| Summary: | Functional Magnetic Resonance Imaging, or fMRI, is today a well established tool used to assess both resting state connectivity and task activation in neuroscience. It has also been used for the study of brain development in neonates and there are a small number of pilot studies that seek to use fMRI in utero. However, there are formidable challenges in this application as the fetus lies within the mother and is moved by her respiration as well as performing its own sporadic and unpredictable motion. Thus motion is a core issue for any fetal fMRI study. The first chapter of the thesis discusses a pipeline that was developed to analyse fetal fMRI data acquired with standard sequences. The approach addresses motion correction as a primary requirement, both to stabilise anatomical content for each voxel in a fMRI time series, but also to correct the data from other sources of image artefacts that can be modulated by movement, such as bias eld, spin history and distortions. From the results of this study, it emerges that functional MRI is feasible in the developing fetus. The magnetic properties of fetal and infant brain tissue are very different from adults, leading to a longer T2* relaxation time. This would suggest the use of longer echo times to optimise the BOLD eect, with the downside of decreasing imaging speed. Therefore, the second chapter explores the use of an echo shifted EPI (es-EPI) sequence that achieves an improved signal sensitivity while maintaining ecient sampling. The sequence has been extensively tested on phantom experiments and an improved signal detection is demonstrated on a series of fMRI experiments run on preterm and term-equivalent babies. The long T2* and the lack of air-tissue boundaries between the fetal head and the womb encourages the use of EVI as favourable tool for fetal fMRI. A main benefit of an EVI sequence could indeed be imaging speed and robustness to motion. In a third chapter, EVI fetal imaging is explored and the methods developed allowed the fetal brain to be imaged in full 3D. Despite the challenges of making this work robustly, we speculate that further refinements of the sequence could constitute the ground work with which to perform fetal fMRI in the near future.
|
|---|
