Shrinkage of the hippocampus is a primary biomarker for Alzheimer’s disease and can be measured through accurate segmentation of brain MR images. The paper will describe the problem of initialisation of a 3D level set algorithm for hippocampus segmentation that must cope with the some challenging characteristics, such as small size, wide range of intensities, narrow width, and shape variation. In addition, MR images require bias correction, to account for additional inhomogeneity associated with the scanner technology. Due to these inhomogeneities, using a single initialisation seed region inside the hippocampus is prone to failure. Alternative initialisation strategies are explored, such as using multiple initialisations in different sections (such as the head, body and tail) of the hippocampus. The Dice metric is used to validate our segmentation results with respect to ground truth for a dataset of 25 MR images. Experimental results indicate significant improvement in segmentation performance using the multiple initialisations techniques, yielding more accurate segmentation results for the hippocampus.
Thoracic Aortic Aneurysm (TAA) is a localized swelling of the thoracic aorta. The progressive growth of an aneurysm
may eventually cause a rupture if not diagnosed or treated. This necessitates the need for an accurate measurement which
in turn calls for the accurate segmentation of the aneurysm regions. Computer Aided Detection (CAD) is a tool to
automatically detect and segment the TAA in the Computer tomography angiography (CTA) images. The fundamental
major step of developing such a system is to develop a robust method for the detection of main vessel and measuring its
diameters. In this paper we propose a novel adaptive method to simultaneously segment the thoracic aorta and to
indentify its center line. For this purpose, an adaptive parametric 3D region growing is proposed in which its seed will be
automatically selected through the detection of the celiac artery and the parameters of the method will be re-estimated
while the region is growing thorough the aorta. At each phase of region growing the initial center line of aorta will also
be identified and modified through the process. Thus the proposed method simultaneously detect aorta and identify its
centerline. The method has been applied on CT images from 20 patients with good agreement with the visual assessment
by two radiologists.
A computerized image analysis technology suffers from imperfection, imprecision and vagueness of the input data and
its propagation in all individual components of the technology including image enhancement, segmentation and pattern
recognition. Furthermore, a Computerized Medical Image Analysis System (CMIAS) such as computer aided detection
(CAD) technology deals with another source of uncertainty that is inherent in image-based practice of medicine. While
there are several technology-oriented studies reported in developing CAD applications, no attempt has been made to
address, model and integrate these types of uncertainty in the design of the system components, even though uncertainty
issues directly affect the performance and its accuracy. In this paper, the main uncertainty paradigms associated with
CAD technologies are addressed. The influence of the vagueness and imprecision in the classification of the CAD, as a
second reader, on the validity of ROC analysis results is defined. In order to tackle the problem of uncertainty in the
classification design of the CAD, two fuzzy methods are applied and evaluated for a lung nodule CAD application.
Type-1 fuzzy logic system (T1FLS) and an extension of it, interval type-2 fuzzy logic system (IT2FLS) are employed as
methods with high potential for managing uncertainty issues. The novelty of the proposed classification methods is to
address and handle all sources of uncertainty associated with a CAD system. The results reveal that IT2FLS is superior
to T1FLS for tackling all sources of uncertainty and significantly, the problem of inter and intra operator observer
variability.
This paper deploys a wavelet based scale-space approach to extract the boundary of the object of interest in medical CT images. The classical approach of the active contour models consists of starting with an initial contour, to deform it under the action of some forces attracting the contour towards the edges by means of a set of forces. The mathematical model involves in the minimisation of an objective function called energy functional, which depends on the geometry of the contour as well as of the image characteristics. Various strategies could be used for the formulation of the energy functional and its optimisation. In this study, a wavelet based scale-space approach has been adopted. The coarsest scale is able to enlarge the capture region surrounding an object and avoids the trapping of contour into weak edges. The finer scales are used to refine the contour as close as possible to the boundary of the object. An adaptive scale coefficient for the balloon energy has been introduced. Four levels of resolution have been applied in order to get reproducibility of the contour despite poor different initialisations. The scheme has been applied to segment the regions of interest in CT lung and colon images. The result has been shown to be accurate and reproducible for the cases containing fat, holes and other small high intensity objects inside lung nodules as well as colon polyps.
Automatic polyp detection is a challenging task as polyps come in different sizes and shape. The detection generally consists of colon segmentation, identification of suspected polyps and classification. Classification involves discriminating polyps from among many suspected regions based on a number of features extracted from the detected regions. This paper presents the work on the first two stages of the detection. For the colon segmentation, the fuzzy connectivity region growing technique is used while for the identification of suspected polyps concave region searching is applied. A rule-based filtering based on 3D volumetric features is used to reduce a large number of non-polyp structures (false positives). The method is fast, robust and validated with a number of high-resolution colon datasets.
Computer assisted methods for the detection of pulmonary nodules have become more important as the resolution of CT scanners has increased and as more accurate and reproducible detections are needed. In this paper we describe the results of a CAD system for the detection of lung nodules and compare them against the interpretations of three independent radiologists.
