Russell Ouellette

Karolinska Institutet | KI · Department of Clinical Neuroscience

Background and purpose: Corpus callosum (CC) atrophy is a strong predictor of multiple sclerosis (MS) disability but the contributing pathological mechanisms remain uncertain. We aimed to apply advanced MRI to explore what drives the often nonuniform callosal atrophy. Methods: Prospective brain 7 Tesla and 3 Tesla Human Connectom Scanner MRI wer...

Background and purpose: Corpus callosum (CC) atrophy is predictive of future disability in multiple sclerosis (MS). However, current segmentation methods are either labor- or computationally intensive. We therefore developed an automated deep learning-based CC segmentation tool and hypothesized that its output would correlate with disability. Met...

Cortical demyelination occurs early in multiple sclerosis (MS) and relates to disease outcome. The brain cortex has endogenous propensity for remyelination as proven from histopathology study. In this study, we aimed at characterizing cortical microstructural abnormalities related to myelin content by applying a novel quantitative MRI technique in...

Objective This study aimed to investigate at 7.0-T MRI a) the role of multiple sclerosis (MS) cortical lesions in cortical tissue loss b) their relation to neurological disability.Methods In 76 relapsing remitting and 26 secondary progressive MS patients (N = 102) and 56 healthy subjects 7.0-T T2*-weighted images were acquired for lesion segmentati...

SARS-CoV-2 uses ACE2, an inhibitor of the Renin-Angiotensin-Aldosterone System (RAAS), for cellular entry. Studies indicate that RAAS imbalance worsens the prognosis in COVID-19. We present a consecutive retrospective COVID-19 cohort with findings of frequent pulmonary thromboembolism (17%), high pulmonary artery pressure (60%) and lung MRI perfusi...

Background and purpose: Corpus callosum atrophy is a sensitive biomarker of multiple sclerosis (MS) neurodegeneration but typically requires manual 2D or volumetric 3D-based segmentations. We developed a supervised machine learning algorithm, DeepnCCA, for corpus callosum segmentation and relate callosal morphology to clinical disability using con...

We used 7 T MRI to: (i) characterize the grey and white matter pathology in the cervical spinal cord of patients with early relapsing-remitting and secondary progressive multiple sclerosis; (ii) assess the spinal cord lesion spatial distribution and the hypothesis of an outside-in pathological process possibly driven by CSF-mediated immune cytotoxi...

In order to optimize diagnostic workup of the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, we systematically reviewed neurological and neuroradiological manifestations of SARS-CoV-2 and all other known human coronavirus species (HCoV). Which lessons can we learn? We identified relevant publications (until July 26h...

To optimize diagnostic workup of the current severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic, we systematically reviewed neurological and neuroradiological manifestations of SARS‐CoV‐2 and all other known human coronavirus species (HCoV). Which lessons can we learn? We identified relevant publications (until 26 July 2020) usin...

Background Neurological complications in coronavirus disease 2019 (COVID-19) have been described, but the understanding of their pathophysiology and neuroanatomical correlates remains limited. Purpose To report on the frequency and type of neuroradiological findings in COVID-19. Materials and Methods In this retrospective study, all consecutive adu...

Background Thalamic pathology is a marker for neurodegeneration and multiple sclerosis (MS) disease progression. Objective To characterize (1) the morphology of thalamic lesions, (2) their relation to cortical and white matter (WM) lesions, and (3) clinical measures, and to assess (4) the imaging correlates of thalamic atrophy. Methods A total of...

Despite important efforts to solve the clinico-radiological paradox, correlation between lesion load and physical disability in patients with multiple sclerosis remains modest. One hypothesis could be that lesion location in corticospinal tracts plays a key role in explaining motor impairment. In this study, we describe the distribution of lesions...

SARS-CoV-2 enters the cell through the ACE2 receptor, which is considered one of the main inhibitors in the Renin-Angiotensin-Aldosterone System (RAAS).1 ,2 The virus has been shown to downregulate the ACE2 receptor, leading to a subsequent increase in the vasopressoragentangiotensinII.3 Evidently,criticalcoronavirusdisease2019(COVID-19)is thought...

SARS-CoV-2 enters the cell through the ACE2 receptor, which is considered one of the main inhibitors in the Renin-Angiotensin-Aldosterone System (RAAS).1 ,2 The virus has been shown to downregulate the ACE2 receptor, leading to a subsequent increase in the vasopressoragentangiotensinII.3 Evidently,criticalcoronavirusdisease2019(COVID-19)is thought...

BACKGROUND AND PURPOSE Hereditary diffuse leukoencephalopathy with spheroids (HDLS) and multiple sclerosis (MS) are demyelinating and neurodegenerative disorders that can be hard to distinguish clinically and radiologically. HDLS is a rare disorder compared to MS, which has led to occurrent misdiagnosis of HDLS as MS. That is problematic since thei...

