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Harmonic Motion Microwave Doppler Imaging: A Simulation Study Using a Simple Breast Model

A hybrid method for tissue imaging using dielectric and elastic properties is proposed and investigated with simple bi-layered breast model. In this method, local harmonic motion is generated in the tissue using a focused ultrasound probe. A narrow-band microwave signal is transmitted to the tissue. The Doppler component of the scattered signal, which depends on the dielectric and elastic properties of the vibrating region, is sensed. A plane-wave spectrum technique is used together with reciprocity theorem for calculating the response of a vibrating electrically small spherical tumor in breast tissue. The effects of operating frequency, antenna alignment and distance, and tumor depth on the received signal are presented. The effect of harmonic motion frequency on the vibration amplitude and displacement distribution is investigated with mechanical simulations using the finite element method. The safety of the method is analyzed in terms of microwave and ultrasound exposure of the breast tissue. The results show that the method has a potential in detecting tumors inside fibro-glandular breast tissue.

Simulation of the Scattered Field From a Vibrating Tumor Inside the Tissue Using 3D-FDTD Method

A simulation method for calculating the scattered field from a small, vibrating breast tumor is given. The Volume Equivalence Principle together with subcell type finite difference time domain formulation is used for obtaining the scattered field from the tumor. The Doppler component of the scattered field is calculated using the simulation results for the undisplaced and the displaced positions of the tumor. The method is validated by comparing the results obtained on a sample problem with the results of a semi-analytical analysis.

A circularly polarized omni-directional low loss Ka-band slot antenna

Design of a Ka-band low loss circularly polarized omni-directional slot array antenna is presented. The slot array is conformal on a circular waveguide and the slots are radiating into a parallel plate region for circular polarization. Elevation beam is directed to +10 degrees for the required elevation coverage of -10°/+30°. Simulation results show that the return loss is better than 20 dB in 1% bandwidth. Gain of the antenna greater than 1 dBi and the axial ratio better than 4.2 dB in the full sector of coverage.

Microwave Sensing of Acoustically Induced Local Harmonic Motion: Experimental and Simulation Studies on Breast Tumor Detection

Sensing acoustically induced local harmonic motion using a microwave transceiver system may provide useful information for detecting nonpalpable tumors in dense breast tissue. For this purpose, we propose the harmonic motion microwave Doppler imaging method, in which the first harmonic of the phase modulated signal due to local harmonic motion is sensed. This signal is related to the dielectric, elastic, and acoustic properties of the vibrating region. The purpose of this paper is twofold: 1) to demonstrate the concept of this method with experiments using phantom materials mimicking the elastic and electrical properties of the breast tissue and 2) to investigate the effect of fibroglandular region size and vibration frequency on the received signal, using numerical simulations. A breast phantom with a tumor phantom inclusion (5-mm diameter and 7-mm height) inside fibroglandular region is constructed for the experimental study. The response due to a focused ultrasound probe is linearly scanned at 30-mm depth from the phantom surface, and the Doppler signal level is tracked using a spectrum analyzer. It is shown that the tumor phantom is resolvable inside the surrounding fibroglandular region with about a 3-5-dB decrease in the signal level. The simulations, using the finite-difference time-domain method, show that the received signal level depends on the relative size of the fibroglandular region with respect to the vibrating region size. Further experimental and numerical studies are needed to investigate the feasibility of this method and to optimize the imaging system design.

Received signal in harmonic motion microwave doppler imaging as a function of tumor position in a 3D scheme

Harmonic Motion Microwave Doppler Imaging method, which was proposed as an alternative method for breast tumor detection, is a combination of microwave radar and focused ultrasound techniques yielding data depending on electrical and mechanical properties of the tissue. In this study, Harmonic Motion Microwave Doppler Imaging data from a small tumor inside homogeneous fat is analyzed as a function of tumor location on three orthogonal planes using Finite Difference Time Domain simulations. The results show that the resolution on the order of millimeters is achievable with this method.

