Foremost, I would like to express my deep appreciation to my supervisor, Prof. Xue-Cheng Tai for his wise guidance and encouraging engagement in supervising my PhD study these four years. He had the phone interview with me, introduced me to the interesting imaging field, led me to learn more and deeper, supported me to investigate the beauty of mathematics. I really appreciate all his help and suggestions as a supervisor, family and friend. I also want to thank for his generous financial supports that gave me the chance to travel for conference. I am happy to live and study at Nanyang Technological University. I also enjoy the lively and productive environment of the School of Physical and Mathematical Sciences. In particular, I appreciate the management and leadership of Prof. San