58
major source of error that contributes to the display uncertainty.
The displayed MI and TI values are based on calculations that use a set of acoustic output
measurements that were made using a single reference ultrasound system with a single
reference transducer that is representative of the population of transducers of that type.
The reference system and transducer are chosen from a sample population of systems
and transducers taken from early production units, and they are selected based on having
an acoustic output that is representative of the nominal expected acoustic output for all
transducer/system combinations that might occur. Of course every transducer/system
combination has its own unique characteristic acoustic output, and will not match the
nominal output on which the display estimates are based. This variability between systems
and transducers introduces an error into displayed value. By doing acoustic output
sampling testing during production, the amount of error introduced by the variability is
bounded. The sampling testing ensures that the acoustic output of transducers and
systems being manufactured stays within a specified range of the nominal acoustic output.
Another source of error arises from the assumptions.
9.8
Uncertainty of measurement
Ispta
31.2%
Isppa
30.4%
center frequency (fc)
2%
Total power (W)
30.1%
(
5.6% Scan mode and combination mode
)
Peak negative pressure(pr)
15.5%
9.9
Reference literature for sound power
and its safety
(1)
“Bio-effects and Safety of Diagnostic Ultrasound” issued by AIUM in 1993
(2)
“Medical Ultrasound Safety” issued by AIUM in 1994
(3)
"Acoustic Output Measurement Standard for Diagnostic Ultrasound Equipment,
Revision 3" issued by AIUM/NEMA in 2004
(4)
"Standard for real-time display of thermal and mechanical acoustic output
indices on diagnostic ultrasound equipment, Revision 2" issued by AIUM/NEMA
in 2004
(5)
"Information for Manufacturers Seeking Marketing Clearance of Diagnostic
Ultrasound Systems and Transducers" issued by FDA in 2008.
(6)
“Medical electrical equipment - Part 2-37: Particular requirements for the basic
safety and essential performance of ultrasonic medical diagnostic and
monitoring equipment” issued by IEC in 2015.