Wireless video capsule endoscope (VCE) provides a noninvasive method to examine the entire gastrointestinal
(GI) tract, especially small intestine, where other endoscopic instruments can barely reach. VCE is able to
continuously provide clear pictures in short fixed intervals, and as such researchers have attempted to use image
processing methods to track the video capsule in order to locate the abnormalities inside the GI tract. To
correctly estimate the speed of the motion of the endoscope capsule, the radius of the intestinal track must be
known a priori. Physiological factors such as intestinal contraction, however, dynamically change the radius of
the small intestine, which could bring large errors in speed estimation. In this paper, we are aiming to estimate
the radius of the contracted intestinal track. First a geometric model is presented for estimating the radius of
small intestine based on the black hole on endoscopic images. To validate our proposed model, a 3-dimentional
virtual testbed that emulates the intestinal contraction is then introduced in details. After measuring the size
of the black holes on the test images, we used our model to esimate the radius of the contracted intestinal track.
Comparision between analytical results and the emulation model parameters has verified that our proposed
method could preciously estimate the radius of the contracted small intestine based on endoscopic images.