AVS 53rd International Symposium
    Ultra-Bright Light Sources Topical Conference Wednesday Sessions
       Session UB-WeM

Invited Paper UB-WeM5
X-ray Tomography: Imaging Biological Cells at Better than 50 nm Resolution

Wednesday, November 15, 2006, 9:20 am, Room 2001

Session: Ultra-Bright Light Sources Topical Conference
Presenter: C. Larabell, University of California at San Francisco and Lawrence Berkeley National Laboratory
Authors: C. Larabell, University of California at San Francisco and Lawrence Berkeley National Laboratory
M.A. Le Gros, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
X-ray tomography is an emerging new imaging technique that can examine whole, hydrated specimens with a spatial resolution approaching 15 nm. X-ray imaging at photon energies below the K- absorption edge of oxygen, referred to as the water window, exploits the strong natural contrast for organic material embedded in a mostly water matrix. With a transmission X-ray microscope using Fresnel zone plate optics, specimens up to 10 microns thick can be examined. Because of the low NA of X-ray lenses (NA=0.05), combined with the effect of polychromatic illumination and a wavelength dependant focal length, the effective depth of field is large (6-10 microns). The experiments presented here were performed at the Advanced Light Source using a full field transmission X-ray microscope, which employs a bend magnet X-ray source and zone plate condenser and objective lenses. The condenser zone plate acts as a monochromator and the X-ray images are recorded directly on a cooled, back-thinned 1024x1024 pixel CCD camera. Live cells were rapidly frozen by a blast of liquid nitrogen-cooled helium gas, and maintained at –140 degrees C by a steady flow of cold helium. We have used this imaging approach to obtain 3D reconstructions of cells in their native state at better than 50 nm isotropic resolution. These images reveal remarkable details of the nuclear and cytoplasmic architecture of fully hydrated whole cells. With X-ray imaging, the internal structures are not masked by ice and the resulting images are inherently of high contrast. In addition the proteins, lipids and nucleic acids are detected by the amount of carbon and nitrogen they contain, generating quantifiable data based on their absorption coefficient. Data collection is extremely fast, with a complete data set for tomographic reconstruction requiring less than 3 minutes. Consequently, X-ray tomography is an exciting new high-throughput approach for obtaining 3-D, quantifiable information from whole, hydrated cells