Inaugural - Dissertation

zur nichtinvasiven Evaluation der Gewebevitalität darstellen. The goal of this work was to provide techniques and hardware for 23 Na MRI of the human brain, heart and muscle in a clinical scanner at 1.5 T. For this purpose, radiofrequency (RF) coils were developed and a transmit/receive switch was adapted to 16.84 MHz. A 3D radial gradient echo (GRE) sequence was implemented, with a minimum echo time T E min = 70 µs for 1 H and 200 µs for 23 Na, allowing to detect both the short (T * 2 = 0.5 ms) and the long (T * 2 = 12−25 ms) components of the 23 Na NMR signal for total 23 Na content evaluation. A gridding reconstruction algorithm with a Kaiser-Bessel window and a rho filter was implemented and optimised for both 23 Na and 1 H MRI. At an acquisition time T acq = 10 min and a nominal resolution ∆x = 4 mm, the signal-to-noise ratio SNR of the in-vivo 23 Na 3D radial images was twofold higher than in standard cartesian GRE MRI (T E min = 2 ms). In the radial images blurring due to T 2 signal decay during data acquisition was observed, reducing the resolution by approximately a factor of two. Both cartesian and radial GRE methods were compared at 1.5 T and 4 T. An SNR increase of SN R 4T /SN R 1.5T ∼ 4 was measured in-vivo. In brain tumour patients, a 20% 23 Na MRI signal increase in the tumour region was detected. A contrast-to-noise ratio CN R = 23% between healthy tissue and tumour achieved with the 3D radial was 20% higher than the CNR of the cartesian sequence. In patients with a 23 Na channel disfunction, a 23 Na MRI signal increase of ∼ 10% was measured. This method allows for the detection of changes in the intracellular 23 Na concentration and may provide a new tool to non-invasively evaluate tissue vitality. A la meva família, amb tot el meu amor. To my family, with all my love.