The variation in user drawn outlines on digital images: effects on quantitative autoradiography.

Variation in user outlines drawn to delineate neural regions is the only source of error added to autoradiographic images after the images have been digitized. By analyzing data compiled from many outlines drawn by several different investigators, it was demonstrated that this variation constitutes a major source of error affecting quantitative autoradiography. Both the gray level variation and average within a region, as well as the specific pixels included in an outline, were affected. However, using the intersection of multiple outlining attempts surrounding any given region and a consistent set of outlining criteria, it was possible to delineate a region which remained consistent from user to user. A technique for automating the consistent outlining process is discussed.