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The Precision of Standard Cranial Measurements in Dry Bones and Multi-Slice Computed Tomography (MSCT) Images: A Preliminary Study

The osteometric analysis of skeletal remains is a fundamental step in reconstructing an individual’s biological profile, especially when estimating ancestry, sex, and/or stature. The emergence of virtual anthropological methods bypassed the lack of documented skeletal collections but also raised the still unanswered question: Do the virtual measurements correspond to the physical ones? This question is essential when considering the requirements for admissibility of such evidence in court. Since those questions were still not completely considered, this study aimed to examine the repeatability of standard cranial measurements in a real and virtual environment. The sample comprised 21 crania from the Early Medieval archaeological site Velim-Velištak located in southern Croatia. CT scanning was done at the University Hospital Dubrava, Zagreb, Croatia, with an MSCT. Scanning parameters were 120kV and 320mA, respectively, with isometric slices using16 × 0.75mm collimation. Digital Imaging and Communications in Medicine (DICOM) data files were imported into the Stratovan Checkpoint software, version 2018.08.07. This study included 31 standard cranial measurements from Data Collection Procedures for Forensic Skeletal Material 2.0. (DCP 2)[1]. Sliding and spreading calipers were used to take measurements on bones, while MSCT measurements were obtained as interlandmark distances. Four observers took part in the study. Two observers took measurements on crania, and two placed landmarks on MSCT images. For each measuring method, one of the observers repeated measurements/landmarking. MCST Images were viewed in 2D (axial, coronal, and sagittal view) and 3D using semi-transparent 3D volume rendering. On each cranium, a total of 47 landmarks were placed using both 2D and 3D views. R (version 3.6.2), Rstudio (version 1.2.5033), and geomorph package were used to read landmarks, calculate interlandmark distances, and obtain 31 standard cranial measurements[2]. A paired-samples t-test was used to examine intra-observer and inter-observer variability and differences between dry bone and “virtual” measurements. Technical Error of Measurement (TEM) and relative Technical Error of Measurements (rTEM) were calculated for measurements that showed statistically significant differences. rTEM values lower than 1.5% were considered acceptable for intra-observer error, while this threshold was set at 2.0% for inter-observer error [3]. The level of statistical significance was set at P ≤0.05 with Bonferonni’s adjustment for multiple comparisons. The results showed high intra-observer agreement both for dry bone and virtual measurements. High inter-observer agreement was reached on bones and images for most measurements, except for several measurements that include sutural landmarks and minimum frontal breadth. When the dry boneand virtual measurements were compared, they showed consistency in most of the cases. The most pronounced discrepancies were noted for mastoid measurements and breadth measurements. Per research, this is the first study that examined cranial measurements from novel data collection standards both in a real and virtual environment. The results showed that most cranial measurements were repeatable and relatively consistent regardless of whether they were measured directly on crania or on CT images. Unlike previous studies that mostly used 3D reconstructions only, this study also employed traditional radiological views, which probably positively impacted precision ; however, due to the limited sample size and number of parameters considered, further studies are needed to obtain additional confirmations. Reference(s): [1] Langley, N.R. ; Jantz, R.L. ; Ousley, S.D. ; Jantz, R.L. ; Milner, G. Data collection procedures for forensic skeletal material. Knoxville, TN: Forensic Anthropology Center, Department of Anthropology, University of Tennessee, 2016 ; 107. [2] Adams, D.C. ; Otárola-Castillo, E. geomorph: an R package for the collection and analysis of geometric morphometri shape data. Methods Ecol Evol. 2013 ; 4(4):393–9. https://doi.org/10.1111/2041-210X.12035. [3] Langley, N.R. ; Meadows Jantz, L. ; McNulty, S. ; Maijanen, H. ; Ousley, S.D. ; Jantz, R.L. Error quantification of osteometric data in forensic anthropology. Forensic Sci Int 2018 ; 287:183–9.

Craniometry ; Virtual Anthropology ; MSCT

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