Tamer Ibrahim

Elise Fear

Stuart Crozier

New Electromagnetic Methods and Applications of Antennas in Biomedicine

We have proposed a 31.5 GHz patch antenna for medical implants. The design is based on the transmission line model and is simulated in CST. The patch antenna performs reasonably well in terms of return loss and radiation efficiency. However, the most attractive feature of this design is its form factor. Typical antennas designed for the microwave range are quite large in size, which makes them unsuitable for implants. The proposed design is much smaller in size but still retains the essential characteristics for reliable communication.

Yasir Ahmed

Yang Hao

Clive Parini

A 31.5 GHz Patch Antenna Design for Medical Implants

Computational methods such as the finite difference time domain (FDTD)  play an important role in simulating radiofrequency (RF) coils used in magnetic resonance imaging (MRI). The choice of absorbing boundary conditions affects the final outcome of such studies. We have used FDTD to assess the Berenger&#x27;s perfectly matched layer (PML) as an absorbing boundary condition for computation of the resonance patterns and electromagnetic fields of RF coils. We first experimentally constructed a high-pass birdcage head coil, measured its resonance pattern, and used it to acquire proton <svg style="vertical-align:-2.21957pt;width:27.9125px;" id="M1" height="16.5375" version="1.1" viewBox="0 0 27.9125 16.5375" width="27.9125"  xmlns="http://www.w3.org/2000/svg">
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Yunsuo Duan

Tamer S. Ibrahim

Bradley S. Peterson

Feng Liu

Alayar Kangarlu

Assessment of a PML Boundary Condition for Simulating an MRI Radio Frequency Coil

With the movement of magnetic resonance imaging (MRI) technology towards higher field (and therefore frequency) systems, the interaction of the fields generated by the system with patients, healthcare workers, and internally within the system is attracting more attention. Due to the complexity of the interactions, computational modeling plays an essential role in the analysis, design, and development of modern MRI systems. As a result of the large computational scale associated with most of the MRI models, numerical schemes that rely on a single computer processing unit often require a significant amount of memory and long computational times, which makes modeling of these problems quite inefficient. This paper presents dedicated message passing interface (MPI), OPENMP parallel computing solvers for finite-difference time-domain (FDTD), and quasistatic finite-difference (QSFD) schemes. The FDTD and QSFD methods have been widely used to model/ analyze the induction of electric fields/ currents in voxel phantoms and MRI system components at high and low frequencies, respectively. The power of the optimized parallel computing architectures is illustrated by distinct, large-scale field calculation problems and shows significant computational advantages over conventional single processing platforms.

Hua Wang

Adnan Trakic

Bing Keong Li

Ewald Weber

Parallel Solvers for Finite-Difference Modeling  of Large-Scale, High-Resolution Electromagnetic Problems in MRI

We have evaluated a modified delay-and-sum (DAS) beamforming algorithm for breast cancer detection with a microwave
radar-based system. The improved DAS algorithm uses an additional weight factor calculated at each focal point to improve image
quality. These weights essentially represent the quality of preprocessing and coherent radar operation. Using a multistatic UWB
radar system based on a hemispherical antenna array, we present experimental detection of 7&#x02009;mm and 10&#x02009;mm phantom tumours.
We show that the new proposed DAS algorithm improves signal-to-clutter ratio in focused images by 2.65&#x02009;dB for 10&#x02009;mm tumour,
and by 4.4&#x02009;dB for 7&#x02009;mm tumour.

M. Klemm

I. J.  Craddock

J. A.  Leendertz

A. Preece

R. Benjamin

Improved Delay-and-Sum Beamforming Algorithm for Breast Cancer Detection

There is a need for a medical imaging technology, that supplements current
clinical brain imaging techniques, for the near-patient and mobile assessment of cerebral
vascular disease. Microwave tomography (MWT) is a novel imaging modality that has
this potential. The aim of the study was to assess the feasibility, and potential
performance characteristics, of MWT for brain imaging with particular focus on stroke
detection. The study was conducted using MWT computer simulations and 2D head
model with stroke. A nonlinear Newton reconstruction approach was used.
The MWT imaging of deep brain tissues presents a significant challenge, as the
brain is an object of interest that is located inside a high dielectric contrast shield,
comprising the skull and CSF. However, high performance, nonlinear MWT inversion
methods produced biologically meaningful images of the brain including images of
stroke. It is suggested that multifrequency MWT has the potential to significantly
improve imaging results.

