Local and global panoramic imaging for fluorescence bladder endoscopy
Endoscopic treatment of bladder cancer is more and more often based on photodynamic diagnostics (PDD), a specialized endoscopic technique where a narrow-band bluish illumination causes tumors to fluoresce reddish. Contrast between tumors and healthy bladder tissue is thus noticeably increased compared to white light endoscopy. A downside of PDD is the low illumination power, which requires that the distance between endoscope and bladder wall be kept low, thus resulting in a small field of view (FOV). We therefore describe an approach to combine several successive frames into a local PDD panorama, which provides a larger and sufficiently bright FOV for treatment. Furthermore, the endoscopic cancer treatment generally starts with a complete scan of the bladder to detect the tumors. For diagnosis, navigation and reporting, a global overview image of the bladder wall is often desired. While construction of such a global panorama can be based on the same algorithm as the local panorama, direct planar visualization of the sphere-shaped bladder may cause severe distortions. Apart from the global panorama computation itself, we therefore analyze these distortions, and provide an alternative visualization which is based on bladder depictions used in standard reporting forms and anatomy textbooks.