A New Method for the Analysis of Soft Tissues with Data Acquired under Field Conditions

Abstract

Analyzing soft-tissue structures is particularly challenging due to the lack of homologous landmarks that can be reliably identified across time and specimens. This is particularly true when data are to be collected under field conditions. Here, we present a method that combines photogrammetric techniques and geometric morphometrics methods (GMM) to quantify soft tissues for their subsequent volumetric analysis. We combine previously developed methods for landmark data acquisition and processing with a custom program for volumetric computations. Photogrammetric methods are a particularly powerful tool for field studies as they allow for image acquisition with minimal equipment requirements and for the acquisition of the spatial coordinates of points (anatomical landmarks or others) from these images. For our method, a limited number of homologous landmarks, i.e., points that can be found on any specimen independent of space and time, and further distinctive points, which may vary over time, space and subject, are identified on two-dimensional photographs and their three-dimensional coordinates estimated using photogrammetric methods. The three-dimensional configurations are oriented by the spatial principal components (PCs) of the homologous points. Crucially, this last step orients the configuration such that x and y-information (PC1 and PC2 coordinates) constitute an anatomically-defined plane with the zvalues (PC3 coordinate) in the direction of interest for volume computation. The z-coordinates are then used to estimate the volume of the tissue. We validate our method using a physical, geometric model of known dimensions and physical (wax) models designed to approximate perineal swellings in female macaques. To demonstrate the usefulness and potential of our method, we use it to estimate the volumes of Barbary macaque sexual swellings recorded in the field with video images. By analyzing both the artificial data and real monkey swellings, we validate our method’s accuracy and illustrate its potential for application in important areas of biological research. Citation: Sonnweber RS, Stobbe N, Zavala Romero O, Slice DE, Fieder M, et al. (2013) A New Method for the Analysis of Soft Tissues with Data Acquired under Field Conditions. PLoS ONE 8(6): e67521. doi:10.1371/journal.pone.0067521 Editor: Alistair Robert Evans, Monash University, Australia Received October 15, 2012; Accepted May 21, 2013; Published June 24, 2013 Copyright: ß 2013 Sonnweber et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: While writing the manuscript, Ruth Sonnweber and Nina Stobbe were supported by ERC (European Research Council) Advanced Grant SOMACCA (The Syntax of Mind: A Computational Comparative Apporach) (230604) awarded to W. Tecumseh Fitch. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: ruth-sophie.sonnweber@univie.ac.at . These authors contributed equally to this work. The perineal swellings of female Barbary macaques (Macaca sylvanus) are an example of a soft tissue structure whose 3D nature would be of interest to describe morphometrically. As with many other females of Old World monkeys, these primates develop distinct anogenital swellings during sexually active phases [2]. Swelling size changes over the female cycle and tumescence and de-tumescence were shown to be related to female sex steroids [3,4,5]. What information these secondary sexual characteristics convey is not yet fully understood. All published studies relating to the morphology of this feature have so far been restricted to analyses of two-dimensional data. We chose this morphological trait as an example for

Cite

@article{sonnweber2013new,
  title = {A New Method for the Analysis of Soft Tissues with Data Acquired under Field Conditions},
  author = {Sonnweber, Ruth S. and Stobbe, Nina and Zavala-Romero, Olmo and Slice, Dennis E. and Fieder, Martin and Wallner, B.},
  year = {2013},
  doi = {10.1371/journal.pone.0067521},
  url = {https://doi.org/10.1371/journal.pone.0067521},
}