Nicole Yuen - Academia.edu (original) (raw)

Papers by Nicole Yuen

Research paper thumbnail of Quantification of Penumbral Volume in Association With Time From Stroke Onset in Acute Ischemic Stroke With Large Vessel Occlusion

JAMA Neurology

ImportanceThe benefit of reperfusion therapies for acute ischemic stroke decreases over time. Thi... more ImportanceThe benefit of reperfusion therapies for acute ischemic stroke decreases over time. This decreasing benefit is presumably due to the disappearance of salvageable ischemic brain tissue (ie, the penumbra).ObjectiveTo study the association between stroke onset-to-imaging time and penumbral volume in patients with acute ischemic stroke with a large vessel occlusion.Design, Setting, and ParticipantsA retrospective, multicenter, cross-sectional study was conducted from January 1, 2015, to June 30, 2022. To limit selection bias, patients were selected from (1) the prospective registries of 2 comprehensive centers with systematic use of magnetic resonance imaging (MRI) with perfusion, including both thrombectomy-treated and untreated patients, and (2) 1 prospective thrombectomy study in which MRI with perfusion was acquired per protocol but treatment decisions were made with clinicians blinded to the results. Consecutive patients with acute stroke with intracranial internal caroti...

Research paper thumbnail of Abstract WP100: Elevated Hypoperfusion Intensity Ratio (HIR) Observed In Patients With A Large Vessel Occlusion (LVO) Presenting In The Evening

Stroke

Introduction: Circadian variability has been implicated in timing of stroke onset, yet the impact... more Introduction: Circadian variability has been implicated in timing of stroke onset, yet the impact of circadian rhythm on stroke evolution is not known. We aimed to describe this relationship in patients with large vessel occlusion (LVO) with perfusion imaging. Methods: A retrospective observational study was conducted from (1) prospective registries of two stroke centers with systematic use of perfusion imaging and (2) two thrombectomy trials where enrollment was not based on perfusion imaging results. Included patients had stroke due to ICA, M1 or M2 occlusion and baseline perfusion imaging performed within 24h from last-seen-well (LSW). Stroke onset was examined in 8hrs intervals: (1) Night: 23:00-6:59, (2) Day: 7:00-14:59, (3) Evening: 15:00-22:59. Core volume was estimated on CT perfusion (rCBF <30%) or DWI (ADC <620) and the collateral circulation was estimated with the hypoperfusion intensity ratio (HIR = [Tmax>10s]/[Tmax>6s]). Non-parametric testing was conducted ...

Research paper thumbnail of Abstract WP104: Core/perfusion Mismatch Prevalence According To ASPECT Score In Acute Ischemic Stroke With Large Vessel Occlusion

Stroke

Background: In acute ischemic stroke (AIS) with large vessel occlusion (LVO), core/perfusion mism... more Background: In acute ischemic stroke (AIS) with large vessel occlusion (LVO), core/perfusion mismatch modifies the effect of mechanical thrombectomy (MT) on clinical outcome, MT appears to have greater benefit in patients with significant mismatch. We aimed to study the prevalence of core/perfusion mismatch according to ASPECT score in a large population of LVO-related AIS imaged either with MRI or CT. Methods: Retrospective study including AIS patients with ICA/M1 occlusion and baseline perfusion imaging (MRI or CT) performed within 24hrs from last seen well. To avoid selection bias, patients were selected from (1) the registries of 3 comprehensive centers with systematic use of MRI- or CT-perfusion imaging and including both MT-treated and untreated patients, and (2) one thrombectomy trial where MT decisions were performed blinded to the results of MRI perfusion imaging. Core/perfusion mismatch was defined as mismatch ratio (Tmax>6s volume/ core volume) >1.8 and volume (Tmax...

