Quantifying Error in Virtual Data Collection: the Impact of MSCT Scan Segmentation Protocol and Inter-observer Error in 3-D Landmark Placement on the Human Subadult Pelvis

• NCJ Number: 254055
• Journal: American Journal of Physical Anthropology Volume: 168 Dated: 2019 Pages: 239-239
• Author(s): Michala K. Stock; Louise K. Corron; Laura E. Girillo; Heather M. Garvin; Cortney N. Hulse; Stephanie J. Cole; Kyra E. Stull; Alexandra R. Klales
• Date Published: 2019
• Length: 1 page
• Grant Number(s): 2015-DN-BX-K409; 2017-DN-BX-K0144
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical); Report (Study/Research); Report (Grant Sponsored); Program/Project Description
• Award: Development of Modern Subadult Standards: Improved Age and Sex Estimation in U.S. Forensic Practice

Annotation

Since the utility of CT scan data for creating skeletal reference databases has gained recognition, but requires protocol standardization to ensure accuracy and comparability between specimens, the current study examined the impact of scan processing protocols and landmark placement on error in virtual data collection.

Abstract

MSCT postmortem scans of subadult individuals were obtained from the University of New Mexico Health Sciences Center, Office of the Medical Investigator. Four researchers segmented the pelves of four randomly sampled individuals, and each performed four trials on a fifth individual. Deviation analyses in Geomagic Studio were used to visualize discrepancies and calculate pairwise comparisons of the root-mean-square error (RMSE) and the average deviation distances. Resultant RMSE values ranged from 0.13-0.78mm (mean of 0.33mm), with an average deviation of 0.17mm between model vertices, although certain regions (e.g., ASIS) were prone to larger deviations. The effects of threshold value selection and smoothing protocol on overall deviation and variance at specific anatomical locations are discussed. For the examination of error from landmark placement, three researchers each collected 32 pelvic landmarks on a set of 30 segmented pelves in Amira. Error was assessed using distances from mean landmark placement and a Procrustes MANOVA. The overall average error was 2.4mm. Mean error at individual landmarks ranged from 0.9-7.4mm; landmarks associated with pelvic height exhibited the highest error. The MANOVA demonstrated significantly more variation among individuals than within landmark placement (p=0.27). The study concludes that results suggest inter- and intra-observer errors associated with CT scan segmentation and landmark placement are generally acceptable, but can improve with further protocol standardization. (publisher abstract modified)