Fractal branching quantifies vascular changes and predicts survival in pulmonary hypertension: a proof of principle study

ObjectivesTo develop a non-invasive method of assessing disease severity in pulmonary hypertension by quantifying the overall degree of vascular pruning using fractal geometry.DesignA retrospective analysis of ECG-gated CT pulmonary angiograms.SettingA single national referral centre for the investigation and treatment of children with pulmonary hypertension.PatientsConsecutive CT pulmonary angiograms in children and young adults (mean age 10.3 years, range 0.7–19.1) with pulmonary arterial hypertension assessed between January 2007 and April 2009.Main outcome measuresThe fractal dimension (FD) of skeletonised CT pulmonary angiograms was calculated using the box counting method. The FD was compared with pulmonary vascular resistance, the percentage of predicted 6-min walk distance, WHO functional class and survival.ResultsDiagnostic plots confirmed that the pulmonary artery angiograms were all fractal. The FD correlated negatively with the pulmonary vascular resistance index (r=−0.55, p=0.01, n=21) and with WHO functional class (p