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Circulation 07/2010; 122(3):311-5. · 14.74 Impact Factor
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ABSTRACT: There were 56 articles published in the Journal of Cardiovascular Magnetic Resonance in 2009. The editors were impressed with the high quality of the submissions, of which our acceptance rate was about 40%. In accordance with open-access publishing, the articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. We have therefore chosen to briefly summarise the papers in this article for quick reference for our readers in broad areas of interest, which we feel will be useful to practitioners of cardiovascular magnetic resonance (CMR). In some cases where it is considered useful, the articles are also put into the wider context with a short narrative and recent CMR references. It has been a privilege to serve as the Editor of the JCMR this past year. I hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication.
Journal of Cardiovascular Magnetic Resonance 03/2010; 12:15. · 3.72 Impact Factor
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ABSTRACT: The relationship between the morphology and blood flow of the Left Ventricle (LV) during myocardial remodelling is complex
and not yet fully understood. Cardiovascular MR (CMR) velocity imaging is a versatile tool for the observation of general
flow patterns in-vivo. More detailed understanding of the coupled relationship between blood flow patterns and myocardial wall motion can be further
enhanced by the combined use of Computational Fluid Dynamics (CFD) and CMR. This permits the generation of comprehensive high-resolution
velocity fields and the assessment of dynamic indices, such as mass transport and wall shear stress, that are important but
cannot be measured directly by using imaging alone. One of the key drawbacks of ventricular flow simulation using CFD is that
it is sensitive to the prescribed inflow boundary conditions. Current research in this area is limited and the extent to which
this affects in-vivo flow simulation is unknown. In this work, we measure this sensitivity as a function of the inflow direction and determine
the limit that is required for accurate ventricular flow simulation. This represents an important step towards the development
of a combined MR/CFD technique for detailed LV flow analysis.
KeywordsCardiovascular Magnetic Resonance-Computational Fluid Dynamics-Left Ventricle Flow-Boundary Condition
09/2004: pages 229-236;
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ABSTRACT: The combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) offers a promising tool that enables the prediction of blood flow patterns in subject-specific cardiovascular models. The influence of the model geometry on the accuracy of the simulation is well recognized. This paper addresses the impact of different boundary conditions on subject-specific simulations of left ventricular (LV) flow. A novel hybrid method for prescribing effective inflow boundary conditions in the mitral valve plane has been developed. The detailed quantitative results highlight the strengths as well as the potential pitfalls of the approach.
Journal of Biomechanical Engineering 01/2004; 125(6):922-7. · 1.90 Impact Factor
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ABSTRACT: This study demonstrates a subject specific approach for simulating blood flow within a left ventricle (LV) by a combined analysis of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Time dependent LV morphology and wall movements are measured by 3D multi-slice MRI. The information is then used to build numerical meshes for CFD simulation which provides detailed 3D LV velocity and pressure distributions in the LV cavity. Issues related to mesh generation and the prescription of valvular boundary conditions are also discussed. The predicted flow patterns are compared to that of the published MR measurements, demonstrating the effectiveness of the proposed approach.
Information Technology Applications in Biomedicine, 2003. 4th International IEEE EMBS Special Topic Conference on; 05/2003
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ABSTRACT: The Ross operation has several theoretical advantages. However, concern exists regarding evolving pathology in the pulmonary homograft.
Consecutive patients (n=144; mean age 31 years, range 2 months to 64 years) undergoing the Ross operation were studied between 1993 and 2000. Echocardiographic examination of the pulmonary homograft was performed immediately after surgery, then at yearly intervals for a mean interval of 48 months. Fifteen patients (mean age 37 years) in whom echocardiography revealed peak pulmonary gradients >/=30 mm Hg (mean 46+/-18 mm Hg) underwent MRI with velocity mapping in a Picker 1.5-T magnet. No patient had more than mild pulmonary regurgitation. Four patients required reoperation for rapidly progressive pulmonary homograft stenosis; in all 4, there was macroscopic and microscopic evidence of a pronounced chronic adventitial reaction, with perivascular infiltration producing extrinsic compression. Freedom from any pulmonary homograft stenosis at 7-year follow-up was 79.7%, with instantaneous hazard falling to zero after 4 years. Freedom from reoperation at 7 years was 96.7%. In those studied with MRI, there was evidence of narrowing of the whole homograft or distal suture line in 14 of 15 patients, with obvious excess surrounding tissue in 11. Mean minimum diameter and peak velocity by MRI were 11+/-2 mm and 3.2+/-0.7 m/s, respectively. Multivariate analysis of patient-, surgery-, and homograft-related variables did not reveal any significant risk factors for development of neopulmonary stenosis.
