Abstract
While color video endoscopy has enabled wide-field examination of the gastrointestinal tract, it often misses or incorrectly classifies lesions. Many of these missed lesions exhibit characteristic three-dimensional surface topographies. An endoscopic system that adds topographical measurements to conventional color imagery could therefore increase lesion detection and improve classification accuracy. We introduce photometric stereo endoscopy (PSE), a technique which allows high spatial frequency components of surface topography to be acquired simultaneously with conventional two-dimensional color imagery. We implement this technique in an endoscopic form factor and demonstrate that it can acquire the topography of small features with complex geometries and heterogeneous optical properties. PSE imaging of ex vivo human gastrointestinal tissue shows that surface topography measurements enable differentiation of abnormal shapes from surrounding normal tissue. Together, these results confirm that the topographical measurements can be obtained with relatively simple hardware in an endoscopic form factor, and suggest the potential of PSE to improve lesion detection and classification in gastrointestinal imaging.
Highlights
Many clinically important lesions of the gastrointestinal tract have unique surface topographies
We emphasize that the topographical data presented in the surface normal map and the 3-D rendering are complementary to the color information in the conventional image—this topography cannot be reconstructed from the conventional image alone
Accurate normal reconstruction in photometric stereo endoscopy (PSE) relies on intensity differences for each pixel in a series of images, and lighting changes that are consistent across the PSE image series should primarily affect the signalto-noise ratio (SNR) of the measurements rather than introduce topographical bias
Summary
Many clinically important lesions of the gastrointestinal tract have unique surface topographies. For some lesions, this topographical contrast is more pronounced than their coloration. Precancerous lesions of the colon (polyps) can be difficult to detect using conventional color imagery. These lesions, can protrude (or be recessed) significantly relative to the surrounding mucosa.[1,2] Conventional colonoscopy relying primarily on coloration is estimated to miss one out of every four lesions.[3,4] A method to provide endoscopic measurement of surface topography paired with conventional color imagery could reduce this high missed lesion rate. In CTC, which relies entirely on topographical contrast, multiple studies have reported high lesion detection sensitivity.[5,6] In chromoendoscopy, surface dyes that highlight topography are used, and
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