Objective: MRI is essential for multiple sclerosis diagnostics but is not specific to demyelination. Myelin imaging is often hampered by long scanning times, complex post-processing or lack of clinical approval. This study aimed to assess the specificity, robustness and clinical value of Rapid Estimation of Myelin for Diagnostic Imaging, a new mye...

Background and purpose: Corpus callosum atrophy is a neurodegenerative biomarker in multiple sclerosis (MS). Manual delineations are gold standard but subjective and labor intensive. Novel automated methods are promising but require validation. We aimed to compare the robustness of manual versus automatic corpus callosum segmentations based on Fre...

Background: Neuroinflammation with microglia activation is thought to be closely related to cortical multiple sclerosis (MS) lesion pathogenesis. Objective: Using 11C-PBR28 and 7 Tesla (7T) imaging, we assessed in 9 relapsing–remitting multiple sclerosis (RRMS) and 10 secondary progressive multiple sclerosis (SPMS) patients the following: (1) micro...

Background Neuroinflammation with microglia activation is thought to be closely related to cortical multiple sclerosis (MS) lesion pathogenesis. Objective Using ¹¹ C-PBR28 and 7 Tesla (7T) imaging, we assessed in 9 relapsing–remitting multiple sclerosis (RRMS) and 10 secondary progressive multiple sclerosis (SPMS) patients the following: (1) micro...

Background: Activated microglia, which can be detected in vivo by 11C-PBR28 positron emission tomography (PET), represent a main component of MS pathology in the brain. Their role in the cerebellum is still unexplored, although cerebellar involvement in MS is frequent and accounts for disability progression. Objectives: We aimed at characterizin...

Background Cortical lesions develop early in multiple sclerosis (MS) and play a major role in disease progression. MRI at 7.0 T shows high sensitivity for detection of cortical lesions as well as better spatial resolution and signal-to-noise ratio compared with lower field strengths. Purpose To longitudinally characterize (a) the development and ev...

In multiple sclerosis (MS), it would be of clinical value to be able to track the progression of axonal pathology, especially before the manifestation of clinical disability. However, non-invasive evaluation of short-term longitudinal progression of white matter integrity is challenging. This study aims at assessing longitudinal changes in the rest...

Irreversible white matter (WM) damage, including severe demyelination and axonal loss, is a main determinant of long-term disability in multiple sclerosis (MS). Non-invasive detection of changes in microstructural WM integrity in the disease is challenging since commonly used imaging metrics lack the necessary sensitivity, especially in the early p...

Spinal cord lesions detected on MRI hold important diagnostic and prognostic value for multiple sclerosis. Previous attempts to correlate lesion burden with clinical status have had limited success, however, suggesting that lesion location may be a contributor. Our aim was to explore the spatial distribution of multiple sclerosis lesions in the cer...

Supplementary Figure 1. CHARMED-FR changes in multiple sclerosis normal appearing white matter Regions (highlighted in blue) in which TBSS found significantly lower FR in multiple sclerosis NAWM compared to healthy controls for the subsampled protocol. Abbreviations: FR = restricted fraction; NAWM = normal-appearing white matter.

The spinal cord is frequently affected by atrophy and/or lesions in multiple sclerosis (MS) patients. Segmentation of the spinal cord and lesions from MRI data provides measures of atrophy and lesion burden, which are key criteria for the diagnosis, prognosis and longitudinal monitoring in MS. Achieving robust and reliable segmentation across multi...

Objective: To investigate the long-term progression of cognitive dysfunction and its neuroanatomical correlates and predictors in multiple sclerosis (MS). Methods: A cohort of 37 MS patients reflecting five decades of disease duration and all subtypes was followed over 17.5 years. Matched controls were recruited at the last follow-up. Global cog...

The aim of this study was to investigate the interplay between structural connectivity and cortical demyelination in early multiple sclerosis. About 27 multiple sclerosis patients and 18 age-matched controls underwent two MRI scanning sessions. The first was done at 7T and involved acquiring quantitative T1 and T2* high-resolution maps to estimate...

Neuroaxonal pathology is a main determinant of disease progression in multiple sclerosis; however, its underlying pathophysiological mechanisms, including its link to inflammatory demyelination and temporal occurrence in the disease course are still unknown. We used ultra-high field (7 T), ultra-high gradient strength diffusion and T 1 /T 2-weighte...

Conventional diffusion-weighted MR imaging techniques provide limited specificity in disentangling disease-related microstructural alterations involving changes in both axonal density and myelination. By simultaneously probing multiple diffusion regimens, multi-shell diffusion MRI is capable of increasing specificity to different tissue sub-compart...

Objective: In multiple sclerosis (MS), using simultaneous magnetic resonance-positron emission tomography (MR-PET) imaging with (11) C-PBR28, we quantified expression of the 18kDa translocator protein (TSPO), a marker of activated microglia/macrophages, in cortex, cortical lesions, deep gray matter (GM), white matter (WM) lesions, and normal-appea...