Medical Implant Communications Service Tutorial
More than you probably want to know about MICS.
Established in 1999, the MICS rules apply to transmitters that support the diagnostic and/or therapeutic functions associated with implantedmedical devices to enable individuals and medical practitioners to utilize potential life-saving medical technology without causing interference to other users in the spectrum – that’s the official text from the original Order.
The Commission set aside the 402-405 MHz bandbecause the signal propagation characteristics in the band are particularly well suited for implantable applications due to signal propagation characteristics in the human body, the relative dearth of other users in the band, and the ability to stake out the band internationally. The MICS use of this band is secondary to the primary users of this spectrum – Meteorological Aids Service (Medaids), the Meteorological Satellite Services, and the Earth Satellite Service.
Technical rules were established to minimize interference and ensure safe coexistence of multiple MICS devices. The MICS band is broken into 300 kHz wide channels. The rules specify that devices must “listen” for other devices before transmitting, called Listen Before Talk (LBT). If interference is encountered, the radio switches channels and listens again – known as ”frequency agility.” The rules also allow MICS devices to transmit without prior frequency monitoring in response to a non-radio frequency actuation signal generated by a device external to the body (i.e., manual activation), or in response to a medical implant event (i.e., alert or alarm condition).
You can read more about MICS here (FCC Deals with MICS – Vendors Help and Hinder), here (FCC Announces Regulatory Changes for Wireless Medical Devices) and here (Medtronics Brags on New Wireless ICD).
FCC Deals with MICS – Vendors Help and Hinder
Government documents are a great way to get an insiders view of several industries, and health care is no exception. This FCC Request for Waiver document is a gold mine of information. In this Request, DexCom asks for a waiver to the Medical Implant Communications Service (MICS) rules. (You can read my post on the product in question here.) We learn about the FCC's attitudes towards MICS, a lot about DecCom's product, and learn who opposed and supported the waiver before the FCC.
The reason for the Request fror Waiver was that DexCom did not want to comply with all the requirements of MICS. In short, they felt that fully supporting MICS would increase the size of their implants and impact battery life to an unacceptable degree, and add too much cost to the product.
The implantable blood glucose monitoring sensors come in two flavors, STS (short term – injectible probe that is replaced every several days) and LTS (long term – a fully implanted unit that lists up to 1 year). They will operate on only one frequency 402.142 MHz +/-40 kHz), using only 120 kHz of bandwidth. The power will be -20dBm conducted, less than that permitted in the MICS band. The sensors will broadcast for only 6-9 milliseconds every 5 minutes. DexCom stated that the combination of bandwidth, power and duration make the likelihood of causing interference virtually nil – an argument the FCC agreed with. The close proximity of the patient carried receiver with the implanted sensors make it unlikely that another MICS device will interfere with the DexCom device during data communications.
Of course the way things should work in theory and what happens in the real world are frequently different. To ensure patient safety accommodations must be made for potential failures. Here's what DexCom worked out for interference. If interference were to cause the loss of a set of data, one of 288 per day, the loss of any one data set would not be critical. The DexCom system is not a life critical patient monitor; instead, it provides a tighter feedback loop between blood glucose levels and a patient's diet or use of insulin. To delay the display of a reading (even one that's out of range) by 5, 10 or even 15 minutes would still be an improvement over current blood glucose monitoring techniques. Not a particularly sexy technical solution, but one that is reasonable.
So who supported and objected to this waiver? The waiver was supported by DexCom's chip vendor AMI Semiconductor, and more surprisingly, Biotronik. The sole party opposing the waiver request was bare-knuckle competitor Medtronic. (You can read a profile on Medtronic here.) Of course, Medtronic makes a variety of implantable medical devices, many of which are wireless, some of which use MICS; they are a direct competitor to DexCom. They objected that because the STS transmitter lies outside the body, it did not qualify for use in MICS. Medtronic also complains that DexCom does not disclose, “key RF system operating parameters, or [...] a complete description of its sensor systems,” thus making it impossible to fully assess interference potential. Medtronic also contended that the waiver was unnecessary because other spectrum was available that would permit it to operate with in the FCC's rules. They suggested the FCC limit their waiver to just 2 years and require DexCom notify physicians and patients of the potential for interference. It seems that Medtronic also opposed a waiver request for the Biotronik Philos DR-T, on the basis that the periodic operation of the device without LBT functionality violates the MICS rules.
The FCC did not buy any of Medtronic's arguments for denying the waiver. The FCC issued the waiver, making it dependent on the timing and outcome of any relevant rule making they may conclude, with a minimum of three years as a reasonable timeframe for successfully marketing and implementing use of the devices in their current configuration. Based on this waiver and the previous waiver for Biotronic, the FCC acknowledged that they may need to revise their rules for MICS to accommodate other technical solutions that are consistent with the goals for MICS – new more effective medical implant technologies that are assured to offer very low levels of potential interference.
OQO Kicks Off Health Care Advisory Board
This week inaugurates the new health care advisory board for OQO. Behind this unassuming facade lies a company that's creating a new
product category – a pocketable Windows device. You can read the specs here. Their goal is to transform personal computing the way the cell phone revolutionized telecommunications. Given the big dogs that are trying to follow, OQO must be on to something!
I saw my first OQO a few years ago on Gizmodo. I actually laid my hands on an OQO last month at HIMSS (thanks Enoch!). That's when I met Baochi Nguyen who asked me to come speak at their first health care advisory board meeting. They have assembled almost a dozen wild eyed early innovator physicians from leading
institutions on both coasts. I was asked to talk about “Wireless in
Health Care” to help frame their discussions about health care adoption.
This device offers a number of advantages for health care. As a Windows XP platform, it should be a snap to port applications to this device – much easier than dealing with PDAs. The size is just right – small enough for a lab coat pocket and a display big enough for my age-challenged eyes. Integrated Wi-Fi and Bluetooth provide the connectivity. Finally, while they don't claim they have a “ruggedized” device, the OQO has a magnesium case and I think should survive most waist-level drops.
You can't find an industry with a more mobile workforce than health care, except maybe bike messengers. Consequently, health care is one of OQO's key vertical markets. I wish I could tell you about all the rocket-science stuff I saw and heard, but I can't. After my presentation, I had a chance to talk with Jory Bell – more on that conversation later.
