Cheemun Lum

University of Ottawa, Ottawa, Ontario, Canada

Are you Cheemun Lum?

Claim your profile

Publications (38)146.25 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Recanalization rates are higher in acute anterior stroke treated with stent-retrievers when compared with older techniques. However, some still have sizeable infarcts and poor outcome. This may be related to underestimation of core infarct on nonenhanced computed tomography (NECT). CT angiography (CTA) source images (CTASI) and CT perfusion may be more informative. We hypothesize that core infarct estimation with NECT, CTA, and CT perfusion predicts infarct at 24 hours and outcome after fast recanalization.
    Stroke 08/2014; · 6.16 Impact Factor
  • The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 03/2014; 41(2):193-9. · 1.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Variability in computed tomography angiography (CTA) acquisitions may be one explanation for the modest accuracy of the spot sign for predicting intracerebral hemorrhage expansion detected in the multicenter Predicting Hematoma Growth and Outcome in Intracerebral Hemorrhage Using Contrast Bolus CT (PREDICT) study. This study aimed to determine the frequency of the spot sign in intracerebral hemorrhage and its relationship with hematoma expansion depending on the phase of image acquisition. PREDICT study was a prospective observational cohort study of patients with intracerebral hemorrhage presenting within 6 hours from onset. A post hoc analysis of the Hounsfield units of an artery and venous structure were measured on CTA source images of the entire PREDICT cohort in a core laboratory. Each CTA study was classified into arterial or venous phase and into 1 of 5 specific image acquisition phases. Significant hematoma expansion and total hematoma enlargement were recorded at 24 hours. Overall (n=371), 77.9% of CTA were acquired in arterial phase. The spot sign, present in 29.9% of patients, was more frequently seen in venous phase as compared with arterial phase (39% versus 27.3%; P=0.041) and the later the phase of image acquisition (P=0.095). Significant hematoma expansion (P=0.253) and higher total hematoma enlargement (P=0.019) were observed more frequently among spot sign-positive patients with earlier phases of image acquisition. Later image acquisition of CTA improves the frequency of spot sign detection. However, spot signs identified in earlier phases may be associated with greater absolute enlargement. A multiphase CTA including arterial and venous acquisitions could be optimal in patients with intracerebral hemorrhage.
    Stroke 01/2014; 45(3):734-9. · 6.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Rationale and Objectives Patients presenting with transient ischemic attack or stroke may have symptom-related lesions on acute computed tomography angiography (CTA) such as free-floating intraluminal thrombus (FFT). It is difficult to distinguish FFT from carotid plaque, but the distinction is critical as management differs. By contouring the shape of these vascular lesions (“virtual endarterectomy”), advanced morphometric analysis can be performed. The objective of our study is to determine whether quantitative shape analysis can accurately differentiate FFT from atherosclerotic plaque. Materials and Methods We collected 23 consecutive cases of suspected carotid FFT seen on CTA (13 men, 65 ± 10 years; 10 women, 65.5 ± 8.8 years). True-positive FFT cases (FFT+) were defined as filling defects resolving with anticoagulant therapy versus false-positives (FFT−), which remained unchanged. Lesion volumes were extracted from CTA images and quantitative shape descriptors were computed. The five most discriminative features were used to construct receiver operator characteristic (ROC) curves and to generate three machine-learning classifiers. Average classification accuracy was determined by cross-validation. Results Follow-up imaging confirmed sixteen FFT+ and seven FFT− cases. Five shape descriptors delineated FFT+ from FFT− cases. The logistic regression model produced from combining all five shape features demonstrated a sensitivity of 87.5% and a specificity of 71.4% with an area under the ROC curve = 0.85 ± 0.09. Average accuracy for each classifier ranged from 65.2%–76.4%. Conclusions We identified five quantitative shape descriptors of carotid FFT. This shape “signature” shows potential for supplementing conventional lesion characterization in cases of suspected FFT.
