MPhil Thesis Defence


"Segmentation of vessels using weighted local variances and an active
contour model"

By

Mr. Wai Kong Law


Abstract

Vessel segmentation plays an important role in diagnosing patients with
vascular problems. Vascular segmentation refers to the distinguishing of
vasculature from background regions in images. Performing segmentation of
vasculature with blurry and low contrast boundaries in noisy images is a
challenging problem. The main reason is that low contrast and noise
reduces recognizibility of vasculature. It is observed that traditional
operations, like low pass filtering, is not suitable in this situation.
This is because such operations annhilate narrow objects such as vascular
structures.

This thesis presents a novel approach on segmenting blood vessels using
weighted local variances and an active contour model. In this work, object
boundary orientation is estimated locally based on the calculation of
weighted local variance. Such estimation is less sensitive to noise
compared with other common approaches. Edge clearness is measured by the
relation of weighted local variances obtained along different
orientations. The formulation of the proposed method is independent of the
edge intensity contrast and capable of locating weak boundaries.

Integrating the orientation and clearness of edges, an active contour
model is employed to align contours that match the contour tangent
direction and edge orientation. Contours of the active contour model is
based on a level set framework, which can handle the merging or splitting
of contours naturally. With such ability, segmenting vessels using the
proposed method can either be fully automatic, or involve manual
interactions in order to permit users to specify the target vessels.

The proposed method is validated by three synthetic images and nine
clinical cases. It is experimentally shown that our method is suitable for
dealing with noisy images which consist of structures having blurry and
low contrast boundaries, such as blood vessels.


Date:				Friday, 25 August 2006

Time:				2:00p.m.-4:00p.m.

Venue:				Room 4480
				Lifts 25-26

Committee Members:		Dr. Albert Chung (Supervisor)
				Dr. Dit-Yan Yeung (Chairperson)
				Dr. Philip Fu


**** ALL are Welcome ****