Teaching file: Mammography artifact

This artifact showed up at one of our mammography sites when the daily artifact evaluation was being performed.

On the left is the full artifact evaluation image. On the right is the cropped in view of the artifact. Try to guess what’s going on.

One possibility is that it’s an artifact introduced by flat field corrections applied to the raw data. In my experience, these types of artifacts tend to have a more dimple-like appearance which this artifact doesn’t have, so that can be ruled out.

The blurred appearance of the artifact suggests that whatever is causing the artifact is moving during the x-ray acquisition. Based on the shape of the blur, it looks like something semi-circular

The image comes from a mammography unit, and the only thing that moves on a mammography unit during acquisition is the grid. A good guess would be that something’s managed to get onto the grid.

In this particular case, the artifact turned out to be caused by a metal washer in the grid mechanism that broke, sending pieces of the washer onto the grid. During the exposure, a motor moves the grid laterally to blur the grid lines. Thus the blurred appearance of the broken piece of washer.