In this dissertation, my Ph.D. research during the past six years will be presented. My research mainly focused on design, fabrication and characterization of devices based on carbon nanotubes (CNT). Since the discovery of CNT in 1991, the research focus has gradually shifted from material synthesis and characterization to devices and applications. During early stages of my Ph.D. study, I worked on synthesizing CNT using laser ablation method, and fabricating CNT-AFM tips and magnetic wire MFM tips. During the second half of my Ph.D. study, my research focused more on design, fabrication, and testing the xray sources and imaging systems based on CNT, including both single-beam system (microCT) and multi-beam system (tomosysthesis). During the last two years, I worked on the project to develop a novel imaging system (Argus) using CNT x-ray source array for breast cancer detection. This is the first stationary digital breast tomosynthesis (DBT) imaging system in the world. My research result has shown great clinical potentials of these imaging systems using x-ray source based on CNTs. This dissertation is composed by five chapters. In chapter one, the physics behind xray and field emission theory will be reviewed. Chapter two covers discovery, property and synthesis of CNT. Methods to fabricate CNT emitters and their emission property will also be introduced there. Single and multi beam x-ray sources and applications will be discussed in chapter three. The design and characteristic test results are presented. The application includes micro-CT, tomosynthesis and multiplexing. Chapter four is dedicated to the Argus system, the first stationary digital breast tomosynthesis imaging system. At last, conclusion is given in chapter five.