Browsing by Author "Demchuk, Andrew M."

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    A Psychological Perspective on Image Interpretation in Acute Ischemic Stroke: Factors Affecting Non-Contrast CT ASPECTS Reliability
    (2018-06-27) Wilson, Alexis Terrin Connett; Menon, Bijoy K.; Demchuk, Andrew M.; Hill, Michael D.; Saposnik, Gustavo
    The Alberta Stroke Program Early CT Score (ASPECTS) is a semiquantitative scale to assess the extent of early ischemic changes on non-contrast CT in acute ischemic stroke patients. This is crucial for prognostication and treatment selection. Recent studies have revealed significant heterogeneity in reported measures of inter-rater reliability in ASPECTS, and this thesis aims to investigate the reasons underlying this phenomenon from the perspective of clinicians’ cognitive processes. First, this work explores relevant topics in the psychology of image interpretation and, on this psychological basis, proposes potential causes of inconsistent ASPECTS reliability. Possible strategies to improve clinicians’ inter- and intra-rater reliability are also discussed. The effect of image reading context variables and rater expertise on ASPECTS inter-rater reliability was then investigated. Raters of different experience levels scored ASPECTS on baseline non-contrast CT scans under three prior-information conditions (NCCT only, NCCT with access to clinical information, NCCT with access to clinical information and multiphase CT angiography) and three reading-context conditions (high/low ambient light, time pressure). The results indicate that these variables have the capacity to affect ASPECTS reliability. This work highlights the importance of acknowledging that medical image interpretation can be influenced by seemingly irrelevant external and internal factors like reading environment characteristics or physician-level variables. Giving more consideration to these variables in clinical and educational settings could improve the utility of tools like ASPECTS.
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    Drip and Ship versus Mothership: Transportation and Treatment Strategies for Acute Ischemic Stroke Patients
    (2019-07-22) Holodinsky, Jessalyn Kathryn; Hill, Michael D.; Williamson, Tyler S.; Demchuk, Andrew M.; Patel, Alka B.
    Ischemic stroke with large vessel occlusion can be treated with alteplase and/or endovascular therapy. While endovascular therapy has been proven more effective than alteplase the administration of both treatments is highly time sensitive. There are geographic disparities in access to endovascular therapy. For patients outside the immediate vicinity of a hospital equipped to perform endovascular therapy it is unknown whether transport directly to an endovascular center for alteplase and endovascular therapy (mothership) or transport to the closest centre for immediate alteplase treatment followed by transfer to the endovascular center (drip-and-ship) will result in best patient outcomes. In this thesis, this is explored using theoretical conditional probability. Models were generated using existing data from clinical trials of stroke treatment, the accuracy of prehospital large vessel occlusion screening tools, and time from onset to stroke treatment (a function of both geography and hospital efficiency). The models were used to determine which strategy predicts the greatest probability of excellent outcome for stroke patients in several different scenarios. The optimal transport strategy is influenced by three different factors, the impact of which is summarized as follows from the perspective of the drip and ship approach. First, the most probable diagnosis of the patient. As the positive predictive value of the large vessel occlusion screening tool decreases the importance of the drip and ship model is appreciated. Second, the speed of treatment at the receiving hospitals. Fast treatment at thrombolysis centres is key for the drip and ship model to remain viable. Finally, the patient’s travel time to and between the different hospitals. As the distance between the thrombolysis and endovascular centre increases again the importance of the drip and ship model is realized. This thesis presents a novel way of conceptualizing the pre-hospital transport of suspected stroke patients. Decision-making for pre-hospital transport can be modelled using existing clinical trial data; these models can be dynamically adapted to changing realities. As the radius of superiority of the different transport strategy is context specific regional customization transport protocols for stroke patients is essential.
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    Final 2 year results of the vascular imaging of acute stroke for identifying predictors of clinical outcome and recurrent ischemic eveNts (VISION) study
    (BioMed Central, 2011-04-23) Coutts, Shelagh B.; Hill, Michael D.; Eliasziw, Misha; Fischer, Karyn; Demchuk, Andrew M.
