Tag Archives: 3D images

Cortical morphology and ancestry

Fan et al 2015_2A recent study published by a large neuroscience team involved in imaging, cognition, and genetics, showed that cortical geometry is correlated with genetic ancestry. Using a sample of US citizens from the PING data, they reconstructed 3D cortical surfaces to obtain information on the morphological variation of the sulci and gyri. To calculate proportions of genetic ancestry they used as reference populations from west Africa, east Asia, a sample of native Americans and a sample of European descendants. The main finding of the study is that cortical folding patterns are strongly related to the genetic ancestry. According to the authors, African ancestry is associated with more posterior and narrower temporal areas. Frontal and occipital surfaces are more projected in Europeans and flatter in Native Americans. Asians have more variability in the temporal and parietal regions. Their results were similar to  Howells’ craniometric analysis. Moreover, all but Europeans display increased morphological variation in the posterolateral-temporal region. Due to these  morphological differences among populations, the authors warn for a possible methodological bias when mixing sample from different geographical origins in imaging studies.

Sofia Pedro


Surface Scanning and Morphometrics

The use of three dimensional imaging techniques is becoming more and more prominent among morphometrics studies. As a complementary technique to computed tomography (CT) and magnetic resonance imaging (MRI), laser scanning provides the possibility to obtain 3D images from the surface of objects. Martin Friess published a detailed review on this subject , free to download on the webpage of the Journal of Anthropological Sciences. Laser scanners are optical systems that use visible light to capture the surface shapes of the objects under study. The light is emitted onto the object or area of interest and its reflection is then captured by a detector in the scanner, resulting in a dense cloud of 3D points. After acquiring more images though different views, these are processed, by aligning and fusing the images/views to obtain a single point cloud object. The final 3D image is obtained after the post-processing steps (decimation, smoothing, and gap-filling) performed by suitable software (e.g. freeware Meshlab).

The major advantage of laser scanners is that its methods are non-invasive and non-destructive. The acquisition of point clouds is fast and its resolution can be high to very high. Besides, information on the texture of the object can be obtained, and the portability of some devices allows its outdoor use. On the other hand, some disadvantages can be pointed out, as the impossibility to get information about internal structures, the low processing steps in contrast to rapid acquisition, and the lessen stability of the portable scanners which leads to reduction in accuracy and precision. When acquiring a laser scanner various parameters should be taken into account: the field of view or measurement volume, from which depends the size of the object that can be measured; the resolution; the accuracy and precision; the acquisition speed; the portability and the cost. The prices of the laser scanners can range from hundreds to thousands of dollars.

These scanners are used in engineering, but they can also be of great use for other fields, such as archaeology and medicine. As regards to physical and paleoanthropology, the main benefit of these scanners is that they contribute to the preservation of the specimens, as these are digitized and can be studied without handling. The surface scanning of fossils has even led to the building of digital databases. The digital fossils are the object of study of geometric morphometrics, which include studies on morphology (shape, size, etc.) and are also methods for reconstruction of specimens.

Ana Sofia Pedro

***

For more technical information about laser scanners, visit:

For more information on digital databases, see the Smithsonian 3D collection and the list by Nespos.

The image of this post is from: Friess, M. 2010. Calvarial shape variation among Middle Pleistocene hominins: an application of surface scanning in palaeoanthropology. Comptes Rendus Palevol, 9:435-443.