Pulmonary homograft stenosis after the Ross operation is clinically important and appears to represent an early postoperative inflammatory reaction to the pulmonary homograft that leads to extrinsic compression and/or shrinkage.
Circulation 09/2001; 104(12 Suppl 1):I16-20. · 14.74 Impact Factor
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ABSTRACT: A combined MR and computational fluid dynamics (CFD) study is made of flow in the upper descending thoracic aorta. The aim was to investigate further the potential of CFD simulations linked to in vivo MRI scans. The three-dimensional (3D) geometrical images of the aorta and the 3D time-resolved velocity images at the entry to the domain studied were used as boundary conditions for the CFD simulations of the flow. Despite some measurement uncertainties, comparisons between simulated and measured flow structures at the exit from the domain demonstrated encouraging levels of agreement. Moreover, the CFD simulation allowed the flow structure throughout the domain to be examined in more detail, in particular the flow separation region in the distal aortic arch and its influence on the downstream flow during late systole. Additional information such as relative pressure and wall shear stress, which could not be measured via MRI, were also extracted from the simulation. The results have encouraged further applications of the methods described. J. Magn. Reson. Imaging 2001;13:699-713.
Journal of Magnetic Resonance Imaging 06/2001; 13(5):699-713. · 2.70 Impact Factor
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ABSTRACT: A combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) methodology has been developed to simulate blood flow in heart chambers, with specific application in the present study to the human left ventricle. The proposed framework employs MRI scans of a human heart to obtain geometric data, which are then used for the CFD simulations. These latter are accomplished by geometrical modeling of the ventricle using time-resolved anatomical slices of the ventricular geometry and imposition of inflow/outflow conditions at orifices notionally representing the mitral and aortic valves. The predicted flow structure evolution and physiologically relevant flow characteristics were examined and compared to existing information. The CFD model convincingly captures the three-dimensional contraction and expansion phases of endocardial motion in the left ventricle, allowing simulation of dominant flow features, such as the vortices and swirling structures. These results were qualitatively consistent with previous physiological and clinical experiments on in vivo ventricular chambers, but the accuracy of the simulated velocities was limited largely by the anatomical shortcomings in the valve region. The study also indicated areas in which the methodology requires improvement and extension.
Annals of Biomedical Engineering 05/2001; 29(4):275-83. · 2.37 Impact Factor
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ABSTRACT: Magnetic resonance (MR) imaging is a versatile technique for providing detailed information on blood vessel morphology and function. With its ability to acquire multi-dimensional cine flow data, MR is also an important tool for providing insight into blood flow patterns in vivo. The purpose of this paper is to describe the application of texture synthesis for flow visualisation. Two related issues are addressed, one is the removal of image noise from the acquired velocity data to ensure a correct representation of the underlying flow structure, and the other is the formation of transient streamlines through flow texture synthesis. The process of noise removal is achieved by using a convex projection algorithm based on the principle of mass conservation, whereas transient streamlines are formed via an iterative orientated pattern formation and enhancement procedure. The method described provides realistic visualisation of the flow patterns and avoids distortions caused by integration errors associated with conventional streamline tracking techniques. Effectiveness of the method applied to MR flow data acquired in healthy volunteers and patients is demonstrated.
International Journal of Cardiac Imaging 07/2000; 16(3):175-84.
