Prospective Graduate Students / Postdocs
This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.
Alexander Rauscher
Professor
Research Classification
Research Interests
magnetic resonance imaging
physics
quantitative susceptibility mapping
myelin water imaging
brain
maschine learning
Relevant Thesis-Based Degree Programs
Affiliations to Research Centres, Institutes & Clusters
Research Options
I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.
I am interested in working with undergraduate students on research projects.
Research Methodology
Magnetic Resonance Imaging
numerical simulations
machine learning
Physics
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Gradient and spin echo magnetic resonance imaging for the characterization of myelin health in multiple sclerosis (2020)
Multiple sclerosis (MS) is a complex, autoimmune disease that results in demyelination and neurodegeneration. Magnetic resonance imaging (MRI) is an essential cornerstone of MS diagnosis and clinical decision making, however, clinical MRIs lack specificity to the pathological mechanisms influencing myelin health.In this thesis, two quantitative MRI techniques were probed for their potential to study myelin health in MS. First, multi-echo spin-echo myelin water imaging (MWI) was tested for its specificity to myelin lipids, proteins and iron. We demonstrated to-date unknown sensitivity of MWI and identified MS lesion changes indicative of late-stage remyelination. Thereafter, the accuracy of MWI and its potential application at ultra-high magnetic fields were investigated. Using signal simulations, the dependence of the non-negative least-squares analysis on processing and tissue parameters was described. Myelin underestimations due to B⁺₁-inhomogeneities and noise were shown to be minimized by adjusting the T₂ range according to the echo time. To translate MWI to 7T, T₂ tissue properties in seven healthy subjects were studied in comparison to 3T. We demonstrated the feasibility of 7T-MWI and discussed current limitations in assessing short T₂ times.Secondly, susceptibility-sensitive MRI was explored, which provides greater sensitivity, albeit possibly lower specificity to myelin, than MWI. Using the phase component, we showed that the MS lesion contrast is typically not driven by iron accumulation. In simulations and with post-mortem data, it was demonstrated that iron and myelin loss in combination determine the lesions’ appearance. Thereafter, the potential of the technique to become a marker of tissue damage and repair was evaluated by studying the evolution and pathological underpinnings of acute MS lesions in eleven patients over five years. Current models and their shortcomings were discussed.Finally, two technical developments were introduced. First, a multi-dynamic, high-spatial resolution susceptibility-sensitive imaging approach was presented for visualizing the central vein sign. Using phantom and in vivo data, qualitative and quantitative agreement of the proposed approach with other imaging strategies was demonstrated. Secondly, FLAIR² was introduced, a novel contrast that improves contrast-to-noise, while shortening scan time. The potential of FLAIR² to aid automated lesion segmentation was demonstrated on real-world multi-centre clinical data.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Predicting primary diffusion directions in white matter from T1-weighted magnetic resonance images (2024)
Orientation dependence studies are an ongoing research area in Magnetic Resonance Imaging (MRI), often relying on diffusion MRI to gain nerve fiber direction, a time-consuming scan not always included in research and clinical protocols. Using paired 3D T₁-weighted and diffusion images from the Human Connectome Project (HCP), a U-Net was trained to find voxel-wise principal diffusion directions from 3D T₁-weighted images. Different loss functions and data augmentations were used in model training. The models trained with different data augmentations and loss functions were evaluated using cosine distance during training. The trained model with the best performance had a group average cosine distance of 0.349 ± 0.007 and a group average difference in absolute polar angle of 8.762° ± 0.293° on the independent test set.
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Impact of formalin fixation on multi-compartment T2 relaxation and its tissue orientation dependence in excised pig spinal cord white matter (2023)
In this MRI study, we investigated multi-compartment T₂ relaxation times of fresh, fixed, and washed pig spinal cord white matter (WM) and their dependence on tissue orientation relative to the main magnetic field. Multi-echo spin echo scans from eight pig spinal cord samples were acquired at 9.4 T with their axes parallel to the main magnetic field B₀. Four of these spinal cord segments were imaged at six different orientations with respect to B₀. After fixation, short fraction T₂ times and myelin water fraction (MWF) increased, while long fraction T₂ times decreased. After washing, short and long fraction T₂ times increased relative to fixed tissue, and MWF decreased relative to fresh tissue. We found a considerable orientation dependence in the short fraction relaxation rate R₂ (=1/T₂) in fresh tissue, which is reduced in washed tissue, and absent in fixed tissue. A similar, but reduced, orientation dependence was observed in long fraction R₂. This work presents a direct comparison of orientation dependence in a WM tissue sample in the fresh, fixed, and washed state. Understanding the changes caused by fixation and tissue orientation can aid in the correction of fixation and orientation-induced alterations of MRI metrics for more accurate and reliable measurements.
