Interstitial lung disease is one of the main treat to the health .Computer Tomography is used for assessment of interstitial lung disease .But sometimes it is difficult to visually interpret because of the crossing and overlapping of the vessels in the CT. There a vessel segmentation techniques is used for detecting lung disease Different techniques is available for lung segmentation for diagnosing lung disease. Vessel tree extraction is one of the challenging technique for several years and it is under open research. Automatic segmentation of vessel tree is one of the most important requirement for Computer Aided Diagnosis(CAD).In this paper we investigate lung vessel extraction and enhancement technique and present the capabilities of most important algorithms concerning lung vessel segmentation.