Sidney A. Rebergen

Pulmonary regurgitation in the late postoperative follow-up of tetralogy of Fallot. Volumetric quantitation by nuclear magnetic resonance velocity mapping.

BackgroundPulmonary regurgitation frequently occurs after surgical correction of tetralogy of Fallot. To date, reliable quantitation of pulmonary regurgitation has not been possible, and therefore the clinical significance of pulmonary regurgitation is controversial. Nuclear magnetic resonance (NMR) velocity mapping allows accurate measurement of volumetric flow. The feasibility and accuracy of NMR velocity mapping to quantify pulmonary regurgitation volumes are studied in patients after Fallot repair. Methods and ResultsIn 18 patients (mean age, 16.5±6.5 years), late (12.6±5.2 years) after Fallot surgery, forward and regurgitant volume flow was measured in the main pulmonary artery with NMR velocity mapping. To validate the measurements of pulmonary forward flow, right ventricular stroke volume was used as an internal reference standard. Pulmonary regurgitation volumes were compared with the differences between the corresponding right and left ventricular stroke volumes. Ventricular volumes were measured with a multisection gradient echo NMR method. In addition, the relation between pulmonary regurgitation and right ventricular volumes was studied. Measurements of pulmonary regurgitation volume with NMR velocity mapping closely corresponded with the tomographically determined volumes (r=.93). Forward pulmonary volume flow was neariy identical to right ventricular stroke volume (r=.98). Pulmonary regurgitation volume was significantly correlated with end-diastolic volume (r=.82, P<.0005), end-systolic volume (r=.63, P<.01), and stroke volume (r=.89, P<.0005) of the right ventricle but not with right ventricular ejection fraction (r= −.41, P=NS). ConclusionsNMR velocity mapping is an accurate method for the noninvasive, volumetric quantification of pulmonary regurgitation after surgical correction of tetralogy of Fallot.

Comparison of echocardiographic methods with magnetic resonance imaging for assessment of right ventricular function in children

Assessment of right ventricular (RV) function is clinically relevant in the follow-up of various forms of congenital heart disease. Agreement on the value of different echocardiographic approaches for this purpose is lacking. Magnetic resonance imaging (MRI) provides dimensionally accurate RV volumes and ejection fraction. Transthoracic 2-dimensional echocardiography from 3 different views and gradient-echo tomographic MRI were performed in 16 children with congenital heart disease and 17 age-matched healthy children. RV volumes and ejection fraction were calculated with 5 mono- and biplane area-length and multiple-slice echocardiographic methods. Adequate MRI and echocardiographic apical 4-chamber images could be obtained in all 33 children. The best correlation between MRI and echocardiographic volumes was with the biplane pyramidal approximation method. End-diastolic volume by MRI was 92 +/- 27 ml: systematic difference with echocardiography was +14 +/- 16 ml (r = 0.86). End-systolic volume by MRI was 33 +/- 13 ml: systematic difference with echocardiography was -4 +/- 7 ml (r = 0.82). Ejection fraction by MRI was 65 +/- 8%: systematic difference with echocardiography was +5 +/- 7% (r = 0.72), using monoplane ellipsoid approximation. For all echocardiographic methods, significant effects of RV geometry were noted. Echocardiographic mono- and biplane area-length and multiple-slice calculations demonstrated moderate correlation and significant systematic errors compared with MRI-derived RV volumes. Echocardiographic results were influenced by RV geometry. The relatively simple monoplane area-length method provides ejection fraction results acceptable for clinical practice; results are not improved by more complex biplane and/or multislice methods.

Magnetic resonance measurement of velocity and flow: Technique, validation, and cardiovascular applications

With a newly developed magnetic resonance (MR) technique for blood flow measurements, qualitative and quantitative information on both flow volume and flow velocity in the great vessels can be obtained. MR flow quantitation is performed with a gradient-echo MR sequence with high temporal resolution enabling measurements at frequent intervals throughout the cardiac cycle. MR flow quantitation uses the phase rather than the amplitude of the MR signal to reconstruct the images. These images, often referred to as MR velocity maps or velocity-encoded cine MR images, are two-dimensional displays of flow velocity. From these velocity maps, velocity and volume flow data can be obtained. Previous validation experiments have demonstrated the accuracy of MR velocity mapping, and this technique is now being applied successfully in several clinical fields. MR velocity mapping may be of considerable value when Doppler echocardiography results are unsatisfactory or equivocal, particularly because MR is suited for the analysis of volumetric flow and complex flow patterns. Among the vastly growing number of clinical cardiovascular applications that have been reported are the great arteries and veins, coronary vessels, valvular disease, and the abdominal and peripheral vessels. These items are reviewed, and some aspects of the technique that need improvement are discussed.

