The conducted RF test level is 3 V, and the system has a compliance level of
0.08 V. For the system, this means that the imaging system is extremely sensitive
to RF interference in the transducer passband. For example, for a 5-MHz imaging
transducer, the frequency range of interference from a 3-V/m field may be from
2 to 10 MHz and manifest itself as described in "Electromagnetic Interference"
on page 78.
The 0.08-V level is where the interference becomes acceptable to some clinical
specialists.
Sensitivity to interference is dependent on operating mode and imaging control
settings. The order of increasing sensitivity to interference as a function of
operating mode is 2D mode, 3D mode, M-mode, Color mode, PW Doppler
mode, and CW Doppler mode. The system is more sensitive to interference in
the CW Doppler or PW Doppler operating modes, but the probability of
interference is lower than in 2D mode or Color mode, because the susceptible
frequency range is lower. Therefore, you are more likely to see interference in
2D or Color modes.
As an example, if a portable transmitter has maximum radiated power of 1 W
and an operating frequency of 156 MHz, it should only be operated at distances
greater than 1.2 m (3.9 ft) from the system. Likewise, a 0.01-W Bluetooth wireless
LAN device operating at 2.4 GHz should be placed no closer than 0.24 m (9.5 in)
from any part of the system.
Avoiding Electromagnetic Interference
A medical device can either generate or receive electromagnetic interference.
The EMC standards describe tests for both emitted and received interference.
Emission tests deal with interference generated by the device being tested. Philips
ultrasound systems do not generate interference based on the tests described
in the referenced standards.
An ultrasound system is designed to receive signals at radio frequencies and is
therefore susceptible to interference generated by RF energy sources. Examples
of other sources of interference are medical devices, information technology
products, and radio and television transmission towers. Tracing the source of
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Safety
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