Research paper thumbnail of Abstract 6: Relationship Between Hypoperfusion Intensity Ratio And Ischemic Core Growth Rate Is Similar On CT And MRI For Unselected Acute LVO Patients

Stroke

Background: Predicting infarct growth rate (IGR) in acute stroke with large vessel occlusion (LVO... more Background: Predicting infarct growth rate (IGR) in acute stroke with large vessel occlusion (LVO) is important for treatment decision-making. IGR has typically been studied in patients treated with thrombectomy, which likely has underestimated the prevalence of ‘fast progressors’, as large core patients are less frequently treated. We aimed to study IGR in an unselected LVO population and study the association between Hypoperfusion Intensity Ratio (HIR, a surrogate marker of collaterals) and IGR as assessed by both CT and MRI. Methods: Retrospective study including ICA/M1 stroke patients with witnessed stroke onset and baseline perfusion imaging (MRI or CT) performed within 24hrs from symptoms onset. To avoid selection bias, patients were selected from (1) the registries of 3 centers with systematic use of MRI- or CT-perfusion and including both MT-treated and untreated patients, and (2) one trial where thrombectomy decisions were performed blinded from perfusion MRI results. IGR w...

Research paper thumbnail of Imaging Factors Associated With Poor Outcome in Patients With Basilar Artery Occlusion Treated With Endovascular Thrombectomy

Stroke: Vascular and Interventional Neurology

BACKGROUND Acute ischemic stroke attributed to basilar artery occlusion (BAO) results in high rat... more BACKGROUND Acute ischemic stroke attributed to basilar artery occlusion (BAO) results in high rates of death and significant morbidity. Endovascular thrombectomy an effective treatment for BAO, but imaging parameters that predict a favorable response to thrombectomy are not well defined. We determined which imaging parameters were associated with poor outcome in patients with BAO treated by thrombectomy. METHODS We performed a retrospective cohort study of patients with BAO who underwent thrombectomy at multiple international stroke centers. All patients underwent computed tomography or magnetic resonance perfusion imaging before treatment. Clinical and imaging variables were measured and correlated to poor functional outcomes (modified Rankin scale score ≥4) after thrombectomy. Imaging variables included the following: Critical Area Perfusion Score, Posterior Circulation Alberta Stroke Program Early Computed Tomography Score, ischemic core volume (30% cerebral blood flow on compute...

Research paper thumbnail of Driving With Distraction: Measuring Brain Activity and Oculomotor Behavior Using fMRI and Eye-Tracking

Frontiers in Human Neuroscience

IntroductionDriving motor vehicles is a complex task that depends heavily on how visual stimuli a... more IntroductionDriving motor vehicles is a complex task that depends heavily on how visual stimuli are received and subsequently processed by the brain. The potential impact of distraction on driving performance is well known and poses a safety concern – especially for individuals with cognitive impairments who may be clinically unfit to drive. The present study is the first to combine functional magnetic resonance imaging (fMRI) and eye-tracking during simulated driving with distraction, providing oculomotor metrics to enhance scientific understanding of the brain activity that supports driving performance.Materials and MethodsAs initial work, twelve healthy young, right-handed participants performed turns ranging in complexity, including simple right and left turns without oncoming traffic, and left turns with oncoming traffic. Distraction was introduced as an auditory task during straight driving, and during left turns with oncoming traffic. Eye-tracking data were recorded during fM...

Research paper thumbnail of Cerebral perfusion imaging predicts final infarct volume after basilar artery thrombectomy

Journal of Stroke and Cerebrovascular Diseases

Research paper thumbnail of Abstract 126: Cerebral Perfusion Imaging And Posterior Circulation ASPECTS Identify Stroke Patients Who Benefit From Basilar Artery Thrombectomy

Stroke, 2022

Introduction: Acute ischemic stroke due to basilar artery occlusion (AIS-BAO) results in signific... more Introduction: Acute ischemic stroke due to basilar artery occlusion (AIS-BAO) results in significant morbidity and mortality. Endovascular thrombectomy (ET) has not been shown to improve outcomes in AIS-BAO patients in randomized trials, which may be due to insufficient selection before ET. We determined whether the Critical Area Perfusion Score (CAPS) and posterior circulation ASPECTS (PC-ASPECTS) predict a favorable response to ET. Methods: We performed a multicenter retrospective study of AIS-BAO patients with perfusion imaging prior to ET. PC-ASPECTS was determined on NCCT by evaluating the cerebellum (1 point/hemisphere), pons (2 points), midbrain (2 points), thalamus (1 point/hemisphere), and posterior cerebral artery (1 point/hemisphere) territories, and points were subtracted for hypodensity in these regions. CAPS was quantified severe hypoperfusion (Tmax >10s) in cerebellum (1 point/hemisphere), pons (2 points), midbrain and/or thalamus (2 points). The primary outcome wa...