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    Near-infrared measurements of brain oxygenation in stroke
    (Society of Photo-optical Instrumentation Engineers, 2016-02-11) Moreau, Francois; Yang, Runze; Nambiar, Vivek; Demchuk, Andrew M.; Dunn, Jeff F.
    We investigated the feasibility of using frequency-domain near-infrared spectroscopy (fdNIRS) to study brain oxygenation in the first few hours of stroke onset. The OxiplexTS® fdNIRS system was used in this study. Using a standard probing protocol based on surface landmarks, we measured brain tHb and StO2 in healthy volunteers, cadavers, and acute stroke patients within 9 h of stroke onset and 3 days later. We obtained measurements from 11 controls, 5 cadavers, and 5 acute stroke patients. StO2 values were significantly lower in cadavers compared to the controls and stroke patients. Each stroke patient had at least one area with reduced StO2 on the stroke side compared to the contralateral side. The evolution of tHb and StO2 at 3 days differed depending on whether a large infarct occurred. This study shows the proof of principle that quantified measurements of brain oxygenation using NIRS could be used in the hectic environment of acute stroke management. It also highlights the current technical limitations and future challenges in the development of this unique bedside monitoring tool for stroke.
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    Predicting the Risk of Intracerebral Haemorrhage in Patients with Acute Ischemic Stroke Receiving IV-alteplase with or Without Endovascular Thrombectomy
    (2016) Batchelor, Connor; Menon, Bijoy K.; Demchuk, Andrew M.; Goyal, Mayank; Lee, Ting-Yim; Sajobi, Tolulope
    Intracerebral Haemorrhage (ICH) is a devastating complication of acute ischemic stroke (AIS) treatment with no known effective management protocols. The need to identify patients at risk of developing this condition is becoming increasingly recognized among the stroke community. Computed tomography perfusion (CTP) is a powerful diagnostic imaging tool that measures blood flow in the brain. This tool can also be used to provide information regarding the integrity of the blood-brain barrier (BBB). Severe brain ischemia and consequent disruption of the BBB are probable mechanisms for why ICH occurs after AIS treatment. The goal of my research is to investigate the potential role of CTP primarily and other imaging and clinical parameters in predicting ICH secondary to AIS treatment in patients.
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    Testing ASPECTS Reliability Using Color Coded Algorithm Enhanced Gray- White Matter Non Contrast CT
    (2018-07-09) Hafeez, Moiz; Menon, Bijoy K.; Qiu, Wu; Federico, Paolo; Demchuk, Andrew M.; Krupinski, Elizabeth A.; Sajobi, Tolulope T.
    The Alberta Stroke Program Early CT Score (ASPECTS) is widely used to assess and diagnose Acute Ischemic Stroke Patients (AIS). Inter-rater reliability for ASPECTS however, is very poor even amongst physicians with extensive expertise. Much of this limitation has to do with the lack of agreement amongst physicians in identifying Early Ischemic Changes (EIC) on Non- Contrast Computed Tomography (NCCT) scans. This lack of agreement is due to the extremely subtle findings that the human eye is exposed to on gray scale NCCT scans during the acute period of ischemia. We therefore sought to use post processing algorithms to develop Color- Coded Algorithm Enhanced Gray- White Matter (AEGWM) NCCT scans. Increased differentiation between Gray- White matter on AEGWM NCCT scans was developed to act as a powerful imaging tool allowing for better delineation of EIC for AIS patients. In this thesis I investigated the utility of AEGWM NCCT scans for the purposes of detecting EIC in AIS patients. Overall, we found that AEGWM scans performed better as opposed to gray scale NCCT scans when using DWI as ground truth. In addition, inter rater agreement increased consistently across raters of all levels of expertise while using AEGWM scans. Although with some limitations, the use of AEGWM scans may be a promising research direction to pursue for future work.