Publications by authors named "George Medvedev"

6 Publications

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Functional MRI evaluation of the effect of carotid artery stenting: a case study demonstrating cognitive improvement.

Acta Radiol Open 2021 Feb 10;10(2):2058460120988822. Epub 2021 Feb 10.

Health Sciences and Innovation, Surrey Memorial Hospital, Fraser Health Authority, British Columbia, Canada.

Background: The narrowing of the carotid arteries with plaque formation represents a major risk factor for ischemic stroke and cognitive impairments. Carotid angioplasty and stenting is a standard clinical treatment to reduce stroke risk. The cognitive effect of carotid angioplasty and stenting remains largely unknown.

Purpose: This study aims to provide direct evidence of possible effects of carotid angioplasty and stenting on cognition, using task-phase functional magnetic resonance imaging.

Material And Methods: This study received harmonized institutional ethics board approval (Grant number REB ID =H18-02495/FHREB 2018-058). Two patients had MRI scans pre-carotid angioplasty and stenting and two-month post-carotid angioplasty and stenting. Case 1 had severe (>95%) flow-limiting stenosis in the right carotid artery. Case 2 had 70% non-flow limiting stenosis in the left carotid artery. At each scan, patients completed two functional magnetic resonance imaging sessions while performing a working memory task. Accuracy, reaction time, and brain activation were analyzed for each patient for possible pre-post carotid angioplasty and stenting changes.

Results: Case 1 showed increased activation in the right (treated-side) frontal and temporal lobes post-carotid angioplasty and stenting; associated with improvements in accuracy (from 58% to 74%) and task completion rate (from 17% to 72%). Case 2 completed the tasks pre- and post-carotid angioplasty and stenting with >90% accuracy, while decreased functional magnetic resonance imaging activation in the contralateral (untreated) hemisphere and mildly increased activation in the left (treated -side) anterior circulation territory were observed post-carotid angioplasty and stenting.

Conclusion: These cases provided the first task-phase functional magnetic resonance imaging data demonstrating that carotid angioplasty and stenting improved cognitive function in the re-perfused vascular territory. The finding supports the role of carotid angioplasty and stenting in improving cognitive performance beyond reducing stroke risk.
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http://dx.doi.org/10.1177/2058460120988822DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7878956PMC
February 2021

Is This Contrast? Is This Blood? An Agreement Study on Post-thrombectomy Computed Tomography Scans.

Front Neurol 2020 22;11:593098. Epub 2020 Dec 22.

Ottawa Stroke Program, Department of Medicine (Neurology), University of Ottawa, Ottawa, ON, Canada.

Hemorrhagic transformation after acute ischemic stroke is a dreaded and severe complication of thrombolysis and thrombectomy. However, its detection on post-thrombectomy conventional non-contrast computed tomography (CT) scan can be complicated by the frequent (and sometimes concomitant) presence of contrast, resulting in changes in management. Our objective was to assess the inter- and intra-rater reliability for the detection of blood and/or contrast on day-1 post-thrombectomy CT scans. A total of 18 raters across 3 different specialties independently examined 30 post-thrombectomy CT scans selected from the Aspiration vs. STEnt-Retriever (ASTER) trial. They were asked to judge the presence of blood and contrast. Thirty days later, the same 18 raters again independently judged the 30 scans, in randomized order. Agreement was measured with Fleiss' and Cohen's statistics. Overall agreement on blood and/ or contrast presence was only fair, = 0.291 (95% CI = 0.273-0.309). There were 0 scans with consensus among the 18 readers on the presence of blood and/or contrast. However, intra-rater global agreement across all 18 physicians was relatively high, with a median kappa value of 0.675. This intra-rater consistency was seen across all specialties, regardless of level of training. Physician judgment for the presence of blood and/or contrast on day-1 post-thrombectomy non-contrast CT scan shows limited inter-observer reliability. Advanced imaging modalities may then be warranted for challenging clinical cases.
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http://dx.doi.org/10.3389/fneur.2020.593098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7783397PMC
December 2020

A fast and fully-automated deep-learning approach for accurate hemorrhage segmentation and volume quantification in non-contrast whole-head CT.

Sci Rep 2020 11 9;10(1):19389. Epub 2020 Nov 9.

Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.

This project aimed to develop and evaluate a fast and fully-automated deep-learning method applying convolutional neural networks with deep supervision (CNN-DS) for accurate hematoma segmentation and volume quantification in computed tomography (CT) scans. Non-contrast whole-head CT scans of 55 patients with hemorrhagic stroke were used. Individual scans were standardized to 64 axial slices of 128 × 128 voxels. Each voxel was annotated independently by experienced raters, generating a binary label of hematoma versus normal brain tissue based on majority voting. The dataset was split randomly into training (n = 45) and testing (n = 10) subsets. A CNN-DS model was built applying the training data and examined using the testing data. Performance of the CNN-DS solution was compared with three previously established methods. The CNN-DS achieved a Dice coefficient score of 0.84 ± 0.06 and recall of 0.83 ± 0.07, higher than patch-wise U-Net (< 0.76). CNN-DS average running time of 0.74 ± 0.07 s was faster than PItcHPERFeCT (> 1412 s) and slice-based U-Net (> 12 s). Comparable interrater agreement rates were observed between "method-human" vs. "human-human" (Cohen's kappa coefficients > 0.82). The fully automated CNN-DS approach demonstrated expert-level accuracy in fast segmentation and quantification of hematoma, substantially improving over previous methods. Further research is warranted to test the CNN-DS solution as a software tool in clinical settings for effective stroke management.
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http://dx.doi.org/10.1038/s41598-020-76459-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7652921PMC
November 2020

MRI-based evaluation of structural degeneration in the ageing brain: Pathophysiology and assessment.

Ageing Res Rev 2019 01 22;49:67-82. Epub 2018 Nov 22.

ImageTech Laboratory, Health Sciences and Innovation, Surrey Memorial Hospital, Surrey, British Columbia, Canada; Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada; Health Sciences and Innovation, Surrey Memorial Hospital, Surrey, British Columbia, Canada. Electronic address:

Advances in MRI technology have significantly contributed to our ability to understand the process of brain ageing, allowing us to track and assess changes that occur during normal ageing and neurological conditions. This paper focuses on reviewing structural changes of the ageing brain that are commonly seen using MRI, summarizing the pathophysiology, prevalence, and neuroanatomical distribution of changes including atrophy, lacunes, white matter lesions, and dilated perivascular spaces. We also review the clinically accessible methodology for assessing these MRI-based changes, covering visual rating scales, as well computer-aided and fully automated methods. Subsequently, we consider novel assessment methods designed to evaluate changes across the whole brain, and finally discuss new directions in this field of research.
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http://dx.doi.org/10.1016/j.arr.2018.11.004DOI Listing
January 2019

Automation of CT-based haemorrhagic stroke assessment for improved clinical outcomes: study protocol and design.

BMJ Open 2018 04 19;8(4):e020260. Epub 2018 Apr 19.

Health Sciences and Innovation, Fraser Health Authority, Surrey, British Columbia, Canada.

Introduction: Haemorrhagic stroke is of significant healthcare concern due to its association with high mortality and lasting impact on the survivors' quality of life. Treatment decisions and clinical outcomes depend strongly on the size, spread and location of the haematoma. Non-contrast CT (NCCT) is the primary neuroimaging modality for haematoma assessment in haemorrhagic stroke diagnosis. Current procedures do not allow convenient NCCT-based haemorrhage volume calculation in clinical settings, while research-based approaches are yet to be tested for clinical utility; there is a demonstrated need for developing effective solutions. The project under review investigates the development of an automatic NCCT-based haematoma computation tool in support of accurate quantification of haematoma volumes.

Methods And Analysis: Several existing research methods for haematoma volume estimation are studied. Selected methods are tested using NCCT images of patients diagnosed with acute haemorrhagic stroke. For inter-rater and intrarater reliability evaluation, different raters will analyse haemorrhage volumes independently. The efficiency with respect to time of haematoma volume assessments will be examined to compare with the results from routine clinical evaluations and planimetry assessment that are known to be more accurate. The project will target the development of an enhanced solution by adapting existing methods and integrating machine learning algorithms. NCCT-based information of brain haemorrhage (eg, size, volume, location) and other relevant information (eg, age, sex, risk factor, comorbidities) will be used in relation to clinical outcomes with future project development. Validity and reliability of the solution will be examined for potential clinical utility.

Ethics And Dissemination: The project including procedures for deidentification of NCCT data has been ethically approved. The study involves secondary use of existing data and does not require new consent of participation. The team consists of clinical neuroimaging scientists, computing scientists and clinical professionals in neurology and neuroradiology and includes patient representatives. Research outputs will be disseminated following knowledge translation plans towards improving stroke patient care. Significant findings will be published in scientific journals. Anticipated deliverables include computer solutions for improved clinical assessment of haematoma using NCCT.
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http://dx.doi.org/10.1136/bmjopen-2017-020260DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5914893PMC
April 2018

Isolated renal giant cell arteritis.

Am J Kidney Dis 2002 Sep;40(3):658-61

Department of Pathology and Laboratory Medicine, and Division of Nephrology, University of British Columbia, Vancouver, British Columbia, Canada.

Giant cell arteritis, which most commonly affects the temporal arteries, may involve intrarenal vessels and may be associated with a variety of renal lesions, including necrotizing arteritis, necrotizing glomerulonephritis, granulomatous glomerulonephritis, and membranous glomerulopathy. Isolated giant cell arteritis of the kidney is a rare cause of renal failure. We report a case of a previously healthy 54-year-old white woman who presented with nonoliguric renal failure and a 4-week history of persistent low-grade fever associated with diffuse mild myalgias. She had no history of previous renal or neurologic disease and denied any headaches or visual disturbances. Antinuclear antibody and antineutrophilic cytoplasmic antibody were negative. Renal biopsy revealed noncaseating granulomatous infiltration of arterial and arteriolar walls, a patchy mononuclear cell interstitial infiltrate, and no significant glomerular changes. Treatment with prednisone resulted in dramatic improvement of renal function.
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http://dx.doi.org/10.1053/ajkd.2002.34931DOI Listing
September 2002