For patients with ACHD in whom abnormalities and changes that may be identified on echocar- diography (eg, valvular or ventricular function or pulmonary pressures) commonly influence man- agement decisions; echocardiography is an indis- pensable tool in the initial and serial follow-up evaluation. TTE is also valuable in the initial and serial evaluation of patients without symptoms or changes in examination (Table 8). 3.4.4. CMR Imaging Recommendations for CMR Imaging Referenced studies that support recommendations are summarized in Online Data Supplement 8. COR LOE Recommendations I B-NR In patients with ACHD who have or who are at risk of developing RV enlargement and dysfunction, serial CMR is recommended for quantitative assessment of RV size and IIa C-LD CMR can be useful in the initial evaluation and serial assessment of selected patients with CHD based on anatomic complexity and clinical status.S3.4.4-1,S3.4.4-2,S3.4.4-4 S3.4.4-10 Recommendation-Specific Supportive Text 1. CMR plays a valuable role in assessment of RV size and function, because it provides data that are re- producible and more reliable than data obtained with alternative imaging techniques.S3.4.4-1 S3.4.4-4 Real-time 3-dimensional (3D) echocardiography is an emerging technique that shows some promise for replacing CCT and even CMR for serial studies, especially when focusing on ventricular volumes and intracardiac structures only, and if reasonably complete data sets can be obtained.S3.4.4-11 2. CMR has unique value in the assessment and serial follow-up of patients with ACHD, because it offers unrestricted access to the heart and great vessels noninvasively and without ionizing radi- ation. 