Philips Expression MR400 - Guidelines and References; Guidelines for the Prevention of Excessive Heating and Burns Associated with Magnetic Resonance Procedures

ExpressionMR400InstructionsforUse GuidelinesandReferencesE‐1
APPENDIX E
Guidelines and References
Guidelines for the Prevention of Excessive Heating and Burns
Associated with Magnetic Resonance Procedures
Ingeneral,magneticresonance(MR)imagingisconsideredtobearelativelysafediagnostic
modality.However,theuseofradiofrequencycoils,physiologicmonitors,electronically‐
activateddevices,andexternalaccessoriesorobjectsmadefromconductivematerialshas
causedexcessiveheating,resultinginburninjuriestopatientsundergoingMRprocedures.
Heatingof
implantsandsimilardevicesmayalsooccurinassociationwithMRprocedures,but
thistendsbeproblematicprimarily forobjectsmadefromconductivematerialsthathave
elongatedshapessuchasleads,guidewires,andcertaintypesofcatheters(e.g.,catheterswith
thermistorsorotherconductingcomponents).
Notably,morethan30incidents
ofexcessiveheatinghavebeenreportedinpatientsundergoing
MRproceduresintheUnitedStatesthatwereunrelatedtoequipmentproblemsorthepresence
ofconductiveexternalorinternalimplantsormaterials[reviewofdatafilesfromU.S.Foodand
DrugAdministration,CenterforDevicesandRadiologicalHealth,Manufacturerand
UserFacility
DeviceExperienceDatabase,MAUDE,http://www.fda.gov/cdrh/maude.htmlandU.S.Foodand
DrugAdministration,CenterforDevicesandRadiologicalHealth,MedicalDeviceReport,(http://
www.fda.gov/CDRH/mdrfile.html)].Theseincidentsincludedfirst,second,andthirddegree
burnsthatwereexperiencedbypatients.Inmanyofthesecases,thereportsindicatedthatthe
limbsorother
bodypartsofthepatientswereindirectcontactwithbodyradiofrequency(RF)
coilsorotherRFtransmitcoilsoftheMRsystemsortherewereskin‐to‐skincontactpoints
suspectedtoberesponsiblefortheseinjuries.
MRsystemsrequiretheuseofRFpulsestocreatetheMR
signal.ThisRFenergyistransmitted
readilythroughfreespacefromthetransmitRFcoiltothepatient.Whenconductingmaterials
areplacedwithintheRFfield,theresultmaybeaconcentrationofelectricalcurrentssufficient
tocauseexcessiveheatingandtissuedamage.Thenatureofhighfrequencyelectromagnetic
fieldsissuchthattheenergycanbetransmittedacrossopenspaceandthroughinsulators.
Therefore,onlydeviceswithcarefullydesignedcurrent pathscanbemadesafeforuseduring
MRprocedures.Simplyins ulatingconductivematerial(e.g.,wireorlead)orseparatingitfrom
thepatientmaynotbesufficientto
preventexcessiveheatingorburnsfromoccurring.
Furthermore,certaingeometricalshapesexhibitthephenomenonof“resonance”which
increasestheirpropensitytoconcentrateRFcurrents.Attheoperatingfrequenciesofpresent
dayMRsystems,conductingloopsoftensofcentimetersinsizemaycreateproblemsand,
therefore,mustbeavoided,unlesshigh
impedanceisusedtolimitRFcurrent.Importantly,even
loopsthatincludesmallgapsseparatedbyinsulationmaystillconductcurrent.
Topreventpatientsfromexperiencingexcessiveheatingandpossibleburnsinassociationwith
MRprocedures,thefollowingguidelinesarerecommended: