Imperial College London

DrDeclanO'Regan

Faculty of MedicineInstitute of Clinical Sciences

Reader in Imaging Sciences
 
 
 
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Contact

 

+44 (0)20 3313 1510declan.oregan

 
 
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Location

 

Imaging Sciences DepartmentHammersmith HospitalHammersmith Campus

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Summary

 

Publications

Publication Type
Year
to

133 results found

Shi W, Lombaert H, Bai W, Ledig C, Zhuang X, Marvao A, Dawes T, O'Regan D, O'Regan Det al., 2014, Multi-atlas spectral PatchMatch: application to cardiac image segmentation., Pages: 348-355

The automatic segmentation of cardiac magnetic resonance images poses many challenges arising from the large variation between different anatomies, scanners and acquisition protocols. In this paper, we address these challenges with a global graph search method and a novel spectral embedding of the images. Firstly, we propose the use of an approximate graph search approach to initialize patch correspondences between the image to be segmented and a database of labelled atlases, Then, we propose an innovative spectral embedding using a multi-layered graph of the images in order to capture global shape properties. Finally, we estimate the patch correspondences based on a joint spectral representation of the image and atlases. We evaluated the proposed approach using 155 images from the recent MICCAI SATA segmentation challenge and demonstrated that the proposed algorithm significantly outperforms current state-of-the-art methods on both training and test sets.

Conference paper

Woodbridge M, Fagiolo G, O'Regan DP, 2013, MRIdb: Medical Image Management for Biobank Research, JOURNAL OF DIGITAL IMAGING, Vol: 26, Pages: 886-890, ISSN: 0897-1889

Journal article

Corden B, Keenan NG, Dawes TJW, De Marvao ASM, Durighel G, Diamond T, Cook SA, O'Regan DPet al., 2013, Lean mass, fat mass and eccentric left ventricular remodelling in obesity, Congress of the European-Society-of-Cardiology (ESC), Publisher: OXFORD UNIV PRESS, Pages: 145-146, ISSN: 0195-668X

Conference paper

Childs AS, Malik SJ, O'Regan DP, Hajnal JVet al., 2013, Impact of number of channels on RF shimming at 3T, Magnetic Resonance Materials in Physics, Biology and Medicine, Vol: 26, Pages: 401-410, ISSN: 0968-5243

ObjectAt high-field strengths (≥3T) inhomogeneity of the radio frequency (RF) field and RF power deposition become increasingly problematic. Parallel Transmission (PTx)—the use of segmented transmission arrays with independently driven elements—affords the ability to combat both of these issues. There are a variety of existing designs for PTx coils, ranging from systems with two channels to systems with eight or more. In this work, we have investigated the impact of the number of independent channels on the achievable results for both homogeneity improvement and power reduction in vivo.Materials and methodsA 3T Philips Achieva MRI system fitted with an 8-channel PTx body coil was driven so as to emulate configurations with 1, 2 4 and 8 independent channels. RF shimming was used in two different anatomies in order to assess improvements in RF homogeneity.ResultsSignificant homogeneity improvements were observed when increasing from 1 to 2, 2 to 4, and 4 to 8 channel configurations. Reductions in RF power requirements and local SAR were predicted for increasing numbers of channels.ConclusionIncreasing the number of RF transmit channels adds extra degrees of freedom which can be used to benefit homogeneity improvement or power reduction for body imaging at 3T.

Journal article

Corden B, Keenan NG, De Marvao ASM, Dawes TJW, Diamond T, Durighel G, Cook SA, O'Regan DPet al., 2013, Sex differences in the relationship between adiposity and left ventricular morphology, Congress of the European-Society-of-Cardiology (ESC), Publisher: OXFORD UNIV PRESS, Pages: 150-150, ISSN: 0195-668X

Conference paper

O'Regan DP, Harden SP, Cook SA, 2013, RATIONAL IMAGING Investigating stable chest pain of suspected cardiac origin, BMJ-BRITISH MEDICAL JOURNAL, Vol: 347, ISSN: 1756-1833

Journal article

Bai W, Shi W, O'Regan DP, Tong T, Wang H, Jamil-Copley S, Peters NS, Rueckert Det al., 2013, A probabilistic patch-based label fusion model for multi-atlas segmentation with registration refinement: application to cardiac MR images, IEEE Transactions on Medical Imaging, Vol: 32, Pages: 1302-1315, ISSN: 0278-0062

