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Quantification aspects of chemical exchange saturation transfer MRI

Kujawa, Aaron Sarwar; (2020) Quantification aspects of chemical exchange saturation transfer MRI. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Chemical exchange saturation transfer (CEST) is a magnetic resonance imaging (MRI) acquisition technique that generates an image contrast based on proton exchange processes between water molecules and metabolites. This contrast depends on several parameters, for example metabolite concentration and exchange rate which can be used to characterize pathologies such as stroke or cancer. The quantification of these parameters is important because they fully describe the CEST processes and represent sequence and scanner independent biomarkers. However, in vivo the quantification of CEST parameters is difficult because of the high number of different CEST metabolites and their highly correlated model parameters, as well as confounding effects that contribute to the measured signal. Furthermore, the general mathematical model that describes the exchange processes is computationally demanding and requires long processing times. The aim of this thesis was to develop methods for the improved quantification of CEST parameters. To address both, the parameter correlations and the long processing times, a Bayesian fitting algorithm was combined with approximate analytical solutions of the general model equations. A significant reduction of computational time was achieved when fitting continuous-wave saturation data (about 50-fold) and pulsed saturation data (more than 100-fold) with the analytical approximation while the estimated parameters were largely consistent with the parameters from the general numerical solution. In vivo the algorithm was evaluated based on healthy mouse data from a 9.4T animal scanner. Furthermore, an acquisition technique called PRO-QUEST was translated and optimized for a 3T clinical scanner based on a 3D readout. The aim of this technique is to quantify CEST parameters based on signal acquisition during the approach of the magnetization towards steady-state. Modifications of the technique were suggested to correct for the enhanced direct saturation effect at lower field strengths. The methods were evaluated and compared based on measurements of healthy human volunteers.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Quantification aspects of chemical exchange saturation transfer MRI
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10096899
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