Novel magnetic resonance antennas and applications

This dissertation describes novel magnetic resonance imaging (MRI) surface antennas and arrays, and their applications at both 3 and 7 Tesla. While the first half of this work describes flexible lightweight antenna arrays, the other half focuses on the use of solid ceramic high-permittivity materials as a substantial part of the antenna. NWOLUMC / Geneeskund

Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory

In an oxide apertured quantum dot (QD) micropillar cavity-QED system, we found strong QD hysteresis effects and lineshape modifications even at very low intensities corresponding to less than 0.001 intracavity photons. We attribute this to the excitation of charges by the intracavity field; charges that get trapped at the oxide aperture, where they screen the internal electric field and blueshift the QD transition. This in turn strongly modulates light absorption by cavity QED effects, eventually leading to the observed hysteresis and lineshape modifications. The cavity also enables us to observe the QD dynamics in real time, and all experimental data agrees well with a power-law charging model. This effect can serve as a novel tuning mechanism for quantum dots.Comment: 7 pages, 6 figure

Shielded-coaxial-cable coils as receive and transceive array elements for 7T human MRI

Purpose: To investigate the use of shielded-coaxial-cable (SCC) coils as elements for multi-channel receive-only and transceive arrays for 7T human MRI and to compare their performance with equivalently sized conventional loop coils.Methods: The SCC coil element consists of a coaxial loop with interrupted central conductor at the feed-point side and an interrupted shield at the opposite point. Interelement decoupling, transmit efficiency, and sample heating were compared with results from conventional capacitively segmented loop coils. Three multichannel arrays (a 4-channel receive-only array and 8- and 5-channel transceive arrays) were constructed. Their inter-element decoupling was characterized via measured noise correlation matrices and additionally under different flexing conditions of the coils. Thermal measurements were performed and in vivo images were acquired.Results: The measured and simulated B-1(+) maps of both SCC and conventional loops were very similar. For all the arrays constructed, the inter-element decoupling was much greater for the SCC elements than the conventional ones. Even under high degrees of flexion, the coupling coefficients were lower than -10 dB, with a much smaller frequency shift than for the conventional coils.Conclusion: Arrays constructed from SCC elements are mechanically flexible and much less sensitive to changes of the coil shape from circular to elongated than arrays constructed from conventional loop coils, which makes them suitable for construction of size adjustable arrays.Radiolog

Design and characterization of receive-only surface coil arrays at 3T with integrated solid high permittivity materials

A receive-only surface coil array for 3 Tesla integrating a high-permittivity material (HPM) with a relative permittivity of 660 was designed and constructed and subsequently its performance was evaluated and compared in terms of transmit field efficiency and specific absorption ratio (SAR) during transmission, and signal-to-noise ratio during reception, with a conventional identically-sized surface coil array. Finite-difference time-domain simulations, bench measurements and in-vivo neck imaging on three healthy volunteers were performed using a three-element surface coil array with integrated HPMs placed around the larynx. Simulation results show an increase in local transmit efficiency of the body coil of similar to 10-15% arising from the presence of the HPM. The receiver efficiency also increased by approximately 15% close to the surface. Phantom experiments confirmed these results. In-vivo scans using identical transmit power resulted in SNR gains throughout the laryngeal area when compared with the conventional surface coil array. In particular specifically around the carotid arteries an average SNR gain of 52% was measured averaged over the three subjects, while in the spine an average of 20% SNR gain was obtained. (C) 2019 The Authors. Published by Elsevier Inc.Radiolog

Twisted Pair Transmission Line Coil -- A Flexible, Self-Decoupled and Extremely Robust Element for 7T MRI

This study evaluates the performance of a twisted pair transmission line coil as a transceive element for 7T MRI in terms of physical flexibility, robustness to shape deformations, and interelement decoupling. Each coil element was created by shaping a twisted pair of wires into a circle. One wire was interrupted at the top, while the other was interrupted at the bottom, and connected to the matching circuit. Electromagnetic simulations were conducted to determine the optimal number of twists per length (in terms of B$_1^+$ field efficiency, SAR efficiency, sensitivity to elongation and interelement decoupling properties) and for investigating the fundamental operational principle of the coil through fields streamline visualization. A comparison between the twisted pair coil and a conventional loop coil in terms of B$_1^+$ fields, maxSAR10g, and stability of $S_{11}$ when the coil was deformed, was performed. Experimentally measured interelement coupling between individual elements of multichannel arrays was also investigated. Increasing the number of twists per length resulted in a more physically robust coil. Poynting vector streamline visualization showed that the twisted pair coil concentrated most of the energy in the near field. The twisted pair coil exhibited comparable B$_1^+$ fields and improved maxSAR10g to the conventional coil but demonstrated exceptional stability with respect to coil deformation and a strong self-decoupling nature when placed in an array configuration. The findings highlight the robustness of the twisted pair coil, showcasing its stability under shape variations. This coil holds great potential as a flexible RF coil for various imaging applications using multiple-element arrays, benefiting from its inherent decoupling.Comment: Revised version; 20 pages, 16 figures, preprin

Improvements in high Resolution laryngeal Magnetic Resonance Imaging for preoperative Transoral laser Microsurgery and Radiotherapy considerations in early lesions

Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Polarization degenerate solid-state cavity quantum electrodynamics

Quantum Matter and Optic

Polarization degenerate solid-state cavity quantum electrodynamics

Quantum Matter and Optic