Reliving the past requires the integration of multi-modal sensory details into a coherent mental impression of the initial event. In most people, memory for life episodes, or Autobiographical Memory (AM), is rich in sensory-perceptual elements that provide the vivid impression of travelling back in time. Abundant evidence indicates that the hippocampus plays a central role in AM recollection, but much research is still needed to determine which AM attributes engage the hippocampus at retrieval. My work assessed the relationship between hippocampal function and the perceptual richness of memory episodes. I designed a paradigm that captured the complexity of AM, and that manipulated perceptual richness while controlling for other AM confounds, such as recency, rehearsal, personal relevance, and “story” content. Participants studied and recalled perceptually enriched and impoverished laboratory events (film clips and written narratives, respectively) matched for the complexity of their storyline. An AM condition was also included for comparison. I tested healthy individuals and participants with unilateral medial temporal lobe epilepsy (mTLE), a clinical population with well documented hippocampal damage, on this paradigm. Perceptual richness was greatly reduced in people with mTLE, an effect that was most salient in the perceptually enriched conditions (AM and film clips). In a functional MRI version of this paradigm conducted on healthy individuals, I identified neural regions sensitive to the perceptual richness of AM and laboratory events, which included the anterior portion of the right hippocampus and other regions known to play a role in imagery and visual processing. In patients with right-lateralized mTLE, activation in these brain regions was markedly reduced in all memory conditions, which was consistent with the reduced perceptual richness I observed behaviourally. I reveal a clear relationship between hippocampal function and the perceptual richness of episodic memory, suggesting that the hippocampus plays a central role among brain regions that support the integration of multi-modal details into enriched memory experiences. My findings also advance our knowledge of how pathology and the nature of memory representation affect the neural correlates of episodic memory.

Pulmonary arterial hypertension (PAH) alters pulmonary hemodynamics by changing the vascular wall mechanics. Currently, pulmonary vascular resistance is used clinically to assess the disease. However, the invasive nature of pressure measurements, needed for calculating the resistance, prevents longitudinal monitoring of patients during therapy. This work employs wave reflection as an alternative measure of the downstream stiffness and proposes a new method for wave reflection assessment using only non-invasive phase contrast magnetic resonance (PCMR) flow data. The feasibility of the proposed method was investigated in a numerical model of blood flow in the right pulmonary artery. Furthermore, it was validated experimentally using a flow phantom and compared with an existing invasive technique. Finally, the feasibility of the method was tested in a study of the right pulmonary artery of a volunteer. This approach may provide a non-invasive method to evaluate PAH and its response to therapy.

PURPOSE: The objective was to determine if particular magnetic resonance, clinical and demographic findings were associated with functional status prior to surgery and predictive of functional outcomes at follow-up. RESULTS: The study included 65 consecutive CSM patients. The modified Japanese Orthopaedic Association Scale (mJOA) was used as the primary outcome measure. Higher baseline mJOA scores were associated with younger age, shorter duration of symptoms, fewer compressed segments and less severe cord compression. Better post-operative mJOA scores were associated with younger age, shorter duration of symptoms and higher baseline scores. Using multivariate analysis, baseline and follow-up mJOA scores adjusted for baseline mjOA score were best predicted by age. CONCLUSION: Age and clinical severity scores at admission can both provide valuable information. However, MR imaging features of the spinal cord before surgery cannot accurately predict the functional prognosis for patients with CSM and hence alternative imaging approaches may be required.

Anger is commonly referred to in the context of aggressive behaviors. However, little is known about more nuanced effects of this emotion on behavior, nor its neural correlates as a subjective feeling state. For instance, several studies suggest that angry people, in contrast to anxious individuals, perceive risks optimistically. It remains unknown whether these opposing effects of trait anxiety and trait anger on risk perceptions manifest in a direct behavioral measure of risk taking. Our first experiment showed, as predicted, that high trait anxiety was associated with pessimism, whereas anger exerted an optimistic bias on likelihood perceptions. However, these biases did not translate into differences in risk taking behavior. Instead of optimism, impulsivity was highlighted as a mediator of risk proneness in individuals who tend to express anger. A second project investigated the neural basis of anger as an affective state elicited by emotionally evocative social scenes. Participants' attention was directed towards transgressors or their victim, which elicited feelings of anger and sadness respectively. These distinct emotions were associated with differential activity patterns in regions related to affective processing; the amygdala, insula and subgenual anterior cingulate cortex. Individual differences in trait empathy emerged as strong modulators of these activity patterns. In contrast, the ventromedial prefrontal cortex response to transgressors versus victims correlated positively with an individual's tendency to express anger, suggesting a role of this region in the regulation of angry feelings.

