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 
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 .
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.
Size: 860KB Download file |
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.
Size: 9.3MB Download file |