Abstract

Three-dimensional surface scanning (3DSS) documentation of external patterned injuries in human,¹ veterinary,^2,3 and comparative forensic medicine^4-6 can help researchers to determine the shape and size of the injury, and enable the true-to-scale correlation of the wound and inflicting tool⁷. While routine cetacean virtopsy collected volumetric scans as a means of examining stranded carcass in a digital environment,⁸ additional surface scans may reveal the external conditions including size, surface area, volume and possible texture. Like any measurement technique, 3DSS is subject to a number of limitations and methodological caveats, and thus should not be applied without any reference of standardization. The present study aimed to establish a new standardized 3DSS protocol for surface documentation of stranded cetaceans.

Stranded cetaceans in the Hong Kong waters were included in the present study. The operator scanned the carcass while it was first laid prone and then supine on a stainless steel necropsy table. The carcass was first scanned whole-body using the Artec Eva™ (Artec Group, Inc., Luxembourg). Results from several scans were fused together with additional scans on head, flippers, dorsal fin/ridge and fluke using the Artec Space Spider™ (Artec Group, Inc., Luxembourg). The 2 handheld scanners were used in conjunction with a high-performance laptop installed with a 3D modelling software, Artec Studio 12 (Artec Group, Inc., Luxembourg). Approximately 20 minutes were required to complete a full documentation of the carcass external conditions.

After acquisition of the 3DSS images, point clouds were generated to represent the scanned surface. Computation of point clouds into a polygon mesh structure of the 3D model required alignment, polygonization, mesh smoothing and thinning. Measuring deviations were first selectively eliminated (max error values >0.5 [Artec Space Spider™] and >1.2 [Artec Eva™]). Individual measurements were aligned based on point and surface. Measuring point clouds were then converted into a mesh of non-overlapping triangles, and were recalculated using the highest point resolution. Overlapping areas were deleted, and the resulting single measurements were merged into one polygon mesh. In smoothing and thinning processes, the polygon mesh data was shifted and reduced to minimize the measuring noise and outliners for important details preservation.

The 3DSS protocol developed has integrated into a virtopsy-driven stranding response workflow to provide surface documentation, which gives insights on potential cause of death, and pose precise conservation measure of local cetaceans with the external conditions caused by anthropogenic and natural injury.

Acknowledgements

The authors would like to thank the Agriculture, Fisheries and Conservation Department of the Hong Kong SAR Government for the support in the virtopsy project. Sincere appreciation is also extended to veterinarians, staff, and volunteers from Ocean Park Hong Kong, Ocean Park Conservation Foundation Hong Kong for paying great effort on the stranding response and necropsy in this project. Special gratitude is owed to technicians from Peace Avenue Veterinary Clinic, City University of Hong Kong for operating the CT units to collect volumetric data in the present study. This project was financially supported by the Marine Ecology Enhancement Fund (Grant number: MEEF2017014/L01). Any opinions, findings, conclusions or recommendations expressed herein do not necessarily reflect the views of the Marine Ecology Enhancement Fund or the Trustee.

* Presenting author

Literature Cited

1.  Treleaven P, Wells J. 2007. 3D body scanning and healthcare applications. Computer. 40:7:28–34.

2.  Poll CP, Naples LM, Neria K, O’Connor MR, Van Bonn WG. 2016. Prosthetic foot development using commercial 3D printer technology after surgical treatment of a soft tissue sarcoma in a caiman lizard (Dracaena guianensis). IAAAM 47th Annual Conference Proceedings, Virginia Beach, VA, USA.

3.  Friedman C, Joel BW, Schult AR, Leftwich MC. 2015. Noninvasive 3D geometry extraction of a sea lion foreflipper. Journal of Aero Aqua Bio-Mechanisms. 4(1):25–31.

4.  Schweitzer W, Häusler M, Bär W, Schaepman M. 2007. Evaluation of 3D surface scanners for skin documentation in forensic medicine: comparison of benchmark surfaces. BMC Medical Imaging. 7:1.

5.  Errickson D, Thompson TJU, Rankin BWJ. 2014. The application of 3D visualisation of osteological trauma for the courtroom: a critical review. Journal of Forensic Radiology and Imaging. 2(3):132–137.

6.  Sivanandan J, Liscio E, Eng P. 2017. Assessing structured light 3D scanning using Artec Eva for injury documentation during autopsy. Journal of the Association for Crime Scene Reconstruction. 21:5–13.

7.  Ehlert A, Bartz D. 2008. 3D processing and visualization of scanned forensic data. In: Srihari SN, Franke K, editors. Computational Forensics. International Workshop on Computational Forensics 2008, Berlin, Heidelberg: Springer:70–83.

8.  Kot BCW, Fernando N, Gendron S, Heng HG, Martelli P. 2016. The virtopsy approach: bridging necroscopic and radiological data for death investigation of stranded cetaceans in the Hong Kong waters. IAAAM 47th Annual Conference Proceedings, Virginia Beach, VA, USA.