This article is from in the January 2008 issue of DOTmed Business News. A list of registered users that provide sales & service can be found at the end.

Today's MRIs incorporate powerful magnets that must be kept at sub-freezing temperatures of about 4 degrees Kelvin or minus 450 Fahrenheit. To reach these temperatures, high-field (about 1.5T) and ultra high-field (3T) MRIs uses a cryogenic cooling technique. This design supports a segment of the medical industry that produces and distributes liquid helium and nitrogen to cool the MRIs in service at U.S. hospitals and imaging centers.

DOTmed.com estimates the cryogenic services industry distributes more than $25 million in helium each year just to top off MRI systems as part of their regular maintenance.

Inside these powerful imaging systems is an electromagnetic coil cooled in a vacuum of cryogenic liquid helium to keep the unit at sub-freezing temperatures where electrical resistance is minimized in order to maximize image quality. Even at these temperatures, a continual boil-off of helium still takes place, requiring constant replenishment. While the newer MRIs have less boil-off and require less frequent service, the overall growth in the use of MRI supports an estimated 2-4% yearly global increase in the medical consumption of helium.

In addition to regular service, more significant quantities of helium, as well as less costly nitrogen, are used for the initial cool down of the magnet and to re-cool it in the event of a quench-a massive helium release, which can occur when the MRI is malfunctioning.




"Liquid helium is the coldest substance known to man. In that MRI you are trying your best to insulate it against the outside world [where] heat is trying to make its way into that helium," explains Mark Glajchen, Head of Liquid Helium and Associated Services, Linde Inc. The company's acquisition of BOC makes it a major player in the distribution of medical cryogenic products to thousands of MRI systems in the U.S. "Our focus in this market space is not only providing the helium but actually transferring it from the dewar [portable insulated vessel] into the magnet, Glajchen says. "We view it as a vendor-managed inventory process."

Helium is a byproduct of natural gas production so it is separated and refined in conjunction with natural gas fields; nitrogen is extracted from the atmosphere. These products are distributed by medical gas suppliers including Linde, Inc., Praxair, Air Liquide, and Air Products.

In addition to the suppliers, selected specialized independent service organizations also provide helium service, including remote monitoring of the MRI to check helium levels, topping off the helium regularly, and providing cool down service when needed.

Cool Down Service Requires Great Care

MRI magnets are contained in sealed vacuums with a vent to allow gas to escape since the helium is always boiling. But if a leak breaks the seal on that venting, ice (frozen air) could get into the magnet, triggering the dreaded quench. Once that occurs, the magnet must be brought back up to room temperature and cooled down again. (Think of defrosting a freezer.) Because of the high cost of helium, a warm magnet is first pre-cooled with nitrogen, a process that takes several days to "soak." Nitrogen is then carefully extracted and helium introduced into the thermal vacuum of the MRI.




"With a liquid that is very expensive if you were to just start pouring helium into [the MRI], it would vaporize because it's like pouring drops of water on a hot frying pan," says Thomas Freund, Director of MRI Services, Oxford Instruments. "What we do is fill it with liquid nitrogen first, which is very very cold but also very cheap compared to helium. This is a pre-cooling process-just as you would pre-heat an oven, you would pre-cool a magnet."

The cost of cooling down the magnet runs in the 10,000 to $20,000 range just for labor, not including the significant cost of about 5,000 liters of helium at about $5 per liter.

"Another important thing is the time it takes because, if it's in a hospital or clinic, you are looking at least three weeks of down time: the warming up process, pre-cool when we put nitrogen in, then pump the nitrogen out, and fill with helium," Freund says.

Clearly you want to be sure your servicers know what they're doing. A mistake can be not just costly but dangerous. For example, odorless helium or nitrogen can quickly displace oxygen if they leak into the suite. This can cause suffocation so technicians need personal oxygen monitors. To work on the magnet, the technicians use a variety of specialized tools and instruments including turbo-molecular vacuum pumps and mass spectrometer leak detectors.

"The quench may occur for any number of reasons: procedural, hardware failure, magnet problem such as ice or air getting in through a leaking venting connection...this could divert the helium fill to the exhaust line, not the magnet," cautions Mike Profeta, President, Magnetic Resonance Technologies. "Or, if the vacuum line is compromised the liquid might turn to gas being pumped into the magnet instead of liquid-it's not as cold and the magnet can quench."

Profeta recommends choosing MRI servicers carefully: Check the credentials of those you are dealing with. Ask for written procedures. And confirm who is responsible for the cryogens. "Some [companies] do the cool down but you provide the cryogen. Put a cap on that or they may use too much helium or not take the needed time with the nitrogen soak [pre-cool]," Profeta suggests. "Qualify responsibility for cryogen and quantify amounts."

You may want to find technicians such as independent service organizations that can also provide related MRI services such as maintenance of the cold head component of the MRI refrigeration system. Another MRI service is shimming, which is the adjustment of the magnetic field to ensure uniformity. Ramping the magnet is yet another specialized process since electrical current is introduced gradually when you place the unit into operation.

Future Trends

MRI manufacturers are coming up with new cooling techniques to lower maintenance costs and reduce downtime for the equipment. For example the older MRIs require helium to be added every few weeks while some of the newest designs claim they need filling only every few years. Other technologies are also on the horizon.

"Right now companies are working on using liquid neon instead of liquid helium. The expense and scarcity of liquid helium is driving the market," says Marc Fessler, Partner, Independence Cryogenic Engineering. "Manufacturers are trying to find ways to use less liquid helium and to keep what you have longer, to recycle or re-condense the liquid that boils off using cryogenic pumps and a cold head that can reach liquid helium temperature. These trends add to our business because in the past people let cold heads and compressors run till they weren't efficient. Now it's more optimal to do preventive maintenance."

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DOTmed Registered MRI Helium Service and Cool Down Sales and Service Companies
Names in boldface are Premium Listings.

Domestic
David Baldwin, Genesis Magnet Services, IL
Marc Fessler, Independence Cryogenic Engineering, NJ
Bill McCue, Magnet Resources, Inc., NJ
Thomas Freund, Oxford Instruments, NJ
DOTmed Certified
Michael Profeta, Magnetic Resonance Technologies, OH
Marshall Shannon, Image Technology Consulting, LLC, TX
DOTmed Certified/100
Larry Knight, Sunrise Medical Technology, TX
DOTmed Certified/100

International
Brijesh Suneja, Rad Imaging Pvt. Ltd., India
Jan Glavimans, Glavimans Electronics BV, Netherlands

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