Level-based MRI brain image classification

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-
6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 2, March – April (2013), © IAEME
403
LEVEL BASED NORMAL- ABNORMAL CLASSIFICATION OF MRI
BRAIN IMAGES
Sumesh M. S.1
, GopakumarC.2
, RejiRajan Varghese3
, Abraham Varghese4
1
(Computer Engineering, College of Engineering, Chengannur, Kerala, India,)
2
(Dept. of Electronics & Communication Engineering, College of Engineering, Chengannur,
India)
3
(Senior Resident, Radio diagnosis, Cochin Medical College, Cochin, India)
4
(Dept. of Computer science and Engg, Adi- SankaraInsitute of Engineering and Technology,
Kalady, India)
ABSTRACT
This work proposes a new concept for the normal- abnormal classification of MRI
brain images, a level based approach, and compare the result with the existing methods. The
existing works does not consider the anatomical structure of the brain slices for the
classification of MRI brain images. In the aspect of image processing, the anatomically
similarity of the brain slices can be treated as the similarity of brain slices in the viewing
aspect along with the actual anatomical structure. This work aimed to prove that the
consideration of the anatomical structure for the normal– abnormal classification will
improve the result of the classification.
The existing work shows that the feature vector, statistical features along with gray
level co-occurrence matrix (GLCM) features with support vector machine (SVM) classifier
produce better results than other methods. It uses statistical features along with GLCM
features as feature vector and SVM classifier. Related works in current literatures for the
normal/abnormal classification of MRI images does not consider the anatomical structure of
the brain slices. Because of the dissimilarity in the anatomical structure, it may produce
undesirable results. In this proposed work, the anatomical structure of the brain slices is
considered for the classification. To accompany this level based concept is introduced here.
In the level based concept, the brain slices are classified into four levels depending on the
similarity in the anatomical structure to implement the normal/abnormal classification at that
particular level.
INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING
& TECHNOLOGY (IJCET)
ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online)
Volume 4, Issue 2, March – April (2013), pp. 403-409
© IAEME: www.iaeme.com/ijcet.asp
Journal Impact Factor (2013): 6.1302 (Calculated by GISI)
www.jifactor.com
IJCET
© I A E M E

404
Keywords: Brain tumour, Level based classification, Magnetic resonance imaging, Medical
imaging, Support vector machine.
1. INTRODUCTION
Medical imaging is widely used for disease diagnosis and treatment evaluation.
Medical imaging techniques and analysis tools enable both doctors and radiologists to
identify and diagnose various disorders [1, 2]. The medical image data obtained from bio-
medical devices have important roles in disease diagnosis. MRI is a non-hazardous method
which detects signals emitted from normal and abnormal tissue, providing clear images of
most tumours [3, 4]. The radiologist or doctor can identify abnormal tissues by examining the
MRI slices based on the visual interpretation. The shortage of radiologists and the large
volume of MRI to be analysed make such readings laborious and cost expensive. Also the
manual classification by mere visual interpretation of the radiologists may cause bad results
due to vision problems. This leads to automated system to aid the doctors and radiologists in
the identification of abnormal brain slices.
To develop an accurate and sensitive automated system for the normal- abnormal
classification of MRI brain slices, it has to identify a good set of feature vectors that can be
substituted instead of the original image without losing its actual meaning and a good
classifier. The related works suggests several feature vectors and classifiers which are shown
in Table 1. This works shows that the combination of statistical features and GLCM features
[6, 7] along with SVM classifier [8, 9] provides better results than the other methods.
Table 1: Related woks for the classification of MRI brain slices
Pre-processing Feature Extraction Feature Reduction Classification
WAVELET
TRANSFORM [10, 1
],
HISTOGRAM
EQUALISATION
[15].
DWT [1, 8,14,16],
GLCM [11,12 ],
SLANTLET
TRANSFORM
[13].
PCA [14,15 ],
GA [16].
SVM [11,12,13,16],
ANN [14,15 ],
K-NN [11,14,15],
MLP [11].
The proposed method also use the combination of statistical features along with
GLCM features as feature vector and is used as the input to the SVM classifier. The related
works for the normal/abnormal classification of MRI images does not consider the
anatomical structure of the brain slices. Because of the dissimilarity in the anatomical
structure, it may produce undesirable results. So in this proposed work, the anatomical
structure of the brain slices is considered for the classification. In the aspect of image
processing, the anatomical similarity of the brain slices can be treated as the similarity of
brain slices in the viewing aspect along with the actual anatomical structure. To accompany
this level based concept is introduced here. In the level based concept, the brain slices are
classified into four levels depending on the similarity in the anatomical structure of the brain
slices [17]. That is, classify the brain slices into one of the four levels and implement the
normal/abnormal classification at that particular level.

