Cardiac imaging: MR or CT? Which to use when

Over the last 5 years there has been a sea-change in the imaging pathways used to investigate patients with congenital heart disease. Prior to 2003 in our own institution, patients would undergo an echocardiogram (ECHO), and, if diagnostic, the appropriate management pathway would be followed. For example, a patient with a large ASD seen at ECHO would be referred for surgical closure of the septal defect. However, if ECHO was not able to resolve the diagnostic problem, cardiac catheterization was performed. This obviously entailed a general anaesthetic in most patients, an interventional procedure with the potential to damage vascular access, and potentially long screening times with high radiation doses. Since 2003 in our institution, we have introduced a second tier of investigations: cardiovascular MR and CT. Thus, if ECHO cannot resolve the diagnostic problem, patients will now be referred for cardiovascular MR/CT. Diagnostic cardiac catheterization is now reserved for those patients where there remain diagnostic dilemmas, when measurement of pressure is essential (for example in the assessment of pulmonary vascular resistance), or when ECHO suggests that there may be a lesion that requires treatment and a diagnostic/query proceed catheter is performed. Over this time period, we have seen a gradual increase in the number of cardiovascular MR and CT investigations, and interestingly, the overall number of diagnostic tests we perform has also increased significantly (Fig. 1).