Carbon Nanotube Based Stationary X-ray Tomosynthesis Scanner for Detection of Breast Cancer Guang Yang A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics and Astronomy. Chapel Hill 2008 Approved by Advisor: Professor Otto Zhou Committee: Professor Thomas B. Clegg Committee: Professor David S. Lalush Committee: Professor Jianping Lu Committee: Professor Lu-Chang Qin © 2008 Guang Yang ALL RIGHTS RESERVED ii Abstract Guang Yang Carbon Nanotube Based Stationary X-ray Tomosynthesis Scanner for Detection of Breast Cancer (Under the direction of Professor Otto Zhou) 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 x- ray 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. iii This dissertation is composed by five chapters. In chapter one, the physics behind x- ray 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. iv To my parents Xiulan, and Hongbin v Acknowledgements I am indebted to many people with whom I had the honor of working and without whom the completion of this dissertation would have been much more difficult. Dr. Otto Zhou’s expertise and encouragement are always dependable during my entire doctoral study. I must also acknowledge to all of my committee members for their advice and guidance: Drs. Jianping Lu, David Lalush, Lu-Chang Qin, and Thomas Clegg. I want to thank all my colleagues I have been working with. Dr. Jian Zhang passed me hands-on experience in system design and test. Ramya Rajaram has taken charge of the imaging reconstruction of all the systems I have worked on. Dr. Guohua Cao, Matthew McIntosh, Shabana Sultana, Tuyen Phan, Zhijun Liu are also key contributors for the tomosynthesis project. Colleagues I have been working with for other projects include Dr. Jie Tang, Dr. Huaizhi Geng, Dr. Lei An, Dr. Peng Wang, Dr. Yueh Lee, Rui Peng, David Bordelon, Xiomara Calderon, Christy Redmon, Dr. Yuan Cheng, Dr. Bo Gao, Qi Qiu. It has been a great honor for me to work with them during the past six years. At last, I recognize that this research would not have been possible without the support from the following organizations: National Cancer Institute, NASA, Xintek, and the Office of Naval Research. vi Table of contents Chapter 1: Introduction and Background ....................................................................... 1 1.1 Discovery of X-ray ................................................................................................... 1 1.2 Basics of X-ray Radiation......................................................................................... 3 1.2.1 The Bremsstrahlung Radiation ......................................................................... 5 1.2.2 The Characteristic Radiation............................................................................. 6 1.3 The Production of X-ray........................................................................................... 7 1.3.1 The Conventional X-ray Tubes......................................................................... 8 1.3.2 The Heel Effect................................................................................................. 9 1.3.3 The Effective Focal Spot Size......................................................................... 10 1.3.4 The Low Efficiency of X-ray Production....................................................... 11 1.3.5 Transmission Targets...................................................................................... 12 1.3.6 Synchrotron X-ray Source .............................................................................. 13 1.4 The Interaction of X-ray with Matter...................................................................... 15 1.4.1 The Photoelectric Effect ................................................................................. 15 1.4.2 The Compton Scattering................................................................................. 16 1.5 The Attenuation Coefficients.................................................................................. 17 1.6 The Detection of X-ray........................................................................................... 21 1.7 X-ray Source Based on CNT .................................................................................. 25 vii Chapter 2: CNT and Field Emission Electron Source.................................................. 26 2.1 Basics about CNT ................................................................................................... 26 2.1.1 Discovery of CNT........................................................................................... 26 2.1.2 The Structure of CNT ..................................................................................... 27 2.1.3 Properties of CNT........................................................................................... 30 2.1.4 Applications of CNTs..................................................................................... 32 2.2 Field Emission Theory............................................................................................ 34 2.2.1 Electron Emission from a Metal Surface........................................................ 35 2.2.2 Field Emission ................................................................................................ 38 2.2.3 Thermionic and Intermediate Emission.......................................................... 41 2.2.4 Ideal Field Emitters......................................................................................... 43 2.3 Point Electron Source Based on CNT..................................................................... 46 2.3.1 Cathode Fabrication........................................................................................ 47 2.3.2 Field Emission Characteristics........................................................................ 51 Chapter 3: FE X-ray Source and Application ............................................................... 55 3.1 Area Electron Source Based on CNT ..................................................................... 55 3.1.1 Area CNT Cathode Fabrication...................................................................... 56 3.1.2 CNT Cathode on Silicon Wafer...................................................................... 57 3.1.3 Parallel Fabrication......................................................................................... 60 3.2 Single Beam X-ray Source and Application........................................................... 62 3.2.1 First X-ray Source and Imaging System......................................................... 62 3.2.2 Micro Computed Tomography Based on Micro-focus Tube.......................... 63 viii 3.3 Multi-Beam Field Emission X-ray Source ............................................................. 69 3.3.1 MBFEX Design .............................................................................................. 71 3.3.2 MBFEX System Performance......................................................................... 72 3.3.3 Imaging Test ................................................................................................... 75 3.4 Multiplexing Using MBFEX .................................................................................. 77 3.4.1 Orthogonal Frequency Division Multiplexing (OFDM)................................. 78 3.4.2 Imaging Results .............................................................................................. 82 3.4.3 Further Discussion.......................................................................................... 84 Chapter 4: Digital Breast Tomosynthesis Using Multi-Beam X-ray Source Array... 86 4.1 Background............................................................................................................. 86 4.1.1 Screen-Film Mammography........................................................................... 86 4.1.2