Research Of Quality Assessment And Image Processing Of In-line X-ray Phase-contrast Imaging

From the mid 90's of the last century, phase-contrast imaging has been introduced into the field of x-ray imaging, and has drawn much attention because of its high resolution and signal-to-noise ratio in imaging materials made up of light elements. For 10 years'time, this technique has gradually become mature, especially the in-line method, which is already in elementary business application. Because of the technique's perspective in application in medical science, biology and material science, a deep study into its theory and application has great value.I first examine the existing theory of in-line phase-contrast imaging, getting the formulas for imaging of both pure phase objects and normal objects, under different illuminations. Based on this, the imaging model of phase-propagation and absorbing-attenuation are brought forward, which doesn't rely on the assumption of pure phase object, and clearly shows the two main mechanisms that affect the imaging: the recording of the Laplacian of phase distribution, and the attenuation of x-ray intensity.Next, from both the aspect of acquired images and imaging parameters, imaging quality assessment methods are studied. Commonly used index for quality assessment are introduced; a method to quantitatively evaluate the weight of phase information and absorption information in images is brought forward, utilizing the Edge Visibility; applying the imaging model of phase-propagation and absorbing-attenuation, I show that Area Contrast is mainly determined by projected linear attenuation coefficient; assessments of the acquired images are made, and the appropriate tube voltage and current for good imaging quality as well as short exposure time are found out.Finally, considering that this technique is stepping out of laboratories and into markets, I comprehensively study image processing methods of the technique, including grey-level adjustment, noise reduction from both light sources and detectors, image mosaic, the flatting of pure noise area and phase retrieval methods. They are applied to experimental images, having greatly enhanced visual effects and signal-to-noise ratio and produced 10M-pixels-images of high spatial resolution.