1. A method of segmenting lungs from a Computerized Tomography (CT) volume comprising a plurality of slices, said method comprising: using a processor to perform steps comprising: thresholding said CT volume using a predetermined threshold; segmenting a middle slice of said CT volume using a region-based technique; and segmenting a plurality of non-middle slices of said CT volume using a contour-based technique, without using a region-based technique for the non-middle slices.