Publications
52 results found
Chahal NS, Senior R, 2021, Severe Patient-Prosthesis Mismatch Compelling Entity or an Epiphenomenon of Low Flow?, CIRCULATION-CARDIOVASCULAR IMAGING, Vol: 14, ISSN: 1941-9651
Chahal N, Senior R, 2020, Assessing systolic function in aortic stenosis: the earlier the better?, HEART, Vol: 106, Pages: 1200-1201, ISSN: 1355-6037
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- Citations: 1
Vamvakidou A, Jin W, Danylenko O, et al., 2019, Low transvalvular flow rate predicts mortality in patients with low-gradient aortic stenosis following aortic valve intervention, JACC: Cardiovascular Imaging, Vol: 12, Pages: 1715-1724, ISSN: 1936-878X
OBJECTIVES: This study aimed to assess the value of low transvalvular flow rate (FR) for the prediction of mortality compared with low stroke volume index (SVi) in patients with low-gradient (mean gradient: <40 mm Hg), low aortic valve area (<1 cm2) aortic stenosis (AS) following aortic valve intervention. BACKGROUND: Transaortic FR defined as stroke volume/left ventricular ejection time is also a marker of flow; however, no data exist comparing the relative prognostic value of these 2 transvalvular flow markers in patients with low-gradient AS who had undergone valve intervention. METHODS: We retrospectively followed prospectively assessed consecutive patients with low-gradient, low aortic valve area AS who underwent aortic valve intervention between 2010 and 2014 for all-cause mortality. RESULTS: Of the 218 patients with mean age 75 ± 12 years, 102 (46.8%) had low stroke volume index (SVi) (<35 ml/m2), 95 (43.6%) had low FR (<200 ml/s), and 58 (26.6%) had low left ventricular ejection fraction <50%. The concordance between FR and SVi was 78.8% (p < 0.005). Over a median follow-up of 46.8 ± 21 months, 52 (23.9%) deaths occurred. Patients with low FR had significantly worse outcome compared with those with normal FR (p < 0.005). In patients with low SVi, a low FR conferred a worse outcome than a normal FR (p = 0.005), but FR status did not discriminate outcome in patients with normal SVi. By contrast, SVi did not discriminate survival either in patients with normal or low FR. Low FR was an independent predictor of mortality (p = 0.013) after adjusting for age, clinical prognostic factors, European System for Cardiac Operative Risk Evaluation II, dimensionless velocity index, left ventricular mass index, left ventricular ejection fraction, heart rate, time, type of aortic valve intervention, and SVi (p = 0.59). CONCLUSIONS: In patients with low-gradient, low valve area aortic stenosis undergoi
Toulemonde MEG, Corbett R, Papadopoulou V, et al., 2018, High frame rate contrast echocardiography –in human demonstration, JACC: Cardiovascular Imaging, Vol: 11, Pages: 923-924, ISSN: 1936-878X
Li Y, Ho CP, Toulemonde M, et al., 2018, Fully automatic myocardial segmentation of contrast echocardiography sequence using random forests guided by shape model, IEEE Transactions on Medical Imaging, Vol: 37, Pages: 1081-1091, ISSN: 0278-0062
Myocardial contrast echocardiography (MCE) is animaging technique that assesses left ventricle function and myocardialperfusion for the detection of coronary artery diseases.Automatic MCE perfusion quantification is challenging and requiresaccurate segmentation of the myocardium from noisy andtime-varying images. Random forests (RF) have been successfullyapplied to many medical image segmentation tasks. However, thepixel-wise RF classifier ignores contextual relationships betweenlabel outputs of individual pixels. RF which only utilizes localappearance features is also susceptible to data suffering fromlarge intensity variations. In this paper, we demonstrate howto overcome the above limitations of classic RF by presentinga fully automatic segmentation pipeline for myocardial segmentationin full-cycle 2D MCE data. Specifically, a statisticalshape model is used to provide shape prior information thatguide the RF segmentation in two ways. First, a novel shapemodel (SM) feature is incorporated into the RF frameworkto generate a more accurate RF probability map. Second, theshape model is fitted to the RF probability map to refineand constrain the final segmentation to plausible myocardialshapes. We further improve the performance by introducinga bounding box detection algorithm as a preprocessing stepin the segmentation pipeline. Our approach on 2D image isfurther extended to 2D+t sequences which ensures temporalconsistency in the final sequence segmentations. When evaluatedon clinical MCE datasets, our proposed method achieves notableimprovement in segmentation accuracy and outperforms otherstate-of-the-art methods including the classic RF and its variants,active shape model and image registration.
