SonoSite S-Cath - Direct Controls; Indirect Controls; Receiver Controls; Acoustic Artifacts

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Thesonographerusesthesystemcontrolstoadjustimagequalityandlimitultrasoundoutput. 
Thesystemcontrolsaredividedintothreecategoriesrelativetooutput:controlsthatdirectly
affectoutput,controlsthatindirectlyaffectoutput,andreceivercontrols.
Direct controls
Thesystemdoesnotexceedaspatialpeaktemporalaverageintensity(ISPTA)of720 mW/cm
2

forallimagingmodes.(FortheOphthalmicexam,theacousticoutputislimitedtothe
followingvalues:ISPTAdoesnotexceed50mW/cm2;TIdoesnotexceed1.0,andMIdoesnot
exceed0.23.)Themechanicalind ex(MI)andthermalindex(TI)mayexceedvaluesgreatertha n 
1.0onsome
transducersinsomeimagingmodes.OnemaymonitortheMIandTIvaluesand
adjustthecontrolstoreducethesevalues.See“GuidelinesforreducingMIandTI”onpage 81.
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attenuation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).