Enhancement of visual contrast in fluorescence endoscopy
Bladder tumors are difficult to recognize during an endoscopy of the bladder (cystoscopy) using a conventional white light source. Therefore, a technique called photo dynamic diagnosis (PDD) or fluorescence endoscopy is used to enhance both sensitivity and specificity of tumor detection. As preparation for a PDD cystoscopy, a marker substance is brought into the patient's bladder which leads to a fluorescence of cancerous tissue if a suitable light source is used. Even though tumors are better distinguishable from healthy bladder tissue, the contrast between both types of tissue can still be low and it further decreases with the decay of the marker substance. To overcome these difficulties, we enhance the contrast between fluorescence and background. To this end, we perform a color space transformation which separates fluorescence information from the remaining information. In this new color space, we apply a non-linear transformation to the fluorescence component which leads to a better separation of fluorescing and non-fluorescing pixels. Finally, the image is transferred back to the RGB color space. For clinical evaluation, we implemented the proposed algorithm as plug-in for the real-time capable software framework RealTimeFrame.