Relationship between cardiac diffusion tensor imaging parameters and anthropometrics in healthy volunteers

BACKGROUND

In vivo cardiac diffusion tensor imaging (cDTI) is uniquely capable of interrogating laminar myocardial dynamics non-invasively. A comprehensive dataset of quantative parameters and comparison with subject anthropometrics is required.

METHODS

cDTI was performed at 3T with a diffusion weighted STEAM sequence. Data was acquired from the mid left ventricle in 43 subjects during the systolic and diastolic pauses. Global and regional values were determined for fractional anisotropy (FA), mean diffusivity (MD), helix angle gradient (HAg, degrees/%depth) and the secondary eigenvector angulation (E2A). Regression analysis was performed between global values and subject anthropometrics.

RESULTS

All cDTI parameters displayed regional heterogeneity. The RR interval had a significant, but clinically small effect on systolic values for FA, HAg and E2A. Male sex and increasing left ventricular end diastolic volume were associated with increased systolic HAg. Diastolic HAg and systolic E2A were both directly related to left ventricular mass and body surface area. There was an inverse relationship between E2A mobility and both age and ejection fraction.

CONCLUSIONS

Future interpretations of quantitative cDTI data should take into account anthropometric variations observed with patient age, body surface area and left ventricular measurements. Further work determining the impact of technical factors such as strain and SNR is required.

Review of Journal of Cardiovascular Magnetic Resonance 2014

There were 102 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2014, which is a 6% decrease on the 109 articles published in 2013. The quality of the submissions continues to increase. The 2013 JCMR Impact Factor (which is published in June 2014) fell to 4.72 from 5.11 for 2012 (as published in June 2013). The 2013 impact factor means that the JCMR papers that were published in 2011 and 2012 were cited on average 4.72 times in 2013. The impact factor undergoes natural variation according to citation rates of papers in the 2 years following publication, and is significantly influenced by highly cited papers such as official reports. However, the progress of the journal's impact over the last 5 years has been impressive. Our acceptance rate is <25% and has been falling because the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. For this reason, the Editors have felt that it is useful once per calendar year to summarize the papers for the readership into broad areas of interest or theme, so that areas of interest can be reviewed in a single article in relation to each other and other recent JCMR articles. The papers are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought in the journal. We 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 papers to JCMR for publication.

Prevalence and prognostic implication of restenosis or dilatation at the aortic coarctation repair site assessed by cardiovascular MRI in adult patients late after coarctation repair

BACKGROUND

Cardiovascular magnetic resonance (CMR) is ideal for assessing patients with repaired aortic coarctation (CoA). Little is known on the relation between long-term complications of CoA repair as assessed by CMR and clinical outcome. We examined the prevalence of restenosis and dilatation at the repair site and the long-term outcome in patients with repaired CoA.

METHODS AND RESULTS

CMR imaging and clinical data for adult CoA patients (247 patients aged 33.0 ± 12.8 years, 60% male), were analyzed. The diameter of the aorta at the repair site was measured on CMR and its ratio to the aortic diameter at the diaphragm (repair site-diaphragm ratio, RDR) was calculated. Restenosis (RDR≤70%) was present in 31% of patients (and significant in 9% [RDR<50%]), and dilatation (RDR>150%) in 13.0%. A discrete aneurysm at the repair site was observed in 9%. Restenosis was more likely after resection and end-end anastomosis, whereas dilatation after patch repair. Systemic hypertension was present in 69% of patients. Of the hypertensive patients, blood pressure (133 ± 20/73 ± 10 mm Hg) was well controlled in 93% with antihypertensive therapy. Mortality rate over a median length of 5.9 years was low (0.69% per year, 95% CI: 0.33-1.26), but significantly higher than age-matched healthy controls (standardised mortality ratio 2.86, CI 1.43-5.72, p<0.001).

