X-ray video fluoroscopy as a key technology in research on motion systems

Already in 1981, Martin S. Fischer at his stay in the lab of Jean-Pierre Gasc in Paris became inspired by the potential of X-ray fluoroscopic recordings for a better understanding of how animals move. In 1988 he started his first projects into this field with recordings of walking and climbing in the rock hyrax (Procavia capensis). X-ray radiographs were made at the Institute of Scientific Media Production in Göttingen, where a uniplanar Phillips system was available. The system worked with an Arritechno 35 mm camera at a maximum frame rate of 150 frames per second. The image intensifier had a maximum diameter of 200 mm. In the early beginnings, X-ray images were recorded on classic film reels, later on video tapes. The project was conducted together with Hanns Ruder from the Institute of Theoretical Physics at the University of Tübingen and granted by the German Research foundation. It led to the habilitation thesis of Martin S. Fischer in 1993.

X-ray lab at the Institute of Scientific Media Production in Göttingen: self-constructed treadmills, improvisational skills, highly motivated young scientists, and much patience of the whole team with not always cooperative animals are the basic requirements for successful experimental sessions up to today. Right: Nadja Schilling at her experiments with the tree shrew (Tupaia glis) 1997.

With the professorship of Martin S. Fischer at the new Institute of Systematic Zoology and Evolutionary Biology at the Friedrich Schiller University Jena and the foundation of the DFG-Innovation center “Motion Systems” together with Reinhard Blickhan (Institute for Sport Sciences), Hans-Christoph Scholle (Clinic for Trauma and Reconstructive Surgery) and Klaus Zimmermann (Mechanical Engineering, Technical University Ilmenau) a new center of research on motion systems was established in Thuringia. Unique not only to Germany, this center forms an aggregate of researchers in evolutionary biology, biomechanics, medicine and technology in order to explore the perspectives of utilization of biological knowledge in medical diagnostic and disease prevention on one hand and in robotics and bionics on the other hand. During the past 20 years this network expanded far beyond Thuringia, it benefits today from numerous collaborations with other national and international institutions. Hundreds of papers, book chapters and books were published and many young scientists started their career with a diploma and PhD Thesis in the Jena-Ilmenau research network. Financial support was granted by the German Research Foundation (DFG), the German Ministry of Education and Science (BMBF), the state of Thuringia and by foreign institutions, which for example provided support for guest researchers from other European countries, from the US and from Japan. With the BMBF project “InspiRat – Engineering of a bionically inspired climbing robot for the external inspection of linear structures” by Martin S. Fischer, Hartmut Witte (Department of Biomechantronics, TU Ilmenau), Stanislav N. Gorb (Department of Functional Morphology and Biomechanics, Kiel University) and Andreas Karguth (Tetra GmbH, Ilmenau) a new high-resolution biplanar C-arm fluoroscope was installed in Jena in 2006. The system was custom built based on angiography equipment in collaboration with the Siemens AG, Germany.

X-ray lab in Jena: biplanar C-arm fluoroscope (Siemens AG), various experimental set-ups: left: horizontal pole with integrated force plate, right: perforated treadmill (Tetra GmbH).

X-ray video fluoroscopy is one of the key technologies in our research on motion systems, because it enables the view under the skin and so, the direct observation of the moving skeletal elements and joints. Alternative techniques of motion analysis such as the utilization of skin markers are limited in resolution and accuracy, particularly with respect to movements of proximal limb elements (shoulder, hip) and the vertebral column. In order to obtain comprehensive insights into the biomechanics of the whole motion system, we combine X-ray video fluoroscopy with synchronous recordings of substrate reaction forces. Such dynamic analyses enable the investigation of forces and torques acting at the joints as well as of the mechanical work required to move the skeleton and provided by the musculature. Which muscles actually are active during particular movements, and whether these muscles work to produce or to prevent movement, is studied using implanted electrodes (electromyography, EMG). In addition, the variation of experimental set-ups, e.g. the change of treadmill velocity, the installation of disturbances, the change of substrate inclination or substrate diameter allows us to imitate some of the physical conditions of the natural locomotor substrate used by a certain species. So, we can explore how the motion system deals with the daily challenges in the natural habitat. However, a highly detailed functional analysis of motion requires an equally precise analysis of the underlying structures in order to obtain a comprehensive understanding of form-function-relationships. Therefore, we investigate the influence of body size on body proportions both in ontogeny and phylogeny, we study the size and shape of joints, the ratio between articular surfaces and we demonstrate how the internal architecture of a muscle is related to the contractile properties of its fiber type population.

Frames from an XROMM animation of forelimb movement in a Chihuahua, made by Jonas Lauströer.

A new quality of visualization of form-function-relationships in motion systems has been achieved by the development of the XROMM-technology („X-ray reconstruction of moving morphology“) by our colleagues at the Brown-University, Providence. We use this technology to animate a skeletal model generated by high-resolution computer tomography on the basis of biplanar X-ray radiographs. However, XROMM is by far not only developed to create sophisticated graphics, especially when used by a skilled designer, it enables a highly accurate description of complex three-dimensional movements as they occur, for example, between the vertebrae in the axial skeleton or in the jaw during mastication. Also, the movement of the whole skeleton can be reconstructed in larger animals for which the field of the image intensifier is too small to record all regions in one frame. The development of such new methods in motion analysis is one of the purposes of the “Research Coordination Network for X-ray Motion Analysis” founded in 2009 and financed by the National Science Foundation. Major goal of this network, on which we participate, is to connect the working groups active in motion research, to organize summer schools and workshops for young scientists, and to develop concepts for databases, archives and collections of X-ray radiographs and other sorts of research data.

Animal welfare

All experiments are conducted in accordance with German animal welfare regulations. They are registered and verified by the official veterinarian of the University and by the Thuringian Committee for Animal Research. Only approved projects are carried out. If we keep the animals for some weeks or months at the institute, they are housed in large enriched cages to promote natural movement activity and to facilitate locomotor skills. The conditions are regularly verified by the responsible veterinarians and follow German animal welfare regulations as well. Experiments on human beings in our laboratory are prohibited.