A. Zamani

Fast Frequency-Based Multistatic Microwave Imaging Algorithm With Application to Brain Injury Detection

A multistatic microwave imaging technique is presented for fast diagnosis of medical emergencies pertaining to brain injuries. The frequency-based imaging method utilizes Bessel functions to estimate the scattered power intensity inside the imaged region from measured multistatic scattered signals outside the imaged region in a quasi-real-time manner. A theory is used to prove that the relation between the scattered fields outside the imaged object (the head) and the internal scattering profile follows the first order of first type Bessel function. To reconstruct the internal scattered power intensity accurately, the average-trace subtraction method is used to remove the skin reflections and clutters. The presented algorithm is verified using realistic numerical simulations and experimental measurements, which are performed using a radar-based head imaging system that includes an antenna array containing eight elements, microwave transceiver, and switching network. To emulate different brain injuries, realistic head phantoms are utilized. The obtained results using frequency steps that meet Nyquist criterion confirm the reliability of the proposed method in the successful detection of different sizes and locations of injuries inside the head phantom in a fast and consistent way. In comparison with existing multistatic time-domain methods, the presented approach is faster and more accurate.

3-D Wideband Antenna for Head-Imaging System with Performance Verification in Brain Tumor Detection

A 3-D slot-rotated antenna for a microwave head- imaging system is presented. The antenna is designed to have a wideband and unidirectional performance at the low microwave frequency band that are the requirements of the specified imaging system. Starting from a traditional wide-slot antenna, several conventional techniques are applied to enhance its bandwidth and directivity while miniaturizing its size. In that regard, four series of staircase-shaped slots are applied to lower the operating frequency, whereas a folding process is used to enhance the directivity and reduce the overall size. In addition, two parasitic patches are connected to the slot area to increase the operating bandwidth. The final design has the dimensions of 0.11 λ×0.23 λ×0.05 λ. ( λ is the wavelength of the lowest measured operating frequency.) It has a measured VSWR fractional bandwidth of 87% (1.41-3.57 GHz) and a peak front-to-back ratio of 9 dB. To verify the suitability of the antenna in head imaging, it is connected to a wideband microwave transceiver and used to circularly scan an artificial head phantom in 20° angle steps in a monostatic mode. The collected backscattered data are then processed and used to generate an image that successfully shows brain tumors. The compact size, wide operating bandwidth, unidirectional radiation, and detection viability are merits of the presented antenna and the subsequent system.

Feasibility of Using Wideband Microwave System for Non-Invasive Detection and Monitoring of Pulmonary Oedema.

Pulmonary oedema is a common manifestation of various fatal diseases that can be caused by cardiac or non-cardiac syndromes. The accumulated fluid has a considerably higher dielectric constant compared to lungs’ tissues, and can thus be detected using microwave techniques. Therefore, a non-invasive microwave system for the early detection of pulmonary oedema is presented. It employs a platform in the form of foam-based bed that contains two linear arrays of wideband antennas covering the band 0.7–1 GHz. The platform is designed such that during the tests, the subject lays on the bed with the back of the torso facing the antenna arrays. The antennas are controlled using a switching network that is connected to a compact network analyzer. A novel frequency-based imaging algorithm is used to process the recorded signals and generate an image of the torso showing any accumulated fluids in the lungs. The system is verified on an artificial torso phantom, and animal organs. As a feasibility study, preclinical tests are conducted on healthy subjects to determinate the type of obtained images, the statistics and threshold levels of their intensity to differentiate between healthy and unhealthy subjects.

Hybrid Clutter Rejection Technique for Improved Microwave Head Imaging

The accuracy of microwave head imaging is adversely affected by strong clutters that can completely mask the target response. To that end, different clutter removal techniques are modified for multistatic frequency-based imaging. It is shown that some deficiencies of those methods in time domain, such as time overlapping, can be alleviated when they are modified for use in frequency domain. Based on the explored performance of different methods in the frequency domain, a hybrid technique, which combines the benefits of average subtraction and entropy-based filtering methods, is proposed. In this method, the average value of the multistatic scattered signals is subtracted from them at each frequency sample to remove late-stage clutters, whereas an entropy-based method is applied to mitigate early-stage strong clutters. The proposed technique is verified in realistic environments using simulations and experiments. The utilized system for verification is 1.1-3.2 GHz frequency-domain multistatic with an eight-element antenna array, and compact microwave transceiver. The simulations are performed on MRI-derived head model, whereas the experiments are done on realistic artificial head phantom. The obtained results from different locations and sizes of emulated brain injuries confirm the effectiveness of the proposed method in producing high quality images of the head after mitigating the clutter.

Loop-Dipole Composite Antenna for Wideband Microwave-Based Medical Diagnostic Systems With Verification on Pulmonary Edema Detection

A unidirectional and compact antenna for wideband microwave-based medical diagnostic applications is presented. The main part of the antenna is formed from the combination of loop and dipole interleaved structures. To enable the antenna to resonate at a low frequency within a compact substrate area, a pair of slots is created on the loops vertical arms, whereas the dipoles structure is tapered to compensate for the negative effect of the capacitively loaded slots. With the proposed configuration, the antenna acts as an array of two dipoles and a quasi-Yagi antenna at lower and higher frequencies, respectively, and thus radiates mainly in one direction. The antenna has a compact size (with respect to the wavelength at the lowest operating frequency) of 0.23 × 0.23, making it 50% smaller than similar designs. It has a measured fractional bandwidth of 55% at 0.65-1.15 GHz and peak gain and front-to-back ratio of 3.8 dBi and 11 dB, respectively. To verify the practicality of the antenna, it is applied in an array configuration and successfully tested in detecting pulmonary edema in realistic simulation and experimental environments.

