Segmenting Internal Brain Nuclei in MRI Brain Image
using Morphological Operators
D.Selvaraj
1
1
Research Scholar, Department of Electronics &
Communication Engg., Sathyabama University
Chennai, India
1
mails2selvaraj@yahoo.com
R.Dhanasekaran
2
2
Principal,
Syed Ammal Engineering College,
Ramanathapuram, India
2
rdhanasekar@yahoo.com
Abstract— We present a new technique for segmenting brain
nuclei from MRI brain images. Our method performs the
segmentation using a combination approach of thresholding with
morphological operators. The MRI brain image contains skull
and noisy background. The latter have to be removed for further
analysis. Elimination of any obstacles and noise from the image is
the primary function of the morphological operators. We use
simple morphological operators like dilation, erosion, opening
and closing to the binarized MRI brain image. The results of
skull stripped MR image with the use of disk shaped structuring
elements are presented in the paper. The proposed method has
been applied to a large number of MR images showing promising
results for various image qualities, encouraging for future.
Keywords— Image segmentation, Image processing, skull
stripping, Morphological operator, brain segmentation
I. INTRODUCTION
Magnetic resonance imaging (MRI) of the human brain is
the most common type of medical imaging used in the
medical diagnosis among a variety of imaging modadilities
such as computer tomography (CT), positron emission
tomography, ultrasound, mammography and radiography. So,
MR images are widely used not only for detecting tissue
deformities such as cancer and injuries but also for studying
brain pathology [8]. Also, many neurological diseases and
conditions alter the normal volume and regional distribution
of brain parenchyma (Gray and white matter), cerebrospinal
fluid. Such abnormalities are commonly related to the
conditions of hydrocephalus, cystic formation, brain atrophy
and tumour growth.
The basis for reliable measurement of the brain
parenchyma, CSF volume and shape is segmentation. Image
segmentation is to divide the image into disjoint homogenous
regions, where all the pixels in the same class must have some
common characteristics but the major problems that affect the
quality of MRI segmentation are noise, inhomogeneous pixel
intensity distribution and blunt boundaries in the medical MR
images caused by MR data acquisition process [2, 3, and 4].
These problems do make manual quantitative analysis of brain
imaging data a tedious and time consuming procedure, prone
to observer variability [2]. Due to the characteristics of brain
MRI, development of automated segmentation algorithms
require pre-processing which includes denoising, stripping of
skull.
This paper presents a method for skull segmentation using a
sequence of mathematical morphological operations: erosion
and dilation, and their compositions i.e., opening and closing.
The operators of morphological processing are particularly
useful for the analysis of binary images so that MRI images
need to be previously binarized. The background and brain
mask of the image are obtained by applying a combination
approach of thresholding with morphology.
The next section presents some basics on morphological
operations. Section 3 describes our methodology. Finally we
show some results in section 4 and draw some conclusions
and future work perspectives in section 5.
II.
MATHEMATICAL MORPHOLOGY CONCEPTS
Mathematical morphology is a non-linear image analysis
technique that extracts image objects information by
describing its geometrical structure in a formal way [7].
Mathematical morphology has been largely used in several
practical image processing and analysis problems. Here we
briefly review some mathematical morphology operators and
the corresponding operations used in this work.
Mathematical operators take two data as an input: an image
to be processed and a structuring element, which is a matrix
used for defining a neighbourhood shape and size [1]. By
choosing the shape and size of the element, we can influence
the morphological operations sensitivity to specific shapes
appearing in the processed image. The elementary shapes of
symmetrical structuring elements used in the following
processing are shown in Fig. 1.
The erosion of binary image I by structuring element S is
defined by the formula [1]:
I ⊗ S = {x,y : S
xy
⊆ I} (1)
The dilation of binary image I by structuring element S is
defined by the formula [1]:
I ⊕ S = {x,y : S
xy
∩ I≠∅} (2)
Let f: D⊂ R
n
→ R is an image function and g: G⊂ R
n
→
R is a structuring function. The two fundamental operations of
gray-scale morphology, erosion and dilation, are defined as:
Definition 1 (Dilation) The dilation of the function f(x) by
the structuring function g(x), (f
⊕
g)(x), is given by:
(f
⊕
g)(x) = max {f(z) + (g
x
)(z) : z ∈ D[g
x
]} (3)
Definition 2 (Erosion) The erosion of the function f(x) by
the structuring function g(x), (f Θ g) (x), is given by:
(f Θ g)(x) = min {f (z) − (g
x
) (z): z ∈ D[g
x
]} (4)
Where g
x
indicates the translation by x (g
x
) (z) = g(z − x),
and D[g
x
] denotes the domain of the translated structuring
function.
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