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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