Eliminating Medical Device RF Interference

How organizations are attempting to solve the problem of wireless interference in medical devices.

by Christopher Keuling, Associate Editor

Christopher_150Wireless RF interference found in medical devices causes tainted results and misdiagnoses. Medical professionals and patients rely on these results to pursue the correct course of action for a given illness. There are several companies and collaborations looking into solutions of how to reduce and/or remove interference in the medical field. This month, we take a look at some of the causes of wireless interference and answers that are being worked on now in today’s medical devices, as well as future devices.

Causes of Wireless RF Interference
ec812if101aThe most common cause of wireless interference is two or more devices operating on the same frequency spectrum at the same time. This interference is seen in cellular phones when used in hospitals since they are on the same frequency as medical equipment, such as ECG/EKG machines and instruments found in operating rooms. Robin Heydon, standards architect at CSR, says that the frequency bands for use in in-hospital medical devices in the U.S. are the 608 MHz to 614 MHz, 1,395 MHz to 1,495 MHz, and 1,427 MHz to 1,432 MHz bands.

ec812if101bScott Carson, senior manager of business development for the diagnostics, therapy, and monitoring medical division at ON Semiconductor, says that medical devices outside of the clinical setting operate in the ISM (2.4 GHz and 902 MHz to 928 MHz), MICS (402 MHz to 405 MHz), and MedRadio (401 MHz and 406 MHz) bands. Heydon states that a less common reason for obstruction is that “a wireless device shows harmonics interference when the wireless signals interfere with other devices that are running in adjacent bandwidths.” According to David Niewolny, product manager of the microcontrollers group at Freescale Semiconductor, another cause of wireless interference is the presence of too many wireless nodes in the same area at the same time. These problems are being investigated and different solutions are being looked into, which could impact the way medical devices work.

Continua Health Alliance
The Continua Health Alliance consists of medical device customers and companies that are looking to see what the wireless standards will be for in-hospital and home medical devices. Niewolny states that Bluetooth is the wireless protocol of choice since the alternative protocol on the 2.4 GHz bandwidth, WiFi, consumes more energy. The other low-energy protocol out there is ZigBee, but that suits the home betterec812if101c than it does devices. For portable devices worn outside of the home is superior since, according to Niewolny, “data from the medical device can be transferred onto cell phones via a Bluetooth chip, and then get transferred to a router and call center where a larger bank of information for a patient is held.”

Heydon declares that Intel and AMD have open standards in medical devices, but Bluetooth is seen as the more robust, cost-friendly, and easy to access protocol because “the access point for the data is in the pocket (i.e. cell phone), and cell phone companies use so many Bluetooth chips that the cost for them has lowered down to $1.10 per chip. In five years, up to three to four billion devices will implement Bluetooth.”

Telehealth, also known as telemedicine, has been in motion for a while, but will be seen first in the U.S since, according to Niewolny, “the U.S. is where almost, if not all, medical innovations and advancements start.” This is where doctor visits can occur from home since the doctor will be able to get data from the patient’s machines and only notify the patient if there’s an issue with their health.

Niewolny says that vital analysis of a patient’s health, such as ECG readings, heart rate, and blood pressure, can all be looked at by a doctor after the software performs the calculations. The next step for this solution is to start using software for diagnostics because the software has “96.8 percent accuracy with the extra percentage being deemed a ‘false positive’. However, it’s a long way down the road to completely replace a human doctor.” Today’s hospitals contain some IT, but there are still inefficiencies due to human error, but Telehealth is growing at a year-on-year rate of 30% annually. However, it hasn’t been adopted faster since people want face-to-face visitation with doctors.

Other Solutions in Preventing Interference
There are other solutions that guard medical devices from wireless interference. Heydon says that hardware filtering of unwanted signals is one way to go. Another solution, according to Heydon, is time division multiplexing, which means that certain networks are going to be active during certain points with more important networks getting priority. A third solution is to put restrictions on certain devices. For example, Carson claims that a wireless pulseoximeter enables a channel between the body and the server, holds and transmits data, and allows for a patient to move from a hospital to a home. The restrictions on this sort of technology, for instance, would be that a listen before talk, or clear channel, assessment needs to be in tact, along with a maximum power of -15 dBm and the ability to move to different channels easily. These solutions are some of the implementations being taken into consideration for future medical devices. However, testing for interference is a key factor in knowing how a medical device will work.

ec812if101dTest Protocols
In order to be able to tell how much wireless interference is effecting certain medical devices, tests need to be administered. However, according to Dan Mullen, president of AIM Global, “there isn’t a definitive set of test protocols for testing of RF emitters to ensure a benign effect in a healthcare setting since RFID and medical devices have been developed over the course of many years and are just now crossing paths.” Mullen adds that there are currently three test protocol suites that have been identified. These suites will look at RF emissions and the susceptibility of medical devices (i.e. implantables and wearables), RF emissions and clinical instrument susceptibility (i.e. bedside and operating room equipment), and the effects on RF on products including pharmaceuticals and biological blood (the donate blood itself). Mullen states that “initial testing will begin around May 2009, and that by next November, the protocols are expected to be finished and testing for wireless interference in medical devices will be available.”