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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Achieving Invisible Balance: Utilizing Novel Elliptical Traps for Improved Radiofrequency Coil Thermodynamic Stability, Minimized Field Distortion, and Common-Mode Current Suppression

Jana Vincent (10711377) 29 April 2021 (has links)
<p>Advances in Magnetic Resonance Imaging (MRI) have been made possible through increased field strengths and innovations in radiofrequency (RF) coils. With increasing field strengths, unique challenges are presented in RF coil development, namely the suppression of common-mode currents present along the shields of the cabling that connect the RF coil to the MR scanner. These currents can lead to coupling with the coil, resulting in a reduction of coil sensitivity and signal-to-noise ratio. These currents can induce local electric fields that beyond a certain level can exceed SAR limits and even cause patient burns. Several cable trap designs exist to help address this problem; however, many of the existing designs, such as bazooka cable traps, are rigid and bulky. This leads to increased overall coil weight and impedes the flexibility of the cable. Improving upon these designs, a small, 3D-printed, lightweight elliptical cable trap is presented. The unique geometry makes it invisible to the MR scanner while maintaining significant mutual inductance that can produce up to 380 Ω on the cable. These structures were wrapped with stranded wire containing four breaks for tuning capacitors. 60 of these elliptical cable traps were placed along the length of a 139-cm cable, replacing the standard 4 bazooka cable traps. The results of B<sub>1</sub> distortion and heating tests showed that these elliptical baluns improve RF coil thermodynamic stability, produce less B<sub>1</sub> distortion, and reduce overall coil weight and bulk compared to a cable with four bazooka traps. </p>
12

Radiofrequency Induced Heating of Implanted Stereo-electroencephalography Electrodes During MRI Scan: Theory, Measurements and Simulations

Bhusal, Bhumi Shankar 23 May 2019 (has links)
No description available.

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