Image reconstruction for Magnetic Particle Imaging using an Augmented Lagrangian Method

Magnetic particle imaging (MPI) is a relatively new imaging modality that images the spatial distribution of superparamagnetic iron oxide nanoparticles administered to the body. In this study, we use a new method based on Alternating Direction Method of Multipliers (a subset of Augmented Lagrangian Methods, ADMM) with total variation and l1 norm minimization, to reconstruct MPI images. We demonstrate this method on data simulated for a field free line MPI system, and compare its performance against the conventional Algebraic Reconstruction Technique. The ADMM improves image quality as indicated by a higher structural similarity, for low signal-to-noise ratio datasets, and it significantly reduces computation time.

Two-dimensional multi-frequency imaging of a tumor inclusion in a homogeneous breast phantom using the harmonic motion Doppler imaging method

Harmonic motion microwave Doppler imaging (HMMDI) is a novel imaging modality for imaging the coupled electrical and mechanical properties of body tissues. In this paper, we used two experimental systems with different receiver configurations to obtain HMMDI images from tissue-mimicking phantoms at multiple vibration frequencies between 15 Hz and 35 Hz. In the first system, we used a spectrum analyzer to obtain the Doppler data in the frequency domain, while in the second one, we used a homodyne receiver that was designed to acquire time-domain data. The developed phantoms mimicked the elastic and dielectric properties of breast fat tissue, and included a [Formula: see text] mm cylindrical inclusion representing the tumor. A focused ultrasound probe was mechanically scanned in two lateral dimensions to obtain two-dimensional HMMDI images of the phantoms. The inclusions were resolved inside the fat phantom using both experimental setups. The image resolution increased with increasing vibration frequency. The designed receiver showed higher sensitivity than the spectrum analyzer measurements. The results also showed that time-domain data acquisition should be used to fully exploit the potential of the HMMDI method.

Electronically rotated and translated field‐free line generation for open bore magnetic particle imaging

Purpose: We propose a coil arrangement for open bore field‐free line (FFL) magnetic particle imaging (MPI) system, which is suitable for accessing the subject from the sides. The purpose of this study is twofold, to show that the FFL can be rotated and translated electronically in a volume of interest with this arrangement and to analyze the current, voltage and power requirements for a 1 T/m gradient human sized scanner for a 200 mm diameter × 200 mm height cylindrical field of view (FOV). Methods: We used split coils side by side with alternating current directions to generate a field‐free line. Employing two of these coil groups, one of which is rotated 90 degrees with respect to the other, a rotating FFL was generated. We conducted numerical simulations to show the feasibility of this arrangement for three‐dimensional (3D) electronical scan of the FFL. Using simulations, we obtained images of a two‐dimensional (2D) in silico dot phantom for a human size scanner with system matrix‐based reconstruction. Results: Simulations showed that the FFL can be generated and rotated in one plane and can be translated in two axes, allowing for 3D imaging of a large subject with the proposed arrangement. Human sized scanner required 63–215 kW power for the selection field coils to scan the focus inside the FOV. Conclusions: The proposed setup is suitable for FFL MPI imaging with an open bore configuration without the need for mechanical rotation, which is preferable for clinical usage in terms of imaging time and patient access. Further studies are necessary to determine the limitations imposed by peripheral nerve stimulation, and to optimize the system parameters and the sequence design.

Passive localization and classification of cavitation activity using group sparsity

In therapeutic high intensity focused ultrasound (HIFU) applications, cavitation mapping is a powerful tool to monitor and guide the treatment procedure. Furthermore, the frequency spectrum of the cavitation activity can be used to classify the mode of cavitation (stable/inertial), enabling a means for increasing the safety of the application. In this study, we formulate the cavitation mapping as a group sparse constrained optimization problem, minimizing l2,1 -norm of the solution. The frequency bins related to a class of cavitation activity (harmonic, ultra-harmonic, or broadband) are grouped using l2-norm for each voxel, and l1 -norm of the image is minimized. We solve this problem using an Augmented Lagrangian Method, specifically the Alternating Direction Method of Multipliers (ADMM). We used a simulation model to test this method on a 300 mm diameter 128-element hemispherical receiver array application. We calculate the radiated pressure from the microbubbles inside the HIFU beam using a rigid vesse...