CONCLUSION

Restenosis or dilatation at the CoA repair site as assessed by CMR is not uncommon. Medium term survival remains good, however, albeit lower than in the general population. Life-long follow-up and optimal blood pressure control are likely to secure a good longer term outlook in these patients.

Imaging congenital heart disease in adults

Transthoracic echocardiography is the first-line modality for cardiovascular imaging in adults with congenital heart disease (ACHD). The windows of access that are possible with transthoracic echocardiography are, however, rarely adequate for all regions of interest. The choice of further imaging depends on the clinical questions that remain to be addressed. The strengths of MRI include comprehensive access and coverage, providing imaging of all parts of the right ventricle, the pulmonary arteries, pulmonary veins and aorta. Cine images and velocity maps are acquired in specifically aligned planes, with stacks of cines or dynamic contrast angiography providing more comprehensive coverage. Tissues can be characterised if necessary, and MRI provides relatively accurate measurements of biventricular function and volume flow. These parameters are important in the assessment and follow-up of adults after repairs for tetralogy of Fallot or transposition of the great arteries and after Fontan operations. The superior spatial resolution and rapid acquisition of CT are invaluable in selected situations, including the visualisation of anomalous coronary or aortopulmonary collateral arteries, the assessment of luminal patency after stenting and imaging in patients with pacemakers. Ionising radiation is, however, a concern in younger patients who may need repeated investigation. Adults with relatively complex conditions should ideally be imaged in a specialist ACHD centre, where dedicated echocardiographic and cardiovascular MRI services are a necessary facility. General radiologists should be aware of the nature and pathophysiology of congenital heart disease, and should be alert for previously undiagnosed cases presenting in adulthood, including cases of atrial septal defect, aortic coarctation, patent ductus arteriosus, double-chambered right ventricle and congenitally corrected transposition.

Review of Journal of Cardiovascular Magnetic Resonance 2009

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.

The influence of inflow boundary conditions on intra left ventricle flow predictions

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.

Incidence, location, pathology, and significance of pulmonary homograft stenosis after the Ross operation

BACKGROUND

The Ross operation has several theoretical advantages. However, concern exists regarding evolving pathology in the pulmonary homograft.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

Combined MR imaging and CFD simulation of flow in the human descending aorta

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.

Computational flow modeling of the left ventricle based on in vivo MRI data: initial experience

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.

Transient streamlines: texture synthesis for in vivo flow visualisation

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.

Asymmetric redirection of flow through the heart

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.

Repaired coarctation: a "cost-effective" approach to identify complications in adults

OBJECTIVES

The study was done to determine the most "cost-effective" approach to follow adults after repair of coarctation of the aorta.

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

The aortic outflow and root: a tale of dynamism and crosstalk

Although the aortic outflow and root (AoR) constitute a short channel connecting the left ventricle to the aorta, its different components have been shown to be highly specialized structures, interacting with each other as well as with surrounding structures, thus providing a "tale of dynamism and crosstalk." Thorough knowledge of the AoR and morphological and structural changes, that occur during pathological processes, can have important implications in evolving and executing surgical procedures designed to preserve and restore the "dynamism and crosstalk." The crown-shaped annulus, fibrous trigones, aortic cusps components, aortic sinuses, and the sinotubular junction share a dynamic coordinated behavior, which can be partially or completely restored in various repair or replacement procedures of the AoR. The interaction and the specific operations are presented with evidence supporting the notion that the dynamic behavior of the root does influence the pattern of instantaneous movements of the aortic cusps after different types of operations. Further studies are required to evaluate the influence of adopting these ideas on the long-term results of operative procedures.

