Microwave Antenna System for Muscle Rupture Imaging with a Lossy Gel to Reduce Multipath Interference

Injuries to the hamstring muscles are an increasing problem in sports. Imaging plays a key role in diagnosing and managing athletes with muscle injuries, but there are several problems with conventional imaging modalities with respect to cost and availability. We hypothesized that microwave imaging could provide improved availability and lower costs and lead to improved and more accurate diagnostics. In this paper, a semicircular microwave imaging array with eight antennae was investigated. A key component in this system is the novel antenna design, which is based on a monopole antenna and a lossy gel. The purpose of the gel is to reduce the effects of multipath signals and improve the imaging quality. Several different gels have been manufactured and evaluated in imaging experiments. For comparison, corresponding simulations were performed. The results showed that the gels can effectively reduce the multipath signals and the imaging experiments resulted in significantly more stable and repeatable reconstructions when a lossy gel was used compared to when an almost non-lossy gel was used

On the Forward Scattering of Microwave Breast Imaging

Microwave imaging for breast cancer detection has been of significant interest for the last two decades. Recent studies focus on solving the imaging problem using an inverse scattering approach. Efforts have mainly been focused on the development of the inverse scattering algorithms, experimental setup, antenna design and clinical trials. However, the success of microwave breast imaging also heavily relies on the quality of the forward data such that the tumor inside the breast volume is well illuminated. In this work, a numerical study of the forward scattering data is conducted. The scattering behavior of simple breast models under different polarization states and aspect angles of illumination are considered. Numerical results have demonstrated that better data contrast could be obtained when the breast volume is illuminated using cross-polarized components in linear polarization basis or the copolarized components in the circular polarization basis

Modeling and reconstruction in a 3D microwave imaging system

In this paper we discuss the design and modeling of a 3D system for microwave imaging. The antenna system consists of 32 monopoles in a cylindrical configuration. A FDTD model of the system is used in the imaging reconstruction algorithm. Here we show a comparison of the data generated from the numerical FDTD model with measured data, as well as imaging of a simple target using this system. The agreement in the model is good and the imaging of a test object is successful

3D Simulations of Intracerebral Hemorrhage Detection Using Broadband Microwave Technology

Early, preferably prehospital, detection of intracranial bleeding after trauma or stroke would dramatically improve the acute care of these large patient groups. In this paper, we use simulated microwave transmission data to investigate the performance of a machine learning classification algorithm based on subspace distances for the detection of intracranial bleeding. A computational model, consisting of realistic human head models of patients with bleeding, as well as healthy subjects, was inserted in an antenna array model. The Finite-Difference Time-Domain (FDTD) method was then used to generate simulated transmission coefficients between all possible combinations of antenna pairs. These transmission data were used both to train and evaluate the performance of the classification algorithm and to investigate its ability to distinguish patients with versus without intracranial bleeding. We studied how classification results were affected by the number of healthy subjects and patients used to train the algorithm, and in particular, we were interested in investigating how many samples were needed in the training dataset to obtain classification results better than chance. Our results indicated that at least 200 subjects, i.e., 100 each of the healthy subjects and bleeding patients, were needed to obtain classification results consistently better than chance (p < 0.05 using Student\u27s t-test). The results also showed that classification results improved with the number of subjects in the training data. With a sample size that approached 1000 subjects, classifications results characterized as area under the receiver operating curve (AUC) approached 1.0, indicating very high sensitivity and specificity

Comparison between two phase-retrieval methods for electromagnetic source modeling

Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phase-retrieval methods, namely the adjoint field method and the phase angle gradient method, are compared using 3D numerical test cases. The methods were previously presented by us, but the adjoint field method was at that time only implemented in 2D. In this study the adjoint field method has been extended to 3D, which makes it possible to test the method for more realistic test cases and to compare it with the phase angle gradient method. The results show that the phase angle gradient method is able to retrieve the phase with better accuracy than the adjoint field method. Moreover it gives results that agree well with correct phase. The phase angle gradient method was also tested with measured magnetic field. The obtained phase angles on a measurement plane in front of the source gave calculated field amplitudes that agree well with measured field

