Julien Cohen-Adad

Thomas Dagonneau

Master's Research - Polytechnique Montréal

Naga Karthik Enamundram

PhD - Polytechnique Montréal

Co-supervisor :

Sarath Chandar

emvnagakarthik@gmail.com

Master's Research - Polytechnique Montréal

Nilser Laines Medina

PhD - Polytechnique Montréal

Nathan Molinier

PhD - Polytechnique Montréal

Kalum Ost

Collaborating researcher

Julien Thouveny

Master's Research - Université de Montréal

Arthur Toulouse

Master's Research - Polytechnique Montréal

Jan Valosek

Postdoctorate - Polytechnique Montréal

Website

Google Scholar

Publications

Dynamic shimming in the cervical spinal cord for multi-echo gradient-echo imaging at 3 T

Eva Alonso‐Ortiz

Daniel Papp

Alain D’astous

2021-07-21

ArXiv (preprint)

arxiv.org

Rapid simultaneous acquisition of macromolecular tissue volume, susceptibility, and relaxometry maps

Fang Frank Yu

Susie Y. Huang

T. Witzel

Ashwin S. Kumar

Congyu Liao

Tanguy Duval

Berkin Bilgic

Purpose A major obstacle to the clinical implementation of quantitative MR is the lengthy acquisition time required to derive multi-contrast… (see more) parametric maps. We sought to reduce the acquisition time for quantitative susceptibility mapping (QSM) and macromolecular tissue volume (MTV) by acquiring both contrasts simultaneously by leveraging their redundancies. The Joint Virtual Coil concept with generalized autocalibrating partially parallel acquisitions (JVC-GRAPPA) was applied to reduce acquisition time further. Methods Three adult volunteers were imaged on a 3T scanner using a multi-echo 3D GRE sequence acquired at three head orientations. MTV, QSM, R2*, T1, and proton density maps were reconstructed. The same sequence (GRAPPA R=4) was performed in subject #1 with a single head orientation for comparison. Fully sampled data was acquired in subject #2, from which retrospective undersampling was performed (R=6 GRAPPA and R=9 JVC-GRAPPA). Prospective undersampling was performed in subject #3 (R=6 GRAPPA and R=9 JVC-GRAPPA) using gradient blips to shift k-space sampling in later echoes. Results Subject #1’s multi-orientation and single-orientation MTV maps were not significantly different based on RMSE. For subject #2, the retrospectively undersampled JVC-GRAPPA and GRAPPA generated similar results as fully sampled data. This approach was validated with the prospectively undersampled images in subject #3. Using QSM, R2*, and MTV, the contributions of myelin and iron content to susceptibility was estimated. Conclusion We have developed a novel strategy to simultaneously acquire data for the reconstruction of five intrinsically co-registered 1-mm isotropic resolution multi-parametric maps, with a scan time of 6 minutes using JVC-GRAPPA.

2021-06-09

bioRxiv (preprint)

Quantitative magnetic resonance imaging of spinal cord microstructure in adults with cerebral palsy

The search for appropriate treatments of cerebral palsy (CP) would be facilitated if researchers could non-invasively monitor anatomical cha… (see more)nges in the spinal cord. The study by Trevarrow et al. aims to validate the relevance of magnetization transfer ratio and diffusion tensor imaging, both magnetic resonance imaging (MRI) techniques, to quantify microstructural abnormalities in the spinal cord of adult patients with CP. The authors used a semi-automated atlas-based analysis pipeline based on Spinal Cord Toolbox software to compute cord and gray matter atrophy and to quantify MRI metrics in specific spinal tracts. In line with their hypothesis, Trevarrow et al. observed differences in cord and gray matter size between participants with CP and typically developing peers. Interestingly, they also demonstrated an association between these morphometric biomarkers and clinical scores of hand dexterity. Magnetization transfer ratio was also reduced in the corticospinal tract of patients with CP. The study by Trevarrow et al. is a remarkable tour de force in that it is extremely difficult to image patients with CP as they are prone to motion (spasticity). In particular, gradient-echo sequences, used for magnetization transfer imaging, are particularly sensitive to motion, as can be seen on Figure 1b of the article. Echo planar imaging sequences, used for diffusion imaging, are sensitive to magnetic field inhomogeneities, which are prevalent in the spine region. The authors used an MRI acquisition protocol similar to a recently proposed standardized quantitative spinal cord MRI protocol (https://spine-generic.rtfd.io/), which likely helped them to obtain satisfactory images despite the many aforementioned challenges. From an image analysis standpoint, one limitation associated with atlas-based analysis (acknowledged by the authors) is that the registration to the template only relies on the spinal cord contour, not its internal structure. In other words, the white matter atlas is adjusted to the participant’s spinal cord contour, and the internal structure of the cord is quasi-linearly scaled (based on a B-spline regularized deformation). This quasi-linearity assumption might not hold true if, for example, the gray/white matter ratio differs between the participant and the template, and/ or the spatial location of the white matter tracts differs between the participant and the atlas, and/or specific tracts (e.g. corticospinal) degenerate. All these effects would cause a mismatch between the warped atlas’ and the participant’s white matter tracts. Unfortunately, there is no solution to this problem (yet). There are ways, however, to mitigate it. For example, using imaging sequences that are sensitive to some internal structures of the spinal cord, such as gray matter, or even some white matter tracts. These internal structures could then be accounted for during registration. However, these advanced contrast techniques are themselves noisy and sensitive to participant motion. In conclusion, the study by Trevarrow et al. is a remarkable technical achievement and a concrete first step towards the inclusion of microstructure MRI to the assessment of spinal cord integrity in patients with CP. Limitations, mostly related to data acquisition, could be tackled with the development of better solutions for gradient echo sequences in participants that are prone to motion. Navigator and/or advanced shimming approaches will hopefully mitigate these issues, making spinal cord quantitative MRI more amenable to clinical routine.