The accurate identification and delineation of the Lungs structure from computerized tomography images would be extremely helpful in the clinical understanding of a patient's condition. The ability to view the Lungs in three dimensions and to zoom in on problem areas would also be of great assistance to a clinician in the decision making process. This paper focuses on the development of a method for the automatic segmentation and three dimensional visualization of the Lungs structure.
Neurosurgery is an extremely specialized area of medical practice, requiring many years of training. It has been suggested that virtual reality models of the complex structures within the brain may aid in the training of neurosurgeons as well as playing an important role in the preparation for surgery. This paper focuses on the application of a probabilistic neural network to the automatic segmentation of the ventricles from magnetic resonance images of the brain, and their three dimensional visualization.
Images are statistical in nature due to random changes and noise,therefore it is sometimes an advantage to treat image functions as a realization of a stochastic process. An advantage of stochastic random field models is that they need only a few parameters to describe a region or texture. In this paper textural images are modeled as a realization of Markov Random Fields such as binomial and autoregressive Markov random fields. Parameters of each model are estimated and considered as features of the textural images. The extracted features are incorporated in either a probabilistic neural network (PNN) or a deterministic back propagation neural networks for the purpose of classification and differentiation between various textural images. The PNN and the learning algorithm are discussed in this paper in details. To train back propagation neural network, a hybrid training algorithm is proposed. This hybrid algorithm takes advantage of both simulated annealing and deterministic learning algorithms. The former algorithm is more reliable since it locates a more likely global minimum, but it is slow. The latter algorithm is fast but less reliable, and it can converge to a local minimum. There are many practical uses for the above proposed textural analysis tool such as remote sensing, mineralogical analysis, and medical image processing. In this paper, successful applications of the present stochastic model to synthetic texture images and MRI tongue and brain images are described.
This paper describes the development of a novel automated and efficient vision system to obtain velocity and concentration measurement within a porous medium. An aqueous fluid lace with a fluorescent dye to microspheres flows through a transparent, refractive-index-matched column packed with transparent crystals. For illumination purposes, a planar sheet of laser passes through the column as a CCD camera records all the laser illuminated planes. Detailed microscopic velocity and concentration fields have been computed within a 3D volume of the column. For measuring velocities, while the aqueous fluid, laced with fluorescent microspheres, flows through the transparent medium, a CCD camera records the motions of the fluorescing particles by a video cassette recorder. The recorded images are acquired automatically frame by frame and transferred to the computer for processing, by using a frame grabber an written relevant algorithms through an RS-232 interface. Since the grabbed image is poor in this stage, some preprocessings are used to enhance particles within images. Finally, these enhanced particles are monitored to calculate velocity vectors in the plane of the beam. For concentration measurements, while the aqueous fluid, laced with a fluorescent organic dye, flows through the transparent medium, a CCD camera sweeps back and forth across the column and records concentration slices on the planes illuminated by the laser beam traveling simultaneously with the camera. Subsequently, these recorded images are transferred to the computer for processing in similar fashion to the velocity measurement. In order to have a fully automatic vision system, several detailed image processing techniques are developed to match exact images that have different intensities values but the same topological characteristics. This results in normalized interstitial chemical concentrations as a function of time within the porous column.
Transport of contaminants and bacteria in aqueous heterogeneous saturated porous systems have been studied experimentally using a novel fluorescent microscopic imaging technique. The approach involves color visualization and quantification of bacterium and contaminant distributions within a transparent porous column. By introducing stained bacteria and an organic dye as a contaminant into the column and illuminating the porous regions with a planar sheet of laser beam, contaminant and bacterial transport processes through the porous medium can be observed and measured microscopically. A computer controlled color CCD camera is used to record the fluorescent images as a function of time. These images are recorded by a frame accurate high resolution VCR and are then analyzed using a color image analysis code written in our laboratories. The color images are digitized this way and simultaneous concentration and velocity distributions of both contaminant and bacterium are evaluated as a function of time and pore characteristics. The approach provides a unique dynamic probe to observe these transport processes microscopically. These results are extremely valuable in in-situ bioremediation problems since microscopic particle-contaminant- bacterium interactions are the key to understanding and optimization of these processes.
