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Biomedical subjects

N Maglaveras

Publications and source records attributed to N Maglaveras.

At least 19 recordsLinked to original sources
PubMed2000

Spatial filtering methods for local activation determination in fractionated electrograms from simulated infarcted hearts.

The purpose of this work is the enhancement of local activation in multiphasic extracellular recordings coming from infarcted myocardial tissue and, consequently, the distinction of local from distal activation. Deconvolution procedures are applied, in the form of spatial filtering, in order to estimate transmembrane currents from the extracellular recordings. Simulated data are used in order to test the methods. The current source estimates are compared to the actual transmembrane currents and to Laplacian estimates.

Computer Simulation↗
PubMed2000

Prospects of medical informatics education in Greece: can we bridge the gap?

Medical Informatics education is a complex task,, since it aims in educating inhomogeneous groups of people coming from different disciplines. In Greece, recently considerable advancements in the medical informatics education field are made. These advancements aim in bridging gaps in various areas of MI users interactions. In particular, an overview of the strategy of the Greek ministry of education shall be given, some examples of MI related educational programs shall be referred to, and finally the MI educational structure used in the Aristotelian University shall be presented in detail, laying out the strategy of this University for bridging various types of gaps.

Curriculum↗
PubMed1999

Model-based morphological segmentation and labeling of coronary angiograms.

A method for extraction and labeling of the coronary arterial tree (CAT) using minimal user supervision in single-view angiograms is proposed. The CAT structural description (skeleton and borders) is produced, along with quantitative information for the artery dimensions and assignment of coded labels, based on a given coronary artery model represented by a graph. The stages of the method are: 1) CAT tracking and detection; 2) artery skeleton and border estimation; 3) feature graph creation; and iv) artery labeling by graph matching. The approximate CAT centerline and borders are extracted by recursive tracking based on circular template analysis. The accurate skeleton and borders of each CAT segment are computed, based on morphological homotopy modification and watershed transform. The approximate centerline and borders are used for constructing the artery segment enclosing area (ASEA), where the defined skeleton and border curves are considered as markers. Using the marked ASEA, an artery gradient image is constructed where all the ASEA pixels (except the skeleton ones) are assigned the gradient magnitude of the original image. The artery gradient image markers are imposed as its unique regional minima by the homotopy modification method, the watershed transform is used for extracting the artery segment borders, and the feature graph is updated. Finally, given the created feature graph and the known model graph, a graph matching algorithm assigns the appropriate labels to the extracted CAT using weighted maximal cliques on the association graph corresponding to the two given graphs. Experimental results using clinical digitized coronary angiograms are presented.

Algorithms↗
PubMed1999

DIABCARD core system--a chip card medical information system for diabetes care.

A chip card based medical information system was developed as a good possibility to create a portable electronic patient record. The produced software module provides an on-line, portable diabetes medical record information system. In particular the patient data card makes the up-to-date patient's record available whenever needed. The developed Core System includes a patient record management system that has the ability to handle topics such as medical anamnesis, administrative, medical and physical examination data. Issues tackled were simplicity, data security and reporting. Customization and internationalization were also covered by presenting a novel approach using native initialization files. Proper care has been addressed during the development of the software modules for matters of security, data integrity and confidentiality.

Computer Security↗
PubMed1998

Integration and communication for the continuity of cardiac care (I4C).

The project I4C (Integration and Communication for the Continuity of Cardiac Care) is carried out for the advancement of cardiac care, from prevention to follow-up. The goals of I4C are: (1) integrated access to patient data, wherever they are stored; (2) support of evidence-based care; (3) consistent recording of patient data (eg, patient history, electrocardiograms IECGs] or cine-angios) in a multimedia patient record; and (4) a documented reference data set for research. In several clinics, workstations are being installed to serve the four goals. Integration with other information systems in clinical care is realized by encapsulation. A computer-based patient record (ORCA) has been developed to support the collection, consultation, and sharing of patient data. In I4C, ORCA is intended for use in a research setting as well as routine patient care. The functionality of ORCA covers the collection of patient history data in a highly structured manner, the recording of drug prescriptions, an overview of laboratory test results, and viewers for ECGs and angiographic images. At present, structured data entry and consultation is supported in six European languages.

