2024-03-29T04:59:42Z
http://eprints.drcmr.dk/cgi/oai2
oai:www.drcmr.dk:30
2010-04-02T00:05:43Z
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74797065733D746865736973
MRI in Severe Traumatic Brain Injury: Micro- and Macrostructural Changes
2009-03-31
Sidaros, Annette
Diffuse Axonal Injury
Craniocerebral Trauma
Treatment Outcome
Diffuse Axonal Injury
Wallerian Degeneration
Brain Concussion
The principal aim of the present PhD project was to study quantitatively the long-term microand macrostructural brain changes in survivors from severe traumatic brain injury (TBI). A total of 31 patients admitted for early rehabilitation following severe TBI were included and underwent magnetic resonance imaging (MRI), including Diffusion Tensor Imaging (DTI), at mean 8 weeks post-injury. Follow-up MRI at mean 12 months post-injury was acquired in 25 of the patients. For comparison, healthy matched controls were scanned twice with a similar time interval. Clinical rating during rehabilitation and at 1-year follow-up was performed by experienced staff.
Two papers make up the basis of this thesis. Paper I considers the DTI results. This MRI modality was chosen in order to evaluate diffusional changes in brain tissue, potentially useful for characterising the extent of microscopic white matter injury, as well as for tracking microstructural changes during recovery. Using a region-of-interest approach, four white matter regions were studied with additional regions in grey matter and CSF. At the initial scan, patients had abnormal fractional anisotropy (FA) in all white matter regions, which in the cerebral peduncle correlated with 1-year outcome, suggesting that DTI may have prognostic value. At follow-up, FA had partly normalised in some white matter regions, but deviated even more from normal values in other regions. Although these longitudinal findings warrant cautious interpretation, they might indicate microstructural reorganization. Paper II describes a study on the macrostructural brain changes during recovery. Global and regional brain volume changes between the two scan time points were investigated using voxelwise analyses. Despite remarkable clinical improvement in most patients, they all exhibited continued brain volume loss during the scan interval. Global volume change correlated with clinical injury severity, functional status at both scans, and with 1-year outcome. The areas which underwent the most change were structures particularly susceptible to traumatic axonal injury and consequent Wallerian degeneration, indicating that the long-term atrophy is attributable to consequences of axonal injury.
Together, these MRI analyses complemented each other in the quantitative assessment of structural brain changes following severe TBI. Applied in the late subacute/early chronic phase of TBI, DTI may capture biological severity at the microstructural level and provide prognostic information. Serial application of the MRI techniques applied in this study enables the monitoring of the extent and distribution of micro- and macrostructural changes during TBI rehabilitation.
2009-03
Thesis
http://eprints.drcmr.dk/30/
http://eprints.drcmr.dk/30/1/PhDThesis_AnnetteSidaros.pdf
application/pdf
phd
Copenhagen University Hospital, Hvidovre
Danish Research Centre for Magnetic Resonance
oai:www.drcmr.dk:42
2010-12-02T11:47:36Z
7374617475733D756E707562
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7375626A656374733D453031:45303178333730
74797065733D746865736973
Corrections in clinical Magnetic Resonance Spectroscopy and SPECT: Motion correction in MR spectroscopy, downscatter correction in SPECT
2009-08
de Nijs, Robin
Diagnostic Techniques and Procedures
Magnetic Resonance Spectroscopy
Magnetic Resonance Spectroscopy
Infant, Newborn
The quality of medical scanner data is often compromised by several mechanisms. This can be caused by both the subject to be measured and the scanning principles themselves. In this PhD project the problem of subject motion was addressed for Single Voxel MR Spectroscopy in a cohort study of preterm infants. In Iodine-123 SPECT the problem of downscatter was addressed. This thesis is based on two papers. Paper I deals with the problem of motion in Single Voxel Spectroscopy. Two novel methods for the identification of outliers in the set of repeated measurements were implemented and compared to the known mean and median filtering. The data comes from non-anesthetized preterm infants, where motion during scanning is a common problem. Both the novel outlier identification and the independent component analysis (ICA) perform satisfactory and better than the common mean and median filtering. ICA performed best in the sense that it recovered most of the lost peak height in the spectra. The ICA motion correction algorithm described in paper I and in this thesis was applied to a quantitative analysis of the Single Voxel Spectroscopy data from the cohort study of preterm infants. This analysis revealed that differences between term and preterm infants are not to be found in the concentrations of Lactate (caused by inflammation or hypoxia-ischemia) and/or NAA (caused by hypoxia-ischemia) as hypothesized before the cohort study. Instead choline levels were decreased in the preterm infants, which might indicate a detrimental effect of the extra-uterine environment on brain development. Paper II describes a method to correct for downscatter in low count Iodine-123 SPECT with a broad energy window above the normal imaging window. Both spatial dependency and weight factors were measured. As expected, the implicitly assumed weight factor of one for energy windows with equal width is slightly too low, due the presence of a backscatter peak in the energy spectrum coming from high-energy photons. The effect on the contrast was tested in 10 subjects and revealed a 20% increase in the specific binding ratio of the striatum due to downscatter correction. This makes the difference between healthy subjects and patients more profound. Downscatter in Iodine-123 SPECT is not the only deteriorating mechanism. Normal scatter compromises the images quality as well. Since scatter correction of SPECT-images also can be performed by the subtraction of an energy window, a method was developed to perform scatter and downscatter correction simultaneously. A phantom study has been performed, where the in paper II described downscatter correction was extended with scatter correction. This new combined correction was compared to the known Triple Energy Window (TEW) correction method. Results were satisfying and indicate that TEW is more correct from the physics point of view, while the in paper II described method extended with scatter correction gives reasonable results, but is far less noise sensitive than TEW.
2009-08
Thesis
http://eprints.drcmr.dk/42/
http://eprints.drcmr.dk/42/1/phd221_rdn.pdf
application/pdf
phd
Technical University of Denmark
Informatics and Mathematical Modelling