Vessel segmentation algorithms are the critical components of circulatory blood vessel analysis systems. We present a survey of vessel extraction techniques and algorithms. We put the various vessel extraction approaches and techniques in perspective by means of a classification of the existing research. While we have mainly targeted the extraction of blood vessels, neurosvascular structure in particular, we have also reviewed some of the segmentation methods for the tubular objects that show similar characteristics to vessels. We have divided vessel segmentation algorithms and techniques into six main categories: (1) pattern recognition techniques, (2) model-based approaches, (3) tracking-based approaches, (4) artificial intelligence-based approaches, (5) neural network-based approaches, and (6) miscellaneous tube-like object detection approaches. Some of these categories are further divided into sub- categories. We have also created tables to compare the papers in each category against such criteria as dimensionality, input type, pre-processing, user interaction, and result type.

I would like to express my deep and sincere gratitude to my supervisor, Assoc. Prof. Leow Wee Kheng. His wide knowledge and his logical way of thinking have been a great value for me. His understanding and guidance have provided a good basis of my thesis work. His enthusiasm in research has encouraged me a lot. I also thank my colleagues: Ding Feng, Li hao, Song Zhiyuan, Zhang Xiaopeng, etc. I really appreciate the help they gave me in the past three years. I really enjoyed the pleasant stay with these brilliant people at Computer Vision Lab of School of Computing (SOC), NUS. Finally, I would like to thank my family for their endless love and support.

First of all, I would like to express my sincere gratitude to my supervisor, Assoc. Prof. Leow Wee Kheng, for his instructive advice and useful sugges-tions on my thesis. I am deeply grateful of his help in the completion of this thesis. I am also deeply indebted to all colleagues in Computer Vision Lab-oratory, National University of Singapore. I really enjoyed the pleasant stay with these brilliant people for the past 4 years. Special thanks should go to my friends who have put considerable time and effort into their comments on the draft. Finally, I am indebted to my parents for their continuous support and encouragement.