Mohan Sivananthan | University of Leeds (original) (raw)

Papers by Mohan Sivananthan

The Veterinary Journal, 2010

Over the last decade, magnetic resonance imaging (MRI) has become established as a useful referra... more Over the last decade, magnetic resonance imaging (MRI) has become established as a useful referral diagnostic method in veterinary medicine that is widely used in small animal brain and spinal diseases, aural, nasal and orbital disorders, planning soft tissue surgery, oncology and small animal and equine orthopaedics. The use of MRI in these disciplines has grown due to its unparalleled capability to image soft tissue structures. This has been exploited in human cardiology where, despite the inherent difficulties in imaging a moving, contractile structure, cardiac MRI (CMRI) has become the optimal technique for the morphological assessment and quantification of ventricular function.

Journal of Magnetic Resonance Imaging

Steady-state free precession imaging is a promising technique for cardiac magnetic resonance imag... more Steady-state free precession imaging is a promising technique for cardiac magnetic resonance imaging (MRI), as it provides improved blood/myocardial contrast in shorter acquisition times compared with conventional gradient-echo acquisition. The better contrast could improve observer agreement and automatic detection of cardiac contours for volumetric assessment of the ventricles, but measurements might differ from those obtained using conventional methods. We compared volumetric measurements, observer variabilities, and automatic contour detection between a steady-state free precession imaging sequence (BFFE = balanced fast field echo) and segmented k-space gradient-echo acquisition (TFE = turbo field echo) in 41 subjects. With BFFE, significantly higher end-diastolic and end-systolic volumes and lower wall thickness, ventricular mass, ejection fraction, and wall motion were observed (P < 0.0001), while interobserver variabilities were lower and automatic contour detection of endocardial contours was more successful. We conclude that the improved image quality of BFFE reduces the observer-dependence of volumetric measurements of the left ventricle (LV) but results in significantly different values in comparison to TFE measurements.

LEARNING OBJECTIVES 1. Demonstrate how to use a combination of MR techniques and Cardiac landmark... more LEARNING OBJECTIVES 1. Demonstrate how to use a combination of MR techniques and Cardiac landmarks in order to consistently achieve the desired imaging plane.2. Iluustrate the errors that can be made when attempting to acquire: functional 4 Chamber, LV Short Axis Volume and Flow Quantification of the Aorta, Pulmonary Artery, Mitral & Tricuspid Valves. ABSTRACT The axis of the left ventricle changes dependent upon the patients stature and clinical condition. Therefore unless the method of selecting an imaging plane can adapt for these changes inconsistent planes will be imaged; a problem compounded when the images are acquired by a team of technologists. The authors describe a methodology which can successfully achieve standardisiation of the selection of imaging planes for functional and flow quantitaton data sets.This methodology uses a combination of visualising the movement of the cardiac structures throughout the cardiac cycle, in order to plan the desired imaging plane at the t...

LEARNING OBJECTIVES 1. Identify and Modify the optimal Inversion Time (TI) for optimal DE Viabili... more LEARNING OBJECTIVES 1. Identify and Modify the optimal Inversion Time (TI) for optimal DE Viability imaging.2. Illustrate the optimised appearances of DE Viability Images in Post MI patients. 3. Illustrate the appearances of DE Viability Images in: Myocarditis, Amyloid, ARVC & HOCM.4. Demonstrate the Imaging Pitfalls and how to avoid them. ABSTRACT CMR is rivalling PET as the gold standard for the assessment of myocardial viability.DE Viability has begun to be receive widesparead accpetance as a means of evaluating regions of non-viable myocardium. This poster will demonstrate the appaerance of DE Viability in post MI patients and in the more complex conditions of Myocarditis, Amyloid, ARVC & HOCM.As DE Viability is a dynamic examination of the wash out of contrast from normal myocardium, as well as fibrous regions, the pulse sequence requires optimising in order to:1. achieve myocardial suppression through the selection of an Inversion Time that will null normally perfused myocardi...

LEARNING OBJECTIVES The presentation will discuss 1)various scanning protocols for left and right... more LEARNING OBJECTIVES The presentation will discuss 1)various scanning protocols for left and right ventricles, 2)a selection of MR sequences and their relative merits, 3)artefacts (& how to eliminate them) 4) post-processing algorithms 5)clinical indications and 6) normal ranges ABSTRACT MR is currently the �reference-standard� method for LV/RV morphology & function. We will discuss all available scanning sequences & their merits. Steady-state free precession (SSFP) is superceding turbo gradient echo (TGE) & echo planar imaging (EPI) to become the technique of choice. We will discuss short axis, axial & radial scanning protocols & compare the mean values of volume and mass, & reproducibility for the following pulse sequences; SSFP, EPI, TGE and dual inversion recovery black blood. We also demonstrate our normal range for the two most widely used pulse sequences; TGE and SSFP. Limitations such as in the short-axis method - difficulty in determining the most basal slice and its partial...

