By Jun Alejo and Wilson Wei Sheng Wang
The medical equipment industry has always remained at the cutting
edge of technology to enhance or complement the skills of medical
personnel in saving lives. Millions of dollars, and sometimes billions,
have been spent by hospitals, medical units and clinics in acquiring
the latest equipment. The question is, why does the medical sector
invest so much in these equipment? The answer is clear: the medical
industry is all about saving lives. Medical equipment are mission
critical devices that must not fail under any circumstance despite
being deployed in pretty harsh conditions such as ambulances and
mobile transportation units. In addition, advances in imaging and
data processing have automated diagnostic evaluation, reflecting
the need for a storage device that can ensure the high-performance
and reliability of such systems.
Critical Issues in Medical Equipment
Size and Weight - Size can be critical in systems destined
for use in healthcare environments such as laboratories, emergency
rooms, doctors' offices, and ambulances. Therefore, an embedded
computer may take up space no greater than the ones used by single-chip
microcontrollers. Weight is also an important factor if the equipment
is portable or intended for mobile use.
Power Consumption - System reliability is reduced by
high heat buildup. Therefore, it is important to minimize power
consumption when replacing microcontrollers with embedded PCs. Power
consumption and heat generation are important criteria in the design
of portable and mobile systems.
Shock and Vibration Resistance - Whether intended for
fixed or mobile use, every medical product must be transported from
where it is made to where it will be used. Desktop PC motherboards
and plug-in cards are notorious for needing adjustment by a trained
technician after delivery, prior to use.
Such sensitivity to shock and vibration is not acceptable in embedded
applications. In portable or mobile systems, system electronics
undergo a wide range of movement during storage, handling, and operation.
Vibration and sudden jerking may subject components and solder joints
to continual mechanical stress until chips, modules, and boards
become partially or fully dislodged or disconnected. In addition,
connector pin conductivity can be degraded by corrosion resulting
from electrochemical effects that are exacerbated by vibration.
Operating Temperature Range - Most medical systems are
used in relatively benign indoor environments. Embedded electronics
intended for such use are typically rated for operation at temperatures
up to 55°C. However, some medical equipment enclosures need to be
fully sealed-to protect against spilled liquids such as blood or
chemicals, therefore air vents and cooling fans may not be permissible.
In these cases, internal temperature can become elevated, which
may require embedded electronics to be rated for operation up to
70°C. In mobile or portable equipment, an extended operating temperature
range of -20° to 80°C may be called for.
Environmental Factors
Electrostatic discharge (ESD) and electromagnetic interference
(EMI), both generated and received, are key concerns in medical
applications. High frequency microprocessor clocks, which for PCs
commonly fall in the range of 33-166 MHz, can easily interfere with
low-level signal detection or stimulus generation. Additionally,
medical systems often must operate in the presence of strong electromagnetic
emissions from other devices situated nearby. As a result, components
embedded in these systems must be designed with high noise immunity
and low noise generation. Consideration also must be given to conductive
radiation and susceptibility on power supply and I/O connections.
Undesired system resets and data loss must, of course, be prevented,
but the potential danger to human lives from high levels of electric,
electrostatic, or electromagnetic emissions is a far greater concern
in medical applications, requiring designers to incorporate preventive
measures.
Quality and Reliability
Naturally, the required level of system quality and reliability
depends on the particular application. For example, equipment used
in the entry or retrieval of non-critical information can include
fewer fail-safe mechanisms than systems performing life-critical
patient monitoring or blood chemistry control. However, it is categorically
safe to say that medical users are never as forgiving of system
malfunctions or crashes as are the users of desktop PCs. Practically
every PC user experience messages such as"Fatal error #XYZ" from
time to time, but such incidents are totally unacceptable in medical
equipment, where consequences can range from loss of critical data
to loss of life.
Product Life Span
Regarding product longevity, desktop PC manufacturers and users
have a different set of priorities compared with the medical systems
industry. Desktop PC vendors strive to bring out new technologies
constantly, and the typical half-life (to obsolescence) of PC chipsets
is around 1.5 years. Clearly, while it may benefit PC manufacturers
to market a new motherboard, video card, disk controller, or network
controller every year or so, this situation is unacceptable for
medical equipment manufacturers. Medical products typically require
two or more years of development, followed by several more years
to gain FDA approval. Therefore, medical systems design cannot be
based on components with a lifespan of as short as 18 to 24 months.
Medical Diagnosis in the Digital Age
The advent of digital technologies gave birth to a variety of
electronic medical equipment requiring high performance and reliability.
The following are some examples:
Magnetic resonance imaging (MRI)
MRI is an imaging technique used primarily for diagnostic purposes
to produce high quality images of the human body, both internal
and external. MRI is based on the principle of nuclear magnetic
resonance, a spectroscopic technique used by scientists to obtain
microscopic chemical and physical information about molecules.
Computed axial tomography (CAT scan or CT scan)
CAT scan is a computerized x-ray procedure that produces cross-sectional
images of the human body. The images are far more detailed than
x-ray films, and can reveal disease or abnormalities in tissue and
bone. The procedure is usually noninvasive and brief.
Positron emission tomography (PET scan)
PET scan is a test that combines computed tomography (CT) and
nuclear scanning. Compared to CT scans and MRI, PET produces less-detailed
pictures of an organ. A PET scan is often used to detect and evaluate
cancer, such as of the lung or breast. It also can be used to evaluate
the heart's metabolism and blood flow and examine brain function.
Ultrasound (Sonography)
This diagnostic imaging technique uses high-frequency sound waves
and a computer to create images of blood vessels, tissues, and organs.
Ultrasounds are used to view internal organs as they function, and
to assess blood flow through various vessels.
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