MRI Safety

1
MRI Safety
Jody Culham Department of Psychology University
of Western Ontario
http//www.fmri4newbies.com/
Last Update November 29, 2008 fMRI Course,
Louvain, Belgium
2
Magnetic Fields

• main magnetic field is very strong
• BUT static magnetic fields are less of a concern
  than changing magnetic fields
• moving quickly through a magnetic field,
  especially the head, is a BAD idea -- like doing
  whole brain TMS on yourself
• some people experience dizziness, nausea,
  metallic tastes
• BUT these were also reported in 45 of subjects
  when the magnet was OFF!
• consent form lingo no known risks
• you can never prove anything is safe, only that
  something is unsafe

3
Magnet Safety Big Things
Source www.howstuffworks.com
Source http//www.simplyphysics.com/ flying_objec
ts.html
Large ferromagnetic objects that were reported
as having been drawn into the MR equipment
include a defibrillator, a wheelchair, a
respirator, ankle weights, an IV pole, a tool
box, sand bags containing metal filings, a vacuum
cleaner, and mop buckets. -Chaljub et al.,
(2001) AJR
4
Very Serious Risk
Westchester NY, 2001
Source http//www.mrireview.com/docs/mrideath.pd
f
5
Magnet Safety Little Things
Aneurysm clips can be pulled off vessels, leading
to death
Flying things can kill people. Even in less
severe incidents, they can fly into the magnet
and damage it or require an expensive shutdown.
6
Subject Safety

• Anyone going near the magnet subjects, staff
  and visitors must be thoroughly screened
• Subjects must have no metal in their bodies
• pacemaker
• aneurysm clips
• metal implants (e.g., cochlear implants)
• interuterine devices (IUDs)
• some dental work (but fillings are okay)
• Subjects must remove metal from their bodies
• jewellery, watch, piercings
• coins, etc.
• wallet
• any metal that may distort the field (e.g.,
  underwire bra)
• Females must not be pregnant or at risk of
  conceiving
• Some institutions even require pregancy tests
  for any female, every session
• Subjects must be given ear plugs (acoustic noise
  can reach 120 dB)

This subject was wearing a hair band with a 2 mm
copper clamp. Left with hair band. Right
without. Source Jorge Jovicich
7
Fall-off of Magnetic Field
8
Very Serious Risk
Source http//www.fmrib.ox.ac.uk/7Epeterj/safety
_docs/fda_primer.html
9
Magnet Safety

• Principal Investigators should be sure all lab
  members are aware of hazards.
• Make sure that anyone who is about to enter the
  magnet room has been filled out consent and
  screening forms (subjects, lab members,
  visitors).
• Remove all metal, coins, credit cards etc. as
  soon as you enter the magnet area.
• Think! Train yourself to mini-screen yourself
  every time you approach the magnet room.
• Do not enter the magnet room with any tools
  (e.g., scissors). Use only magnet-friendly tools
  in the toolbox in the magnet room.

Think!
Do the Metal Macarena!
10
Specific Absorption Rate (SAR)

• excess energy heats body tissues
• if body heats faster than natural cooling,
  temperature rises
• Specific Absorption Rate (SAR) amount of heat
  absorbed by body
• magnets have SAR limits to prevent overheating
• limited to 1 degree rise in core body temperature
  
• depends on body size, geometry, thermoregulation
• depends on pulse sequences (e.g., larger flip
  angles greater SAR)

11
Other safety issues

• fire safety
• always give subjects a panic button
• make sure that subject can be evacuated quickly
  if needed
• have an MR-compatible fire extinguisher available
• operator must know safety protocols
• quenching
• rapid decrease in magnetic field strength
• helium boils off and can fill room (displacing
  oxygen)
• can occur spontaneously
• only voluntarily initiated in extreme situations
• burns
• do not loop any wires or cables
• do not place electrodes on subjects skin

12
Other safety issues

• claustrophobia
• subject screening
• acoustic noise
• soundproofing
• earplugs
• headphones