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

Mechanical and GWP Assessment of Concrete Using Blast Furnace Slag, Silica Fume and Recycled Aggregate

Demolition waste and cement production is responsible for 36% of total waste produced on earth and 8% of the worlds CO2 emissions, respectively. Due to limited research on concrete mixes containing ternary cementitious mixes (Ground Granulated Blast-furnace Slag (GGBS) and Silica Fume (SF)) and demolition waste, the paper reviewed the mechanical properties of concrete, and structural performance of reinforced beams. Thereafter, life cycle analysis (LCA) was investigated to understand the true environmental impact, focusing on Global Warming Potential (GWP). Results show that recycled concrete aggregates (RCA) had no significant negative impact on the compressive strength, tensile strength, and modulus of rupture of concrete. The inclusion of GGBS and SF in mixes containing RCA eliminated any negative impact and for all mixes produced greater strengths in comparison to the control mix, due to the secondary reaction of Ca (OH)2 and pore refinement. The flexural behavior of the concrete beams with 0%, 25%, 50% and 100% RCA, 25% GGBS and 5% SF is similar. LCA results showed that replacing NA with 25%, 50% or 100% RCA has no significant impact on the GWP emissions. This is because of the similar emissions associated with manufacturing and processing of recycled and natural aggregates. However, replacing cement with 5% SF and 25% GGBS improves the GWP environmental response of concrete significantly. Additionally, natural aggregates have a higher GWP contribution than that of recycled concrete aggregates by almost 80% since the process of NA required quarry operation and transportation while the RCA are produced on site from an existing building waste

Dual-Tuned Removable Common-Mode Current Trap for MRI

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are preferred methods of gathering information from the body due to their non-invasive approach of obtaining a diagnosis. MRI can obtain spatial mappings from a region of interest, while MRS can obtain metabolic information from different elements. Dual-tuned radiofrequency (RF) coils are able to capture signals produced by both hydrogen atoms and a second atom of interest. Unwanted shield currents occur in these scans, which can cause image distortion, while the high energy dissipated can create harmful heat, which can injure the patient. These shield currents, also known as common-mode currents, need to be suppressed in the RF coils by non-magnetic current traps, or chokes. Typically, chokes are soldered directly onto the coax cables and require precise placement. In this paper, a novel dual-tuned current choke that is not soldered to the cable is presented. The design was manufactured with 3D printing to allow for optimal customization. The current trap attenuates shield currents at the Larmor frequency for hydrogen and phosphorous at 3T, 127.74MHz and 51.72MHz by -17.8 dB and -8.39 dB respectively. This novel device facilitates dual-tuned coil operation by not having to place two current traps for two frequencies, while also being able to relocate the trap to where common-mode currents are highest

Assessment of Natural Resources Use for Sustainable Development - DPSIR Framework for Case Studies in Portsmouth and Thames Gateway, U.K.

This chapter reports on the uses of the DPSIR framework to assess the sustainability of the intertidal environments within the two UK case study areas, Portsmouth and Thames Gateway. It focuses on statutory conservation areas dominated by intertidal habitats. Two are located in Portsmouth (Portsmouth and Langstone Harbours) and four in the Thames Gateway (Benfleet Marshes, South Thames Estuary, Medway Estuary and the Swale in the Thames Gateway). Based on the reduction of a number of pressures and impacts observed in recent decades and the improvement of overall environmental quality, all six SSSIs are considered to be sustainable in the short and medium term. In the future, it is possible that the impacts of climate change, especially sea-level rise, might result in further reduction in the area and/or quality of intertidal habitats. Further integration between conservation and planning objectives (both for urban development and management of flood risk) at local level is needed to support the long-term sustainability of intertidal habitats

Wake interaction in offshore wind farms with mesoscale derived inflow condition and sea waves

Numerical simulation is an indispensable tool for the design and optimization of wind farms layout and control strategies for energy loss reduction. Achieving consistent simulation results is strongly related to the definition of reliable weather and sea conditions, as well as the use of accurate computational fluid dynamics (CFD) models for the simulation of the wind turbines and wakes. Thus, we present a case study aiming to evaluate the wake-rotor interaction between offshore multi-MW wind turbines modelled using the Actuator Line Model (ALM) and realistic wind inflow conditions. In particular, the interaction between two DTU10 wind turbines is studied for two orientations of the upstream turbine rotor, simulating the use of a yaw-based wake control strategy. Realistic wind inflow conditions are obtained using a multi-scale approach, where the wind field is firstly computed using mesoscale numerical weather prediction (NWP). Then, the mesoscale vertical wind profile is used to define the wind velocity and turbulence boundary conditions for the high-fidelity CFD simulations. Sea waves motion is also imposed using a dynamic mesh approach to investigate the interaction between sea waves, surface boundary layer, and wind turbine wakes and loads

Mechanical and GWP assessment of concrete using Blast Furnace Slag, Silica Fume and recycled aggregate

Data Availability: Data will be made available on request.Demolition waste and cement production is responsible for 36 % of total waste produced on earth and 8 % of the worlds CO2 emissions, respectively. Due to limited research on concrete mixes containing ternary cementitious mixes (Ground Granulated Blast-furnace Slag (GGBS) and Silica Fume (SF)) and demolition waste, the paper reviewed the mechanical properties of concrete, and structural performance of reinforced beams. Thereafter, life cycle analysis (LCA) was investigated to understand the true environmental impact, focusing on Global Warming Potential (GWP). Results show that recycled concrete aggregates (RCA) had no significant negative impact on the compressive strength, tensile strength, and modulus of rupture of concrete. The inclusion of GGBS and SF in mixes containing RCA eliminated any negative impact and for all mixes produced greater strengths in comparison to the control mix, due to the secondary reaction of Ca (OH)2 and pore refinement. The flexural behaviour of the concrete beams with 0 %, 25 %, 50 % and 100 % RCA, 25 % GGBS and 5 % SF is similar. LCA results showed that replacing NA with 25 %, 50 % or 100 % RCA has no significant impact on the GWP emissions. This is because of the similar emissions associated with manufacturing and processing of recycled and natural aggregates. However, replacing cement with 5 % SF and 25 % GGBS improves the GWP environmental response of concrete significantly. Additionally, natural aggregates have a higher GWP contribution than that of recycled concrete aggregates by almost 80 % since the process of NA required quarry operation and transportation while the RCA are produced on site from an existing building waste

Diagnostic and therapeutic aspects of hemiplegic migraine

Hemiplegic migraine (HM) is a clinically and genetically heterogeneous condition with attacks of headache and motor weakness which may be associated with impaired consciousness, cerebellar ataxia and intellectual disability. Motor symptoms usually last <72 hours and are associated with visual or sensory manifestations, speech impairment or brainstem aura. HM can occur as a sporadic HM or familiar HM with an autosomal dominant mode of inheritance. Mutations in CACNA1A, ATP1A2 and SCN1A encoding proteins involved in ion transport are implicated. The pathophysiology of HM is close to the process of typical migraine with aura, but appearing with a lower threshold and more severity. We reviewed epidemiology, clinical presentation, diagnostic assessment, differential diagnosis and treatment of HM to offer the best evidence of this rare condition. The differential diagnosis of HM is broad, including other types of migraine and any condition that can cause transitory neurological signs and symptoms. Neuroimaging, cerebrospinal fluid analysis and electroencephalography are useful, but the diagnosis is clinical with a genetic confirmation. The management relies on the control of triggering factors and even hospitalisation in case of long-lasting auras. As HM is a rare condition, there are no randomised controlled trials, but the evidence for the treatment comes from small studies