She said many of these patients also will not qualify for MRI, which is the preferred imaging modality for congenital heart. She said this is often because these patients have MRI incompatible devices implanted such as ICDs or pacemakers. Patients also may have limited access to Cardiac MRI or be claustrophobic. In some instances, cardiac CT may have better spacial resolution than cardiac MR when assessing the coronary arteries, coronary anomalies and stents, including pulmonary stents and pulmonary valves, Bullock-Palmer explained. 

Often in congenital patients, an imaging study needs to be customized to the clinical question being asked because of septic nature of each patient's anatomical anomalies and prior surgeries, she said. 

"They can be porporri of patients, ranging from very simple ASDs, or they can be very complex single ventricle Fontan patient," Bullock-Palmer said. "So we use the adult congenital heart disease (ACHD) classification system, which is based on anatomy and physiology classifications.

The anatomy is graded as simple, moderate complex and great complexity. The physiological stages follow the New York Heart Association functional classifications, with Class I being no hemodynamic sequelae and Class IV being severe hypoxemia or cyanosis.

"At our center we do see a good mix of these patients," she said. "Usually we use CT for the very complex cases when MRI is unavailable or not possible. For the simple cases, we usually do not see those on CT because those cases can be assessed using echo. This is particularly true for atrial septal defects (ASDs) and ventricular septal defects (VSDs)."

Bullock-Palmer said CT is often used for structural heart procedure planning to size the anatomy and create a table of measurements used by surgeons or interventionists implanting transcatheter devices or valves. There pre-procedural workups are done for Tetralogy of Fallot, Fontan procedures and pulmonary valve replacements. Sometimes 3D modeling is done to help surgeons and interventionalists better understand the complex anatomy and use as a reference during the procedure.

Advanced visualization software used to help automate measurements and create specific views of the anatomy can be problematic in congenital patients because it was designed around and validated using normal patient anatomy imaging. Congenital patients are often missing parts of the normal cardiovascular anatomy, or vessels and cardiac anatomy are not located where they should be normally, which usually causes issues with automated software. So, she warns imagers will likely have to spend more time post-processing these exams. 

"Most times I am having to change were the contours are, and that is important, because you do not want to give inaccurate information to the referring physician. This is especially important for information on left ventricular or right ventricular volumes and function," she said. "For example, in a Fontan patient where there is only a single ventricle, the software is going to try and find the other ventricle, and most time it is going to give you inaccurate information. So you have to go through manually in each of the phases to fix the contours."

If it is too difficult to assess, she said she has sometimes given a visual estimate that ventricular function is reduced and suggest the patient should undergo an echo or MRI assessment. 

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