A system, method, and article of manufacture for imaging tubular structures of the human body, such as the digestive tract of a living person, with a medical imaging device such as a computed tomography (CT) scanner and a computer workstation. The CT scanner is used to generate cross-sectional axial images of a human colon which are then transferred to the computer workstation. A colon midline is defined which follows the colon lumen. The computer workstation supports colon midline definition by generating and displaying reformatted cross-sectional images, volume rendered scouts, and interluminal views. Semi-automatic midline defining tools are also included. After the midline is defined, a montage of images is displayed for diagnostic purposes. The images include axial sections, transluminal cross section, and intraluminal volume rendered images.