    Academic radiology 01/2014; 21(3):345–354. · 2.09 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Filling defects at the internal carotid artery (ICA) origin in the work-up of stroke or transient ischemic attack may be an ulcerated plaque or free-floating thrombus (FFT). This may be challenging to distinguish, as they can appear morphologically similar. This is an important distinction as FFT can potentially embolize distally, and its management differs. We describe a series of patients with suspected FFT and evaluate its imaging appearance, clinical features, and evolution with therapy. Between 2008 and 2013, we prospectively collected consecutive patients with proximal ICA filling defects in the axial plane surrounded by contrast on CT/MR angiography. We defined FFT as a filling defect that resolved on follow-up imaging. We assessed the cranial-caudal dimension of the filling defect and receiver operating characteristics to identify clinical and radiological variables that distinguished FFT from complex ulcerated plaque. Intraluminal filling defects were identified in 32 patients. Filling defects and resolved or decreased in 25 patients (78 %) and felt to be FFT; there was no change in 7 (22 %). Resolved defects and those that decreased in size extended more cranially than those that remained unchanged: 7.3 mm (4.2-15.9) versus 3.1 mm (2.7-3.7; p = 0.0038). Receiver operating characteristic analysis established a threshold of 3.8 mm (filling defect length), sensitivity of 88 %, specificity of 86 %, and area under the curve of 0.86 (p < 0.0001) for distinguishing FFT from plaque. Filling defects in the proximal ICA extending cranially >3.8 mm were more likely to be FFT than complex ulcerated plaque. Further studies evaluating filling defect length as a predictor for FFT are warranted.
    Neuroradiology 11/2013; · 2.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND AND PURPOSE: The spot sign score (SSS) provides risk stratification for hematoma expansion in acute intracerebral hemorrhage; however, external validation is needed. We sought to validate the SSS and assess prognostic performance of individual spot characteristics associated with hematoma expansion from a prospective multicenter intracerebral hemorrhage study. METHODS: Two hundred twenty-eight intracerebral hemorrhage patients within 6 hours after ictus were enrolled in the Predicting Hematoma Growth and Outcome in Intracerebral Hemorrhage Using Contrast Bolus CT (PREDICT) study, a multicenter prospective intracerebral hemorrhage cohort study. Patients were evaluated with baseline noncontrast computerized tomography, computerized tomography angiography, and 24-hour follow-up computerized tomography. Primary outcome was significant hematoma expansion (>6 mL or >33%) and secondary outcome was absolute and relative expansion. Blinded computerized tomography angiography spot sign characterization and SSS calculation were independently performed by 2 neuroradiologists and a radiology resident. Diagnostic performance of the SSS and individual spot characteristics were examined with multivariable regression, receiver operating characteristic analysis, and tests for trend. RESULTS: SSS and spot number independently predicted significant, absolute, and relative hematoma expansion (P<0.05 each) and demonstrated near perfect interobserver agreement (κ=0.82 and κ=0.85, respectively). Incremental risk of hematoma expansion among spot-positive patients was not identified for SSS (P trend=0.720) but was demonstrated for spot number (P trend=0.050). Spot number and SSS demonstrated similar area under the curve (0.69 versus 0.68; P=0.306) for hematoma expansion. CONCLUSIONS: Multicenter external validation of the SSS demonstrates that the spot number alone provides similar prediction but improved risk stratification of hematoma expansion compared with the SSS.
    Stroke 02/2013; 44(4):972-7. · 6.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Prodigious efforts and landmark discoveries have led toward significant advances in our understanding of atherosclerosis. Despite significant efforts, atherosclerosis continues globally to be a leading cause of mortality and reduced quality of life. With surges in the prevalence of obesity and diabetes, atherosclerosis is expected to have an even more pronounced impact upon the global burden of disease. It is imperative to develop strategies for the early detection of disease. Positron emission tomography (PET) imaging utilizing [(18)F]fluorodeoxyglucose (FDG) may provide a non-invasive means of characterizing inflammatory activity within atherosclerotic plaque, thus serving as a surrogate biomarker for detecting vulnerable plaque. The aim of this review is to explore the rationale for performing FDG imaging, provide an overview into the mechanism of action, and summarize findings from the early application of FDG PET imaging in the clinical setting to evaluate vascular disease. Alternative imaging biomarkers and approaches are briefly discussed.
