German Title: Erforschung von Quadrupolinteraktionen von 23Na und 35Cl mit Tripelquanten-MRI/MRS

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Abstract

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) can be used to investigate the quadrupolar nuclei 23Na and 35Cl, each with a nuclear spin of 3/2. The Na+ cations and Cl- anions are involved in cellular functions and can undergo quadrupolar interactions with oppositely charged macromolecules. These interactions give rise to triple-quantum (TQ) signals. Compromised physiological functions change the macromolecular composition and ion content, which can be investigated with TQ MRI/MRS. The goal was to develop a sequence to acquire single-quantum (SQ) and TQ images and to map relaxation parameters in vivo within one measurement. First, a density-adapted radial MRI technique (DA-R) was implemented at a 9.4 T scanner. Phantom images demonstrated superior image quality and measurement time efficiency. High-resolution 23Na and 35Cl images allowed for distinction of anatomical features in rat. Second, TQ spectroscopy with time-proportional phase incrementation (TQ-TPPI) was used to acquire data in cells and in rat head. The results revealed interesting discrepancies in 23Na and 35Cl TQ signals, uncovering differences in the quadrupolar interactions of Na+ and Cl- on a molecular level. Finally, TQ-TPPI was combined with DA-R to create TQ and SQ TPPI imaging (TASTI). The sequence was sucsessfully applied to rat head. For the first time, localized ratios between TQ and SQ signal were mapped in different head regions. Furthermore, it enabled the distinction between TQ signal fractions in the intra- and extracellular space. With its ability to analyze local changes in ion content, relaxation times and TQ signal, the TASTI sequence has the potential to become the one tool to combine all major approaches to address 23Na NMR.