Noninvasive Focused Monitoring and Irradiation of ... - Semantic Scholar

IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 14, NO. 3, MAY 2010

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Noninvasive Focused Monitoring and Irradiation of Head Tissue Phantoms at Microwave Frequencies Konstantinos T. Karathanasis, Ioannis A. Gouzouasis, Irene S. Karanasiou, Member, IEEE, Melpomeni I. Giamalaki, George Stratakos, and Nikolaos K. Uzunoglu, Fellow, IEEE

Abstract—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. Index Terms—Focused monitoring, hyperthermia, microwave radiometry, noninvasive irradiation, phantoms.

I. INTRODUCTION ASSIVE imaging techniques use only naturally generated signals from the body and are therefore entirely safe for the subject. In this context, a microwave radiometry imaging system (MiRaIS) has been developed in the Microwave and Fiber Optics Laboratory of the National Technical University of Athens [1]–[5]. The operating principle of the system is based on the use of an ellipsoidal conductive wall cavity for beamforming and focusing on the brain areas of interest. One of the most important advantages of this method is that it operates in an entirely passive and noninvasive manner. Mirais has been used for the past four years in various experiments in order to evaluate the system as a potential intracranial imaging device as well as a system for performing and monitoring hyperthermia treatment [6], [7]. The MiRaIS system is

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Manuscript received June 30, 2009; revised November 30, 2009. First published March 25, 2010; current version published June 3, 2010. The authors are with the School of Electrical and Computer Engineering, National Technical University of Athens, Athens 15780, Greece (e-mail: [email protected]; [email protected]; [email protected]. ntua.gr; [email protected]; [email protected]; [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TITB.2010.2040749

able to provide real-time temperature and/or conductivity variation measurements in water phantoms and animals and potentially in subcutaneous biological tissues. Both spatial resolution and detection depth provided by the system have been estimated through detailed theoretical analysis and validation experimental procedures using phantoms and animals [1], [2], [5]. In the range 1.3–3.5 GHz, imaging of the head model areas placed at the ellipsoid’s focus is feasible with a variety of detection/penetration depths (ranging from 2 to 4.5 cm) and spatial resolution (ranging from less than 1 cm to over 3 cm), depending on the frequency used [1]–[7]. The system’s temperature resolution ranges from 0.5 ◦ C to less than 1 ◦ C in phantom and small animal experiments [3]. Importantly, the system has been used in human experiments in order to explore the possibility of passively measuring brain activation changes that are possibly attributed to local conductivity changes. The results indicate the potential value of using focused microwave radiometry to identify brain activations possibly involved or affected in operations induced by particular psychophysiological tasks [1]. As stated earlier, the MiRaIS system measures temperature and/or conductivity fluctuations at low microwave frequencies. It has been suggested that brain temperature fluctuations reflect neural activation [8]. Although it is known that relatively large increases in local brain temperature may occur during behavioral tasks and in response to various stressful and emotionally arousing environmental stimuli, the source of this increase is not clearly understood. Empirical data obtained with fMRI suggest that increases in regional cerebral blood flow during functional stimulation can cause local changes in brain temperature and subsequent local changes in oxygen metabolism [9]. Nevertheless, brain temperature in humans remains generally unknown because of lack of actual direct experimental studies [10]. Additionally, knowledge of the electrical conductivity properties of excitable tissues could be essential for relating such measurements to the underlying neurophysiological mechanisms. The electrical conductivity of the brain is determined by the relative volumes and differing impedances of the neurons, glial cells, blood, and extracellular fluid. If changes in the relative volume of these components occur, brain conductivity will be affected. During functional activity, there is a predominant impedance decrease as a result of an increase in blood volume, producing conductivity changes [11]. Following this rationale, if such temperature and/or conductivity changes can be measured with the proposed method, then it could be used to image brain activity in an entirely passive and noninvasive manner that it is completely harmless and can be

