SfM-3DULC: Reliability of a new 3D wound measurement procedure and its accuracy in projected area

Three-dimensional (3D) wound measurement lacks a gold standard to test accuracy. It is useful to develop procedures to scan wounds and reconstruct their 3D model with low-cost techniques. We present a new procedure (Structure from Motion [SfM]-3DULC) that uses photographs for measuring nine wound variables. We also propose a new variant of ImageJ in which an orthophoto is used to measure the projected area (Ortho-ImageJ). In addition, we compare the wound measurements made by dermatologists and non-experts. A group of five experts in dermatology and five non-specialists measured 33 leg wounds five times per procedure. Intra-rater and inter-rater reliability scores of SfM-3DULC were evaluated with the intraclass correlation coefficient (ICC 2,1). The accuracy of the two new procedures (SfM-3DULC and Ortho-ImageJ) in the measurement of projected area was assessed by comparing their values with those obtained using ImageJ, with the Wilcoxon matched-pairs signed rank test (α = 0.05). This test was also used to analyse the differences between the measurements made by dermatologists and non-experts. All the variables measured by dermatologists using SfM-3DULC showed excellent scores of intra-rater reliability (ICC > 0.99) and inter-rater reliability (ICC > 0.98). No significant differences between the three procedures were found when comparing their projected area values. Significant differences between the measurements of dermatologists and non-experts were found in most of the variables: circularity coefficient, perimeter, projected area, surface area, and reference surface area. The wound measurement procedure SfM-3DULC has an excellent reliability, is accurate for the measurement of projected area, and can be used by dermatologists for wound monitoring in everyday clinical practice.