Icex: Advances in the automatic extraction and volume calculation of cranial cavities

Abstract

The use of non-destructive approaches for digital acquisition (e.g. computerised tomography-CT) allows detailed qualitative and quantitative study of internal structures of skeletal material. Here, we present a new R-based software tool, Icex, applicable to the study of the sizes and shapes of skeletal cavities and fossae in 3D digital images. Traditional methods of volume extraction involve the manual labelling (i.e. segmentation) of the areas of interest on each section of the image stack. This is time-consuming, error-prone and challenging to apply to complex cavities. Icex facilitates rapid quantification of such structures. We describe and detail its application to the isolation and calculation of volumes of various cranial cavities.The R tool is used here to automatically extract the orbital volumes, the paranasal sinuses, the nasal cavity and the upper oral volumes, based on the coordinates of 18 cranial anatomical points used to define their limits, from 3D cranial surface meshes obtained by segmenting CT scans. Icex includes an algorithm (Icv) for the calculation of volumes by defining a 3D convex hull of the extracted cavity. We demonstrate the use of Icex on an ontogenetic sample (0-19 years) of modern humans and on the fossil hominin crania Kabwe (Broken Hill) 1, Gibraltar (Forbes' Quarry) and Guattari 1. We also test the tool on three species of non-human primates. In the modern human subsample, Icex allowed us to perform a preliminary analysis on the absolute and relative expansion of cranial sinuses and pneumatisations during growth. The performance of Icex, applied to diverse crania, shows the potential for an extensive | 1173

Normal human craniofacial growth and development from 0 to 4 years

“…The second aim of this study concerns ontogenetic allometry, assessed through PCAs of shape and form, multivariate regressions of shape and form on age. By applying a recently published method of assessment of the inner volume of cranial cavities 37 , we were able to measure both absolute and proportional changes in volumes of specific cranial regions and relate changes in these to cranial allometric growth. The cavities of the brain, tongue, eyes and nose were assessed because they are believed to play key roles in driving the morphological changes observed in the growing cranium 24 , 37 – 39 .…”

“…By applying a recently published method of assessment of the inner volume of cranial cavities 37 , we were able to measure both absolute and proportional changes in volumes of specific cranial regions and relate changes in these to cranial allometric growth. The cavities of the brain, tongue, eyes and nose were assessed because they are believed to play key roles in driving the morphological changes observed in the growing cranium 24 , 37 – 39 . Our study shows the accelerations and decelerations of changes in form during early childhood (0–48 months of age).…”

“…(6) we examined the relationships between only four cranial volumes and cranial shape or form in this study, but the contributions of other volumes e.g. frontal and maxillary sinuses 37 may also be important and should be investigated in further work.…”

“…1 D). These volumetric measurements were extracted from cranial surface scans and taken using the R package: Arothron and the functions Icex and Icv 37 , 57 . The raw volumetric measurements were cube root transformed to obtain a normal distribution.…”

Functional adaptation of the infant craniofacial system to mechanical loadings arising from masticatory forces

“…From 0 to 48 months, the infant cranium undergoes rapid morphological changes in size and shape [14,15]. It is well accepted that the infant cranium alters in response to, and to accommodate, the volumetric changes of key organs and cavities [3,14,16]. This involves displacement, expansion and modelling of skeletal elements [7,17], as well as tissue differentiation across the craniofacial sutures [2,[18][19][20][21].…”