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repeated as often as necessary without any risk even for sensitive populations such as children and pregnant women. Microwave radiometry monitoring, which is well known for more than 50 years [12], has many applications in medicine (e.g., see [13]–[18]). In this work, it is implemented using innovative approaches, with the view to achieve: 1) completely passive and noninvasive functional imaging, and 2) temperature monitoring during noninvasive intracranial hyperthermia treatment. Apart from diagnostic applications, the system is examined as a potential therapeutic device, implementing hyperthermia treatment. Hyperthermia has long been known to improve the results of other treatments for brain tumors by enhancing the effects of both chemotherapy and radiation therapy [19]–[24]. The main difficulty of noninvasive microwave hyperthermia is focusing electromagnetic power at a depth in high water content biological tissue. Therefore, in order to use a diagnostic and therapeutic device such as the proposed one, it is of great importance to have the ability to image or irradiate any arbitrary area inside the human head, placed on the ellipsoid’s focal point where maximum peak of radiation is achieved. New aspects of our research are presented in this paper regarding both radiometry and hyperthermia modules. On one hand, it is examined whether the system is capable of sensing realtime gradual local variations of temperature and/or conductivity in customized phantom setups; on the other hand, the focusing attributes of the system are experimentally explored during hyperthermia. Specifically, the use of a double-layered matching material is introduced for the first time while the appropriate phantom placement in order to achieve energy convergence on the area of interest is investigated. Microwave radiometry and hyperthermia experiments have been also previously presented showing that dielectric materials generally improve the hybrid system’s focusing capabilities [25]–[28]. II. MATERIALS AND METHODS A. System Description The novel system presented in this study is investigated as a device to provide focused radiometry measurements and hyperthermia treatment at microwave frequencies. Its main module is an ellipsoidal conductive wall cavity, providing the necessary focusing of the electromagnetic energy on the area of interest. The geometrical properties of the ellipse indicate that rays, emitted from one focal point, will merge coherently on the other focal point. Exploiting this characteristic, when the system is used for microwave radiometry, the medium of interest is placed at one focal point, whereas a receiving antenna is placed at the other one. In this way, the electromagnetic energy emitted by the medium is received by the antenna and driven to a radiometer for detection (see Fig. 1). On the other hand, when hyperthermia is performed, the receiving antenna is replaced by an emitting one. In this case, the emitted electromagnetic energy is focused on a certain area of the medium of interest, depending on its position in respect to the focal point (see Fig. 1). Apart from the ellipsoidal cavity, the remaining main parts of the system comprise a biconical antenna in conjunction with

Fig. 1. Block diagram of the hybrid system. All the main modules are illustrated implementing its dual use.

a receiver, used in radiometry measurements, and a generator connected to a dipole antenna, used in hyperthermia. The constructed multiband total power radiometer is based on the parallel processing concept, where the spectrum has been split in four subbands 1.1, 1.8, 2.4, and 2.8 GHz each one of 150 MHz bandwidth approximately. For each band, a dedicated detector is used, which gives the capability of power sensing down to −110 dBm, converting input power to output voltage. The system’s temperature resolution has been experimentally found to be approximately 0.1 mV/◦ C at 2.4 GHz. According to previous theoretical studies (see [1] and [3]), the measured voltage at the output of the radiometer is proportional to 2 ω0 µo k ∼ I= ΓA (r )T (r )σ(r )dr (1) ∆ω π V

where k is the Boltzman’s constant, ω0 is the center frequency (in radians per second) of the bandwidth of the observed microwave spectrum, µ0 is the free space magnetic permeability, V is the volume of the focusing area, T (r ) is the temperature spatial distribution within the medium of interest, σ(r ) is the spatial distribution within the medium of interest for the electric conductivity, and ΓA (r ) is the Kernel function related to the observed medium Green’s function, taking into account the electromagnetic properties of the receiving antenna. The hyperthermia module comprises a magnetron generator operating at 2.45 GHz in conjunction with the ellipsoidal reflector. The electromagnetic energy is fed to a matched dipole antenna and gel saline phantoms are placed on the opposite focal point receiving the emitted electromagnetic waves [7]. B. Experiments Experiments using microwave radiometry that were conducted in previous studies investigated the system’s ability to detect phantoms of constant conductivity but being at different temperatures [1]–[5]. The results showed that the system was able to provide different output for the various phantom temperatures. In this paper, the temperature of only a partial volume of the phantom is gradually changed and detected by the system in real time. Similar experiments were performed for local progressive phantom conductivity changes. These procedures were chosen after their similarity with possible clinical applications

