With any smartROI outline showing hit the Outer to ROI button. Now use the roi button in the imcalc tool to segment the image. Doing this for other outlines provides images which may be compared using subtraction and image histogramming to count pixel differences. In this way you are able to score the performance of the algorithm when used to extract the boundary of a given image. Use the poly roi to hand draw around the aorta of the missing data images. Ask another person who has not seen your outline to do the same. Compare the reproducibility of the resulting roi's. How do they compare to your PCA results?