    Journal of Nuclear Cardiology 10/2012; · 2.85 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: Neuroprotection with NA-1 (Tat-NR2B9c), an inhibitor of postsynaptic density-95 protein, has been shown in a primate model of stroke. We assessed whether NA-1 could reduce ischaemic brain damage in human beings. METHODS: For this double-blind, randomised, controlled study, we enrolled patients aged 18 years or older who had a ruptured or unruptured intracranial aneurysm amenable to endovascular repair from 14 hospitals in Canada and the USA. We used a computer-generated randomisation sequence to allocate patients to receive an intravenous infusion of either NA-1 or saline control at the end of their endovascular procedure (1:1; stratified by site, age, and aneurysm status). Both patients and investigators were masked to treatment allocation. The primary outcome was safety and primary clinical outcomes were the number and volume of new ischaemic strokes defined by MRI at 12-95 h after infusion. We used a modified intention-to-treat (mITT) analysis. This trial is registered with, number NCT00728182. FINDINGS: Between Sept 16, 2008, and March 30, 2011, we randomly allocated 197 patients to treatment-12 individuals did not receive treatment because they were found to be ineligible after randomisation, so the mITT population consisted of 185 individuals, 92 in the NA-1 group and 93 in the placebo group. Two minor adverse events were adjudged to be associated with NA-1; no serious adverse events were attributable to NA-1. We recorded no difference between groups in the volume of lesions by either diffusion-weighted MRI (adjusted p value=0·120) or fluid-attenuated inversion recovery MRI (adjusted p value=0·236). Patients in the NA-1 group sustained fewer ischaemic infarcts than did patients in the placebo group, as gauged by diffusion-weighted MRI (adjusted incidence rate ratio 0·53, 95% CI 0·38-0·74) and fluid-attenuated inversion recovery MRI (0·59, 0·42-0·83). INTERPRETATION: Our findings suggest that neuroprotection in human ischaemic stroke is possible and that it should be investigated in larger trials. FUNDING: NoNO Inc and Arbor Vita Corp.
    The Lancet Neurology 10/2012; 11(11):942-950. · 23.92 Impact Factor
  • Source
    The Canadian journal of cardiology 09/2012; 28(5):S162. · 3.12 Impact Factor
  • Source
    Society of Nuclear Medicine (SNM) 2012; 06/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND AND PURPOSE: Diffusion weighted imaging (DWI) may be used to evaluate post-coiling ischemia. Heparinization protocols for cerebral aneurysm coiling procedures differ among operators and centers, with little literature surrounding its effect on DWI lesions. The goal of this study was to determine which factors, including heparinization protocols, may affect DWI lesion load post-coiling. MATERIALS AND METHODS: A review of 135 coiling procedures over 5 years at our centre was performed. Procedural data including length of procedure, number of coils used, stent or balloon assistance and operators were collected. Procedures were either assigned as using a bolus dose (>2000 U at any one time) or small aliquots of heparin (≤2000 U). Postprocedure DWI was reviewed and lesions were classified as small (< 5mm), medium (5-10 mm) or large (>10 mm). The cases were then classified into group 1 (≤5 small lesions) or group 2 (>5 small lesions or ≥1 medium or large lesion). Multivariate regression of the procedural variables for the two groups was calculated. A p value of <0.05 was considered significant. RESULTS: There were 78 procedures in group 1 and 57 procedures in group 2. Patients who received small aliquots (n=37) versus boluses of heparin (n=98) intraprocedurally had significantly greater frequency and size of DWI lesions (p=0.03). None of the other procedural variables was found to impact on lesion load. CONCLUSIONS: More substantial DWI lesions were associated with small aliquots of heparin dosage compared with bolus doses. Heparin boluses should be preferentially administered during aneurysm coiling.
    Journal of Neurointerventional Surgery 05/2012; · 2.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: INTRODUCTION: The most significant factors leading to restenosis are yet to be described in the literature. The purpose of our study was to identify the incidence of restenosis in our patients with carotid artery stenting (CAS) for carotid atherosclerotic disease and to identify risk factors that are significantly responsible or related to the restenosis. METHODS: In this retrospective analysis of patients who underwent CAS for atherosclerotic disease between years 2002 and 2006, we studied various demographic, clinical, and medical factors, plaque characteristics, and technical aspects of CAS. All patients were followed up with carotid Doppler ultrasound at baseline (after 2 to 4 weeks of CAS) and then with Doppler ultrasound and clinically for various intervals of time. The restenosis was classified based on carotid Doppler ultrasound results. Clinically, restenosis was classified as symptomatic or asymptomatic. Pearson correlation coefficient was used to assess the statistical correlation of the different factors with the incidence of restenosis. RESULTS: We had a total of 105 patients, with a total of 204.6 patient-year follow-up (mean, 1.95 years; range, 0-7.3 years). The overall incidence of restenosis was 26.7 % (n = 28): mild, 7.6 % (n = 8); moderate, 10.5 % (asymptomatic, 11; symptomatic, 0); and severe, 8.6 % (asymptomatic, 5; symptomatic, 4). Overall, 14.3 % (n = 4) patients with restenosis were symptomatic and 7.1 % (n = 2) underwent retreatment. Post-stenting residual stenosis greater than either 30 % (p = 0.016) or 50 % (p = 0.05) were significant for long-term restenosis. Plaques longer than 20 mm were significantly related to restenosis (p < 0.001). CONCLUSION: The most important factor to explain restenosis was the immediate post-CAS residual stenosis and length of the plaque.
