Fetal Blood Flow Mapping with Magnetic Resonance Imaging

Phase contrast magnetic resonance imaging (MRI) has the potential to assess fetal blood flow. However, it faces challenges such as the small size of fetal vessels, the high fetal heart rate, uncontrolled fetal motion, limited methods to measure the fetal heart rate and the considerable complexity of the fetal circulatory system. In this thesis, methods allowing rapid fetal flow measurement are developed with retrospective motion correction and derivation of the fetal heart rate which allow generating dynamic volumetric fetal flow networks providing novel ways for comprehensive evaluation of the normal circulation and its disruption by pathologies. The thesis first presents the healthy fetal circulatory system and how it is altered by intrauterine growth restriction and congenital heart diseases in Chapter 1. Assessment and management of fetal pathologies with ultrasound are presented along with a discussion of associated limitations. Applications of MRI for fetal blood flow quantification along with an overview of the relevant acquisition, acceleration and reconstruction techniques are discussed. The achievements in this work are then discussed in three incremental stages. First, a pipeline for rapid single slice phase contrast MRI for fetal blood flow measurement with retrospective motion correction is demonstrated in Chapter 2. Second, motion corrected and conventional phase contrast MRI are compared in Chapter 3 to show the effects of motion correction on fetal blood flow measurement. Third, rapid multislice phase contrast MRI measurements from multiple stacks are combined with motion correction to reconstruct dynamic volumetric fetal blood flow networks. Finally, Chapter 5 presents the scope of the contributions from this thesis in the contemporary scientific literature along with further applications of and improvements in the developed tools.Ph.D