This paper is concerned with development of an automated and efficient system for quality control of coal. This is achieved by distinguishing between different major maceral groups present in the polished coal blocks when viewed under a microscope. Coal utilization processes can be significantly affected by the distribution of macerals in the feed coal. Manual petrographic analysis of coal requires a highly skilled operator and the results obtained can have a high degree of subjectivity. One way of overcoming these problems is to employ automated image analysis. The system described here consists of two stages: segmentation and interpretation. In the segmentation stage, the aim is to partition the images into different types of macerals. We have implemented a multi-scale segmentation technique in which the result of each process at a given resolution is used to adjust the other process at the next resolution. This approach combines a suitable statistical model for distribution of pixel values within each macerals group and a transition distribution from coarse to fine scale, based on a son-father relationship, which is defined between the nodes in adjacent levels. At each level, segmentation is performed by maximizing the a posteriori probability (MAP) which is achieved by a relaxation algorithm, similar to Besegs work. There are two major reasons for carrying out the segmentation estimation over a hierarchy of resolutions: to speed up the estimation process, and to incorporate large scale characteristics of each pixel. The speed can be further improved by restricting the operation on the pixels which are introduced as mixed in each resolution, by which the number of pixels to be considered are significantly reduced. In the interpretation stage, the coal macerals are identified according to the measurement information on the segmented region and domain knowledge. The paper describes the knowledge base used in this application in some detail. The system has been particularly successful in correctly classifying difficult cases, such as liptinite, vitrinite, semi-fusinite and pyrite.
This paper discusses the application of stochastic labeling of remotely sensed images. A cooperative, iterative approach to segmentation and model parameter estimation is defined which is a stochastic variant of the expectation maximization (EM) algorithm, adapted to our model. Classical statistical modeling forces each pixel to be associated with exactly one class. This assumption may not be realistic, particularly in the case of satellite data. Our approach allows the possibility of mixed pixels. The labeling used in this technique involves two parts: a hard component, which describes pure pixels, and a soft component, which describes mixed pixels. The technique is illustrated by the classification of a SPOT HRV image. Because of the high resolution of these images, the pixel size is significantly smaller than the size of most of the different regions of interest, so adjacent pixels are likely to have similar labels. In our stochastic expectation maximization (SEM) method the idea that neighboring pixels are similar to one another is expressed by using Gibbs distribution for the priori distribution of regions (labels). This paper also presents a statistical model for the distribution of pixel values within each region. The initial parameters of the model can be estimated by using a K-means clustering or ISODATA, in the case of unsupervised segmentation. These parameters are then modified in each iteration of SEM. In the case of supervised segmentation, the initial parameters can be obtained from a classifier training data set and then re-estimated in SEM method. The reason for this re-estimation is that a set of classification parameters obtained from a classifier training data set may not produce satisfactory results on images which were not used to train the classifier. Our study shows that this SEM method provides reliable model parameter estimators as well as segmentation of the image.
This paper describes development of an automated and efficient system for classifying of different major maceral groups within polished coal blocks. Coal utilization processes can be significantly affected by the distribution of macerals in the feed coal. In carbonization, for example, maceral group analysis is an important parameter in determining the correct coal blend to produce the required coking properties. In coal liquefaction, liptinites and vitrinites convert more easily to give useful products than inertinites. Microscopic images of coal are inherently difficult to interpret by conventional image processing techniques since certain macerals show similar visual characteristics. It is particularly difficult to distinguish between the liptinite maceral and the supporting setting resin. This requires the use of high level image processing as well as fluorescence microscopy in conjunction with normal white light microscopy. This paper is concerned with two main stages of the work, namely segmentation and interpretation. In the segmentation stage, a cooperative, iterative approach to segmentation and model parameter estimation is defined which is a stochastic variant of the Expectation Maximization algorithm. Because of the high resolution of these images under study, the pixel size is significantly smaller than the size of most of the different regions of interest. Consequently adjacent pixels are likely to have similar labels. In our Stochastic Expectation Maximization method the idea that neighboring pixels are similar to one another is expressed by using Gibbs distribution for the priori distribution of regions (labels). We also present a suitable statistical model for distribution of pixel values within each region. In the interpretation stage, the coal macerals are identified according to the measurement information on the segmented region and domain knowledge. Studies show that the system is able to distinguish coals macerals, especially Fusinite from Pyrite or liptinite from mineral which previous attempts have been unable to resolve.
KEYWORDS: Image segmentation, Principal component analysis, Magnetic resonance imaging, Stochastic processes, Magnetism, Fuzzy logic, Visualization, Data compression, Data modeling, Signal to noise ratio
Visualization of large multidimensional magnetic resonance images (MRI) can be augmented by reducing the noise and redundancies in the data. We present details of an automatic data compression and region segmentation technique applied to medical MRI data sampled over a wide range of inversion recovery times (TI). The example images were brain slices, each one sampled with 15 different TI values, varying from 10ms to 10s. Visually, details emerged as TI increased, but some features faded at higher values. A principal component analysis reduced the data by over two thirds without noticeable loss of detail. Conventional image clustering and segmentation techniques fail to produce satisfactory results on MR images. Among the stochastic methods, independent Gaussian random field (IGRF) models were found to be suitable models when region classes have differing grey level means. We developed an automatic image segmentation technique, based on the stochastic nature of the images, that operated in two stages. First, IGRF model parameters were estimated using a modified fuzzy clustering method. Second, image segmentation was formulated as a statistical inference problem. Using a maximum likelihood function, we estimated the class status of each pixel from the IGRF model parameters. The paper elaborates on this approach and presents practical results.
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