Multi-Directional Phase-Contrast Flow MRI in Real Time

by Jost M. Kollmeier
Doctoral thesis
Date of Examination:2020-08-31
Date of issue:2021-01-28
Advisor:Prof. Dr. Jens Frahm
Referee:Prof. Dr. Jens Frahm
Referee:Prof. Dr. Jörg Enderlein
Referee:Prof. Dr. Klaus Scheffler
Persistent Address: http://dx.doi.org/10.53846/goediss-8413

 

 

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Abstract

English

This work describes the development of a phase-contrast MRI technique that achieves multi-directional velocity quantification in real time, i.e. at high spatio-temporal resolution and without any physiological gating or data sorting. The technique exploits highly undersampled radial acquisitions with time-efficient flow encoding, a correction strategy for concomitant fields applicable to radial imaging, and an iterative solution for the non-linear image reconstruction problem. MRI is a potent and versatile imaging technique that allows to measure flow velocities, e.g. of blood flow. Unfortunately, MRI is intrinsically slow. Recent advances in real-time MRI based on radial FLASH and non-linear inversion offer high spatio-temporal resolutions and the realization of cross-sectional MRI movies. This real-time approach had been combined with uni-directional phase-contrast flow MRI that quantifies velocities only perpendicular to the imaging plane. In this work, the imaging technique is extended to more velocity dimensions. Opening with a brief overview on the basic principles of phase-contrast and real-time MRI (Chapter 2), this thesis presents the uni-directional flow technique in Chapter 3 followed by proposals for further improvements. Chapter 4 describes the development of a multi-directional extension and its optimization towards high spatio-temporal resolutions, while Chapter 5 proposes further methodological refinements. Chapter 6 addresses the technical accuracy and presents a correction strategy to eliminate background phase errors by concomitant magnetic fields applicable to radial imaging. Preliminary in vivo results demonstrated in Chapter 7 include cardiac flow imaging with velocity quantification in all three directions at less than 2 x 2 mm² pixel-size and more than 60 frames per second. The novel MRI technique developed in this thesis increases the potential of MRI based cross-sectional velocimetry.
Keywords: real-time MRI; phase-contrast MRI; radial MRI; model-based reconstruction; radial Maxwell correction; multi-directional flow; 4D flow; velocimetry; Karman vortex shedding; blood flow; CSF flow; 3D flow
 
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