title: Advantages of intermediate X-ray energies in Zernike phase contrast X-ray microscopy.
abstract: Understanding the hierarchical organizations of molecules and organelles within the interior of large eukaryotic cells is a challenge of fundamental interest in cell biology. Light microscopy is a powerful tool for observations of the dynamics of live cells, its resolution attainable is limited and insufficient. While electron microscopy can produce images with astonishing resolution and clarity of ultra-thin (<1 μm thick) sections of biological specimens, many questions involve the three-dimensional organization of a cell or the interconnectivity of cells. X-ray microscopy offers superior imaging resolution compared to light microscopy, and unique capability of nondestructive three-dimensional imaging of hydrated unstained biological cells, complementary to existing light and electron microscopy. Until now, X-ray microscopes operating in the "water window" energy range between carbon and oxygen k-shell absorption edges have produced outstanding 3D images of cryo-preserved cells. The relatively low X-ray energy (<540 eV) of the water window imposes two important limitations: limited penetration (<10 μm) not suitable for imaging larger cells or tissues, and small depth of focus (DoF) for high resolution 3D imaging (e.g., ~1 μm DoF for 20 nm resolution). An X-ray microscope operating at intermediate energy around 2.5 keV using Zernike phase contrast can overcome the above limitations and reduces radiation dose to the specimen. Using a hydrated model cell with an average chemical composition reported in literature, we calculated the image contrast and the radiation dose for absorption and Zernike phase contrast, respectively. The results show that an X-ray microscope operating at ~2.5 keV using Zernike phase contrast offers substantial advantages in terms of specimen size, radiation dose and depth-of-focus.
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230026, China.
authors.forename: Zhili
authors.initials: Z
authors.lastname: Wang
authors.forename: Kun
authors.initials: K
authors.lastname: Gao
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
authors.forename: Youli
authors.initials: Y
authors.lastname: Hong
authors.forename: Xin
authors.initials: X
authors.lastname: Ge
authors.forename: Dajiang
authors.initials: D
authors.lastname: Wang
authors.forename: Zhiyun
authors.initials: Z
authors.lastname: Pan
authors.forename: Peiping
authors.initials: P
authors.lastname: Zhu
authors.forename: Wenbing
authors.initials: W
authors.lastname: Yun
authors.forename: Chris
authors.initials: C
authors.lastname: Jacobsen
authors.forename: Ziyu
authors.initials: Z
authors.lastname: Wu
mesh_terms: D021621:Imaging, Three-Dimensional / Q000379:methods*; D008858:Microscopy, Phase-Contrast / Q000379:methods*; D008962:Models, Theoretical; D011829:Radiation Dosage; D014867:Water; D014965:X-Rays
chemical_list: D014867:Water