A method and apparatus for guiding image reading for colon screening, includes calculating a centerline for a colon; scrolling through a succession of two dimensional (2D) cross-sectional images of a colon in respective image planes, such that a current image plane includes a respective current focus point formed by an intersection of the centerline with the current image plane. The method further includes performing a three-dimensional (3D) region growing process for growing a region of a suitable given thickness around a current seed point in a current image plane, the current seed point being at the respective current focus point in the current image plane, such that the region growing “floods” folds within a prescribed distance from the current seed point such that part of the region intersects the current image plane. Portions of the region intersecting the current image plane that meets at least one of conditions (A) and (B) are removed from consideration where: condition (A) includes the region intersecting the given current image plane containing a further connected component not containing the current seed point, and containing a further intersection of the image plane with the centerline other than the current seed point, and condition (B) includes the further connected component exhibiting a larger area than that exhibited by a connected component containing the current seed point; and marking remaining portions of the region intersecting the current image plane, not removed from consideration, as seen areas.