Elsevier

Pattern Recognition

Volume 42, Issue 6, June 2009, Pages 1017-1028
Pattern Recognition

A narrow band graph partitioning method for skin lesion segmentation

https://doi.org/10.1016/j.patcog.2008.09.006Get rights and content

Abstract

Accurate skin lesion segmentation is critical for automated early skin cancer detection and diagnosis. In this paper, we present a novel multi-modal skin lesion segmentation method based on region fusion and narrow band energy graph partitioning. The proposed method can handle challenging characteristics of skin lesions, such as topological changes, weak or false edges, and asymmetry. Extensive testing demonstrated that in this method complex contours are detected correctly while topological changes of evolving curves are managed naturally. The accuracy of the method was quantified using a lesion similarity measure and lesion segmentation error ratio, Our results were validated using a large set of epiluminescence microscopy (ELM) images acquired using cross-polarization ELM and side-transillumination ELM. Our findings demonstrate that the new method can achieve improved robustness and better overall performance compared to other state-of-the-art segmentation methods.

Introduction

Early detection of a cancerous skin lesion is crucial for successful treatment and cure. For example, malignant melanoma, the deadliest form of all skin cancers, has a cure rate of more than 95% if detected at an early stage [1]. To facilitate early detection, several methods have been developed for melanoma detection [2], [3], [4], [5]. In all these methods, delineating the skin lesion correctly is key to lesion analysis and accurate diagnosis.

Extracting the lesion area from the background is an essential step in all computer-aided melanoma detection systems and it has attracted continuous research efforts. Thresholding [6], [7], [8], [9], [10] and region growing are two simple yet widely used algorithms in the literature. They produce a satisfactory segmentation when skin lesions have clear boundaries. To account for noise and unclear boundaries, several clustering-based methods have been developed that demonstrated improved robustness [10], [11], [12]. Another family of popular segmentation methods is based on active contours (or snakes) [13], [14], [15], whereby a curve, defined based on partial differential PDEs evolves toward the local optimum, with respect to an objective function. Typical objective functions are chosen to identify the region of interest and are mostly edge-based or region-based. Chung [16] and Erkol [17] applied edge-based active contours to segment skin lesions. However, leakage occurs at the presence of weak edges and the method is sensitive to the initial conditions. Chan and Vese [18] proposed a region-based active contour method that models non-overlapping homogeneous regions with Gaussian distributions. The method performs well on images with two regions of distinct intensities; however, it presents under-segmentation problems if there are more than two regions of interest in the image. A hierarchical approach has also been proposed [19] to tackle this problem by splitting manually identified subregions.

Following our previous work on region-based object identification [20], [21], [22], we developed an active contour-based region-fusion framework. In this approach, a lesion is first segmented into small regions by imposing strict constraints on homogeneity and strong edges on the region-based snakes. Then, these regions are merged based on a centroid distance criterion and gradient information. To improve the performance and computational efficiency of segmentation, a narrow-band graph-partitioning (NBGP) method has been developed.

Experiments and comparison results on more than 200 skin lesion images demonstrate that the proposed algorithm produces segmentation results that are very close to the manual segmentation provided by specialists, even for those images with highly asymmetric lesions, weak and/or false edges, or strong hair and bubble artifacts.

The rest of the paper is organized as follows: in Section 2, we present a short review on skin lesion characteristics and image acquisition. In Section 3, we start with an introduction on the level set formulation of the region-based active contours, and then the derivation and development of the NBGP curve evolution for image segmentation is presented in detail. Section 4 describes the new region-fusion algorithm for skin lesion segmentation based on NBGP, whereas Section 5 presents experimental results on more than 200 images from three different imaging modalities. The results obtained with the new method are compared with results from our previously developed methods [10] and from active contours [18], [28] and validated against manual segmentation by expert dermatologists. Finally, Section 6 concludes this paper with a discussion on our findings and a summary of future work.

Section snippets

Characteristics of skin lesion images

In epiluminescence microscopy (ELM), a halogen light is projected into the object rendering the surface translucent [2]. There are two modes of ELM used in clinical applications, oil immersion [23], [24] and cross-polarization (XLM) [25]—the latter was developed to reduce light reflection from the epidermis. In side-transillumination ELM (TLM), a bright ring of light positioned around the periphery of a lesion is projected onto the center of the lesion at 45 forming a virtual light source at a

Level set formulation of region-based curve evolution

Given an image IΩ, the region-based active contour model [18] aims to find the curve C that minimizes the energy-based objective function:E(C)=λ1inside|I(x,y)-c1|2dxdy+λ2outside|I(x,y)-c2|2dxdy+μL(C)+vA(inside(C),where c1 is the average intensity inside C; c2 is the average intensity outside C; μ, v0; and λ1, λ2>0 are fixed weight defined based on a priori knowledge. L(C) and A(C) are two regulation terms. Following Chan's approach [18], we can fix the weights as λ1=λ2=1, μ>0, and v=

Skin lesion segmentation algorithm based on region fusion of narrow band graph partitioning

In this section, we describe in detail a two-stage framework that integrates region fusion and narrow band graph partitioning (NBGP) active contour. The resulting skin lesion segmentation algorithm can efficiently and effectively segment challenging images as outlined in Section 2.

