Performance of Cardiac MRI in Pediatric and Adult Patients with Fontan Circulation

Abstract

Cardiac MRI has become a widely accepted standard for anatomic and functional assessment of complex Fontan physiology, because it is noninvasive and suitable for comprehensive follow-up evaluation after Fontan completion. The use of cardiac MRI in pediatric and adult patients after completion of the Fontan procedure are described, and a practical and experience-based cardiac MRI protocol for evaluating these patients is provided. The current approach and study protocol in use at the authors' institution are presented, which address technical considerations concerning sequences, planning, and optimal image acquisition in patients with Fontan circulation. Additionally, for each sequence, the information that can be obtained and guidance on how to integrate it into clinical decision-making is discussed. Keywords: Pediatrics, MRI, MRI Functional Imaging, Heart, Congenital © RSNA, 2022.

Keywords: Congenital; Heart; MRI; MRI Functional Imaging; Pediatrics.

Figure 1:

Cardiac imaging planes are essential for the evaluation of cardiac sizes and function. In this figure, each imaging plane is represented by a distinct color (frame colors and line colors correspond, ie, orange frame is sagittal view and orange line represents the same sagittal plane crossing through coronal image). Typically, evaluation begins with an initial anatomic survey (ie, scout imaging) in the coronal, axial, and sagittal planes. These series are used for planning the cardiac vertical long-axis (VLA) view (red frame), horizontal long-axis or four-chamber (4CH) view (blue frame), left ventricular outflow tract (LVOT) and LVOT cross-cut (XC) views (green frames), and the short-axis stack (SAX) at basal level (black frame) and SAX at mid ventricular level (light blue frame) views.

Figure 2:

Examples of different total cavopulmonary connections. (Left) MR images of the so-called old atriopulmonary Fontan procedure versus the (right) so-called modern extracardiac conduit Fontan procedure. ECC = extracardiac conduit, IVC = inferior vena cava, LPA = left pulmonary artery, RAA = right atrial appendage, RA = right atrium, RPA = right pulmonary artery, SVC = superior vena cava.

Figure 3:

Cardiac MRI study in a 3-year-old child with double-inlet, double-outlet right ventricle (RV) after right Blalock-Taussig (BT) shunt. Note the double-inlet aortic valve (AV) connection to the RV with (2, 5, 6) straddling left AV valve, (5–7) hypoplastic left ventricle (LV), (1–4, 9) double-outlet RV, and (1, 2, 5–7) large noncommitted ventricular septal defect. AO = aorta, IVC = inferior vena cava, LA = left atrium, LPA = left pulmonary artery, LPVS = left pulmonary veins, MV = mitral valve, PA = pulmonary artery, PV = pulmonary valve, RA = right atrium, RPA = right pulmonary artery, RPVS = right pulmonary veins, SVC = superior vena cava, TV = tricuspid valve.

Figure 4:

Cardiac MRI study in a 13-year-old child with hypoplastic left heart syndrome, double-outlet right ventricle (RV), and aortic coarctation after Damus-Kaye-Stansel (DKS) procedure, coarctation repair, and Fontan completion. Note the (1, 4) double-outlet RV, (1, 3, 11, 12) DKS anastomosis, (2, 7) hypoplastic left ventricle (LV), (3–5) Fontan pathways, and (5–12) persistent left superior vena cava (LSVC) connected to the left upper pulmonary vein (LUPV) draining into the left atrium (LA). AO = aorta, IVC = inferior vena cava, LLPV = left lower pulmonary vein, LPA = left pulmonary artery, RA = right atrium, RPA = right pulmonary artery, RPVS = right pulmonary veins, RSVC = right superior vena cava.

Figure 5:

Cardiac MRI volumetric analysis in a patient with hypoplastic left heart syndrome. Ventricular volumes are calculated using the Simpson disk summation method, starting from endocardial contouring of the ventricular cavities in a short-axis stack of the functionally univentricular heart. The dominant single right ventricle is outlined in yellow, and the hypoplastic left ventricle is outlined in red.

