Acoustic Output
23-6
transducer and the focal point. Again, all solid tissues within the body have higher
attenuation than the proscribed 0.3 dB/cm/MHz value, and therefore, the actual
peak-rarefactional pressure will be lower. Further, the actual peak-rarefactional pressure
will change depending upon the region of the body being scanned.
For these reasons, the TI and MI displays should only be used to assist the operator in
implementing ALARA at the time of the patient examination.
23.8 Measurement Uncertainty
Power
32.9 % (non-scanning mode）
5.1% (Scanning mode）
Frequency 2%
Peak-rarefactional pressure 16.4 %
MI 16.4 %
23.9 References for Acoustic Power and
Safety
1. “Bioeffects 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 1997.
6. “Medical electrical equipment – Part 2-37: Particular requirements for the safety of
ultrasonic medical diagnostic and monitoring equipment” issued by IEC in 2005
(Amendment 2).
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