Safety in Numbers
MRI safety and cardiovascular implantable electronic
devices
Beau Pontré
University of Auckland
MR User Group Study Day
29th March 2014
Monitoring
(mV)
Intervention
(V)
Devices perform two primary tasks…
Potential Risks
Heating
!
!
Induced currents
!
!
Displacement
!
!
Disrupt/modify
device function
Potential Risks
Heating
!
!
Induced currents
!
!
Displacement
!
!
Disrupt/modify
device function
Problems are even worse at 3T!
Static Magnetic Field
Translation force
Turning force
m
F
B0
Bore
opening
Isocentre
3.0T
1.8T
1.2T
0.6T
15mT
150 gauss
2.4m
2.0m
1.6m
1.2m
0.8m
Distance from isocentre along z
0.4m
0.0m
Field strength
2.4T
Isocentre
5000
3.0T
4000
2.4T
3000
1.8T
Magnetic Field
Gradients
2000
1.2T
1000
0.6T
Gradient coils
(<80mT/m)
Main Magnetic
Field
2.4m
2.0m
1.6m
1.2m
0.8m
Distance from isocentre along z
0.4m
0.0m
Field strength
Gradient (mT/m)
Bore
opening
Device
Type
Field
Strength
Year Range
Force
(N)
Leuchinger et al.
(2001)
Pacemaker
1.5T
pre 1985 - 2001
0.05 - 3.6
Leuchinger et al.
(2001)
ICD
1.5T
pre 1985 - 2001
1.0 - 5.9
Roguin et al.
(2004)
Permanent
pacemaker
1.5T
after 1996
<0.98
Roguin et al.
(2004)
ICD
1.5T
after 2000
<0.98
For pacemakers and most modern ICDs
- acceleration is lower than the gravity of the earth (9.81N/kg)
Luechinger R, et al. (2001) Pacing Clin Electrophysiol 24:199–205.
Roguin A et al. (2004) Circulation 110:475–482
No magnetic field
Open at 0.7+/-0.2 mT (7 gauss)
Reed
switch
Magnetic field
Closes at 1.0+/-0.2 mT (10 gauss)
Observation
Sommer et al.
(1998)
Reed switch activation noted
Sommer et al
(2000)
Reed switch deactivated in 4/16 patients in bore
Vahlhaus et al.
(2001)
Reed switch deactivation seen in 12/32 patients in bore
Leuchinger et al.
(2002)
Reed switches reopened in 50% of orientations
Sommer et al.
(2006)
Reed switch remained inactive in 44.7% of patients
- Reed switch activation can occur in the magnetic field
- Reopening observed in some cases once in the magnet bore
- Hall sensors used in some recent models
Sommer T et al. (1998) Rofo;168:36–43
Sommer T et al. (2000) Radiology 215:869–879.
Vahlhaus C et al. (2001) Pacing Clin Electrophysiol 24(4 pt 1):489–495
Luechinger R et al. (2002) Pacing Clin Electrophysiol 25:1419–1423
Sommer T et al. (2006) Circulation 114:1285–1292.
Magnetic Field Gradients
Induced current depends on
- how much the magnetic field changes
- how quickly the magnetic field changes
- the area covered by the coil of wire
Theoretically…
!
- Pacing from gradients is possible
- Up to 20V in unipolar leads!
- Too small in bipolar leads
!
!
!
Experimentally…
!
- <0.5mA induced current
- >30mA is possible
- Multiple loops required!
Tandri H et al. (2008) Heart Rhythm 5:462–468
Radio Frequency
Body Region
→
Operating
Mode ↓
Normal
1st Level
Controlled
2nd Level
Controlled
Short duration
SAR
Whole body SAR
Partial body SAR
Head SAR
Local SAR
whole body
exposed body part
head
(W/kg)
(W/kg)
(W/kg)
2
2 - 10
3.2
10
10
20
4
4 - 10
3.2
20
20
40
>4
>(4 - 10)
>3.2
>20
>20
>40
head
trunk extremities
(W/kg) (W/kg)
(W/kg)
The SAR limit over any 10 s period shall not exceed two times the stated values
Temperature increase depends on SAR, tissue properties and time
Model
Field Strength
Observation
Achenbach et al. (1997)
In vitro
1.5T
Temperature increase of 63.1ºC
Leuchinger et al. (2005)
Animal
1.5T
Temperature increase of 20.8ºC
Hayes et al. (1987)
Animal
1.5T
Rapid pacing seen in 7/8
What happens in patients?
