| The goal of this dissertation is to analyze the contributions of different vascular responses to the fMRI signal, to develop new fMRI techniques that are sensitive to a single vascular parameter, and to combine information from multi-modality fMRI to study the brain physiology in terms of neuro-vascular control during neural activation. Special concentration was focused on physiological changes in cerebral blood volume (CBV), cerebral blood flow (CBF) and blood oxygenation.; The most commonly used brain mapping technique, Blood Oxygenation Level Dependent (BOLD) fMRI, is based on the detection of small changes in venous blood oxygenation during brain activation. However, it is also sensitive to flow velocity changes in large vessels. This so-called "inflow effect" can reduce the spatial specificity of the BOLD method.; In studying the inflow effects of BOLD fMRI, we found that the CBV changes can also contribute to the total signal changes because the blood T1 (∼1350ms at 1.5T) is longer than tissue TI (∼1000ms). We then designed a new MR pulse sequence to maximize such an effect and minimize other vascular-related effects (e.g. oxygenation, flow), which resulted in an fMRI technique that is only sensitive to CBV changes, termed Vascular Space Occupancy (VASO) dependent fMRI.; The invention of the VASO method for non-invasive monitoring of CBV changes allowed us to, for the first time, simultaneously measure the changes of different physiological parameters, such as blood volume, flow and oxygenation, from which we can directly obtain information regarding the oxygen metabolism of brain tissue.; In order to use the VASO fMRI for advanced brain mapping, this technique needed to be extended to perform multi-slice acquisition so that more portions of the brain could be covered. We designed a novel acquisition scheme called Multiple Acquisition with Global Inversion Cycling (MAGIC) to maintain the VASO contrast for a long period of time during which many slices can be sampled. (Abstract shortened by UMI.)... |
