Wireless Medical Telemetry

OUTLINE

IntroductionWireless Medical Telemetry System (WMTS)Benefits of WMTSFrequency AllocationInterference to WMTSBiotelemetryDiscussionKey market ParticipantsReferences

INTRODUCTION

WMTS is reserved for transmission of life-critical data in healthcare facilities.

In contrast to the Industrial, Scientific and Medical (ISM) band (in which 802.11 systems operate) which is a large, unlicensed spectrum space for a growing variety of devices that can be used to transmit virtually any kind of data.

It is also licensed spectrum, which gives hospitals that go through the licensing process the advantage of primary user status if an interfering system shows up.

BLOCK DIAGRAM OF WIRELESS MEDICAL TELEMETRY SYSTEM

Telemetry antenna

Telemetry Server

Wireless Transceiver

Instrument Radio/Wireless Transceiver

Ambulatory Telepack

BENEFITS

To provides best clinical outcomes –clinicians need medical information from anywhere using a variety of devices.

Enables Clinicians to do real time documentation and more easily access information-freeing them up to do what they do best and that is providing care.

Improve patient mobility

Improves efficiency of medical personnel

Is a step towards full electronic medical record implementation

FREQUENCY ALLOCATION

In earlier days telemetry allocations allowed operation on unused channels from 174MHZ to 668MHZ

WMTS report and order sets aside 608 to 614MHZ, 1395 to 1400MHZ, and 1429 to 1432 MHZ for primary and co-primary use by eligible wireless medical telemetry users.

Eligible telemetry users are limited to health care providers, licensed physicians, health care facilities and certain trained and supervised technicians. Ambulances and other monitoring services are not included within this definition.

The WMTS will significantly reduce the risk of EMI with vital medical telemetry signals.

The FDA is committed to working with device manufacturers and users to facilitate migration to the WMTS frequencies in a least burdensome manner

INTEFERENCE TO WMTS

Prior to year 2000 most wireless medical telemetry devices operate as secondary users in commercial broadcast TV bands and in the private land mobile radio service (PLMRS) band. As secondary users, medical telemetry must accept interference from, and not interfere with, primary licensed users. Typically, if there is interference from a primary user, the medical telemetry system will be unusable.

On Feb 27 1998 Dallas TV station WFAA became the first to test new digital television (DTV) transmitter on what was supposed to be a vacant TV channel.

Coincidentally both Baylor University Medical center and Methodist Dallas Medical center were using the channel for cardiac telemetry systems.

The resulting interference became a national story and led to wireless telemetry service.

1n 2000 the final rules establishing WMTS was made and since then medical telemetry systems are protected from interference as long as they are registered according to FCC rules.

Emissions from electromagnetic security systems have been reported to disturb WMTS

OTHER ISSUES

Concerns about patient medical information security

Security associated with wireless systems include

-authentication-Encryption-open architecture designed for medical

applications-rogue wireless users-multiple technologies

INTRODUCTION TO BIOTELEMETRY

Provides wireless communication from outside of the body to inside of the body and vice versa.

Current systems are designed for communication with implantable system like cardiac pacemaker and defibrillators, cochlear and retina implants.

For cardiac telemetry a dipole or spiral micro strip has been designed for implantation in the shoulder.

Emerging medical telemetry has led to the design of small biocompatible antennas that can be implanted in the body.

The absorption fields by the body limits the distance an external transceiver can be placed from the body.

Maximum bandwidth that can be used by a single device is 300KHZ and the range is typically 2 meters.

INTRODUCTION TO BIOTELEMETRY

The maximum power limit is 2 micro Watts equivalent radiated power (ERP); if power is increased battery life suffers and may exceed regulation for maximum power absorption in the body.

Improvement in transceiver architecture and data mining and data compression(reduce the actual bits that are transmitted) are used to provide chip rates of 20KPB/s at distance of 2 meters using low power telemetry.

One method to achieve this efficiency is the design of an ultra efficient sleep mode followed by short burst of data transmission activity.

Improved design of hardware

FUTURE OF BIOTELEMETRY

One area of future development is retrieving communication from implanted electrode for neural recording and/or simulation-tiny electrodes may be implanted in the brain or the nerves.

Previously experiments have been used to receive brain signal or transmit small amount of data through the skin.

ANTENNA FOR BIOTELEMETRY

DISCUSSION

The major constraint with WMTS is that 608-614MHz, you have 6MHz of bandwidth. Since the modulation is GMSK (Gaussian Minimum Shift Keying), the channel spacing is 25KHz. So doing the math, 25KHz into 6MHz, gives you 240 channel, that is without any guard bands.

As a result, spread spectrum systems that use this band render useless nearby second-generation systems that are transmitting in the 608-614MHz band.

Large hospitals, especially those in dense metropolitan areas continue to struggle with limitations of their WMTS systems due to restricted bandwidth (BW).

This is further complicated by documented cases where WMTS bandwidth had to be further restricted in some cases to only 2.5MHz, or where legal broadcast stations have cause interference, there again, causing restrictions on the bandwidth.

KEY MARKET PARTICIPANTS

GE Medical systems

Mennen Medical corp.

Philips Medical systems

Siemens Medical systems

Welch-Allyn Protocol, Inc

REFERENCES

1.Steven D. Baker and David H. Hoglund: Medical Grade Mission Critical Wireless Networks.

2.Rick Harmton: Interference to wireless medical telemetry systems: http://www.aami.org/tmcconnect/it/Lessons%20Learned.pdf.

3.Kok -Swang tan, Irwin Hinberg and Jesuzette Washman : EMI RISK: Electro magnetic Interference in Medical Devices page 76 of class notes EE406/506 Biomedical Engineering by Dr Christopher Druzgalski

4. About medical telemetry: http://www.fda.gov/Radiation EmittingProducts/RadiationSafety/ElectromagneticCompatibilityEMC/ucm116574.htm

5. Donald Witters: Facing the Challenges of Electromagnetic Interference With Medical Devices in the Wireless World: www.ursi.org/Proceedings/ProcGA02/papers/p2233.pdf

END

ABSTRACT

Wireless medical telemetry deals with the remote monitoring-measurement and recording of physiological parameters and other patient related information via radiated bi-directional or unidirectional electromagnetic signals.

This presentation discusses frequency allocation for wireless medical telemetry system, incidences of interference with wireless medical systems, the future spectrum needs for wireless medical telemetry as well as the benefits and constraints of current wireless medical telemetry.