Tuesday, November 2, 2010

FOD happens!

Pieces of metal, especially magnetic ones, will find their way into all sorts of strange and potentially detrimental locations inside an MRI. During your safety training you will have learned a lot about the hazards of chairs, keys, rotary mops, oxygen cylinders and other objects that have, at one time or another, found their way into or onto an MRI – often with disastrous consequences.

Yet there is another category of foreign objects or debris - known as FOD to aviation types - that doesn’t get as much attention during safety training, largely because there are fewer safety issues. There are, however, serious implications for the quality of your data.

Finding FOD

Take yesterday, for example. There we were, a service engineer and I, rooting around in the back of the magnet checking for carbonization, testing locking nut security and the like, in a quest to identify sources of spikes that had shown up in the morning’s QA data. (I’ll do a separate post on spikes another day.) We (meaning the engineer) had already found, cleaned and replaced “standoff” spacers for the gradient power cables. These spacers – especially the one for the X coil, which gets the most use as the read axis gradient for EPI – are prone to micro-arcing, a phenomenon that can be discerned by the telltale black carbon deposits on one or both ends of the metal tube.