Contouring techniques in cardiac magnetic resonance assessment of right ventricular volumes in repaired tetralogy of fallot.

Introduction: Right ventricular size and function on cardiac MRI provides thresholds for referral for pulmonary valve intervention in repaired Tetralogy of Fallot (RTOF). However, different contouring techniques are available to calculate right ventricular volumes and ejection fraction. It is not known whether these contouring techniques impact on threshold triggers for intervention.

Methods: Right ventricular volumes on cardiac MRI for 24 consecutive subjects with RTOF were measured by two independent, experienced observers using three contouring techniques: , detailed and detailed with semi-automated .

Results: End-diastolic and end-systolic volumes were significantly different between contouring techniques: largest for contours, intermediate for and smallest for (EDV: 233 ml, SD 105 ml; 215 ml, SD 95 ml; 206 ml, SD 94 ml; ESV: 122 ml, SD 71 ml; 113 ml, SD 67 ml; 103 ml, SD 64 ml; p < 0.001 for all comparisons). Stroke volume from contours by correlated most strongly with velocity mapping (r = 0.87, p < 0.001). Interobserver agreement was strongest for (end-diastolic volume ICC = 1.0 (confidence interval (CI):0.999-1.0, p < 0.001); end-systolic volume ICC = 0.999 (CI:0.994-1.0, p < 0.001) and weakest for contours ((end-diastolic volume ICC = 0.89 (CI:0.33-0.99, p = 0.01); end-diastolic volume ICC = 0.88 (CI:0.30-0.99, p = 0.01). Intra-observer agreement was uniformly high (ICC≥0.996, p < 0.001 for all). In 4/24 cases, contouring technique altered threshold triggers for pulmonary valve intervention.

Conclusions: Differences in contouring technique for measuring right ventricular volumes in patients with RTOF can affect thresholds triggering referral for pulmonary valve intervention. Standardisation of right ventricular measurement is needed in congenital cardiac MRI practice.