Heike Scherf

A new high-resolution computed tomography (CT) segmentation method for trabecular bone architectural analysis

In the last decade, high-resolution computed tomography (CT) and microcomputed tomography (micro-CT) have been increasingly used in anthropological studies and as a complement to traditional histological techniques. This is due in large part to the ability of CT techniques to nondestructively extract three-dimensional representations of bone structures. Despite prior studies employing CT techniques, no completely reliable method of bone segmentation has been established. Accurate preprocessing of digital data is crucial for measurement accuracy, especially when subtle structures such as trabecular bone are investigated. The research presented here is a new, reproducible, accurate, and fully automated computerized segmentation method for high-resolution CT datasets of fossil and recent cancellous bone: the Ray Casting Algorithm (RCA). We compare this technique with commonly used methods of image thresholding (i.e., the half-maximum height protocol and the automatic, adaptive iterative thresholding procedure). While the quality of the input images is crucial for conventional image segmentation, the RCA method is robust regarding the signal to noise ratio, beam hardening, ring artifacts, and blurriness. Tests with data of extant and fossil material demonstrate the superior quality of RCA compared with conventional thresholding procedures, and emphasize the need for careful consideration of optimal CT scanning parameters.

Functional Analysis of the Primate Shoulder

Studies of the shoulder girdle are in most cases restricted to morphological comparisons and rarely aim at elucidating function in a strictly biomechanical sense. To fill this gap, we investigated the basic functional conditions that occur in the shoulder joint and shoulder girdle of primates by means of mechanics. Because most of nonhuman primate locomotion is essentially quadrupedal walking—although on very variable substrates—our analysis started with quadrupedal postures. We identified the mechanical situation at the beginning, middle, and end of the load-bearing stance phase by constructing force parallelograms in the shoulder joint and the scapulo-thoracal connection. The resulting postulates concerning muscle activities are in agreement with electromyographical data in the literature. We determined the magnitude and directions of the internal forces and explored mechanically optimal shapes of proximal humerus, scapula, and clavicula using the Finite Element Method. Next we considered mechanical functions other than quadrupedal walking, such as suspension and brachiation. Quadrupedal walking entails muscle activities and joint forces that require a long scapula, the cranial margin of which has about the same length as the axillary margin. Loading of the hand in positions above the head and suspensory behaviors lead to force flows along the axillary margin and so necessitate a scapula with an extended axillary and a shorter cranial margin. In all cases, the facies glenoidalis is nearly normal to the calculated joint forces. In anterior view, terrestrial monkeys chose a direction of the ground reaction force requiring (moderate) activity of the abductors of the shoulder joint, whereas more arboreal monkeys prefer postures that necessitate activity of the adductors of the forelimb even when walking along branches. The same adducting and retracting muscles are recruited in various forms of suspension. As a mechanical consequence, the scapula is in a more frontal, rather than parasagittal, position on the thorax. In both forms of locomotion—quadrupedal walking and suspension—the compression-resistant clavicula contributes to keeping the shoulder complex distant from the rib cage. Future studies should consider the consequences for thorax shape. The morphological specializations of all Hominoidea match the functional requirements of suspensory behavior. The knowledge of mechanical functions allows an improved interpretation of fossils beyond morphological similarity.

Structural Adaptation of Trabecular Bone Revealed by Position Resolved Analysis of Proximal Femora of Different Primates

The anisotropic arrangement of trabeculae in the proximal femur of humans and primates is seen as striking evidence for the functional adaptation of trabecular bone architecture. Quantitative evidence to demonstrate this adaptation for trabecular bone is still scarce, because experimental design of controlled load change is difficult. In this work, we use the natural variation of loading caused by a different main locomotor behavior of primates. Using high‐resolution computed tomography and advanced image analysis techniques, we analyze the heterogeneity of the architecture in four proximal femora of four primate species. Although the small sample number does not allow an interspecies comparison, the very differently loaded bones are well suited to search for common structural features as a result of adaptation. A cubic volume of interest of size (5 mm)3 was moved through the proximal femur and a morphometric analysis including local anisotropy was performed on 209 positions on average. The correlation of bone volume fraction (BV/TV) with trabecular number (Tb.N) and trabecular thickness (Tb.Th) leads to the suggestion of two different mechanisms of trabecular bone adaptation. Higher values of BV/TV in highly loaded regions of the proximal femur are due to a thickening of the trabeculae, whereas Tb.N does not change. In less loaded regions, however, lower values of BV/TV are found, caused by a reduction of the number of the trabeculae, whereas Tb.Th remains constant. This reduction in Tb.N goes along with an increase in the degree of anisotropy, indicating an adaptive selection of trabeculae. Anat Rec, 2010.

