Objective To review and describe optimal contrast enhanced CT imaging of the pulmonary arteries and inferior conduit in patients with a Fontan (total cavo-pulmonary connection, TCPC) circulation for the purposes of evaluation of Fontan circuit thrombosis.

Methods A retrospective review of all Fontan patients undergoing computed tomographic pulmonary angiography (CTPA) at a large NHS trust commissioned for congenital heart disease practice between 2015 and 2022 was performed. Both paediatric and adult patients were included. Patients with a superior cavo-pulmonary anastomosis (bidirectional Glenn circuit) only were also included. Demographic, clinical, scan and contrast data were collected by 2 clinicians. Measurements were internally validated by 2 consultant cardiac radiologists. Data was analysed and reported.

Results 52 CTPA were performed during the study period and included for evaluation. A protocol using a low voltage (e.g. 80 kilovolt) with 800 mg/kg of contrast and a scan time delay of 70 seconds yields a mean intravascular attenuation of >250 Hounsfield units (HU) in the Fontan conduit and pulmonary arteries in patients with TCPC.

Conclusion Consistent and accurate diagnosis of Fontan thrombosis in both paediatric and adult patients must involve an adaptive approach by radiology departments to ensure CT protocols yield quality diagnostic data for this unique group of patients. Our institutional approach meets the international standards of mean intravascular attenuation of >250HU within the target vasculature of interest. This data presents a significant sample size to contribute toward developing an evidence base for CTPA imaging in Fontan patients.