Circular microwave tomographic imaging. Experimental comparison between quantitative and qualitative algorithms

The iterative Time Domain Inversion tomographic algorithm (TDI) proposed by Chalmers University of Technology is compared in terms of image quality to the UWB Magnitude Combined tomographic algorithm (MC-UWB) proposed by the Universitat Politcnica de Catalunya (UPC). The first is able to provide quantitative permittivity images of the object under test, while the second provides quantitative images, being its major strength the short reconstruction time (real time) and robustness. The comparison between the algorithms will be performed based on experimental measurements acquired with two tomographic setups, available at both universities. The Chalmers setup provides a short acquisition time but a narrow band behavior due to the monopole antennas, while the UPC setup is slower but uses broadband antennas

Accuracy Evaluation of Ultrawideband Time Domain Systems for Microwave Imaging

We perform a theoretical analysis of the measurement accuracy of ultrawideband time domain systems. The theory is tested on a specific ultrawideband system and the analytical estimates of measurement uncertainty are in good agreements with those obtained by means of simulations. The influence of the antennas and propagation effects on the measurement accuracy of time domain near field microwave imaging systems is discussed. As an interesting application, the required measurement accuracy for a breast cancer detection system is estimated by studying the effect of noise on the image reconstructions. The results suggest that the effects of measurement errors on the reconstructed images are small when the amplitude uncertainty and phase uncertainty of measured data are less than 1.5 dB and 15 degrees, respectively

Design and Performance Evaluation of a Time Domain Microwave Imaging System

We design a time domain microwave system dedicated to medical imaging. The measurement accuracy of the system, that is, signal-to-noise ratio, due to voltage noise and timing noise, is evaluated. Particularly, the effect of coupling media on the measurement accuracy is investigated both numerically and experimentally. The results suggest that the use of suitable coupling media betters the measurement accuracy in the frequency range of interest. A signal-to-noise ratio higher than 30 dB is achievable in the range of 500 MHz to 3 GHz when the effective sampling rate is 50 Gsa/s. It is also indicated that the effect of the timing jitter on the strongest received signal is comparable to that of the voltage noise

Experimental Investigation of the Accuracy of an Ultrawideband Time-Domain Microwave-Tomographic System

The measurement accuracy of an ultrawideband (UWB) time-domain microwave-tomographic system is investigated. In order to make an assessment of the random variation of the measurements, the measurement repeatability of the system is evaluated by comparison with an UWB frequency-domain system. A phantom is imaged with the time-domain microwave-tomographic system, and the reconstructed images are compared with those obtained by using the frequency-domain system. The results suggest that with the averaging tens of measurements, the time-domain system can achieve the same level of measurement repeatability as that of the frequency-domain system in the interesting frequency range of microwave tomography. The imaging results, however, indicate that the phantom reconstruction does not require such high measurement accuracy. The permittivity profile of the phantom reconstructed from the nonaveraging time-domain measurements is very similar with that obtained by means of the frequency-domain system

Investigation of an ultra wideband noise sensor for health monitoring

Quick on-scene assessment and early intervention is the key to reduce the mortality of stroke and trauma patients, and it is highly desirable to develop ambulance-based diagnostic and monitoring devices in order to provide additional support to the medical personnel. We developed a compact and low cost ultra wideband noise sensor for medical diagnostics and vital sign monitoring in pre-hospital settings. In this work, we demonstrated the functionality of the sensor for respiration and heartbeat monitoring. In the test, metronome was used to manipulate the breathing pattern and the heartbeat rate reference was obtained with a commercial electrocardiogram (ECG) device. With seventeen tests performed for respiration rate detection, sixteen of them were successfully detected. The results also show that it is possible to detect the heartbeat rate accurately with the developed sensor