Unidirectional Slot-Loaded Loop Antenna With Wideband Performance and Compact Size for Congestive Heart Failure Detection

A slot-loaded meandered loop antenna for congestive heart failure (CHF) detection system is presented. To meet the requirements for a CHF detection system, the antenna is designed to have a compact size, wideband at the ultra-high frequency band and unidirectional radiation. To that end, several techniques are applied to the main utilized structure, which is a conventional loop antenna. To lower the resonant frequency and enhance the directivity within a compact size, the loop is capacitively loaded using a pair of slots. To compensate for the effect of the capacitive coupling on the input impedance matching, an inductive reactance is added by meandering the loops structure. With the applied modifications, the proposed antenna has a compact size of 0.21 × 0.21 with respect to the wavelength at the lowest operating frequency. The realized dimension represents only a quarter of the size of its counterpart planar designs. The proposed antenna achieves a wide measured fractional bandwidth of 50% (0.66-1.1 GHz), 9 dB peak front-to-back ratio and 4.1 dBi gain. The antenna is then used as part of a CHF detection system that also includes a compact transceiver, scanning platform, and laptop for control and processing. Using a suitable frequency-domain processing and imaging algorithm, the system successfully detects an early CHF in an artificial torso phantom.

Foam Embedded Wideband Antenna Array for Early Congestive Heart Failure Detection With Tests Using Artificial Phantom With Animal Organs

A foam-embedded wideband antenna array is used to build a portable system for congestive heart failure (CHF) detection. In addition to the array, which has a pair of four-element antenna subarrays, the system includes a portable vector network analyzer (VNA), a switching system, and a laptop, which contains control, signal processing, and image formation algorithms. The main aim of the built system is to provide a noninvasive, convenient, low cost, fast, and reliable platform for detection and monitoring of CHF. In that regard, the antenna elements are built using a three-dimensional (3-D) structure, which utilizes a combination of loop, monopole, and parasitic patches to cover the needed band (0.7-1 GHz) while keeping the size compact. A differential technique is utilized to distinguish between healthy and unhealthy cases. The performance of the system is tested on an artificial phantom and a phantom with a pair of lamb lungs, which are confirmed to have electrical properties close to those of humans. Several possible cases are investigated to validate the reliability of the system in the early detection of CHF.

Multistatic Biomedical Microwave Imaging Using Spatial Interpolator for Extended Virtual Antenna Array

The accuracy of multistatic microwave imaging is highly dependent on the number of antennas used for data acquisition. The antenna size, available space for antennas, mutual coupling between antennas and acceptable hardware complexity (switching and processing) limit the usable number of antennas. To address this issue, the concept of virtual array is utilized. In this regard, a spatial interpolator is designed to predict the received signals at the location of the virtual elements using the recorded signals by a limited number of real antennas. Consequently, a frequency-based imaging algorithm is used to process the virtual-array signals and produce clear images that enable accurate detection. The presented method is tested via simulations and experiments using a multistatic-radar-based head imaging system operating using the band 1.1–3.2 GHz. The data recorded by eight antennas around the head is used to form equivalent data from an extended virtual array of 12, 16, and 32 elements. Using quantitative metrics, it is shown that the constructed images from the extended virtual array are more accurate than the images created only from the real antennas. It is also shown that a virtual array that has twice the number of elements of the real array, which meet the minimum limit of degree-of-freedom of the problem, is enough to generate an accurate image with optimized computational resources. In comparison with existing correlation-based methods, the presented approach provides more accurate images.

Fast multi-static technique for microwave brain imaging

A fast microwave imaging method for brain stroke detection is presented. The method estimates the power distribution of the scattering waves inside the head based on the measured multistatic scattered signals around the head. In that regard, Average Trace Subtraction (ATS) and Bessel function are used to remove the background reflections and calculate the scattering electromagnetic waves in the frequency domain. The imaging algorithm is verified using a round-shaped 8-element antenna array which surrounds a realistic head model in the simulation environment. The obtained images using the presented technique demonstrate its ability in brain stroke detection and localization.

Microwave imaging using frequency domain method for brain stroke detection

Brain Stroke is the leading cause of disability and death in the world in which the supply of blood to the brain is stopped by a clot or burst of blood vessel. Microwave techniques have been investigated as a reliable solution for the immediate detection of brain strokes. To that end, an appropriate signal acquisition and processing method is needed to detect the damaged tissue using the extremely weak back scattered microwave signals from the imaged head. In that regard, a frequency domain method integrated with a multi-static ultra wide band antenna array is proposed. The utilized array comprises 24 tapered slot antennas which are located around the head to collect the back scattered signals in a multi-static mode. An image reconstruction method based on Mathieu function is utilized to predict the scattered electric field and power inside the elliptical shape imaging region. The systems configuration, imaging method and obtained results are reported in this paper.