Patterns of activity adaptation in humeral trabecular bone in Neolithic humans and present-day people

OBJECTIVE The annual turnover rate of trabecular bone by far exceeds that of cortical bone and, therefore, is very sensitive to its daily loading regime. Here we test the hypothesis that the study of the trabecular bone architecture of the human humerus is able to differentiate between different habitual manual activities. MATERIALS AND METHODS For this purpose, we compared the trabecular architecture of the humeral head in a Neolithic population to that of a sample of contemporary Europeans using micro-computed tomography (microCT). We defined in each specimen a spherical volume of interest with a diameter of 57.5 ± 2.5% of the maximal diameter of the humeral head to metrically analyze the bulk of humeral head trabecular architecture. We subsequently quantified the trabecular architectures in the VOIs, measuring seven standard 3D-morphometric parameters, and used univariate and multivariate statistical analyses for comparisons within and between populations. RESULTS Univariate statistical analysis showed significant differences in a combination of 3D-morphometric parameters. A principal components analysis of the 3D-morphometrics of the trabecular architectures separated the Neolithic from the contemporary samples on the basis of differences in their gross trabecular architecture, including differences in the bone volume fraction (BV/TV), the number of trabeculae per unit length (Tb N), and the distance between trabeculae (Tb Sp). DISCUSSION We interpret the significant differences found in the humeral trabecular bone of the Neolithic and the contemporary group as likely reflecting the distinct manual working routines. The trabecular bone configuration in the Neolithic sample shows presumably functional signatures of prehistoric subsistence techniques and activity levels.

Locomotion-related Femoral Trabecular Architectures in Primates — High Resolution Computed Tomographies and Their Implications for Estimations of Locomotor Preferences of Fossil Primates

Bones and teeth are often the only preserved items of extinct animals. Soft tissue remnants, stomach contents or tracks are only preserved under specific embedding and fossilization conditions. As palaeontology seeks to understand how extinct creatures appeared and existed, fossil bone provides the best source of information for reconstructions of fossil species. Additional information about the ecology of extinct animals may be gained from the embedding sediment and associated plant fossils. Since the beginning of palaeontology, the form and locomotor features of extinct animals were inferred from the external characteristics and proportions of their bones. For locomotor studies, their bone surface morphologies and proportions were compared with those of extant animals, with special attention to locomotor relevant features. This kind of comparative analyses may encounter difficulties if the fossil species practiced a unique locomotor pattern which can not be compared with locomotor patterns in extant forms (Day 1979).

A comparison of proximal humeral cancellous bone of great apes and humans

The shoulder is the most mobile joint in the primate body, and is involved in both locomotor and manipulative activities. The presumed functional sensibility of trabecular bone can offer a way of decoding the activities to which the forelimbs of fossil primates were subjected. We examine the proximal humeral trabecular architecture in a relatively closely related group of similarly sized hominids (Pongo pygmaeus, Pan troglodytes, and Homo sapiens), in order to evaluate the effect of diverging habitual motion behaviors of the shoulder complex in a coherent phylogenetic group. In order to characterize and compare the humeral trabecular architectures of the three species, we imaged a large sample by high-resolution computed tomography (HrCT) and quantified their trabecular architectures by standard bone 3D morphometric parameters. Univariate statistical analysis was performed, showing significant differences among the species. However, univariate statistics could not highlight the structural particularity in the cancellous bone of each species. A principal component analysis also showed clear separation of the three taxa and enabled a structural characterization of the humeral trabecular bone of each species. We conclude that the differences in the architectural setup of the three hominids likely reflect multiple differences in their habitual activity patterns of their shoulder joint, although individual structural features are difficult to relate to specific loading conditions.

Computed tomography in paleoanthropology — an overview

Computed tomography (CT) was first applied in the early 1970s and introduced subsequently a new perspective towards anatomical imaging. In the last decade, high-resolution CT (HR-CT) had a high impact on anthropology and paleoanthropology through its ability to define and explore subtle differences in hard tissue structures in fossil and extant humans and nonhuman primates. CT is very suitable for unique fossil material, because it is destruction free and the original material stays intact while the internal structures are digitized. The imaging yields a virtual copy of the object, which can be used for the generation of detailed copies of original fossil material. CT data allow multiple studies in parallel and independently on specimens which are not commonly accessible. Diverse CT systems with different performance characteristics as designed for different functions can make it difficult for a researcher to choose the most appropriate CT system and to check the image quality of CT scans. The physical principles involved in CT imaging and the principles of signal processing and computer graphics can help to choose the best scan setting and the most suitable CT system for a study. Quantitative and qualitative analysis can also be improved and comparisons between different studies can be facilitated when the above mentioned principles are taken into account. In the following, I will give an overview of the different CT systems and discus both theoretical and practical matters of CT imaging using the example of trabecular bone.