Biomedical subjects

Konstantina S Nikita

Publications and source records attributed to Konstantina S Nikita.

13 recordsLinked to original sources

PubMed2007

Computer-aided diagnosis of carotid atherosclerosis based on ultrasound image statistics, laws' texture and neural networks.

Quantitative characterisation of carotid atherosclerosis and classification into symptomatic or asymptomatic is crucial in planning optimal treatment of atheromatous plaque. The computer-aided diagnosis (CAD) system described in this paper can analyse ultrasound (US) images of carotid artery and classify them into symptomatic or asymptomatic based on their echogenicity characteristics. The CAD system consists of three modules: a) the feature extraction module, where first-order statistical (FOS) features and Laws' texture energy can be estimated, b) the dimensionality reduction module, where the number of features can be reduced using analysis of variance (ANOVA), and c) the classifier module consisting of a neural network (NN) trained by a novel hybrid method based on genetic algorithms (GAs) along with the back propagation algorithm. The hybrid method is able to select the most robust features, to adjust automatically the NN architecture and to optimise the classification performance. The performance is measured by the accuracy, sensitivity, specificity and the area under the receiver-operating characteristic (ROC) curve. The CAD design and development is based on images from 54 symptomatic and 54 asymptomatic plaques. This study demonstrates the ability of a CAD system based on US image analysis and a hybrid trained NN to identify atheromatous plaques at high risk of stroke.

Algorithms↗

PubMed2006

A computer simulation of in vivo tumour growth and response to radiotherapy: new algorithms and parametric results.

The aim of this paper is to present the newest algorithms and simulation results of a computer model of in vivo tumour growth and response to radiotherapy. The new algorithms are analytically presented. A set of parametric simulations has been performed with special emphasis on the influence of the genetic profile of a tumour on its radiosensitivity. The results of the simulation procedure are three-dimensionally visualized and critically surveyed. The long-term goal of this work is twofold: the development of a computational tool for getting insight into cancer biology and the development of a patient-specific decision support system.

Algorithms↗

PubMed2005

Preattentive deficits in developmental disorders of scholastic skills.

Working memory deficiency has been implicated in developmental disorders of scholastic skills. The auditory P50 component of event-related potentials reflecting preattentive processing was investigated in 38 children with developmental disorders of scholastic skills and 19 sibling control children, as elicited during a working memory test. The P50 was evoked by two tones of low and high frequency (500 Hz and 3000 Hz). The group with developmental disorders of scholastic skills showed prolonged P50 latency induced by the low tone, located at the frontal area. The amplitude of P50 induced by the low tone exhibited significantly negative associations with both age and memory performance, whereas age and memory performance were associated positively. These findings indicate that preattentive processing deficits may be implicated not only in auditory cognition but also in developmental disorders of scholastic skills.

Acoustic Stimulation↗

PubMed2005

Telematics enabled virtual simulation system for radiation treatment planning.

In this paper, GALENOS, a Telematics Enabled Virtual Simulation System for Radiation Treatment Planning (RTP) is described. The design architecture of GALENOS is in accordance with the dual aim of virtual simulation of RTP, i.e. to allow (a) delineation of target volume and critical organs, and (b) placement of irradiation fields. An important feature of GALENOS is the possibility for on-line tele-collaboration between health care professionals under a secure framework. The advantages of GALENOS include elimination of patient transfers between departments and health care institutions as well as availability of patient data at sites different than those of his/her physical presence.

Computer Simulation↗

PubMed2005

Investigating the enhancement of three-dimensional diffraction tomography by using multiple illumination planes.

The three dimensional (3-D) extension of the two well-known diffraction tomography algorithms, namely, direct Fourier interpolation (DFI) and filtered backpropagation (FBP), are presented and the problem of the data needed for a full 3-D reconstruction is investigated. These algorithms can be used efficiently to solve the inverse scattering problem for weak scatterers in the frequency domain under the first-order Born and Rytov approximations. Previous attempts of 3-D reconstruction with plane-wave illumination have used data obtained with the incident direction restricted at the xy plane. However, we show that this restriction results in the omission of the contribution of certain spatial frequencies near the omegaz axis for the final reconstruction. The effect of this omission is studied by comparing the results of reconstruction with and without data obtained from other incident directions that fill the spatial frequency domain. We conclude that the use of data obtained for incident direction in only the xy plane is sufficient to achieve a satisfactory quality of reconstruction for a class of objects presenting smooth variation along the z axis, while abrupt variations along the z axis cannot be imaged. This result should be taken into account in the process of designing the acquisition geometry of a tomography scanner.

Algorithms↗

PubMed2004

A four-dimensional simulation model of tumour response to radiotherapy in vivo: parametric validation considering radiosensitivity, genetic profile and fractionation.