The evaluation of ventricular function is important for the diagnosis of cardiovascular diseases. It typically involves measurement of the left ventricular (LV) mass and LV cavity volume. Manual delineation of the myocardial contours is time-consuming and dependent on the subjective experience of the expert observer. In this paper, a multi-atlas method is proposed for cardiac magnetic resonance (MR) image segmentation. The proposed method is novel in two aspects. First, it formulates a patch-based label fusion model in a Bayesian framework. Second, it improves image registration accuracy by utilizing label information, which leads to improvement of segmentation accuracy. The proposed method was evaluated on a cardiac MR image set of 28 subjects. The average Dice overlap metric of our segmentation is 0.92 for the LV cavity, 0.89 for the right ventricular cavity and 0.82 for the myocardium. The results show that the proposed method is able to provide accurate information for clinical diagnosis.

Journal article

Corden B, Keenan NG, de Marvao ASM, Dawes TJW, DeCesare A, Diamond T, Durighel G, Hughes AD, Cook SA, O'Regan DPet al., 2013, Body Fat Is Associated With Reduced Aortic Stiffness Until Middle Age, HYPERTENSION, Vol: 61, Pages: 1322-1327, ISSN: 0194-911X

Journal article

Shi W, Jantsch M, Aljabar P, Pizarro L, Bai W, Wang H, O'Regan D, Zhuang X, Rueckert Det al., 2013, Temporal sparse free-form deformations, Medical Image Analysis

Journal article

O'Regan DP, Ariff B, Baksi AJ, Gordon F, Durighel G, Cook SAet al., 2013, Salvage assessment with cardiac MRI following acute myocardial infarction underestimates potential for recovery of systolic strain, EUROPEAN RADIOLOGY, Vol: 23, Pages: 1210-1217, ISSN: 0938-7994

Journal article

Grapsa J, Cabrita IZ, Durighel G, Dawson D, O'regan D, Gin-Sing W, Howard LS, Gibbs S, Nihoyannopoulos Pet al., 2013, Right heart failure and clinical deterioration: the study of idiopathic pulmonary arterial hypertensive patients, EUROPEAN JOURNAL OF HEART FAILURE, Vol: 12, Pages: S280-S280, ISSN: 1388-9842

Journal article

Kousera CA, Wood NB, Seed WA, Torii R, O'Regan D, Xu XYet al., 2013, A Numerical Study of Aortic Flow Stability and Comparison With In Vivo Flow Measurements, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 135, ISSN: 0148-0731

Journal article

Shi W, Caballero J, Ledig C, Zhuang X, Bai W, Bhatia K, de Marvao AMSM, Dawes T, O'Regan D, Rueckert Det al., 2013, Cardiac Image Super-Resolution with Global Correspondence Using Multi-Atlas PatchMatch, 16th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI), Publisher: SPRINGER-VERLAG BERLIN, Pages: 9-16, ISSN: 0302-9743

Conference paper

de Marvao A, Dawes T, Keenan NG, Bai W, Shi W, Durighel G, Diamond T, Monje-Garcia L, Cook SA, O'Regan DPet al., 2013, The UK GenScan study - population-based imaging genetics research using 3D Cardiac Magnetic Resonance, Journal of Cardiovascular Magnetic Resonance, Vol: 15

Journal article

Durighel G, Dawes T, Ashwin C, Cook SA, O'Regan DPet al., 2013, Paradoxical effect of smoking following acute myocardial infarction, Journal of Cardiovascular Magnetic Resonance, Vol: 15

Journal article

Pszczolkowski S, Pizarro L, O'Regan DP, Rueckert Det al., 2012, Gradient projection learning for parametric nonrigid registration, Pages: 226-233, ISSN: 0302-9743

A potentially large anatomical variability among subjects in a population makes nonrigid image registration techniques prone to inaccuracies and to high computational costs in their optimisation. In this paper, we propose a new learning-based approach to accelerate the convergence rate of any chosen parametric energy-based image registration method. From a set of training images and their corresponding deformations, our method learns offline a projection from the gradient space of the energy functional to the parameter space of the chosen registration method using partial least squares. Combined with a regularisation term, the learnt projection is subsequently used online to approximate the optimisation of the energy functional for unseen images. We employ the B-spline approach as underlying registration method, but other parametric methods can be used as well. We perform experiments on synthetic image data and MR cardiac sequences to show that our approach significantly accelerates the convergence -in number of iterations and total computational cost- of the chosen registration method, while achieving similar results in terms of accuracy. © 2012 Springer-Verlag.

