Medical Device Link.

Originally Published MEM Fall 2005

DATA STORAGE

Solid-state storage devices can boost data security, enhance power management, and lower overall costs of medical electronics development.

Gary Drossel

In healthcare applications, storage solutions often contain sensitive data. Storage devices used in medical electronics should enhance data security as mandated by the Health Insurance Portability and Accountability Act (HIPAA). In general, healthcare providers must be assured that data can be collected and stored with the highest levels of integrity. The information must match the correct patient, and it must be secure so that it effectively protects patient privacy.

Medical devices are frequently required to be portable, so their storage solutions must have a small form factor, and they must be able to operate at lower power rates. They must be rugged enough for long-term use in medical equipment that is expected to maintain multiyear life cycles.

Solid-State Technology

Solid-state technology meets the size and power demands of this industry while increasing the reliability of storage exponentially in terms of both physical viability and data security. The overall benefits of using this technology translate into improved patient care and lower total cost of system storage.

Rotating disk drives are mechanically limited to 2.5- or 3.5-in. form factors because of the size of their mechanics and magnetic platters. By contrast, recent advances in solid-state technology have enabled their form factors to be scaled down considerably. They consume much less power than the typical 2.5 W dissipated in a rotating hard drive.

Solid-state storage devices use ultra-low-power RISC (reduced instruction set computing) technology to function as host interface and to provide solid-state storage. This technology consumes less than one-tenth the power of traditional rotating hard drives (0.2 W typical). The mechanical footprint allows solid-state devices to fit in several industry-standard form factors such as Type I CompactFlash, Type II PC cards, and plug-in modules (see Table I).

Small form factors with high capacities enable portability. Smaller, lighter equipment is unobtrusive and easy to manipulate in an operating room or in remote environments. Solid-state storage capacities are increasing at a rate exceeding Moore's Law; that is, for a given form factor, the maximum capacity is doubling in less than 18 months. For example, the maximum capacity for a Type I CF form factor will double to 8 GByte by the end of the year and will double again to 16 GByte by early 2007.

With higher capacities in these smaller packages, designers of medical equipment can use solid-state technology to reduce the size of equipment developed for use in operating rooms, where space is at a premium. For example, consider a chemical analysis machine that currently uses a rotating hard drive for its data storage. A solid-state storage solution in the identical 2.5-in. form factor could be used as a drop-in replacement and could decrease the storage power consumption by a factor of 10. At the time of the next system redesign, that exact storage technology could shrink to one-fifth the size by moving to a CompactFlash form factor.

More and more hospitals are looking toward operating rooms that are streamlined, clutter free, and, most important, efficient for providing the best possible patient care. With small form factors housing higher capacities, solid-state storage should find its way into more equipment designed for use in this critical setting.

Cost per Usable Gigabyte

Solid-state storage, because it has no moving parts, performs much better in high shock and vibration applications than rotating hard disk drives. The precision mechanics of rotating drives simply cannot take the rigors of portable medical equipment. In addition, these portable devices might be subject to extreme temperatures and, in the case of in-flight medical equipment, extreme altitudes. Finally, portable medical equipment is run on battery power, so the lower power requirement results in significantly longer life. Table II compares these parameters in solid-state storage versus rotating hard disk drives.

What may not be well understood is the concept that solid-state storage can actually be less expensive than rotating hard drives in some applications. This is what is called cost per usable gigabyte. To understand this concept, it is important to fully understand the requirements of the host system in terms of operating system and data-capacity requirements.

Many portable devices rely on an embedded operating system that can fit in less than 100 MByte. Most portable medical equipment does not store video or audio files, so data collection needs are minimal. In many cases, data collection can be supported by a 512-MByte solid-state drive. These drives can be purchased in OEM quantities for significantly less than the price of a 20-GByte hard disk drive. In this case, the price per gigabyte is irrelevant. Both capacities satisfy the requirement, and the solid-state drive costs less. Hence the term cost per usable gigabyte.