Quantification of right ventricular function with magnetic resonance imaging in children with normal hearts and with congenital heart disease.

In clinical treatment of children with congenital heart disease (CHD) assessment of right ventricular (RV) function is important. Available imaging techniques have been of limited value because of technical factors and the complex geometry of the right ventricle. To validate magnetic resonance (MR) imaging measurements of RV function in children, gradient echo MR imaging of both ventricles and MR flow mapping of great vessel and tricuspid flow was performed in 20 children with CHD affecting the right ventricle and in 22 healthy children ranging in age from 5 to 16 years. Close correlation between RV versus LV stroke volumes (r = 0.96) and RV stroke volume versus great artery (r = 0.97) or tricuspid flow (r = 0.97) was observed with small interobserver and intraobserver variability. Results of healthy children were end-diastolic volume: 70 +/- 9 ml/m2, end-systolic volume: 21 +/- 5 ml/m2, and ejection fraction: 70% +/- 4%. In the patient groups clinically important differences were noted. We conclude that MR imaging provides accurate noninvasive measurements of RV function in healthy children and patients with (operated) CHD.

Postoperative pulmonary flow dynamics after fontan surgery: Assessment with nuclear magnetic resonance velocity mapping

OBJECTIVES This study was performed to assess the value of nuclear magnetic resonance (NMR) velocity mapping for the measurement of pulmonary blood flow after Fontan surgery. BACKGROUND Echocardiographic studies of pulmonary flow after Fontan surgery are not always satisfactory. The newly developed technique of NMR velocity mapping may contribute to the elucidation of the Fontan circulation. METHODS At frequent intervals during the cardiac cycle, forward and backward flow volumes in the pulmonary arteries of nine volunteers were measured, summed and compared with right ventricular stroke volume to validate the velocity mapping technique. In 14 patients after Fontan surgery, assessment of pulmonary flow volumes enabled the evaluation of atriopulmonary and atrioventricular (AV) Fontan connections. The findings were correlated with precordial echocardiography. RESULTS Validation of the NMR technique, obtained from volunteer experiments, showed a high correlation (r = 0.97) between right ventricular stroke volume and volumetric pulmonary stroke flow. In all patients with an atriopulmonary Fontan connection (n = 8), forward flow in the pulmonary artery was biphasic, similar to normal venous flow. Monophasic systolic pulmonary flow curves indicating right ventricle-dependent pulmonary blood flow were found in three of six patients with an AV Fontan connection. In the remaining three patients, the pulmonary flow pattern did not reflect right ventricular contraction. Measurement of flow velocity alone may give a false impression of forward flow and thus of right ventricular contribution. Pulmonary regurgitation was demonstrated in six of eight patients with an atriopulmonary connection. CONCLUSIONS Nuclear magnetic resonance velocity mapping provides accurate and valuable information on pulmonary flow volume and velocity after Fontan surgery. The success of AV Fontan surgery can be deduced from the presence of a monophasic systolic pulmonary flow pattern as demonstrated by NMR velocity mapping. With NMR flow volume analysis, substantial pulmonary regurgitation occurring after atriopulmonary Fontan surgery can be measured.

Congenital heart disease. Evaluation of anatomy and function by MRI.