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Orientation dependence of transverse relaxation rates in magnetic resonance imaging of the newborn and adult brain (2022)
In MRI the transverse relaxation rate, R₂=1/T₂, shows dependence on the orientation of ordered tissue relative to the main magnetic field. In previous studies, orientation effects of R₂ relaxation in the mature brain's white matter have been found to be described by a susceptibility-based model of diffusion through local magnetic field inhomogeneities created by the diamagnetic myelin sheaths. Orientation effects in human newborn white matter have not yet been investigated. The newborn brain is known to contain very little myelin and is therefore expected to exhibit a decrease in orientation dependence driven by susceptibility-based effects. We measured R₂ orientation dependence in the white matter of human newborns.R₂ data were acquired with a 3D Gradient and Spin Echo (GRASE) sequence and fibre orientation was mapped with diffusion tensor imaging (DTI). We found orientation dependence in newborn white matter that is not consistent with the susceptibility-based model and is best described by a model of residual dipolar coupling. In the near absence of myelin in the newborn brain, these findings suggest the presence of residual dipolar coupling between motionally restricted water molecules. This has important implications for quantitative imaging methods such as myelin water imaging, and suggests orientation dependence of R₂ as a potential marker in early brain development.
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Publications
- Cerebrovascular Reactivity Following Spinal Cord Injury (2022)
- Quantitative MRI and histopathology detect remyelination in inactive multiple sclerosis lesions (2022)
- Recovering SWI‐filtered phase data using deep learning (2022)
Magnetic Resonance in Medicine, 87 (2), 948--959 - In vivo investigation of the multi‐exponential T 2 decay in human white matter at 7 T: Implications for myelin water imaging at UHF (2021)
NMR in Biomedicine, - Myelin water imaging depends on white matter fiber orientation in the human brain (2021)
Magnetic Resonance in Medicine, 85 (4), 2221--2231 - Quantitative Susceptibility Mapping of Venous Vessels in Neonates with Perinatal Asphyxia (2021)
American Journal of Neuroradiology, - Myelin water imaging and R 2 * mapping in neonates: Investigating R 2 * dependence on myelin and fibre orientation in whole brain white matter (2020)
NMR in Biomedicine, 33 (3) - Non‐negative least squares computation for in vivo myelin mapping using simulated multi‐echo spin‐echo T 2 decay data (2020)
NMR in Biomedicine, - Cortical morphology predicts placebo response in multiple sclerosis (2019)
- Quantitative Analysis of Punctate White Matter Lesions in Neonates Using Quantitative Susceptibility Mapping and R2* Relaxation (2019)
American Journal of Neuroradiology, 40 (7), 1221--1226 - Rapid myelin water imaging for the assessment of cervical spinal cord myelin damage (2019)
NeuroImage: Clinical, 23, 101896 - The role of diffusion and perivascular spaces in dynamic susceptibility contrast MRI (2019)
- The role of iron and myelin in orientation dependent R 2 * of white matter (2019)
NMR in Biomedicine, - What Have We Learned from Perfusion MRI in Multiple Sclerosis? (2018)
American Journal of Neuroradiology, - Cerebral Microbleeds: A Call for Standardized Advanced Neuroimaging (2017)
American Journal of Neuroradiology, 38 (11), E90--E91 - Cover Image, Volume 30, Issue 8 (2017)
NMR in Biomedicine, 30 (8), i--i - Susceptibility-sensitive MRI of multiple sclerosis lesions and the impact of normal-appearing white matter changes (2017)
NMR in Biomedicine, 30 (8), e3727 - A Prospective Pilot Investigation of Brain Volume, White Matter Hyperintensities, and Hemorrhagic Lesions after Mild Traumatic Brain Injury. (2016)
- Anisotropic cerebral vascular architecture causes orientation dependency in cerebral blood flow and volume measured with dynamic susceptibility contrast magnetic resonance imaging. (2016)
- Characterization of white matter integrity deficits in cocaine-dependent individuals with substance-induced psychosis compared with non-psychotic cocaine users. (2016)
- Corticospinal tract integrity measured using transcranial magnetic stimulation and magnetic resonance imaging in neuromyelitis optica and multiple sclerosis. (2016)
- FLAIR2: A Combination of FLAIR and T2 for Improved MS Lesion Detection. (2016)
- Microbleeds in Alzheimer’s Disease: A Neuropsychological Overview and Meta-Analysis (2016)
Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques, 43 (06), 753--759 - Motor Skill Acquisition Promotes Human Brain Myelin Plasticity. (2016)
- Myelin Water Fraction Is Transiently Reduced after a Single Mild Traumatic Brain Injury--A Prospective Cohort Study in Collegiate Hockey Players. (2016)
- Operationalizing Neuroimaging for Disorders of Consciousness: The Canadian Context. (2016)
