Strategies for Artifact Correction and Motion Monitoring in MRI Through Innovations in Radiofrequency Coil Design
type: CreativeWork
description: In the reconstruction of magnetic resonance (MR) images, two important assumptions that are made are that the main magnetic field B_0 is homogeneous and that there is no bulk movement of the subject. This work proposes various strategies using innovations in radio-frequency (RF) coil design to address the problems that arise when these assumptions are broken. Typically, B_0 inhomogeneities are caused by susceptibility differences at air/tissue interfaces and result in image artifacts such as geometric distortions and signal loss. B_0 inhomogeneities can be corrected through a process called shimming, which generates magnetic field patterns that have a similar spatial distribution but are opposite in polarity. 2\nd order spherical harmonic shimming is used on most clinical scanners, however, it is unable to correct highly localized \B_0 inhomogeneities found in the inferior frontal and temporal brain regions. By integrating a direct current (DC) path onto an RF surface coil, thereby allowing both DC current and an RF current at the Larmor frequency to flow on the same coil, localized B_0 shimming and MR imaging can be performed with the same coil array. This technology, referred to as an integrated parallel reception, excitation, and shimming (iPRES) coil array, was previously used to correct for distortions in spin-echo echo-planar imaging (EPI) and is further developed here to also recover signal loss in gradient-echo EPI, which is used for blood-oxygenation level-dependent (BOLD) functional MRI (fMRI). This was done through modification of the cost function used in the shim optimization, which typically uses a single term representing the B_0 inhomogeneity, to include a second term representing the signal loss, with an adjustable weight to optimize the trade-off between distortion correction and signal recovery. Simulations and experiments were performed to investigate the shimming performance. Slice-optimized shimming with iPRES and the proposed cost function sub…
abstract: In the reconstruction of magnetic resonance (MR) images, two important assumptions that are made are that the main magnetic field B_0 is homogeneous and that there is no bulk movement of the subject. This work proposes various strategies using innovations in radio-frequency (RF) coil design to address the problems that arise when these assumptions are broken. Typically, B_0 inhomogeneities are caused by susceptibility differences at air/tissue interfaces and result in image artifacts such as geometric distortions and signal loss. B_0 inhomogeneities can be corrected through a process called shimming, which generates magnetic field patterns that have a similar spatial distribution but are opposite in polarity. 2\nd order spherical harmonic shimming is used on most clinical scanners, however, it is unable to correct highly localized \B_0 inhomogeneities found in the inferior frontal and temporal brain regions. By integrating a direct current (DC) path onto an RF surface coil, thereby allowing both DC current and an RF current at the Larmor frequency to flow on the same coil, localized B_0 shimming and MR imaging can be performed with the same coil array. This technology, referred to as an integrated parallel reception, excitation, and shimming (iPRES) coil array, was previously used to correct for distortions in spin-echo echo-planar imaging (EPI) and is further developed here to also recover signal loss in gradient-echo EPI, which is used for blood-oxygenation level-dependent (BOLD) functional MRI (fMRI). This was done through modification of the cost function used in the shim optimization, which typically uses a single term representing the B_0 inhomogeneity, to include a second term representing the signal loss, with an adjustable weight to optimize the trade-off between distortion correction and signal recovery. Simulations and experiments were performed to investigate the shimming performance. Slice-optimized shimming with iPRES and the proposed cost function sub…
author: Willey, Devin
keywords: Medical imaging, Electrical engineering
date published: 2022
date modified: 2026-07-24T02:06:57Z
provider: Duke University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Duke University

PropertyValue
property ID: Handle
value: https://hdl.handle.net/10161/25120