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ABSTRACT: Through cardiac looping during embryonic development, paths of flow through the mature heart have direction changes and asymmetries whose topology and functional significance remain relatively unexplored. Here we show, using magnetic resonance velocity mapping, the asymmetric redirection of streaming blood in atrial and ventricular cavities of the adult human heart, with sinuous, chirally asymmetric paths of flow through the whole. On the basis of mapped flow fields and drawings that illustrate spatial relations between flow paths, we propose that asymmetries and curvatures of the looped heart have potential fluidic and dynamic advantages. Patterns of atrial filling seem to be asymmetric in a manner that allows the momentum of inflowing streams to be redirected towards atrio-ventricular valves, and the change in direction at ventricular level is such that recoil away from ejected blood is in a direction that can enhance rather than inhibit ventriculo-atrial coupling. Chiral asymmetry might help to minimize dissipative interaction between entering, recirculating and outflowing streams. These factors might combine to allow a reciprocating, sling-like, 'morphodynamic' mode of action to come into effect when heart rate and output increase during exercise.
Nature 05/2000; 404(6779):759-61. · 36.28 Impact Factor
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ABSTRACT: The study was done to determine the most "cost-effective" approach to follow adults after repair of coarctation of the aorta.
Recoarctation and/or aneurysm formation following surgical repair or angioplasty for coarctation of the aorta carry a significant morbidity and mortality. Various screening tests to detect such complications are used, but little is known of their sensitivities and specificities; as a consequence, the most "cost-effective" approach to follow such patients is undefined.
Retrospective analysis was done on the sensitivity and specificity of symptomatology, physical examination, electrocardiogram, chest radiograph, exercise testing and transthoracic echocardiography to detect recoarctation and/or aneurysm formation in 84 adult patients following surgical repair or angioplasty of coarctation of the aorta, using magnetic resonance imaging (MRI) as the gold standard test.
Echocardiography had the highest sensitivity in detecting recoarctation (87%) and chest radiograph the highest sensitivity in detecting aneurysm formation (67%). Combined clinical visit and echocardiography had a high sensitivity for diagnosing recoarctation and/or aneurysm formation (97%), but performing a clinical visit and an MRI on every patient without any prior screening test emerged as the most "cost-effective" strategy.
The most "cost-effective" approach to diagnose complications at the site of repair in patients after surgical repair or balloon angioplasty of coarctation of the aorta appears to be the combination of clinical assessment and MRI scan on every patient. If MRI resources are scant, performing a clinical assessment plus a transthoracic echocardiography and an MRI on patients with positive results is an acceptable alternative.
Journal of the American College of Cardiology 04/2000; 35(4):997-1002. · 14.16 Impact Factor
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ABSTRACT: We discuss a patient with recoarctation of the aorta who, 4 weeks after reoperation, presented with fresh haemoptysis and was subsequently found at delayed emergency surgery to have a leaking false aortic aneurysm. The case emphasizes the significance of haemoptysis following repair of recoarctation, the difficulty of reoperation due to abnormalities of the aortic wall, and the value of serial magnetic resonance imaging in demonstrating regions of different signal intensity from haemorrhages of varying age around a leaking false aortic aneurysm.
Cardiology in the Young 06/1997; 7(03):340 - 343. · 0.76 Impact Factor
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Circulation 03/1997; 95(4):1083-4. · 14.74 Impact Factor
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ABSTRACT: Pulmonary regurgitation (PR) is an important determinant of outcome after repair of tetralogy of Fallot. Baseline PR was measured by magnetic resonance (MR) phase velocity mapping and from real-time right ventricular pressure-volume loops with a conductance catheter. Subsequently, the impact of two loading maneuvers (increased airway pressure, simulated branch pulmonary artery stenosis) on PR was assessed by the conductance catheter method.
Thirteen patients, 3 to 35 years after tetralogy of Fallot repair or pulmonary valvotomy, had PR measured by MR phase velocity mapping while breathing spontaneously. During catheterization under general anesthesia. PR was estimated from right ventricular pressure-volume loops generated by conductance and microtip pressure catheters. The effect of increased airway pressure (continuous positive airway pressure, 20 cm H2O; n = 12) and simulated branch pulmonary artery stenosis (transient balloon occlusion of a branch pulmonary artery, n = 7) was measured. Basal PR fraction derived by MR and from right ventricular pressure-volume loops had a correlation coefficient of .76 and mean of differences of 2.0 +/- 18.2% (95% limits of agreement). Increased airway pressure increased PR (16.3 +/- 11.4% to 25.7 +/- 17.3%, P < .01). Simulated branch pulmonary artery stenosis increased right ventricular end-systolic pressure (69.1 +/- 21.4 to 78.7 +/- 23.1 mm Hg, P < .05) and PR (27.5 +/- 11.3% to 36.9 +/- 12.8%, P < .05).