- Prevalence of Brain Microbleeds in Alzheimer Disease: A Systematic Review and Meta-Analysis on the Influence of Neuroimaging Techniques. (2016)
- Quantifying visual pathway axonal and myelin loss in multiple sclerosis and neuromyelitis optica (2016)
NeuroImage: Clinical, 11, 743--750 - RE: Elucidating Pretreatment Cognitive Impairment in Breast Cancer Patients: The Impact of Cancer-Related Post-traumatic Stress. (2016)
- Reduced Myelin Water in the White Matter Tracts of Patients with Niemann-Pick Disease Type C. (2016)
- Subcortical grey matter alterations in cocaine dependent individuals with substance-induced psychosis compared to non-psychotic cocaine users. (2016)
- Changes in cerebral vascular reactivity and structure following prolonged exposure to high altitude in humans. (2015)
- Mortality from treatable illnesses in marginally housed adults: a prospective cohort study. (2015)
- Orientation Dependent MR Signal Decay Differentiates between People with MS, Their Asymptomatic Siblings and Unrelated Healthy Controls. (2015)
- Trajectories of subcortical iron accumulation in MS. (2015)
- A prospective study of the influence of acute alcohol intoxication versus chronic alcohol consumption on outcome following traumatic brain injury. (2014)
- Increased spinal cord movements in cervical spondylotic myelopathy (2014)
The Spine Journal, - Prevalence of extracranial venous narrowing on catheter venography in people with multiple sclerosis, their siblings, and unrelated healthy controls: a blinded, case-control study. (2014)
- To exclude or not to exclude: further examination of the influence of white matter hyperintensities in diffusion tensor imaging research. (2014)
- Evaluation of white matter myelin water fraction in chronic stroke. (2013)
- Magnetic resonance frequency shifts during acute MS lesion formation. (2013)
- A prospective study of physician-observed concussion during a varsity university hockey season: white matter integrity in ice hockey players. Part 3 of 4. (2012)
- Rapid whole cerebrum myelin water imaging using a 3D GRASE sequence. (2012)
- Bilateral filtering of magnetic resonance phase images. (2011)
- The influence of white matter fibre orientation on MR signal phase and decay. (2011)
- Susceptibility weighted imaging with multiple echoes. (2010)
- Localization of the subthalamic nucleus: optimization with susceptibility-weighted phase MR imaging. (2009)
- MR relaxation in multiple sclerosis. (2009)
- Phase unwrapping of MR images using Phi UN--a fast and robust region growing algorithm. (2009)
- Quantification of modulated blood oxygenation levels in single cerebral veins by investigating their MR signal decay. (2009)
- ToF-SWI: simultaneous time of flight and fully flow compensated susceptibility weighted imaging. (2009)
- Improved elimination of phase effects from background field inhomogeneities for susceptibility weighted imaging at high magnetic field strengths. (2008)
- Informatics in Radiology: GUIBOLD: a graphical user interface for image reconstruction and data analysis in susceptibility-weighted MR imaging. (2008)
- Investigation of the influence of carbon dioxide concentrations on cerebral physiology by susceptibility-weighted magnetic resonance imaging (SWI). (2008)
- Investigations on the effect of caffeine on cerebral venous vessel contrast by using susceptibility-weighted imaging (SWI) at 1.5, 3 and 7 T. (2008)
- Susceptibility weighted imaging at ultra high magnetic field strengths: theoretical considerations and experimental results. (2008)
- Detection of multiple intracranial hemorrhages in a child with acute lymphocytic leukemia (ALL) by susceptibility weighted imaging (SWI). (2007)
- Obtaining blood oxygenation levels from MR signal behavior in the presence of single venous vessels. (2007)
- Contrast-enhanced, high-resolution, susceptibility-weighted magnetic resonance imaging of the brain: dose-dependent optimization at 3 tesla and 1.5 tesla in healthy volunteers. (2006)
- Demonstration of paramagnetic and diamagnetic cerebral lesions by using susceptibility weighted phase imaging (SWI). (2006)
- Susceptibility weighted imaging: data acquisition, image reconstruction and clinical applications. (2006)
- Application of an exogenous hyperoxic contrast agent in MR mammography: initial results. (2005)
- High resolution susceptibility weighted MR-imaging of brain tumors during the application of a gaseous agent. (2005)
- Magnetic susceptibility-weighted MR phase imaging of the human brain. (2005)
- Nonnvasive assessment of vascular architecture and function during modulated blood oxygenation using susceptibility weighted magnetic resonance imaging. (2005)
- Subtraction of in-phase and opposed-phase images in dynamic MR mammography. (2005)
- Optimized 3 T EPI of the amygdalae. (2004)
- Robust field map generation using a triple-echo acquisition. (2004)
- Automated unwrapping of MR phase images applied to BOLD MR-venography at 3 Tesla. (2003)
Current Students & Alumni
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