MR image formation can be viewed as having two distinct phases: excitation and signal reception. Imaging relies on three-dimensional spatial localization of this signal, which is achieved either wholly in the reception phase by use of frequency/phase encoding, or in conjunction with 1D localization in the excitation phase (slice encoding). Parallel receiver coils have been used to accelerate this Fourier encoding, primarily during reception but more recently also during excitation via use of ‘Multiband’ excitation pulses. These advances have revolutionized MRI in the last 10-15 years, allowing this typically slow imaging modality to perform rapid imaging with vastly reduced artefacts.
While encoding in the reception phase is well studied, excitation encoding is not. It is in fact possible to apply large amounts of spatial encoding to the excitation, with the potential to excite arbitrary localized volumes, not just slices as done currently. This type of “zoomed” MRI would potentially allow encoding effort to be focused only on a region of interest, which is particularly relevant when imaging a small object embedded within a larger field of view, as is the case for fetal, cardiac or prostate imaging for example. Spatial localization in this way would interact with current reduced encoding methods which operate in the Fourier domain and the two are complementary; studying this synergy is the aim of this project.