Vamvakidou A, Jin W, Danylenko O, et al., 2018, FLOW RATE NOT STROKE VOLUME IS A SUPERIOR PROGNOSTIC MARKER OF TRANSORTIC FLOW AND FLOW RESERVE IN PATIENTS WITH LOW-FLOW LOW-GRADIENT AORTIC STENOSIS UNDERGOING LOW-DOSE DOBUTAMINE ECHOCARDIOGRAPHY, 67th Annual Scientific Session and Expo of the American-College-of-Cardiology (ACC), Publisher: ELSEVIER SCIENCE INC, Pages: 1458-1458, ISSN: 0735-1097
Saeed S, Senior R, Chahal NS, et al., 2017, Lower Transaortic Flow Rate Is Associated With Increased Mortality in Aortic Valve Stenosis, JACC-CARDIOVASCULAR IMAGING, Vol: 10, Pages: 912-920, ISSN: 1936-878X
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- Citations: 37
Li Y, Chahal N, Senior R, et al., 2017, Reproducible computer assisted quantification of myocardial perfusion with contrast enhanced ultrasound, Ultrasound in Medicine & Biology, Vol: 43, Pages: 2235-2246, ISSN: 1879-291X
Myocardial perfusion can be quantified by myocardial contrast echocardiography (MCE) and is used for the diagnosis of coronary artery disease (CAD). However, existing MCE quantification software is highly operator dependent and has poor reproducibility and ease of usage. The aim of this study was to develop robust and easy-to-use software that can perform MCE quantification accurately, reproducibly and rapidly. The developed software has the following features: (i) semi-automatic segmentation of the myocardium; (ii) automatic rejection of MCE data with poor image quality; (iii) automatic computation of perfusion parameters such as myocardial blood flow (MBF). MCE sequences of 18 individuals (9 normal, 9 with CAD) undergoing vasodilator stress with dipyridamole were analysed quantitatively using the software. When evaluated against coronary angiography, the software achieved a sensitivity of 71% and a specificity of 91% for hyperemic MBF. With the automatic rejection algorithm, the sensitivity and specificity further improved to 77% and 94%, respectively. For MBF reproducibility, the percentage agreement is 85% (κ = 0.65) for inter-observer variability and 88% (κ = 0.72) for intra-observer variability. The intra-class correlation coefficients are 0.94 (inter-observer) and 0.96 (intra-observer). The time taken to analyse one MCE sequence using the software is about 3 min on a PC. The software has exhibited good diagnostic performance and reproducibility for CAD detection and is rapid and user-friendly.
