The National Center for X-ray Tomography (NCXT) is a full-service user facility for biomedical imaging and research. NCXT Users, whether working on site or remotely, have access to specialized microscopes and imaging techniques, in particular soft x-ray tomography (SXT) and super-resolution cryogenic fluorescence tomography. SXT is the only imaging technique that can provide structural measurements of unlabeled, whole eukaryotic cells up to 20 µm in diameter at 30-60 nm resolution. SXT is a non-invasive, 3D imaging technique that can measure volumes, surfaces, interfaces, membranes, and organelle connectivity within an intact cell. With SXT, the specimen is illuminated with photons at energies from within the X-ray water window (i.e., photon energies between the K-absorption edges of carbon at 282 eV and oxygen at 533 eV). As photons in this energy range pass through the specimen, they are absorbed an order of magnitude more strongly by carbon- and nitrogen-containing compounds than by water. For this reason, cell structures dense in carbon, for example membranes or lipid bodies, absorb the X-rays approximately an order of magnitude more than surrounding water, while highly solvated regions such as endosomes are of lower contrast. Since the absorption adheres to Beer-Lambert’s law, image contrast is linear with respect to the species and density of biomolecules in each voxel. As a result, each voxel has an associated Linear Absorption Coefficient (LAC). The greater the concentration of biomolecules in a voxel, the higher the LAC value; conversely, voxels with fewer organic molecules have lower LAC values. Since SXT generates a tomographic image of a whole cell in less than 10 minutes, investigators are able to obtain statistically significant information. In addition, the LAC values yield quantitative information that has enabled a variety of experiments regarding molecular movements and molecular organization in organelles.
Our Research Capabilities
Optimizing software and hardware for users.
NCXT staff training a new user to collect data on the x-ray microscope
Training new user to use the robotic cryo-freezing and storage apparatus
New users at the x-ray microscope.