Figure 6:

Three-dimensional volume-rendered contrast-enhanced MR angiographic images in a patient with double-outlet right ventricle and aortic stenosis and coarctation after Damus-Kaye-Stansel (DKS) anastomosis, coarctation repair, and Fontan completion. The images show discrete narrowing of the transverse arch (arrow) with poststenotic dilatation (*). Cavopulmonary anastomoses and branch pulmonary arteries appear unobstructed.

Figure 7:

The acquired three-dimensional (3D) isotropic data sets from contrast-enhanced MR angiography or 3D steady-state free precession can be displayed as maximum intensity projection (MIP), multiplanar reconstruction (MPR), or 3D volume rendering. (A) The MIP postprocessing algorithm selects the voxel with the maximum intensity along a ray through the 3D volume of data and displays these data as a two-dimensional projection. Shortcomings include decreased visibility of vessels passing among highly attenuating structures, poor depiction of 3D relationships, and volume averaging. (B) The MPR postprocessing algorithm generates coronal, sagittal, and axial reconstructions from source images and is useful in demonstrating and evaluating lesions after they have been detected or suspected using other means. Isolated examination of MPR images to evaluate sites of disease or abnormality, although providing the most detailed views, may be extremely time-consuming because of the large number of images generated. (C) 3D volume rendering is an interactive postprocessing algorithm that produces 3D volumetric images. The algorithm computes a weighted sum of the contributions of individual voxels along rays through the 3D volume of data. The interactive nature of volume rendering allows real-time manipulation of the 3D images and editing with clip planes. As a result, this reconstruction may provide clearer differentiation of overlapping vessels and better depiction of 3D spatial relationships.

Figure 8:

Time-resolved contrast-enhanced MR angiographic images in a 5-year-old boy with tricuspid atresia after a bidirectional Glenn procedure. Contrast material injection through the left arm shows contrast material filling the left subclavian vein (LSCV) which is obstructed at the costoclavicular space (2, 3). Contrast material proceeds through a major collateral to both lungs (arrow), rapidly filling the left upper pulmonary veins and the single ventricle (SV) without opacification of the pulmonary arteries (PAs), consistent with a systemic-to-pulmonary venovenous collateral (3, 4). The superior vena cava (SVC) and PAs are visualized later after contrast material returns from the head and neck (6). * = pulmonary arteriovenous malformation in the right lower lobe. Ao = aorta, RPA = right PA.

Figure 9:

Illustration of sites of the through-plane flows used for complete hemodynamics assessment of patients with Fontan circulation. In the absence of regurgitant lesions, patent fenestration, or significant systemic-to-collateral flow, aortic forward flow should be equal to total systemic venous return (superior vena cava [SVC] + inferior vena cava [IVC] flows) and also to total pulmonary venous return (right pulmonary veins [RPVs] + left pulmonary veins [LPVs] flows). Discrepancy in flows should indicate the presence of any of the aforementioned lesions, whereas segmental analysis of flows in the circuit may allow quantification of their entity at each level. Ao = aorta, ECC = extracardiac conduit, LPA = left pulmonary artery, RPA = right pulmonary artery.

Figure 10:

Flow assessment in a 15-year-old patient with double-outlet right ventricle and pulmonary atresia after extracardiac Fontan procedure. Flows are assessed by imaging the vessel perpendicular to its long axis using phase-contrast imaging. Through-plane velocity maps of the ascending aorta, superior vena cava (SVC), inferior vena cava (IVC), right pulmonary artery (RPA), left pulmonary artery (LPA), right pulmonary veins (RPVs), and left pulmonary veins (LPVs) are shown. The pulmonary arteries appear unobstructed (RPA:LPA net flow split ratio, approximately 60%:40%). Estimated systemic-to-pulmonary collateral flow is approximately 10% (systemic estimator: AO − [SVC + IVC]; pulmonary estimator: [RPV + LPV] − [RPA + LPA]).