2021-05-15

Developmental Medicine & Child Neurology (published)

Impact of individual rater style on deep learning uncertainty in medical imaging segmentation

Olivier Vincent

Charley Gros

While multiple studies have explored the relation between inter-rater variability and deep learning model uncertainty in medical segmentatio… (see more)n tasks, little is known about the impact of individual rater style. This study quantifies rater style in the form of bias and consistency and explores their impacts when used to train deep learning models. Two multi-rater public datasets were used, consisting of brain multiple sclerosis lesion and spinal cord grey matter segmentation. On both datasets, results show a correlation (

2021-05-05

ArXiv (preprint)

arxiv.org

Tracking white and grey matter degeneration along the spinal cord axis in degenerative cervical myelopathy

Kevin Vallotton

Gergely David

Markus Hupp

Nikolai Pfender

Michael Fehlings

Rebecca S. Samson

Claudia A. M. Gandini Wheeler-Kingshott

Armin Curt

Patrick Freund

Maryam Seif

Objective: To determine tissue-specific neurodegeneration across the spinal cord in patients with mild-moderate degenerative cervical myelop… (see more)athy (DCM). Methods: Twenty-four mild-moderate DCM and 24 healthy subjects were recruited. In patients, a T2-weighted scan was acquired at the compression site, while in all participants a T2*-weighted and diffusion-weighted scan was acquired at the cervical level (C2-C3) and in the lumbar enlargement (i.e. rostral and caudal to the site of compression). We quantified intramedullary signal changes, maximal canal and cord compression, white (WM) and grey matter (GM) atrophy, and microstructural indices from diffusion-weighted scans. All patients underwent clinical (modified Japanese Orthopaedic Association (mJOA)) and electrophysiological assessments. Regression analysis assessed associations between MRI readouts and electrophysiological and clinical outcomes. Results: Twenty patients were classified with mild and four with moderate DCM using the mJOA scale. The most frequent site of compression was at C5-C6 level with maximum cord compression of 4.68{+/-}0.83 mm. Ten patients showed imaging evidence of cervical myelopathy. In the cervical cord, WM and GM atrophy and WM microstructural changes were evident, while in the lumbar cord only WM showed atrophy and microstructural changes. Remote cervical cord WM microstructural changes were pronounced in patients with radiological myelopathy and associated with impaired electrophysiology. Lumbar cord WM atrophy was associated with lower limb sensory impairments. Conclusion: Tissue-specific neurodegeneration revealed by quantitative MRI, already apparent across the spinal cord in mild-moderate DCM prior to the onset of severe clinical impairments. WM microstructural changes are particularly sensitive to remote pathologically and clinically eloquent changes in DCM.

2021-04-22

medRxiv (preprint)

Associations Between Relative Morning Blood Pressure, Cerebral Blood Flow, and Memory in Older Adults Treated and Controlled for Hypertension

Adrián Noriega de la Colina

Atef Badji

Marie-Christine Robitaille-Grou

Christine Gagnon

Tommy Boshkovski

Maxime Lamarre-cliche

Sven Joubert

Claudine J. Gauthier

Louis Bherer

Hélène Girouard

Supplemental Digital Content is available in the text. Hypertension, elevated morning blood pressure (BP) surges, and circadian BP variabili… (see more)ty constitute risk factors for cerebrovascular events. Nevertheless, while evidence indicates that hypertension is associated with cognitive dysfunctions, the link between BP variability and cognitive performance during aging is not clear. The purpose of this study is to determine the interaction between relative morning BP, cerebral blood flow (CBF) levels, and cognitive performance in hypertensive older adults with controlled BP under antihypertensive treatment. Eighty-four participants aged between 60 and 75 years old were separated into normotensive (n=51) and hypertensive (n=33) groups and underwent 24-hour ambulatory BP monitoring. They were also examined for CBF in the gray matter (CBF-GM) by magnetic resonance imaging and 5 cognitive domains: global cognition, working memory, episodic memory, processing speed, and executive functions. There was no difference in cognitive performance and CBF between normotensive and controlled hypertensive participants. Through a sensitivity analysis, we identified that, among relative morning BP variables, the best fit for CBF values in this cohort was the morning-evening difference in BP. The relative morning BP was negatively associated with CBF-GM in these hypertensive older adults only. In turn, CBF-GM levels were negatively associated with working and episodic memory scores in hypertensive older adults. This is the first extended study demonstrating an association between high relative morning BP and lower levels of CBF-GM, including the further impact of CBF-GM levels on the cognitive performance of specific domains in a community-based cohort of older adults with hypertension.

2021-03-29

HYPERTENSION (published)