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 system's focusing attributes. The theoretical study investigates the effect of dielectric matching materials on the system's detection depth, whereas measurements with phantoms focus on the investigation of the system's detection level and spatial resolution. The combined results suggest that the dielectric matching layers lead to the improvement of the system's detection depth and temperature detection level. Also, the system's 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.

A Glucose Sensing System Based on Transmission Measurements at Millimetre Waves using Micro strip Patch Antennas.

We present a sensing system operating at millimetre (mm) waves in transmission mode that can measure glucose level changes based on the complex permittivity changes across the signal path. The permittivity of a sample can change significantly as the concentration of one of its substances varies: for example, blood permittivity depends on the blood glucose levels. The proposed sensing system uses two facing microstrip patch antennas operating at 60 GHz, which are placed across interrogated samples. The measured transmission coefficient depends on the permittivity change along the signal path, which can be correlated to the change in concentration of a substance. Along with theoretical estimations, we experimentally demonstrate the sensing performance of the system using controlled laboratory samples, such as water-based glucose-loaded liquid samples. We also present results of successful glucose spike detection in humans during an in-vivo Intravenous Glucose Tolerance Test (IVGTT). The system could eventually be developed into a non-invasive glucose monitor for continuous monitoring of glucose levels for people living with diabetes, as it can detect as small as 1.33 mmol/l (0.025 wt%) glucose concentrations in the controlled water-based samples satisfactorily, which is well below the typical human glucose levels of 4 mmol/l.

Experimental study of a hybrid microwave radiometry-hyperthermia apparatus with the use of an anatomical head phantom.

This paper presents the latest progress made concerning a hybrid diagnostic and therapeutic system able to provide focused microwave radiometric temperature and/or conductivity variation measurements and hyperthermia treatment. Previous experimental studies of our group have demonstrated the system performance and focusing properties in phantom as well as human experiments. The system is able to detect temperature and conductivity variations with frequency-dependent detection depth and spatial sensitivity. Numerous studies have also demonstrated the improvement of the system focusing properties attributed to the use of dielectric and left handed matching layers. In this study, similar experimental procedures are performed but this time using an anatomical head model as phantom aiming to achieve a more accurate modeling of the system's future real function. This way, another step is made toward the deeper understanding of the system's capabilities, with the view to further use it in experimental procedures with laboratory animals and human volunteers.

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.

FDTD study of the focusing properties of a hybrid hyperthermia and radiometry imaging system using a realistic human head model.

Aim of this study is twofold; on one hand, the investigation of the focusing attributes of a microwave radiometry tomography system with the use of a realistic human head model and on the other hand, the system's ability to perform a hyperthermia treatment. The operation principle of the device is based on an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing. The biological tissue under treatment and/or measurement is placed on one of the two focal points whereas on the other one, a radiating or receiving antenna, which measures the black body type radiation emitted from the head's tissue, is placed. In previous studies simple spherical head models were used, comprising one or two layers for simulating the head tissues, along with a commercial FEM tool. In this work, a realistic adult head model developed from MRI scans of a human head is used. The realistic model with detailed structural and electromagnetic tissue characteristics enables more in depth theoretical investigation of the system capabilities. Extensive simulations using a commercial FDTD tool are performed in a wide range of operating frequencies. In order to explore the feasibility of heating and monitoring specific brain areas, the capability of focusing the electric field in specific areas inside the human head is investigated and further discussed. The results show that simple spherical head models, used in previous studies, provide similar results with the realistic one used herein for the given geometry; that is, the electric field focuses on the head's center, assuming the head as a homogeneous sphere. However, the deposition of the electromagnetic energy on the head tissues depends on the operating frequency and position of the head in the given geometry, so in therefore calculated, revealing the ability of the system to operate as a hyperthermia clinical tool, not as a stand alone device but in conjunction with other already validated devices/methods.