title: Cutaneous bioengineering instrumentation standardization: the Tissue Viability Imager.
abstract: BACKGROUND
  Tissue Viability Imaging (TiVi) is a new bioengineering technology intended for remote two-dimensional mapping of skin red blood cell concentration (RBC(conc)). Before use in the laboratory, work-site and dermatology clinic, critical performance parameters of this emerging technology require careful evaluation.
  
  
  OBJECTIVE
  To assess short- and long-term stability, image uniformity, distance and image size dependence, ambient light and curvature influence in a production batch of Tissue Viability Imagers.
  
  
  METHODS
  Four Tissue Viability Imagers from the same production batch were evaluated at two laboratories (one industrial and one dermatological) with respect to critical parameter performance.
  
  
  RESULTS
  The average systematic drift in sensitivity over time was 0.27% and <1.02% for all four units tested. Difference in sensitivity between units was limited to 4.1% and was due to offset rather than gain deviation. Spatial variation in image uniformity was below 3.08% and 1.93% in the corners and centre of an individual image, respectively. This spatial variation could be further reduced to 0.25% and 0.13%, respectively by image normalization. Ambient light from a 40 W bulb or a 11 W fluorescent light source at a distance of 50-60 cm above the object, reduced the recorded values by about 10%, while the camera to object distance and image size had no detectable influence on sensitivity. Curved objects, such as human forearm, demonstrated an edge effect limited to below 10%.
  
  
  CONCLUSIONS
  The critical TiVi performance parameters evaluated proved stable in relation to expected variations in skin RBC(conc) over time. Calibration by way of a two-point method may reduce differences in sensitivity between instruments to further facilitate inter-laboratory comparison of results.
authors.affiliation: Department of Biomedical Engineering, Linköping University, Linköping, Sweden. gerni@glocalnet.net
authors.forename: Gert E
authors.initials: GE
authors.lastname: Nilsson
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zhai
authors.forename: Heidi P
authors.initials: HP
authors.lastname: Chan
authors.forename: Sara
authors.initials: S
authors.lastname: Farahmand
authors.forename: Howard I
authors.initials: HI
authors.lastname: Maibach
mesh_terms: D001698:Biomedical Engineering; D046169:Dermoscopy / Q000592:standards*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004906:Erythrocyte Count / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012867:Skin / Q000166:cytology*; D012879:Skin Physiological Phenomena; D013057:Spectrum Analysis / Q000295:instrumentation* / Q000592:standards; D013548:Sweden; D014022:Tissue Survival / Q000502:physiology*