ZPC employs a phase modulator in the back focal plane of the microscope objective that acts only on the wave scattered (or unscattered) by the sample. Zernike's phase contrast (ZPC) 6 is one of the most standard methods used in microscopy. The phase shift can be converted to a detectable intensity change by a phase contrast method. The GI system exhibits twin image artifacts that need to be resolved for practical applications of the technique. The quantitativeness of the GI system with the phase-stepping measurement was also demonstrated over the ZPC system, which generates halo and shade-off artifacts. Although the sensitivity depends on the sample size, the signal-to-noise ratio of polystyrene spheres with a few microns in diameter was used for sensitivity comparison, showing the superior sensitivity of the GI system to that of the ZPC system. By the Fourier analysis of images of a logarithmic ruler pattern, the spatial resolution was found to be identical between the two systems. The ZPC system and the GI system are compared in terms of detectability of phase objects. The ZPC system generates a phase contrast image by using a phase plate and a corresponding condenser device. The GI system is based on a Lau interferometer consisting of an absorption grating and a π/2 phase grating, which extracts a magnified phase shift map of a sample via a phase-stepping measurement. The GI and ZPC systems are switchable, and their performances of phase information extraction have been compared. A grating interferometer (GI) system has been installed in an X-ray microscope equipped with a Zernike phase contrast (ZPC) system and a Cu rotating anode X-ray source.
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