Achenbach S et al. (1997) Am Heart J 134:467–73.
Hayes DL et al. (1987) J Am Coll Cardiol
Luechinger R et al. (2005) Eur Heart J 26:376–83.
The leads pose the biggest problem with RF pulses
!
- no heating observed in device
- leads behave like an antenna!
- RF wavelength vs lead length
- RF coupling
!
Critical length in saline is 30cm (1.5T)
OK at 3T doesn’t necessarily mean OK at 1.5T
Selected in vivo studies
Field
Strength
Notes
Vahlhaus et
al. (2001)
0.5T
Diminished battery voltage, recovered at 3 month
followup
Gimbel et al.
(2005)
1.5T
SAR < 2W/kg, Tx/Rx coil
All scans uneventful
Del Ojo et al.
(2005)
2T
No adverse effects reported
Sommer et
al. (2006)
1.5T
Troponin increase from normal baseline to above normal
after MRI observed in 4/114 examinations
Schemiedel
et al. (2006)
1.5T
SAR limited to < 1.2W/kg.
Temperature increases of <2.98ºC observed
Naehle et al.
(2009)
3T
No adverse effects reported
Vahlhaus C et al. (2001) Pacing Clin Electrophysiol 24(4 pt 1):489–495
Gimbel JR, et al. (2005) Pacing Clin Electrophysiol 28:1041–1046
Del Ojo JL et al. (2005) Pacing Clin Electrophysiol 28:274–278.
Sommer T et al. (2006) Circulation 114:1285–1292.
Naehle CP et al. (2009) Pacing Clin Electrophysiol 32:1526–1535.
Conclusion
- Theoretical dangers exist
!
- Anecdotal evidence of severe adverse effects
!
- Evidence suggests that the risk of adverse effects is low
- When performed under appropriate supervision and conditions
!
- Risk is not zero!
!
- MR conditional devices - not an immediate contraindication
!
- Check details of device compatibility prior to scanning
Conclusion
- Theoretical dangers exist
!
- Anecdotal evidence of severe adverse effects
!
- Evidence suggests that the risk of adverse effects is low
- When performed under appropriate supervision and conditions
!
- Risk is not zero!
!
- MR conditional models - not an immediate contraindication
!
- Check details of device compatibility prior to scanning
http://www.mrisafety.com/TheList_search.asp
Firearm
Safety
MR Imaging
in the
Materials
Emanuel
Kanal, MD
Ali Shaibani,
MD
The safety of small-caliber
firearms
in
a 1.5-T magnetic
resonance
(MR) imaging environment
was assessed
with six
handguns,
which were unloaded
before
testing.
Each firearm was withdrawn
barrel-first
to assess the interaction
of
the magnetic
field with the hammer
and/or
trigger. Two of the six weapons
discharged
reproducibly.
A firearm in
an MR imaging
suite should be unloaded before removal
or any other
manipulation
is attempted.
Firearms
Magnetic
#{149}
resonance
Methods
Six
handguns
barrel,
volver
model
(Smith
Mass);
a 0.22-magnum
(North
American
were
tested:
66-3, 357 magnu
and Wesson,
minirevo
Arms,
Spanis
Utah);
a model
PT-92C,
9-mm
matic
(Taurus
International,
a model
19, 9-mm
semiautomatic
Smyrna,
Ga); a model
BDA-38
caliber
semiautomatic
(Browni
gan, Utah);
and a model
M-4
9-mm
semiautomatic
(Star B
Echeverria,
Eibar
[Guipuzcoa],
For any of these
weapons
charge,
the firing pin must
with
Index terms:
(MR), safety
and
E
moderate
(or its equivalent)
on the hammer
force
by
the
by (a) pullin
(or its equivale
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