LEARNING OBJECTIVES 1)Functional assessment:systolic and diastolic function; LV & RV function2)Di... more LEARNING OBJECTIVES 1)Functional assessment:systolic and diastolic function; LV & RV function2)Diagnosis of etiology: ischemic & non-ischemic;constriction & restriction;Infiltrative & inflammatory disease;Primary & secondary valvular dysfunction3)Wall motion at rest and stress4)charecteristics of myocardial perfusion5)Temporal Follow up5)Pharmacokinetics & remodelling ABSTRACT Heart failure is common disorder & its incidence is rising.Accurate, non invasive imaging modality such as MRI has great deal to offer in diagnosis & management of heart failure.Accurate diagnosis is vital, so appropriate management strategy can be planned to improve symptoms & survival. Measurement of systolic & diastolic LV volume & mass can asssist in optimal treatment planning which could potentially lead to positive ventricular remodelling. Moreover MRI can differentiate ischemic, infiltrative and inflammatory disease processes. Assessment of the viability & visualisation of scar tissue along with outlini...

PURPOSE To evaluate the clinical role of MR myocardial perfusion to discriminate significant from... more PURPOSE To evaluate the clinical role of MR myocardial perfusion to discriminate significant from non-significant coronary disease by both qualitative and semi-quantitative methods. METHOD AND MATERIALS 27 Patients with single vessel coronary disease underwent the above MR protocol before & after percutaneous coronary intervention (when appropriate) combined with intra-coronary pressure wire assessment of FFR.Dynamic first pass contrast agent myocardial perfusion studies,and delayed enhancement were performed under stress & rest conditions using a mulislice turbogradient echo sequence adopting sensitivity encoded imaging on a Philips Gyroscan 1.5 Tesla scanner.The following parameters were utilised - slice thickness 8 mm slice gap=10.3;FOV=390;TE=1.6;TR=3.3.Gadolinium was injected at a dose of 0.05 mmol/kg for the perfusion studies & a further 0.1mmol/kg was injected for delayed enhancement imaging.Adenosine was administered intravenously at 140 mcg/kg/min in both the non-invasive a...

The Journal of heart valve disease

The diameters and distensibility of the native pulmonary root and their effect on pulmonary autog... more The diameters and distensibility of the native pulmonary root and their effect on pulmonary autograft performance were examined pre- and postoperatively using cardiac ultrasound and magnetic resonance imaging (MRI). Eight patients undergoing the Ross procedure were prospectively involved. The diameters of the native aortic, native pulmonary and autograft roots were measured at the level of the annulus, sinus, sinotubular junction and in the main root using MRI through the cardiac cycle. Ultrasound was also used to estimate the degree of regurgitation, both pre- and postoperatively. The pulmonary root implanted into the systemic circulation increased in size but decreased in distensibility significantly at the sinus, sinotubular junction and main root, but not at the annulus. Postoperatively, the pulmonary autograft annulus showed a similar size and distensibility to that of the native aortic annulus. A wide range of aortic annular sizes (22-30 mm) produced clinically competent valve...

LEARNING OBJECTIVES 1)to describe and explain the pulse sequences available and their limitations... more LEARNING OBJECTIVES 1)to describe and explain the pulse sequences available and their limitations and techniques 2)to describe the role of stress agents 3)the physiology of coronary flow and myocardial perfusion 4)the quantitative and qualitative assessment of myocardial perfusion and its limitations 5)artefacts and howto minimise them 6)future directions of perfusion ABSTRACT Magnetic resonance myocardial perfusion imaging has the potential to be an important non-invasive imaging modality for the future in ischaemic heart disease. There are many MR pulse sequences which have the potential to be used for the qualitative and quantitative assessment of myocardial perfusion. This along with various scanning parameters and post-processing algorithms has been used by different centres. In this review we will discuss all perfusion protocols and their merits. We will also analyse in depth coronary flow and myocardial perfusion and the change in perfusion and flow mechanisms in ischaemia. W...

