RF IN ACTION: Microwaves in Medicine-- Meridian Medical Systems Takes On the Status Quo

Meridian Medical Systems (MMS) is the microwave technology company you've likely never heard of. Founded in 1985 by industry luminary Dr. Kenneth Carr, MMS applies the inherent characteristics of electromagnetic energy to solve problems in medical treatment that elude more conventional technologies. The company's products use microwave energy to generate heat, measure radiation and motion, and monitor and maintain the temperature of blood and other fluids. MMS has garnered awards from NASA, the U.S. Army, the Small Business Administration, the National Institutes of Health, and the Massachusetts Technology Collaborative, many of its products have received FDA approval, and a folder of unsolicited letters testifies to their effectiveness. Carr, an Institute of Electrical and Electronics Engineers (IEEE) Life Fellow, is considered a pioneer in the medical application of microwave technology, and has nearly 40 patents in the discipline.

So why haven't you heard about MMS? "It's a big leap from product development to industry acceptance," says Bob Allison, since 1998 the company's vice president and engineering manager, and a veteran of more than 30 years in the microwave industry. "It's also hard to walk in the front door and generate interest in an innovative product using an unknown technology in such a conservative industry. People often equate innovation with risk". Fortunately, the company's latest product seems destined to bring the company into the mainstream of the medical equipment industry.

A Winner In the Works
The product is an aid for treatment of cardiac arrhythmia (when the heart beats too slowly, too fast, or irregularly), may change that forever. The procedure for treating the disorder (called cardiac ablation) selectively destroys tissue to ensure that the "signal" controlling the heartbeat follows the proper path.

A catheter is inserted into the patient's leg that runs upward and into the heart, where, through cryogenic cooling or electromagnetic or ultrasonic radiation, the target tissue is destroyed " with the decision criteria for how much tissue to destroy being based largely upon the doctor's level of experience with the procedure. The temperature sensor in conventional catheters can measure only the value in the tip, which is typically cooled, so the value returned is not very precise. Without an accurate feedback mechanism, doctors tend to apply less-than-optimum energy levels to ensure patient safety (i.e., minimize risk), which reduces the procedure's effectiveness.

1. The MMS combination catheter/antenna for treating cardiac arrhythmia.

The catheter/antenna developed by MMS provides precise, real-time feedback to the doctor about how much energy to apply while he or she is performing the procedure. It combines the ability to deliver microwave radiation to heat tissue with a radiometer (essentially a remote sensing device) fabricated as a microwave monolithic integrated circuit (MMIC) to sense the temperature of the heart wall. The Dicke radiometer employed in the design obtains tissue temperature measurements noninvasively and operates by comparing an internal reference temperature with an actual radiometric measurement and using the difference to calculate body temperature.

Early results show the technique to be extremely accurate. Although radiometers have been used for years in applications ranging from measuring atmospheric and terrestrial radiation from space to oceanographic remote-sensing, the radiometer designed by MMS incorporates several proprietary technologies that optimize its use for cardiac ablation.

The MMS MMIC was designed using AWR® Microwave Office® electronic design automation (EDA) software along with a process design kit (PDK) developed by AWR for TriQuint Semiconductor that accurately represents TriQuint's foundry process. Allison has used AWR tools since their earliest development, but his experience with EDA tools, as well as with virtually every other high-frequency design solution, dates back to the days of mainframe time-sharing.

"Microwave Office is unique among these tools for its ability to make the design process comparatively simple," says Allison. "It's created by engineers who understand the difference between designing a microwave circuit and digital one " and it shows in the software." Allison designed the circuit, selected the features from the PDK library, performed design rule checking, and sent the result to TriQuint, all in a very short time. Measurements on the devices received from TriQuint agree extremely well with the Microwave Office simulation.

The company's next step is to conduct additional field studies and product procedure tests and ultimately to offer it as an alternative solution to the techniques universally used by doctors to treat cardiac arrhythmia. "There is incredible potential for use of the device," says Allison. "It eliminates the inherent problems of current products, and doctors have already expressed considerable interest because it can make the procedure easier for the doctor and safer and more effective for the patient."

So Much for the "Better Mousetrap" Theory
The MMS fluid warmer provides a great example of the problems the company has encountered throughout its history. Hospitals typically use warm water baths to heat fluids, including blood, which poses a risk of infection from the water, which can harbor bacteria. The risk of infection is compounded because very fragile, thin-walled tubing is used to heat the fluid within the tubing. In contrast, the ThermoStat 900 is a dry system that uses a disposable cartridge with a short length of standard IV tubing so there is no risk of infection. It uses microwave power with radiometric sensing to safely measure, control temperature, accurately measure fluid flow-rate, and detect air emboli. It is competitive in cost with conventional solutions, and has technical features they don't provide. It offers other advantages as well.