KARATHANASIS et al.: NONINVASIVE FOCUSED MONITORING AND IRRADIATION OF HEAD TISSUE PHANTOMS

Fig. 2. Setup used for the microwave radiometry measurements. (Right) The biconical antenna placed at the opposite focal point of the ellipsoidal.

of the system. During hyperthermia, the temperature inside the cancerous tissue is deliberately elevated in the range of 42 ◦ C– 45 ◦ C, while the surrounding healthy tissue remains at temperatures well below 42 ◦ C. It is very crucial, during this procedure, to have an accurate and fast method to monitor the thermal dose delivered to the cancerous tissue, as well as to monitor the temperature of the healthy tissue. As far as functional imaging is concerned, when a certain area of the brain is activated as a result of an external stimulus, the temperature and/or conductivity in this area is slightly elevated from the “resting state” level. The phantoms used were deionized-aqua based and the conductivity variations were performed using saline solutions. During the hyperthermia experiments, different positions of the phantom in respect to the focal point are investigated and the energy-absorbing areas are observed. The experimental procedure also included for the first time a double dielectric matching layer placed around the phantom. The dielectric materials, placed as intermediary layers between the air and the medium of interest, create a stepped change of the refraction index on this interface, and thus, reduce the scattering effects of the electromagnetic energy, as previous theoretical studies have shown [28]–[30]. Importantly, efforts are made to determine the appropriate positioning of the phantom in respect to the ellipsoid’s focus in order to achieve focusing and consequently energy convergence on the area of interest. III. RESULTS A. Focused Microwave Radiometry Experiments In this section, the results of the microwave radiometry measurements are presented. The experimental setup is depicted in Fig. 2. Since the hyperthermia module operates at 2.45 GHz, the radiometric measurement results are presented at 2.45 GHz for consistency and to enable comparison of the findings. All the experimentation was carried out in an anechoic chamber. For the temperature experimentation, the setup involved the use of two cylindrical containers; one of 7 cm radius and 6 cm height (container A) and a smaller one of 2 cm radius and equal height (container B). The experimental procedure for the temperature measurements was as follows (see Fig. 3): Until time point t = 50 s, the radiometer measured the background noise (baseline). At that moment, container A was placed in the system filled with deionized water at 35 ◦ C, centered at the focal point (phase I). At t = 80 s, container B was placed at the focal point filled with deionized water of 43 ◦ C (phase II).

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Fig. 3. Radiometric voltage output. (Left) Temperature measurements. (Right) Conductivity measurements.

