# Non-Contact Dermatoscope with Ultra-Bright Light Source and Liquid Lens-Based Autofocus Function
## 1 Introduction
### Prototype of the New Non-Contact Device  
The main advantages of the non-contact prototype system presented in this work are the large working distance while providing the high-resolution level of contact-type dermatoscopes. At present, the prototype is optimized for a working distance of 45 cm \(\pm\) 3 cm. This is realized with a liquid lens-based autofocus, which has not yet been used for this purpose so far. In principle, other working distances are also possible requiring only marginal changes to the current design as further discussed in Section 2.  
As an illumination source, an ultra-bright LED light source with full polarization control is used. This choice makes the device independent from the surrounding light situation and allows reproducible color measurements. Also, the color of different skin sites and lesions can more easily be compared between different images. Such analysis is, for example, important for skin cancer screening as multiple colors and color changes can be indicative of melanoma [6]. Due to the design on a swivel arm the ultra-bright light source can easily be powered. By controlling the polarization state of the measured light, the physician can increase or decrease the contrast of the surface morphology as desired. The presented autofocus function is fast compared to iterative autofocus solutions, which are based on contrast analysis of the captured image. Also, the built-in infrared distance sensor can provide information about the scale in the taken image. The new non-contact system allows for automated imaging functionality so the physician is able to map the skin without manual activity.  
First preclinical studies with an earlier version of our non-contact dermatoscope indicated the potential benefit of the system [8]. For example, in the investigation of inflammatory skin diseases such as lichen ruber planus and psoriasis subtle details of the lesions could be visualized and natural color appearance ensured. With the early stage of the system structural changes such as hypergranulosis [15] were visible for lichen ruber planus. In psoriasis, variations of the capillary vessels could be seen. For this inflammatory skin disease, characteristic blood vessels are opening in the upper skin. These vessels are normally seen in the histopathology of the diseased skin. With the non-contact prototype, it was possible to observe these vessels as round structures in the image. This success could lead to a reduction of necessary biopsies for differential diagnosis. In the future, the newly designed setup described here could be part of an automated skin scanner where the patient is screened at a first examination stage without the need for a dermatologist to be present. However, the system described in [8] did not feature an autofocus function. Also it was mounted on a stable substrate board so that the patients had to move in front of it. Thus, not all regions of interest on a patient's body could be reached and handling by the dermatologist was still limited. Also, image acquisition took longer so that fewer patients could be examined. Using the new system presented in this work, even lesions on hard-to-reach areas of the body could be examined with high resolution.