Browsing by Subject "Diffusion Tensor Imaging"
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Item Diffusion Kurtosis Imaging as a Diagnostic Tool for Parkinson's Disease(2015-01-26) Vento, Joseph; Cardoso, Ellison; Otaduy, MariaReliable diagnosis of Parkinson's disease requires long-term assessment of a patient's motor performance tests and response to medication. Though the development of magnetic resonance imaging (MRI) presents an additional tool in making a diagnosis, limited imaging biomarkers have been reported that support a clinical diagnosis of Parkinson's disease or its differentiation from similarly presenting diseases. Diffusion Kurtosis Imaging (DKI) is an MRI method that quantifies deviation of water diffusion from normal Gaussian distribution. DKI is a more sensitive technique than conventional diffusion tensor imaging (DTI) for assessing tissue microstructure. The parameters provided by DKI analysis, particularly the mean kurtosis, reflect structural changes within brain regions and demonstrate potential as a diagnostic tool for Parkinson's disease where the basal ganglia are known to markedly change. Here we examine the DKI maps of 86 patients from Hospital das Clinicas da FMUSP in Sao Paulo, Brazil. 49 patients presented with a previous diagnosis of Parkinson's disease based on the UK Parkinson's Brain Bank criteria (mean age, 65.3 + 8.7 [standard deviation]), 19 patients with a previous diagnosis of essential tremor based on the Movement Disorder Society standards (mean age, 64.7 + 6.7) and 27 patients were age-matched healthy controls (mean age, 64.5 + 10.9). All patients underwent the same 3T MRI procedure, consisting of a DTI scan with 32 different gradient directions and b values of 0, 1000, and 2000 s/mm2, necessary to construct a DKI map. Using a region of interest (ROI) analysis on the substantia nigra (rostral, middle, and caudal) and putamen for each patient and comparing mean kurtosis values, we find no significant differentiation of Parkinson's disease patients in the substantia nigra, but significantly higher mean kurtosis values in the putamen of Parkinson's patients (0.82 + 0.05 [standard deviation]) than healthy controls (0.60 + 0.04, p = 0.0158). Neither analysis demonstrated significant difference from essential tremor patients. Higher mean kurtosis estimates in the basal ganglia of Parkinson's disease patients may reflect changes in the microstructural environment of these structures related to disease progression. Further studies should investigate the histological correlates of these values and the reliability of DKI estimates as a diagnostic tool in various stages of the disease.Item Image Processing Considerations for High Resolution Diffusion Tensor Imaging of the Human Brainstem(2012-07-17) Hulsey, Keith McLeod; McColl, Roderick W.Diffusion weighted MRI is used to measure the diffusivity of water in the human brain noninvasively. Diffusion tensor imaging (DTI) fits the diffusivity measurements from many directions to a tensor model of the diffusivity of water in brain tissue. DTI is particularly useful for interrogating the health and organization of white matter in the brain. The human brainstem has many white matter tracts that connect small nuclei in the brainstem to other regions of the brain. High resolution DTI of the brainstem may be helpful in understanding diseases that implicate brainstem nuclei. There are technical challenges for DTI which must be addressed to provide the most sensitive and meaningful measurements. Some of these challenges are: accurate registration between diffusion weighted images, accurate fitting of the data to the tensor model, measuring significance of group differences using DTI results, and increasing image resolution. This study has focused on finding solutions for accurate fitting of data to the tensor model in the presence of signal void artifacts and on increasing image resolution beyond the point at which signal aliasing occurs. To meet the aims of this study I have; 1) developed an innovative approach to detect and remove signal void artifacts caused by subject motion, brain motion induced by cardiac pulsation and scanner vibration, 2) developed an innovative approach to mask aliased signal in DTI scans which have a field of view smaller than the subject's head, and 3) shown that removing signal void artifacts from the DTI scans acquired for the Gulf War Illness study produces significant changes in FA for most subjects in the study. Removing signal void artifacts from the Gulf War Illness study data did not, however, alter the conclusions of group comparisons for the samples of Gulf War veterans studied. Two conclusions of this study are that signal void artifacts should be removed from DTI data before conducting analysis and that an image with a field of view larger than the subject's head can be used to estimate the location of aliased signal in DTI scans acquired with fields of view smaller than the subject's head.Item Longitudinal Changes in Resting-State Connectivity after Traumatic Axonal Injury(2014-07-24) Krishnan, Kamini; Marquez de la Plata, Carlos; Cullum, C. Munro; Ringe, Wendy; Aslan, Sina; Spence, JeffreyLittle is known about neural network connectivity immediately after a traumatic axonal injury (TAI). This is the first longitudinal study in TAI to examine functional connectivity in the Default Mode Network (DMN) and Central Executive Network (CEN) within 48 hours after traumatic brain injury with repeat imaging 7 months later. Aims: (a) characterize connectivity in these networks at the sub-acute stage of injury, (b) evaluate longitudinal change in networks with recovery, and (c) explore how this change might be associated with structural connectivity and neurocognitive outcome. Resting-state fMRI and diffusion tensor imaging (DTI) scans were acquired from 21 patients with moderate-severe brain injuries consistent with TAI compared with 8 non-injured controls. Neurocognitive outcome was assessed at 7 months. Results revealed lower resting-state DMN connectivity 48 hours after TAI compared to non-injured controls, and this persisted 7 months after injury. CEN connectivity was comparable between acutely injured patients and controls, though patients demonstrated increased CEN connectivity at 7 months. These patterns of functional connectivity in patients were associated with alterations in structural connectivity, where areas of decreased functional connectivity were associated with decreased integrity of white matter tracts connecting those regions. However, some regions within these networks demonstrated increased functional connectivity despite presence of structural damage. Taken together, results suggest disruptions in functional and structural connectivity are present as early as 48 hours after a TAI. Alterations in functional connectivity during the recovery period may be explained either by structural damage or could suggest the presence of neural compensation in functional connectivity.