micro-CT Laboratory
head: Katarzyna Janiszewska
e-mail: k.janiszewska@twarda.pan.pl
micro-CT Form (link)
Laboratory Regulations (link)
Micro-computed tomography (micro-CT) in Earth and Biological sciences
X-ray microtomography enables three-dimensional imaging of the morphology of even the smallest objects. In a non-destructive way, it provides data on the internal microstructure of samples, e.g. the arrangement of incremental layers in scales, the thickness and spatial relations of the layers forming the teeth of extinct organisms. Such data reveal information about the rate and pattern of growth of the examined structures, enabling further paleobiological interpretations. Microtomography replaces destructive preparation methods for fossils whose remains are dispersed in the rock. (e.g. skeletal plates, spicules, teeth). The spatial arrangement of individual elements can be preserved, allowing for drawing conclusions about their function and original position within the creature’s body. Similarly, in the case of today's organisms, micro-CT is used to study animals in which skeletal elements (sclerites, needles) are loosely dispersed in the soft body. Microtomography provides visualization of skeletal 3D architecture without the risk of damage during extraction.
Micro-CT is also an ideal tool for non-destructive studies of fragments of vertebrate skeletons. For instance, it is possible to reconstruct the internal structure of bones and the blood vessels system (including pathologies and tissue porosity). The possibility of creating digital models of even the smallest specimens allows for morphometric analyses and comparison of series of fossils (e.g. skulls, long bones, teeth).
Our micro-CT system
The Laboratory at the Institute is equipped with a Zeiss XRadia 200 microtomograph with an X-ray source with an adjustable voltage in the range of 20-90 keV. With sample sizes of several millimeters, the microtomograph can achieve very high contrast and image resolution <2 µm. The device allows for imaging of samples up to 5 cm in diameter and 1 kg in weight. Micro-CT is equipped with a source operating in relatively low energy ranges which gives a good contrast in imaging not only skeletons but also various types of soft tissues, including those in which staining is impossible. Studies of lizard embryos and snails have shown that the microtomograph is effective in examining biological samples. The design of the XRadia micro-CT system also enables imaging and separating structures of similar density, including non-destructive, virtual extraction of fossils preserved in amber (despite the similar, low density of the remains and the surrounding resin).
Micro-computed tomography technique
X-ray microtomography, like X-ray images, is based on the difference in the absorption of radiation by materials of different densities. The higher the density of the material, the greater the absorption. In addition to density, the absorption of radiation is also influenced by the thickness of the sample - i.e. the path that the radiation must travel through the sample. During scanning, the object is placed on a rotating table (360°). The radiation beam passes through the sample (some of it is absorbed) and hits a scintillator-detector, which "converts" X-ray radiation into visible light. In this way, information about the absorption of radiation by the object in a given position is recorded. Then, the sample is rotated by a given angle and another image is created. During scanning, hundreds of such two-dimensional X-ray absorption images - i.e. projections - are created. The next step is the process of the reconstruction of the interior of the sample as a superposition of those two-dimensional projections. Then we obtain a three-dimensional image of the sample and a series of cross-sections in any plane. The next step is visualization. Based on those micro-CT data, we can create a virtual model of the object and perform morphometric analysis. The model created in this way can be 3D printed. We can also process information about the sample's porosity, grain size, crack width, etc.
Sample preparation
The most important step of the sample preparation process is their immobilization - to prevent the sample from moving during scanning, it can be placed in a dedicated holder, glued to a SEM stub or placed in a plastic container. Additional stabilization can be provided by wrapping the sample in a low-density material (e.g. thin layers of paper tightly filling the space between the specimen and the walls of the test tube) or embedding it in agar. Samples can be scanned in air or immersed in liquid (to avoid drying/shrinking of the sample during long-term scanning). Samples for microCT should not be metal-sputtered. [examples in photos]