When Conventional Memory is Not Worth Remembering

The disadvantages of using consumer memory products in medical devices and why specialised memory tokens should be used instead.

By: Michael Barrett

Originally Published MDT [6] March/April 2009

MARKET PLACE

The scenario to avoid

Lifespan is a critical issue in many medical devices. Thus it is a surprise that design engineers consider using conventional memory products such as universal serial bus (USB) sticks and camera cards when designing their devices. For example, a designer is working on a fluid removal instrument that he hopes will be on the market in 18 months’ time. He builds in a memory device to ensure usage of the instrument for a limited amount of time to meet testing and validation requirements. After this period, the device must be withdrawn from use and resterilised. His design includes a USB stick, produced by a commercial manufacturer. In 18 months time, just as the machine is about to be mass produced, a colleague in purchasing contacts the USB manufacturer to place an order. He/she receives the unwelcome news that a final order must be placed now, because the USB stick is end of line and the manufacturer has stopped making them.

This is a typical scenario. According to Moore’s law, that is, the Intel founder Gordon Moore, speaking in 1965, computer chips double their output every 18 months. This law can be applied to most products in the IT world. As a result, to maintain their position in the consumer market, memory manufacturers need to increase the capacity of their products massively on a regular basis. This means that the cheap 64 MB memory stick sourced now for the new medical instrument is not going to be available by the time it reaches the market place. Instead, a 6 GB model must be considered; however, this will cost a lot more, and in this example provides more than 90 times the memory needed by the fluid removal instrument.

The solution

The solution is to source a rugged, industrial, memory token that offers the necessary sterilisation capability and the lifespan to ensure spares will still be available in 20 years’ time. Typical uses of this type of portable nonvolatile memory product include calibration, limit-use, data upload, firmware updates, data transfer, data logging, user authentication and access control. Calibration allows the user to automatically upload parameters from a token to another device to eliminate manual errors.

One current application is a heart monitor with a single use balloon catheter. Each catheter is precisely calibrated before use, using a token, which saves time, reduces implementation costs and eliminates errors.

Limit-use allows the tokens to monitor how many times the device has been used and for how long, as in the fluid removal instrument.

Another application example is a DNA analysis system that uses disposable gel cartridges. Here, the token activates the equipment, monitors the usage and notifies the system once the cartridge has reached the end of its life and needs to be replaced.

The memory tokens shown in Figure 1 are used worldwide by many multinational corporations. The message here is, if the medical device still needs to be on the market in 20 years’ time, or even five, avoid conventional memory products and select specialised, rugged ones instead.

Information supplied by Michael Barrett, Operations Director, Nexus GB, Rushdene House, Dodsley Grove, Midhurst GU29 9BE, UK, tel. +44 1730 816 502, e-mail: michael@nexusgb.co.uk [7], www.nexusgb.co.uk [8]