Cardiac Care Facilities↗
PubMed1998

An adaptive backpropagation neural network for real-time ischemia episodes detection: development and performance analysis using the European ST-T database.

A supervised neural network (NN)-based algorithm was used for automated detection of ischemic episodes resulting from ST segment elevation or depression. The performance of the method was measured using the European ST-T database. In particular, the performance was measured in terms of beat-by-beat ischemia detection and in terms of the detection of ischemic episodes. The algorithm used to train the NN was an adaptive backpropagation (BP) algorithm. This algorithm drastically reduces training time (tenfold decrease in our case) when compared to the classical BP algorithm. The recall phase of the NN is then extremely fast, a fact that makes it appropriate for real-time detection of ischemic episodes. The resulting NN is capable of detecting ischemia independent of the lead used. It was found that the average ischemia episode detection sensitivity is 88.62% while the ischemia duration sensitivity is 72.22%. The results show that NN can be used in electrocardiogram (ECG) processing in cases where fast and reliable detection of ischemic episodes is desired as in the case of critical care units (CCU's).

Algorithms↗
PubMed1998

Medical informatics education.

Medical Informatics is a multidisciplinary field, dealing mainly with informatics and technology applications in health care. Medical Informatics is composed from a number of sub-areas such as computer based patient record (CPR), processing of multimedia information (signals, images), coding and transmission through high speed networks of medical information (telematics), medical decision support systems, data security and integrity, integration of technologies in hospital and regional environments, and development of educational tools. The people who receive such an education are capable of development, integration and maintenance of complex hospital and health information systems both at departmental and regional levels. A very important issue however is the acceptance of information technology (IT) solutions engineered by medical informaticians from the medical personnel. In this paper we shall deal with the set-up of a medical informatics and medical technology educational environment, as well as the areas from medical informatics that the average user needs to be familiar with in order for the successful deployment of IT solutions in health care.

Curriculum↗
PubMed1998

An integrated environment for ECG processing.

The huge amount of information involved in clinical cardiological examination raises the need for efficient patient data management and for the fusion of modern information processing techniques in the everyday clinical workstation. An integrated medical information system has been developed in order to organize the local cardiological legacy system in the AHEPA hospital. An ODBC based database (like Ms SqlServer or MSAccess) holds patient and ECG data. The system incorporates data management (storing and retrieval) and data processing modules. The processing module is added as an independent DLL. The visualization component results in a better view of the information. The components are integrated in a friendly window interface that lets the doctor browse patient information, apply modern signal processing techniques, make special measurements and store them in the database for research reasons.

Database Management Systems↗
PubMed1997

RHINE-AM. An inter-regional health information network for Europe.

RHINE is an inter-regional network in Europe having as an aim, the promotion of know-how transfer in the area of Information Technology methods and tools in the regions involved. The RHINE network's significance will be demonstrated in the health sector. Within the main scope of the project, the aims and objectives of RHINE and the participating partners encompass the extension of the nucleus network and the furtherance of Information Technology research. Application areas include distributed data base and knowledge base technologies for open regional information systems supported by other technologies for business processes.

Computer Communication Networks↗
PubMed1997

Coronary artery skeleton detection based on topographic features.

A new approach to the problem of detecting the skeletons of coronary arteries in coronary angiograms is proposed. The digitized grayscale coronary angiograms are regarded as noisy sampling of the underlying continuous surface. After the application of Gaussian filtering to reduce noise, the topographic features of the smoothed image are detected based on first and second order image derivatives. Then, the candidate arteries skeleton points are detected based on the observation that arteries are smooth elongated objects having approximately a Gaussian smoothed semi-elliptical profile. Experimental results on real digitized coronary angiograms are presented.