Computational fluid dynamic and magnetic resonance analyses of flow distribution between the lungs after total cavopulmonary connection

Total cavopulmonary connection is a surgical procedure adopted to treat complex congenital malformations of the right heart. It consists basically in a connection of both venae cavae directly to the right pulmonary artery. In this paper a three-dimensional model of this connection is presented, which is based on in vivo measurements performed by means of magnetic resonance. The model was developed by means of computational fluid dynamics techniques, namely the finite element method. The aim of this study was to verify the capability of such a model to predict the distribution of the blood flow into the pulmonary arteries, by comparison with in vivo velocity measurements. Different simulations were performed on a single clinical case to test the sensitivity of the model to different boundary conditions, in terms of inlet velocity profiles as well as outlet pressure levels. Results showed that the flow distribution between the lungs is slightly affected by the shape of inlet velocity profiles, whereas it is influenced by different pressure levels to a greater extent.

Vortical flow feature recognition: a topological study of in vivo flow patterns using MR velocity mapping

PURPOSE

To describe an automatic method for studying vortical flow features using multidirectional magnetic resonance velocity imaging.

METHODS

The technique relied on the use of linear differential equations to provide local approximation to the acquired MR velocity data and to identify vortical flow patterns that were characterised by their circular or swirling motion. Two directional MR velocity images were acquired on a 0.5 T system with a TE of 14 ms, slice thickness of 10 mm, and field of view of 30-40 cm.

RESULTS

The method was validated using numerical simulation, and the potential of this technique for studying blood flow features was demonstrated in the ascending aorta of a healthy volunteer and that of a patient with Marfan's syndrome. The difference in vortex flow dynamics of the left ventricle between a normal subject and a patient with dilated ventricle was also compared.

CONCLUSION

The approach of detecting critical flow features prior to analysing dynamical indices of the fluid is suited to the topological study of complex flow patterns depicted by MR velocity mapping techniques.

Blood flow patterns in the thoracic aorta studied with three-directional MR velocity mapping: the effects of age and coronary artery disease

The objective was to investigate how the blood flows in the thoracic aorta, with special emphasis on flow reversal and flow into the coronary arteries. Three-directional MR velocity mapping was used to map multidirectional flow velocities in the aorta in 14 normal subjects and 14 patients with coronary artery disease. Dynamic flow vector maps and through-plane velocity maps were used. The flow reversed in all subjects in the upper ascending aorta and usually also in the distal aortic arch. Retrograde flow became antegrade again at various levels in the ascending aorta and in the coronary sinuses. Seven flow characteristics were investigated that, lumped together, were significantly different (P = .0005) in normal subjects compared with patients and in normal subjects 70 years of age and older compared with those younger than 70 years of age.

Increased airway pressure and simulated branch pulmonary artery stenosis increase pulmonary regurgitation after repair of tetralogy of Fallot. Real-time analysis with a conductance catheter technique

BACKGROUND

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.

METHODS AND RESULTS

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).

CONCLUSIONS

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.

Our tortuous heart in dynamic mode--an echocardiographic study of mitral flow and movement in exercising subjects

Blood traces tortuous paths of flow through the heart. We postulate that momentum changes associated with direction changes optimize dynamic coupling between ventricular and atrial function, particularly on exercise. Traces of pulsed Doppler mitral flow and M-mode long-axis mitral ring movement were recorded before and during exercise, increased in 25-W steps to strenuous levels (146 +/- 30 W), in 16 healthy volunteers, aged 38 +/- 10 years. R-R intervals fell from 821 +/- 151 to 437 +/- 51 ms, and diastole from 458 +/- 134 to 169 +/- 33 ms. Peak mitral flow velocities rose from 0.68 +/- 0.17 to 1.27 +/- 0.16 m/s, and mitral valve ring displacements from 13.8 +/- 3.3 to 19.3 +/- 3.4 mm. Biphasic diastolic curves of flow and movement became monophasic as R-R fell below 500 ms, with atrial systole apparently coming to coincide with elastic ventricular recoil to give a single elevated peak of mitral flow. The increased slope and amplitude of Doppler curves indicate increased rates of change of momentum, which imply enhanced inertial forces. The illustrated patterns of flow and movement on exercise accord with the postulated "dynamic" mode of function, in which forces between atria, ventricles, and passing blood masses become tightly coupled to achieve a sling-like redirection of momentum through tortuous paths of flow, but more extensive data are needed to adequately model and quantify inertial force exchanges of the exercising heart.