With the increasing number of patients surviving after therapeutic intervention for congenital heart disease (CHD), accurate and frequent follow-up of their morphologic and functional cardiovascular status is required, preferably with a noninvasive imaging technique.Echocardiography, either transthoracic or transesophageal, has been the first choice for this purpose, and will probably keep that status, at least in a large segment of the CHD spectrum. Magnetic resonance imaging (MRI) is an established method for high-resolution visualization of cardiovascular morphology. In the past decade, newer MRI techniques have been developed that allow functional evaluation of CHD patients. Particularly the introduction of breath-hold imaging, contrast-enhanced MRA and user-friendly computer software for image analysis may move functional MRI of CHD from the science laboratory to clinical use. It is already evident that MRI is superior to echocardiography in certain areas of limited echocardiographic access, such as the pulmonary artery branches and the aortic arch in adult patients. But MRI has also a unique potential for accurate volumetric analysis of ventricular function and cardiovascular blood flow, without any geometric assumptions. If supported by increased cooperation between cardiologists and radiologists, MRI will grow into a useful noninvasive imaging tool that, together with echocardiography, will obviate the need for invasive catheter studies for diagnostic purposes.ZusammenfassungWeltweit werden jährlich etwa 1,5 Millionen Kinder mit kongenitalen Herzerkrankungen (CHD, congenital heart disease) geboren. Durch Verbesserung der verschiedenen chirurgischen und interventionellen Techniken ist die Überlebensrate von CHD-Patienten drastisch gestiegen. Immer mehr Patienten mit postoperativen Residuen, Folgezuständen und Komplikationen benötigen eine umfassende Nachsorge. Die Darstellung und Quantifizierung morphologischer und funktioneller kardiovaskulärer Anomalien erfordern zuverlässige und vorzugsweise nichtinvasive bildgebende Verfahren.Die Röntgenkontrastangiokardiographie, der bisherige Goldstandard, eignet sich nicht zur wiederholten Anwendung. Die transthorakale Echokardiographie (TTE) ist die meistverwendete nichtinvasive Methode, doch bei älteren Patienten, insbesondere mit komplexen oder operativ behandelten Malformationen, sind die damit gewonnenen Informationen unter Umständen unbefriedigend. Narben-, Knochen- und Lungengewebe sowie Thoraxdeformitäten können mit dem Schallfenster interferieren. Die transösophageale Echokardiographie (TEE) liefert bei Erwachsenen mit verschiedenen CHD-Formen eindeutig einen weitaus besseren Bildausschnitt, ist jedoch als semiinvasiv einzustufen. Bei Kleinkindern ist die TEE für die auf Intensivstationen und in Operationssälen erforderliche unmittelbare prä- und postoperative Überwachung inzwischen unentbehrlich.Die Kernspintomographie (Magnetresonanztomographie, MRT) hat sich zu einem klinischen nützlichen Verfahren zur Untersuchung des Herzens entwickelt, vor allem bei angeborenen Fehlbildungen. Sie gilt heute als etablierte nichtinvasive Methode, mit der sich die Anatomie des Herzens in jeder gewünschten Ebene mit hoher Auflösung und naturgetreuen Kontrast zwischen kardialen Strukturen und strömendem Blut darstellen läßt. Das konventionelle Spin-Echo eignet sich hervorragend zur morphologischen Beurteilung, liefert jedoch nicht unbedingt funktionelle Informationen. Die durch neuere Impulssequenzen mögliche funktionelle Analyse verleiht der MRT ihren besonderen Wert. Mehrere dieser neuen MRT-Verfahren werden gegenwärtig klinisch eingesetzt. Die Gradienten-Echo-MRT liefert ein Bild des Blutflusses. Mit ihr können Stenosen, Regurgitation oder Shunts aufgrund der durch diese hämodynamischen Läsionen verursachten Strömungsturbulenzen entdeckt werden. Außerdem ermöglicht die Gradienten-Echo-MRT eine fortlaufende Schleifendarstellung der Ventrikelwandbewegung und eine Quantifizierung der Kammerfunktion. Mit der quantitativen Phasenkontrast-MR-Angiographie lassen sich Blutströmungsgeschwindigkeit und Volumendurchfluss in den mittleren und großen Gefäßen messen. Diese Besonderheit der MRT läßt sich zur Quantifizierung von Stenosen, Regurgitation, intrakardialen Shunts und des differentiellen pulmonalen Blutstroms nutzen. Vor allem ihre Fähigheit zur Messung des Volumendurchflusses ist ein klarer Vorteil der MRT. Die kontrastverstärkte MR-Angiographie ist besonders nützlich zur Darstellung der Pulmonalarterienäste und des Aortenbogens.Pulmonaler Blutfluss, rechtsventrikuläre Funktion, pathologische Aortenbefunde und Fontan-Umgehungskreislauf sind u. a. hochinteressante Fragestellungen, die mit multifunktioneller MRT untersucht wurden.Bei Patienten mit Pulmonalstenose oder Fallot-Tetralogie lassen sich mittels MRT Morphologie und Schwere jeder pulmonalen (Rest-)Stenose beurteilen, die rechtsventrikuläre Hypertrophie bewerten sowie eine postoperative Insuffizienz der Pulmonalklappe oder ventrikuläre Dysfunktion quantifizieren. Bei Patienten, die wegen Koarktation operiert wurden, kann die Morphologie von Rest- oder Restenosen MR-tomographisch mit Hilfe von Spin-Echo-Bildern und der kontrastverstärkten MR-Angiographie des Aortenbogens beurteilt werden. Die quantitative Phasenkontrastangiographie erlaubt zusätzlich, den Druckgradienten über der Stenose und das Ausmaß des Kollateralflusses zu bestimmen. Patienten mit Transposition der großen Arterien werden in der Regel mit Umkehroperationen auf Vorhofebene behandelt. Eine Dysfunktion des rechten systemischen Ventrikels ist bei diesen Patienten eine wesentliche Frage, die mit funktionellen MRT-Verfahren untersucht wurde. Andere Komplikationen nach Vorhofumkehroperation wie Obstruktionen im pulmonalen oder systemisch-venösen Kreislauf lassen sich mit der Gradienten-Echo-MRT mühelos aufdecken. Der Fongan-Umgehungskreislauf bleibt nach wie vor ein faszinierendes, in vielerlei Hinsicht noch nicht völlig verstandenes Thema. Zahlreiche Modifikationen der ursprünglichen Fontan-Operation wurden eingeführt, mit jeweils eigenen hämodynamischen Charakteristika. Zweifellos kann die kombinierte morphologisch-funktionelle MRT zur Entwicklung weiterer Verbesserungen des Fontan-Verfahrens beitragen.Trotz aller technischen Verbesserungen, insbesondere der Einführung des Atemanhalteverfahrens, bleibt die MRT nach wie vor eine Ergänzung zu Echokardiographie und Angiokardiographie. Verfügbarkeit, Ortsgebundenheit und die bei Säuglingen und Kindern erforderliche Sedierung sind bekannte Hindernisse. Nicht zuletzt gilt es, gegen die relativ begrenzte Einbeziehung von Kardiologen in die MRT-Abteilung und die eingeschränkte Verfügbarkeit von Radiologen mit Erfahrung in CHD anzugehen, um die MRT zu einem “vollwertigen Mitglied im Klub” der bildgebenden Verfahren bei CHD zu machen.

