The EMR051 phantom and Image Owl processing software are designed to work regardless of phantom position and orientation in the scanner, as long as sufficient contrast and resolution are obtained. Since distortion typically varies within a scanner, changing the position of the phantom from scan to scan will usually result in changes to measured study parameters. For example, as the phantom is moved farther and farther from the isocenter, the maximum distortion typically increases. Small changes in phantom position of a few centimeters or less from scan to scan typically do not cause alarming changes in measurements. Users should be aware of this effect and eliminate variation in phantom position as the cause of scanner variation before taking further action.