Research paper thumbnail of Driving with Distraction: Brain Activity and Oculomotor Behaviour using fMRI and Eye-tracking

Research paper thumbnail of Perfusion Imaging Predicts Favorable Outcomes after Basilar Artery Thrombectomy

Annals of Neurology, 2021

Perfusion imaging identifies anterior circulation stroke patients who respond favorably to endova... more Perfusion imaging identifies anterior circulation stroke patients who respond favorably to endovascular thrombectomy (ET), but its role in basilar artery occlusion (BAO) is unknown. We hypothesized that BAO patients with limited regions of severe hypoperfusion (time to reach maximum concentration in seconds [Tmax] > 10) would have a favorable response to ET compared to patients with more extensive regions involved.

Research paper thumbnail of Intrinsic Frequencies of the Resting-State fMRI Signal: The Frequency Dependence of Functional Connectivity and the Effect of Mode Mixing

Frontiers in Neuroscience, 2019

The frequency characteristics of the resting-state BOLD fMRI (rs-fMRI) signal are of increasing s... more The frequency characteristics of the resting-state BOLD fMRI (rs-fMRI) signal are of increasing scientific interest, as we discover more frequency-specific biological interpretations. In this work, we use variational mode decomposition (VMD) to precisely decompose the rs-fMRI time series into its intrinsic mode functions (IMFs) in a datadriven manner. The accuracy of the VMD decomposition of constituent IMFs is verified through simulations, with higher reconstruction accuracy and much-reduced mode mixing relative to previous methods. Furthermore, we examine the relative contribution of the VMD-derived modes (frequencies) to the rs-fMRI signal as well as functional connectivity measurements. Our primary findings are: (1) The rs-fMRI signal within the 0.01-0.25 Hz range can be consistently characterized by four intrinsic frequency clusters, centered at 0.028 Hz (IMF4), 0.080 Hz (IMF3), 0.15 Hz (IMF2) and 0.22 Hz (IMF1); (2) these frequency clusters were highly reproducible, and independent of rs-fMRI data sampling rate; (3) not all frequencies were associated with equivalent network topology, in contrast to previous findings. In fact, while IMF4 is most likely associated with physiological fluctuations due to respiration and pulse, IMF3 is most likely associated with metabolic processes, and IMF2 with vasomotor activity. Both IMF3 and IMF4 could produce the brain-network topology typically observed in fMRI, whereas IMF1 and IMF2 could not. These findings provide initial evidence of feasibility in decomposing the rs-fMRI signal into its intrinsic oscillatory frequencies in a reproducible manner.

Research paper thumbnail of Abstract TMP68: Core/perfusion Mismatch In Acute Ischemic Stroke With M2 Occlusion: Prevalence And Associated Factors

Stroke

Background: The benefit of mechanical thrombectomy (MT) in acute ischemic stroke (AIS) patients w... more Background: The benefit of mechanical thrombectomy (MT) in acute ischemic stroke (AIS) patients with M2 occlusion is uncertain. Observational studies suggest that perfusion imaging may help select optimal M2 candidates for MT. We aimed to study the prevalence and factors associated with core/perfusion mismatch, as assessed by both CT and MRI, in an unselected population of AIS with M2 occlusion. Methods: Retrospective observational study including AIS patients with M2 occlusion and baseline perfusion imaging (MRI or CT) performed within 24hrs from last seen well. To avoid selection bias, patients were selected from the prospective registries of 3 centers with systematic use of perfusion imaging, including both MT-treated and untreated patients. Core/perfusion mismatch was defined as mismatch ratio (Tmax>6s/ core volume) >1.8 and mismatch volume (Tmax>6s - core volume) >15mL. Results: Overall, 156 and 196 patients were included in the MRI and CT cohorts, respectively. Las...