Consider the business model of rotating hard disk drives originally designed for the personal computer market. While OEMs may be able to purchase a 20-GByte hard disk drive today for $100, they will not be able to buy that same drive for $50 in 12–18 months. Rather, they will need to buy a new 40-GByte drive for the same $100. This could also result in costly requalification for a product or product line. Solid-state drives are, in general, designed specifically for the medical market and not for digital media for consumer electronics. They are driven by technology and product longevity, rather than by designing to price points. Therefore, OEMs can expect price declines to continue beyond the levels of more-consumer-oriented products.

Multiyear Life Cycles

Storage devices integrated into healthcare equipment must be reliable enough to be used consistently over long periods to minimize the turnover rate of costly medical devices. Healthcare equipment is subject to intense testing and certifications. Medical devices are expected to have a long life span. The ruggedness of a solid-state drive with no moving parts (compared with that of a rotating disk drive) makes this technology better suited to operate effectively over a longer period. Equipment that incorporates a more reliable storage medium can slow the overall replacement rate, thereby lowering the total cost of equipment ownership.

Enhanced Data Security

Data security has long been a priority of healthcare organizations. The more-stringent HIPAA regulations have elevated patient privacy to a new level, challenging designers of medical equipment to find new and better ways to help providers stay compliant. Advanced data-security technologies found in some solid-state storage devices can help.

Different types of healthcare applications require varying levels of data security. These levels can range from password protection to data sweep and scrub features. These features are initiated and fully controlled by the host, usually with a vendor-specific command. Data sweep is defined as completely erasing the data by changing the values of all bytes to hex value FFh.

For ultrasensitive requirements, additional security can be achieved by implementing a scrub feature. This scrub command allows the host system to initiate a sequence in which it erases and writes a host-defined data pattern. This sequence can be repeated as many times as necessary. Fully secure erasure is a key factor to data security, especially for equipment being used by multiple practitioners on multiple patients.

Solid-state technology offers password-protected features that can be beneficial to healthcare professionals who rely on established tables for charting patient progress or for working on clinical studies. Features such as write protection that offers read-only access, read-and-write access, or even the ability to set different security parameters for various zones, can effectively save specific look-up tables. These tables cannot be altered but still allow identified personnel to access information.

Power Management

Power management is an issue in any healthcare facility, as providers rely heavily on electronic equipment to store pertinent data. HIPAA's focus on standardized data collection at the bedside and with portable devices requires storage that operates effectively in low-power, battery-operated portable applications.

The use of RAM, either DRAM or SRAM, as a cache in a hard disk drive introduces the design challenge of retaining the integrity of the drive in the event of a power disturbance. RAM is a volatile memory architecture. If power is lost during a write operation, not only are the data lost, but also drive corruption could result.

Figure 1. Integrating voltage detection circuitry allows the storage solution to make rapid decisions and perform an orderly shutdown. It also minimizes the mechanical footprint. (click to enlarge)

An alternative is to design the solid-state drive so that it uses the least amount of cache possible while maintaining acceptable levels of read-write performance. Only very high-end data-recording applications truly require data rates in excess of about 15 MByte/sec. Transactional types of applications can often sacrifice some speed for a high level of drive integrity. Integrating voltage-detection circuitry allows the storage device to make rapid decisions and perform an orderly shutdown. The optimal solution is to integrate this into the controller architecture itself so that mechanical footprints can be minimized (see Figure 1).

It is important to address the possibility of power disturbance. Many medical devices run on battery power. Considering this, designers should have a tool that can help characterize the integrity of the storage subsystem during power events. Integrating voltage detection and logic into solid-state storage can enable designers to eliminate storage system failures in these instances. Critical files can be protected with internal circuitry to block commands from a host system so that files can be written before voltage levels become too low.

Conclusion

Solid-state technology meets the size and power demands of the medical electronics industry. This technology also increases the reliability of storage in terms of both physical viability and data security. These devices are rugged enough for long-term use in medical equipment. The small-form-factor devices operate at lower power rates, which makes them ideal for portable medical applications.

The benefits of incorporating solid-state technology into medical applications are still being discovered as designers add new features to their designs. These new features cannot, however, come at the expense of increased size and power consumption, so new technologies tailored to the medical market must continue to evolve.

Gary Drossel is director of product marketing for Silicon Systems Inc. (Aliso Viejo, CA). He can be reached at 949-900-9400.

Copyright ©2005 Medical Electronics Manufacturing