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. Cardiac Computed Tomography Recommendation for Cardiac Computed Tomography Referenced studies that support the recommendation are summarized in Online Data Supplement 9. COR LOE Recommendation IIa C-LD CCT imaging can be useful in patients with ACHD when information that cannot be obtained by other diagnostic modalities is important enough to justify the exposure to Table 9. Comparison of Imaging Modalities Useful in ACHD Evaluation Radiation Exposure Relative Cost Ventricular Volumes/ Function Valvular Structure/ Function Coronary Anatomy and Course Extracardiac Vascular Anatomy Echocardiography No $ ++ +++ +/- +/- CMR No $$ +++ ++ ++* +++ CCT Yes $$ +* + +++ +++ Cardiac catheterization Yes $$ + ++ +++ ++ $ indicates less expensive; $$, more expensive; +/-, possible value; +, good; ++, very good; and +++, excellent. *In specific gated imaging protocols. ACHD indicates adult congenital heart disease; CCT, cardiac computed tomography; and CMR, cardiovascular magnetic resonance. CLINICAL STATEMENTS AND GUIDELINES Recommendation-Specific Supportive Text 1. The most important disadvantage of CCT (in- cluding CT angiography) as an imaging technique is the associated exposure to ionizing radiation. 