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. The complexity and variability of lesions, repairs, and sequelae in CHD constrain the use of standard protocols and sequences, and often require modification of plans during acquisi- tion of images, as well as specialized skills in Thus,adedicatedCMR service is integral to an ACHD program.S3.4.4-4,S3.4.4-5 CMR can provide exquisite anatomic detail and unique physiological information in many forms of CHD. It has a particularly important role in the assessment of extracardiac cardiovascular defects (eg, CoA, aortic aneurysm, and abnor- malities of the thoracic arterial and venous anatomy and connections).S3.4.4-6,S3.4.4-7 The eluci- dation of uncommon, complex forms and vari- ations of CHD is routinely facilitated by a CMR Contraindications to CMR are com- mon in patients with ACHD, so they should be sought and confirmed. However, the high value of serial CMR has encouraged modification of newer pacemakers, leads, and other devices and imaging protocols to facilitate imaging in an expanding subset of patients with ACHD who have had previous instrumentation. If a contraindication is confirmed, alternative forms of imaging, especially CCT, can obtain much of the information otherwise obtained from CMR and some unique information not provided by However, CCT has the disadvan- tage of substantial patient exposure to ionizing radiation, especially when serial studies are con- templated over a lifetime.S3.4.4-9 Real-time 3D ech- ocardiography shows 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 (Tables 8 and 9).S3.4.4-11,S3.4.4-15 3.4.5. 