Conference paper

O'Regan DP, Shi W, Ariff B, Baksi AJ, Durighel G, Rueckert D, Cook SAet al., 2012, Remodeling after acute myocardial infarction: mapping ventricular dilatation using three dimensional CMR image registration, Journal of Cardiovascular Magnetic Resonance, Vol: 14, ISSN: 1532-429X

Background: Progressive heart failure due to remodeling is a major cause of morbidity and mortality followingmyocardial infarction. Conventional clinical imaging measures global volume changes, and currently there is nomeans of assessing regional myocardial dilatation in relation to ischemic burden. Here we use 3D co-registration ofCardiovascular Magnetic Resonance (CMR) images to assess the long-term effects of ischemia-reperfusion injury onleft ventricular structure after acute ST-elevation myocardial infarction (STEMI).Methods: Forty six patients (age range 33–77 years) underwent CMR imaging within 7 days following primarypercutaneous coronary intervention (PPCI) for acute STEMI with follow-up at one year. Functional cine imaging andLate Gadolinium Enhancement (LGE) were segmented and co-registered. Local left ventricular wall dilatation wasassessed by using intensity-based similarities to track the structural changes in the heart between baseline andfollow-up. Results are expressed as means, standard errors and 95% confidence interval (CI) of the difference.Results: Local left ventricular remodeling within infarcted myocardium was greater than in non-infarctedmyocardium (1.6% ± 1.0 vs 0.3% ± 0.9, 95% CI: -2.4% – -0.2%, P = 0.02). One-way ANOVA revealed that transmuralinfarct thickness had a significant effect on the degree of local remodeling at one year (P < 0.0001) with greatestwall dilatation observed when infarct transmurality exceeded 50%. Infarct remodeling was more severe whenmicrovascular obstruction (MVO) was present (3.8% ± 1.3 vs −1.6% ± 1.4, 95% CI: -9.1% – -1.5%, P = 0.007) and whenend-diastolic volume had increased by >20% (4.8% ± 1.4 vs −0.15% ± 1.2, 95% CI: -8.9% – -0.9%, P = 0.017).Conclusions: The severity of ischemic injury has a significant effect on local ventricular wall remodeling with onlymodest dilatation observed within non-ischemic myocardium. Limitatio

Journal article

O'Regan DP, Cook SA, 2011, Myocarditis or myocardial infarction? MRI can help, HEART, Vol: 97, Pages: 1283-1283, ISSN: 1355-6037

Journal article

Kourliouros A, Soni M, Rasoli S, Grapsa J, Nihoyannopoulos P, O'Regan D, Athanasiou Tet al., 2011, Evolution and Current Applications of the Cabrol Procedure and Its Modifications, ANNALS OF THORACIC SURGERY, Vol: 91, Pages: 1636-1641, ISSN: 0003-4975

Journal article

O'Regan DP, Ariff B, Neuwirth C, Tan Y, Durighel G, Cook SAet al., 2011, The ischemic area-at-risk on T2-weighted MRI shows recovery of systolic strain at 1 year, Journal of Cardiovascular Magnetic Resonance, Vol: 13, Pages: P90-P90, ISSN: 1532-429X

Journal article

O'Regan DP, Ariff B, Neuwirth C, Tan Y, Durighel G, Cook SAet al., 2010, Assessment of severe reperfusion injury with T2*cardiac MRI in patients with acute myocardial infarction, HEART, Vol: 96, Pages: 1885-1891, ISSN: 1355-6037

Journal article

Malamateniou C, McGuinness AK, Allsop JM, O'Regan DP, Rutherford MA, Hajnal JVet al., 2010, Snapshot Inversion Recovery: An Optimized Single-Shot T1-weighted Inversion-Recovery Sequence for Improved Fetal Brain Anatomic Delineation., Radiology

