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How to get the most life out of your MR coldhead

by John R. Fischer, Senior Reporter | September 17, 2018
If not addressed, problems with coldheads
can cause serious damage that may
require the costly replacement of
helium for repairs.
From the September 2018 issue of HealthCare Business News magazine

Designed to prevent the burn-off of the liquid helium inside the scanner, a coldhead is a vital piece of the MR puzzle. Issues with the coldhead can directly affect temperature and magnet pressure, potentially putting a scanner out of commission if not addressed immediately.

Severe issues, such as a quenched magnet, require replacing the liquid helium in a costly and time-consuming multiple-step process.

While there’s no panacea for all coldhead-related issues, experts agree that the best approach for fixing a coldhead is through early detection and troubleshooting issues as they arise.
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Living life to the fullest
Like any part, coldheads and their components have a limited lifespan and wear with age. But improper maintenance can erode them before their time, leading to earlier replacements and greater expense to overall lifetime use.

Judy Serrano, vice president for support services at Oxford Instruments Healthcare, said maintaining environmental components such as the chiller and air conditioning with routine inspections is extremely important for ensuring coldheads continue functioning correctly.

“Proper and timely preventive maintenance of the cryo-refrigeration system, including the chiller, is key,” she told HCB News. “Replacing the adsorber in the compressor once a year, for instance, reduces the risk of contamination from the compressor to the coldhead. There should also be constant monitoring of environmental conditions of the magnet room as well as helium levels and vessel pressures.”

Consistent breakdowns of chillers, helium lines and compressors, as well as power failures, enable oil to slide through protection systems within the compressor and enter into the coldhead, contaminating and causing it to fail early. Another issue is ensuring a positive flow of helium within the coldhead unisock during coldhead replacement, as air and moisture can cryopump into the unisock, leading to losses in liquid helium and performance.

When oil is present in the old coldhead, simply replacing it does not fix the issue with the compressor, flex line and other parts, such as a bad oil separator within the compressor. These components also must be replaced, so as not to recontaminate the new coldhead.

“Most people just come in and put a coldhead in. It’s probably going to work initially, but if they don’t know there’s oil in the system, that’s going to shorten the coldhead’s life,” Sean Mykleby, president of ThermoMagnetics and Cryogens, Inc., a division of Southwest Medical Resources, Inc., said. “Maybe six months or a year down the road, depending on the severity, the coldhead starts to fail again, leading you back on-site to send out for another replacement coldhead.”

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