RSNA Follow-UP:
New MRI Shield Systems

By Tobias Gilk

This year’s RSNA might have been appropriately dubbed ‘the year of the CT’, what with 256 and 320-slice products being unveiled in the exhibit hall. Despite the buzz emanating from the slice wars, there were many new offerings that are likely to be of interest to you and other readers of the MRI Newsletter. Over the next few months, we will be featuring a few of these products. This month, we begin with new MRI shield materials. Kajima Corporation of Japan unveiled two revolutionary new products for MR shielding, one for RF windows and another for magnetic shielding.

RF shielding requires a contiguous box of electrically conductive material. Most often, this is accomplished with copper or galvanized steel, though aluminum and other metals can be made to work. The windows into MRI rooms, however have typically been sheets of glass covering specially engineered copper versions of insect screen: a fine scrim of metal mesh that maintains the continuity of the RF enclosure behind the window pane.

Laminated glass, the kind used in automobile windshields for example, is made from two panes of glass that are adhered into a sandwich assembly by a transparent plastic film between them. Kajima has apparently merged the RF shield screen materials with the laminated glass process to come up with a new RF glazing product that has the RF shield built-in.

While the Kajima RF shield glass does make use of a copper-coated screen between the panes of glass, the mesh is so fine as to be nearly invisible. There are two available grades of mesh and both have a just-barely-frosted appearance (though the finer mesh is noticeably closer to clear). Apart from a slight moiré pattern that sometimes appears when viewing tightly-patterned surfaces through the glass, they do provide a clearer view than any other shield window I’ve seen. The glass can be used for both control room observation windows and also for windows for patient comfort in the scan room itself.

Breaking the opaque barrier of MR rooms in more than one way, Kajima also unveiled an innovative magnetic shielding assembly. In the typical passive magnetic shield installation, steel plates are mounted inside the wall / ceiling / floor assemblies. Penetrations through the shield diminish its effectiveness, so magnetically shielded MR rooms are often opaque boxes.

Kajima’s magnetic shield system resembles Venetian blinds with the individual slats spaced many inches apart. With the vertical supports, the system begins to look like a shoji grid into which can be affixed their RF glass, providing a unified RF and magnetic shield assembly.

ETS Lindgren, the largest MRI shield vendor in the US, is the US distributor for Kajima’s innovative MRI shield products.

Please watch for other forthcoming RSNA follow-up coverage, including:

• Point of care GFR testing
• Magmedix’s nonferromagnetic wheelchair
• New FerroMagnetic Detection systems

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