by
Gus Iversen, Editor in Chief | November 28, 2014
From the October 2014 issue of HealthCare Business News magazine
Another independent magnet monitor is Southwest Medical Resources. Don McCormack III, field service engineer, says their service gives end-users a unique opportunity to take remote monitoring into their own hands. “Our remote display unit (RDU) offers the option for the customer to [remote monitor their cryogens] themselves,” says McCormack.
By linking in-house engineer and tech support cellphones to the RDU, McCormick says hospitals can become less dependent on outside assistance, including that of OEMs. He sees a trend of image outpatient centers being bought up by larger hospital chains. “These large chain hospitals are moving more and more towards in-house engineers and biomed programs,” says McCormick. Schuetz, with Siemens, describes the process of adding helium to an MR system. “We have helium fill kits that we stock in our depot in Memphis,” says Schuetz. “They are sealed in a vacuum casing, which means there is very little heat transfer from the outside to the inside.”
The engineers receive the liquid helium in dewars of 250 to 500 liters. Helium push-gas is then used to pressurize the vessels and force the liquid helium out of the dewar, through a transfer line, and into the system’s fill port.
While the day-to-day goal of remote monitoring is to ensure optimal performance from the MR system, it also ensures dangerous situations do not evolve over time. “Cold-head failures cause the shield to warm up, which increases the helium boil off,” says Schuetz. “If it’s not detected and corrected then the system may fall below the alarm threshold.” If nothing is done, then the system may fall to a critical level which may prevent the use of the system until entirely refilled. In such an extreme case there may be risk of a quench.
A quench happens when the system goes resistive and the liquid helium converts into gas form. Marshall, the magnet expert from Siemens, says that one liter of liquid helium could warm up and become 770 liters of helium gas at room temperature.
Today the vast majority of quenches are deliberate, although sometimes they happen when loading helium into the system. McCormick says a full quench recovery can typically take three days.
“A quench is the result of instability in the actual magnet coil or a warm spot on the coil,” says Schuetz. “With a warm spot, if you think about oxygen getting sucked into a magnet vessel, it freezes that oxygen into ice. Even though that ice is exceptionally cold, if it falls off and lands on the coil, it’s actually much warmer than the liquid helium.” Quenches produce a noise Schuetz compares to a tornado or a freight train.
