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Measurement uncertainty mainly include repeated measurement uncertainty and the system
uncertainty,
the system uncertainty is an order of magnitude higher than repeated measurement uncertainty, so the main
analysis is the system uncertainty. Mainly decided by the following factors:
1.
The sensitivity of hydrophone:According to hydrophone calibration report provided by ONDA
company, the
maximum allowable error of sound pressure for hydrophone is plus or minus 12%;
2.
Scope: according to agilent DSO6502A specifications, its effect on the sound pressure is plus or
minus 2%;
3.
Temperature: effect of the thermocouple on sound pressure error is plus or minus 4%;
Above all uncertainty components are not related, synthetic standard uncertainty of sound pressure is:plus or
minus 13%.
1.2.4 Operator Control Property
There are three types of operation control related to the generation of mechanical/thermal effect:
direct
control and indirect control, receiver control. Qualified operator should try to cut down the
acoustic output in the
premise of effective diagnostic images.
Direct control
The direct control of the acoustic output of this system is adjusting voltage size.But its maximum
acoustic output shouldn't be more than displayed acoustic output limit in any modes.
Indirect control
The controls that indirectly affect output are many imaging parameters. These are operating modes,
frequency,focal point number/position, image depth and pulse repetition frequency (PRF)(By adjusting
the [Scale] of the toolbar).
The operating mode determines whether the ultrasound beam is scanning or non-scanning. Thermal
effect is closely connected to M Mode, PW Doppler and Color Mode.
Acoustic attenuation of tissue is directly related to transducer frequency.
The focal point number and position is related to active aperture of transducer and beam width.
For the pulse repetition frequency( PRF)(By adjusting the [Scale] of the toolbar), the higher the PRF,
the more acoustic output power increased over a period of time.
The receiver control
The receiver control does not affect the acoustic output, including gain, dynamic range, and image
processing, etc. Therefore, in the image optimization, should adjust the receiver control to optimize
images firstly, the second are through direct control and indirect control.
When acquiring images, it is recommended to use the default (or as low as possible) acoustic output
location, and use the gain control to compensate. The default setting is commonly 70% of maximum
allowed acoustic output value, which will not cause harm to the operator, and for the probe is the most
effective value
1.2.5 Acoustic Power Settings
The ultrasound system has been preset the parameters for each exam mode with different probes
before shipment. When the ultrasound system is powered on, a new patient is created or the application
mode is changed, the system will retrieve the default settings. You can also reset the parameters.
1.2.6 ALARA
It is required to practice ALARA when using ultrasound energy. Practicing ALARA ensures that the total