There was reasonable agreement between MR phase velocity-derived PR fraction and that obtained from right ventricular pressure-volume loops generated by use of conductance and pressure-microtip catheters. Exacerbation of PR by increased airway pressure and branch pulmonary stenosis may be relevant to the acute postoperative and long-term management, respectively, of patients after repair of tetralogy of Fallot.
Circulation 03/1997; 95(3):643-9. · 14.74 Impact Factor
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ABSTRACT: Magnetic resonance phase velocity mapping has unrivalled capacities for acquiring in vivo multi-directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier-Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated with in vitro flow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/flow relationships associated with normal and impaired cardiovascular function.
Magnetic Resonance in Medicine 11/1996; 36(4):520-6. · 2.96 Impact Factor
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ABSTRACT: Magnetic resonance imaging with multidirectional cine velocity mapping was used to study relationships between aortic blood flow patterns and the geometry of thoracic aortic aneurysms and grafts. Ten patients with 13 thoracic aortic aneurysms, single or multiple, or grafts (4) participated in the study. The causes of disease were atherosclerosis (4), Marfan's syndrome (2), trauma (1), and unknown (1), and there were two dissections. Spin-echo imaging and cine velocity mapping in 10 mm thick slices with vertical and horizontal velocity encoding were done. Maps of the two velocity components were processed into multiple computer-generated streaks whose orientation and length corresponded to velocity vectors in the chosen plane. The dynamic arrow maps were compared with previously reported aortic arrow maps from normal subjects. The forward flow occupied the entire lumen in the normal aorta in systole and small vortices were only present in the sinuses of Valsalva. Atherosclerotic aneurysms in the ascending aorta were located at the anterior right and had oblique, eccentric jet flows that created a large secondary vortex in the aneurysm. Patients with Marfan's syndrome had a central jet and two large vortices, one on each side. All other aneurysms, dissections, and grafts had irregular flows and vortices not seen in normal subjects. Magnetic resonance imaging with multidirectional velocity mapping is a powerful noninvasive tool to assess morphologic features and disturbed blood flow in aortic aneurysms and grafts. Recognizably altered flow patterns were found to be associated with altered vessel geometry. The significance of this requires further investigation.
Journal of Thoracic and Cardiovascular Surgery 10/1995; 110(3):704-14. · 3.41 Impact Factor
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ABSTRACT: The inability to obtain complete diagnoses with transthoracic echocardiography in many adults with congenital heart disease provided the incentive to evaluate prospectively the individual and combined roles of magnetic resonance imaging (MRI) and transesophageal echocardiography (TEE) as "second-line" techniques for unresolved diagnostic problems.
Eighty-five patients were studied; 81 had MRI with a 0.5-T magnet to obtain spin-echo images, cine-MRI, and flow-velocity maps. Seventy-nine patients had TEE (37 biplane). A simple score (range, 0 to 1) was used for quantification of the results of MRI and TEE alone, for their comparison (in the 75 patients who had both), and for assessment of their combination. MRI, TEE, or their combination achieved a score of at least 0.75 in 18 of 25 diagnostic categories. A summary of the scores showed that for intracardiac anatomy. MRI scored 0.34, TEE scored 0.71 (P < .0001), and MRI plus TEE scored 0.84 (P < .003); for extracardiac anatomy, MRI scored 0.76, TEE scored 0.23 (P < .0001), and MRI plus TEE scored 0.84 (P = NS); and for hemodynamics and function, MRI scored 0.58, TEE scored 0.41 (P < .05), and MRI plus TEE scored 0.67 (P = NS). Total scores were MRI, 0.52; TEE, 0.50 (P = NS); and MRI plus TEE, 0.80 (P < .0001). MRI and TEE were inadequate for collateral and coronary arteries and pulmonary vascular resistance. Cine-MRI and flow-velocity maps comprised 43% of the MRI scores. Biplane TEE was better than single plane (scores of 0.59 versus 0.42, P < .0001).