Computation of flow pressure fields from magnetic resonance velocity mapping

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.

Dynamic range extension of cine velocity measurements using motion-registered spatiotemporal phase unwrapping

A motion-registered spatiotemporal phase-unwrapping method for extending the dynamic range of cine magnetic resonance phase velocity measurements is presented. The interframe cardiac movement is estimated from the magnitude image derived from the velocity encoded raw data, which ensures that the phase signal is unwrapped in the temporal direction with reference to pixels belonging to the same anatomic flow region. An extra step of spatial phase correction is then used to further eliminate any residual errors. The combination of spatial and temporal information for phase unwrapping provides a robust way of extending the dynamic range of cine velocity data in the presence of large phase aliasing errors.

Magnetic resonance velocity vector mapping of blood flow in thoracic aortic aneurysms and grafts

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.

Diagnosis in adolescents and adults with congenital heart disease. Prospective assessment of individual and combined roles of magnetic resonance imaging and transesophageal echocardiography

BACKGROUND

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.

METHODS AND RESULTS

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).

CONCLUSIONS

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.

Venoatrial pathways after the Mustard operation for transposition of the great arteries: anatomic and functional MR imaging

PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Visualization of flow by vector analysis of multidirectional cine MR velocity mapping

OBJECTIVE

We describe a noninvasive method for visualization of flow and demonstrate its application in a flow phantom and in the great vessels of healthy volunteers and patients with aortic and pulmonary arterial disease. The technique uses multidirectional MR velocity mapping acquired in selected planes. Maps of orthogonal velocity components were then processed into a graphic form immediately recognizable as flow.

MATERIALS AND METHODS

Cine MR velocity maps of orthogonal velocity components in selected planes were acquired in a flow phantom, 10 healthy volunteers, and 13 patients with dilated great vessels. Velocities were presented by multiple computer-generated streaks whose orientation, length, and movement corresponded to velocity vectors in the chosen plane.

RESULTS

The velocity vector maps allowed visualization of complex patterns of primary and secondary flow in the thoracic aorta and pulmonary arteries. The technique revealed coherent, helical forward blood movements in the normal thoracic aorta during midsystole and a reverse flow during early diastole. Abnormal flow patterns with secondary vortices were seen in patients with dilated arteries.

CONCLUSION

The potential of MR velocity vector mapping for in vitro and in vivo visualization of flow patterns is demonstrated. Although this study was limited to two-directional flow in a single anatomical plane, the method provides information that might advance our understanding of the human vascular system in health and disease. Further developments to reduce the acquisition time and the handling and presenting of three-directional velocity data are required to enhance the capability of this method.

Magnetic resonance volume flow and jet velocity mapping in aortic coarctation

OBJECTIVES

Nuclear magnetic resonance (MRI) velocity mapping was used to characterize flow waveforms and to measure volume flow in the ascending and descending thoracic aorta in patients with aortic coarctation and in healthy volunteers. We present the method and discuss the relation between these measurements and aortic narrowing assessed by MRI. Finally, we compare coarctation jet velocity measured by MRI velocity mapping with that obtained from continuous wave Doppler echocardiography.

BACKGROUND

The development of a noninvasive imaging method for morphologic visualization of aortic coarctation and for measurement of its impact on blood flow is highly desirable in the preoperative and postoperative management of patients.

METHODS

Magnetic resonance imaging phase-shift velocity mapping was used to measure ascending and descending aortic volume flow in 39 patients with aortic coarctation and in 12 healthy volunteers. Magnetic resonance imaging was also used for anatomic and peak jet velocity measurements. The latter were compared with those available from continuous wave Doppler study in 40% of the patients.

