A microscope using Zernike’s phase contrast method and a hard x-ray Gabor hologram

Kiyofumi Matsuda,Akihisa Takeuchi,Shakil Rehman,Juan C Aguilar,Yoshio Suzuki,Masaki Misawa,Ilpo Niskanen,Masato Yasumoto

doi:10.1186/s41476-016-0027-3

Abstract

In hard X-ray phase imaging using interferometry, the spatial resolution is limited by the pixel size of digital sensors, inhibiting its use in magnifying observation of a sample. To solve this problem, we describe a digital phase contrast microscope that uses Zernike’s phase contrast method with a hard X-ray Gabor holography associated with numerical processing and spatial frequency domain filtering techniques. The hologram is reconstructed by a collimated beam in a computer. The hologram intensity distributions itself become the reconstructed wavefronts. For this transformation, the Rayleigh- Sommerfeld diffraction formula is used. The hard X-ray wavelength 0.1259 nm (an energy of 9.85 keV) was employed at the SPring-8 facility. We succeeded in obtaining high-resolution images by a CCD sensor with a pixel size of 3.14 μm, even while bound by the need to satisfy the sampling theorem and by the CCD pixel size. The test samples used here were polystyrene beads of 8 μm, and human HeLa cells. We thus proved that the resolution 0.951 μm smaller than the pixel size of CCD (3.14 μm) was achieved by the proposed reconstruction techniques and coherent image processing in the computer, suggesting even higher resolutions by adopting greater numerical apertures.

Highlights

In hard X-ray phase imaging using interferometry, the spatial resolution is limited by the pixel size of digital sensors, inhibiting its use in magnifying observation of a sample
The hard X-ray Gabor hologram is reconstructed by a collimated beam parallel to the axis, so the hologram intensity distribution is multiplied by unity
Samples of polystyrene sphere beads with 8-μm diameter and dried HeLa cells are used as phase objects; in the used hologram, the aperture diameter magnitude can be considered to produce a wavefront originating from a point source

Summary

Introduction

In hard X-ray phase imaging using interferometry, the spatial resolution is limited by the pixel size of digital sensors, inhibiting its use in magnifying observation of a sample. Hard X-rays allow visualization of objects at high resolutions because of their inherent smaller wavelengths [1]; they are highly desirable in various application areas, including biological studies [2, 3]. Phase imaging using hard X-ray makes it possible to visualize phase objects using interferometry or holography. Computed tomography using an X-ray interferometer [5] and observation of biological soft tissues using interferometry [6] have been used for phase imaging. Given that samples are imaged on a digital sensor, the spatial resolution in such methods is limited, because of the pixel size

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Conclusion