User's Manual

Table Of Contents
Chapter 6: Safety 105
Safety
Acoustic output measurement
Sincetheinitialuseofdiagnosticultrasound,thepossiblehumanbiologicaleffects(bioeffects)
fromultrasoundexposurehavebeenstudiedbyvariousscientificandmedicalinstitutions.In
October1987,theAmericanInstituteofUltrasoundinMedicine(AIUM)ratifiedareportfrom
itsBioeffectsCommittee(BioeffectsConsiderationsfortheSafetyofDiagnosticUltrasound,
J
UltrasoundMed.,Sept.1988:Vol.7,No.9Supplement).Thereport,sometimesreferredtoas
theStoweReport,reviewedavailabledataonpossibleeffectsofultrasoundexposure.Another
report,“BioeffectsandSafetyofDiagnosticUltrasound,”datedJanuary28,1993,provides
morecurrentinformation.
Theacousticoutputforthisultrasound
systemhasbeenmeasuredandcalculatedin
accordancewith“A c o u s t i c OutputMeasurementStandardforDiagnosticUltrasound
Equipment”(NEMAUD22004),and“StandardforRealTimeDisplayofThermaland
MechanicalAcousticOutputIndicesonDiagnosticUltrasoundEquipment”(NEMA
UDe32004).
In Situ, derated, and water value intensities
Allintensityparametersaremeasuredinwater.Sincewaterdoesnotabsorbacousticenergy,
thesewatermeasurementsrepresentaworstcasevalue.Biologicaltissuedoesabsorbacoustic
energy.Thetruevalueoftheintensityatanypointdependsontheamount,typeoftissue,and
thefrequencyoftheultrasoundpassing
throughthetissue.Theintensityvalueinthetissue,
In Situ,hasbeenestimatedbyusingthefollowingformula:
In Situ=Water[e
(0.23alf)
]
where:
In Situ=In Situintensityvalue
Water=Waterintensityvalue
e=2.7183
a=attenuationfactor(dB/cm MHz)
Table 7: Transducer Surface Temperature Rise, Internal Use (°C )
Test ICTx SLAx TEEx
Still air 9.2 9.5 9.3
Simulated
Use
5.2 4.8 5.8