RESULTS

Whereas ascending aortic volume flow measurement did not show significant differences between the patient and healthy control groups, volume flow curves in the descending aorta did show significant differences between the two groups. Peak volume flow (mean +/- SD) was 10.6 +/- 5.3 liters/min in patients and 19.6 +/- 4.7 liters/min in control subjects (p < 0.001). Time-averaged flow was 2.5 +/- 0.9 liters/min in patients and 3.9 +/- 1.1 liters/min in control subjects (p < 0.05). The descending/ascending aorta flow ratio was 0.47 +/- 0.19 in patients and 0.64 +/- 0.08 in control subjects (p < 0.05). These variables correlate well with the degree of aortic narrowing. Peak coarctation jet velocity measured by MRI velocity mapping is comparable to that obtained from continuous wave Doppler study (r = 0.95).

CONCLUSIONS

We established normal ranges for volume flow in the descending aorta and demonstrated abnormalities in patients with aortic coarctation. These abnormalities are likely to be related to resistance to flow imposed by the coarctation and could represent an additional index for monitoring patients before and after intervention.

Helical and retrograde secondary flow patterns in the aortic arch studied by three-directional magnetic resonance velocity mapping

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

Magnetic resonance jet velocity mapping in mitral and aortic valve stenosis

BACKGROUND

Magnetic resonance (MR) phase-shift velocity mapping is an established method for measurement of nonturbulent intravascular flow. Shortening the echo time of the MR sequence to 3.6 msec allowed application of the technique to turbulent jet flow. The objective of this study was validation of MR jet velocity mapping in patients with cardiac valve stenosis.

METHODS AND RESULTS

We used a 0.5-T Picker MR machine to measure peak poststenotic jet velocity in 15 consecutive patients recruited with known valve disease (six mitral stenosis, three of these restudied after valvoplasty, and 11 aortic stenosis). On the same day as the MR study, these patients underwent independent Doppler echocardiographic measurement of peak jet velocity. The results of 10 further MR investigations of aortic stenosis are also reported and compared with Doppler studies performed within 6 months. Of the 29 MR studies, 28 (97%) produced interpretable velocity maps, the one failure being attributed to misplacement of the imaging slice in a case of severe aortic stenosis. Agreement between MR and Doppler measurements of peak jet velocity in the recruited group was as follows: n = 18; range, 1.4-6.1 m/sec; mean, 3 m/sec; mean of differences (MR-Doppler), 0.23 m/sec; standard deviation of differences, 0.49 m/sec.

CONCLUSIONS

In vivo MR peak jet velocity measurements agree well with those made by Doppler ultrasound. The technique, which is not subject to restricted windows of access and has potential for further refinements, could contribute to improved evaluation of stenoses, especially at locations where ultrasonic access is limited.

Obstruction in extracardiac ventriculopulmonary conduits: value of nuclear magnetic resonance imaging with velocity mapping and Doppler echocardiography

OBJECTIVES

This study was designed to investigate the value of noninvasive imaging modalities for the detection of obstruction in extracardiac ventriculopulmonary conduits.

BACKGROUND

the diagnosis of obstruction in a conduit by noninvasive methods can be difficult. Obstruction may be silent and its progression unnoticed. Nuclear magnetic resonance imaging (NMR) with velocity mapping is a new noninvasive technique that can provide high resolution images and has been shown to be a reliable method of measuring blood flow velocity.

METHODS

Two-dimensional echocardiography, pulsed wave Doppler echocardiography and NMR spin echo imaging were used in 52 patients with an extracardiac ventriculopulmonary conduit. Continuous wave Doppler echocardiography was used in 30 of these, Doppler color flow mapping in 26 and NMR velocity mapping in 12. Cardiac catheterization data were available in 27 patients and operative or autopsy findings in 11.

