A5009413275- Electromagnetic Simulation and Numerical Methods
- Advanced MRI Techniques and Applications
- Electromagnetic Scattering and Analysis
- Microwave Imaging and Scattering Analysis
- Electrical and Bioimpedance Tomography
- Model Reduction and Neural Networks
- Atomic and Subatomic Physics Research
- Geophysical and Geoelectrical Methods
- Numerical methods in inverse problems
- NMR spectroscopy and applications
- Magnetic Properties and Applications
- Geophysical Methods and Applications
- Microwave Engineering and Waveguides
- Advanced NMR Techniques and Applications
- Ultrasound and Hyperthermia Applications
- Sparse and Compressive Sensing Techniques
- Seismic Imaging and Inversion Techniques
- Medical Imaging Techniques and Applications
- Numerical methods for differential equations
- Matrix Theory and Algorithms
- Ultrasonics and Acoustic Wave Propagation
- Non-Destructive Testing Techniques
- Electron Spin Resonance Studies
- Advanced Wireless Communication Techniques
- Photonic and Optical Devices
Delft University of Technology
2015-2024
University of Michigan
2020
Leiden University Medical Center
2017-2018
Schlumberger (United States)
2017
Electric properties tomography (EPT) is an imaging modality to reconstruct the electric conductivity and permittivity inside human body based on B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sup xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> maps acquired by a magnetic resonance (MRI) system. Current implementations of EPT are local Maxwell equations assume piecewise constant media. The accuracy reconstructed may therefore be...
Optical resonators are widely used in modern photonics. Their spectral response and temporal dynamics fundamentally driven by their natural resonances, the so-called quasinormal modes (QNMs), with complex frequencies. For optical made of dispersive materials, QNM computation requires solving a nonlinear eigenvalue problem. This raises difficulty that is only scarcely documented literature. We review our recent efforts for implementing efficient accurate solvers computing normalizing QNMs...
Abstract Low-field MRI scanners are significantly less expensive than their high-field counterparts, which gives them the potential to make technology more accessible all around world. In general, images acquired using low-field tend be of a relatively low resolution, as signal-to-noise ratios lower. The aim this work is improve resolution these images. To end, we present deep learning-based approach transform low-resolution MR into high-resolution ones. A convolutional neural network was...
The in vivo electric conductivity (σ) values of tissue are essential for accurate electromagnetic simulations and specific absorption rate (SAR) assessment applications such as thermal dose computations hyperthermia. Currently used σ-values mostly based on ex measurements. In this study the human muscle, bladder content cervical tumors is acquired non-invasively using MRI.
Introduction The reliability of hyperthermia treatment planning (HTP) is strongly dependent on the accuracy electric properties each tissue. values currently used are mostly based ex vivo measurements. In this study, in conductivity human muscle, bladder content and cervical tumours, acquired with magnetic resonance-based tomography (MR-EPT), exploited to investigate effect HTP for cancer patients. Methods Temperature-based optimisation five different patients was performed using...
We show that the Newton-Kantorovich and distorted Born methods for computational solution of nonlinear inverse scattering problem are equivalent. This was already shown discrete matrix case. Here we present an analysis based on analytic representations integral operators. first briefly review both then they
Contrast source inversion-electrical properties tomography (CSI-EPT) is an iterative reconstruction method to retrieve the electrical (EPs) of tissues from magnetic resonance data. The based on integral representations electromagnetic field and has been shown allow EP reconstructions small structures as well tissue boundaries with compelling accuracy. However, date, CSI-EPT implemented for 2-D configurations only, which limits its applicability. In this paper, a full 3-D extension presented,...
In this study, we analyzed dielectric shimming by formulating it as an electromagnetic scattering problem using integral equations.Three-dimensional simulations of the radiofrequency field in two configurations different materials were terms induced currents and secondary fields. A two-dimensional equation method with backgrounds was used to identify underlying physical mechanisms. This framework then develop inversion for design pads.The effects a pad can be attributed interference that is...
Magnetic resonance electrical properties tomography (MR‐EPT) is a technique used to estimate the conductivity and permittivity of tissues from MR measurements transmit magnetic field. Different reconstruction methods are available; however, all these present several limitations, which hamper clinical applicability. Standard Helmholtz‐based MR‐EPT severely affected by noise. Iterative such as contrast source inversion (CSI‐EPT) typically time‐consuming dependent on their initialization. Deep...
