Tham khảo tài liệu 'advanced biomedical engineering part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fine Biomedical Imaging Using X-Ray Phase-Sensitive Technique 111 To obtain a quantitative phase map showing the spatial distribution of d6 a sub-fringe method such as Fourier transfer FT Takeda et al. 1982 and fringe scanning FS Bruning et al. 1974 is required. The former method is traditionally used in in vivo observations as it is used to detect phase shifts from only one interference pattern. The latter method which requires multiple interference images to calculate phase shift has a wide dynamic range of density and high spatial resolution compared to that of FT. Therefore this method is normally used for fine observations of static samples such as formalin-fixed biomedical soft tissues. To broaden the scope of X-ray interferometric imaging in biomedical applications such as in vivo observations a large-area field of view and suppression of the thermal disturbance caused by a sample s heat are indispensable. However the monolithic X-ray interferometer cannot cope with these requirements because the field of view is limited by the size of the silicon ingot from which the interferometer was cut and the sample cannot be set apart from the optical components of the interferometer due to the geometrical limitations. To overcome these limitations a two-crystal X-ray interferometer consisting of two silicon-crystal blocks each having two crystal wafers has been developed Fig. 2 b Becker Bonse 1974 . By dividing the crystal block of the interferometer into two blocks the field of view can be extended by four times or more. In addition the distance between the crystal blocks and the sample can be kept long the thermal influence such as deformation of the crystal wafers caused by the sample s heat is negligible and can be applied for the observation of living samples. On the other hand a relative rotation between the blocks changes the X-ray phase very sensitively and therefore rotational stabilization of the subnano-radian order is necessary for performing fine .