LEARNING OBJECTIVES 1)identify and modify the influence of MR scanning parameters, have on the qu... more LEARNING OBJECTIVES 1)identify and modify the influence of MR scanning parameters, have on the quantification of flow within the heart; atrio-ventricular and semilunar valves and great vessels 2) illustrate normal and abnormal blood flow profiles 3) demonstrate pitfalls and artefacts encountered and how to avoid them 4) discuss the post-processing algorithms available ABSTRACT Scanning parameters; voxel size, echo time, velocity encoding, flow direction, No. of phases influence quantification. Normal flow patterns of the semilunar, atrioventricular and LV flow will be shown. Abnormal flow in semilunar valves due to stenosis/regurgitation, can lead to increase in systolic velocities and with incompetence increase in volume to compensate for regurgitant volume. Abnormal flow in LV can be turbulence and flow/areas of stagnant flow (is dependant on ventricular morphology/function) caused by inflow/outflow conditions as well as high velocity regurgitant/stenotic jets. There are several a...

Journal of the American College of Cardiology, 2015

Netherlands heart journal : monthly journal of the Netherlands Society of Cardiology and the Netherlands Heart Foundation, 2010

The onset of sudden cardiac death and large inter- and intra-familial clinical variability of hyp... more The onset of sudden cardiac death and large inter- and intra-familial clinical variability of hypertrophic cardiomyopathy pose an important clinical challenge. Cardiac magnetic resonance imaging is a high-resolution imaging modality that has become increasingly available in the past decade and has the unique possibility to demonstrate the presence of fibrosis or scar using late gadolinium enhancement imaging. As a result, the diagnostic and prognostic potential of cardiac magnetic resonance imaging has been extensively explored in acute and chronic ischaemic cardiomyopathy, as well as in several nonischaemic cardiomyopathies.This review aims to provide a critical overview of recently published studies on hypertrophic cardiomyopathy and discusses the role of cardiac magnetic resonance imaging in differentiating underlying causes of hypertrophic cardiomyopathy, such as familial hypertrophic cardiomyopathy, cardiac involvement in systemic disease and left ventricular hypertrophy due to...

The British journal of radiology, 2001

Magnetic resonance (MR) is well suited to imaging the pericardium. High resolution images synchro... more Magnetic resonance (MR) is well suited to imaging the pericardium. High resolution images synchronized with the cardiac cycle can be obtained in any plane. The wide field of view allows additional anatomical and functional information to be obtained from adjacent structures such as the aorta, pleura, lungs and mediastinum. MR is particularly useful in cases of pericardial constriction without an associated effusion, in patients with complex or loculated pericardial effusions and in pericardial tumours. In this article we illustrate the characteristic MR features of a variety of pericardial pathologies.

European heart journal, 1994

Cardiopulmonary Support (CPS) was employed electively in 13 patients during high risk percutaneou... more Cardiopulmonary Support (CPS) was employed electively in 13 patients during high risk percutaneous transluminal coronary angioplasty (PTCA) in accordance with a selection criteria, which included at least two of the following; (i) left ventricular ejection fraction of less than 35%, (ii) target vessel(s) supplying more than 50% of the viable myocardium, and (iii) patients refused coronary bypass surgery. The mean age of the patients was 56.8 +/- 10.7 years (range 39-77). PTCA was attempted in a total of 35 lesions in 12 patients; 29 lesions were successfully dilated (technical success rate of 82.9%). On average, 2.7 lesions were attempted in each patient, and 2.2 lesions were successfully dilated per patient. In one patient the procedure was abandoned due to dissection of the iliac artery during cannulation. One patient died of a large pulmonary embolism 72 h after the procedure. All the surviving 11 patients who had successful PTCA on CPS showed symptomatic improvement during a mea...

Lancet, Jan 29, 1992

Percutaneous cardiopulmonary support (CPS) was initiated in 9 patients to provide haemodynamic st... more Percutaneous cardiopulmonary support (CPS) was initiated in 9 patients to provide haemodynamic stability after failure of conventional resuscitation. 4 patients were in cardiogenic shock and 4 remained in asystole, with 1 in resistant ventricular fibrillation, after cardiac arrest. During CPS for those in cardiogenic shock, the mean intra-arterial pressures ranged from 65 to 100 mm Hg (mean 84), at flow rates of between 3 to 5 l/min (mean 3.9). 2 patients underwent technically successful coronary angioplasty. No patient in this group survived. In the cardiac arrest group, acceptable mean intra-arterial blood pressures were achieved (mean 95, range 90-100 mm Hg) at flow rates of between 2 to 3 l/min (mean 2.6). All 5 subjects underwent technically successful coronary angioplasty whilst on CPS. 4 survived. 2 were alive and well at 12 months follow-up, 1 of whom had returned to work; the third is alive and well at 4 months.

