This system automatically returns to the settings whenever changes are made to
the values (when you turn on the power, switch between probes, press [End Exam],
or select [Save] in the Setup menu). In the factory default settings, the Acoustic
Output is limited below 100%. Following the ALARA restriction, you are allowed to
increase the acoustic power under FDA 510(k) Guidance-Track3 limits and to set it
in the image preset screen.
The acoustic output of the system has been measured and calculated in accordance with
IEC60601-2-37: 2007, FDA 510(K) GUIDANCE, Acoustic Output Measurement Standard for
Diagnostic Ultrasound Equipment (NEMA UD-2 2004) and the “Standard for Real-Time
Display of Thermal and Mechanical Indices on Diagnostic Ultrasound Equipment (AIUM and
NEMA UD-3 2004).
14.6 Acoustic Power Control
The qualified operator may use the system controls to limit the ultrasound output and to
adjust the quality of the images. There are three categories of system controls relative to
output. They are controls that have direct effect on the output, controls that indirectly control
output and controls that are receiver controls.
◼ Direct Controls
It is possible to control, if necessary, the acoustic output with the menu control. In this case,
the maximum value of the acoustic output never exceeds an MI of 1.9, TI of 6 and an I
SPTA.3
of 720 mW/cm
2
in any mode of operation.
◼ Indirect Controls
The controls that indirectly affect output are many imaging parameters. These are operating
modes, frequency, focal point positions, image depth and pulse repetition frequency (PRF).
The operating mode determines whether the ultrasound beam is scanning or non-scanning.
Thermal bioeffect is closely connected to M mode.
Acoustic attenuation of tissue is directly related to transducer frequency.
The focal point is related to active aperture of transducer and beam width.
For the higher PRF (pulse repetition frequency), the more output pulses occur over a period
of time.
◼ Receiver Controls
The receiver controls (for example, gain, dynamic range, and image post-processing, etc.)
do not affect output. These controls should be used, when possible, to improve the image
quality before using controls that directly or indirectly affect output.
14.7 Acoustic Output
14.7.1 Derated Ultrasonic Output Parameters
In order to determine the relevant Ultrasonic Output Parameters, a method is used which
allows for the comparison of ultrasound systems which operate at different frequencies and
are focused at different depths. This approach, called "derating" or "attenuating", adjusts the
acoustic output as measured in a water tank to account for the effect of ultrasound
propagation through tissue. By convention, a specific average intensity attenuation value is
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