Abstract

In this paper, we present some experimental results on X-ray holography, holographic tomography, and a new holographic tomography method called pre-amplified holographic tomography is proposed.

Due to the shorter wavelength and the larger penetration depths, X-rays provide the potential of higher resolution in imaging techniques, and have the ability to image intact, living, hydrated cells without slicing, dehydration, chemical fixation or stain.

Recently, using X-ray source in National Synchrotron Radiation Laboratory in Hefei, we have successfully performed some soft X-ray holography experiments on biological specimen. The specimens used in the experiments was the garlic clove epidermis, we got their X-ray hologram, and then reconstructed them by computer program s, the feature of the cell walls, the nuclei and some cytoplasm were clearly resolved.

However, there still exist some problem s in realization of practical 3D microscopic imaging due to the near-unity refractive index of the matter. There is no X-ray optics having a sufficient high numerical aperture to achieve a depth resolution that is com parable to the transverse resolution. On the other hand, computer tomography needs a record of hundreds of views of the test object at different angles for high resolution. This is because the number of views required for a densely packed object is equal to the object radius divided by the desired depth resolution. Clearly, it is impractical for a radiation-sensitive biological specimen. Moreover, the X-ray diffraction effect makes projection data blur, this badly degrades the resolution of the reconstructed image.

In order to observe 3D structure of the biological specimens, McNulty proposed a new method for 3D imaging called “holographic tomography (HT)” in which several hologram s of the specimen are recorded from various illumination directions and combined in the reconstruction step. This perm its the specimens to be sampled over a wide range of spatial frequencies to improve the depth resolution. In NSRL, we performed soft X-ray holographic tomography experiments. The specimen was the spider filaments and PM M A as recording medium. By 3D CT reconstruction of the projection data, three dimensional density distribution of the specimen was obtained.

Also, we developed a new X-ray holographic tomography method called pre-amplified holographic tomography. The method perm its a digital real-time 3D reconstruction with high-resolution and a simple and com pact experimental setup as well.

© 2003 SPIE