The aim of this paper is to present the current state of a four-dimensional simulation model of solid tumour growth and response to radiotherapy developed by our group. The most prominent points of the algorithms describing the fundamental biological phenomena involved are outlined. A specific application of the model to a selected clinical case of glioblastoma multiforme is described and comparative studies are performed, using various exploratory values of the model parameters. Qualitative agreement with clinical observations has been achieved. Special emphasis is laid on the variability of radiosensitivity parameters throughout the cell cycle and on the influence of the genetic profile of the tumour on its radiosensitivity. The results of the simulation are three-dimensionally reconstructed. A valuable tool for getting insight into the biology of tumour growth and response to radiotherapy and at the same time an advanced patient specific decision support system is expected to emerge after the completion of the necessary extensive clinical evaluation.

Brain Neoplasms↗

PubMed2004

Simulating growth dynamics and radiation response of avascular tumour spheroids-model validation in the case of an EMT6/Ro multicellular spheroid.

The goal of this paper is to provide both the basic scientist and the clinician with an advanced computational tool for performing in silico experiments aiming at supporting the process of biological optimisation of radiation therapy. Improved understanding and description of malignant tumour dynamics is an additional intermediate objective. To this end an advanced three-dimensional (3D) Monte-Carlo simulation model of both the avascular development of multicellular tumour spheroids and their response to radiation therapy is presented. The model is based upon a number of fundamental biological principles such as the transition between the cell cycle phases, the diffusion of oxygen and nutrients and the cell survival probabilities following irradiation. Efficient algorithms describing tumour expansion and shrinkage are proposed and applied. The output of the biosimulation model is introduced into the (3D) visualisation package AVS-Express, which performs the visualisation of both the external surface and the internal structure of the dynamically evolving tumour based on volume or surface rendering techniques. Both the numerical stability and the statistical behaviour of the simulation model have been studied and evaluated for the case of EMT6/Ro spheroids. Predicted histological structure and tumour growth rates have been shown to be in agreement with published experimental data. Furthermore, the underlying structure of the tumour spheroid as well as its response to irradiation satisfactorily agrees with laboratory experience.

Algorithms↗

PubMed2004

Echogenicity of B-mode sonographic images of the carotid artery: work in progress.

OBJECTIVE: The echogenicity of the carotid atheromatous plaque estimated from B-mode sonographic images may be related to plaque content and has been analyzed with a number of techniques. The purpose of this study was to compare plaque with surrounding muscle tissue echogenicity and to validate the use of first-order mathematical descriptors as determinants of tissue echogenicity. METHODS: We estimated echogenicity descriptors for regions in the following 3 distinct areas of a typical B-mode sonographic image of a diseased carotid artery: plaque, blood, and sternocleidomastoid muscle. Two-dimensional B-mode sonographic images from 19 symptomatic and asymptomatic plaques (17 subjects) were interrogated, in which the following estimators were calculated: minimal, maximal, mean, and median gray levels, SD of gray levels, coefficient of variation, and gray level skewness, kurtosis, entropy, and energy. Plaque echogenicity was estimated at systole and diastole for studying the effect of the phase of the cardiac cycle. To assess the effect of different fascial tissue-muscle fiber composition on the first-order mathematical descriptors, we estimated echogenicity at 3 different sites within the muscle tissue. RESULTS: Compared with the echogenicity of surrounding muscle tissue, plaque echogenicity was characterized by (1) significantly lower (Student t test, P < .05) gray level mean, median, SD, and entropy; (2) significantly higher (Student t test, P < .05) coefficient of variation, gray level skewness, and kurtosis; and (3) similar minimal and maximal gray levels and gray level energy. The phase of the cardiac cycle, systole or diastole, did not affect the estimation of plaque echogenicity. Echogenicity was found to vary within the muscle tissue. The coefficient of variation was significantly higher in the asymptomatic plaques in the small group that was investigated. CONCLUSIONS: First-order statistical descriptors may be used to characterize atheromatous plaques and the surrounding muscle tissue.

Aged↗

PubMed2003

A computer-aided diagnostic system to characterize CT focal liver lesions: design and optimization of a neural network classifier.

