B0 Shimming of the Human Brain at Ultrahigh Field MRI with a Multi-Coil Shim Setup

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dc.contributor.advisor Scheffler, Klaus (Prof. Dr.)
dc.contributor.author Aghaeifar, Ali
dc.date.accessioned 2019-11-15T08:57:02Z
dc.date.available 2019-11-15T08:57:02Z
dc.date.issued 2019-11-15
dc.identifier.other 1681956624 de_DE
dc.identifier.uri http://hdl.handle.net/10900/94815
dc.identifier.uri http://nbn-resolving.de/urn:nbn:de:bsz:21-dspace-948157 de_DE
dc.identifier.uri http://dx.doi.org/10.15496/publikation-36199
dc.description.abstract Magnetic resonance imaging (MRI) is widely used for contemporary diagnostics and research. Higher static magnetic field enables imaging with a higher resolution because of the increased signal-to-noise-ratio in comparison to low field MRI. However, this benefit is not cost-free. Less B1+ field uniformity, higher B0 inhomogeneity, higher specific absorption rate (SAR), and shortened T2 and T2* are some of the challenges of measurement at ultrahigh-field (UHF). The aim of this thesis is to address higher B0 inhomogeneity at a magnet with a strength of 9.4 tesla. To this end, the shimming hardware and software required for homogenization of the B0 field were designed, and the performance of the constructed setups has been validated by simulation and in vivo measurements. The first part of the thesis (Chapter 1) describes the source of B0 inhomogeneity, how it changes the FID signal, its consequences, and why UHF intensifies the B0 inhomogeneity. Then, the process of field homogenization, known as shimming, is introduced, and shimming with spherical harmonics is explained. Next, the standard method for B0 field measurement and inhomogeneity quantification is presented, and least squares minimization is described in order to optimal currents calculation for a constrained shimming. Then, dynamic slice-wise shimming is introduced as an approach to achieve a better B0 uniformity by breaking VOI to sub-volumes. Finally, the multi-coil shim setup is presented which benefits from small local coils for a more efficient shimming. The second part of the thesis (Chapter 2) focuses on construction and application of multi-coil shim setup as achievements of this thesis. First, the construction process of the setup and comparison with spherical harmonic basis sets are provided. Later, the impact of the improved B0 uniformity with the dynamic multi-coil shimming on fMRI contrast is studied. Finally, a novel multi-coil design approach is presented in which a multi-coil shim setup is optimized for shimming of the human brain. Sections 3.4 and 3.5 present a summary of the collaborations in other related projects. First, a novel method to design the shim coils’ wiring pattern based on stream function is introduced which allows higher order shimming with limited number of the coils to be achieved. Next, an application of the small local coils for parallel imaging is demonstrated. Small local coils are employed for a local modulation of the magnetic field and superimpose a unique phase variation to the spin distribution that can be used to disentangle different part of the object. The last part of the thesis starts with conclusions and outlook. Later, the resultant publications are listed, and the relevant publications are appended at the end. en
dc.language.iso en de_DE
dc.publisher Universität Tübingen de_DE
dc.rights ubt-podok de_DE
dc.rights.uri http://tobias-lib.uni-tuebingen.de/doku/lic_mit_pod.php?la=de de_DE
dc.rights.uri http://tobias-lib.uni-tuebingen.de/doku/lic_mit_pod.php?la=en en
dc.subject.classification Magnetische Kernresonanz , Gehirn de_DE
dc.subject.ddc 500 de_DE
dc.subject.ddc 530 de_DE
dc.subject.ddc 610 de_DE
dc.subject.other MRI en
dc.subject.other B0 shimming en
dc.subject.other inhomogeneity en
dc.subject.other multi-coil en
dc.subject.other brain en
dc.subject.other amplifier en
dc.subject.other Ultra-high field en
dc.title B0 Shimming of the Human Brain at Ultrahigh Field MRI with a Multi-Coil Shim Setup en
dc.type Dissertation de_DE
dcterms.dateAccepted 2019-10-16
utue.publikation.fachbereich Biologie de_DE
utue.publikation.fakultaet 7 Mathematisch-Naturwissenschaftliche Fakultät de_DE


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