Biomedical Engineering Reference
In-Depth Information
These sources of electromagnetic radiation, as seen from
the previous lists, can be intentional or unintentional.
The challenges and the institutional responses imposed
by the presence of these EMI sources can be divided,
for all intents and purposes, into four parts: Mitigation,
detection, correction, and prevention. Although the
mitigation and prevention phases appear to be similar,
they differ in their approaches and applications.
Radiator
INTENTIONAL
TARGET
INTENTIONAL
Controlling the effect of EMI
Mitigation
In the mitigation phase, the principal concern is reducing
risk to, or victimization of, clinical devices by devices
emitting unintentional or intentional electromagnetic
radiation. The sources of the devices may be internal or
external to the institution. The devices may be in-
tentional or unintentional radiators of electromagnetic
fields, and the electromagnetic energy may be radiated or
conducted.
Figure 5.6-1
illustrates the electromagnetic
interaction among intentional and unintentional radiators
and intentional and unintentional targets.
Mitigation is accomplished in part by the careful
analysis of a device, including the accessories to be used
with it, and the electromagnetic environment in which it
will be used. A successful approach has been imple-
mented at Texas Children's Hospital. This approach is
accomplished in two phases: Thorough analysis of the
environment in which the device is to be placed, called
''footprinting,'' and an equally thorough analysis of the
clinical device itself, called ''fingerprinting.'' The pro-
cedures of quantifying potential EMI and mitigating the
effects through environment analysis are described in
greater detail later in this chapter.
Another vital part of the mitigation process occurs
during facility planning. Whether planning a new facility,
an expansion of an existing facility, or remodeling of a fa-
cility, clear and concise communications between affected
departments, architects, contractors, and the clinical en-
gineering department are vital at all stages of the project.
For example, one institution installed expensive, screened
rooms at great cost. When the clinical engineer, acting on
complaints of erratic EMGoperation, determined that the
room played a role in the culprit/victim relationship, the
rooms were disassembled, also at great cost. In this case,
the relocation of the affected department was not an
option. The clinical engineering department had not been
made aware of these rooms, or of their intended applica-
tion that involved the use of known culprit devices.
TARGET
UNINTENTIONAL
Radiator
UNINTENTIONAL
Figure 5.6-1 The complexities of EMI-radiators and targets:
Culprits and victims.
Land mobile radio: Fixed base (FB), mobile, and
portable two-way radio sources (walkie talkies)
*
Paging: One-way and two-way wireless messaging
service transmitters
Cellular telephones and sites
*
Wireless personal digital assistants (PDAs)
Wireless networking devices (an increasing threat in
the 2.4 GHz industrial, scientific, and medical ISM
band)
Unlicensed and unauthorized users of two-way radio
communications equipment (Pirates)
*
Unintentional radiators:
Lighting systems (especially florescent), including
energy saving electronic ballasts
*
High energy control systems (HVAC controllers),
especially variable-speed controllers
*
Malfunctioning electrical services
*
Universal-type electric motors
*
Pulse oximeters
*
Displays (CRT and plasma), computer, television,
and instrumentation
Wired computing networks
''Smart'' fire detection and alarm devices
*
Electrosurgical units (ESU)
*
Defibrillators
*
Sources (the culprits) of incidents attributed to EMI encountered at Texas Children's Hospital.