Algorithms↗
PubMed1996

Interferon alpha-2a and combined chemotherapy as first line treatment in SCLC patients: a randomized trial.

BACKGROUND: Interferons (IFNs) are known to act synergistically with antineoplastic agents when applied to SCLC cell cultures. This study was conducted in order to detect the clinical benefits, if any, of the addition of IFN-alpha in the induction chemotherapy (CT) of SCLC patients. PATIENTS AND METHODS: Ninety previously untreated patients with SCLC were randomly assigned to receive either CT alone (arm A) or CT plus IFN alpha-2a in a dose of 3 MU/m2 twice weekly (arm B). CT for both arms consisted of carboplatin 420 mg/m2, etoposide 200 mg/m2 and ifosfamide 3.5 g/m2 or epirubicin 80 mg/m2 every 28 days for a total of eight cycles. Responding patients received primary site and prophylactic cranial irradiation and then had maintenance CT with cyclophosphamide 100 mg/m2/day for 20 days every month. Patients in arm B received IFN throughout these treatments. RESULTS: Eighty-one patients were evaluable for response, 39 in arm A and 42 in arm B. Both arms were comparable in terms of age, performance status and extent of disease. Overall response rates were not significantly different between the two arms (90% vs. 86%), although complete response rate was higher in arm B (38% vs. 28%). More importantly, Kaplan-Meier analysis disclosed a clear survival benefit in the arm receiving IFN-alpha (P < 0.05). For limited disease the difference was even more significant (P < 0.0067), while for extensive disease no significant difference was found (P < 0.35). Fever, fatigue and anorexia were more frequent in arm B (P < 0.001), as also leukopenia (P < 0.01). CONCLUSION: The addition of IFN-alpha to induction CT appears to confer a survival benefit to SCLC patients but optimal dosing schedule has yet to be defined.

Adult↗
PubMed1996

Cardiological database management system as a mediator to clinical decision support.

An object-oriented medical database management system is presented for a typical cardiologic center, facilitating epidemiological trials. Object-oriented analysis and design were used for the system design, offering advantages for the integrity and extendibility of medical information systems. The system was developed using object-oriented design and programming methodology, the C++ language and the Borland Paradox Relational Data Base Management System on an MS-Windows NT environment. Particular attention was paid to system compatibility, portability, the ease of use, and the suitable design of the patient record so as to support the decisions of medical personnel in cardiovascular centers. The system was designed to accept complex, heterogeneous, distributed data in various formats and from different kinds of examinations such as Holter, Doppler and electrocardiography.

Cardiovascular Diseases↗
PubMed1995

Effects of barriers on propagation of action potentials in two-dimensional cardiac tissue. A computer simulation study.

A two-dimensional anisotropic model of cardiac ventricular muscle was used to study the effects of discontinuities (barriers), such as dead cells or high-resistance areas, on longitudinal plane-wave propagation. Problems in propagation appear when long barriers become thicker and their spacing closer. Short barriers with large widths and small spacing also cause propagation disturbances and significant delays in their vicinity. If the plane wave front propagates through the barriers, the velocity returns to near normal within one-length constant away from the end of the barrier region. For a funnel-like structure, an opening of 13 cells should exist for longitudinal plane wave propagation. For smaller openings, the ratio of openings required for propagation to occur when traveling from a narrow to a wider area of tissue is proportional to the anisotropy ratio, which can cause unidirectional block. Tortuosity, created by spatial distribution of dead cell barriers, can facilitate propagation by changing the effective impedance the wave front sees, and can create multiple local delays, which may result in discrepancies when measuring propagation velocity.

Action Potentials↗
PubMed1995

Activation delay in healed myocardial infarction: a comparison between model and experiment.

