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

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.

Functional Brain Imaging Using Non-Invasive Non-Ionizing Methods: Towards Multimodal and Multiscale Imaging

“…Considering the above, as well as the wide variety of potentially harmful agents that coexist in contemporary everyday life, entirely passive, non-invasive and painless assessment of brain function in living subjects constitutes a wishful perspective and scientific vision. Under this rationale, the functional imaging perspective of a novel passive microwave imaging device is being investigated during the past 7 years (Karanasiou et al, 2004(Karanasiou et al, , 2008Karathanasis et al, 2010;Gouzouasis et al, 2010). Microwave radiometry is an important scientific research and application area of microwave sensing because it provides a passive sensing technique for detecting naturally emitted electromagnetic radiation.…”

“…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 (e.g. Karanasiou et al, 2004Karanasiou et al, , 2008Karathanasis et al, 2010;Gouzouasis et al, 2010). 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 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.…”

Enhancement of a Microwave Radiometry Imaging System's Performance Using Left Handed Materials

“…A Microwave Radiometry Imaging System (MiRaIS) has been developed and it mainly consists of an ellipsoidal conductive cavity which ensures the focusing on the brain areas of interest and a multifrequency sensitive radiometric receiver [1][2][3][4][5] (Fig. 1).…”

“…1). Various experimental data provide promising results concerning the system's ability of detecting temperature and/or conductivity variation distributions in phantoms and biological tissues [3][4][5].…”

“…Towards the enhancement of the system's focusing properties, in previous recent work carried out by our group, various setups have been investigated aiming to improve the transition of the diffraction index from air to the head and vice versa. Specifically, initially the receiving antenna was covered by two layers of different dielectric properties, then a thin lossless dielectric layer was placed on the surface of the human head model [1] and various configurations using lossless dielectric materials placed around the head models/phantoms or used as filling material inside the ellipsoidal cavity were also implemented [4,5]. With appropriate adaptation of values of the dielectric properties and the thicknesses of each layer, a stepped change of the refraction index on the scattering objects-air interface has been achieved, hence a better radiation focusing inside the brain has been observed.…”