7/28/2019 Evaluating EMI
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With the integration of wireless communica-
tion technology into hospital infrastruc-
tures across the nation, many hospitals are
concerned about the impact of radio frequency (RF)
electromagnetic interference (EMI) between wirelesstechnologies
and medical equipment. Such interference
may cause undesirable effects to medical equipment,
possibly, resulting in misdiagnosis, mistreatment, and/or
patient injury.
These wireless communication devices include wire-
less LAN, Bluetooth, wireless PBX, telecommunica-
tions, paging, two-way radios, telemetry devices,
Blackberry, wireless Personal Digital Assistants (PDA),
and PC tablet/laptop. While most medical instruments
are manufactured now with a recommended 3V/m (10
V/m for life support devices) immunity level againstinterference
from RF emissions (IEC 60601-1-2), older
equipment may have inadequate shielding and, there-
fore, be more susceptible to interference.1
Wireless devices are becoming main stream in todays
society. The prevalence of such wireless devices in the
medical field is inevitable and probably here to stay. So,
what is a hospital to do? One option is to do nothing and
deal with the interference if it happens. Another option
is to test every microprocessor-based medical device in
the hospital to understand the potential interference
issues. Unfortunately, it is virtually impossible to testevery
combination of transmitting wireless device and
microprocessor-based medical device. Genesis
Technology Partners took a midline approach and tested
a variety of medical devices with some mainstream wire-
less devices. We tested a sample of the most commonly
used medical devices in the hospital. These devices
included basic vital signs monitors to life support
devices.
Where to Begin
Testing of the hospital environment should begin with a
RF survey, particularly before the installation of new
medical telemetry. RF surveys should be done for all
hospitals that need to deal with radio and TV stations in
close proximity. The FDA has written communications
regarding digital television and potential interference
with medical telemetry systems.2 Such interference from
RF sources is a function of power, frequency, and dis-
tance. Fortunately, radio and TV stations are
physicallystationary; therefore, the distance a hospital is
situated
from a stations antenna is relatively constant.
A frequency survey will help define the current inter-
ference potential. In addition, information about future
plans of local TV stations to broadcast digital signals are
needed to determine if the potential exists for EMI
issues between TV digital signals and medical devices.
Digital TV signals are transmitted at very high output
powers and transmit at or near frequencies that have
been traditionally used for medical telemetry (e.g. 460-
470MHz range).1
Evaluating EMI in a
Multi-Hospital Facility
Barry Bruns and Shawn Dimantha
Wireless Technology
Barry Bruns is the director of biomedical engineering forGenesis
Technology Partners. He has a Masters in SystemEngineering from
Wright State University, Dayton, OH, and aMasters in Business
Administration from Xavier University,Cincinnati, OH. He works at
the GTP account with the HealthAlliance of Greater Cincinnati. The
Health Alliance is a systemcomprised of six hospitals in the
Greater Cincinnati area.
Shawn Dimantha worked as a summer intern for GenesisTechnology
Partners. He is an engineering student with theUniversity of
Pennsylvania.
40 IT Horizons www.aami.org 2006
Testing of the hospital
environment should begin
with a RF survey, particularlybefore the installation of
new medical telemetry.
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7/28/2019 Evaluating EMI
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Barry Bruns and Shawn Dimantha
IT Horizons www.aami.org 41
Hospitals still operating medical telemetry at those
frequencies may be at risk for EMI between the station
and telemetry systems. As a result, the FCC has dedi-cated
frequency bands for medical telemetry use known
as the Wireless Medical Telemetry Spectrum (WMTS).
Registration of these telemetry devices with the
American Society of Hospital Engineers (ASHE) is
necessary.
Testing for EMI between mobile wireless communi-
cation and medical devices should also be performed.
We tested wireless devices such as laptops, tablet PCs,
and PDAs, which communicate using internal wireless
access points and wireless network cards. Hospitals have
set up distributed access point systems to help improvesignal
strength between the access points and the net-
work interface cards (NIC). These wireless access points
are typically fixed near the ceiling and tend to operate at
0.1 watts or lower.
The devices most vulnerable to EMI from the access
point are telemetry antennae. Fortunately, the access
points operate at different frequencies beyond the
WMTS band and pose little threat. However, the asso-
ciated wireless network cards for mobile computers usedin
systems for computerized physician order entry
(CPOE) and electronic medical records (EMR) can
potentially come in close contact with medical devices.
Despite the low power, we did test for EMI between
wireless network cards and medical devices.
The wireless devices, which do not rely on internal
antenna systems, include cell phones, Blackberry, and
Wi-Fi devices. Cell phones and wireless PDAs in gener-
al have an average power output of 0.6 watts, but they
can increase to 2 watts when there is relatively low signal
strength.3
Most cellular wireless devices do not generatemuch EMI at
distances greater than 50 cm from the unit.
However, their mobility increases the chance of a close
encounter (less than 50 cm) with a medical device.
Coupled with an increase in output power (1W) due to
low signal strength, the chance for EMI does exist.
Despite the low power, cell phones in close proximity to
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