In this paper, a computer-aided diagnostic (CAD) system for the classification of hepatic lesions from computed tomography (CT) images is presented. Regions of interest (ROIs) taken from nonenhanced CT images of normal liver, hepatic cysts, hemangiomas, and hepatocellular carcinomas have been used as input to the system. The proposed system consists of two modules: the feature extraction and the classification modules. The feature extraction module calculates the average gray level and 48 texture characteristics, which are derived from the spatial gray-level co-occurrence matrices, obtained from the ROIs. The classifier module consists of three sequentially placed feed-forward neural networks (NNs). The first NN classifies into normal or pathological liver regions. The pathological liver regions are characterized by the second NN as cyst or "other disease." The third NN classifies "other disease" into hemangioma or hepatocellular carcinoma. Three feature selection techniques have been applied to each individual NN: the sequential forward selection, the sequential floating forward selection, and a genetic algorithm for feature selection. The comparative study of the above dimensionality reduction methods shows that genetic algorithms result in lower dimension feature vectors and improved classification performance.

Algorithms↗

PubMed2003

Secure environment for real-time tele-collaboration on virtual simulation of radiation treatment planning.

A secure framework is described for real-time tele-collaboration on Virtual Simulation procedure of Radiation Treatment Planning. An integrated approach is followed clustering the security issues faced by the system into organizational issues, security issues over the LAN and security issues over the LAN-to-LAN connection. The design and the implementation of the security services are performed according to the identified security requirements, along with the need for real time communication between the collaborating health care professionals. A detailed description of the implementation is given, presenting a solution, which can directly be tailored to other tele-collaboration services in the field of health care. The pilot study of the proposed security components proves the feasibility of the secure environment, and the consistency with the high performance demands of the application.

Computer Graphics↗

PubMed2003

CT-MRI automatic surface-based registration schemes combining global and local optimization techniques.

Medical image registration is commonly required in order to combine the complementary information provided by different medical imaging modalities. In this paper, a new automatic registration scheme is proposed to register 3-D CT-MR head images and is currently tested on a clinical environment. The proposed scheme, after the preprocessing and the outer surface extraction of the data, is based on the use the rigid transformation method, in conjunction with a combination of global and local optimization techniques. Analytically, the paper exploits the optimization efficiency of three widely used optimization techniques, in obtaining the parameters of the rigid transformation model: the Downhill Simplex Method, the Genetic Algorithms and the Simulated Annealing. These optimization techniques are further combined by the sequential application of the Powell optimization method in order to refine the registration and increase its accuracy. A comparative study involving these optimization techniques in conjunction with the rigid transformation, and two other methods, the ICP and the manual methods, is also presented, for a sufficient number of clinical CT-MR brain images. Finally, quantitative and qualitative results are also presented to validate the performance of these automatic surface-based registration schemes, in terms of consistency and accuracy. Throughout of this study, the automatic registration scheme comprising of the rigid transformation in conjunction with the Simulated Annealing method sequentially combined with the Powell method has been performed superior regarding all the other compared registration schemes.

Algorithms↗

PubMed2002

Fractal dimension estimation of carotid atherosclerotic plaques from B-mode ultrasound: a pilot study.

In this paper, a pilot study regarding carotid atherosclerotic plaque instability using B-mode ultrasound (US) images was carried out. The fractal dimension of plaques obtained from ten symptomatic subjects (i.e., subjects having experienced neurological symptoms) as well as from nine asymptomatic subjects, was estimated using a novel method, called the kth nearest neighbour (KNN) method. The results indicated a significant difference, as per the fractal dimension, between the two groups, providing a significantly lower value for the asymptomatic group. Moreover, the phase of the cardiac cycle (systole/diastole) during which the fractal dimension was estimated had no systematic effect on the calculations. The fractal dimension of the plaques was also estimated using a well-known method, namely the box-counting (BC) method. No significant differences between the two groups, as per the fractal dimension, were observed using the BC method. The presented pilot study suggests that the fractal dimension, estimated by the proposed method, could be used as a single determinant for the discrimination of symptomatic and asymptomatic subjects.

Aged↗

PubMed2002

Real-time collaborative environment for radiation treatment planning virtual simulation.

A virtual simulation (VS) system is a software system that enables the delineation of anatomical structures, and the placement of irradiation fields for the purpose of radiation treatment planning, making use of patient's tomographic data, instead of the real patient. Since patient's tomographic data can be communicated between distinct radiotherapy departments, collaborative work on VS, connecting remote health care professionals, becomes feasible. In this paper, an environment enabling real-time collaboration on VS is presented. The environment architecture is based on both offline and online communication of data under a secure framework and can be directly integrated into the infrastructure of a radiotherapy department. The online collaboration relies on the simultaneous execution of all actions at both collaborating sites, and prerequisites the offline communication of the data set on which the collaboration will be performed. Analytical description of the custom-made layered service, which supports the offline communication is given, along with a detailed presentation of the secure management of messages, which enables the real-time collaboration. The technical evaluation of the environment highlights the effectiveness of the proposed methodology, since real-time secure collaboration on VS is achieved.

Computer Graphics↗