Objective: The overall objective is to develop a new diagnostic x-ray imaging technique that acquires both attenuation- and phase-images simultaneously. Challenges: Pioneer research performed with the 3rd generation synchrotron x-ray sources with high spatial coherence has proved that phase-contrast can significantly improve the sensitivity of diagnostic imaging. However, the costs, size and availability of a synchrotron x-ray source do not fit to clinical applications. A novel field-emission x-ray source with high spatial coherence and a dual-detector system is therefore proposed. Methods: Cutting-edge nanotechnology will be applied to fabricate a super tip for the electron gun of the x-ray source. The tip is made of the nanocrystal material, whose zero-dimensional electronic structure and non-Ohmic hopping conduction will allow a current density as high as 2 x 107 A/cm2 without burning out. By using the electron beam induced deposition the super tip will be integrated with a miniature Orbitron vacuum pump and an ion mirror to avoid contamination and the ion bombardment of the electron emitter. The anticipated end product is an x-ray source with a small focal spot (less than 0.025 ram), and at the same time, a high tube current (greater than 25mA), thus providing a bright source with high spatial coherence. With such a new source, a dual detector system will be developed to acquire both attenuation- and phase-contrast images based on the in-line holography principle, and an algorithm will be developed to reconstruct a phase-image from these two images. Comprehensive measurements will be conducted to characterize the performance of the proposed system under clinical conditions. That includes objective measurements of resolution, contrast and quantum efficiency, and observer-based subjective measurements. Clinical benefits: The proposed technique has the following clinically friendly features: (1) The source-to-detector distance of the system is no more than 1 m; this is achieved by using the proposed field emission source with high spatial coherence; (2) Two images, a phase-contrast and an attenuation image are acquired at one exposure at the conventional dose level to enable phase-retrieval. (3) The reconstructed phase-image provides a significantly improved tissue-lesion contrast as compared with conventional x-ray images, because the phase differences between tissue and lesion are hundreds times larger than conventional attenuation contrast. Summary: By combining the nano-technology-based field emission source, a dual-detector system, and a phase-reconstruction algorithm, the proposed research would create a new sensitive way in diagnostic x-ray imaging.

R01EB002604

2003-09-01

2007-07-31