RESULTS

The conduit could be assessed by two-dimensional and pulsed wave Doppler echocardiography in only 17% of patients. Doppler color flow and continuous wave echocardiography provided technically satisfactory data in 19% and 83%, respectively. The anatomy of the conduit was adequately displayed by NMR imaging in 90%. A minimal diameter less than 18 mm indicated conduit obstruction, although failure to detect calcification resulted in obstruction being missed in some patients. Calculated gradients in obstructed conduits derived from NMR velocity mapping correlated well with results of continuous wave Doppler echocardiography and gave an accurate localization of the site of obstruction as well as a measure of its severity.

CONCLUSION

NMR imaging with velocity mapping is the most effective noninvasive method of assessing obstruction in ventriculopulmonary conduits and can obviate the need for invasive investigation before an interventional procedure is performed.

Haemoptysis from false aneurysm: near fatal complication of repair of coarctation of the aorta using a Dacron patch

We report a case of haemoptysis from a leaking false aneurysm associated with a Dacron patch used to repair coarctation of the aorta twelve years earlier in a 17-year-old girl. This case illustrates a late and potentially fatal complication of this type of operation after a long period of apparent normality. It emphasises the need for informed follow-up and appropriate correctly timed investigations.

Valve and great vessel stenosis: assessment with MR jet velocity mapping

For measurement of poststenotic jet velocities with magnetic resonance (MR) imaging, the authors reduced the echo time (TE) of the field even-echo rephasing (FEER) velocity mapping sequence from 14.0 to 3.6 msec, so minimizing the problem of MR signal loss from turbulent fluid. In vitro use of rotating disk and stenotic flow phantoms confirmed that the 3.6-msec TE sequence enables accurate measurement of jet velocities of up to 6.0 m/sec (r = .996). Peak jet velocity measurements were made with MR imaging in 36 patients with stenosis of native heart valves (n = 9), conduits (n = 19), or Fontan connections (n = 2) or with aortic coarctation (n = 6). Peak velocity measurements made with MR imaging agreed well with measurements made with Doppler ultrasound (US), which were available in 18 cases (standard deviation = 0.2 m/sec). Velocity mapping with fast-echo MR imaging is likely to have considerable importance as a noninvasive means of locating and evaluating stenoses, particularly at sites inaccessible to US, but care must be taken to prevent errors caused by malalignment, signal loss, phase wrap, or partial-volume effects.

The application of phase shifts in NMR for flow measurement

A brief overview of the history of the application of phase shifts in NMR, and in particular NMR imaging, is presented. The imaging methods include direct phase mapping, Fourier flow imaging (where the flow data are Fourier transformed into one dimension of an image), and alternative methods, where flow-related phase shifts are utilized for flow measurement from the magnitude of the signal. A discussion then follows of the principal errors that can affect the accuracy of the various flow imaging techniques, with particular reference to the phase mapping methods that have been used extensively in our institution. The results from a number of experiments are included to illustrate the extent of the errors and methods of removing or minimizing these effects are suggested.

Cardiovascular cavities cast in silicone rubber as an adjunct to post-mortem examination of the heart

We used silicone rubber as a material for making post-mortem casts of cavities in 21 human hearts, 16 of them congenitally malformed, 13 after surgical reconstruction (Fontan and Norwood procedures) and 4 after reconstruction had been performed posts mortem for study purposes. The organs were either fresh, or had been perfusion fixed with formalin prior to casting. When suitable silicone rubber and catalyst were used, we found that casts allowed a very clear view of chamber morphology, and, where surgery had been performed, of any vascular constriction or distortion. We made casts of the aortic sinus and coronary arteries in 3 adult hearts, demonstrating the location and extent of indentation due to atheromatous deposits. The resilience and non-adhesiveness of the silicone rubber allowed casts to be extracted without recourse to corrosion. The surrounding tissues, with the exception of trapped trabeculations and valve structures, were then available for conventional pathological examination. We propose that the relatively simple technique has important applications, not practicable using earlier casting materials, for the study of cardiovascular morphology, and for post-mortem evaluation of stenosed or surgically reconstructed vessels.