Seals keep pace with long-lasting MRI equipment

Edited by the Engineeringtalk editorial team Jun 25, 2008

Sealing the helium venting system of the superconducting magnet is critically important to avoid the ingress of air into the magnet.

A "fit for purpose" seal on the venting system of a superconducting magnet of an MRI body scanner must maintain an absolute seal for the life of the scanner.

One problem with this requirement is that scanners don't tend to wear out, they just keep on going.

Siemens Magnet Technology produces superconducting magnets for MRI body scanners.

Sealing the helium venting system of the superconducting magnet is critically important to avoid the ingress of air into the magnet.

Sealing is required to prevent helium gas escaping, but more importantly to avoid air from getting in.

Air within the helium venting vessel creates ice, which can block the venting system and make scanner performance unreliable.

Superconducting magnet technology allowsa dramatic reduction in size compared to conventional electromagnets by using superconducting wires immersed in liquid helium at -269C.

The reduced power requirement is what makes magnetic resonance imaging (MRI) economically viable.

Working closely with Garlock Sealing Technologies, Siemens addressed the potential leak issue in this area by using Garlock Helicoflex metallic seals and the QDS clamping system.

Replacing PTFE seals and conventional clamps removed a potential risk area.

Tony Puffer, Business Excellence Manager, Siemens, said, "What we're trying to do all the time is to improve our product's performance, efficiency and cut its cost".

"For example the magnet's length has reduced from 2.4m in the eighties to its current 1.2m".

"This provides patients with a much friendlier 'open' scanner unit".

"This evolution sees us continuously pushing the technological boundaries, but also requires us to consider system life cycle costs".

"Air ingress has to be prevented, while at the same time a cost-effective service solution needs to be provided".

Garlock's Helicoflex seals are positioned on the inlet and outlets of the venting system and using industry standard NW25 flanges and Garlock QDS flange clamps allows components to be removed quickly for service or repair.

The sealing concept of Helicoflex is based on plastic deformation of a metallic lining.

Available in a selection of lining materials, selected on the basis that it needs to have better plasticity than the flange material, seal deformation is controlled by compressing an internal spring.

The Garlock QDS clamps maintain high levels of joint integrity while allowing quick connection and disconnection of pipework.

Supplied with two conical flanges, a Helicoflex seal and an articulated collar, the QDS clamping collar offers excellent mechanical efficiency.

"Each collar set is designed to provide optimum distribution of tightening force by adapting the rollers to a corresponding flange diameter".

Tony Puffer said "We don't expect any one area of the venting system to create a problem but if one should occur then the QDS clamps help to reduce downtime".

"We look for components that are fit for purpose and reliability is the key - with scanners operating around 20 hours per day and with loaded schedules any down time has horrendous associated costs and lost revenue".

""With this seal development and ongoing developments into new areas, Garlock has worked closely with us providing know-how and producing special seals to meet our requirements".

"We're pushing the technology boundaries hard all the time and it's essential we use the specialist knowledge of our suppliers".