At t = 110 s, container B was misplaced by 2 cm away from the focal point (phase III) until t = 140 s, when it was centered again exactly at the focal point (phase IV) and stayed till t = 170 s, when it was totally removed (phase V). Finally, at t = 200 s, container A was also removed. In Fig. 3 (left), the radiometric output at 2.45 GHz during the previous procedure is presented. It is observed that the placement of container A resulted in a radiometric output increase from the baseline, producing a new voltage level. Then, the presence of container B resulted in a new voltage increase, greater than the first one, due to the higher temperature of the contained deionized water. When container B was moved by 2 cm, the radiometric output decreased, but not till the level of container A, showing that despite the displacement, container B was still detectable by the system. Finally, when it was placed again at the focal point and then totally removed, the voltage output reached the same levels as during the insertion period, respectively. It is therefore concluded that the radiometer detected the five separate phases of the experiment achieving the aim of this setup, showing that the system can successfully detect local changes of temperature in a cool environment with spatial sensitivity of at least 2 cm. For the conductivity experimentation, container A was filled with deionized-water-based gel, containing one hemispherical area of 3 cm diameter at its center, which during the procedure was filled with a saline water solution in the same temperature. The procedure for the conductivity measurements was as follows: until time point t = 30 s, only the deionized-water-based gel phantom was present in the system, in a way that its geometrical center was placed at the focal point. At point t = 30 s, a saline water solution (of the same temperature as the gel) was infused in the hemispherical area (phase I) and remained for 30 s when it was removed. At time point t = 90 s, the hemispherical area of 3 cm diameter was filled with deionized water (of the same temperature as the gel) again for 30 s (phase II). Finally, the two previous steps were repeated to check the repeatability of the system’s response. In Fig. 3 (right), the radiometric output at 2.45 GHz is again depicted. The radiometric levels of phases II and IV indicate that the system detected the added volume of deionized water inside the hemispherical area. The radiometric levels of phases I and III indicate that the same volume of saline water produced a greater increase of the radiometric output. Thus, it can be concluded that the system can detect local conductivity variations.

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Fig. 4. Saline-water-based gel used for the hyperthermia experiments. Three laser beams accurately indicate the position of the focal point.

B. Hyperthermia Experiments The hyperthermia experiments were performed in order to investigate the system’s focusing properties at 2.45 GHz. More specifically, the system’s spatial sensitivity was tested using saline water gel phantoms that were placed at several positions in respect to the ellipsoid’s focal point. Another aspect concerning the system’s focusing properties is the use of a dielectric matching layer placed around the gel phantom. For this reason, a second experimentation included the placement of low-loss dielectric single and double layers around the phantom prior to the irradiation and the effect on the energy-absorbing areas was observed. During hyperthermia experiments, the same container was used as in the radiometry measurements. In this case, however, the container was filled with saline-water-based gel at 9 ◦ C (see Fig. 4). The matching layers were lossless of dielectric permittivity values εr = 6 and εr = 12 and thickness 1 cm. The dielectric permittivity values were chosen based on two criteria: 1) implementation of the stepped change of the refraction index between the values of the brain tissues and air, and 2) commercial availability, in order to use them in the experiments. The thickness of the dielectric layers has been chosen after several simulations as optimal, between the value of 0.5 and 2.5 cm. Under this value window, the effect of the dielectric layer is insignificant, whereas above the value of 2.5 cm, the layer significantly attenuates the electromagnetic field. The generator was adjusted to operate at 200 W for 200 s. During hyperthermia experiments, two different phantom areas were placed at the ellipsoidal focal area and irradiation was performed with and without the dielectric matching materials. Given that the ellipsoidal focal point is the origin axis (0, 0, 0), in the first case, the geometrical center of the container was placed at (0, 0, 0) and was irradiated. After the irradiation, the temperature distribution on the container’s surface was measured. As Fig. 5 shows, there were two small areas on the edge of the container that were particularly heated. These two areas coincide with the direction of propagation of the electromagnetic wave and an important temperature increase of about 10 ◦ C was observed as deep to 1 cm from the edge of the container. Also, it is shown that the electromagnetic energy has mainly been absorbed 2 cm inside the water-based phantom, as it can be assumed that the temperature rise till this depth was due to the irradiation and not to the heat diffusion inside the phantom. Furthermore, a circular area of 3 cm radius around the focal point seemed to be unaffected by the irradiation.

Fig. 5. Temperature distribution projected on the surface of the gel phantom after irradiation. The center of the phantom is placed on the ellipsoidal’s focal point. (Left) No-dielectric layer case. (Right) εr = 6 dielectric layer case.

Fig. 6. Water-based gel phantom surrounded by the double matching layer before the irradiation. (Right) Close snapshot of the configuration.

