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Biology Articles » Methods & Techniques » Real-time phase-contrast x-ray imaging: a new technique for the study of animal form and function » Conclusion

- Real-time phase-contrast x-ray imaging: a new technique for the study of animal form and function

Synchrotron x-ray phase contrast imaging shows great promise as a powerful new tool for internal visualization in biological and medical research. This is the only generally applicable technique that has the necessary spatial and temporal resolutions, penetrating power, and sensitivity to soft tissue that is required to visualize the internal physiology of small living animals on a scale from millimeters to microns. The impact of this technique is just beginning to be seen as it is applied to some of the more easily arranged experiments such as those on the respiratory systems of insects, where it has already had a major impact. The discovery of rhythmic tracheal compressive movements in taxa in which it was previously unknown [6] has opened whole new areas of research, for example those aimed at determining morphological mechanisms of compression and the role of associated convection in insect physiology and evolution. Another exciting possibility is the visualization of previously unknown, complex circulatory patterns within insects that have only been inferred before from changes in body surface temperature [34].

Current uses of the technique include the analysis of the rapidly moving internal mouthparts of biting insects and the visualization of fluid motion in the pumping organs of fluid feeding insects such as flies and butterflies. The ability to see inside the animal, including the internal workings of jaws, legs, and wing hinges, may be of significant utility in the exploration of functional diversity. Although more challenging due to lower density differences, this approach has also yielded impressive x-ray video of insect digestive (Figure 1e–l; see also Additional files 2 and 3) and circulatory system function, including the pumping of the tiny pulsatile organs that maintain the internal pressure of the antennae of ants. The first synchrotron research on living vertebrate musculoskeletal systems has recently begun with successful video of the interior bones of the pharynx and skull during fish respiratory pumping. The potential for investigation of model systems in genetics and medicine such as fly, zebrafish, and mouse is considerable, as the natural and normal mechanisms of heart, circulatory, digestive, and locomotor systems can be analyzed in new ways and compared to mutants or disease models that may be used to study human health concerns. Ultimately, the ability to clearly visualize internal functions in small animals will have a large impact in both biology and medicine.

Additional file 2. Passage of food bolus through the esophagus of the butterfly Pieris rapae. View (1.3 × 1.0 mm) is a lateral projection through the thorax of the butterfly (mass ~50 mg), with food moving from anterior (upper right) to posterior (lower left). The butterfly was feeding on a mixture of sugar water and iodine compound (Isovue). X-ray energy (33.2 keV) was tuned just above the K-edge for iodine, making the food bolus appear dark. This clip demonstrates how synchrotron imaging can be used to visualize internal food transport during feeding in small animals. Note that the esophagus is collapsed until the bolus passes through; the light structure running along the same diagonal axis is a tracheal tube. From this clip, it can be seen that the bolus is tapered at both ends and is transported at a speed of ~1.5 mm/s.

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Additional file 3. Movements of the foregut and gut contents of the carabid beetle Pterostichus stygicus. View (3.3 × 2.5 mm) is a dorsoventral projection through the pterothorax, posterior to the mesocoxae (circular structures seen at top of image). The beetle (mass ~210 mg) was fed macerated larva sprinkled with cadmium powder to increase x-ray (25 keV) absorption contrast; the gut boundaries and food movement can only be seen in places with cadmium powder. In this sequence, the crop (bag-like structure, center left) is squeezed anteriorly and then slowly settles back into its initial orientation. Mixing movements and peristalsis of the proventriculus (cylindrical structure, right side) can also be seen. Note that the proventriculus is closed, preventing food from moving posteriorly into the midgut. Dark bands on the left side of the video are artifacts from the incident beam.

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