Special requirements challenge handheld computer designers for telemedicine applications
Handheld computers need to include special features before they can become fully compatible with medical applications such as telemedicine. These additional features affect the design at all levels, and turn a generic device into a powerful new tool for medical usage.
Telemedicine involves the use of computers, mobile network connectivity, and information technology within the patient care environment, with mobile access in medical centers or at the patient’s home. At first it may appear that any suitably powerful handheld computing device could potentially fulfill this role for telemedicine. However, the medical environment requires a particular set of capabilities, peripherals, interfaces, and connectivity that are needed before a generic handheld computer can become acceptable and usable as an all-in-one clinical tool. Medical handheld computers are therefore a special class of mobile handheld device that are needed for mobile telemedicine. The special requirements of these devices affect the design at every level, from module to system, and some specific examples of this include the medical device-specific electrical certifications required, SBC considerations, and special hot-swap redundancy features included in the battery management and charging circuits. Medical application-specific interface devices, network connectivity and OS, and longevity and change traceability are also vital considerations.
Medical handheld device design features
Typically, inside a handheld medical computer is a powerful small form factor SBC or module, with a baseboard, a high-resolution and easy-to-clean touch-screen display, batteries, and a carefully chosen set of interface modules that provide specific capabilities for the medical application. The enclosure itself that carries all these components is custom made and has a number of special features required for the medical environment. For example, easy cleaning of the enclosure exterior is a necessity, and protective covers with gaskets are required for exposed electrical connectors to prevent cleaning fluid from entering the connector or the internals of the enclosure. Some applications still benefit from programmable function keys or dedicated selection/navigation keys so these are typically provided at the display periphery for improved user flexibility, but these keys must also be easily cleanable and drip-proof.
The handheld device must be lightweight (less than 4 lbs) and both easy to carry and easy to operate. A comfortable built-in handle is also often provided on the enclosure to improve portability. Docking stations are commonly used in medical facilities, for example, on walls or on medical carts that are wheeled around the medical facility, and are also used to provide a desktop alternative when needed. The handheld enclosure needs to be easily and reliably inserted into the docking station without needing any careful alignment, which influences the design choices made for the docking connector. The overall device must be tough and fully drop resistant for day-to-day use, so rugged design of all parts is a key requirement.
Medical standards compliance
Electronic devices for use in medical settings require high levels of performance and reliability, and patient safety is a foremost consideration. Medical computers are therefore expected to meet demanding standards compliance requirements. ISO 13485 is a Medical Quality System certification that ensures a device meets strict quality requirements for the international medical equipment market. This standard also covers the detailed process by which end-user requirements and specifications are incorporated into the design. Certification to ISO 13485 ensures that the product has been developed and manufactured using a full quality management process. A medical device must also conform to medical safety standard UL60601 in the U.S. and to EN60601 in Europe. To achieve successful approval to UL60601-1/EN60601-1 requires special care in the design. All external electrical interfaces such as USB ports, serial ports, and Ethernet must have high levels of electrical isolation performance to meet medical standards, with very low leakage currents and transformer isolation where necessary. Implementing the standard can also be a particular design challenge at the PCB design stage because of the requirement to comprehensively achieve the various conductor spacing requirements specified, and also care is required when integrating an SBC with all the various interface modules into the enclosure.
Specific single board computer considerations
The SBC module within the enclosure is designed to provide a fast and responsive computer operation, but along with relatively low power requirements (typically the whole system power, including screen, should be below 15 W). The choice of module is therefore a key part of the device’s design. Focus is placed on power efficiency, which is always beneficial for handheld devices, and the provision of a sufficient set of interfaces on the module that well match the application requirements. Medical applications generally need multiple USB ports to cater to the relatively large number of USB-based peripherals such as web cameras, Bluetooth, barcode scanners, SD and SmartCard readers, and RFID. Touch-screen controllers, whether using projective capacitive or resistive touch, also typically use a USB interface. A mini-card slot is also needed in the design for the flexibility to add in any special requirement functions for specific custom applications.
