User's Manual
Table Of Contents
- S Series Ultrasound System User Guide
- Contents
- Introduction
- Chapter 1: Getting Started
- Chapter 2: System Setup
- Chapter 3: Imaging
- Chapter 4: Measurements
- Chapter 5: Troubleshooting and Maintenance
- Chapter 6: Safety
- Ergonomic safety
- Electrical safety classification
- Electrical safety
- Equipment safety
- Battery safety
- Clinical safety
- Electromagnetic compatibility
- ALARA principle
- Acoustic artifacts
- Guidelines for reducing MI and TI
- Output display
- Transducer surface temperature rise
- Acoustic output measurement
- Acoustic output tables
- Labeling symbols
- Chapter 7: Specifications
- Glossary
- Index
Chapter 6: Safety 67
Safety
Mechanical and thermal indices output display accuracy
Theaccuracyresultforthemechanicalindex(MI)isstatedstatistically.With90%confidence,
90%ofthemeasuredMIvalueswillbewithin+16%to–31%ofthedisplayedMIvalue,or+0.2
ofthedisplayedvalue,whichevervalueislarger.
Theaccuracyresultforthethermalindex(TI)isstated
statistically.With90%confidence,90%
ofthemeasuredTIvalueswillbe within+26%to–50%ofthedisplayedTIvalue,or+0.2ofthe
displayedvalue,whichevervalueislarger.Thevaluesequateto+1dBto–3dB.
Adisplayedvalueof0.0forMIorTImeansthatthecalculated
estimatefortheindexislessthan
0.05.
Factors that contribute to display uncertainty
Thenetuncertaintyofthedisplayedindicesisderivedbycombiningthequantifieduncertainty
fromthreesources;measurementuncertainty,systemandtransducervariability,and
engineeringassumptionsandapproximationsmadewhencalculatingthedisplayvalues.
Measurementerrorsoftheacousticparameterswhentakingthereferencedataarethemajor
sourceoferror
thatcontributestothedisplayuncertainty.Themeasurementerrorisdescribed
in“A c o u s t i cmeasurementprecisionanduncertainty”onpage 79.
ThedisplayedMIandTIvaluesarebasedoncalculationsthatuseasetofacousticoutput
measurementsthatweremadeusingasinglereferenceultrasoundsystemwithasingle
referencetransducer
thatisrepresentativeofthepopulationoftransducersofthattype.The
referencesystemandtransducerarechosenfromasamplepopulationofsystemsand
transducerstakenfromearlyproductionunits,andtheyareselectedbasedonhavingan
acousticoutputthatisrepresentative ofthenominalexpectedacousticoutputfor
all
transducer/systemcombinationsthatmightoccur.Ofcourseeverytransducer/system
combinationhas itsownuniquecharact erist icacousticoutput,andwillnotmatchthenominal
outputonwhichthedisplayestimatesarebased.Thisvariabilitybetweensystemsand
transducersintroducesanerrorintodisplayedvalue.Bydoingacousticoutputsampling
testing
duringproduction,theamountoferrorintroducedbythevariabilityisbounded.The
samplingtestingensuresthattheacousticoutputoftransducersandsystemsbeing
manufacturedstayswithinaspecifiedrangeofthenominalacousticoutput.
Anothersourceoferrorarisesfromtheassumptionsandapproximationsthataremadewhen
deriving
theestimatesforthedisplayind ices.Chief amongtheseassumptionsisthatthe
acousticoutput,andthusthederiveddisplayindices,arelinearlycorrelatedwith thetransmit
drivevoltageofthetransducer.Generally,thisassumptionisverygood,butitisnotexact,and
thussomeerrorinthedisplaycan
beattributedtotheassumptionofvoltagelinearity.
Related guidance documents
• Informationfor ManufacturersSeekingMarketingClearanceofDiagnosticUltrasound
SystemsandTransducers,FDA,1997.
•MedicalUltrasoundSafety,AmericanInstituteofUltrasoundinMedicine(AIUM),1994.(A
copyisincludedwitheachsystem.)