User Manual

58
)10/3.0
－
(
10
zf
wateratten
c
II


Among them, I
atten
is the attenuation of sound intensity, I
water
is in the tank the measured sound
intensity (at a distance z), fc is the center frequency of the ultrasonic (measured in water), and Z is
the distance apart. The attenuation value of pressure probe formula is similar, but the attenuation
coefficient is 0.15 dB/cm/MHz, half of the sound strong. Because of pressure and pressure is
proportional to the square, so the sound intensity coefficient is two times of pressure coefficient.
Although the 0.3 dB/cm/MHz than any solid body tissue attenuation coefficients are much lower,
but it can be treated as the examination of the fetal condition. In early pregnancy test, ultrasonic
probe arrived from the fetus, through the middle of almost all liquid, and the liquid attenuation is
very small. Because of this 0.3 dB/cm/MHz lower than the actual attenuationcoefficientcheckthe
number。
9.7.2 Acoustic output limit
In accordance with the FDA requirements of Track 3, the acoustic output limits using the derating
(or attenuation) method, as shown in the table below. The use of any probe in any mode of
operation, the maximum acoustic output should be listed in the following table limits.
FDA 3 Track maximum sound output limit (attenuation)
Application
I
spta.3
(mW/cm
2
)
I
sppa.3
(W/cm
2
)
or
MI
Other parts (in
addition to the eye)
720 ≤ 190 ≤ 1.9
9.7.3 The difference between the actual MI/TI value
and the display value
During operation, the system always show the acoustic output parameters, thermal and mechanical
index TI index MI. of these parameters is the ultrasonic thermal effect and mechanical effect of
risk indicators. They are a set of system to the operator that may increase or reduce the possibility
of thermal or mechanical effects. More precisely, these parameters are for the implementation of
ALARA design principles. When the operator changes a control system, the system will display
the change of acoustic output changes. However, the heat index is not equal to the body
temperature. First of all, in order to provide a single display index, had to make several
simplifying assumptions, one hypothesis is that the frontThe attenuation method for animal body,
most of the organization the actual value is much smaller (such as attenuationproducedinmuscle
or organ when the scan is far higher than 0.3 dB/cm/MHz), for the thermal property of
organization also made simplified. Therefore, when scanning high perfusion tissue (such as
cardiac or vascular system), the thermal effect will have the heat index is much lower than that.