Alexandros T Tzallas

Prof. Dr. Alexandros T Tzallas

Informatics and Communications, University of Ioannina, Ioánnina, Ípeiros, Greece
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Research Focus & Metrics

Academic Career Length

22Years (2005-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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16 March 2009 in IEEE Transactions on Information Technology in Biomedicine
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Journal Article
Closed access
Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Markos G. TsipourasMarkos G. Tsipouras
Markos G. Tsipouras
DFDimitrios I. Fotiadis
Dimitrios I. Fotiadis
The detection of recorded epileptic seizure activity in EEG segments is crucial for the localization and classification of epileptic seizures. However, since seizure evolution is typically a dynamic and nonstationary process and the signals are composed of multiple frequencies, visual and conventional frequency-based methods have limited application. In this paper, we demonstrate the suitability of the time-frequency ( t - f ) analysis to classify EEG segments for epileptic seizures, and we compare several methods for t - f analysis of EEGs. Short-time Fourier transform and several t - f distributions are used to calculate the power spectrum density (PSD) of each segment. The analysis is performed in three stages: 1) t - f analysis and calculation of the PSD of each EEG segment; 2) feature extraction, measuring the signal segment fractional energy on specific t - f windows; and 3) classification of the EEG segment (existence of epileptic seizure or not), using artificial neural networks. The methods are evaluated using three classification problems obtained from a benchmark EEG dataset, and qualitative and quantitative results are presented.

5 December 2007 in Computational Intelligence and Neuroscience
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Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Markos G. TsipourasMarkos G. Tsipouras
Markos G. Tsipouras
Dimitrios FotiadisDimitrios Fotiadis
Dimitrios Fotiadis
The recording of seizures is of primary interest in the evaluation of epileptic patients. Seizure is the phenomenon of rhythmicity discharge from either a local area or the whole brain and the individual behavior usually lasts from seconds to minutes. Since seizures, in general, occur infrequently and unpredictably, automatic detection of seizures during long-term electroencephalograph (EEG) recordings is highly recommended. As EEG signals are nonstationary, the conventional methods of frequency analysis are not successful for diagnostic purposes. This paper presents a method of analysis of EEG signals, which is based on time-frequency analysis. Initially, selected segments of the EEG signals are analyzed using time-frequency methods and several features are extracted for each segment, representing the energy distribution in the time-frequency plane. Then, those features are used as an input in an artificial neural network (ANN), which provides the final classification of the EEG segments concerning the existence of seizures or not. We used a publicly available dataset in order to evaluate our method and the evaluation results are very promising indicating overall accuracy from 97.72% to 100%.

27 May 2023 in Data
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Journal Article
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AMAndreas Miltiadous
Andreas Miltiadous
Katerina D. TzimourtaKaterina D. Tzimourta
Katerina D. Tzimourta
Theodora AfrantouTheodora Afrantou
Theodora Afrantou
Panagiotis IoannidisPanagiotis Ioannidis
Panagiotis Ioannidis
NGNikolaos Grigoriadis
Nikolaos Grigoriadis
Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Recently, there has been a growing research interest in utilizing the electroencephalogram (EEG) as a non-invasive diagnostic tool for neurodegenerative diseases. This article provides a detailed description of a resting-state EEG dataset of individuals with Alzheimer’s disease and frontotemporal dementia, and healthy controls. The dataset was collected using a clinical EEG system with 19 scalp electrodes while participants were in a resting state with their eyes closed. The data collection process included rigorous quality control measures to ensure data accuracy and consistency. The dataset contains recordings of 36 Alzheimer’s patients, 23 frontotemporal dementia patients, and 29 healthy age-matched subjects. For each subject, the Mini-Mental State Examination score is reported. A monopolar montage was used to collect the signals. A raw and preprocessed EEG is included in the standard BIDS format. For the preprocessed signals, established methods such as artifact subspace reconstruction and an independent component analysis have been employed for denoising. The dataset has significant reuse potential since Alzheimer’s EEG Machine Learning studies are increasing in popularity and there is a lack of publicly available EEG datasets. The resting-state EEG data can be used to explore alterations in brain activity and connectivity in these conditions, and to develop new diagnostic and treatment approaches. Additionally, the dataset can be used to compare EEG characteristics between different types of dementia, which could provide insights into the underlying mechanisms of these conditions.

12 July 2023 in IEEE Access
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Journal Article
Open access
AMAndreas Miltiadous
Andreas Miltiadous
EGEmmanouil Gionanidis
Emmanouil Gionanidis
Katerina D. TzimourtaKaterina D. Tzimourta
Katerina D. Tzimourta
Nikolaos GiannakeasNikolaos Giannakeas
Nikolaos Giannakeas
Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Objective: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that affects a significant percentage of the elderly. EEG has emerged as a promising tool for the timely diagnosis and classification of AD or other dementia types. This paper proposes a novel approach to AD EEG classification using a Dual-Input Convolution Encoder Network (DICE-net). Approach: Recordings of 36 AD, 23 Frontotemporal dementia (FTD), and 29 age-matched healthy individuals (CN) were used. After denoising, Band power and Coherence features were extracted and fed to DICE-net, which consists of Convolution, Transformer Encoder, and Feed-Forward layers. Main results: Our results show that DICE-net achieved an accuracy of 83.28% in the AD-CN problem using Leave-One-Subject-Out validation, outperforming several baseline models, and achieving good generalization performance. Significance: Our findings suggest that a convolution transformer network can effectively capture the complex features of EEG signals for the classification of AD patients versus control subjects and may be expanded to other types of dementia, such as FTD. This approach could improve the accuracy of early diagnosis and lead to the development of more effective interventions for AD.

2 January 2012 in IEEE Transactions on Information Technology in Biomedicine
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Journal Article
Closed access
GRGeorge Rigas
George Rigas
Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Markos G. TsipourasMarkos G. Tsipouras
Markos G. Tsipouras
PBPanagiota Bougia
Panagiota Bougia
ETEvanthia E. Tripoliti
Evanthia E. Tripoliti
SKSpyridon Konitsiotis
Spyridon Konitsiotis
Tremor is the most common motor disorder of Parkinson's disease (PD) and consequently its detection plays a crucial role in the management and treatment of PD patients. The current diagnosis procedure is based on subject-dependent clinical assessment, which has a difficulty in capturing subtle tremor features. In this paper, an automated method for both resting and action/postural tremor assessment is proposed using a set of accelerometers mounted on different patient's body segments. The estimation of tremor type (resting/action postural) and severity is based on features extracted from the acquired signals and hidden Markov models. The method is evaluated using data collected from 23 subjects (18 PD patients and 5 control subjects). The obtained results verified that the proposed method successfully: 1) quantifies tremor severity with 87 % accuracy, 2) discriminates resting from postural tremor, and 3) discriminates tremor from other Parkinsonian motor symptoms during daily activities.

1 April 2013 in Computer Methods and Programs in Biomedicine
Verified
Journal Article
Closed access
ETEvanthia E. Tripoliti
Evanthia E. Tripoliti
Alexandros T TzallasAlexandros T Tzallas
Alexandros T Tzallas
Markos G. TsipourasMarkos G. Tsipouras
Markos G. Tsipouras
GRGeorge Rigas
George Rigas
PBPanagiota Bougia
Panagiota Bougia
DFDimitrios I. Fotiadis
Dimitrios I. Fotiadis