Vamvakidou A, Chahal N, Hampson R, et al., 2017, STROKE VOLUME DETERMINED FLOW RESERVE DOES NOT PREDICT THE TRUE SEVERITY OF LOW-FLOW LOW-GRADIENT AORTIC STENOSIS AND IS NOT A ROBUST MARKER OF CONTRACTILE RESERVE IN PATIENTS UNDERGOING LOW-DOSE DOBUTAMINE ECHOCARDIOGRAPHY, JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY, Vol: 69, Pages: 1419-1419, ISSN: 0735-1097
Shah BN, Chahal NS, Kooner JS, et al., 2017, Contrast-enhanced ultrasonography vs B-mode ultrasound for visualization of intima-media thickness and detection of plaques in human carotid arteries, ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES, Vol: 34, Pages: 723-730, ISSN: 0742-2822
Cheung WK, Shah BN, Stanziola A, et al., 2017, DIFFERENTIAL INTENSITY PROJECTION FOR VISUALISATION AND QUANTIFICATION OF PLAQUE NEOVASCULARISATION IN CONTRAST-ENHANCED ULTRASOUND IMAGES OF CAROTID ARTERIES, ULTRASOUND IN MEDICINE AND BIOLOGY, Vol: 43, Pages: 831-837, ISSN: 0301-5629
Izgi C, Alpendurada F, Chahal N, 2016, Pericardial inflammation with reversible constriction: prediction of recovery with cardiovascular magnetic resonance., Int J Cardiovasc Imaging, Vol: 32, Pages: 1425-1426
Gujral DM, Cheung WK, Shah BN, et al., 2016, Contrast enhancement of carotid adventitial vasa vasorum as a biomarker of radiation-induced atherosclerosis., Radiotherapy and Oncology, ISSN: 0167-8140
PURPOSE: Abnormal proliferation of adventitial vasa vasorum (vv) occurs early at sites of atherosclerosis and is thought to be an early biomarker of vascular damage. Contrast-enhanced ultrasound (CEUS) can detect this process. Its usefulness in irradiated arteries as a measure of accelerated atherosclerosis is unknown. This study investigates contrast intensity in carotid adventitia as an early marker of radiation-induced damage in head and neck cancer (HNC) patients. MATERIALS/METHODS: Patients with HNC treated with a wedged-pair and matched neck technique or hemi-neck radiotherapy (RT) (unirradiated side as control) at least 2years previously were included. Patients had been prescribed a dose of at least 50Gy to the neck. CEUS was performed on both carotid arteries and a region of interest was selected in the adventitia of the far wall of both left and right distal common carotid arteries. Novel quantification software was used to compare the average intensity per pixel between irradiated and unirradiated arteries. RESULTS: 48 patients (34 males) with median age of 59.2years (interquartile range (IQR) 49.2-64.2) were included. The mean maximum point dose to the irradiated artery was 61.2Gy (IQR 52.6-61.8) and 1.1Gy (IQR 1.0-1.8Gy) to the unirradiated side. The median interval from RT was 59.4months (IQR 41-88.7). There was a significant difference in the mean (SD) contrast intensity per pixel on the irradiated side (1.1 (0.4)) versus 0.96 (0.34) on the unirradiated side (p=0.01). After attenuation correction, the difference in mean contrast intensity per pixel was still significant (1.4 (0.58) versus 1.2 (0.47) (p=0.02). Previous surgery or chemotherapy had no effect on the difference in contrast intensity between the 2 sides of the neck. Mean intensity per pixel did not correlate to traditional risk prediction models (carotid intima-medial thickness, QSTROKE score). CONCLUSIONS: Proliferation of vv is demonstrated by increased contrast intensity in irradiated car
Shah BN, Gujral DM, Chahal NS, et al., 2016, Plaque Neovascularization Is Increased in Human Carotid Atherosclerosis Related to Prior Neck Radiotherapy A Contrast-Enhanced Ultrasound Study, JACC-Cardiovascular Imaging, Vol: 9, Pages: 668-675, ISSN: 1936-878X
ObjectivesThe aim of this study was to determine the effect of radiotherapy (RT) on intraplaque neovascularization (IPN) in human carotid arteries.BackgroundExposure of the carotid arteries to RT during treatment for head and neck cancer is associated with increased risk for stroke. However, the effect of RT on IPN, a precursor to intraplaque hemorrhage and thus associated with plaque vulnerability, is unknown.MethodsIn this cross-sectional study, patients who had undergone unilateral RT for head and neck cancer ≥2 years previously underwent B-mode and contrast-enhanced ultrasound of both RT-side and non–RT-side carotid arteries. Presence of IPN during contrast-enhanced ultrasound was judged semiquantitatively as grade 0 (absent), grade 1 (present but limited to plaque base), or grade 2 (extensive and noted within plaque body).ResultsOf 49 patients studied, 38 (78%) had plaques. The number of plaques was significantly greater in the RT than the non-RT arteries. Overall, 48 of 64 RT-side plaques (75%) had IPN compared with 9 of 23 non-RT-side (39%) plaques (p = 0.002). Among patients with plaques, IPN was present in 81% of patients with RT-side plaques and 41% of patients with non-RT-side plaques (p = 0.004). Grade 0 IPN was significantly more common in patients with non-RT-side plaques (25% vs. 61%; p = 0.002), whereas grade 2 plaques were more common on the RT side (31% vs. 9%; p = 0.03). The only clinical variable that predicted the presence or absence of IPN was RT laterality.ConclusionsThis is the first study in humans to reveal a significant association between RT and the presence and extent of IPN. This may provide insights into the mechanisms underlying the increased stroke risk among survivors of head and neck cancer treated by RT.
