Puzzling image artifact

It's not often I run into problems when testing x-ray equipment, but when I do they're usually puzzling ones.

While I was testing a cath lab today, the lateral plane was giving me images that looked like


Ignore the grid pattern. That's just one of my test objects.

At first I thought it was just a bolus filter getting in the way, but none of the usual buttons and joysticks for moving the filters made it go away. Wasn't the bolus filters.

After giving it a little bit more thought, I realized it was the anti-scatter grid. It's the exact type of artifact you expect to see for an upside down focused grid.

Popped the grid cover off to check, and sure enough the grid was put in backwards. Couldn't figure out how to remove the grid to flip it around so I'll have to leave it for the service guys to take care of. Coincidentally enough, the pages in the manual for inserting and removing the grid were missing.

In radiography, it's not too unusual (although somewhat rare these days) to use a reversed focus grid as a kind of "poor man's filter", usually for chest imaging to even out the exposure differences between the lung fields and the mediastinum. I've never heard of this being this done for a fluoroscopy unit though. I don't know if it was done deliberately or by accident.