User's Manual

Chapter 6: Safety 99
Safety
onpage 99.Additionally,onemeansformeetingtheALARAprincipleistosettheMIorTI
valuestoalowindexvalueandthenmodifyingthisleveluntilasatisfactoryimageorDoppler
modeisobtained.FormoreinformationonMIandTI,seeBSEN60601‐2‐37:2001:Annex
HH.
Indirect controls
Thecontrolsthatindirectlyaffectoutputarecontrolsaffectingimagingmode,freeze,and
depth.Theimagingmodedeterminesthenatureoftheultrasoundbeam.Tissueatt enuationis
directlyrelatedtotransducerfrequency.ThehigherthePRF(pulserepetitionfrequency),the
moreoutputpulsesoccuroveraperiodoftime.
Receiver controls
Thereceivercontrolsarethegaincontrols.Receivercontrolsdonotaffectoutput.Theyshould
beused,ifpossible,toimproveimagequalitybeforeusingcontrolsthatdirectlyorindirectly
affectoutput.
Acoustic artifacts
Anacousticartifact isinformation,presentorabsentinanimage,thatdoesnotproperly
indicatethestructureorflowbeing imaged.Therearehelpfulartifactsthataidindiagnosisand
thosethathinderproperinterpretation.Examplesofartifactsinclude:
• Shadowing
• Throughtransmission
• Aliasing
• Reverberations
•Comettails
Formoreinformationondetectingandinterpretingacoustic
artifacts,seethefollowing
reference:
Kremkau,FrederickW.DiagnosticUltrasound:PrinciplesandInstruments.7thed.,W.B.
SaundersCompany,(Oct. 17,2005).
Guidelines for reducing MI and TI
ThefollowingaregeneralguidelinesforreducingMIorTI.Ifmultipleparametersaregiven,
thebestresultsmaybeachievedbyminimizingtheseparameterssimultaneously.Insome
modeschangingtheseparametersdoesnotaffectMIorTI.Changestootherparametersmay
alsoresultinMIandTIreductions.Please
notetheMIandTIvaluesontherightsideofthe
screen.