Metasurface-Enhanced Antennas for Microwave Brain Imaging

Abstract

Stroke is a very frequent disorder and one of the major leading causes of death and disability worldwide. Timely detection of stroke is essential in order to select and perform the correct treatment strategy. Thus, the use of an efficient imaging method for an early diagnosis of this syndrome could result in an increased survival’s rate. Nowadays, microwave imaging (MWI) for brain stroke detection and classification has attracted growing interest due to its non-invasive and non-ionising properties. In this paper, we present a feasibility study with the goal of enhancing MWI for stroke detection using metasurface (MTS) loaded antennas. In particular, three MTS-enhanced antennas integrated in different brain scanners are presented. For the first two antennas, which operate in a coupling medium, we show experimental measurements on an elliptical brain-mimicking gel phantom including cylindrical targets representing the bleeding in haemorrhagic stroke (h-stroke) and the not oxygenated tissue in ischaemic stroke (i-stroke). The reconstructed images and transmission and reflection parameter plots show that the MTS loadings improve the performance of our imaging prototype. Specifically, the signal transmitted across our head model is indeed increased by several dB‘s over the desired frequency range of 0.5–2.0 GHz, and an improvement in the quality of the reconstructed images is shown when the MTS is incorporated in the system. We also present a detailed simulation study on the performance of a new printed square monopole antenna (PSMA) operating in air, enhanced by a MTS superstrate loading. In particular, our previous developed brain scanner operating in an infinite lossy matching medium is compared to two tomographic systems operating in air: an 8-PSMA system and an 8-MTS-enhanced PSMA system. Our results show that our MTS superstrate enhances the antennas’ return loss by around 5 dB and increases the signal difference due to the presence of a blood-mimicking target up to 25 dB, which leads to more accurate reconstructions. In conclusion, MTS structures may be a significant hardware advancement towards the development of functional and ergonomic MWI scanners for stroke detection.

The Use of Metasurfaces to Enhance Microwave Imaging: Experimental Validation for Tomographic and Radar-Based Algorithms

“…A preliminary investigation of testing both our tomographic and radar-based algorithms on phantom-based measurements, inspiring this work has recently been published by the authors in [23]. Furthermore, we also note that our tomographic approach has been experimentally validated in [24]. This work however provides further investigation by presenting CST results and verifying target detection and localization on two phantoms with different target locations.…”

“…The MTS' impedancematching property refers to this transmission enhancement, rather than to improving the impedance match of the antenna itself. However, improving the antenna's impedance match is also possible, as we have shown in our previous work with spear patch antennas [24], where improvements in both transmission and reflection measured coefficients were observed when using the MTS. The impact of the distance of the MTS from the radiating element was also studied.…”

A low‐cost and multifunctional long‐life anthropomorphic head phantom for microwave brain imaging systems

“…4 In recent years, numerous MWI systems and antennas have been proposed in the literature for brain imaging purposes. [5][6][7][8][9] These systems differentiate between healthy and unhealthy brain tissues based on the contrast in dielectric properties. As blood primarily consists of water, it displays higher dielectric properties compared to most brain tissues, excluding the CSF.…”

A Performance-Enhanced Antenna for Microwave Biomedical Applications by Using Metasurfaces

“…Nevertheless, there is a substantial lack in the literature of design guidelines of suitable metasurfaces for impedance matching purposes and radiating performance enhancement. Therefore, the potential use of metasurfaces is significantly under exploited and only moderate advantages have been proved in different works [12], [40].…”