The penetration depth inside the water phantom that corresponds to the frequency of 2.45 GHz is about 2–3 cm and this explains why the electromagnetic energy is focused at the outer regions. The location of these areas is in the direction of the propagation of the electric wave due to the electric field distribution inside the ellipsoidal. Theoretical results that depict this distribution are presented in [31] and [32]. Finally, the circular area in the phantom’s center is not affected by the radiation because of the high attenuation that the phantom introduces at 2.45 GHz. In the next case, the dielectric matching layer of εr = 6 is placed around the phantom (see Fig. 5, right). Again the center of the phantom is placed at the focal point and the same areas were heated, but, in this case, the temperature increase was greater and observed at a larger depth (11 ◦ C–14 ◦ C for 1 cm deep, and 8 ◦ C–10 ◦ C for 2 cm deep). These findings indicate that the dielectric matching layer results in higher penetration of the energy inside the phantom’s interior by reducing the reflected electromagnetic energy on the air–phantom interface, verifying previous theoretical findings [28]–[30]. Toward the same direction, a layer of εr = 12 was used simultaneously, with the εr = 6 layer being the outer one (see Fig. 6). In this case, the transition of the refraction index from the air to the phantom is gradually achieved in three stages. The experimental results are shown in Fig. 7, where the impact of the double layer is depicted. The temperature pattern of the phantom’s surface is similar to the single layer case, but the recorded temperatures of the main heated areas are even greater (a maximum temperature increase of 19 ◦ C from the initial temperature was recorded). Also, the phantom absorbs, in general, greater amount of energy, as indicated by the wider main heated areas (45◦ instead of 30◦ ) and the smaller (2 cm radius) unaffected


Fig. 7. Temperature distribution projected on the surface of the gel phantom after irradiation. The center of the phantom is placed on the ellipsoidal’s focal point. Both dielectric matching layers are placed around the phantom.

Fig. 8. Temperature distribution projected on the surface of the gel phantom after irradiation. The center of the phantom is −4 cm far from the focal point in the y-axis. (Left) No-layer case. (Right) εr = 6 layer case.

circular area in phantom’s center. It is worth to mention that the results elicited from the double-layer configuration are consistent with previous simulation results, showing an increase of the absorbed energy of 100% when compared to the no-layer case (see Fig. 5) [28]. As previous results showed, when the center of the phantom is located at the focal point two heated areas are created at the outer perimeter of the phantom. The location of these areas depends on the operation frequency, the size and the dielectric characteristics of the phantom and its position in respect to the focal point. Following this rationale, extensive simulations have been carried out investigating the distribution of the field inside the phantom in respect to its position around the focal point at 2.4 GHz. The results showed that as the phantom moves along the y-axis, the two energy-absorbing areas are shifted, and finally, converge to a single one when the phantom lies tangential to the focal point. In order to confirm these findings, two more experimental procedures were carried out, involving the placement of the phantom at two different positions on the y-axis. First, the phantom’s center was placed at (0, −4, 0), and second, at (0, −7, 0), where the focal point lies tangentially on the outer perimeter of the phantom. Fig. 8 shows that during the first procedure the shift of the phantom’s center resulted in a similar shift of the two heated areas of Fig. 5. These areas appear to be shifted anticlockwise retaining the angular distance between them. More specifically, the area on the x-axis appears to have absorbed greater amounts

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Fig. 9. Temperature distribution projected on the surface of the gel phantom after irradiation. The center of the phantom is −7 cm far from the focal point in the y-axis. (Left) No-layer case. (Right) εr = 6 layer case.