    Neuroradiology 04/2012; · 2.70 Impact Factor
  • Emergency Radiology 03/2012; 19(4):359-62.
  • [Show abstract] [Hide abstract]
    ABSTRACT: In patients with intracerebral haemorrhage (ICH), early haemorrhage expansion affects clinical outcome. Haemostatic treatment reduces haematoma expansion, but fails to improve clinical outcomes in many patients. Proper selection of patients at high risk for haematoma expansion seems crucial to improve outcomes. In this study, we aimed to prospectively validate the CT-angiography (CTA) spot sign for prediction of haematoma expansion. PREDICT (predicting haematoma growth and outcome in intracerebral haemorrhage using contrast bolus CT) was a multicentre prospective observational cohort study. We recruited patients aged 18 years or older, with ICH smaller than 100 mL, and presenting at less than 6 h from symptom onset. Using two independent core laboratories, one neuroradiologist determined CTA spot-sign status, whereas another neurologist masked for clinical outcomes and imaging measured haematoma volumes by computerised planimetry. The primary outcome was haematoma expansion defined as absolute growth greater than 6 mL or a relative growth of more than 33% from initial CT to follow-up CT. We reported data using standard descriptive statistics stratified by the CTA spot sign. Mortality was assessed with Kaplan-Meier survival analysis. We enrolled 268 patients. Median time from symptom onset to baseline CT was 135 min (range 22-470), and time from onset to CTA was 159 min (32-475). 81 (30%) patients were spot-sign positive. The primary analysis included 228 patients, who had a follow-up CT before surgery or death. Median baseline ICH volume was 19·9 mL (1·5-80·9) in spot-sign-positive patients versus 10·0 mL (0·1-102·7) in spot-sign negative patients (p<0·001). Median ICH expansion was 8·6 mL (-9·3 to 121·7) for spot-sign positive patients and 0·4 mL (-11·7 to 98·3) for spot-negative patients (p<0·001). In those with haematoma expansion, the positive predictive value for the spot sign was61% (95% CI 47–73) for the positive predictive value and 78% (71–84) for the negative predictive value, with 51% (39–63) sensitivity and 85% (78–90) specificity[corrected]. Median 3-month modified Rankin Scale (mRS) was 5 in CTA spot-sign-positive patients, and 3 in spot-sign-negative patients (p<0·001). Mortality at 3 months was 43·4% (23 of 53) in CTA spot-sign positive versus 19·6% (31 of 158) in CTA spot-sign-negative patients (HR 2·4, 95% CI 1·4-4·0, p=0·002). These findings confirm previous single-centre studies showing that the CTA spot sign is a predictor of haematoma expansion. The spot sign is recommended as an entry criterion for future trials of haemostatic therapy in patients with acute ICH. Canadian Stroke Consortium and NovoNordisk Canada.
    The Lancet Neurology 03/2012; 11(4):307-14. · 23.92 Impact Factor
  • Circulation 01/2012; 126(21 Supplement):A17612. · 15.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Heparin induced thrombocytopenia and thrombosis is a potential complication of any procedure following previous heparin exposure. A case is described of acute in-stent occlusion during carotid stenting due to heparin induced thrombocytopenia and thrombosis. Management options are also discussed.