Image acquisition

Our XLM and TLM images were acquired with a Nevoscope [35], [36] that uses a 5× optical lens (manufactured by Nikon, Japan). An Olympus C2500 digital camera was attached to this Nevoscope. Fifty one XLM images and 60 TLM images were used in our experiments. The image resolution is 1712×1368 pixels. A region of interests (ROI), identified in every image, was segmented, manually by dermatologists and automatically using our method. This step was performed on a 236×236 region obtained from a

Discussion

In our experiments, we observed that active contours were attracted by structures on healthy skin or noise near the boundary. This is because the band size (ebs in Algorithm 2) used to compute the energy function is very small (since we chose a small ebs for the level set function update to reduce computational cost) compared to the dimension of the image, and thus the method is almost an edge based scheme. We mitigated the effect of edge leaking by using the multiscale approach.

Our method

Acknolwedgments

The authors are grateful to Dr. William Stoeker, M.D. and Nizar Mullani for providing the ELM, XLM and TLM images and clinical expertise.

About the Author—XIAOJING YUAN received B.S. in electrical engineering from Hefei University of Technology in China in 1994, followed by a M.S. in computer engineering from University of Science and Technology of China in 1997 and another M.S. degree computer science in 2001 and a Ph.D. degree in Intelligent Systems in 2003, both from Tulane University. She joined the Engineering Technology Department of the University of Houston in 2004, where she has been actively involved in research areas

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    About the Author—XIAOJING YUAN received B.S. in electrical engineering from Hefei University of Technology in China in 1994, followed by a M.S. in computer engineering from University of Science and Technology of China in 1997 and another M.S. degree computer science in 2001 and a Ph.D. degree in Intelligent Systems in 2003, both from Tulane University. She joined the Engineering Technology Department of the University of Houston in 2004, where she has been actively involved in research areas such as biomedical imaging analysis, data mining, pattern recognition, and information technology in biomedical applications. She founded and served as director for “Intelligent Sensor Grid and Informatics Lab” in 2005. She has years’ experience in embedding intelligence into sensors and actuators to deal with uncertainties. She authored and co-authored more than 40 technical papers; has one patent and another one filed in 2008. She has been very active in professional organization such as IEEE and ISA; being reviewer for top-rank journals and conferences, and chairing and co-chairing conference sessions in “intelligent sensor network”.

    About the Author—NING SITU received a B.S. degree in Computer Science from Sun Yat-sen University in 2006. He has been a Ph.D. student at the Computer Science Department, University of Houston since 2006. His current research interests include pattern recognition, image segmentation, and statistical imaging analysis for cancer detection.

    About the Author—GEORGE ZOURIDAKIS received a Dr.Ing. degree in Electronics Engineering from the University of Rome “La Sapienza” in 1987, followed by an M.S. in Biomedical Engineering in 1990 and a Ph.D. in Electrical Engineering in 1994, both from the University of Houston. He has been on the faculty of The University of Texas-Houston Medical School from 1994 to 2001, where his clinical activities included Intraoperative Monitoring, Functional Brain Mapping, and Deep Brain Stimulation. He joined the University of Houston in 2001 and he is the Director of the Biomedical Imaging Lab. His current research interests are in the areas of Biomedical Imaging, Computational Biomedicine, Functional Brain Mapping, and Biosignal Analysis and Modeling. He is the main author of a book on Intraoperative Monitoring, CRC Press, 2001, and the Co-Editor-in-Chief of the “Handbook of Biomedical Technology and Devices”, CRC Press, 2003. He has developed courses, given lectures, organized sessions at national and international conferences on Medical Imaging and Brain Mapping, and has published more than 160 referred papers and abstracts. He is an Associate Editor of the IEEE Transactions on Biomedical Engineering, the Chair of the IEEE EMBS Houston Chapter, and he is also listed on Who's Who in America.

    This work has been supported in part by NSF Grant 521527, the Grants to Enhance and Advance Research program, and the Texas Learning and Computation Center at the University of Houston.

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