Národní úložiště šedé literatury Nalezeno 1 záznamů.  Hledání trvalo 0.00 vteřin. 
The Study of Artifacts in MR Tomographic Images for Medical and Technical Applications
Al Khaddour, Mouin ; Frollo, Ivan (oponent) ; Jiřík, Radovan (oponent) ; Fiala, Pavel (vedoucí práce)
This dissertation analyses artifacts in NMR images. In medical practice, the artifacts can impede proper diagnostics of pathological tissues and, for this reason, need to be eliminated. In this thesis, an analysis of the most frequent image artifacts is performed to eliminate the occurrence of these undesired effects. In connection with artifacts caused by inhomogeneity of the static magnetic field, a novel dual measurement method is discussed. The thesis describes a method for estimating the basic and RF field inhomogeneity in NMR based on the measurement of T2 and T2*. The technique combines the gradient and spin echo acquisition procedures to differentiate the T2 and T2* relaxation times. Exponential approximation of the relaxation process has to be performed. Importantly, experimental results for the plastic and copper specimens are shown. It is vital to note that a significant and commonly found problem lies in the magnetic susceptibility artifact; different magnetic susceptibility values at the boundary between two materials can result in magnetic field inhomogeneity and even total loss of the signal.

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