    Journal of Neurointerventional Surgery 11/2011; 4(6):e34. · 2.50 Impact Factor
  • Source
    Canadian cardiovascular society (CCS) Congress 2011; 10/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: Coiling of small aneurysms can be technically challenging. These aspects of coiling tend to be less problematic in medium to large aneurysms as they are more accommodating of microcatheters and coils. When physicians are asked their opinion regarding aneurysm coilability in small aneurysms, the decision often lies in the operator's feeling that they could reasonably exclude the aneurysm with a complication rate similar to larger aneurysms. The purpose of our study was to investigate the feasibility, intraprocedural rupture rates and long term durability of endovascular coiling for small (≤4 mm) aneurysms compared with non-small (>4 mm) aneurysms. To control for factors such as vessel tortuosity and aneurysm location, a control group was chosen matched to the study group both in age and aneurysm location. A retrospective review of 360 intracranial aneurysms coiled at our institution between 2003 and 2008 was performed. For the control group, intracranial aneurysms coiled in the same period matched to location and age were chosen. The frequency of intraprocedural perforations was 4/34 (0.12) and 3/68 (0.04) for the small and non-small cohort, respectively (p=0.22). All patients who had a perforation in the small aneurysm groups had a good clinical outcome compared with 1/3 in the non-small group (two mortalities). The frequency of recanalization for the small and non-small groups was 3/34 (0.09) and 23/68 (0.33), respectively (p=0.006). There was no retreatments in the small aneurysm group and five (0.07) in the non-small group (p=0.116). Coiling of small (≤4 mm) aneurysms is feasible with a reasonable complication rate. There is a non-significant increase in frequency of intraprocedural rupture with coiling of small aneurysms compared with controls matched to aneurysm location and age but this is not associated with increased morbidity. Coiling of small aneurysms leads to durable results at long term follow-up.
    Journal of Neurointerventional Surgery 07/2011; 4(3):196-8. · 2.50 Impact Factor
  • Jai Jai Shiva Shankar, Cheemun Lum
    [Show abstract] [Hide abstract]
    ABSTRACT: Computed tomography perfusion (CTP) has been criticized for limited brain coverage. This may result in inadequate coverage of the lesion, inadequate arterial input function, or omission of the lesion within the target perfusion volume. The availability of 320-slice CT scanners offers whole brain coverage. This minimizes the chances of misregistration of lesions regardless of location, and makes the selection of the arterial input function easy. We present different clinical scenarios in which whole brain CTP is especially useful.
    The Indian journal of radiology and imaging 07/2011; 21(3):209-14.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Different endovascular techniques can be employed to achieve vessel recanalization in acute stroke. We assessed whether an endovascular strategy that included angioplasty was safe and effectively recanalized acutely occluded intracranial vessels. We retrospectively reviewed 70 patients that received intra-arterial therapy for acute stroke. Patients were divided into two groups depending on whether they had received angioplasty as part of their endovascular treatment. Angioplasty was used in the treatment of 35/70 patients (50%). Median baseline NIHSS was 15. The site of occlusion was at the M1 in 11 patients, M1/M2 in 3, ICA/M1 in 13 and vertebrobasilar in 8 patients. Intravenous thrombolysis was administered to 16/35 patients (46%). Angioplasty was used alone in 4 patients, in combination with intra-arterial thrombolysis in 27 and with a mechanical retrieval device or stent in 13 patients. Recanalization (TICI 2-3) was achieved in 23/35 patients (66%). Median time from symptom onset to recanalization was six hours. In patients where angioplasty was employed, symptomatic intracranial hemorrhage occurred in 2/35 (6%), which was similar to patients that were not treated with angioplasty. A favorable functional outcome (mRS=2) was achieved in 20% (7/35) at 24 hour and 34% (12/35) at one month. All patients that had a favorable outcome had recanalized. In this small cohort, an endovascular treatment strategy that employed angioplasty was safe and effectively recanalized acutely occluded intracranial vessels. Angioplasty should be considered as a potential treatment option in interventional acute stroke trials.
    The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 07/2011; 38(4):593-9. · 1.33 Impact Factor

Publication Stats

126 Citations
146.25 Total Impact Points


  • 2009–2014
    • University of Ottawa
      • Department of Radiology
      Ottawa, Ontario, Canada
  • 2009–2012
    • The Ottawa Hospital
      • • Department of Medical Imaging
      • • Department of Radiology
      Ottawa, Ontario, Canada
  • 2002
    • Toronto Western Hospital
      Toronto, Ontario, Canada