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Abstract

Sodium (23Na) ions play an essential role in the physiology of living tissue and can be observed non-invasively due to a nuclear spin of 3/2 via magnetic resonance imaging (MRI). The interaction of the electrical quadrupole moment of the nucleus and the external field gradient causes a rapid biexponential signal relaxation, which represents a direct probe into the microscopic environment. The aim of this thesis was to develop a time-efficient in vivo measurement of the apparent transverse relaxation times (T2,s*,T2,l*). This was realized for brain parenchyma by optimization of the temporal sampling and a novel radio frequency coil leading to an increase in signal-to-noise ratio of up to 145 %. With the optimized pattern relaxation times were determined in healthy human white matter to be T2,s*,T2,l* = 4.2 ± 0.4 ms / 34.4 ± 1.5 ms. Compared to linear sampling, up to 29 % reduction in mean uncertainty was achieved. Monte-Carlo simulations further demonstrated a 73 % decrease in bias. Based on the T2 values, the average correlation time of the interaction could be estimated at 39.3 ± 2.5 ns.