Research imaging will include liver assessments of stiffness (ultrasound shear wave elastography), tissue attenuation (if available), and blood flow (gray-scale and Doppler imaging).

to determine if there are differences between patients with regard to liver stiffness (hepatic congestion) pre- and post-Fontan operation or with regard to change in liver stiffness over time. This information will be used to drive future hypothesis-driven research related to predicting Fontan-related outcomes based on measured liver stiffness.

1. Time to anatomic Fontan pathway obstruction or physiologically high resistance, need for Fontan pathway intervention, need for cardiac transplant evaluation or actual transplantation, and need for mechanical cardiac support evaluation or actual implementation (e.g., ventricular assist device)
2. Lymphatic abnormalities (e.g., protein losing enteropathy, plastic bronchitis, intractable ascites)
3. FALD

i. MRI outcomes (e.g., increased liver stiffness [do US and MRI measures of liver stiffness correlate?], portal hypertension, development of focal liver lesions) ii. Liver laboratory assessments (e.g., ALT, AST, bilirubin, alkaline phosphatase, GGT) iii. PELD score iv. VAST score v. Need for liver transplant evaluation or actual transplantation d. Available biopsy (liver and cardiac) data e. Available cardiac catheterization data f. Available cardiac echocardiography and/or cardiac MRI data