Design and Simulation of Coils for High Field Magnetic Resonance Imaging and Spectroscopy

The growing availability of high-field magnetic resonance (MR) scanners has reignited interest in the in vivo investigation of metabolics in the body. In particular, multinuclear MR spectroscopy (MRS) data reveal physiological details inaccessible to typical proton (1H) scans. Carbon-13 (13C) MRS studies draw considerable appeal owing to the enhanced chemical shift range of metabolites that may be interrogated to elucidate disease metabolism and progression. To achieve the theoretical signal-to-noise (SNR) gains at high B0 fields, however, J-coupling from 1H-13C chemical bonds must be mitigated by transmitting radiofrequency (RF) proton-decoupling pulses. This irradiated RF power is substantial and intensifies with increased decoupling bandwidth as well as B0 field strength. The preferred 13C MRS experiment, applying broadband proton decoupling, thus presents considerable challenges at 7 T. Localized tissue heating is a paramount concern for all high-field studies, with strict Specific Absorption Rate (SAR) limits in place to ensure patient safety. Transmit coils must operate within these power guidelines without sacrificing image and spectral quality. Consequently, RF coils transmitting proton-decoupling pulses must be expressly designed for power efficiency as well as B1 field homogeneity. This dissertation presents innovations in high-field RF coil development that collectively improved the homogeneity, efficiency, and safety of high field 13C MRS. A review of electromagnetic (EM) theory guided a full-wave modeling study of coplanar shielding geometries to delineate design parameters for coil transmit efficiency. Next, a novel RF coil technique for achieving B1 homogeneity, dubbed forced current excitation (FCE), was examined and a coplanar-shielded FCE coil was implemented for proton decoupling of the breast at 7 T. To perform a series of simulation studies gauging SAR in the prone breast, software was developed to fuse a suite of anatomically-derived heterogeneous breast phantoms, spanning the standard four tissue density classifications, with existing whole-body voxel models. The effects of tissue density on SAR were presented and guidance for simulating the worst-case scenario was outlined. Finally, for improving capabilities of multinuclear coils during proton coil transmit, a high-power trap circuit was designed and tested, ultimately enabling isolation of 13C coil elements during broadband proton decoupling pulses. Together, this work advanced the hardware capabilities of high-field multinuclear spectroscopy with immediate applicability for performing broadband proton-decoupled 13C MRS in the breast at 7 T

Wide Band Embedded Slot Antennas for Biomedical, Harsh Environment, and Rescue Applications

For many designers, embedded antenna design is a very challenging task when designing embedded systems. Designing Antennas to given set of specifications is typically tailored to efficiently radiate the energy to free space with a certain radiation pattern and operating frequency range, but its design becomes even harder when embedded in multi-layer environment, being conformal to a surface, or matched to a wide range of loads (environments). In an effort to clarify the design process, we took a closer look at the key considerations for designing an embedded antenna. The design could be geared towards wireless/mobile platforms, wearable antennas, or body area network. Our group at UT has been involved in developing portable and embedded systems for multi-band operation for cell phones or laptops. The design of these antennas addressed single band/narrowband to multiband/wideband operation and provided over 7 bands within the cellular bands (850 MHz to 2 GHz). Typically the challenge is: many applications require ultra wide band operation, or operate at low frequency. Low frequency operation is very challenging if size is a constraint, and there is a need for demonstrating positive antenna gain

Antenna Development for Radio Frequency Hyperthermia Applications

This thesis deals with the design steps, development and validation of an applicator for radio frequency hyperthermia cancer therapy. An applicator design to enhance targeted energy coupling is a key enabler for preferential temperature increments in tumour regions. A single-element, near-field approach requires a miniaturised solution, that addresses ergonomic needs and is tolerant to patient anatomy. The antenna war-field rriodality and the high-dielectric patient loading introduce significant analytical and computational resource challenges. The antenna input impedance has to be sufficiently insensitive to in-band resonant cletuning and the fields in the tissue can he targeted to selected areas in the patient. An introduction to the medical and biological background of hyperthermia is presented. The design requirements of antennas for medical and in particular for hyperthermia applications are highlighted. Starting from a conventional circular patch, the antenna evolved into a compact circular patch with a concentric annular ring and slotted groundplane, operating at the 434 MHz Industrial Scientific and Medical frequency band. Feed point location is optimized for an energy deposition pattern aligned with the antenna centre. The applicator is assessed with other published approaches and clinically used loop, dipole and square patch antennas. The antennas are evaluated for the unloaded condition and when loaded with a tri-layer body tissue numerical model. This model comprises skin, fat and transverse fiber of muscle of variable thicknesses to account for different body locations and patient. anatomy. A waterbolus containing de-ionized water is added at the skin interface for superficial tissue cooling aud antelina matching. The proposed applicator achieves a penetration depth that supersedes other approaches while remaining compact and an ergonomic fit to tumour areas on the body. To consider the inner and peripheral complex shapes of human bodies, the full human body numerical model developed by Remcom is used. This model was segmented from 1 mm step computed tomography (CT) and magnetic resonance imaging (MRI) cross-sections through and adult male and it comprises twenty-three tissue types with thermal and frequency-dependent dielectric properties. The applicator performance is evaluated at three anatomical body areas of the model to assess its suitability for treatment of tumours at different locations. These three anatomical regions present different aperture coupling and tissue composition. \u27Different conformal waterbolus and air gap thickness values are evaluated. The models used in this work are validated with measurements performed in a phantom containing a lossy liquid with dielectric properties representative of homogeneous human body tissue. The dosimetric assessment system (DASY) is used to evaluaxe the specific absorption rate (SAR) generated for the antenna into the liquid. The measurement setup with the antenna, phantom and liquid are simulated. Simulated and measured results in terrms of specific absorption rate and return loss are evaluated