A complex physiological system, composed of central and peripheral signals, balances energy intake and expenditure. Among these signals, the enteric and orexigenic hormone ghrelin is a regulator of energy balance with several uncharacterized functions. Although much research has accumulated regarding ghrelin's effects on metabolic parameters, little is known about its other behavioural and cognitive effects. Consequently, this study, using functional magnetic resonance imaging, showed that ghrelin administered intravenously to healthy volunteers increased the neural response to food pictures, as well as faces of fear and disgust, in brain areas regulating the hedonic and incentive evaluation of visual stimuli, such as the amygdala. Moreover, ghrelin exhibited memory enhancing effects for both food pictures and faces of fear and disgust. These findings suggest that ghrelin's activation of the amygdala may serve as a magnitude signal for value judgments of visually-presented food and non-food stimuli, thus engaging critical feeding, emotional and cognitive responses.

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Imaging speed is an important issue in magnetic resonance imaging (MRI), as subject motion during image acquisition is liable to produce artifacts in the image. However, the speed at which data can be collected in conventional MRI is fundamentally limited by physical and physiological constraints. Parallel MRI is a technique that utilizes multiple receiver coils to increase the imaging speed beyond previous limits by reducing the amount of acquired data without degrading the image quality. In order to remove the image aliasing due to k-space undersampling, parallel MRI reconstructions invert the encoding matrix that describes the net effect of the magnetic field gradient encoding and the coil sensitivity profiles. The accuracy, stability, and efficiency of a matrix inversion strategy largely dictate the quality of the reconstructed image. This thesis addresses five specific issues pertaining to this linear inverse problem with practical solutions to improve clinical and research applications. First, for reconstruction algorithms adopting a k-space interpolation approach to the linear inverse problem, two methods are introduced that automatically select the optimal k-space subset samples participating in the synthesis of a missing datum, guaranteeing an optimal compromise between accuracy and stability, i.e. the best balance between artifacts and signal-to-noise ratio (SNR). While the former is based on cross-validation re-sampling technique, the second utilizes a newly introduced data consistency error (DCE) metric that exploits the shift invariance property of the reconstruction kernel to provide a goodness measure of k-space interpolation in parallel MRI. Additionally, the utility of DCE as a metric for characterizing and comparing reconstruction methods is demonstrated. Second, a DCE-based strategy is introduced to improve reconstruction efficiency in real time parallel dynamic MRI. Third, an efficient and reliable reconstruction method that operates on gridded k-space for parallel MRI using non-Cartesian trajectories is introduced with a significant computational gain for applications involving repetitive measurements. Finally, a pulse sequence that combines parallel MRI and multi-echo strategy is introduced for improving SNR and reducing the geometric distortion in diffusion tensor imaging. In addition, the sequence inherently provides a T2 map, complementing information that can be useful for some applications.

Bibliography: leaves 148-155. / xiv, 210 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis provides several methods for assessment of total machine dependent distortion which allows the clinical significance of that distortion to be established. A method for removal of machine dependent distortions is also presented and shown to work for a locally produced, large field of view spatial linearity phantom. Finally, a possible method is developed which is suitable for application of the distortion correction method to actual patients. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1997?

Includes a list of thesis related publications, reviews and thesis related abstracts, awards, book chapters and invited presentations (leaves vii-xii). / Includes bibliographical references (leaves 179-234). / xvii, 234 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A systematic evaluation of magnetic resonance imaging and its use in the ex vivo and in vivo setting, in the aorta and coronary arteries in rabbit and porcine models, leading to the potential for human coronary atherosclerotic imaging. / Thesis (Ph.D.)--Adelaide University, Dept. of Medicine, 2001

Diffusion Tensor Magnetic Resonance Imaging (DTI) is a recently-developed technique that can image in vivo the white matter pathways of the central nervous system. This study used 12-direction diffusion-weighted MRI data from nine stroke patients acquired as part of a three-year stroke rehabilitation study coordinated by the Movement Neuroscience Laboratory at the University of Auckland. DTI was used to investigate corticospinal connectivity. From the FA maps, it is found that in those patients whose motor connectivity has been compromised by the stroke to the extent that no motor evoked potential (MEP) can be elicited from a selected affected muscle group, the asymmetry in mean FA values in the posterior limbs of the internal capsules (PLICs) is correlated with functional recovery as measured by the Fugl-Meyer clinical score. Using probabilistic tractography in the contralesional hemisphere produced CST location and somatotopy results that were consistent with those of previous studies. However, in the ipsilesional hemisphere, connectivity results were highly variable. A measure of change in symmetry of mean connectivity is found to correlate with functional recovery as measured by change in FM score. This supports previous work which has correlated CST integrity and functional improvement and it supports the theory that functional recovery after stroke depends on the extent to which motor CNS symmetry can be regained in the new post-stroke architecture. It also suggests that the movement of the fMRI activations occurs in such a way as to make the most of the preserved white matter connectivity.