Mindray DP-20 - Measurement Uncertainty; References for Acoustic Power and Safety

14-6 Acoustic Output
Similarly, the Mechanical Index was derived to indicate the relative possibility of mechanical
(cavitation) effects. The MI is based on the derated peak-rarefactional pressure and the
center frequency of the ultrasound wave. The actual peak-rarefactional pressure is affected
by the actual attenuation caused by tissue in the path between the 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.
14.8 Measurement Uncertainty
I
spta
28.5%
I
sppa
28.5%
Center frequency (f
c
)
2%
Total power (W)
28.5%
(5.1% for Scan-mode and Combined-mode)
Peak-rarefactional pressure
14.7%
14.9 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 2008.
6. “Medical electrical equipment – Part 2-37: Particular requirements for the safety of
ultrasonic medical diagnostic and monitoring equipment” issued by IEC in 2015.