In this article, we design and construct gradient coils for a Halbach permanent-magnet array magnetic resonance (MR) scanner. The target field method, which is widely applied the case of axial static fields, has been developed transverse as produced by array. Using current densities three directions are obtained subsequently verified using commercial magneto-static solver. Stream functions used to turn surface into wire patterns constructing coils. measured fields in good agreement with...
Low-field permanent magnet-based MRI systems are finding increasing use in portable, sustainable and point-of-care applications. In order to maximize performance while minimizing cost many components of such a system should ideally be designed specifically for low frequency operation. this paper we describe recent developments constructing characterising low-field portable vivo imaging at 50 mT. These include the design i) high-linearity gradient coils using modified volume-based target...
Purpose High‐permittivity materials in the form of flexible “dielectric pads” have proved very useful for addressing RF inhomogeneities high field MRI systems. Finding optimal design such pads is, however, a tedious task, reducing impact this technique. We present an easy‐to‐use software tool which allows researchers and clinicians to dielectric efficiently on standard computer systems, 7T neuroimaging 3T body imaging applications. Methods The incorporates advanced computational methods...
Parallel RF transmission (PTx) is one of the key technologies enabling high quality imaging at ultra-high fields (≥7T). Compliance with regulatory limits on local specific absorption rate (SAR) typically involves over-conservative safety margins to account for intersubject variability, which negatively affect utilization field MR. In this work, we present a method generate subject-specific body model from single T1-weighted dataset personalized SAR prediction in PTx neuroimaging...
The Krylov subspace projection approach is a well-established tool for the reduced-order modeling of dynamical systems in time domain. In this paper, we address main issues obstructing application powerful to time-domain solution exterior wave problems. We use frequency-independent perfectly matched layers simulate extension infinity. Pure imaginary stretching functions based on Zolotarev's optimal rational approximation square root are implemented leading with controlled accuracy over...
Interference effects in the transmit B1+ field can severely degrade image quality high-field Magnetic Resonance Imaging (MRI). High-permittivity pads are increasingly used to counteract these effects, but designing such is not trivial. In this paper, we present an efficient solution methodology for dielectric RF shimming problem. By exploiting fact that form a low rank perturbation of large-scale background model, able efficiently compute fields correspond wide range different pad...
A new method for computing transient electromagnetic wavefields in inhomogeneous and lossy media is presented. The utilizes a modified Lanczos scheme, where so-called reduced model constructed. discretization of the time variable then superfluous. This represents wavefield on certain bounded interval time. Some theoretical aspects are highlighted numerical results showing performance two-dimensional (2-D) configurations given. Also, comparisons between this finite-difference time-domain (FDTD) made.
Purpose Design of a preconditioner for fast and efficient parallel imaging (PI) compressed sensing (CS) reconstructions Cartesian trajectories. Theory PI CS become time consuming when the problem size or number coils is large, due to large linear system equations that has be solved in ‐norm based reconstruction algorithms. Such systems can efficiently using effective preconditioning techniques. Methods In this article we construct such by approximating matrix system, which comprises data...
Purpose High permittivity dielectric pads are known to be effective for tailoring the RF field and improving image quality in high MRI. Despite a number of studies reporting benign specific absorption rate (SAR) effects, their “universal” safety remains an open concern. In this work, we evaluate impact insulation material between pad body, using both simulations as well phantom experiments. Methods A 3T configuration with was simulated characterized experimentally terms B 1 + fields power...
Abstract We consider the MRI physics in a low-field scanner, which permanent magnets are used to generate magnetic field millitesla range. A model describing relationship between measured signal and image is derived, resulting an ill-posed inverse problem. In order solve it, regularization penalty added least-squares minimization generalize conjugate gradient minimal error (CGME) algorithm weighted regularized Analysis of convergence generalized CGME (GCGME) classical least squares (GCGLS)...
Low-cost low-field point-of-care MRI systems are used in many different applications. System design has correspondingly requirements terms of imaging field-of-view, spatial resolution and magnetic field strength. In this work an iterative framework been created to a cylindrical Halbach-based magnet along with integrated gradient RF coils that most efficiently fulfil set user-specified requirements.For efficient integration, target methods for each the main hardware components. These have not...