Sensing Systems for Respiration Monitoring: A Technical Systematic Review

Respiratory monitoring is essential in sleep studies, sport training, patient monitoring, or health at work, among other applications. This paper presents a comprehensive systematic review of respiration sensing systems. After several systematic searches in scientific repositories, the 198 most relevant papers in this field were analyzed in detail. Different items were examined: sensing technique and sensor, respiration parameter, sensor location and size, general system setup, communication protocol, processing station, energy autonomy and power consumption, sensor validation, processing algorithm, performance evaluation, and analysis software. As a result, several trends and the remaining research challenges of respiration sensors were identified. Long-term evaluations and usability tests should be performed. Researchers designed custom experiments to validate the sensing systems, making it difficult to compare results. Therefore, another challenge is to have a common validation framework to fairly compare sensor performance. The implementation of energy-saving strategies, the incorporation of energy harvesting techniques, the calculation of volume parameters of breathing, or the effective integration of respiration sensors into clothing are other remaining research efforts. Addressing these and other challenges outlined in the paper is a required step to obtain a feasible, robust, affordable, and unobtrusive respiration sensing system

Wireless modular multi-sensor systems for the analysis of mechanical coupling between respiration and locomotion in mammals

Die Kopplung zwischen Fortbewegung und Atmung (Locomotion-Respiration-Coupling LRC) basiert bei Säugetieren nach den gängigen Modellvorstellungen sowohl auf mechanischen als auch neuromuskulären Bindungen zwischen beiden Prozessen. Zur artübergreifenden Analyse dieser Interaktionen fehlt es bisher an einfach anpassbaren, modularen Systemen. Damit fehlt es an belastbaren Messdaten zur Beantwortung der Fragen, wie Fortbewegungszyklen zum Atemfluss beitragen oder wie die Atemmuskelkontraktionen die Fortbewegung beeinflussen. Die meisten der bisherigen artspezifischen Studien konzentrierten sich auf LRC während des Laufens, aber einige analysierten auch andere Aktivitäten wie Radfahren, Fliegen (Vögel) oder Tauchen. In dieser Arbeit wurde basierend auf einem modularen Multisensor-Funksystem eine neuartige Methode entwickelt, die es ermöglicht, die Interaktion zwischen Fortbewegung und Atmung bei Säugetieren zu analysieren. Das entwickelte System besteht aus vier Komponenten für die LRC-Analyse: (1) einer Thoraxbinnendruckmessung basierend auf einem implantierbaren Gerät, (2) ein Volumenstrommodul zur Messung des lokomotorisch getriebenen Luftvolumens (LDV - Locomotor driven air volume) während des Atemzyklus, (3) ein Schrittidentifikationsmodul zur Berechnung des LRC-Verhältnisses (Schritt/Atem) und (4) ein Muskelaktivitätsmodul zur Analyse des Verhaltens des Atemmuskels während der Kopplung. Diese Module sind freizügig kombinierbar. Die drahtlose Kommunikation erlaubt es, Untersuchungen im Freifeld durchzuführen, wobei sich das Tier (oder der Mensch) im Gegensatz zu früheren Studien, in denen sich das Subjekt mit einer konstanten Geschwindigkeit auf einem Laufband bewegt, frei mit einer selbstgewählten Laufgeschwindigkeit bewegen kann. Diese Möglichkeit könnte das Stressniveau von Tieren während der Experimente signifikant reduzieren, die Analyseergebnisse liegen absehbar näher am "natürlichen" Laufverhalten (unrestrained) als jene von Laufbandstudien (restrained). Als experimenteller Test des Systems wurde die Methode am Menschen angewendet. Das Respiratory Flow Module (RFM) wurde basierend auf einer „ergonomischen Maske“ und einem Strömungssensor entwickelt. Das Respiratory Muscles Module (RMM) nutzte vier Oberflächen-Elektromyographie-Sensoren (sEMG) an der Bauch- und Brustmuskulatur. Am Knöchel jedes Beines befanden sich zwei Beschleunigungssensoren, um den Fuß-Boden-Kontakt zu erkennen. Fünfzehn Teilnehmer wurden bei einem Sprint-Lauftest in einem Sportzentrum (50 m x 30 m) der Technischen Universität Ilmenau beobachtet. Die erhaltenen Ergebnisse bestätigten ein variables LRC-Verhältnis von 2:1, 3:1, 4:1 wie in früheren Studien gezeigt wurde, zeigte jedoch zusätzlich im Falle des LDV die Nutzung der annähernd maximal möglichen Amplitude (Vitalkapazität) auf. Das Experiment belegt, dass die neue Methode zur Untersuchung von Säugetieren verwendet werden kann.Locomotor-respiratory coupling (LRC) is a mechanical and neuromuscular link between respiration and locomotion in mammals. In the last several decades many researchers have developed studies