Conduction delay in healed myocardial infarction, facilitating reentry, is frequently based on an increased path length the activation has to travel in a matrix of merging and diverging bundles that survive in the infarcted area. Additional delay occurs at sites where bundles bifurcate. The purpose of this study was to investigate conduction delay at sites where bundles bifurcate. A computer model was developed to simulate spread of activation in a two-dimensional sheet of excitable elements. A structure consisting of two isolated bundles merging into a single one was modeled. Extracellular electrograms calculated in the model were comparable to electrograms obtained in a superfused infarcted papillary muscle model. A zone of crowded isochrones or local conduction delay was found at the site where an isolated bundle bifurcated. The position of the isochrones in this area depended on the way activation times were determined. Lines of activation delay were mainly perpendicular to the fiber direction. In conclusion, the results have enabled us to better understand extracellular electrograms at pivoting points and show that activation sequences at a microscopic level can best be constructed on the basis of Laplacian signals.

Computer Simulation↗
PubMed1992

Unidirectional block in cardiac fibers: effects of discontinuities in coupling resistance and spatial changes in resting membrane potential in a computer simulation study.

The mechanisms for conduction and unidirectional block (UDB) in cardiac tissue under spatial changes in cell-to-cell coupling resistivity (Ri) and resting potential (Vrest) were studied. Cable theory was used to simulate the cardiac fiber, and the Beeler and Reuter model, or a modified model based on the Ebihara-Johnson formulation was used to describe the ionic currents. The effects of discontinuities in Ri as would result from collagenous or fibrotic tissue on propagation characteristics were studied. We were especially interested in the effects on propagation characteristics of discontinuities in Ri in the border zone between normal and ischemic tissue. We found that conduction block is more likely to occur when an abrupt decrease in Ri is encountered as compared to an abrupt increase in Ri. Discontinuities in Ri were found to cause changes in propagation characteristics, changing regions of bidirectional block to UDB or bidirectional propagation. Spatial changes in Vrest were also studied. We found that when Vrest alone was altered, block was not likely to occur, while discontinuities in Ri superimposed with Vrest gradients increased the likelihood of block. We also found that Ri discontinuities located in the border zone between normal and ischemic tissue can create exit block or propagation of a parasystolic focus.

Action Potentials↗
PubMedDate not supplied

ECG pattern recognition and classification using non-linear transformations and neural networks: a review.

The most widely used signal in clinical practice is the ECG. ECG conveys information regarding the electrical function of the heart, by altering the shape of its constituent waves, namely the P, QRS, and T waves. Thus, the required tasks of ECG processing are the reliable recognition of these waves, and the accurate measurement of clinically important parameters measured from the temporal distribution of the ECG constituent waves. In this paper, we shall review some current trends on ECG pattern recognition. In particular, we shall review non-linear transformations of the ECG, the use of principal component analysis (linear and non-linear), ways to map the transformed data into n-dimensional spaces, and the use of neural networks (NN) based techniques for ECG pattern recognition and classification. The problems we shall deal with are the QRS/PVC recognition and classification, the recognition of ischemic beats and episodes, and the detection of atrial fibrillation. Finally, a generalised approach to the classification problems in n-dimensional spaces will be presented using among others NN, radial basis function networks (RBFN) and non-linear principal component analysis (NLPCA) techniques. The performance measures of the sensitivity and specificity of these algorithms will also be presented using as training and testing data sets from the MIT-BIH and the European ST-T databases.

Algorithms↗
PubMedDate not supplied

ECG processing techniques based on neural networks and bidirectional associative memories.

Two ECG processing techniques are described for the classification of QRSs, PVCs and normal and ischaemic beats. The techniques use neural network (NN) technology in two ways. The first technique, uses nonlinear ECG mapping preprocessing and subsequently for classification uses a shrinking algorithm based on NNs. This technique is applied to the QRS/PVC problem with good result. The second technique is based on the Bidirectional Associative Memory (BAM) NN and is used to distinguish normal from ischaemic beats. In this technique the ECG beat is treated as a digitized image which is then transformed into a bipolar vector suitable for input in the BAM. The results show that this method, if properly calibrated, can result in a fast and reliable ischaemic beat detection algorithm.

Algorithms↗