Figure 11:

Four-dimensional (4D) flow assessment in an 11-year-old patient with hypoplastic left heart syndrome after intra-atrial lateral tunnel Fontan procedure. (A) Streamline visualization with velocity color coding of 4D flow data. (B) Flow quantification in the aorta (Ao) (red), superior vena cava (SVC) and lateral tunnel (LT) (green), left pulmonary artery (LPA) (yellow), and right pulmonary veins (RPVs) (blue). IVC = inferior vena cava, SV = single ventricle.

Figure 12:

Cardiac MRI scan in a 15-year-old patient with situs inversus, dextrocardia, bilateral superior vena cavas (SVC), atrioventricular discordance with single outlet and pulmonary atresia, large perimembranous ventricular septal defect, and right aortic arch after extracardiac Fontan procedure. (The patient refused cannulation, so angiography could not be performed.) These still images from balanced steady-state free precession cines show incidental finding of dissection of the extracardiac conduit (ECC). (A) Long-axis view of the dissected conduit. (B, C) Short-axis view with very narrowed true lumen (red * in D and E) at the conduit insertion to the pulmonary artery. (D–F) The same images as B, C, and A, respectively, but with labeling showing the Fontan pathway and the respective acquisition planes. Arrows indicate the direction of flow. LPA = left pulmonary artery, LSVC = left SVC, RPA = right pulmonary artery, RSVC = right SVC.

Figure 13:

MR images of thrombus formation in a 28-year-old man with tricuspid atresia after atriopulmonary Fontan procedure. Two crescent-shaped thrombi are noted along the anterior and posterior walls of the right atrium (RA) (black and white *). (1, 2, 5) Balanced steady-state free precession, (3, 6) early gadolinium enhancement, and (4) T1-weighted spin-echo sequences (please refer to the text for signal intensity in each sequence).

Figure 14:

Late gadolinium enhancement images in a 3-year-old patient with hypoplastic left heart syndrome after a Norwood procedure and a bidirectional Glenn procedure. The diffuse subendocardial enhancement of the hypoplastic left ventricle (LV) is compatible with endocardial fibroelastosis. Enhancement of the septal papillary muscle of the tricuspid valve is also observed (white arrow). RV = right ventricle.

Figure 15:

Extracardiac findings in a 26-year-old patient affected by hypoplastic left heart syndrome after Fontan operation. Bright-blood single-shot images generated using T2-weighted MRI, true fast imaging with steady-state free precession in the (left) axial, (middle) coronal, and (right) sagittal planes. Distortion of the gross architecture of the liver with irregular nodular margins and hypertrophy of the caudate lobe as well as severe ascites in the abdominal cavity are seen. These findings are in line with end-stage liver cirrhosis, and dedicated liver imaging and testing are required.

Figure 16:

(A) Steady-state free precession (SSFP) image in a patient with mesocardia, double-inlet indeterminate ventricle with pulmonary atresia, bilateral superior vena cava after a bilateral bidirectional Glenn procedure and Fontan completion with left-sided extracardiac conduit (ECC). There is metal artifact from a stent implanted at the site of inferior vena cava-ECC anastomosis. (B) Spoiled gradient-recalled echo (SPGR) image in a patient after Fontan procedure with dual-chamber epicardial pacemaker (dark artifact) implanted for sick sinus syndrome. Cardiac MRI was performed as part of the transplant assessment workup, specifically, for assessment of pulmonary flow and estimation of pulmonary vascular resistance. Imaging was performed in line with protocol for non–MRI-conditional devices and was limited to half-Fourier single-shot turbo spin-echo images and flow maps. (C, D) SPGR images in a patient with double-outlet right ventricle with pulmonary atresia after extracardiac Fontan procedure. The patient underwent left pulmonary artery stent placement for branch stenosis. Unlike SSFP imaging (panel A), SPGR imaging minimized metal artifacts from the stent.