由 Philip F. Jacobus
, CEO | September 05, 2015
From the September 2015 issue of HealthCare Business News magazine
I’ve moved about in the medical equipment industry for a long time.
But even after all these years, I still find myself learning. Recently, I reached out to a few friends in the industry to get their top coldhead tips to share with HealthCare Business News readers. As you probably know, coldheads sit on top of the MR magnet and help to keep the magnet cool in order to prevent boil off of the liquid helium. A boil-off can be a real problem, especially if it escalates to a quench. At that point, you have the potential for harm to a patient or staff, loss of revenue from machine downtime and, of course, an added expense since the helium will have to be replaced.
With a reasonable amount of planning and knowledge, it’s fairly easy to avoid coldhead problems. Fortunately, James Beier of Sumitomo, Chris Matthews of Oxford Superconducting Technology, Sean Mykleby of Cool Pair Plus, Larry Knight with Altima Diagnostic Imaging Solutions, LLC, and Marshall Shannon with Image Technology Consulting, LLC, were willing to provide much of the information you’ll need to avoid coldhead problems.
According to Larry Knight, coldheads can be divided into two categories — 10K (ten Kelvin) and 4K (four Kelvin) systems. The two systems have some key differences. The first, the 10K, is typically found on legacy systems like the Siemens Symphony and Harmony, Toshiba’s Excelart, Picker magnets and GE’s pre-LCC magnets, says Larry. These coldheads keep the shields of the magnet cool to limit cryogenic loss, but they do not re-condense the helium.
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The fact that these coldheads don’t re-condense the helium means that the liquid helium will turn to gas and boil off over time, with the rate generally being about .7 to 1.2 percent per week. According to Larry, the helium boil-off rate is the best indicator of the 10K coldhead’s performance. If your helium loss is about .1 percent per day, you likely have a healthy coldhead. When you start climbing beyond that and have indications that your shield temperature or magnet pressure is rising, that can be a warning sign that your coldhead needs to be serviced or replaced. Even with a coldhead that’s functioning properly, you can expect to spend money each year recharging your helium and you should budget accordingly.
The 4K coldheads are found on newer systems across the range of OEM MRs. These coldheads re-condense helium and bring it back to a liquid state. These systems are often touted as “zero boil-off.” Even so, many will have a helium loss in the neighborhood of 10 to 200 liters per year. While significantly less than what one should expect with the 10K system, it’s still a factor you should be aware of. Coldhead performance for the 4K is easy to monitor, says Marshall Shannon. “These systems should always have close to the same helium level over time,” he says. In other words, if you take your helium reading on Jan. 1 and see the level is at 78.8 percent, when July comes, you should have a reading of 78.7 percent.