Irene S. Karanasiou

Towards functional noninvasive imaging of excitable tissues inside the human body using focused microwave radiometry

Focused microwave radiometry, aiming mainly in clinical applications at measuring temperature distributions inside the human body, may provide the capability of detecting electrical conductivity variations at microwave frequencies of excitable cell clusters, such as in the case of brain tissues. A novel microwave radiometric system, including an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing, is developed for the imaging of biological tissues via contactless measurements. The measurement is realized by placing the human head in the region of the first focus and collecting the radiation converged at the second by an almost isotropic dipole antenna connected to a sensitive radiometer operating at 3.5 GHz. In order to compute the focusing properties of the ellipsoidal reflector, an accurate electromagnetic numerical analysis is developed using a semianalytical method. The experimental part of this study focuses on measurements of activation of the primary somatosensory (SI) brain area, elicited during the application of the cold pressor test, a standard experimental condition inducing pain. Analysis of the measured data from 16 healthy subjects suggests that this methodology may be able to pick up activation of the SI during the pain conditions as compared with the nonpainful control conditions. Future research is needed in order to elucidate all the interacting factors involved in the interpretation of the presented results. Finally, potential limitations to the generalization of our results and strategies to improve the systems response are discussed.

Electromagnetic Analysis of a Non-Invasive 3D Passive Microwave Imaging System

A technique based on the Green’s function theory is used in the present research in order to study theoretically the focusing properties of a constructed 3D non-invasive microwave imaging system, consisting of an ellipsoidal conductive cavity and a radiometric receiver. A double layered spherical human head model is placed on one focal point of the elliptical reflector, while the receiving antenna is placed on the other focus. Making use of the reciprocity theorem, the equivalent problem of the coupling between an elementary dipole and the double layered lossy dielectric human spherical model is solved. Numerical results concerning the electric field distribution inside the head model and in the rest of the cavity, at two operating frequencies (1.5 GHz and 3.5 GHz), are presented and compared to the results of an electromagnetic simulator. Finally, phantom experimental results validate the proof of concept and determine the temperature and spatial attributes of the system.

Development and Laboratory Testing of a Noninvasive Intracranial Focused Hyperthermia System

During the past two decades, a great deal of research has been carried out with the aim of developing effective techniques for hyperthermia treatment, primarily using RF, microwave, and ultrasound energy. A system for deep brain hyperthermia treatment, designed to also provide passive measurements of temperature and/or conductivity variations inside the human body, is presented in this paper. The proposed system comprises both therapeutic and diagnostic modules, operating in a totally contactless way, based on the use of an ellipsoidal beamformer to achieve focusing on the areas under treatment and monitoring. In previous publications, the performance of the systems diagnostic module in phantom, animal, and human studies has been reported. In the current research, new theoretical and experimental results using the therapeutic hyperthermia module of the system are presented. The main scope of the theoretical analysis is the improvement of the systems focusing attributes. Moreover, phantom experimental results verify the proof of concept. Both computation and phantom measurement results show that deep focused brain hyperthermia may be achievable with adequate spatial resolution and sensitivity using the proposed methodology, subject to the appropriate combination of operation frequency and low-loss dielectric material used as filling in the ellipsoidal.

Temporal processing dysfunction in schizophrenia as measured by time interval discrimination and tempo reproduction tasks.

OBJECTIVE Time perception deficiency has been implicated in schizophrenia; however the exact nature of this remains unclear. The present study was designed with the aim to delineate timing deficits in schizophrenia by examining performance of patients with schizophrenia and healthy volunteers in an interval discrimination test and their accuracy and precision in a pacing reproduction–replication test. METHODS The first task involved temporal discrimination of intervals, in which participants (60 patients with schizophrenia and 35 healthy controls) had to judge whether intervals were longer, shorter or equal than a standard interval. The second task required repetitive self-paced tapping to test accuracy and precision in the reproduction and replication of tempos. RESULTS Patients were found to differ significantly from the controls in the psychoticism scale of EPQ, the proportion of correct responses in the interval discrimination test and the overall accuracy and precision in the reproduction and replication of sound sequences (p < 0.01). Within the patient group bad responders concerning the ability to discriminate time intervals were associated with increased scores in the Positive and Negative Syndrome Scale (PANSS) and in the Brief Psychiatric Rating Scale (BPRS) in comparison to good responders (p < 0.01). There were no gender effects and there were no differences between subgroups of patients taking different kinds or combinations of drugs. CONCLUSIONS Analysis has shown that performance on timing tasks decreased with increasing psychopathology and therefore that timing dysfunctions are directly linked to the severity of the illness. Different temporal dysfunctions can be traced to different psychophysiological origins that can be explained using the Scalar Expectancy Theory (SET).