Senior R, 2016, Lack of Stroke Volume Determined Flow Reserve Does Not Always Preclude Assessment of Severity of Aortic Stenosis in Low-Flow Low-Gradient State During Dobutamine Echocardiography. Vamvakidou A, Chahal N, Senior R. JACC Cardiovasc Imaging. 2016 Jun 10. pii: S1936-878X(16)30242-X. doi: 10.1016/j.jcmg.2016.04.001. [Epub ahead of print] No abstract available., JACC Cardiovasc Imaging
Gujral DM, Shah BN, Chahal NS, et al., 2016, Arterial Stiffness as a Biomarker of Radiation-Induced Carotid Atherosclerosis, ANGIOLOGY, Vol: 67, Pages: 266-271, ISSN: 0003-3197
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- Citations: 18
Gujral DM, Shah BN, Chahal NS, et al., 2016, Carotid intima-medial thickness as a marker of radiation-induced carotid atherosclerosis, RADIOTHERAPY AND ONCOLOGY, Vol: 118, Pages: 323-329, ISSN: 0167-8140
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- Citations: 15
Li Y, Ho CP, Chahal N, et al., 2016, Myocardial segmentation of contrast echocardiograms using random forests guided by shape model, Pages: 158-165, ISSN: 0302-9743
Myocardial Contrast Echocardiography (MCE) with microbubble contrast agent enables myocardial perfusion quantification which is invaluable for the early detection of coronary artery diseases. In this paper,we proposed a new segmentation method called Shape Model guided Random Forests (SMRF) for the analysis of MCE data. The proposed method utilizes a statistical shape model of the myocardium to guide the Random Forest (RF) segmentation in two ways. First,we introduce a novel Shape Model (SM) feature which captures the global structure and shape of the myocardium to produce a more accurate RF probability map. Second,the shape model is fitted to the RF probability map to further refine and constrain the final segmentation to plausible myocardial shapes. Evaluated on clinical MCE images from 15 patients,our method obtained promising results (Dice = 0.81,Jaccard = 0.70,MAD = 1.68 mm,HD = 6.53mm) and showed a notable improvement in segmentation accuracy over the classic RF and its variants.
