Using Solid State Flash Disks as Cure-All for Medical Storage Systems
By: Jun Alejo and Wilson Wei Sheng Wang
BiTMICRO Networks
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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