Liquid helium, shown here,
is needed to
keep MRI magnets
cold enough to work.
GE sets sights on MRI helium conservation
May 17, 2012
by Brendon Nafziger
, DOTmed News Associate Editor
For the second most abundant element in the universe, helium is actually pretty hard to get hold of. On Earth, the only economically viable way to extract the substance now is to separate it from natural gas deposits.
But our supplies of this non-renewable resource are diminishing. Although the U.S. is currently the main producer of helium, and runs the world's only massive underground reserve, in Texas, we're running out. According to expert testimony at a congressional hearing last week on a proposed law that would shore up federal helium reserves, at the current rate of consumption, the U.S. could become a net importer of the stuff in the next 10 years.
Although it's generally not a top concern in the health care industry, roiled as it is by meaningful use regulations, device taxes and other big policy fights, MRI manufacturers and users depend on a secure, long-term helium supply.
Every year, millions of liters of liquid helium are consumed in the production and maintenance of MRIs, which need the substance to keep magnet materials cold enough to be superconducting, allowing them to work.
So, MRI makers are taking some traditional conservation steps in their approach to helium: reducing, reusing and, perhaps even one day, replacing.
One company, GE Healthcare, which testified at the May 10 Senate hearing, says it's even been able to reduce helium consumption on a per unit basis by 5 percent for each of the past five years, a plan it hopes to continue going forward.
"The whole concept of every molecule of helium counts, that's been a focus for us," Peter Jarvis, general manager of GE's global magnet and gradient engineering team, told DOTmed News.
The hearing was held to discuss the need for a proposed bill, floated by Sens. Jeff Bingaman (D-N.M.) and John Barrasso (R-Wyo.), which would help extend the life of the federal government's helium reserves, currently responsible for supplying one-third of the world's needs of the lighter-than-air element, but which could be largely sold off in the next few years.
The MRI industry actually uses a sizable amount of the globe's helium supplies, probably close to 28 percent, according to research done by Moses Chen, a professor with the University of Pennsylvania.
In his testimony before the Senate Energy Committee hearing last week, GE general manager Tom Rauch reckoned his company alone uses close to 5 million liters of helium in the production of the 1,000 MRIs it ships from its Florence, S.C. factory every year.
Breaking down that number, it results in about 5,000 liters being used in the production of each unit. Ultimately, each magnet ships with around 1,500 to 2,000 liters, with the rest having been consumed during testing and cool down, Jarvis explained.
In addition to the 5 million liters used in production, roughly 6 million liters are also used in maintenance of devices already in hospitals and clinics.
Jarvis said newly installed magnets need to be "topped up" with a couple of hundred liters of helium that are lost during transit (the longer the transportation, the more helium is evaporated). However, thanks to technology developed over 15 years ago, modern magnets generally don't need routine helium infusions, Jarvis said.
Routine helium infusions are unneeded because in the late 1990s, GE introduced so-called zero boil-off technology to its MRIs, Jarvis said. In this, helium that evaporates from heat in the magnet is recondensed and returned to the system.
"It stays as a closed cycle system. No helium is required to be added," Jarvis said.
By 2004, GE was selling exclusively zero boil-off technology MRIs, Jarvis said. However, even these "zero boil-off" magnets might need occasional small amounts of helium when the coldhead compressors, used to recondense the gas, are serviced every couple years. They can also need substantially more helium if a power outage causes the cooling systems to crash, resulting in larger boil-offs. This is a danger that besets magnets in countries with less reliable electricity delivery services, Jarvis said.
Also, not all MRIs in operation today were built post-2004. Many "legacy" machines are still working, either in their original place of installation or having been resold to a new buyer, often in another country. Jarvis estimates maybe 20 percent of systems are running with the pre-zero-boil-off technology.
"Old magnets simply never die," he jokes.
In his testimony, Rauch said GE has invested about $1 million in technology in its factory to bolster helium recycling and conservation. One investment was in recapturing equipment, used to snag helium lost in the manufacturing process, which is then recompressed and sold back to the gas suppliers at the factory.
Jarvis said the company's also working on proprietary efficiency-boosting techniques. For instance, workers might pre-cool a magnet with liquid nitrogen, which is cheaper and easier to get, before filling it with helium. He said they have also been running computer dynamic fluid simulations to study how liquid helium is transferred and used, and have committed some engineering know-how to improving the transfer lines from the tankers to the magnet.
"The transfer lines can be heavily optimized, in terms of material construction, control systems, to best match them to the end vehicle, the magnet that's receiving the helium," he said.
But another, longer term answer might be switching the materials used in the magnets themselves.
Nearly all MRI magnets use niobium-titanium wires, which are superconducting only at the extremely cold temperature of 9.5 kelvins, equivalent to about -443 degrees Fahrenheit. (For comparison, Pluto's surface temperature averages about 44 kelvins.) Helium boils at 4.2 kelvins, so it's the only refrigerant that can be used to operate niobium-titanium-based magnets, Jarvis said.
However, GE is investigating alternatives. Two years ago, the company was the recipient of a $3.27 million National Institutes of Health grant to look into using magnesium-diboride wires. Although this alloy is costlier than niobium-titanium right now, its "critical temperature," or the point at which it becomes superconducting, is much higher, at 39 kelvins (a temperature it would reach on the surface of Pluto, incidentally, during the dwarf planet's coldest periods, at 33 kelvins).
"In future there are other superconductors that hold promise that we're continuing to do work with, that could be cooled using other refrigerants or directly without use of refrigerants," Jarvis said. "We're looking at a variety of projects and programs."