405
2. METHODOLOGY
The proposed methodology for the normal- abnormal classification of MRI brain
slices has 2 steps, feature extraction and classification. Significant difference in tissue types,
observed in variety of texture measures of MRI, is used for this classification. The classifier
has 2 phases, training and testing phases. In training phase the statistical and GLCM texture
features of MRI brain slices along with its label and normality or abnormality details, are
given as input to the classifier. In testing phase, if the feature vector of a new slice is given as
input to the classifier, a well-trained classifier can accurately classify it according to the
parameters formed in the training phase. In the level based approach, the brain slices are
grouped into four classes according to the similarity of anatomical structure in visual aspect
of the image and the above texture extraction, training and testing processes are done at each
level independently.
2.1 FEATURE EXTRACTION
The purpose of feature extraction is to reduce the original data set by measuring
certain properties, or features, that distinguish one input pattern from another [18]. The
extracted features provide the characteristics of the input type to the classifier by considering
the description of the relevant properties of the image into a feature space. Most of the
tumour is heterogeneous tissues and the mean values of relaxation times are not at all
sufficient to characterize the heterogeneity of the different tumour types [3]. An alternative
approach, which is being investigated within the framework of this study, is to apply texture
analysis to the T2 FLAIR images to describe quantitatively the brightness and texture of the
images. Texture analysis covers a wide range of techniques based on first- and second order
image texture parameters. In the present study the statistical features based on image intensity
like mean & variance and features from gray level co-occurrence matrices (GLCMs) such as
entropy, contrast, energy, inverse difference moment and correlation [ 6,7 ,11] are used to
investigate the adequacy for the discrimination of normal and abnormal patient.
The gray level co- occurrence matrix (GLCM) calculates how often a pixel with gray
level value occurs either horizontally, vertically, or diagonally to adjacent pixels with the
value j, where i and j are the gray level values in the image. Haralick features [6, 7] based on
GLCM is a proven technique to analyse the object with irregular outlines [6, 7]. Haralick
introduced fourteen textural features from the GLCM and out of these fourteen features five
of the textural features are considered to be the most relevant. Those textural features are
Energy, Entropy, Contrast, Correlation and Inverse Difference Moment. Energy is also called
Angular Second Moment (ASM) where it measures textural uniformity [19]. If an image is
completely homogeneous, its energy will be maximum. Entropy is a measure, which is
inversely correlated to energy. It measures the disorder or randomness of an image [19].
Next, contrast is a measure of local gray level variation of an image. This parameter takes
low value for a smooth image and high value for a coarse image. On the other hand, inverse
difference moment is a measure that takes a high value for a low contrast image. Thus, the
parameter is more sensitive to the presence of the GLCM elements, which are nearer to the
symmetry line x (i, i) [19]. The last feature, correlation, measures the linear dependency
among neighbouring pixels. It gives a measure of abrupt pixel transitions in the image [20].

406
2.2.1 FEATURES USED
Statistical Features
Meanܺത ൌ
1
X ‫כ‬ Y
෍
୶
୧ୀଵ
෍ xሺi. jሻ
୷
୨ୀଵ
VarianceV ൌ
ଵ
ଡ଼‫כ‬ଢ଼
∑୶
୧ୀଵ ∑ ሺxሺi. jሻ
୷
୨ୀଵ െ xതሻ
GLCM Features
Entropyൌ െ ∑୒
୧ୀଵ ∑ ቀ
ሺ୔ሺ୧.୨ሻ
ୖ
ቁ୒
୨ୀଵ ݈‫݃݋‬ሺ
ሺ୔ሺ୧.୨ሻ
ୖ
ሻ Energyൌ െ ∑୒
୧ୀଵ ∑ ቀ
ሺ୔ሺ୧.୨ሻ
ୖ
ቁ
ଶ
୒
୨ୀଵ
Contrastൌ െ ∑୒
୧ୀଵ ∑ ሺi െ jሻ ቀ
ሺ୔ሺ୧.୨ሻ
ୖ
ቁ୒
୨ୀଵ
Correlationൌ
െ ∑୒
୧ୀଵ ∑
ቀ
౟ౠሺౌሺ౟.ౠሻ
౎
ቁିµ౮µ౯
σ౮σ౯
୒
୨ୀଵ
Inverse Difference Momentൌ ∑୒
୧ୀଵ ∑
ቀ
ሺౌሺ౟.ౠሻ
౎
ቁ
ଵାሺ୧ି୨ሻమ
, i ് j୒
୨ୀଵ
Where P(i, j) is the GLCM Matrix, R is the total number of pixel pairs used for the
calculation of GLCM and ߤ௫, ߤ௬, ߪ௫ and ߪ௬ are the mean and standard deviation values of
GLCM values accumulated in the x and y directions respectively.
2.2 CLASSIFICATION
The aim of classification is to group items that have similar feature values into
groups. Classifier achieves this by making a classification decision based on the value of the
linear combination of the features. SVM is a binary classification method that takes as input
labelled data from two classes and outputs a model file for classifying new unlabelled or
labelled data into one of two classes [1, 9,11].
2.3 SUPPORT VECTOR MACHINE
Support Vector Machine (SVM) is a binary classifier based supervised learning
theory, a recent advances in statistical learning theory. SVMs deliver state-of-the-art
performance in real-world applications such as text categorisation, hand-written character
recognition, image classification, bio sequences analysis, etc. The basis of this approach is
the projection of the low-dimensional training data in a higher dimensional feature space,
because in this higher dimensional feature space it is easier to separate the input data. This
projection is achieved by using kernel functions. So kernel functions provides the bridge
between non-linear to linear. Thus kernel function is used to map the low dimensional data
into the high dimensional feature space where data points are linearly separable. There are
many types of kernels are available for SVM and this work uses the following kernels:
Linear, Polynomial and radial basis function (RBF) [1, 9, 11].
3. RESULTS AND DISCUSSIONS
In the proposed work, T2 FLAIR weighted axial MRI Brain images as input data set.
Here two types of databases are used
1. Simulated Brain Database.
2. Brain Database of a Hospital

