title: Evaluation of 3D surface scanners for skin documentation in forensic medicine: comparison of benchmark surfaces.
abstract: BACKGROUND
  Two 3D surface scanners using collimated light patterns were evaluated in a new application domain: to document details of surfaces similar to the ones encountered in forensic skin pathology. Since these scanners have not been specifically designed for forensic skin pathology, we tested their performance under practical constraints in an application domain that is to be considered new.
  
  
  METHODS
  Two solid benchmark objects containing relevant features were used to compare two 3D surface scanners: the ATOS-II (GOM, Germany) and the QTSculptor (Polygon Technology, Germany). Both scanners were used to capture and process data within a limited amount of time, whereas point-and-click editing was not allowed. We conducted (a) a qualitative appreciation of setup, handling and resulting 3D data, (b) an experimental subjective evaluation of matching 3D data versus photos of benchmark object regions by a number of 12 judges who were forced to state their preference for either of the two scanners, and (c) a quantitative characterization of both 3D data sets comparing 220 single surface areas with the real benchmark objects in order to determine the recognition rate's possible dependency on feature size and geometry.
  
  
  RESULTS
  The QTSculptor generated significantly better 3D data in both qualitative tests (a, b) that we had conducted, possibly because of a higher lateral point resolution; statistical evaluation (c) showed that the QTSculptor-generated data allowed the discrimination of features as little as 0.3 mm, whereas ATOS-II-generated data allowed for discrimination of features sized not smaller than 1.2 mm.
  
  
  CONCLUSIONS
  It is particularly important to conduct specific benchmark tests if devices are brought into new application domains they were not specifically designed for; using a realistic test featuring forensic skin pathology features, QT Sculptor-generated data quantitatively exceeded manufacturer's specifications, whereas ATOS-II-generated data was within the limits of the manufacturer's specifications. When designing practically constrained specific tests, benchmark objects should be designed to contain features relevant for the application domain. As costs for 3D scanner hardware, software and data analysis can be hundred times as high compared to high-resolution digital photography equipment, independent user driven evaluation of such systems is paramount. INDEX TERMS: Forensic pathology, Rough surfaces, Surface Scanning, Technology Assessment.
authors.affiliation: Institut für Rechtsmedizin, Universität Zürich, Zürich, Switzerland. shwi@irm.unizh.ch
authors.forename: Wolf
authors.initials: W
authors.lastname: Schweitzer
authors.forename: Martin
authors.initials: M
authors.lastname: Häusler
authors.forename: Walter
authors.initials: W
authors.lastname: Bär
authors.forename: Michael
authors.initials: M
authors.lastname: Schaepman