ABSTRACT Sympathetic activation is implicated in the pathogenesis of hypertension and left ventri... more ABSTRACT Sympathetic activation is implicated in the pathogenesis of hypertension and left ventricular hypertrophy (LVH). LVH, suggested by electro- and echocardiographic criteria, is associated with further sympathetic nerve hyperactivity in patients with essential hypertension (EHT). The present investigation was designed to establish if a relationship between the directly measured level of muscle sympathetic nerve activity (MSNA), and degree of LVH exists, by precisely quantifying left ventricular mass (LVM) using cardiac magnetic resonance imaging (CMRI). Patients with untreated EHT, had LVM quantified and indexed to body surface area (BSA) to give a left ventricular mass index (LVMI), using a steady-state free precession (SSFP) pulse sequence on a 1.5-Tesla Philips Intera CV MRI system. Image analysis was performed off-line using commercially available analysis software (MASS version 5.0) and LVM was calculated by modified Simpson's rule. MSNA was measured by peroneal microneurography and expressed as bursts per 100 cardiac beats (b/100b). LVH was defined as 2SD above normal ranges established in the MRI department for LVM (ie. 83g/m2 for men and 67g/m2 for women). Using this definition there were 7 patients with LVH (EHT+LVH) and 9 below this limit without LVH (EHT-LVH). Patients were similar in terms of age, sex, body mass index (BMI) and level of arterial pressure. The results table shows data expressed as mean ± SEM. There were no significant differences (unpaired t tests) between groups for confounding factors such as age, BMI, mean arterial pressure (mBP) or BSA. MSNA and LVMI were greater in the EHT+LVH group than in the EHT-LVH group (P ≤ 0.02), by an average of 23% and 37% respectively. In addition, there was a striking positive correlation between LVMI and MSNA (r = 0.88, P <0.0001). View this table: In this window In a new window

Heart International, 2011

Cardiac magnetic resonance imaging (MRI) is increasingly used as the optimum modality for cardiac... more Cardiac magnetic resonance imaging (MRI) is increasingly used as the optimum modality for cardiac imaging. An aging population and rising numbers of patients with permanent pacemakers means many such individuals may require cardiac MRI scanning in the future. Whilst the presence of a permanent pacemaker is historically regarded as a contraindication to MRI scanning, pacemaker systems have been developed to limit any associ-ated risks. No reports have been published regarding the use of such devices with cardiac MRI in a clinical setting. We present the safe, successful cardiac MRI scan of a patient with an MRI-conditional permanent pacing system.

Perfusion, 2009

We describe the repair of a root, ascending aortic and arch aneurysm in a 69-year-old man with a ... more We describe the repair of a root, ascending aortic and arch aneurysm in a 69-year-old man with a bioprosthetic Shelhigh conduit and cylinder, employing continuous bilateral antegrade cerebral perfusion through an anomalous innominate artery with a bovine arch variant anatomy. The origin of both the innominate artery and the left common carotid artery from a common stem from the arch in this bovine arch variant puts the whole cerebral circulation at risk, on one hand, yet provides an opportunity of continuous bilateral antegrade cerebral perfusion through the right brachial, right axillary, right subclavian or innominate artery, during arch reconstruction under lower body, deep hypothermic circulatory arrest. Safety and adequacy of selective cerebral perfusion through the right axillary artery in patients with normal arch vessel origin depends on an intact circle of Willis. In this bovine arch variant, both cerebral hemispheres can be perfused through the right brachial, right axilla...

Quantitative measurement of myocardial perfusion based on the first pass of an extracellular cont... more Quantitative measurement of myocardial perfusion based on the first pass of an extracellular contrast agent through the heart relies on the determination of contrast agent concentration during the dynamic phase. Methods th at are based on the alteration of the T1 relaxation time require knowledge of the initial T1 value of the myocardium and its subsequent variation due to the passage of the contrast agent through the myocardium. Previous methods for fast myocardial T1 measurement have been proposed [1,2] however they either only measure a single slice or the data acquisition times and slice locations differ from those of the dynamically acquired data set. This limits their use in post-processing approaches that use pixel map ping. We propose a multiple slice, multiple-point T1 measurement that is both fast and whose slice locations and data acquisition timing exactly match those of the dynamic perfusion measurement pulse sequence.