Quantification of pulmonary and systemic blood flow by magnetic resonance velocity mapping in the assessment of atrial-level shunts

The objective of this study was to assess the feasibility and accuracy of magnetic resonance (MR) velocity mapping to calculate pulmonary-to-systemic flow ratio (Qp : Qs) in patients with a suspected or diagnosed atrial-level shunt. During a one-year period, all patients referred to our department for further evaluation of an atrial-level shunt underwent the same imaging protocol. Multiphase-multisection gradient-echo MR image sets of the heart were acquired to measure left and right ventricular stroke volumes for validation. Ascending aorta and main pulmonary artery volume flow were measured with MR velocity mapping. Qp : Qs ratios were calculated from both stroke volume data and flow data. Twelve patients, including 6 children, were studied. Six patients had an established diagnosis of atrial septal defect, and the other 6 patients were suspected to have an atrial-level shunt. Measurements of left and right ventricular stroke corresponded closely with those of aortic (r=0.98) and pulmonary flow (r=0.99) respectively, and Qp : Qs flow ratios agreed with stroke volume ratios (r=0.92). In 5 patients with a suspected shunt, the diagnosis could be rejected. Shunts were demonstrated in the other 7 patients. MR velocity mapping offers an accurate method to measure aortic and pulmonary artery volume flow that can be useful in the evaluation of atrial-level shunts, in order to establish a definite diagnosis and/or to quantify the Qp : Qs ratio.

Giant true aneurysm of an aortocoronary bypass graft: A rare cause for a mediastinal mass

An aneurysm located at the anastomosis of an aortocoronary bypass graft (pseudoaneurysm) is a known late complication of coronary artery bypass graft (CABG) surgery [ 11. A true aneurysm of the graft, however, is rare. Clinical diagnosis is often difficult. In this paper we report a patient with a giant true aneurysm of a bypass graft presenting as an abnormal mediastinal contour on plain radiography. Although angiography is usually required, CT can be helpful and MR imaging may provide valuable information suggesting the diagnosis.

Cardiovascular applications of magnetic resonance imaging and phosphorus-31 spectroscopy.

Recent advances in cardiovascular applications of magnetic resonance (MR) imaging and phosphorus-31 spectroscopy are reported. MR velocity mapping is a valuable adjunct to conventional imaging techniques, providing information on flow velocities as well as on absolute blood flow volume in the aorta and pulmonary arteries. Recently, ultrafast MR techniques have become available to evaluate myocardial perfusion with the aid of MR contrast agents as perfusion marker. Dynamic MR imaging is a powerful tool to assess cardiac function and ventricular mass. In particular, right ventricular function and mass can be evaluated with great accuracy, contributing to improved assessment of the significance of disease processes which may affect the right heart. The role of phosphorus-31 spectroscopy of the heart is expanding for the evaluation of ischemic myocardial disease and cardiomyopathies. The phosphocreatine to adenosine triphosphate ratio appears to be a marker of disease in patients with cardiac hypertrophy. In conclusion, MR imaging and phosphorus-31 spectroscopy is gaining widespread acceptance for evaluation of many cardiovascular disease processes.

Double outlet left ventricle: diagnosis with magnetic resonance imaging.

A complex congenital cardiac malformation in a female patient was evaluated several times by angiocardiography and echocardiography in childhood but a definite diagnosis was not established. Segmental analysis of the heart and the great vessels by magnetic resonance imaging when the patient was 34, however, showed a double outlet left ventricle in which the aorta was situated anterior to and to the left of the pulmonary trunk and an associated subaortic ventricular septal defect with pulmonary valve stenosis. This is the first time that this extremely rare cardiac malformation has been diagnosed by magnetic resonance imaging.