Research paper thumbnail of Quantification of Penumbral Volume in Association With Time From Stroke Onset in Acute Ischemic Stroke With Large Vessel Occlusion

JAMA Neurology

ImportanceThe benefit of reperfusion therapies for acute ischemic stroke decreases over time. Thi... more ImportanceThe benefit of reperfusion therapies for acute ischemic stroke decreases over time. This decreasing benefit is presumably due to the disappearance of salvageable ischemic brain tissue (ie, the penumbra).ObjectiveTo study the association between stroke onset-to-imaging time and penumbral volume in patients with acute ischemic stroke with a large vessel occlusion.Design, Setting, and ParticipantsA retrospective, multicenter, cross-sectional study was conducted from January 1, 2015, to June 30, 2022. To limit selection bias, patients were selected from (1) the prospective registries of 2 comprehensive centers with systematic use of magnetic resonance imaging (MRI) with perfusion, including both thrombectomy-treated and untreated patients, and (2) 1 prospective thrombectomy study in which MRI with perfusion was acquired per protocol but treatment decisions were made with clinicians blinded to the results. Consecutive patients with acute stroke with intracranial internal caroti...

Research paper thumbnail of Abstract WP100: Elevated Hypoperfusion Intensity Ratio (HIR) Observed In Patients With A Large Vessel Occlusion (LVO) Presenting In The Evening

Stroke

Introduction: Circadian variability has been implicated in timing of stroke onset, yet the impact... more Introduction: Circadian variability has been implicated in timing of stroke onset, yet the impact of circadian rhythm on stroke evolution is not known. We aimed to describe this relationship in patients with large vessel occlusion (LVO) with perfusion imaging. Methods: A retrospective observational study was conducted from (1) prospective registries of two stroke centers with systematic use of perfusion imaging and (2) two thrombectomy trials where enrollment was not based on perfusion imaging results. Included patients had stroke due to ICA, M1 or M2 occlusion and baseline perfusion imaging performed within 24h from last-seen-well (LSW). Stroke onset was examined in 8hrs intervals: (1) Night: 23:00-6:59, (2) Day: 7:00-14:59, (3) Evening: 15:00-22:59. Core volume was estimated on CT perfusion (rCBF <30%) or DWI (ADC <620) and the collateral circulation was estimated with the hypoperfusion intensity ratio (HIR = [Tmax>10s]/[Tmax>6s]). Non-parametric testing was conducted ...

Research paper thumbnail of Abstract WP104: Core/perfusion Mismatch Prevalence According To ASPECT Score In Acute Ischemic Stroke With Large Vessel Occlusion

Stroke

Background: In acute ischemic stroke (AIS) with large vessel occlusion (LVO), core/perfusion mism... more Background: In acute ischemic stroke (AIS) with large vessel occlusion (LVO), core/perfusion mismatch modifies the effect of mechanical thrombectomy (MT) on clinical outcome, MT appears to have greater benefit in patients with significant mismatch. We aimed to study the prevalence of core/perfusion mismatch according to ASPECT score in a large population of LVO-related AIS imaged either with MRI or CT. Methods: Retrospective study including AIS patients with ICA/M1 occlusion and baseline perfusion imaging (MRI or CT) performed within 24hrs from last seen well. To avoid selection bias, patients were selected from (1) the registries of 3 comprehensive centers with systematic use of MRI- or CT-perfusion imaging and including both MT-treated and untreated patients, and (2) one thrombectomy trial where MT decisions were performed blinded to the results of MRI perfusion imaging. Core/perfusion mismatch was defined as mismatch ratio (Tmax>6s volume/ core volume) >1.8 and volume (Tmax...

