Schnelle 1H-NMR-spektroskopische Bildgebung mittels angepasster Phasenkodierung der chemischen Verschiebung

Abstract

The minimum total measuring time T is a crucial parameter for the clinical application of a1H NMR spectroscopic imaging (SI) experiment. To keep it as short as possible is not onlyfor the benefit of the patient, but is also necessary to suppress motion artifacts in thespectroscopic images. In this thesis, Adjusted Chemical Shift Phase Encoding (APE) hasbeen developed as an alternative to the phase encoding scheme used conventionally forspectroscopic U-FLARE, which aims at FFT reconstruction of NMR spectra. For APE,advantage is taken of the fact that often the number of strong resonances K is considerablysmaller than the number of conventional phase encoding steps N. Systematic descriptionand analysis of the NMR signal acquired using the ``constant time´´ encoding scheme leadsto a system of linear equations. Provided that N >= K, this can be solved in the leastsquares sense by exploiting prior knowledge about all resonance frequencies with onlyminor restrictions regarding the choice of encoding times. Thus, the minimum totalmeasuring time, which is proporional to N can be reduced such that an extension ofspectroscopic U-FLARE towards a fast 3D SI method becomes feasible. APE providessimilar signal-to-noise-ratio per unit measuring time as the conventional procedure and hasallowed a reduction of T in recent experiments by a factor of 4. APE lends itself not only toapplications of 1H NMR SI on clinical whole-body scanners, but also to 2D NMRspectroscopic experiments.