Shah BN, Gonzalez-Gonzalez AM, Drakopoulou M, et al., 2015, The Incremental Prognostic Value of the Incorporation of Myocardial Perfusion Assessment into Clinical Testing with Stress Echocardiography Study, JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY, Vol: 28, Pages: 1358-1365, ISSN: 0894-7317
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- Citations: 15
Sehmi JS, Dungu J, Davies SW, et al., 2015, Unsuspected large left ventricular pseudoaneurysm: rapid bedside diagnosis by contrast-enhanced echocardiography., Oxford Medical Case Reports, Vol: 2015, Pages: 358-359, ISSN: 2053-8855
An asymptomatic 72-year-old man with cardiomegaly was referred to our centre for assessment. His medical history comprised metastatic colonic cancer and granulomatosis with polyangiitis.Transthoracic echocardiography was performed. In the apical four-chamber view, a large cavity was identified adjacent to the apex, measuring 45 × 54 mm (Fig. 1A and Supplementary Video 1). All apical segments of the left ventricle were thin and akinetic. On colour Doppler, bidirectional blood flow due to swirling of blood was observed within the cavity (Fig. 1B and Supplementary Video 2). Contrast-enhanced echocardiography established the …
Sehmi JS, West C, Khattar R, et al., 2015, Mass Confusion Defining Aortic Pathology With Ultrasound Contrast, CIRCULATION, Vol: 132, Pages: 1433-1434, ISSN: 0009-7322
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- Citations: 2
Chahal NS, Drakopoulou M, Gonzalez-Gonzalez AM, et al., 2015, Resting Aortic Valve Area at Normal Transaortic Flow Rate Reflects True Valve Area in Suspected Low-Gradient Severe Aortic Stenosis, JACC-CARDIOVASCULAR IMAGING, Vol: 8, Pages: 1133-1139, ISSN: 1936-878X
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- Citations: 51
Gujral DM, Shah BN, Chahal NS, et al., 2015, Do traditional risk stratification models for cerebrovascular events apply in irradiated head and neck cancer patients?, QJM, Vol: 109, Pages: 383-389, ISSN: 1460-2725
BACKGROUND: Primary radical radiotherapy (RT) for head and neck cancer (HNC) often results in significant radiation dose to the carotid arteries. AIM: We assessed whether HNC patients are at increased risk of a cerebrovascular event primarily due to RT or other risk factors for atherosclerosis by (i) risk-stratifying patients according to validated QRISK-2 and QSTROKE scores and (ii) comparing the prevalence of carotid artery stenosis (CAS) in irradiated and unirradiated carotid arteries. DESIGN: HNC patients treated with an RT dose >50 Gy to one side of the neck ≥2 years previously were included. METHODS: QRISK-2 (2014) and Q-STROKE (2014) scores were calculated. We compared the prevalence of CAS in segments of the common carotid artery on the irradiated and unirradiated sides of the neck. RESULTS: Fifty patients (median age of 58 years (interquartile range (IQR) 50-62)) were included. The median QRISK-2 score was 10% (IQR 4.4-15%) and the median QSTROKE score was 3.4% (IQR 1.4-5.3%). For both scores, no patient was classified as high risk. Thirty-eight patients (76%) had CAS in one or both arteries. There was a significant difference in the number of irradiated arteries with stenosis (N = 37) compared with unirradiated arteries (N = 16) (P < 0.0001). There were more plaques on the irradiated artery compared with the unirradiated side - 64/87 (73.6%) versus 23/87 (26.4%), respectively (P < 0.001). CONCLUSIONS: Traditional vascular risk factors do not play a role in radiation-induced carotid atherosclerosis. Clinicians should be aware that traditional risk prediction models may under-estimate stroke risk in these patients.
Echocardiographic Normal Ranges Meta-Analysis of the Left Heart Collaboration, 2015, Ethnic-Specific Normative Reference Values for Echocardiographic LA and LV Size, LV Mass, and Systolic Function: The EchoNoRMAL Study., JACC Cardiovasc Imaging, Vol: 8, Pages: 656-665
OBJECTIVES: This study sought to derive age-, sex-, and ethnic-appropriate adult reference values for left atrial (LA) and left ventricular (LV) dimensions and volumes, LV mass, fractional shortening, and ejection fraction (EF) derived from geographically diverse population studies. BACKGROUND: The current recommended reference values for measurements from echocardiography may not be suitable to the diverse world population to which they are now applied. METHODS: Population-based datasets of echocardiographic measurements from 22,404 adults without clinical cardiovascular or renal disease, hypertension, or diabetes were combined in an individual person data meta-analysis. Quantile regression was used to derive reference values at the 95th percentile (upper reference value [URV]) and fifth percentile (lower reference value [LRV]) of each measurement against age (treated as linear), separately within sex and ethnic groups. RESULTS: The URVs for left ventricular end-diastolic volume (LVEDV), LV end-systolic volume, and LV stroke volume (SV) were highest in Europeans and lowest in South Asians. Important sex and ethnic differences remained after indexation by body surface area or height for these measurements, as well as for the LRV for SV. LVEDV and SV decreased with increasing age for all groups. Importantly, the LRV for EF differed by ethnicity; there was a clear apparent difference between Europeans and Asians. The URVs for LV end-diastolic diameter and LV end-systolic diameter were higher for Europeans than those for East Asian, South Asian, and African people, particularly among men. Similarly, the URVs for LA diameter and volume were highest for Europeans. CONCLUSIONS: Sex- and/or ethnic-appropriate echocardiographic reference values are indicated for many measurements of LA and LV size, LV mass, and EF. Reference values for LV volumes and mass also differ across the age range.