Noninvasive Focused Monitoring and Irradiation of Head Tissue Phantoms at Microwave Frequencies

In this study, new aspects of our research regarding a novel hybrid system able to provide focused microwave radiometric temperature and/or conductivity measurements and hyperthermia treatment via microwave irradiation are presented. On one hand, it is examined whether the system is capable of sensing real-time progressive local variations of temperature and/or conductivity in customized phantom setups; on the other hand, the focusing attributes of the system are explored for different positions and types of phantoms used for hyperthermia in conjunction with dielectric matching layers surrounding the areas of interest. The main module of the system is an ellipsoidal cavity, which provides the appropriate focusing of the electromagnetic energy on the area of interest. The system has been used for the past few years in experiments with different configuration setups including phantom, animal, and human volunteer measurements yielding promising outcome. The present results show that the system is able to detect local concentrated gradual temperature and conductivity variations expressed as an increase of the output radiometric voltage. Moreover, when contactless focused hyperthermia is performed, the results show significant temperature increase at specific phantom areas. In this case, the effect of the dielectric matching layers placed around the phantoms is critical, thus resulting in the enhancement of the energy penetration depth.

Experimental study of 3D contactless conductivity detection using microwave radiometry: a possible method for investigation of brain conductivity fluctuations

The capability of detecting electrical conductivity variations using focused microwave radiometry, a method used in clinical applications for temperature distribution imaging of subcutaneous tissues, is discussed in the present study. A novel microwave radiometric system operating at 3.5 GHz, including an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing, is developed. The system is capable of providing distribution measurements of the product of conductivity and temperature of any object being at a temperature above the absolute zero. The implemented experimental procedure is based on the results of an electromagnetic numerical analysis using a semianalytical method which was developed in order to compute the focusing properties of the ellipsoidal reflector. Each measurement is realized by placing the region of interest in the area of the first focus of the cavity and collecting the radiation converged at the second by an almost isotropic dipole antenna connected to a sensitive radiometer. Experimental data from cylindrical shaped saline or de-ionized water filled tank phantoms in which saline solutions of different concentrations were infused, provide promising results concerning the systems ability of detecting conductivity variations. Future research is needed in order to elucidate the potential of the proposed methodology to be used for brain conductivity measurements.

Non-Invasive Microwave Radiometric System for Intracranial Applications: a Study Using the Conformal L-Notch Microstrip Patch Antenna

Temperature variations in tissues inside the body have been measured using microwave radiometry for more than three decades in a variety of passive body monitoring applications. In this paper, we study a prototype system for passive intracranial monitoring using microwave radiometry. It comprises L-notch microstrip patch antennas in conjunction with a sensitive multiband microwave receiver for detection. The particular design characteristics of the antenna are its conformality and a special L cut on its upper left edge, features that make it suitable for human biomedical applications and lead to its multiband operation in the frequency range of 2{3GHz. The theoretical electromagnetic study indicates that the radiometric contact system in question operates well at two frequencies, with satisfying detection depths and adequate portability (small dimensions). In order to verify the flndings of these simulations, experimental measurements with phantoms and various setups were carried out, resulting in the deflnition of the actual temperature detection level and the spatial resolution of the system. Theoretical and experimental results conclude that with the appropriate combination of conformal patch antennas and microwave receiver it is possible to monitor areas of interest inside human head models with a variety of temperature resolutions and detection depths.

Classification of Error-Related Negativity (ERN) and Positivity (Pe) potentials using kNN and Support Vector Machines

Error processing in subjects performing actions has been associated with the Event-Related Potential (ERP) components called Error-Related Negativity (ERN) and Error Positivity (Pe). In this paper, features based on statistical measures of the sample of averaged ERP recordings are used for classifying correct from incorrect actions. Three feature selection techniques were used and compared. Classification was done by means of a kNN and a Support Vector Machines (SVM) classifier. The use of a leave-one-out approach in the feature selection provided sensitivity and specificity values concurrently higher than or equal to 87.5%, for both classifiers. The classification results were significantly better for the time window that included only the ERN, as compared to time windows including also Pe.

Contactless passive diagnosis for brain intracranial applications: A study using dielectric matching materials

A prototype system for passive intracranial monitoring using microwave radiometry is proposed. It comprises an ellipsoidal conductive wall cavity to achieve beamforming and focusing, in conjunction with sensitive multiband receivers for detection. The system has already shown the capability to provide temperature and/or conductivity variations in phantoms and biological tissue. In this article, a variant of the initially constructed modality is theoretically and experimentally investigated. Specifically, dielectric matching materials are used in an effort to improve the systems focusing attributes. The theoretical study investigates the effect of dielectric matching materials on the systems detection depth, whereas measurements with phantoms focus on the investigation of the systems detection level and spatial resolution. The combined results suggest that the dielectric matching layers lead to the improvement of the systems detection depth and temperature detection level. Also, the systems spatial resolution is explored at various experimental setups. Theoretical and experimental results conclude that with the appropriate combination of operation frequencies and dielectric layers, it is possible to monitor areas of interest inside human head models with a variety of detection depths and spatial resolutions.

Glaucoma risk assessment using a non-linear multivariable regression method

The present research investigates the relationship between the central corneal thickness (CCT), Heidelberg Retina Tomograph II (HRTII) structural measurements and intraocular pressure (IOP) using an innovative non-linear multivariable regression method in order to define the risk factors in future glaucoma development and patient management. The method is implemented to data from ninety-three open angle glaucoma eyes. The results show that in established glaucoma, CCT is significantly associated with HRTII structural measurements (maximum contour depression, cup volume inferotemporally) and IOP. They are also compared to those obtained from the application of standard linear regression methods, improving the coefficient determination R(2) by 35%, exhibiting thus the performance of the proposed methodology.