by
Barbara Kram, Editor | February 04, 2008
A technician in the
process of replacing
a cold head.
(Photo courtesy of
Magnetic Resonance
Technologies)
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 use 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.
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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.
Oxford Instruments
Technician checking the
helium level
probe connection.
(Photo courtesy of
Oxford Instruments)
"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."