MRI and TEE are important and complementary "second-line" investigations for congenital heart disease. Analysis of their performance in a wide range of diagnostic categories provides guidelines for their judicious application. Where both are available, diagnostic catheterizations are either obviated or simplified.
Circulation 12/1994; 90(6):2937-51. · 14.74 Impact Factor
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ABSTRACT: To evaluate spin-echo (SE) and cine gradient-echo (GRE) magnetic resonance (MR) imaging with velocity mapping for detecting late complications of the Mustard operation.
Twenty-one patients were studied with MR imaging 1-22 years after undergoing the Mustard operation. Twenty were also studied with transthoracic echocardiography, 18 with angiocardiography, and five with transesophageal echocardiography.
MR imaging showed no venoatrial obstruction in nine patients. This result was confirmed with angiocardiography in seven cases and postmortem examination in one case. In one case, MR imaging demonstrated a leak at the baffle suture line. Of 12 cases with venoatrial obstruction at MR imaging, nine were confirmed with angiocardiography or surgery. There were two false-positive MR studies and one case in which no conclusion was reached.
With addition of cine GRE sequences and velocity mapping to SE sequences, MR imaging is a useful noninvasive method of investigating late complications of the Mustard operation.
Radiology 11/1994; 193(1):211-7. · 5.73 Impact Factor
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ABSTRACT: We used magnetic resonance imaging with cine velocity vector mapping to study blood flow patterns in the thoracic aorta of patients with aortic aneurysms. Spin-echo images of the thoracic aorta were acquired in orthogonal and oblique planes. Cine phase-shift velocity maps were then acquired in selected aortic planes, with velocity encoded in two orthogonal directions. The two-directional velocity data were processed to generate flow vector maps depicting flow distribution in the chosen plane. Diameter ratios between the aortic valves and aneurysmal ascending aortas were reduced, causing blood to enter as a relatively narrow stream with lateral vortical, recirculating flow. In atherosclerotic aneurysms, there was abnormal angulation between the left ventricular outflow tract and ascending aorta, causing the stream to attach to the anterior aortic wall, with recirculating flow posteriorly. In Marfan patients, the primary stream was central with vortices on either side. In patients with coarctation, the main stream attached to the posterior wall of the descending aorta, with recirculation anteriorly. Magnetic resonance imaging with cine velocity mapping allows comprehensive assessment of aortic anatomy and blood flow patterns. Sequential studies at early stages may provide new information about the natural history of aortic aneurysms.
MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 09/1994; 2(3):335-338. · 1.88 Impact Factor
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ABSTRACT: Helical and retrograde secondary flows have been recorded in the aorta, but their origins and movements in relation to the arch have not been clarified. We set out to do this using magnetic resonance velocity mapping.
Three-directional phase contrast cine magnetic resonance velocity mapping was used to map multidirectional flow velocities in the aortas of 10 healthy volunteers. Computer processing was used to visualize flow vector patterns in selected planes. Right-handed helical flows predominated in the upper aortic arch in late systole, being clearly recognizable in 9 of the 10 subjects. Nonaxial components of velocity in this region reached 0.29 m/s (+/- 0.05 m/s) as axial velocities declined from a peak of 1.0 m/s (+/- 0.1 m/s). Helical flow patterns in the upper descending aorta varied between subjects, apparently depending on arch curvature. End-systolic retrograde flow originated from regions of blood with low momentum, usually along inner wall curvatures. Flow studies in a curved tubular phantom showed right-handed helical flow in the upper "arch" when the inflow section was positioned to simulate ascending aortic curvature, and retrograde flow occurred along the inner wall at end systole during pulsatile flow.
Helical and retrograde streams are consistent features of intra-aortic flow in healthy subjects that result, at least in part, from the curvature of the arch and the pulsatility of flow in it. They may have significance in relation to circulatory dynamics and the pathogenesis of atheroma in the arch.
Circulation 12/1993; 88(5 Pt 1):2235-47. · 14.74 Impact Factor
