Semi-automated brain tumor and edema segmentation using MRI

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Abstract

Purpose:

Manual segmentation of brain tumors from magnetic resonance images is a challenging and time-consuming task. A semi-automated method has been developed for brain tumor and edema segmentation that will provide objective, reproducible segmentations that are close to the manual results. Additionally, the method segments non-enhancing brain tumor and edema from healthy tissues in magnetic resonance images.

Methods and materials:

In this study, a semi-automated method was developed for brain tumor and edema segmentation and volume measurement using magnetic resonance imaging (MRI). Some novel algorithms for tumor segmentation from MRI were integrated in this medical diagnosis system. We exploit a hybrid level set (HLS) segmentation method driven by region and boundary information simultaneously, region information serves as a propagation force which is robust and boundary information serves as a stopping functional which is accurate. Ten different patients with brain tumors of different size, shape and location were selected, a total of 246 axial tumor-containing slices obtained from 10 patients were used to evaluate the effectiveness of segmentation methods.

Results:

This method was applied to 10 non-enhancing brain tumors and satisfactory results were achieved. Two quantitative measures for tumor segmentation quality estimation, namely, correspondence ratio (CR) and percent matching (PM), were performed. For the segmentation of brain tumor, the volume total PM varies from 79.12 to 93.25% with the mean of 85.67 ± 4.38% while the volume total CR varies from 0.74 to 0.91 with the mean of 0.84 ± 0.07. For the segmentation of edema, the volume total PM varies from 72.86 to 87.29% with the mean of 79.54 ± 4.18% while the volume total CR varies from 0.69 to 0.85 with the mean of 0.79 ± 0.08. The HLS segmentation method perform better than the classical level sets (LS) segmentation method in PM and CR.

Conclusions:

The results of this research may have potential applications, both as a staging procedure and a method of evaluating tumor response during treatment, this method can be used as a clinical image analysis tool for doctors or radiologists.

Introduction

The task of manually segmenting brain tumors from magnetic resonance imaging (MRI) is generally time-consuming and difficult. In most settings, the task is performed by marking the tumor regions slice-by-slice, which limits the human rater's view and generates jaggy images as in Fig. 1. As a result, the segmented images are less than optimal. A semi-automated segmentation method is desirable because it reduces the load on the human raters and generates satisfactory segmentation results.

Tumor volume is a significant prognostic factor in the treatment of malignant tumors. Treatment protocols for malignant brain tumors generally call for removal through surgical procedures followed by irradiation of the tumor bed. The goal of three-dimensional (3-D) conformal radiation therapy is to irradiate the tumor volume while limiting damage to the surrounding normal tissues. Achieving this goal requires accurate determination of 3-D treatment volumes.

Although the technology for conformal radiation treatment planning has developed to a high level of accuracy, the definition of the gross tumor volume (GTV) in MRI is still based on time-intensive, highly subjective manual outlining [1], [2], [3]. Manual outlining is the type of process that should be an excellent candidate for automation through the development of a computerized segmentation system. At our institution, several techniques of MRI segmentation have been developed and evaluated specifically for brain tumors.

Tumor volume is a significant prognostic factor in the treatment of malignant tumors [4], [5], [6], [7]. Multivariate modeling has shown that tumor volume is a dominant covariate that overwhelms T stage, N stage and stage group [1], [8], [9]. The TNM classification system recognizes the importance of tumor volume. This article describes the classical level sets (LS) and hybrid level set (HLS) semi-automated methods for brain tumor segmentation and volume measurement. The results of this research may have potential applications, both as a staging procedure and a method of evaluating tumor response during treatment.

Section snippets

Tumor characteristics and assumptions

Brain tumors are difficult to segment because they have a wide range of appearance and effect on surrounding structures. Following are some of the general characteristics of brain tumors: (A) vary greatly in size and position, (B) vary greatly in the way they show up in MRI, (C) may have overlapping intensities with normal tissue, (D) may be space occupying (new tissue that moves normal structure) or infiltrating (changing properties of existing tissue), (E) may enhance fully, partially, or not

Phantom validation

Two hundred and forty six slices of the phantom were processed using those three methods mentioned above. The results are shown in Table 1. The errors of LS and HLS were 3.8–7.4 and 3.6–6.5%, respectively, whereas the error of manual tracing and labeling was 3.5–7.8%.

Brain tumor volume

A total of 246 axial tumor-containing slices obtained from 10 patients were evaluated using manual tracing and semi-automated segmentation methods. The results of tumor volume measurement are presented in Table 2, Table 3. There

Discussion

Segmentation is very important in this system. Some clinically or research available visualization systems had been developed by other researchers and among them, one for head and neck using CT [10], one for liver using CT [11] and two for brain using MRI [12], [13]. For these systems, the pathology segmentation or feature extraction might not be very complex because: (1) for CT, the image intensity distribution feature is simple and (2) for brain, the image content feature is simple. However,

Conclusions

Tumor volume is an important diagnostic indicator in treatment planning and results assessment for brain tumor, which has a high frequency in South China. The measurement of brain tumor volume could assist tumor staging and effective treatment planning.

Imaging plays a central role in the diagnosis and treatment planning of brain tumor. In this study, a semi-automated system for brain tumor volume measurements was developed based on MRI. Due to the image and anatomic features, a HLS method for

Acknowledgements

This work was partly supported by the Programme de Recherches Avancées de Coopérations Franco-Chinoises (PRA SI 03-03) and the Region Rhône-Alpes of France within the project “MIRA Recherche 2003”.

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    Citation Excerpt :

    Deep learning is another widely used supervised machine learning approach [17], but it typically requires a large amount of data for training purposes. There has been considerable research in brain tumor segmentation using conventional images such as T1-W, T2-W, and FLAIR [18,19], as well as combining them with other MRI modalities such as T1-W contrast enhanced images, diffusion-weighted images, and spectroscopy-based techniques [20–22]. Most of these studies have relied on supervised tumor segmentation methods where the ground truth for tumor subparts was delineated by neuroradiologists [3,8].

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