Bladder Volume Tester User’s Manual V1.02
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Chapter Eleven Principle of Sound Power
11.1 Biological effect
It is generally recognized that ultrasonic diagnosis is safe for human’s health. So far, there has been no
report on bodily harm done by ultrasound.
Nevertheless it is also believed that not all types of ultrasound are absolutely safe. Relevant researches
have already indicated that high-intensity ultrasound is harmful for human body.
With the development of ultrasonic diagnosis technology in recent years, people are more aware of
the potential risk in biological effect caused by use of ultrasound and application of ultrasonic diagnostic
technology.
11.2 Mechanical effect and thermal effect
Research indicates that two different ultrasonic properties influence human body: one is when
ultrasonic negative-pressure exceeds some limited number, air pocket forms mechanical effect; another is
when tissues absorb ultrasonic, appearance of heat energy of ultrasonic may cause thermal effect. Two
parameters which are mechanical index MI and thermal index TI can explain two types of effects
influencing level, the smaller value of MI/TI is, the less bio effect produce.
11.3 Prudent-use statement
Whereas it is not proved that ultrasonic diagnostic instrument may result in biological effect in human
body, there is possibility that such biological effect is proved to be true in the future. Therefore we shall
exercise prudence in applying the diagnostic ultrasound to clinical practice. We shall obtain clinical
information necessary for the diagnosis with reasonable ultrasound and avoid using high-intensity
ultrasound for long period of time.
11.4 ALARA (as low as reasonably achievable) principle
Application of ultrasound shall be based on the ALARA principle that requires a minimized,
biological effect-free energy output to obtain necessary diagnostic information. The ultrasonic energy
intensity is related to output power and exposure time. Different patients and cases require different
ultrasonic intensity.
Not all diagnosis can be done with extra-low ultrasonic energy output. The extra-low ultrasound
power produces poor-quality image or weaker Doppler signal that may reduce the diagnostic reliability. On
the other hand, use of sound power larger than diagnostically required makes no more contribution to
improvement of the diagnostic information quality and increase the risk of biological effect possibility.
Therefore, user of the diagnostic ultrasound shall be fully aware of the patient’s safety and choose a
proper output level for a specific purpose based on ALARA principle.
11.5 The limits of acoustic output
When using any probe match in each mode, the acoustic output parameters for thermal index and
mechanical index are below 1.0.
11.6 Factors impacting sound power
Because the settings (transmission voltage, transmission frequency, etc.) are fixed in this system, there
are no factors impacting sound power.
11.7 Image control impact on sound power output
Change of image control and adjustment may have influence on sound power output. See table
below:
Operation Influence on sound power output
Freeze
If freeze function makes the power transmission part of system stop
operation, the system will not be able to transmit the ultrasound.
Depth change
The different patient mode selects different depth; it will change the
acoustic power.
Restart or turn off/on power
Turn off/on the power will set the system in default status and change the
sound power output.
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