Serguei Y. Semenov

Douglas R. Corfield

Microwave Tomography for Brain Imaging: Feasibility Assessment for Stroke Detection

We suggest that center-fed dipole antenna analytics can be employed in the optimized design of high-frequency MRI RF coil applications. The method is illustrated in the design of a single-segmented birdcage model and a short multisegmented birdcage model. As a byproduct, it is shown that for a long single-segmented birdcage model, the RF field within it is essentially a TEM mode and has excellent planar uniformity. For a short shielded multisegmented birdcage model, the RF field is optimized with a target-field approach with an average SAR functional. The planar homogeneity of the optimized RF field is significantly improved compared with that of a single-segmented birdcage model with the same geometry. The accuracy of the antenna formulae is also verified with numerical simulations performed via commercial software. The model discussed herein provides evidence for the effectiveness of antenna methods in future RF coil analysis.

Xin Chen

Victor Taracila

Timothy Eagan

Hiroyuki Fujita

Xingxian Shou

Tanvir Baig

Robert Brown

An Antenna-Theory Method for Modeling High-Frequency RF Coils: A Segmented Birdcage Example

We find the complex dielectric constant of the bolus liquid with the best microwave impedance match to skin-covered fatty breast tissue.  The real dielectric constant and conductivity of the ideal medium are determined by minimizing the magnitude of the reflection coefficient from the two-interface frequency-dependent system, using published measured skin and breast fat dielectric characteristics in the 400 MHz to 10 GHz frequency range. Error bounds are provided to indicate the coupling degradation when using real, nonideal media for the bolus liquid.  Two frequency regimes are identified.  Below 6.45 GHz, conventional liquid mixtures can approach the optimal coupling permittivity, but the reflection magnitudes for these best cases are high. Above 6.45 GHz, perfect coupling is possible, but only for impractically high values of bolus dielectric constant and loss.

Carey Rappaport

Determination of Bolus Dielectric Constant for Optimum Coupling of Microwaves through Skin for Breast Cancer Imaging

A compact and directive ultrawideband antenna is presented in this paper. The antenna is in the form of an antipodal tapered slot with resistive layers to improve its directivity and to reduce its backward radiation. The antenna operates over the frequency band from 3.1 GHz to more than 10.6 GHz. It features a directive radiation with a peak gain which is between 4 dBi and 11 dBi in the specified band. The time domain performance of the antenna shows negligible distortion. This makes it suitable for the imaging systems which require a very short pulse for transmission/reception. The effect of the multilayer human body on the performance of the antenna is also studied. The breast model is used for this purpose. It is shown that the antenna has more than 90% fidelity factor when it works in free space, whereas the fidelity factor decreases as the signal propagates inside the human body. However, even inside the human body, the fidelity factor is still larger than 70% revealing the possibility of using the proposed antenna in biomedical imaging systems.

Amin M. Abbosh

Directive Antenna for Ultrawideband Medical Imaging Systems

Microwave tomographic imaging of the breast for cancer detection is a topic of considerable interest because of the potential to exploit the apparent high-dielectric property contrast between normal and malignant tissue.  An important component in the realization of an imaging system is the antenna array to be used for signal transmission/detection.  The monopole antenna has proven to be useful in our implementation because it can be easily and accurately modeled and can be positioned in close proximity to the imaging target with high-element density when configured in an imaging array.  Its frequency response is broadened considerably when radiating in the liquid medium that is used to couple the signals into the breast making it suitable for broadband spectral imaging.  However, at higher frequencies, the beam patterns steer further away from the desired horizontal plane and can cause unwanted multipath contributions when located in close proximity to the liquid/air interface.  In this paper, we have studied the behavior of these antennas and devised strategies for their effective use at higher frequencies, especially when positioned near the surface of the coupling fluid which is used.  The results show that frequencies in excess of 2 GHz can be used when the antenna centers are located as close as 2 cm from the liquid surface.

Colleen J. Fox

Paul M. Meaney

Fridon Shubitidze

Lincoln Potwin

Keith D. Paulsen

Characterization of an Implicitly Resistively-Loaded Monopole Antenna in Lossy Liquid Media

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<p><em>International Journal of Antennas and Propagation </em>publishes research on the design, analysis, and applications of antennas, along with studies related to the propagation of electromagnetic waves through space, air, and other media.</p>


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<p>Chief Editor, Professor Koziel, engages in research focused on surrogate-based modeling and optimization including space mapping technology for engineering design at Reykjavik University.</p>


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International Journal of Antennas and Propagation

New Electromagnetic Methods and Applications of Antennas in Biomedicine

New Electromagnetic Methods and Applications of Antennas in Biomedicine

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