Research paper thumbnail of Abstract 6: Relationship Between Hypoperfusion Intensity Ratio And Ischemic Core Growth Rate Is Similar On CT And MRI For Unselected Acute LVO Patients

Stroke

Background: Predicting infarct growth rate (IGR) in acute stroke with large vessel occlusion (LVO... more Background: Predicting infarct growth rate (IGR) in acute stroke with large vessel occlusion (LVO) is important for treatment decision-making. IGR has typically been studied in patients treated with thrombectomy, which likely has underestimated the prevalence of ‘fast progressors’, as large core patients are less frequently treated. We aimed to study IGR in an unselected LVO population and study the association between Hypoperfusion Intensity Ratio (HIR, a surrogate marker of collaterals) and IGR as assessed by both CT and MRI. Methods: Retrospective study including ICA/M1 stroke patients with witnessed stroke onset and baseline perfusion imaging (MRI or CT) performed within 24hrs from symptoms onset. To avoid selection bias, patients were selected from (1) the registries of 3 centers with systematic use of MRI- or CT-perfusion and including both MT-treated and untreated patients, and (2) one trial where thrombectomy decisions were performed blinded from perfusion MRI results. IGR w...

Research paper thumbnail of Imaging Factors Associated With Poor Outcome in Patients With Basilar Artery Occlusion Treated With Endovascular Thrombectomy

Stroke: Vascular and Interventional Neurology

BACKGROUND Acute ischemic stroke attributed to basilar artery occlusion (BAO) results in high rat... more BACKGROUND Acute ischemic stroke attributed to basilar artery occlusion (BAO) results in high rates of death and significant morbidity. Endovascular thrombectomy an effective treatment for BAO, but imaging parameters that predict a favorable response to thrombectomy are not well defined. We determined which imaging parameters were associated with poor outcome in patients with BAO treated by thrombectomy. METHODS We performed a retrospective cohort study of patients with BAO who underwent thrombectomy at multiple international stroke centers. All patients underwent computed tomography or magnetic resonance perfusion imaging before treatment. Clinical and imaging variables were measured and correlated to poor functional outcomes (modified Rankin scale score ≥4) after thrombectomy. Imaging variables included the following: Critical Area Perfusion Score, Posterior Circulation Alberta Stroke Program Early Computed Tomography Score, ischemic core volume (30% cerebral blood flow on compute...

Research paper thumbnail of Driving With Distraction: Measuring Brain Activity and Oculomotor Behavior Using fMRI and Eye-Tracking

Frontiers in Human Neuroscience

IntroductionDriving motor vehicles is a complex task that depends heavily on how visual stimuli a... more IntroductionDriving motor vehicles is a complex task that depends heavily on how visual stimuli are received and subsequently processed by the brain. The potential impact of distraction on driving performance is well known and poses a safety concern – especially for individuals with cognitive impairments who may be clinically unfit to drive. The present study is the first to combine functional magnetic resonance imaging (fMRI) and eye-tracking during simulated driving with distraction, providing oculomotor metrics to enhance scientific understanding of the brain activity that supports driving performance.Materials and MethodsAs initial work, twelve healthy young, right-handed participants performed turns ranging in complexity, including simple right and left turns without oncoming traffic, and left turns with oncoming traffic. Distraction was introduced as an auditory task during straight driving, and during left turns with oncoming traffic. Eye-tracking data were recorded during fM...

Research paper thumbnail of Cerebral perfusion imaging predicts final infarct volume after basilar artery thrombectomy

Journal of Stroke and Cerebrovascular Diseases

Research paper thumbnail of Abstract 126: Cerebral Perfusion Imaging And Posterior Circulation ASPECTS Identify Stroke Patients Who Benefit From Basilar Artery Thrombectomy

Stroke, 2022

Introduction: Acute ischemic stroke due to basilar artery occlusion (AIS-BAO) results in signific... more Introduction: Acute ischemic stroke due to basilar artery occlusion (AIS-BAO) results in significant morbidity and mortality. Endovascular thrombectomy (ET) has not been shown to improve outcomes in AIS-BAO patients in randomized trials, which may be due to insufficient selection before ET. We determined whether the Critical Area Perfusion Score (CAPS) and posterior circulation ASPECTS (PC-ASPECTS) predict a favorable response to ET. Methods: We performed a multicenter retrospective study of AIS-BAO patients with perfusion imaging prior to ET. PC-ASPECTS was determined on NCCT by evaluating the cerebellum (1 point/hemisphere), pons (2 points), midbrain (2 points), thalamus (1 point/hemisphere), and posterior cerebral artery (1 point/hemisphere) territories, and points were subtracted for hypodensity in these regions. CAPS was quantified severe hypoperfusion (Tmax >10s) in cerebellum (1 point/hemisphere), pons (2 points), midbrain and/or thalamus (2 points). The primary outcome wa...

