Background Pulmonary artery (PA) anatomy in patients with transposition of the great arteries (TGA) after arterial switch operation (ASO) with Lecompte manoeuvre is different compared to healthy subjects, and stenoses of the PA are common. Magnetic resonance imaging (MRI) is an excellent imaging modality to assess PA anatomy in TGA patients. However, disease‐specific reference values for PA size are scarce. Purpose To establish disease‐specific reference ranges for PA dimensions and for biventricular volumes and mass. Study Type Retrospective. Subjects A total of 69 pediatric patients with TGA after ASO (median age 12.6 years; range 5–17.8 years; 13 females and 56 males). Field Strength/Sequence 3.0 T, steady‐state free precession (SSFP) and gradient echo cine sequences and four‐dimensional time‐resolved magnetic resonance angiography with keyhole. Assessment Right and left PA (RPA, LPA) were each measured at three locations during its course around the aorta. Ventricular volumes, mass, and ejection fraction were measured from a stack of short axis cine images. Statistical Tests The lambda‐mu‐sigma (LMS) method of Cole and Green, univariate and multivariate linear models, and t‐test. Results Centile graphs and tables for PA dimensions, biventricular volumes, mass, and ejection fraction were created. Univariate linear analysis showed significant associations (P < 0.05) between body surface area (BSA), height, and weight with systolic MPA and RPA diameter. In multivariate linear analysis, only BSA remained a strong predictor for main PA and RPA diameters. For biventricular volumes, the univariate linear model revealed a strong influence of BSA, height, weight, and age (all P < 0.05). On multivariate linear analysis, only body height remained associated. Data Conclusion Uni‐ and multivariate linear analyses showed a strong association between BSA and PA diameters, as well as between height and biventricular volumes, and therefore, centile tables and graphs are presented accordingly. Our data may improve MR image interpretation and may serve as a reference in future studies. Level of Evidence 4 Technical Efficacy Stage 2

Funding Acknowledgements Type of funding sources: None. Background Changes in the right ventricular outflow tract (RVOT) and pulmonary arteries (PAs) are often seen in paediatric patients with congenital heart disease (CHD), pulmonary hypertension or genetic disorders (e.g. Marfan syndrome, Loeys-Dietz syndrome, Williams syndrome, DiGeorge syndrome). Cardiovascular magnetic resonance (CMR) imaging is an excellent method to visualize the RVOT and PAs without the use of ionizing radiation and contrast media but for the interpretation of CMR data in the paediatric population the knowledge of normal values is crucial. However, normal values for pulmonary arteries from contrast-free cine CMR images are lacking. Purpose The aim of this retrospective multicentre study was to establish reference ranges for the diameters of the mean PA (MPA), right PA (RPA) and left PA (LPA). Methods 163 CMR scans of healthy children and adolescents (mean age 13.8 ± 2.9 years; range 5-18 years) from two centres in the UK and Germany were included. The diameter of the MPA was measured in sagittal-oblique RVOT cine images and transaxial cine stacks, whereas the diameter of the RPA and LPA were measured from transaxial stacks and specific pulmonary artery branch cine images. Results Mean systolic and diastolic diameters for the MPA were 22.1 ± 2.8 mm (14.4 ± 2.2 mm/m²)/ 17.2 ± 2.3 mm (11.3 ± 1.9 mm/m²) measured in RVOT cine stacks. Mean systolic and diastolic diameters for the RPA and LPA were:  1) RPA, 12.4 ± 1.7 mm (7,9 ± 1,6 mm/m²)/ 9.8 ± 1.6 mm (5.9 ± 1.8 mm/m²) and 2) LPA, 13.3 ± 1.5 mm (8.3 ± 2.1 mm/m²)/ 10.8 ± 1.5 mm (6.8 ± 1.8 mm/m²). Separate centile charts for boys and girls for the MPA were created. Conclusions We established CMR normal values for the MPA, RPA and LPA for children and adolescents. Our data might be useful for the detection of PA stenosis and dilatation and may serve as a reference in future studies.

Funding Acknowledgements Type of funding sources: None. Background The anatomy of the pulmonary arteries (PA) in patients with transposition of the great arteries (TGA) after arterial switch operation (ASO) with Lecompte manoeuvre is different compared to healthy subjects and stenoses of the PA are known to occur. Cardiovascular magnetic resonance (CMR) imaging is an excellent imaging modality to assess PA anatomy in TGA patients. However, disease specific normal values for PA size do not exist. Furthermore, the impact of pulmonary artery size, age and gender on ventricular volumes and function is unknown. Therefore, we sought to establish disease specific normative ranges for PA dimensions as well as biventricular volumes and function. Methods 70 CMR scans of paediatric patients with TGA after ASO with Lecompte manoeuvre (mean age 12.3 ± 3.6 years; range 5-18 years; 57 males) were included. Cine CMR sequences as well as contrast-enhanced magnetic resonance angiography (CE-MRA) data were used to measure pulmonary artery dimensions. Right and left PA were each measured at three locations during its course around the aorta. Ventricular volumes, mass and ejection fraction were measured from a stack of short axis cine images. Results Mean systolic and diastolic diameters of the MPA were 15.0 ± 2.3 mm (10.5 ± 2.7 mm/m²) / 13.2 ± 2.9 mm (9.2 ± 2.9 mm/m²) and mean cross-sectional MPA area was 286.7 ± 81.7 mm². Mean systolic and diastolic diameters for the RPA and LPA at the narrowest point were: RPA 10.5 ± 2.8 mm (7.8 ± 2.4 mm/m²)  / 8.1 ± 2.2 mm (6.0 ± 1.9 mm/m²); LPA 8.4 ± 2.8 mm (6.2 ± 2.1 mm/m²) / 7.4 ± 2.3 mm (5.4 ± 1.6 mm/m²). Mean values for biventricular volumes, ejection fraction and mass were as follows: 1) left  ventricular (LV) end-diastolic volume (EDV) 89.0 ± 20.3 ml/m² and end-systolic volume (ESV) 35.1 ± 11.7 ml/m², 2) right ventricular (RV) EDV 76.4 ± 15.4 ml/m² and ESV 32.4 ± 9.1 ml/m², 3) LV and RV ejection fraction 61.1 ± 6.5 % / 58.9 ± 6.1 % and 4) LV and RV mass 59.6 ± 15.2 g/m² / 23.3 ± 7.4 g/m². Separate centile charts for boys and girls for PA dimensions as well as biventricular volumes, mass and ejection fraction were created. Conclusion We established disease specific CMR normal values for the PA dimensions as well as for ventricular volumes, mass and ejection fraction in paediatric patients with TGA after ASO. Our data will improve CMR image interpretation and may serve as a reference in future studies.