B0 Shimming using Pyrolytic Graphite

Leiden Repository

B0 Shimming using Pyrolytic Graphite

Type: Master thesis
Title: B0 Shimming using Pyrolytic Graphite
Author: Peña, Andrea
Issue Date: 2017-08-31
Keywords: MRI
Passive shimming
B0 shimming
Pyrolytic graphite
Magnetic susceptibility
Abstract: B0 magnetic field non-uniformity is the cause of a large amount of image artifacts in MRI. B0 inhomogeneities arise due to magnetic susceptibility differences between tissues. In particular, the 9 ppm magnetic susceptibility difference between air and tissue generate disturbances in the B0 main field near the skin. We study the B0 passive shimming approach of covering the skin with a susceptibility-matching material from both an experimental and a mathematical viewpoint. In the experimental study, a lightweight and simple to shape pyrolytic graphite composite foam is used to compensate for the field inhomogeneities in the region of the neck. We experimentally demonstrate that the pyrolytic graphite foam improves the uniformity of the static field in a phantom and in vivo at 3T. In the numerical study, we aim for a design of a neck shim which efficiently homogenizes the B0 field while being practically implementable. We propose a level set optimization method as an approach to find the optimum design for a neck shim. Simulations prove that the proposed method is able to solve the topological optimization problem while preserving the imposed constraints.
Supervisor: Webb, Andrew
Faculty: Faculty of Science
Department: Physics (Master)
Specialisation: Quantum matter and optics
ECTS Credits: 5
Handle: http://hdl.handle.net/1887/52133
 

Files in this item

Description Size View
application/pdf thesis_0708.pdf 4.612Mb View/Open

This item appears in the following Collection(s)