in this field measuring LRC in different mammals. However, until now it was not exactly established how many locomotion cycles contribute to the respiratory flow or how the respiratory muscle contractions affect the locomotion cycles. Most of these studies were focused on LRC during running, but some also analyzed other activities like cycling, flying (birds), diving. In this work a novel method was developed based on a modular multi-sensor wireless system which allows analyzing the interaction between locomotion and respiration in mammals. The developed system consists of four modules for the LRC analysis: (1) a thoracic pressure measurement based on an implantable device, (2) a volumetric flow module to measure the locomotor driven air volume (LDV) during the breathing cycle, (3) a step identification module to calculate the LRC ratio (stride/breath), and (4) a muscular activity module to analyze the behavior of the respiratory muscle during the coupling. The wireless communication allows performing studies in open field, where the animal can move freely with a self selected running pace, contrary to previous studies where the object moves at a steady speed on a treadmill. These characteristics could significantly reduce the stress level of animals during the experiments. The method was applied to humans as an experimental test of the system, the Respiratory Flow Module (RFM) was designed based on an ergonomic mask and flow sensor. The Respiratory Muscles Module (RMM) had four surface Electromyography (sEMG) sensors located at the abdominal and thoracic respiratory muscles and two accelerometers were located at the ankle of each leg to detect the foot-ground contact. Fifteen participants were evaluated in a sprint running test at a sport center (50 m x 30 m) of Technische Universität Ilmenau. The obtained results confirmed a variable LRC ratio of 2:1, 3:1, 4:1, as was shown in previous studies. However, in the case of LDV it reached almost the maximum amplitude of the vital capacity. The performed experiment showed that our novel method could also be used to study other mammals

Imaging fetal anatomy.

Due to advancements in ultrasound techniques, the focus of antenatal ultrasound screening is moving towards the first trimester of pregnancy. The early first trimester however remains in part, a 'black box', due to the size of the developing embryo and the limitations of contemporary scanning techniques. Therefore there is a need for images of early anatomical developmental to improve our understanding of this area. By using new imaging techniques, we can not only obtain better images to further our knowledge of early embryonic development, but clear images of embryonic and fetal development can also be used in training for e.g. sonographers and fetal surgeons, or to educate parents expecting a child with a fetal anomaly. The aim of this review is to provide an overview of the past, present and future techniques used to capture images of the developing human embryo and fetus and provide the reader newest insights in upcoming and promising imaging techniques. The reader is taken from the earliest drawings of da Vinci, along the advancements in the fields of in utero ultrasound and MR imaging techniques towards high-resolution ex utero imaging using Micro-CT and ultra-high field MRI. Finally, a future perspective is given about the use of artificial intelligence in ultrasound and new potential imaging techniques such as synchrotron radiation-based CT to increase our knowledge regarding human development

DESIGN AND CONTROL OF A HUMMINGBIRD-SIZE FLAPPING WING MICRO AERIAL VEHICLE

Flying animals with flapping wings may best exemplify the astonishing ability of natural selection on design optimization. They evince extraordinary prowess to control their flight, while demonstrating rich repertoire of agile maneuvers. They remain surprisingly stable during hover and can make sharp turns in a split second. Characterized by high-frequency flapping wing motion, unsteady aerodynamics, and the ability to hover and perform fast maneuvers, insect-like flapping flight presents an extraordinary aerial locomotion strategy perfected at small size scales. Flapping Wing Micro Aerial Vehicles (FWMAVs) hold great promise in bridging the performance gap between engineered flying vehicles and their natural counterparts. They are perfect candidates for potential applications such as fast response robots in search and rescue, environmental friendly agents in precision agriculture, surveillance and intelligence gathering MAVs, and miniature nodes in sensor networks

Physiological Parameter Sensing with Wearable Devices and Non-Contact Dopper Radar.

M.S. Thesis. University of Hawaiʻi at Mānoa 2017