Bhattacharyya S, Khattar R, Chahal N, et al., 2015, Dynamic Mitral Regurgitation Review of Evidence Base, Assessment and Implications for Clinical Management, CARDIOLOGY IN REVIEW, Vol: 23, Pages: 142-147, ISSN: 1061-5377
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- Citations: 6
Shah BN, Gujral DM, Chahal NS, et al., 2014, Plaque neovascularization is increased in human carotid atherosclerosis related to prior neck radiotherapy: a contrast enhanced ultrasound study, Annual Meeting of the European-Society-of-Cardiology (ESC), Publisher: OXFORD UNIV PRESS, Pages: 634-634, ISSN: 0195-668X
Gonzalez-Gonzalez AM, Drakopoulou M, Bhattacharyya S, et al., 2014, THE INCREMENTAL PROGNOSTIC VALUE OF MYOCARDIAL CONTRAST ECHOCARDIOGRAPHY IN CLINICAL PRACTICE: FOLLOW-UP RESULTS FROM THE IMPACT OF MYOCARDIAL PERFUSION ASSESSMENT IN CLINICAL TESTS OF STRESS ECHOCARDIOGRAPHY (IMPACT-SE) STUDY, HEART, Vol: 100, Pages: A84-A84, ISSN: 1355-6037
Senior R, Gujral DM, Chahal NS, et al., 2014, CAROTID INTRAPLAQUE NEOVASCULARIZATION IS INCREASED IN PATIENTS WITH PRIOR IPSILATERAL NECK IRRADIATION - A CONTRAST ENHANCED ULTRASOUND STUDY, HEART, Vol: 100, Pages: A84-A84, ISSN: 1355-6037
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Shah BN, Chahal NS, Bhattacharyya S, et al., 2014, The Feasibility and Clinical Utility of Myocardial Contrast Echocardiography in Clinical Practice: Results from the Incorporation of Myocardial Perfusion Assessment into Clinical Testing with Stress Echocardiography Study, JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY, Vol: 27, Pages: 520-530, ISSN: 0894-7317
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Cheung W, Gujral DM, Shah BNA, et al., 2014, Attenuation correction and normalisation for quantification of contrast enhancement in ultrasound Images of carotid arteries, Ultrasound in Medicine and Biology, Vol: 41, Pages: 1876-1883, ISSN: 0301-5629
An automated attenuation correction and normalisation algorithm was developed to improve the quantification of contrast enhancement in ultrasound images of carotid arteries. The algorithm first corrects attenuation artefact and normalises intensity within the contrast agent-filled lumen and then extends the correction and normalisation to regions beyond the lumen. The algorithm was first validated on phantoms consisting of contrast agent-filled vessels embedded in tissue-mimicking materials of known attenuation. It was subsequently applied to invivo contrast-enhanced ultrasound (CEUS) images of human carotid arteries. Both invitro and invivo results indicated significant reduction in the shadowing artefact and improved homogeneity within the carotid lumens after the correction. The error in quantification of microbubble contrast enhancement caused by attenuation on phantoms was reduced from 55% to 5% on average. In conclusion, the proposed method exhibited great potential in reducing attenuation artefact and improving quantification in contrast-enhanced ultrasound of carotid arteries.
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