title: Advancing Sodium Multi-Quantum Coherences MRI on Clinical Scanners
creator: Licht, Christian
subject: ddc-530
subject: 530 Physics
description: In recent years, sodium (23Na) Magnetic Resonance Imaging (MRI) has gained increased attention, particularly with the development of ultra-high field >=7 T MRI. It provides non-invasive physiological information related to the cell's vitality, making it an exciting tool for medical research. 23Na MRI provides a non-invasive quantitative estimation of the tissue sodium concentration. However, 23Na MRI could provide rich additional contrast information, which can be exploited by leveraging 23Na Multi-Quantum Coherences (MQC) MRI. Unfortunately, 23Na MQC MRI is inherently slow and challenging to use in clinical protocols. As a result, the full potential of 23Na MQC MRI has yet to be explored. This work focused on developing acceleration techniques to obtain 23Na MQC MRI in clinically acceptable scan time. The proposed frameworks were extensively studied on numerical simulations, phantom, and in vivo human brain data acquired at 3 and 7 T.    In the first part of this thesis, a custom-built multi-dimensional (5D) reconstruction framework based on Compressed Sensing (CS) theory is presented. This framework constitutes an advanced sampling strategy to accelerate the acquisition of 23Na MQC MRI up to 3-fold, coupled with an iterative reconstruction algorithm that optimally leverages 23Na MQC MRI's signal structure to reconstruct highly undersampled data reliably. A comprehensive study showed the advantages of the 5D CS over the conventional 3D CS reconstruction. Reliable acceleration factors up to 3-fold were possible, reducing acquisition times or increasing the spatial resolution to unprecedented 6x6x10mm3.    Secondly, the gained experience of MR signal sampling and reconstruction of undersampled 23Na MQC MRI from the first part was leveraged to improve the sequence and the reconstruction framework. The sequence was adapted to simultaneously acquire 23Na and 23Na MQC MRI, with 23Na MQC MRI being highly undersampled. The reconstruction was performed by two advanced low-rank reconstruction frameworks that optimally exploit the coherent information in the acquired data. 6x6x6mm3 in vivo 23Na MRI leveraging the Double Half-Echo technique was demonstrated for the first time. The low-rank reconstruction performance for 23Na MQC MRI was compared to the 5D CS model and outperformed 5D CS regarding SSIM, RMSE, and SNR. Eventually, the novel accelerated acquisition was leveraged to obtain whole-brain 23Na MQC MRI images with an unprecedented spatial resolution of 8mm isotropic in 2x23 minutes, uniquely showcasing the sodium tissue characteristics of white and grey matter. The simultaneously acquired sodium images at 6mm isotropic lay ground for a complete quantitative evaluation of brain sodium MRI for future studies.      This thesis aimed to overcome 23Na MQC MRI's obstacles, mainly targeting the slow acquisition speed leading to lengthy acquisitions and limited spatial resolution. Two advanced reconstruction frameworks have been proposed that efficiently leverage the highly multi-dimensional structure of 23Na MQC MRI and, therefore, outperform conventional reconstruction techniques. Additionally, an efficient sequence was proposed that allows for simultaneous acquisition of 23Na and prospectively undersampled 23Na MQC MRI within clinically acceptable time that allows for a direct comparison of 23Na and 23Na MQC MRI fostering the possibility to be used for clinical studies. Extensive experiments demonstrated applicability on 3 and 7 T clinical MRI, which makes the frameworks highly versatile and robust. In conclusion, the presented sequence and reconstruction algorithms represent a promising framework for future studies exploiting 23Na and 23Na MQC MRI with a clinical research focus.
date: 2024
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/34976/1/Dissertation_Licht.pdf
identifier: DOI:10.11588/heidok.00034976
identifier: urn:nbn:de:bsz:16-heidok-349767
identifier:   Licht, Christian  (2024) Advancing Sodium Multi-Quantum Coherences MRI on Clinical Scanners.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/34976/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng