelines for MR Devices
Acoustic noise level, International standard: 140 dB
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36. RF power
deposition
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37. Specific Absorption Rate (SAR)
o SAR is the RF power absorbed per unit mass of tissue (W/kg)
o Complex function of numerous variables, calculated by software
o An accurate patient weight is vital
o MRI manufacturers use SAR level control
o Normal mode (or clinical mode): admissible for all patients
o First level: increased SAR permissible under “medical supervision”
o Second level: use of higher levels of SAR under IRB approval (research)
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38. Heating, Burns
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39. Heating
o Similar to ultrasound , minimal heating of tissues
o Extra precautions are necessary for patients with compromised
thermoregulation: fever, diabetes, obesity, cardiovascular disease, old
age, medicated, anesthesia & tattos
Remove Devices
o Chest leads
o pulse oximeter BURN
o Looped configuration
Avoid Crossed Limbs
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40. Contrast Agent
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41. Contrast agent in MRI
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o Gd-based agents are significantly safer than iodine based contrast
agents used in X-ray procedures
o Gadolinium may cause from headache to Nephrogenic Systemic
Fibrosis (NSF)
o Extra precautions for:
- patients just before or just after liver transplantation
- those with chronic liver/kidney disease
Contraindications
•GFR<30ms/minute
• pregnancy (poor clearance from amniotic fluid)
• breast feeding mothers (Risks Vs. Benefits)
• infants < 2 years

42. Pregnancy
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43. Pregnancy
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o MRI as powerful tool in assessment of Fetus
o FDA: “MRI safety for fetus and infant has not been
established”
o BNRPB: “exclude pregnant women during the first three
months of pregnancy”
o Particular caution should be exercised with the use of MRI
during the first trimester
o Consent form must be filled

44. Pregnancy (cont.)
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o Careful consideration regarding:
- Acoustic noise
- SAR
o Contrast media are contraindicated
Patients
1st trimester – prudent to avoid CMR where possible
2nd and 3rd trimester – decision made on a risk Vs. benefit
Health Care Workers
Should not remain in the room when scanner is operational

45. Phobia
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46. Distress & Phobia
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 Psychological Distress (before, during and after MRI):
o Claustrophobia
o Anxiety
o Depression
o Panic Disorders
 Countermeasures:
o Informing patient about procedure
o Friend or relative in scan room
o Physical or verbal contact with patient
o Mirrors, prism glasses, video goggles
o Blindfold
o Relaxation strategies
o Good light & Ventilation, Music

47. Emergencies
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48. Emergency Situations
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o Patient Medical Emergencies
• Remove patient to a magnetically safe location
• A code is never to be conducted in Magnet room
o Quench
• The superconductive magnet is kept always on, using liquid Helium
• Pressing Quench button: He release Loss of Magnetic field
• Only in life-threatening situation (trapping, fire,…)

49. Cryogen Safety
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 Magnet QUENCH: extremely bad, MRI nightmare
run the magnetic field to ZERO
liquid helium to gaseous helium, release through vent
 Main cause: Human error
 Risks od Asphyxiation & Conflagration
Let’s not talk
about Money!

50. Safety
Approaches
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51. Restricted Access
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All personnel with access to MR must have qualifications
Level1
 basically trained
(Nurses, anesthesiologists, CPR team, firefighter …)
Level2
 extensively knowledgeable
(MR Radiographer, Physicist, Radiology staff)

52. MRI Zones
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ZONE 1
freely accessible to the general public.
patients and all personnel access the MR suite
ZONE 2
between the accessible zone 1 & the strictly controlled zones.
Patients and personnel are able to move throughout
must be mindful of where zone 3 begins
is marked with a safety sign

53. MRI Zones (cont.)
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• non MR safe equipment can result in serious injury or death
• Personnel are not to move freely through this zone.
• must be accompanied by level 2 staff
• MR safe practice guidelines must be adhered
ZONE 4
• Not screened people will not enter this zone under any circumstances
• Just permitted for level 2 MR staff
• Highly critical

54. Signage
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Be careful about label of items

55. Screening Forms
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• To ensure patient safety, completion of the MRI screening form is
necessary to help identify any potential dangers
• The form consists of a series of questions intended to identify
any metallic objects within the body that could be affected
• Patient or his/her family is in charge of filling it out
• Preparation
Removal of accessories (watch, jewellery (except wedding rings),
body piercing rings, hearing aids, glasses, false teeth, artificial limbs
and prostheses, clothes containing metal eg zips)

56. Screening Forms (Cont.)
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Essential to know
• Cardiac pacemaker?
• Previous neurosurgery?
• Implants or metal in the body?
• Pregnant (prudent approach)?
Important to know
• Previous heart surgery?
• Diabetic or epileptic?
• Asthmatic or allergies? (in relation to contrast)
• Tattoos or permanent eye liner ?
See the example

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MRI = Metal Results (in) Injury
REMEMBER

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