407
The input data involved 100 patients (50 abnormal and 50 normal). At first the
normal- abnormal classification is done without considering the anatomical structure. In this
stage of the work a set of 320 brain slices, 160 normal and 160 abnormal, are used. Out of
these two hundred images, 160 slices, 80 normal and 80 abnormal, are used for training and
remaining hundred are used for testing.
For level based normal- abnormal classification, the whole normal and abnormal
images are divided into 4 levels according to the similarity of the brain slices based on a
viewing aspect of the images. Thus each level contains a total of 160 images with 80 normal
and 80 abnormal. Out of these 160 images 80, 40 normal and 40 abnormal are used for
training phase and remaining 80 are used for testing phase. Results are summarised in Tables
3, 4 and 5.
Table 3: Classification using Polynomial Kernel
Level 1 Level 2 Level 3 Level 4 All Levels
TP 40 39 39 40 78
FN 0 1 1 0 2
TN 40 40 39 40 78
FP 0 0 1 0 2
Sensitivity (TPR) 1 0.975 0.975 1 0.975
(FPR) 0 0.025 0.025 0 0.025
Specificity (TNR) 1 1 0.975 1 0.975
(FNR) 0 0 0.025 0 0.025
Accuracy 1 0.9875 0.975 1 0.975
Table 4: Classification using RBF Kernel
TP 40 39 39 40 73
FN 0 1 1 0 7
TN 40 39 38 40 72
FP 0 1 2 0 8
Sensitivity (TPR) 1 0.975 0.975 1 0.9125
(FPR) 0 0.025 0.025 0 0.0875
Specificity (TNR) 1 0.975 0.95 1 0.9
(FNR) 0 0.025 0.05 0 0.1
Accuracy 1 0.975 0.9625 1 0.90625

408
Table 5: Classification using Linear Kernel
TP 40 40 39 39 72
FN 0 0 1 1 8
TN 40 38 39 40 73
FP 0 2 1 0 7
Sensitivity (TPR) 1 1 0.975 0.975 0.9
(FPR) 0 0 0.025 0.025 0.1
Specificity (TNR) 1 0.95 0.975 1 0.9125
(FNR) 0 0.05 0.025 0 0.0875
Accuracy 1 0.975 0.975 0.9875 0.90625
The results shows that level based normal-abnormal classification got better result than
non-level based classification. Also it shows that SVM with Polynomial kernel got better result
than those with RBF and Linear kernels.
4. CONCLUSION
This work is intended to prove that, the consideration of anatomical structure of the MRI
Brain slices, for the normal/abnormal classification, will help to get more accurate result. Level
based normal abnormal classification got better results than non- level based classification. Here
support vector machine with polynomial kernel of degree 3 shows better results than those with
linear or RBF kernel.
This work will surely help the radiologists and doctors in the identification of abnormal
brain slices. Magnetic Resonance Images are examined by radiologists based on visual
interpretation of the films to identify the presence of tumour abnormal tissue. The shortage of
radiologists and the large volume of MRI to be analysed make such readings labour intensive,
cost expensive and often inaccurate. The sensitivity of the human eye in interpreting large
numbers of images decreases with increasing number of cases, particularly when only a small
number of slices are affected. Hence this automated systems for analysis and classification of
such medical image will surely become an aid for both radiologists and doctors in tumour
analysis and detection. Also it will be the key step for the automated tumour detection system
development.
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