of energy than the area on the y-axis, revealing an asymmetrical temperature pattern and indicating that these areas will converge with further movement of the phantom. Finally, when the dielectric layer of εr = 6 was added, the pattern remained similar and the recorded temperatures were even greater. Again, greater absorption of energy was observed, as there was a 5 ◦ C temperature increase at 4 cm depth, indicating the effect of the material on the phantom’s surface. Fig. 9 shows the final experimental procedure, where it can be observed that the temperature pattern on the phantom’s surface is different. This time, only one main heated area is created as expected, at 1 cm maximum depth from the phantom’s contour, where the maximum temperature (19 ◦ C–20 ◦ C) was recorded. Also, the recorded temperatures indicate that the phantom has received a reduced amount of energy (the circular unaffected area is 4 cm in radius), as it is placed tangentially to the focal point. Again, the εr = 6 layer was placed around the phantom revealing the effect of the material on the phantom’s surface. The temperature pattern remains the same, but the temperature values are higher and the maximum energy absorption has been localized at a depth of 0.5 cm from the phantom’s contour. From the experimental results of Fig. 9, it can be concluded that, with the given operation frequency and dielectric characteristics of the phantom, under the appropriate placement of the phantom around the focal point, it is possible to create a single main heated area and achieve a concentrated deposition of the electromagnetic energy at a specific area on the phantom’s outer regions, as theoretical results have shown. IV. DISCUSSION AND CONCLUSION In this paper, a novel hybrid system was experimentally tested through microwave radiometry and hyperthermia experiments, focusing on the use of a double-layered matching material and the appropriate phantom placement in order to achieve energy convergence on the area of interest. Initially, the system’s ability of providing real-time measurements of local temperature and/or conductivity variations on different phantom setups was presented. The experiments, implementing the focused microwave radiometry technique, revealed the ability to detect the local concentrated gradual temperature and conductivity variations expressed as an increase of the

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output radiometric voltage. More specifically, water phantoms with small volume areas of different temperatures or having different local conductivity values produced different output radiometric voltage. Another aspect investigated was the focusing properties of the system, when hyperthermia is performed. Aqua-based phantoms were used for this reason and were irradiated at 2.45 GHz at several positions in respect to the ellipsoidal’s focal point. The results showed significant temperature increase at specific phantom areas revealing the main energy-absorbing areas of the corresponding frequency. Also, in this case, the effect of dielectric matching layers around the phantoms was tested, resulting in the enhancement of the energy penetration depth. Finally, appropriate placement of the phantom in respect to the ellipsoidal focus was determined, in order to achieve irradiation of a single specific phantom area of interest. By providing estimations of intracranial temperature in an entirely passive manner, the scope of our research efforts is to possibly add to the knowledge on the influence of brain temperature as a parameter that provides information on normal brain functions and the development of brain pathology. The way that brain temperature fluctuates under normal physiological and behavioral conditions may elucidate the mechanisms underlying these fluctuations. A fluctuation in brain temperature within 4 ◦ C may be considered as normal physiological response [33]. It is not known yet whether the fluctuations found in animal experiments occur in the human brain, but, based on similarities found between rats and monkeys [34], it is likely suggested. Since, similar to neuronal discharges, brain temperatures and conductivities are affected by various salient sensory stimuli and drugs, show consistent changes during learning, and fluctuate during motivated behavior, tightly correlating with key behavioral events, the proposed system may add to the clarification of the relationships between these underlying parameters in the future [33], [34]. Deep brain hyperthermia treatment appears to be promising against brain cancerous tumors in conjunction with other cancer treatments. Temperature monitoring during hyperthermia is a crucial factor for successful treatment and the proposed system attempts to provide both and in a total noninvasive contactless way. Future experiments will focus on improving the spatial selectivity and volume size of the heating areas by performing irradiation also at lower microwave frequencies that will enable larger penetration depths. Additional results regarding spatial accuracy attributes will be obtained by using anatomical head phantoms. REFERENCES [1] I. S. Karanasiou, N. K. Uzunoglu, and C. Papageorgiou, “Towards functional non-invasive imaging of excitable tissues inside the human body using Focused Microwave Radiometry,” IEEE Trans. Microw. Theory Tech., vol. 52, no. 8, pp. 1898–1908, Aug. 2004. [2] I. S. Karanasiou and N. K. Uzunoglu, “Experimental study of 3D contactless conductivity detection using microwave radiometry: A possible method for investigation of brain conductivity fluctuations,” in Proc. 26th IEEE EMBS, 2004, pp. 2303–2306. [3] I. S. Karanasiou, N. K. Uzunoglu, S. Stergiopoulos, and W. Wong, “A passive 3D imaging thermograph using microwave radiometry,” Innov. Technol. Biol. Med., vol. 25, no. 4, pp. 227–239, 2004.

