Colorectal cancer is a leading cause of death in older adults, which usuall
y involves a long-term progressive change of normal mucosa into adenomatous
polyps and then cancer. The detection and treatment of this disease in an
early stage can lead to a cure in most cases by simply removing the polyp.
Computed tomographic colonography (CTC), also referred to as virtual colono
scopy (VC), is a recent advance that gives an intraluminal visualization of
the colon that is similar to endoscopy. VC requires fast 3D display (at le
ast 10 frames/sec) of the colon's mucosal surface on a computer screen. Spi
ral/helical computer tomography is used to gather 3D volume data prior to d
isplay. CTC has been demonstrated to be promising for colorectal cancer scr
eening. Studies on unraveling of the colon are underway to map the convolut
ed tubular structure into a straightened and flattened image volume for glo
bal visualization. In this article, we review the current status of CTC wit
h an emphasis on image processing and visualization algorithms. Clinical as
sessment results of existing techniques are summarized, practical issues an
d future perspectives are also discussed.