Purpose: To prospectively evaluate the clinical effectiveness of snapshot inversion recovery (SNAPIR), which is a dedicated optimized inversion-recovery-prepared single-shot fast spin-echo T1-weighted sequence, in the delineation of normal fetal brain anatomy compared with that of the currently used T1-weighted gradient-echo protocol, which often yields images of poor quality due to motion artifacts and inadequate contrast. Materials and Methods: This study was approved by the hospital research ethics committee, and informed written consent was obtained from all patients. Forty-one fetuses were examined at 19-37 weeks gestation (mean, 29 weeks gestation) by using both the standard T1-weighted protocol and the optimized T1-weighted SNAPIR protocol with a 1.5-T imager. Two independent blinded observers performed qualitative analysis, evaluating overall diagnostic quality, detailed anatomic delineation, and severity of motion artifacts. Quantitative analysis comprised calculation of contrast ratios (CRs) for the cortical gray matter, subplate, white matter, and cerebrospinal fluid. The Wilcoxon signed rank test was used to compare image rating scores, the paired t test was used to compare CRs, and κ statistics were used to test interobserver agreement. Results: Both overall diagnostic quality (P < .001) and detailed anatomic delineation (P < .001) were enhanced with SNAPIR compared with the standard T1-weighted acquisition. Also, motion artifacts were less severe (P = .008) and less extensive (P < .001) with SNAPIR. Corresponding CRs were increased with SNAPIR in seven of eight examined regions. Conclusion: SNAPIR is a promising robust alternative to the current T1-weighted acquisitions; its role in the detection of disease requires further study

Journal article

Malik SJ, Larkman DJ, O'Regan DP, Hajnal JVet al., 2010, Subject-Specific Water-Selective Imaging Using Parallel Transmission, MAGNETIC RESONANCE IN MEDICINE, Vol: 63, Pages: 988-997, ISSN: 0740-3194

Journal article

Grapsa J, O'Regan DP, Pavlopoulos H, Durighel G, Dawson D, Nihoyannopoulos Pet al., 2010, Right ventricular remodelling in pulmonary arterial hypertension with three-dimensional echocardiography: comparison with cardiac magnetic resonance imaging, EUROPEAN JOURNAL OF ECHOCARDIOGRAPHY, Vol: 11, Pages: 64-73, ISSN: 1525-2167

Journal article

O'Regan DP, Ahmed R, Neuwirth C, Tan Y, Durighel G, Hajnal JV, Nadra I, Corbett SJ, Cook SAet al., 2009, Cardiac MRI of myocardial salvage at the peri-infarct border zones after primary coronary intervention, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 297, Pages: H340-H346, ISSN: 0363-6135

Journal article

Harvey C, O'Regan D, Allen SJ, 2009, Accident and Emergency Radiology, Publisher: Gardners Books, ISBN: 9781856423151

This book is aimed at accident and emergency doctors, surgical, medical and radiology specialist registrars and medical students. This highly illustrated text facilitates instant consultation when faced with an X-ray.

Book

O'Regan DP, Ahmed R, Karunanithy N, Neuwirth C, Tan Y, Durighel G, Hajnal JV, Nadra I, Corbett SJ, Cook SAet al., 2009, Reperfusion Hemorrhage Following Acute Myocardial Infarction: Assessment with T2*Mapping and Effect on Measuring the Area at Risk, RADIOLOGY, Vol: 250, Pages: 916-922, ISSN: 0033-8419

Journal article

Schmitz SA, O'Regan DP, Fitzpatrick J, Neuwirth C, Potter E, Tosi I, Hajnal JV, Naoumova RPet al., 2008, Quantitative 3T MR imaging of the descending thoracic aorta: Patients with familial hypercholesterolemia have an increased aortic plaque burden despite long-term lipid-lowering therapy, JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY, Vol: 19, Pages: 1403-1408, ISSN: 1051-0443

Journal article

O'Reagan DP, Callaghan MF, Wylezinska-Arridge M, Fitzpatrick J, Naoumova RP, Hajnal JV, Schmitz SAet al., 2008, Liver Fat Content and T2*: Simultaneous Measurement by Using Breath-hold Multiecho MR Imaging at 3.0 T--Feasibility, Radiology

Journal article

O'Regan DP, Callaghan MF, Fitzpatrick J, Naoumova RP, Hajnal JV, Schmitz SAet al., 2008, Cardiac T2* and lipid measurement at 3.0 T-initial experience, EUROPEAN RADIOLOGY, Vol: 18, Pages: 800-805, ISSN: 0938-7994

Journal article

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