Dermascanner plus: Methods of high-precision optical metrology lay the foundations for a constant reproducible quality in computer-aided skin cancer screening

An interdisciplinary group of dermatologists, specialists in optics, high-precision metrology, image processing, computer visualistics and medical engineering has developed a dermatologist assistance system, the DermaScanner Plus. It consists of a fully automatic whole-body-skin-scanner and a dermatological assistance system for the computer-aided image analysis of nevi. A kinematics moves different high-resolution colour cameras, combined with specially adapted daylight illumination, and 3d sensing devices around the body of the patient. The captured images as well as the 3d point cloud of the patient's skin surface have to be free of measurement errors. If it is failed to do so, there is a risk that nevi could be just overlooked or measured to small by the dermatological assistance system for the skin data analysis. In order to prevent this, the whole-body-skin-scanner has been calibrated geometrically and in colour. The necessary basic technologies were laid in the field of high-precision industrial metrology. A method of the intrinsic calibration of cameras and their optics enables an optimal imaging performance. To determine the position and orientation of all sensors (colour camera and 3d sensing devices) as well as their movement kinematics incl. motion behavior, a new approach of extrinsic calibration has been developed. On this basis we calculate an exact reconstruction of the human body in colour and in space. The required sensor data fusion of multi-modal image data and 3d point clouds based on the results of exact intrinsic and extrinsic calibration procedures. Correctness and high quality data is achieved without estimation or approximation procedures. As a result of all these measures, the whole-body-skin-scanner generates spatially registered, colour-calibrated and thus standardized body images which are enriched with additional 3d information. They lay the foundations for a constant reproducible quality in computer-aided skin cancer screening. This is a prerequisite to ensure the comparability of skin cancer screening with different devices, at different places and at varying times. A regular and reliable follow-up is for the first time possible.