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Irene S. Karanasiou (M’05) was born in Athens, Greece. She received the Diploma and the Ph.D. degree in electrical and computer engineering from the National Technical University of Athens (NTUA), Athens, in 1999 and 2003, respectively. Since 1999, she has been a Researcher with the Microwave and Fiber Optics Laboratory (MFOL), NTUA. She has authored or coauthored more than 70 papers in refereed international journals and conference proceedings. Her current research interests include biomedical imaging techniques, medical informatics, bioelectromagnetism, and applications of microwaves in therapy and diagnosis. Dr. Karanasiou is a member of the IEEE Engineering in Medicine and Biology Society (EMBS) and the Technical Chamber of Greece. She was the recipient of the Thomaidio Foundation Award for her doctoral dissertation and three academic journal publications.

Melpomeni I. Giamalaki was born in Athens, Greece, in 1976. She received the B.Sc. degree from the Department of Physics, University of Crete, Crete, Greece, 2002, and the Ph.D. degree in biomedical engineering from the School of Electrical and Computer Engineering, National Technical University of Athens, Athens, in 2009. She is currently with National Technical University of Athens. Her research interests include microwave radiometry and computational electromagnetics. She has authored or coauthored more than ten research papers in international journals and conferences proceedings.

Konstantinos T. Karathanasis was born in Athens, Greece, in 1982. He received the Diploma from the Department of Electrical and Computer Engineering, School of Engineering, University of Patras, Patras, Greece, in 2005, and the M.Sc. degree of the European Postgraduate Course in biomedical engineering from the University of Patras in 2007. He is currently working toward the Ph.D. degree in biomedical engineering with the National Technical University of Athens, Athens. Mr. Karathanasis has been a member of the Technical Chamber of Greece since 2005.

George Stratakos received the Diploma and Ph.D. degrees in Electrical and Computer Engineering from the National Technical University of Athens (NTUA), Athens, Greece, in 1992 and 1995 respectively. He is currently a Senior Researcher with the Institute of Communications and Computer Systems, Microwave and Fiber Optics Laboratory, National Technical University of Athens, Athens, Greece. His research interests include microwave and millimeter wave telecommunication systems, radar, microwave CAD linear and nonlinear techniques, microwave integrated circuit (MIC) and monolithic MIC (MMIC) design, conformal array systems, adaptive antennas and automated microwave measurement techniques, and advanced packaging techniques. He was a key Researcher to projects RACE, ACTS, COST, ESPRIT, and national programs.

Ioannis A. Gouzouasis was born in Athens, Greece, in 1982. He received the Diploma from the Department of Electrical and Computer Engineering, School of Engineering, University of Patras, Patras, Greece, in 2005, and the M.Sc. degree of the European Postgraduate Course in biomedical engineering from the University of Patras in 2007. He is currently working toward the Ph.D. degree in biomedical engineering with the National Technical University of Athens, Athens. Mr. Gouzouasis has been a member of the Technical Chamber of Greece since 2005.

Nikolaos K. Uzunoglu (M’82–SM’97–F’06) was born in Constantinople, Turkey, in 1951. He received the B.Sc. degree in electronics from the Technical University of Istanbul, Istanbul, Turkey, in 1973, and the Ph.D. degree from the University of Essex, Essex, U.K., in 1976. Since 1987, he has been a Professor with the School of Electrical and Computer Engineering, National Technical University of Athens, Athens, Greece. He has authored or coauthored more than 300 papers in refereed international journals and three books. His current research interests include electromagnetic scattering, propagation of electromagnetic waves, fiber-optics telecommunications, and biomedical engineering. Prof. Uzunoglu is the recipient of many honorary awards including the 1981 International G. Marconi Award in telecommunications.