Research paper thumbnail of Driving with Distraction: Brain Activity and Oculomotor Behaviour using fMRI and Eye-tracking

Research paper thumbnail of Perfusion Imaging Predicts Favorable Outcomes after Basilar Artery Thrombectomy

Annals of Neurology, 2021

Perfusion imaging identifies anterior circulation stroke patients who respond favorably to endova... more Perfusion imaging identifies anterior circulation stroke patients who respond favorably to endovascular thrombectomy (ET), but its role in basilar artery occlusion (BAO) is unknown. We hypothesized that BAO patients with limited regions of severe hypoperfusion (time to reach maximum concentration in seconds [Tmax] > 10) would have a favorable response to ET compared to patients with more extensive regions involved.

Research paper thumbnail of Intrinsic Frequencies of the Resting-State fMRI Signal: The Frequency Dependence of Functional Connectivity and the Effect of Mode Mixing

Frontiers in Neuroscience, 2019

The frequency characteristics of the resting-state BOLD fMRI (rs-fMRI) signal are of increasing s... more The frequency characteristics of the resting-state BOLD fMRI (rs-fMRI) signal are of increasing scientific interest, as we discover more frequency-specific biological interpretations. In this work, we use variational mode decomposition (VMD) to precisely decompose the rs-fMRI time series into its intrinsic mode functions (IMFs) in a datadriven manner. The accuracy of the VMD decomposition of constituent IMFs is verified through simulations, with higher reconstruction accuracy and much-reduced mode mixing relative to previous methods. Furthermore, we examine the relative contribution of the VMD-derived modes (frequencies) to the rs-fMRI signal as well as functional connectivity measurements. Our primary findings are: (1) The rs-fMRI signal within the 0.01-0.25 Hz range can be consistently characterized by four intrinsic frequency clusters, centered at 0.028 Hz (IMF4), 0.080 Hz (IMF3), 0.15 Hz (IMF2) and 0.22 Hz (IMF1); (2) these frequency clusters were highly reproducible, and independent of rs-fMRI data sampling rate; (3) not all frequencies were associated with equivalent network topology, in contrast to previous findings. In fact, while IMF4 is most likely associated with physiological fluctuations due to respiration and pulse, IMF3 is most likely associated with metabolic processes, and IMF2 with vasomotor activity. Both IMF3 and IMF4 could produce the brain-network topology typically observed in fMRI, whereas IMF1 and IMF2 could not. These findings provide initial evidence of feasibility in decomposing the rs-fMRI signal into its intrinsic oscillatory frequencies in a reproducible manner.

Research paper thumbnail of Abstract TMP68: Core/perfusion Mismatch In Acute Ischemic Stroke With M2 Occlusion: Prevalence And Associated Factors

Stroke

Background: The benefit of mechanical thrombectomy (MT) in acute ischemic stroke (AIS) patients w... more Background: The benefit of mechanical thrombectomy (MT) in acute ischemic stroke (AIS) patients with M2 occlusion is uncertain. Observational studies suggest that perfusion imaging may help select optimal M2 candidates for MT. We aimed to study the prevalence and factors associated with core/perfusion mismatch, as assessed by both CT and MRI, in an unselected population of AIS with M2 occlusion. Methods: Retrospective observational study including AIS patients with M2 occlusion and baseline perfusion imaging (MRI or CT) performed within 24hrs from last seen well. To avoid selection bias, patients were selected from the prospective registries of 3 centers with systematic use of perfusion imaging, including both MT-treated and untreated patients. Core/perfusion mismatch was defined as mismatch ratio (Tmax>6s/ core volume) >1.8 and mismatch volume (Tmax>6s - core volume) >15mL. Results: Overall, 156 and 196 patients were included in the MRI and CT cohorts, respectively. Las...