Fanless design is a key capability for medical handheld computers because the equipment needs to be cleaned and disinfected often, and fans make such cleaning much more difficult. But there are many other benefits to fanless systems too, including quiet operation, easier design of the enclosure (no air ports or airflow paths needed), and lower power allowing smaller, lighter-weight batteries to be used. However, successfully incorporating a fanless SBC requires that careful attention is paid to the thermal design for effective heat transfer and the use of efficient heat sink structures.
Removable hot-swap battery for continuous operation
Medical handheld computers need to be capable of continuous mobile usage; Waiting for a recharge is not generally an option and might even be a safety issue during mobile patient care, so this class of device usually has a very important hot-swap redundant battery feature. This feature allows for continuous handheld operation of a battery-powered device without needing to connect to AC power adapters for battery recharges. A removable battery is provided along with a fixed internal battery. When the main removable battery is discharged, it can be hot-swap removed and replaced with a fully charged one while the internal battery retains the device power and continues uninterrupted operation for the user. However, the battery management and charging circuit to handle this feature seamlessly and correctly under all circumstances becomes a necessary part of the electronic design. The power architecture modification needed consists of two battery recharge circuits that are managed by firmware on the system microcontroller over a dual SMBus. Diode ORing of the power rails is then used to combine the three possible sources of system power, consisting of the primary removable battery, the fixed internal battery, and the external 12 V power adapter supply. This relatively simple concept of a hot-swap redundant battery feature therefore requires significant additional circuitry and control firmware for the power management section, but the feature itself provides a very large benefit for the day-to-day usability of this class of product.
Medical application-specific interface devices
Medical handheld computers benefit from a combination of specific built-in interface devices that are not commonly found combined on other products. These devices include RFID and barcode scanners that are used, for example, to scan patient tags or drug labels. Aside from the speed and convenience of having this scan capability built in, it also has the key benefit of reducing data entry errors, which is very important in a safety-conscious medical setting. Magnetic Stripe Readers or Smart Card Readers are also sometimes needed and can be included in the docking station if they are not included in the handheld device itself. Cameras are also useful for recording medical symptoms or patient photographs, and a front-facing camera can serve for video communication with medical specialists or other staff.
Network connectivity and OS
Flexible network connectivity is a key requirement for a mobile device and is usually provided by Wi-Fi when mobile, and by Ethernet LAN when installed into a docking station. Bluetooth also allows local connectivity to nearby tools and devices. High-Speed Uplink Packet Access (HSUPA) is included to allow flexible and fast uploads of data from the handheld device when outside of the range of Wi-Fi, such as on a patient home visit when the device is outside the medical center’s Wi-Fi coverage. A major feature of medical handheld computers is the software OS support, and typically this includes a range of choices including Windows XP Embedded, Windows CE, Linux, and QNX. Many software applications for example, are based on Windows, but some medical devices have to integrate with specific existing installed bases of IT infrastructure, so flexibility of OS choice is important.
Longevity and change traceability
Finally, medical products are designed with a long lifetime expected, typically a minimum of five years, and every component and module needs full revision control and compliance provability for the relevant standards, which must be considered during the design phase. Change traceability and quality assurance at all levels from module to full system are more demanding for medical applications than in many other application areas. Figure 1 shows the Arbor Technology M1040, an example of a handheld device that includes medical-specific features. This device is specifically intended to be used by doctors, nurses, and other medical staff as a telemedicine-capable “mobile clinical assistant.”
Telemedicine handhelds: A valuable new medical tool
Special features are needed in a handheld device before it can be considered to be suitable for telemedicine applications. These features affect the system design at all levels from modules and interfaces to the detailed circuitry and mechanical design of the enclosure. Mobile telemedicine using handheld computers that include these features provides clinical staff with powerful tools to access and manage patient information, helping them provide better patient care.
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